Question

how many moles of iron is needed if 4800 kj of energy is released from reaction 3 fe(s) + 2 o₂(g) → fe₃o₄ δh = -1120 kj.
2.15 mole
6.43 mole
4.29 mole
12.86 mole

Explanation:

Step1: Determine mole - energy relationship

From the reaction $3Fe(s)+2O_2(g)
ightarrow Fe_3O_4$, $\Delta H=- 1120\ kJ$. This means that when 3 moles of Fe react, 1120 kJ of energy is released.

Step2: Set up proportion

Let $x$ be the number of moles of Fe. We have the proportion $\frac{3\ mol\ Fe}{1120\ kJ}=\frac{x}{4800\ kJ}$.

Step3: Solve for $x$

Cross - multiply: $1120x = 3\times4800$. Then $x=\frac{3\times4800}{1120}=\frac{14400}{1120}\approx12.86$ moles.

Answer:

12.86 mole