Which of the following chemical equations follows the law of conservation of mass?

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

Answer: (C)

Verified step by step guidance

1. Step 1: Understand the law of conservation of mass, which states that matter cannot be created or destroyed in a chemical reaction. This means the number of atoms of each element must be the same on both sides of the equation.
2. Step 2: For each given chemical equation, count the number of atoms of each element on the reactant side and compare it to the number on the product side.
3. Step 3: For example, in the equation \$2H_2 + O_2 \rightarrow 2H_2O\(, count hydrogen atoms: on the left, there are \)2 \times 2 = 4\( hydrogen atoms, and on the right, \)2 \times 2 = 4\( hydrogen atoms. For oxygen, on the left, there are \)2\( oxygen atoms, and on the right, \)2 \times 1 = 2$ oxygen atoms. Since these match, this equation follows the law of conservation of mass.
4. Step 4: Check the other equations similarly. For instance, \(Na + Cl_2 \rightarrow NaCl_2\) has 1 sodium atom on the left but 1 on the right, but chlorine atoms are 2 on the left and 2 on the right, but the product formula \(NaCl_2\) is unusual and likely incorrect. Also, verify if the formulas are chemically valid.
5. Step 5: Identify the equation where the number of atoms for each element is balanced on both sides and the chemical formulas are correct. That equation follows the law of conservation of mass.