The balanced chemical equation for the synthesis of ammonia by Haber's process is: $N_2(g) + 3H_2(g) \rightleftharpoons 2NH_3(g)$ . According to the stoichiometry of the reaction, $3 \text{ moles}$ of hydrogen molecules ($H_2$) are required to produce $2 \text{ moles}$ of ammonia ($NH_3$) . Therefore, to produce $20 \text{ moles}$ of $NH_3$, the number of moles of $H_2$ required will be: $\text{Moles of } H_2 = \frac{3}{2} \times 20 \text{ mol} = 30 \text{ mol}$.