3.9 CHAPTER 3. REACTION RATES
- Le Chatelier’s Principle states that if a chemical system at equilibriumexperi-
ences a change in concentration, temperature or total pressure the equilibrium
will shift in order to minimise that change andto re-establish equilibrium. For
example, if the pressureof a gaseous system atequilibrium was increased, the
equilibrium would shiftto favour the reaction that produces the lowest quantity
of the gas. If the temperature of the same system was to increase, theequilib-
rium would shift to favour the endothermic reaction. Similar principles apply for
changes in concentration of the reactants or products in a reaction. - The principles of equilibrium are very important in industrial applications such
as the Haber process, sothat productivity can bemaximised.
Chapter 3 End of Chapter Exercises
- Consider the following reaction that has reached equilibrium after
some time in a sealed 1dm^3 flask:
PCl 5 (g)� PCl 3 (g) + Cl 2 (g) ΔH is positiveWhich one of the following reaction conditionsapplied to the system
would decrease the rateof the reverse reaction?
(a) increase the pressure
(b) increase the reactiontemperature
(c) continually removeCl 2 (g) from the flask
(d) addition of a suitable catalyst
(IEB Paper 2, 2001)- The following equilibrium constant expressionis given for a particular
reaction:
Kc= [H 2 O]^4 [CO 2 ]^3 /[C 3 H 8 ][O 2 ]^5For which one of the following reactions is theabove expression of
Kcis correct?
(a) C 3 H 8 (g) + 5O 2 (g)� 4 H 2 O (g) + 3CO 2 (g)
(b) 4 H 2 O (g) + 3CO 2 (g)� C 3 H 8 (g) + 5O 2 (g)
(c) 2 C 3 H 8 (g) + 7O 2 (g)� 6 CO (g) + 8H 2 O (g)
(d) C 3 H 8 (g) + 5O 2 (g)� 4 H 2 O(�) + 3CO 2 (g)
(IEB Paper 2, 2001)- 10 g of magnesiumribbon reacts with a 0.15 mol.dm−^3 solution of
hydrochloric acid at a temperature of 25^0 C.
(a) Write a balanced chemical equation for thereaction.
(b) State two ways of increasing the rate of production of H 2 (g).
(c) A table of the resultsis given below: