Question

For each of the reactions at constant pressure, determine whether the system does work on the surroundings, the surroundings does work on the system, or essentially no work is performed.
(a) 4Fe + 3O2 --> 2Fe2O3
(b) 2H2O2 --> O2 + 2H2O

Answer 1

Explanation:

When work is done then there will occur change in volume. And, most change in volume occurs when there will be production of gas is taking place. We assume that no work is done when no gas is produced.

(a)   For $4Fe(s) + 3O_{2}(g) \rightarrow 2Fe_{2}O_{3}(s)$

Here, 3 moles of gas is producing 0 moles of gas. This means that work is done on the system.

(b)  And, more is the production of a gas taking place in a reaction more will be the amount of work done by the system.

For $2H_{2}O_{2}(g) \rightarrow O_{2}(g) + 2H_{2}O(g)$

Here, 2 moles of a gas is producing 3 moles of a gas. Since, gas is increasing so, work will be done by the system.