TYPICAL QUESTIONS
Q. 1. The equilibrium constant of a reaction is 2.5 ×13-3 at 250C. Is the reaction
exothermic or endothermic?
Ans: The
reaction is endothermic as the increase in temperature shifts the equilibrium
in the formed direction.
Q. 2. The dissociation of hydrogen iodide is independent of
pressure where as the dissociation of PCL5 depends upon pressure.
Justify.
Ans: In the dissociation of
hydrogen iodine, the number of moles of gaseous moles of the reaction is equal
to the number of gaseous moles of the products. Thus, the pressure does not
affect the state of equilibrium but it is not so in the dissociation of PCL5.
Q. 3. The following system is
in equilibrium: SO2CL2+HeatDSO2+CL2. What will happen to the
temperature of the system if some chlorine is added into it at constant volume?
Give reason.
Ans: If the concentration of CL2 is increased, then the
reaction shifts in the backward direction. The reaction is that the backward
reaction is exothermic.
Q.4.Can equilibrium is
achieved between water and its vapours in an open vessel? Explain your answers.
Ans: Equilibrium cannot be achieved in an open vessel. The
reason is that water vapours diffuse into air and their concentration over
water surface is negative. Due to this, the reverse process of concentration of
vapours into liquid is almost negligible.
Q.5.The following system is in
equilibrium: SO2CL2+ HEATDSO2 +CL2. What will happen to
the temperature of the system if some chlorine is added into it at constant volume?
Given reason:
Ans:
If the concentration of Cl2 is increased, then the reaction shifts
in the backward direction. The reaction is that the backward reaction is exothermic.
Q.6. (a) why is chemical equilibrium called dynamic equilibrium?
(b) What would be the effect of increasing the
temperature on the following Equilibrium? 2SO2(g)
+O2(g) D2SO3(g) ∆H◦ = -198 kJ
Ans:
(a)Properties of a system do not change after the
establishment of equilibrium and we may think that the reaction has stopped altogether.
However, this is not true. Actually the rate of forward reaction becomes equal
to the rate of backward reactions so that there is no net change in the concentration
of various species. Thus, it is a dynamic balance between backward and forward
reaction. Thus the chemical equilibrium is dynamic in nature.
(b)The negative value of ∆H◦ shows that the forward reaction is exothermic. Therefore,
backward reaction will naturally be endothermic. On increasing the temperature,
will shifts in the direction of endothermic reaction, which tends to undo the
effect of added heat. Hence lesser amount of sulphur trioxide will be formed on
increasing the temperature.
Q.7.Can
equilibrium be achieved between water and its vapours in an open vessel?
Explain your answer.
Ans: Equilibrium cannot be achived in an open vessel. The
reason is that water vapours diffuse into air and their concentration over
water surface is negative. Due to this, the reverse process of condensation of
vapours into liquid is almost negligible.
Q.8.In
which condition, the rates of the backward reactions are equal ?
Ans:
The rates of the forward and the backward reaction are equal only at the state of equilibrium.
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