Consider the following reaction at equilibrium. What effect will adding 1.4 mole of He to the reaction mixture have on the system? 2 H2S(g) + 3 O2(g) ⇌ 2 H2O(g) + 2 SO2(g) Consider the following reaction at equilibrium. What effect will adding 1.4 mole of He to the reaction mixture have on the system? 2 H2S(g) + 3 O2(g) ⇌ 2 H2O(g) + 2 SO2(g) The reaction will shift to the left in the direction of reactants. No effect will be observed. The reaction will shift to the right in the direction of products. The equilibrium constant will increase. The equilibrium constant will decrease.

The reaction will shift to the left in the direction of reactants.

Explanation:

According to Le Chatelier's principle, when an external constraint is applied to a chemical system in equilibrium, the system adjust in order to annul the effect impose on it by the external system.

Also, from the principle, the addition of an inert gas can affect the equilbrium of a gaseous system, but only if the volume is allowed to change.

There are two cases on which equilibrium depends. These are:

1. Addition of an inert gas at constant volume:

When an inert gas is added to the system in equilibrium at constant volume, the total pressure will increase. But the concentrations of the products and reactants (i.e. ratio of their moles to the volume of the container) will not change.  Hence, there will be no effect on the equilibrium.  

2. Addition of an inert gas at constant pressure:

When an inert gas is added to a system in equilibrium at constant pressure, then the total volume will increase(i.e. the number of moles per unit volume of various reactants and products will decrease). Hence, the equilibrium will shift towards the direction in which there is increase in number of moles of gases.  

Considering the given reaction in equilibrium:

2H₂S(g) + 3O₂(g) ⇌ 2H₂O(g) + 2SO₂(g)

The addition of an inert gas at constant pressure to the above reaction will shift the equilibrium towards the backward direction because the number of moles of reactants is more than the number of moles of the products.

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