Question

For the complete reaction, how many moles of water are formed by a mixture of 100 grams of $H_2$ and 100 grams of $O_2$?

• A. $\frac{100}{32}+\frac{100}{64}$
• B. $100+2\times \frac{(160}{32}$
• C. $2\times \frac{100}{32}$
• D. $100\times \frac{100}{132}$
• E. $200\times \frac{100}{32}$

Answer 1

The correct option is C $2\times \frac{100}{32}$

$2H_2+O_2\to 2H_{2}O$
The molar masses of hydrogen and oxygen are 2 g/mol and 32 g/mole respectively.
The number of moles is the ratio of mass to molar mass.
The number of moles of hydrogen $=\frac{100g}{2\text{g/mol}}=50$ mol.
The number of moles of oxygen $=\frac{100g}{32\text{g/mol}}=\frac{100}{32}$ mol
50 moles of hydrogen reacts with 25 moles of oxygen however only $\frac{100}{32}$ moles of oxygen are present. Hence, oxygen is the limiting reagent.
$\frac{100}{32}$ moles of oxygen will give $2\left(\frac{100}{32}\right)$ moles of water.