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Can matter be created or destroyed when a chemical change occurs?
Answer 1:

A chemical reaction does not create or destroy matter, it simply moves electrons from one atom to another, but does not change the nucleus of the atoms. The total mass of the matter remains a constant in any chemical change. The total mass of the matter can change during a nuclear reaction, the mass loss can convert into energy, which is called the nuclear power. So we can say that a nuclear reaction creates/destroys matter, if we define matter only as its mass.

If we define matter as mass plus energy, then even a nuclear reaction does change matter at all: the sum of mass and energy together remain a constant during a nuclear reaction. Actually, the most general definition of matter, should include mass, energy, and also information. The only possible way to permanently annihilate the most general form of matter as defined above, is to throw matter into a black hole, and after the black hole "evaporates" (black holes do evaporate, which was first studied by Stephen Hawking), these matter may disappear from our universe. But this is not a fully understood subject, scientists are still working hard to understand the relation between black hole and information.

Answer 2:

Einstein’s famous equation, E = mc2 , is often interpreted as meaning that mass can be converted directly to energy. However, a better interpretation is that mass is a form of energy – unless that mass energy is converted into a new form (like thermal energy), then it must be conserved, just like the rest of the energy in the system.

By definition, mass is conserved during a chemical change – no matter is created or destroyed but the matter is rearranged into new structures with different properties. Energy is stored in the bonds between atoms, however, so energy can be released or converted during a chemical change. For example, burning wood is a chemical reaction of hydrocarbons with oxygen that creates carbon dioxide, water and lots of heat energy. Other reactions require heat energy to form new bonds, like calcium carbonate (chalk) can be heated to become calcium oxide and carbon dioxide. For both types of reactions, the mass of the starting materials and the end products is the same.

It is very difficult to convert mass directly into energy, or vice versa, in part because there is so much energy per unit of mass. Conversion only measurably occurs in nuclear reactions where one atom becomes another (or multiple atoms) due to changes in the composition of its nucleus. In this worked example from Perdue University, they calculate the energy released by one uranium atom decaying after neutron irradiation. The total mass only changes by 0.2 amu (atomic mass unit) but releases 3.006 x 10-11 Joules of energy. If you scale this up per mole of uranium, the process releases 1.811 x 1010 kJ/mol of U-235 as heat – which is one hundred million times greater than a typical chemical reaction, like burning hydrogen (4.84 x 102 kJ/mol).

Thankfully, that scale of mass-energy conversion is rare and unlikely to happen without extreme conditions, like those in a nuclear reactor or within a star.

Note from ScienceLine:
The joule, symbol J, is a derived unit of energy in the International System of Units.

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Answer 3:

Sort of. Energy and mass are equivalent entities as governed by the laws of special relativity. Energy cannot be created or destroyed by any means, chemical or otherwise; however, it can be transformed from one state (e.g. matter) into another (e.g. heat). So, for example, if you burn hydrogen and oxygen together to make water and heat, the water will have very slightly less mass than the reactants you burned to get it.

This change in mass in chemical reactions, however, is so small that it's difficult to measure. Really only nuclear reactions can be measured in terms of the reactants weighing more than the products (which is why nuclear reactions are so powerful).

Answer 4:

Matter cannot be created or destroyed in a chemical reaction; it is rearranged. The number of each different elements remains the same. Yet, after the reaction, an element may link to one element that is different from the one it links to before the reaction. That is, during the process of chemical reaction, some old bonds are broken and some new bonds are created. A chemical reaction creates compounds different from reactants.

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