Question

The combustion of methane is a reaction in which methane gas burns in oxygen to produce carbon dioxide and water vapor. It is represented by the equation:

CH4 (g) + 2O2 (g) → CO2 (g) + 2H2O (g)

In the equation, one molecule of methane gas requires two molecules of oxygen gas to produce one molecule of carbon dioxide gas and two molecules of water in vapor form.

The molecules in the equation can be modeled with circles to represent atoms and straight lines to represent the bonds between them, as shown in the picture.



A student observes the model and claims that the total mass of the reaction is conserved. Is the student's claim correct? Why or why not?

a
Yes, because the reactants and products are made of atoms of the same elements.
b
No, because the total number of atoms in products is greater than the total number of atoms in reactants.
c
No, because the arrangement of atoms is different in the reactants and products.
d
Yes, because the number of atoms of each element is the same on both sides of the equation.

Answer 1

d

Yes. The chemical equation shows the same number of each type of atom on both sides (1 C, 4 H, 4 O), so mass is conserved — the atoms are just rearranged into new molecules.