Question

Question 7.25 Does the number of moles of reaction products increase, decrease or remain same when each of the following equilibria is subjected to a decrease in pressure by increasing the volume?

(a) PCl5(g) <--->PCl3(g) + Cl2(g)

(b) CaO(s) + CO2(g) <---> CaCO3(s)

(c) 3Fe(s) + 4H2O(g) <---> Fe3O4(s) + 4H2(g)

Class XI Equilibrium Page 227

Answer 1

we know, according to concept of Le - Chatelier's principle, when pressure decreases , equilibrium shifts in that direction where pressure increases .
and we know, pressure is directly proportional to no of mole .e.g., number of mole in gaseous state are more.

(a) ∆ng = np - nr = (1 + 1) - 1 = 1 => positive
so, number of moles of reaction products in increases.
(b) ∆ng = 0 - 1 = -1 => negative
so, number of moles of reaction products in decreases.
(c) ∆ng = 4 - 4 = 0 => zero
so, number of moles of reaction products in remains the same.

Answer 2

Answer:

(a) The number of moles of reaction products will increase. According to Le Chatelier’s principle, if pressure is decreased, then the equilibrium shifts in the direction in which the number of moles of gases is more. In the given reaction, the number of moles of gaseous products is more than that of gaseous reactants. Thus, the reaction will proceed in the forward direction. As a result, the number of moles of reaction products will increase.

(b) The number of moles of reaction products will decrease.

(c) The number of moles of reaction products remains the same.

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