Question

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In a chemical reaction,





A.
the same number of atoms must be on both sides of the equation.




B.
the same elements must be in the reactants and the products.




C.
the mass of the reactants must equal the mass of the products.




D.
all of these.

Answer 1

D. all of these

Answer 2

D
In a chemical change, all the atoms in the reactants end up in the products. Chemical changes involve rearranging atoms to form different substances, atoms cannot be conjured up from nothing or disappear into thin air! So, the mass of the reactants is always equal to the mass of the products. However, in some situations, it can look otherwise. For example, when magnesium burns (reacts with oxygen) the mass of the magnesium oxide produced is more than the magnesium you started with. But of course, when you weighed the magnesium, you didn't weigh the oxygen gas from the air. If youweighed the magnesium atoms and the oxygen molecules involved, the mass would be equal to the mass of the magnesium oxide product. As another example, consider marble chips (calcium carbonate) reacting with hydrochloric acid. If you weigh the beaker containing the reactants the mass will decrease over time, until the reaction is complete. Of course we can account for this mass loss, because carbon dioxide gas is produced and in an unsealed beaker this will escape into the atmosphere and the mass will decrease. If we did not allow the gas to escape the mass would not change. So, the massof what you start with is always equal to the mass of what you end up with. You always have the same atoms on both sides of a chemical equation (although when gases are involved it can look like mass is lost or gained) they are just rearranged!

Answer 3

d