1.6.2

# Equilibrium Constants

Test yourself

## Equilibrium Constants

It's great to know all about equilibria, but it's even better to be able to do some maths with it.

### Equilibrium constant: Kc

• The equilibrium constant is for a particular reaction at a particular temperature.
• An equilibrium constant greater than one indicates that the forward reaction dominates.
• An equilibrium constant less than one indicates that the backward reaction dominates.

### Maths

• For the reaction aA + bB $\rightleftharpoons$ cC + dD:
• $K_c = \frac{[D]^d[C]^c}{[A]^a[B]^b}$
• The square brackets indicate concentrations.
• The indices are the stoichiometries of the components.
• These are the numbers before each species in the reaction equation - represented above by lower case letters.

### Calculations

• We may be given the value of Kc so we will have to sub the values in for each concentration, this will give us a value for Kc.
• Make sure to sub the units of each concentration into this calculation to make sure the Kc value has the correct units.
• We can also be given the Kc value and may have to rearrange the equation to find a concentration.