Question

At constant temperature and pressure, when 8 volumes of dihydrogen gas react with 4 volumes of dioxygen, the mass of water vapor produced is

• A. 36 g
• B. 72 g
• C. 162 g
• D. 144 g

Hint:

For reactions involving gases at constant temperature and pressure, the volumes of gases react in simple ratios, and the masses can be calculated using the molar mass of the product.

Answer 1

The Correct Option is D

Step 1: Applying the law of combining volumes.
According to the law of combining volumes, the volumes of reacting gases are in simple whole number ratios. Here, 8 volumes of hydrogen (H$_2$) react with 4 volumes of oxygen (O$_2$) to form 8 volumes of water vapor (H$_2$O).
Step 2: Molar relationship.
From the balanced chemical equation: \[ 2H_2 + O_2 \rightarrow 2H_2O \] The molar ratio of hydrogen to water is 2:2, so the volume ratio is 1:1. Thus, 8 volumes of H$_2$ will produce 8 volumes of H$_2$O.
Step 3: Calculating the mass of water produced.
The molar mass of water (H$_2$O) is 18 g/mol. Since the volume of hydrogen is 8 volumes, this corresponds to 8 moles of water. Therefore, the mass of water produced is: \[ \text{Mass of H}_2\text{O} = 8 \times 18 = 144 \, \text{g} \] Step 4: Conclusion.
The correct answer is (D) 144 g.