Summary - Unit 11 - Equilibrium II (9CH0)

Calculating Kc: Kp:
E.g. 1 mole of ethanoic acid and 1 mole of ethanol are allowed = eqm in terms of partial pressures
to reach eqm in a sealed vessel at volume 0.5dm3 - Only for homogeneous systems in the gas phase or
At eqm amount of ethanol = 0.33 moles. Calc Kc heterogeneous systems including gases (IGNORE
1. Equation: SOLIDS AND LIQUIDS)
CH3COOH + CH3CH2OH ⇌ CH3COOCH2CH3 + H2O
2. Kc expression:
Kc = [CH3COOCH2CH3]x[H2O]
[CH3COOH]x[CH3CH2OH]
3. ICE - initial, change, eqm Partial pressure:
(use balancing numbers to work this out) Pa = Xa x Ptot
CH3COOH + CH3CH2OH ⇌ CH3COOCH2CH3 + H2O - Ptot = total pressure in Pa or kPa
I 1 1 0 0 - Xa = mole fraction = moles of a
C -0.67 -0.67 +0.33 +0.33 total moles of all gases present
E 0.33 0.33 0.67 0.67 Calculating Kp:
4. Conc = n/v 1. Work out mole fraction for each GAS species (ICE)
Use vol in dm3 from eq (0.5dm3) - Equation
CH3COOH + CH3CH2OH ⇌ CH3COOCH2CH3 + H2O - Kc expression
0.33 0.33 0.67 0.67 - ICE
0.5 0.5 0.5 0.5 1. Find partial pressure
=0.66 =0.66 =1.34 =1.34 - Pa = Xa x Ptot
(don't need to do this step because the volume is the same for 1. Put partial pressure into Kp eq
all of them ∴ same ratio) 2. Answers with units
5. Into Kc equation & units Units = same as Kc but use kPa instead
Kc = 1.34x1.34
0.66x0.66 Extra things to remember:
= 4.122 no units - Changing temp will affect position of eqm and ∴ change
Summary: Kc and Kp
6. Equation - Changing pressure or conc or adding a catalyst will not
7. Kc expression affect position of eqm ∴ won't affect Kc or Kp
8. ICE
9. Conc = n/v
10. Into Kc equation & units