Which of the following chemical equations best illustrates the law of conservation of mass?

• A. C + O_2 ightarrow CO
• B. N_2 + 3H_2 ightarrow 2NH_3 + H_2
• C. 2H_2 + O_2 ightarrow 2H_2O
• D. Na + Cl_2 ightarrow NaCl_2

Answer: (C)

Verified step by step guidance

1. Step 1: Understand the law of conservation of mass, which states that in a chemical reaction, the total mass of reactants must equal the total mass of products. This means the number of atoms of each element must be the same on both sides of the equation.
2. Step 2: Examine each given chemical equation and count the number of atoms of each element on the reactant side and the product side.
3. Step 3: For the equation \(\mathrm{C + O_2 \rightarrow CO}\), check if the number of carbon and oxygen atoms are balanced. Carbon atoms are balanced, but oxygen atoms are not because \(O_2\) has 2 oxygen atoms and \(CO\) has only 1.
4. Step 4: For the equation \(\mathrm{N_2 + 3H_2 \rightarrow 2NH_3 + H_2}\), count nitrogen and hydrogen atoms on both sides. Notice that there is an extra \(H_2\) molecule on the product side, which makes hydrogen atoms unbalanced.
5. Step 5: For the equation \(\mathrm{2H_2 + O_2 \rightarrow 2H_2O}\), verify that hydrogen and oxygen atoms are balanced. There are 4 hydrogen atoms and 2 oxygen atoms on both sides, illustrating the law of conservation of mass correctly.