Kc: Remember Kc = products/ reactants. Remember the larger the value, further away from

position equilibrium and towards products- AS.

Know how to work out Kc if given equilibrium concentrations. Now looking at how Kc calculated

from experimental results.

Kc Expression: Include symbol formula, state symbol with square brackets around it. Have

balancing number as power.

Any solids and liquids omitted in Kc expression. Only include gas and

aq.

Units of Kc: Sometimes no units. Add powers when brackets expanded.

Homogeneous Equilibria: Homogeneous equilibrium contains equilibrium species that all have

the same state.

Heterogeneous Equilibria: Heterogeneous equilibrium contains equilibrium species that have

different states.

Calculating Kc from Experimental Results:

Question will ask ‘find amounts of X in mol in the equilibrium mixture’ or ‘mixture was allowed

to reach equilibrium’ etc.

1.6 mol of NO and 1.4 mol of O2 mixed in container with volume 4 dm3

. At equilibrium, 1.2 mol

NO2 formed (moles when equilibrium reached). Bold given in question. Work backwards.

Equation 2NO + O2 -> 2NO2

Reacting Amounts 2 1 2 what is in equation

Initial/ mol 1.6 1.4 0 the normal moles, amounts used, given in

Q

Change/ mol -1.2 -0.6 +1.2 use moles reacting amounts

Equilibrium/ mol 0.4 0.8 1.2 product given, work out reactants.

These equilibrium amounts divided by total volume x1000 = equilibrium concentrations mol dm3

.

Then write Kc expression and sub in these equilibrium concentrations as normal. Remember

balancing number as power.

Watch out if volume given in dm3

. Do not need 1000 into calculations.

Check which equilibrium amount given, might not be products like usual.

Remember to minus for reactants but add for products to find equilibrium moles.

If given equilibrium moles straight away, don’t need to do table above, just find equilibrium

concentrations.

May not need volume sometimes as volume cancels in Kc expression.

Sometimes says uses 4 dm3 container- use this value as volume in calculations.

Can do above with Kp and others.

Should never get a large number of these calculations but a decimal.

May require calculations to find initial moles and equilibrium moles. If says ethanoic acid at

equilibrium required 72.5 cm3

of a 1.50 moldm–3 solution of NaOH for complete reaction. Work

out moles of NaOH, which equals moles of ethanoic acid at equilibrium = 0.1. However since

flask contains 0.2 moles of ethanoic acid, 0.2 – 0.1 = 0.1 which is the moles of ethanoic acid

reacted- like table above. Use this and molar ratio to find moles of others.

If H2 initial amount increases, the H2 equilibrium amount increases. So the equilibrium shifts left

and HI increases but I2 decreases.

Ag+ reacts with I– to form AgI. Yellow precipitate forms. Equilibrium 2 shifts to the left.

Equilibrium 1 shifts to left. I2 comes out of solution, I2 precipitates. – Write full equations and

talk about both equilibrium shifts.