Chemistry Regents Practice Test

In the reaction 2H2 + O2 → 2H2O, what is the mass of H2O produced when 10.0 grams of H2 reacts completely with 80.0 grams of O2?

1. 80.0g

2. 90.0g

3. 100.0g

4. 110.0g

The correct answer is: 90.0g

To determine the mass of water (H2O) produced in the reaction, we first need to identify the limiting reactant from the amounts of hydrogen gas (H2) and oxygen gas (O2) available. 1. **Molar Mass Calculation**: First, calculate the molar masses. - The molar mass of H2 is approximately 2.02 g/mol (1.01 g/mol for each hydrogen atom). - The molar mass of O2 is approximately 32.00 g/mol (16.00 g/mol for each oxygen atom). - The molar mass of H2O is approximately 18.02 g/mol (2.02 g/mol for two hydrogen atoms and 16.00 g/mol for one oxygen atom). 2. **Moles of Reactants**: - For H2: \( \text{Moles of H2} = \frac{10.0 \, \text{g}}{2.02 \, \text{g/mol}} \approx 4.95 \, \text{mol} \). - For O2: \( \text{Moles of O2} = \frac{80.0 \,