M5 Equilibrium Q&A
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Describe and explain the effect of an increase in temperature on the composition of the following equilibrium mixture and on the value of Kc
• The forward reaction is exothermic • If temperature increases the position of equilibrium shifts to the left • The reverse (endothermic) reaction takes in the heat • The composition of the reaction mixture: concentration of reactants increases (bottom of Kc) concentration of products decreases (top of Kc) • The value of Kc decreases And vice versa for a decrease in temperature! And vice versa for an endothermic forward reaction!
Describe and explain the effect of an increase in concentration of N2 on the composition of the following equilibrium mixture and on the value of Kc
• If concentration of N2 increases the position of equilibrium shifts to the right • To minimise the effects of the increase in concentration There is no effect on Kc * When the concentration of N2 increases, the bottom/denominator of Kc increases (or the ratio decreases) * So the concentration of products increase to make the top/numerator of Kc increase (or to increase the ratio) * The value of Kc is restored And vice versa for a decrease in concentration! And vice versa for a change in product concentration!
Describe and explain the effect of an increase in pressure on the composition of the following equilibrium mixture and on the value of Kp
• The reaction has 4 moles gas –> 2 moles gas • If pressure increases the position of equilibrium shifts to the right • There are fewer gaseous moles on the right • The pressure decreases There is no effect on Kp * When the total pressure increases, all the partial pressures increase * There are more partial pressures of reactants so the bottom/denominator of Kp increases (or the ratio decreases) more than the top/numerator of Kp * So the partial pressures of products increase to make the top/numerator of Kp increase (or to increase the ratio) * The value of Kp is restored And vice versa for a decrease in pressure! And vice versa for a reaction with more gaseous moles on the right!
Why is it difficult to predict the effect of an increase in temperature and an increase in pressure on the composition of the following equilibrium mixture:
• If temperature increases the position of equilibrium shifts to the left (forward reaction is exothermic) • If pressure increases the position of equilibrium shifts to the right (fewer gaseous moles on the right hand side) • The relative effects of temperature and pressure are not known