Question

Consider the following system at equilibrium where K_c = 7.00×10^-5and delta H° = 182 kJ/mol at 673 K.

NH₄I (s) = NH₃(g) + HI (g)

The production of NH₃(g) is favored by:

Indicate True (T) or False (F) for each of the following:

___TF 1. decreasing the temperature.
___TF 2. decreasing the pressure (by changing the volume).
___TF 3. decreasing the volume.
___TF 4. adding NH₄I .
___TF 5. removing HI .

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Answer 1

According to Le chatlier's principle whenever a constraint is applied to a system at equilibrium the system would try to annul the effect of the constraint. The word constraint means a change in temperature ,pressure or change in concentration of the system

1) False

In the present equilibrium the forward reaction is endothermic that is (proceeds by absorption of temperature )if the temperature of such a system is decreased ,the system would try to resist that effect by favoring the backward reaction,which is exothermic i.e that is NH₄I  doesn't decompose (less ammonia formation)

2)True

The present equilibrium proceeds by an increase in the number of moles of the product therefore an increase of the pressure of the system .When we decrease the pressure the system would try to resist that change by undergoing forward reaction.(Decrease in pressure favors forward reaction)

3)False

Here the forward reaction is accompanied by increase in the number of moles of the products.when we decrease the volume the no. of moles per unit volume increases.According to Le chatlier's principle the system would try to increase the No. of moles per unit volume.this is possible only by the backward reaction (Ammonia formation less favored)

4)True

By adding NH₄I we are increasing the concentration of the reactant .According to Le chatlier's principle to reduce the concentration of the reactant forward reaction takes place.that is Ammonia formation takes place

5)True

By removing the HI we are changing the concentration of the product so to cancel that effect more NH₄I is decomposed to Ammonia( NH₃ )and HI