Which of the following is a correctly balanced chemical equation?

• A. 2 H_2 + O_2 → 2 H_2O
• B. H_2 + O_2 → H_2O
• C. 2 H_2 + 2 O_2 → 2 H_2O
• D. H_2 + 2 O_2 → 2 H_2O

Answer: (A)

Verified step by step guidance

1. Identify the chemical species involved in the reaction: hydrogen gas (H_2) and oxygen gas (O_2) react to form water (H_2O).
2. Write the unbalanced chemical equation: \(\mathrm{H_2 + O_2 \rightarrow H_2O}\).
3. Count the number of atoms of each element on both sides of the equation. On the reactant side, there are 2 hydrogen atoms and 2 oxygen atoms; on the product side, there are 2 hydrogen atoms and 1 oxygen atom.
4. Balance the oxygen atoms by adjusting the coefficients. Since oxygen appears as O_2 on the reactant side and as a single oxygen atom in H_2O on the product side, place a coefficient of 2 in front of H_2O to have 2 oxygen atoms on the product side: \(\mathrm{H_2 + O_2 \rightarrow 2 H_2O}\).
5. Balance the hydrogen atoms by adjusting the coefficient of H_2 on the reactant side. Since there are now 4 hydrogen atoms on the product side (2 molecules of H_2O, each with 2 hydrogens), place a coefficient of 2 in front of H_2: \(\mathrm{2 H_2 + O_2 \rightarrow 2 H_2O}\). This equation is now balanced with 4 hydrogen atoms and 2 oxygen atoms on both sides.