Which statement best describes conservation in chemical reactions?

• A. The total energy must always increase
• B. Matter and energy are neither created nor destroyed
• C. The number of atoms must balance only for elements with transition metals
• D. Energy is conserved but mass can be created

Answer: (B)

Conservation in chemical reactions means that matter and energy aren’t created or destroyed; atoms are simply rearranged into new substances. The number of atoms of each element must be the same on both sides of a reaction, so chemical equations are balanced. Energy can change form during the process—chemical energy can become heat, light, or motion—so you might see the surrounding temperature rise or fall, but the total energy in a closed system stays constant. In ordinary chemistry, mass is conserved too, so reactants and products share the same total mass. The other ideas—energy must always increase or mass can be created—don’t fit with these conservation principles.