A summary of topic 11, organised so the notes are easy to understand. The notes are on slides, so they can be printed out and used as revision cards or posters, for revision on the go. The notes cross-reference the specification so it is easy to see where each bit of information has come from. They...
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
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