the law of conservation of mass essay

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Law of Conservation of Mass

The Law of Conservation of Mass is a fundamental concept in chemistry, stating that mass in an isolated system is neither created nor destroyed by chemical reactions or physical transformations. According to the law, the mass of the reactants in a chemical reaction equals the mass of the products . Further, the number and type of atom s in a chemical reaction is the same before and after the reaction.

Definition and Statement of the Law of Conservation of Mass

The Law of Conservation of Mass was first articulated by Antoine Lavoisier in the late 18th century. It asserts that the total mass of a closed system remains constant over time. This principle is widely applicable in chemical reactions and also applies to other disciplines.

Applicability of the Law

The law holds true in chemical reactions under ordinary conditions. This is because chemical reactions only involve electrons and do not affect the identities of the parts of the atom .

However, the Law of Conservation of Mass does not hold in nuclear reactions, where mass can convert into energy (and vice versa) according to the principle of mass-energy equivalence as proposed by Einstein in the theory of relativity. This conversion occurs in nuclear fission and fusion reactions and some forms of radioactive decay.

Also, the law applies to isolated systems. If matter or energy enters or exits a system, mass may not be conserved.

Historical Overview

The concept of mass conservation dates back to ancient Greece. Mikhail Lomonsov, outlined the principle in 1756. Lavoisier gets credit for formalizing the law in 1773. His work disproved the then-popular theory of phlogiston , a supposed fire-like element released during combustion. Lavoisier demonstrated that combustion results from chemical reactions with oxygen, not from releasing a mysterious substance, and that the mass before and after the reaction was the same.

Examples in Chemical Reactions

Chemical reactions clearly illustrate the Law of Conservation of Mass. Chemists apply the law in balancing chemical equations.

• Combustion: In a simple combustion reaction , such as burning methane (CH₄), the total mass of methane and oxygen equals the mass of the resulting carbon dioxide and water. CH 4​ + 2O 2 ​→ CO 2 ​ + 2H 2 ​O (4 H, 1 C, 4 O atoms on each side of the reaction arrow.)
• Synthesis: When hydrogen and oxygen gases react to form water, the mass of the two gases equals the mass of the water produced. 2H 2 ​+ O 2 ​ → 2H 2 ​O (4 H and 2 O on both sides of the reaction arrow.)

Examples in Organisms

In biological systems, the law applies to metabolic processes. For example, in photosynthesis , plants convert carbon dioxide and water into glucose and oxygen. The total mass of carbon dioxide and water used equals the mass of glucose and oxygen produced:

6 CO 2  + 6 H 2 O → C 6 H 12 O 6  + 6 O 2

On a larger scale, the law applies to the mass of a human body, which encompasses numerous chemical reactions occurring at once. If you maintain a constant weight, the mass you gain from breathing, eating, and drinking equals the mass lost through breathing, perspiration, urination, and defecation.

Examples in Ecosystems

In ecosystems, the law is evident in nutrient cycles, such as the carbon cycle. Carbon atoms are conserved as they move through different components of the ecosystem, including the atmosphere, hydrosphere, lithosphere, and biosphere. For example, the photosynthesis reaction takes carbon from the air and fixes it into a glucose molecule. Photosynthesis does not create mass, nor is any lost in the process.

• Okuň, Lev Borisovič (2009). Energy and Mass in Relativity Theory . World Scientific. ISBN 978-981-281-412-8.
• Pomper, Philip (1962). “Lomonosov and the Discovery of the Law of the Conservation of Matter in Chemical Transformations”. Ambix . 10 (3): 119–127. doi: 10.1179/amb.1962.10.3.119
• Whitaker, Robert D. (1975). “An historical note on the conservation of mass”. Journal of Chemical Education . 52 (10): 658. doi: 10.1021/ed052p658

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The Conservation of Mass

The Law of Conservation of Mass

The Law of Conservation of Mass dates from Antoine Lavoisier's 1789 discovery that mass is neither created nor destroyed in chemical reactions. In other words, the mass of any one element at the beginning of a reaction will equal the mass of that element at the end of the reaction. If we account for all reactants and products in a chemical reaction, the total mass will be the same at any point in time in any closed system. Lavoisier's finding laid the foundation for modern chemistry and revolutionized science.

The Law of Conservation of Mass holds true because naturally occurring elements are very stable at the conditions found on the surface of the Earth. Most elements come from fusion reactions found only in stars or supernovae. Therefore, in the everyday world of Earth, from the peak of the highest mountain to the depths of the deepest ocean, atoms are not converted to other elements during chemical reactions. Because of this, individual atoms that make up living and nonliving matter are very old and each atom has a history. An individual atom of a biologically important element, such as carbon, may have spent 65 million years buried as coal before being burned in a power plant, followed by two decades in Earth's atmosphere before being dissolved in the ocean, and then taken up by an algal cell that was consumed by a copepod before being respired and again entering Earth's atmosphere (Figure 1). The atom itself is neither created nor destroyed but cycles among chemical compounds. Ecologists can apply the law of conservation of mass to the analysis of elemental cycles by conducting a mass balance. These analyses are as important to the progress of ecology as Lavoisier's findings were to chemistry.

Life and the Law of Conservation of Mass

Ecosystems can be thought of as a battleground for these elements, in which species that are more efficient competitors can often exclude inferior competitors. Though most ecosystems contain so many individual reactions, it would be impossible to identify them all, each of these reactions must obey the Law of Conservation of Mass — the entire ecosystem must also follow this same constraint. Though no real ecosystem is a truly closed system, we use the same conservation law by accounting for all inputs and all outputs. Scientists conceptualize ecosystems as a set of compartments (Figure 2) that are connected by flows of material and energy. Any compartment could represent a biotic or abiotic component: a fish, a school of fish, a forest, or a pool of carbon. Because of mass balance, over time the amount of any element in any one of these compartments could hold steady (if inputs = outputs), increase (if inputs > outputs), or decrease (if inputs 2 . Mass balance ensures that the carbon formerly locked up in biomass must go somewhere; it must reenter some other compartment of some ecosystem. Mass balance properties can be applied over many scales of organization, including the individual organism, the watershed, or even a whole city (Figure 4).

Mass Balance of Elements in Organisms

Each organism has a unique, relatively fixed, elemental formula, or composition determined by its form and function. For instance, large size or defensive structures create particular elemental demands. Other biological factors such as rapid growth can also influence elemental composition. Ribonucleic acid (RNA) is the biomolecular template used in protein synthesis. RNA has a high phosphorus content (~9% by mass), and in microbes and invertebrates RNA accounts for a large fraction of an organism's total phosphorus content. As a result, fast-growing organisms such as bacteria (which can double more than 6 times per day) have especially high phosphorus content and therefore demands. By contrast, among vertebrates structural materials such as bones (made of calcium phosphate) account for the majority of an organism's phosphorus content. Among mammals, black-tailed deer ( Odocoileus columbianus ; Figure 6) have a relatively high phosphorus demand due to their annual investment in calcium- and phosphorus-rich antlers. Failure to meet elemental demands can lead to poor health, limited reproduction, and even extinction. The extinction of the majestic Irish Elk ( Megaloceros giganteus ) is thought to have been caused by the shortened growing season that occurred during the last ice age, which reduced the availability of the calcium and phosphorus these animals needed to grow their enormous antlers.

Obtaining the resources required for metabolism, growth, and reproduction is one of the central challenges of life. Animals, particularly those that feed on plants (herbivores) or detritus (detritivores), often consume diets that do not include enough of the nutrients they need. The struggle to obtain nutrients from poor quality diets influences feeding behavior and digestive physiology and has led to epic migrations and seemingly bizarre behavior such as geophagy (feeding on materials such as clay and chalk). For example, the seasonal mass migration of Mormon crickets ( Anabrus simplex ) across western North America in search of two nutrients: protein and salt. Researchers have shown that the crickets stop walking once their demand for protein is met (Figure 7).

The flip side of the struggle to obtain scarce resources is the need to get rid of excess substances. Herbivores often consume a diet rich in carbon — think potato chips, few nutrients but lots of energy. Some of this material can be stored internally, but this is a limited option and excess carbon storage can be harmful, just as obesity is harmful to humans. Thus, animals have several mechanisms for getting rid of excess elements. Excess nutrients are released in feces or urine or sometimes it is respired (i.e., released as carbon dioxide). This release of excess nutrients can influence both food webs and nutrient cycles.

Mass Balance in Watersheds

Ecologists have often used naturally delineated ecosystems, such as lakes or watersheds, for applying mass balances. A forested watershed receives inputs of carbon through photosynthesis, inputs of nitrogen from nitrogen-fixing bacteria, as well as through the deposition of atmospheric nitrogen, inputs of phosphorus from the slow weathering of bedrock, and inputs of water from precipitation. Outputs include gaseous pathways (e.g., H 2 O losses through evapotranspiration, CO 2 production as respiration, N 2 produced by denitrifying bacteria) and dissolved pathways (nutrients and carbon dissolved in stream water). Outputs also include material transport across ecosystem boundaries, such as the movement of migratory animals or harvesting trees in a forest.

The Hubbard Brook Experimental Forest in the White Mountains of New Hampshire, USA, has been the site of ecosystem mass balance studies since the 1960s. This landscape has similar-sized, discreet watersheds drained by streams and underlain by impermeable bedrock. By installing V-notch weirs, investigators could precisely and continuously measure stream discharge. By measuring the concentration of nutrients and ions in stream water, they could quantify the losses of these materials from the ecosystem. After calculating inputs to the ecosystem (by sampling precipitation, dry deposition, and nitrogen fixation), they could also construct mass balances. Additionally, researchers could experimentally manipulate these watersheds to measure the effects of disturbance on nutrient retention. In 1965, an entire experimental watershed was whole-tree harvested, resulting in large increases in nitrate and calcium losses relative to an uncut reference watershed (Figure 8). By studying inputs and outputs, an understanding of the internal functioning of the ecosystem within the watershed was obtained.

Figure 8: An experimental reference watershed at the Hubbard Brook Experimental Forest in the White Mountains of New Hampshire, USA Researchers have manipulated entire watersheds, for example by whole-tree harvesting, and then monitored losses of various elements. The whole-tree harvesting of watershed 2 in 1965 affected the uptake and loss of nutrients and elements within the forest ecosystem and was followed by high loss rates of nitrate, hydrogen ions, and calcium ions in stream waters for several years. (Stream chemistry data were provided by G. E. Likens with funding from the National Science Foundation and The A. W. Mellon Foundation.) © 2011 US Forest Service .

Mass Balance in Human-Dominated Ecosystems

Mass balance constraints apply everywhere, even to highly altered ecosystems such as cities or agricultural fields. Cities import food, fuel, water, and other materials and export materials such as manufactured goods. Cities also produce large quantities of waste products — with solid waste sent to landfills, CO 2 (and other pollutants) produced from the combustion of fossil fuels being released to the atmosphere. Nutrients from sewage and from fertilizer runoff can end up in rivers where they will fertilize downstream aquatic ecosystems.

Human agricultural systems can also be analyzed using a mass-balance, ecosystem approach. Traditional agricultural practices emphasized efficiency, with most production staying on the farm — food for livestock was produced on the farm, food for farmers' families was produced on the farm, and plant and animal waste was composted for use as fertilizer on the farm. As a result, the amount of material cycling within the farm "ecosystem" was large relative to the inputs and outputs to the system (a relatively closed ecosystem). By contrast, modern industrial agriculture emphasizes maximizing yields over efficiency. Farmers import fertilizer in large amounts (often far exceeding the amounts that crops can use) and grow and export commodity crops. Ironically, in these highly open ecosystems (where inputs and outputs can far exceed internal cycling), food for farmers' families must often be imported as well. Highly productive agricultural systems are critical in feeding the world's growing human population, but as many of the ingredients of modern agriculture (e.g., water, petroleum, phosphorus) become increasingly limiting over the next century (due to depleted geologic deposits), we will be faced with the challenge of increasing the efficiency of these systems. Just as the constraints of mass balance provide a useful tool for ecologists in studying natural ecosystems, mass balance also ensures that the increase in human population and material consumption that has characterized the past 200 years cannot continue indefinitely.

References and Recommended Reading

Chapin, F. S. et al . Principles of Terrestrial Ecosystem Ecology . New York, NY: Springer, 2002.

Likens, G. E. & Bormann, F. H. Biogeochemistry of a Forested Ecosystem . 2nd ed. New York, NY: Springer-Verlag, 1995.

Moen, R. A. et al . Antler growth and extinction of Irish Elk. Evolutionary Ecology Research 1, 235–249 (1999).

Sterner, R. W. & Elser, J. J. Ecological Stoichiometry: The Biology of Elements from Molecules to the Biosphere . Princeton, NJ: Princeton University Press, 2002.

Simpson, S. J. et al. Cannibal crickets on a forced march for protein and salt. Proceedings of the National Academy of Sciences of the USA 103, 4152-4156 (2006).

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conservation of mass

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conservation of mass , principle that the mass of an object or collection of objects never changes, no matter how the constituent parts rearrange themselves. Mass has been viewed in physics in two compatible ways. On the one hand, it is seen as a measure of inertia, the opposition that free bodies offer to forces: trucks are harder to move and to stop than less massive cars. On the other hand, mass is seen as giving rise to gravitational force, which accounts for the weight of an object: trucks are heavier than cars. The two views of mass are generally considered equivalent. Thus, from the perspective of either inertial mass or gravitational mass, according to the principle of mass conservation, different measurements of the mass of an object taken under various circumstances should always be the same.

With the advent of relativity theory (1905), the notion of mass underwent a radical revision. Mass lost its absoluteness. The mass of an object was seen to be equivalent to energy , to be interconvertible with energy, and to increase significantly at exceedingly high speeds near that of light. The total energy of an object was understood to comprise its rest mass as well as its increase of mass caused by high speed. The rest mass of an atomic nucleus was discovered to be measurably smaller than the sum of the rest masses of its constituent neutrons and protons. Mass was no longer considered constant, or unchangeable. In both chemical and nuclear reactions, some conversion between rest mass and energy occurs, so that the products generally have smaller or greater mass than the reactants. The difference in mass, in fact, is so slight for ordinary chemical reactions that mass conservation may be invoked as a practical principle for predicting the mass of products. Mass conservation is invalid, however, for the behaviour of masses actively involved in nuclear reactors, in particle accelerators, and in the thermonuclear reactions in the Sun and stars. The new conservation principle is the conservation of mass-energy. See also energy, conservation of ; Einstein’s mass-energy relation.

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2 Easy Examples of the Law of Conservation of Mass

General Education

Chemistry is an important subject that you’ll definitely need to know if you’re planning to pursue a chemistry or other science major in college. One thing you should be familiar with is the law of conservation of mass.  What is it? And how is it used in chemistry?

Keep reading to learn what the law of conservation of mass is and how it came to be. We will also give you some law of conservation of mass examples to help you understand the concept better.

What Is the Law of Conservation of Mass?

First off, exactly what is the law of conservation of mass? This law states that in a closed system, matter can neither be created nor destroyed—it can only change form.

Put differently, the amount, or mass, of matter in an isolated system will always be constant regardless of any chemical reactions or physical changes that take place. (Note that an isolated or closed system is one that does not interact with its environment.)

This law is important in chemistry, particularly when combining different materials and testing the reactions between them.

In chemistry, the law of conservation of mass states that  the mass of the products (the chemical substances created by a chemical reaction) will always equal the mass of the reactants (the substances that make the chemical reaction).

Think of it as being similar to balancing an algebraic equation. Both sides around an equal sign might look different (for example, 6 a + 2 b = 20), but they still represent the same total quantity. This is similar to how the mass must be constant for all matter in a closed system—even if that matter changes form!

But how does the law of conservation of mass work?

When a substance undergoes a chemical reaction, you might assume that some or even all of the matter present is disappearing, but, in actuality, it's simply changing form.

Think about when a liquid turns into a gas. You might think that the matter (in this case, the liquid) has simply vanished. But if you were to actually measure the gas, you'd find that the initial mass of the liquid hasn’t actually changed.  What this means is that the substance, which is now a gas, still has the same mass it had when it was a liquid (yes—gas has mass, too!).

What Is the History Behind the Law of Conservation of Mass?

Though many people, including the ancient Greeks, laid the scientific groundwork necessary for the discovery of the law of conservation of mass, it is French chemist Antoine Lavoisier (1743-1794) who is most often credited as its discoverer. This is also why the law is occasionally called Lavoisier’s law.

In the late 1700s, Lavoisier proved through experimentation that the total mass does not change in a chemical reaction, leading him to declare that matter is always conserved in a chemical reaction.

Lavoisier’s experiments marked the first time someone clearly tested this idea of the conservation of matter by measuring the masses of materials both before and after they underwent a chemical reaction.

Ultimately, the discovery of the law of conservation of mass was immensely significant to the field of chemistry because it proved that matter wasn’t simply disappearing (as it appeared to be) but was rather changing form into another substance of equal mass.

What Are Some Law of Conservation of Mass Examples?

Law of conservation of mass examples are useful for visualizing and understanding this crucial scientific concept. Here are two examples to help illustrate how this law works.

Example 1: The Bonfire/Campfire

One common example you’ll come across is the image of a bonfire or campfire.

Picture this: you’ve gathered some sticks with friends and lit them with a match. After a couple of toasted marshmallows and campfire songs, you realize that the bonfire, or campfire, you've built has completely burned down. All you’re left with is a small pile of ashes and some smoke.

Your initial instinct might be to assume that some of the campfire's original mass from the sticks has somehow vanished. But it actually hasn’t —i t’s simply transformed!

In this scenario, as the sticks burned, they combined with oxygen in the air to turn into not just ash but also carbon dioxide and water vapor. As a result, If we measured the total mass of the wooden sticks and the oxygen before setting the sticks on fire, we'd discover that this mass is equal to the mass of the ashes, carbon dioxide, and water vapor combined.

Example 2: The Burning Candle

A similar law of conservation of mass example is the image of a burning candle.

For this example, picture a regular candle, with wax and a wick. Once the candle completely burns down, though, you can see that there is definitely far less wax than there was before you lit it. This means that some of the wax (not all of it, as you’ve likely noticed with candles you’ve lit in real life!) has been transformed into gases —namely,  water vapor and carbon dioxide.

As the previous example with the bonfire has shown, no matter (and therefore no mass) is lost through the process of burning.

Recap: What Is the Law of Conservation of Mass?

The law of conservation of mass is a scientific law popularized and systematized by the 18th-century French chemist Antoine Lavoisier.

According to the law, in an isolated system, matter cannot be created or destroyed — only changed.  This means that the total mass of all substances before a chemical reaction will equal the total mass of all substances after a chemical reaction. Simply put, matter (and thus mass) is always conserved, even if a substance changes chemical or physical form.

Knowing this scientific law is important for the study of chemistry, so if you plan to get into this field, you'll definitely want to understand what the law of conservation of mass is all about!

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Are there other science topics you want to review? Then you're in luck! Our guides will teach you loads of useful topics, from how to convert Celsius to Fahrenheit , to what the density of water is , to how to balance chemical equations .

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Hannah received her MA in Japanese Studies from the University of Michigan and holds a bachelor's degree from the University of Southern California. From 2013 to 2015, she taught English in Japan via the JET Program. She is passionate about education, writing, and travel.

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Law of Conservation of Mass: Definition, Formula, History (w/ Examples)

One of the great defining principles of physics is that many of its most important properties unwaveringly obey an important principle: Under easily specified conditions, they are ​ conserved ​, meaning that the total amount of these quantities contained within the system you’ve chosen never changes.

Four common quantities in physics are characterized by having laws of conservation that apply to them. These are ​ energy ​, ​ momentum ​, ​ angular momentum ​ and ​ mass ​. The first three of these are quantities often specific to mechanics problems, but mass is universal, and the discovery – or demonstration, as it were – that mass is conserved, while confirming some long-held suspicions in the science world, was vital to prove.

The Law of the Conservation of Mass

The ​ law of conservation of mass ​ states that, in a ​ closed system ​ (including the whole universe), mass can neither be created nor destroyed by chemical or physical changes. In other words, ​ total mass is always conserved ​. The cheeky maxim "What goes in, must come out!" appears to be a literal scientific truism, as nothing has ever been shown to simply vanish with no physical trace.

All of the components of all of the molecules in every skin cell you've ever shed, with their oxygen, hydrogen, nitrogen, sulfur and carbon atoms, still exist. Just as the mystery science fiction show ​ The X-Files ​ declares about the truth, all mass that ever was "is out there ​ somewhere ​."

It could be called instead “the law of conservation of matter” because, absent gravity, there is nothing special in the world about especially “massive” objects; more on this important distinction follows, as its relevance is difficult to overstate.

History of the Mass Conservation Law

The discovery of the law of conservation of mass was made in 1789 by the French scientist Antoine Lavoisier; others had come up with the idea before, but Lavoisier was first to prove it.

At the time, much of the prevailing belief in chemistry about atomic theory still came from the ancient Greeks, and thanks to more recent ideas, it was thought that something within fire ("​ phlogiston ​") was actually a substance. This, scientists reasoned, explained why a pile of ashes is lighter than whatever was burned to produce the ashes.

Lavoisier heated ​ mercuric oxide ​ and noted that the amount the chemical's weight decreased was equal to the weight of the oxygen gas released in the chemical reaction.

Before chemists could account for the masses of things that were difficult to track, such as water vapor and trace gases, they could not adequately test any matter conservation principles even if they suspected such laws were indeed in operation.

In any case, this led Lavoisier to state that matter must be conserved in chemical reactions, meaning the total amount of matter on each side of a chemical equation is the same. This means the total number of atoms (but not necessarily the total number of molecules) in the reactants must equal the amount in the products, regardless of the nature of the chemical change.

• "​ The mass of the products in chemical equations is equal to the mass of the reactants ​" is the basis of stoichiometry, or the accounting process by which chemical reactions and equations are mathematically balanced in terms of both mass and number of atoms on each side. 

Overview of Conservation of Mass

One difficulty people can have with the law of conservation of mass is that the limits of your senses make some aspects of the law less intuitive.

For example, when you eat a pound of food and drink a pound of fluid, you might weigh the same six or so hours later even if you don’t go to the bathroom. This is in part because carbon compounds in food are converted to carbon dioxide (CO 2 ) and exhaled gradually in the (usually invisible) vapor in your breath.

At its core, as a chemistry concept, the law of conservation of mass is integral to understanding physical science, including physics. For instance, in a momentum problem about collision, we can assume the total mass in the system has not changed from what it was before the collision to something different after the collision because mass – like momentum and energy – is conserved.

What Else Is "Conserved" in Physical Science?

The ​ law of conservation of energy ​ states that total energy of an isolated system never changes, and that can be expressed in a number of ways. One of these is KE (kinetic energy) + PE (potential energy) + internal energy (IE) = a constant. This law follows from the first law of thermodynamics and assures that energy, like mass, cannot be created or destroyed.

• The sum of KE and PE is called ​ mechanical energy, ​ and is constant in systems in which only conservative forces act (that is, when no energy is "wasted" in the form of frictional or heat losses).

​ Momentum ​ (m​ v ​) and ​ angular momentum ​ (​ L ​ = m​ vr ​) are also conserved in physics, and the relevant laws strongly determine much of the behavior of particles in classical analytical mechanics.

Law of Conservation of Mass: Example

The heating of calcium carbonate, or CaCO 3 , produces a calcium compound while liberating a mysterious gas. Let's say you have 1 kg (1,000 g) of CaCO 3 , and you discover that when this is heated, 560 grams of the calcium compound remain.

What is the likely composition of the remaining calcium chemical substance, and what is the compound that was liberated as gas?

First, since this is essentially a chemistry problem, you'll need to refer to a periodic table of elements (see Resources for an example).

You are told that you have that initial 1,000 g of CaCO 3 . From the molecular masses of the constituent atoms in the table, you see that Ca = 40 g/mol, C = 12 g/mol, and O = 16 g/mol, making the molecular mass of calcium carbonate as a whole 100 g/mol (remember there are three oxygen atoms in CaCO 3 ). However, you have 1,000 g of CaCO 3 , which is 10 moles of the substance.

In this example, the calcium product has 10 moles of Ca atoms; because each Ca atom is 40 g/mol, you have 400 g total of Ca that you can safely assume was left after the CaCO 3 was heated. For this example, the remaining 160 g (560 – 400) of post-heating compound represents 10 moles of oxygen atoms. This must leave 440 g of mass as a liberated gas.

The balanced equation must have the form

and the "?" gas must contain carbon and oxygen in some combination; it must have 20 moles of oxygen atoms – you already have 10 moles of oxygen atoms to the left of the + sign – and therefore 10 moles of carbon atoms. The "?" is CO 2. (In today's science world, you have heard of carbon dioxide, making this problem something of a trivial exercise. But think to a time when even scientists didn't even know what was in "air.")

Einstein and the Mass-Energy Equation

Physics students might be confused by the famous ​ conservation of mass-energy equation ​ ​ E = mc ​ 2 postulated by Albert Einstein in the early 1900s, wondering if it defies the law of conservation of mass (or energy), since it seems to imply mass can be converted to energy and vice versa.

Neither law is violated; instead, the law affirms that mass and energy are actually different forms of the same thing.

It is kind of like measuring them in different units given the situation.

Mass, Energy and Weight in the Real World

You perhaps cannot help but unconsciously equate mass with weight for the reasons described above – mass is only weight when gravity is in the mix, but when in your experience is gravity ​ not ​ present (when you're on Earth and not in a zero-gravity chamber)?

It is hard, then, to conceive of matter as just stuff, like energy in its own right, that obeys certain fundamental laws and principles.

Also, just as energy can change forms between kinetic, potential, electrical, thermal and other types, matter does the same thing, though the different forms of matter are called ​ states ​: solid, gas, liquid and plasma.

If you can filter how your own senses perceive the differences in these quantities, you might be able to appreciate that there are few actual differences in the physics.

Being able to tie major concepts together in the "hard sciences" may seem arduous at first, but it is always exciting and rewarding in the end.

Related Articles

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• Georgia State University: HyperPhysics: Conservation Laws
• Scitable by Nature Education: The Conservation of Mass
• Chemistry LibreTexts: Lavoisier's Law of Conservation of Mass
• Stanford Encyclopedia of Philosophy: The Equivalence of Mass and Energy
• American Chemical Society: The Chemical Revolution of Antoine-Laurent Lavoisier
• IMDB: The X-Files Trivia
• Ptable: Dynamic Periodic Table of the Elements

About the Author

Kevin Beck holds a bachelor's degree in physics with minors in math and chemistry from the University of Vermont. Formerly with ScienceBlogs.com and the editor of "Run Strong," he has written for Runner's World, Men's Fitness, Competitor, and a variety of other publications. More about Kevin and links to his professional work can be found at www.kemibe.com.

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The Conservation of Matter During Physical and Chemical Changes

Matter makes up all visible objects in the universe, and it can be neither created nor destroyed.

Chemistry, Conservation, Earth Science, Geology, Physics

Water in Three States

Water can exist in three different physical states—as a gas, liquid, and a solid—under natural conditions on Earth. Regardless of its physical state, they all have the same chemical composition. Water is 2 hydrogen atoms bonded to 1 oxygen atom.

Photograph by OJO Images Ltd.

Matter makes up everything visible in the known universe, from porta-potties to supernovas . And because matter is never created or destroyed, it cycles through our world. Atoms that were in a dinosaur millions of years ago—and in a star billions of years before that—may be inside you today. Matter is anything that has mass and takes up space. It includes molecules , atoms, fundamental particles , and any substance that these particles make up. Matter can change form through physical and chemical changes, but through any of these changes matter is conserved . The same amount of matter exists before and after the change—none is created or destroyed. This concept is called the Law of Conservation of Mass . In a physical change, a substance’s physical properties may change, but its chemical makeup does not. Water, for example, is made up of two hydrogen atoms and one oxygen atom. Water is the only known substance on Earth that exists naturally in three states: solid, liquid, and gas. To change between these states, water must undergo physical changes. When water freezes, it becomes hard and less dense, but it is still chemically the same. There are the same number of water molecules present before and after the change, and water’s chemical properties remain constant. To form water, however, hydrogen and oxygen atoms must undergo chemical changes. For a chemical change to occur, atoms must either break bonds and/or form bonds. The addition or subtraction of atomic bonds changes the chemical properties of the substances involved. Both hydrogen and oxygen are diatomic —they exist naturally as bonded pairs (H 2 and O 2 , respectively). In the right conditions, and with enough energy, these diatomic bonds will break and the atoms will join to form H 2 O (water). Chemists write out this chemical reaction as:

2H 2 + O 2 → 2H 2 O

This equation says that it takes two molecules of hydrogen and one molecule of oxygen to form two molecules of water. Notice that there are the same number of hydrogen atoms and oxygen atoms on either side of the equation. In chemical changes, just as in physical changes, matter is conserved. The difference in this case is that the substances before and after the change have different physical and chemical properties. Hydrogen and oxygen are gases at standard temperature and pressure, whereas water is a colorless, odorless liquid. Ecosystems have many chemical and physical changes happening all at once, and matter is conserved in each and every one—no exceptions. Consider a stream flowing through a canyon—how many chemical and physical changes are happening at any given moment? First, let’s consider the water. For many canyon streams, the water comes from higher elevations and originates as snow. Of course that’s not where the water began —it’s been cycled all over the world since Earth first had water. But in the context of the canyon stream, it began in the mountains as snow. The snow must undergo a physical change —melting—to join the stream. As the liquid water flows through the canyon, it may evaporate (another physical change) into water vapor. Water gives a very clear example of how matter cycles through our world, frequently changing form but never disappearing. Next, consider the plants and algae living in and along the stream. In a process called photosynthesis , these organisms convert light energy from the sun into chemical energy stored in sugars. However, the light energy doesn’t produce the atoms that make up those sugars—that would break the Law of Conservation of Mass —it simply provides energy for a chemical change to occur. The atoms come from carbon dioxide in the air and water in the soil. Light energy allows these bonds to break and reform to produce sugar and oxygen, as shown in the chemical equation for photosynthesis :

6CO 2 + 6H 2 O + light → C 6 H 12 O 6 (sugar)+ 6O 2

This equation says that six carbon dioxide molecules combine with six water molecules to form one sugar molecule and six molecules of oxygen. If you added up all the carbon, hydrogen, and oxygen atoms on either side of the equation, the sums would be equal; matter is conserved in this chemical change. When animals in and around the stream eat these plants, their bodies use the stored chemical energy to power their cells and move around. They use the nutrients in their food to grow and repair their bodies—the atoms for new cells must come from somewhere. Any food that enters an animal’s body must either leave its body or become part of it; no atoms are destroyed or created. Matter is also conserved during physical and chemical changes in the rock cycle. As a stream carves deeper into a canyon, the rocks of the canyon floor don’t disappear. They’re eroded by the stream and carried off in small bits called sediments. These sediments may settle at the bottom of a lake or pond at the end of the stream, building up in layers over time. The weight of each additional layer compacts the layers beneath it, eventually adding so much pressure that new sedimentary rock forms. This is a physical change for the rock, but with the right conditions the rock may chemically change too. In either case, the matter in the rock is conserved. The bottom line is: Matter cycles through the universe in many different forms. In any physical or chemical change, matter doesn’t appear or disappear. Atoms created in the stars (a very, very long time ago) make up every living and nonliving thing on Earth—even you. It’s impossible to know how far and through what forms your atoms traveled to make you. And it’s impossible to know where they will end up next. This isn’t the whole story of matter, however, it’s the story of visible matter. Scientists have learned that about 25 percent of the universe’s mass consists of dark matter—matter that cannot be seen but can be detected through its gravitational effects. The exact nature of dark matter has yet to be determined. Another 70 percent of the universe is an even more mysterious component called dark energy, which acts counter to gravity. So “normal” matter makes up, at most, five percent of the universe.

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