A chemical reaction has the following balanced equation: 2 H_2 + O_2 ightarrow 2 H_2O. If you start with 4 grams of H_2, how many grams of H_2O can be produced, assuming excess O_2?

• A. 4 grams
• B. 36 grams
• C. 8 grams
• D. 18 grams

Answer: (B)

Verified step by step guidance

1. Identify the balanced chemical equation: \$2\ H_2 + O_2 \rightarrow 2\ H_2O$.
2. Calculate the molar mass of hydrogen gas (\(H_2\)). Since each hydrogen atom has an atomic mass of approximately 1 g/mol, \(M_{H_2} = 2 \times 1 = 2\ \text{g/mol}\).
3. Convert the given mass of \(H_2\) to moles using the formula: \(\text{moles of } H_2 = \frac{\text{mass of } H_2}{M_{H_2}} = \frac{4\ \text{g}}{2\ \text{g/mol}}\).
4. Use the stoichiometric ratio from the balanced equation to find moles of \(H_2O\) produced. According to the equation, 2 moles of \(H_2\) produce 2 moles of \(H_2O\), so moles of \(H_2O\) produced equals moles of \(H_2\) reacted.
5. Calculate the mass of \(H_2O\) produced by multiplying the moles of \(H_2O\) by its molar mass. The molar mass of water (\(H_2O\)) is \$2 \times 1 + 16 = 18\ \text{g/mol}\(. So, \)\text{mass of } H_2O = \text{moles of } H_2O \times 18\ \text{g/mol}$.