25. Consider the following reaction at equilibrium: C (s) + H 2 O (g) INCLUDEPIC

Question

25. Consider the following reaction at equilibrium:

C (s) + H2O (g) INCLUDEPICTURE "http://session.masteringchemistry.com/problemAsset/1801265/2/doublearrowshort.jpg" * MERGEFORMATINET CO (g) + H2 (g)

Which of the following conditions will decrease the partial pressure of CO?

[A] increasing the pressure of the reaction vessel

[B] decreasing the amount of carbon in the system

[C] adding a catalyst to the reaction system

[D] increasing the amount of H2O (g)

[E] decreasing the pressure of the reaction vessel

26. Consider the following reaction at equilibrium:

2SO2 (g) + O2 (g) INCLUDEPICTURE "http://session.masteringchemistry.com/problemAsset/1801266/2/doublearrowshort.jpg" * MERGEFORMATINET 2SO3 (g) H° = -99 kJ

Le Châtelier's principle predicts that a(n) increase in temperature will result in ________.

[A] an increase in the partial pressure of SO3

[B] an increase in the partial pressure of SO2

[C] a decrease in the partial pressure of SO2

[D] no changes in equilibrium partial pressures

[E] a(n) increase in Keq

27. In which of the following reactions would increasing pressure at constant temperature not change the concentrations of reactants and products, based on Le Châtelier's principle?

[A] N2 (g) + 3H2 (g) INCLUDEPICTURE "http://session.masteringchemistry.com/problemAsset/1801217/1/doublearrowshort.jpg" * MERGEFORMATINET 2NH3 (g)

[B] N2 (g) + 2O2 (g) INCLUDEPICTURE "http://session.masteringchemistry.com/problemAsset/1801217/1/doublearrowshort.jpg" * MERGEFORMATINET 2NO2 (g)

[C] N2 (g) + O2 (g) INCLUDEPICTURE "http://session.masteringchemistry.com/problemAsset/1801217/1/doublearrowshort.jpg" * MERGEFORMATINET 2NO (g)

[D] N2O4 (g) INCLUDEPICTURE "http://session.masteringchemistry.com/problemAsset/1801217/1/doublearrowshort.jpg" * MERGEFORMATINET 2NO2 (g)

[E] 2N2 (g) + O2 (g) INCLUDEPICTURE "http://session.masteringchemistry.com/problemAsset/1801217/1/doublearrowshort.jpg" * MERGEFORMATINET 2N2O (g)

Explanation / Answer

a) C(s)+H2O(g)---->CO(g)+ H2(g)

The reaction is endothermic with delH= 131.4 Kj/mol

K= [CO] [H2]/ [H2O]

for partial pressure of CO to decrease, less CO will have to be produced. If temperature is increases, the reaction being endothermic, proceeds in the exothermic direction leading to reduction in partial pressure of CO. Alternatively, when pressure is increased, the reaction moves in a direction where is a decrease in number of moles, so towards reactants side. Hence less CO and less partial pressure of CO

b)2SO2+O2---> 2SO3 delG= -99 Kj/mol

The reaction is exothermic and increasing the temperature takes the reaction to endothermic direction. So more SO2 and O2 will be formed. Hence B is the correct answer,

c) for the gaseous reaction N2(g)+O2(g)-->2NO(g) increasing the pressur will not influence the reaction since number of moles on the reactants side and products side is same.

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