Question

1. choose the best answer. in the synthesis reaction $2h_2 + o_2 \

ightarrow 2h_2o$, 6.0 moles of hydrogen are reacted with oxygen. how many moles of oxygen are needed? 18.0 mol 3.0 mol 6.0 mol 12.0 mol 9) choose the best answer.

Explanation:

Step1: Balance the Fe-O reaction

Balance Fe first: $4\text{Fe}(s) + \square\text{O}_2(g)
ightarrow 2\text{Fe}_2\text{O}_3(s)$
Balance O next: $4\text{Fe}(s) + 3\text{O}_2(g)
ightarrow 2\text{Fe}_2\text{O}_3(s)$

Step2: List 6 mole ratios

1. $\frac{4\ \text{mol Fe}}{3\ \text{mol O}_2}$, 2. $\frac{3\ \text{mol O}_2}{4\ \text{mol Fe}}$,
2. $\frac{4\ \text{mol Fe}}{2\ \text{mol Fe}_2\text{O}_3}$, 4. $\frac{2\ \text{mol Fe}_2\text{O}_3}{4\ \text{mol Fe}}$,
3. $\frac{3\ \text{mol O}_2}{2\ \text{mol Fe}_2\text{O}_3}$, 6. $\frac{2\ \text{mol Fe}_2\text{O}_3}{3\ \text{mol O}_2}$

Step3: Find moles of $\text{O}_2$ for $\text{H}_2$ reaction

Use mole ratio $\frac{1\ \text{mol O}_2}{2\ \text{mol H}_2}$
$\text{Moles of O}_2 = 6.0\ \text{mol H}_2 \times \frac{1\ \text{mol O}_2}{2\ \text{mol H}_2}$

Answer:

1. Balanced equation: $4\text{Fe}(s) + 3\text{O}_2(g)

ightarrow 2\text{Fe}_2\text{O}_3(s)$

1. 6 mole ratios:

$\frac{4\ \text{mol Fe}}{3\ \text{mol O}_2}$, $\frac{3\ \text{mol O}_2}{4\ \text{mol Fe}}$, $\frac{4\ \text{mol Fe}}{2\ \text{mol Fe}_2\text{O}_3}$, $\frac{2\ \text{mol Fe}_2\text{O}_3}{4\ \text{mol Fe}}$, $\frac{3\ \text{mol O}_2}{2\ \text{mol Fe}_2\text{O}_3}$, $\frac{2\ \text{mol Fe}_2\text{O}_3}{3\ \text{mol O}_2}$

1. C. 3.0 mol