In A-Level Chemistry, we look at how temperature, pressure, presence ot catalyst and concentration affect Kc.
The way the system responds depends on if it is a exothermic or endothermic reaction, however temperature changes do affect the value of Kc.
- Le Chatelier’s principal predicts that increasing the temperature shifts the equilibrium in the direction that is more endothermic.
- When the temperature is increased the system moves to absorb heat (the endothermic reaction).
- When the temperature is decreased the system moves to give out heat (the exothermic reaction).
Exothermic
An increase in temperature causes the system to shift left.
Endothermic
An increase in temperature causes the system to shift right.
💡💡❗️An increase in temperature increases the rate of forward and backward reactions but to different extents.
Kc DOES NOT change when the total pressure changes. When pressure is increased/decreased, concentrations change, however the system will restore equilibrium by shifting left or right.
💡💡❗️Whilst this has no effect on Kc, an increase in pressure will initially increase the forward and backward reactions equally.
- A catalyst increases the rate of the forward and backward reactions equally.
- It has no effect on the Kc value.
- It has lno effect on the position of equilibrium or the yield.
The value of Kc DOES NOT change when concentrations change. If the concentrations change, the system will no longer be in equilibrium and hence will shift to restore the Kc value.
If the reactants increase, more products are produced to minimise the change of added reactants and vice versa.
Drafted by Eunice (Chemistry)