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# Equilibria

#### 2018 Paper One

##### Question Two

###### This question is worth 9-marks.

###### Issues

###### Total pressure as the sum of partial pressures missed

###### Incorrect units for the equilibrium constant

###### Failure to link Le Chatelierâ€™s principle and that equilibrium shifts/moves to oppose the increase in temperature.

###### The total pressure = 150 kPa and the mole fraction of ammonia was 0.80:

###### partial pressure of the ammonia is 150 x 0.80 = 120 kPa

###### The other partial pressures are 150 â€“ 120 = 30 kPa

###### Since there is a 1:3 mole ratio for nitrogen: hydrogen, the mole fraction for nitrogen is 0.25 and for hydrogen it's 0.75 (3 x 0.25)

###### pp nitrogen = 0.25 x 30 = 7.5 kPa

###### pp hydrogen = 0.75 x 30 = 22.5 or 23 kPa

###### pp of ammonia = 0.8 x 150 = 120 kPa

###### Straightforward, but the mark will be lost if square brackets are used

###### Enthalpy change is negative so reaction is exothermic in the forward direction.

###### Increasing temperature will cause a decrease in the value of the equilibrium constant

###### Equilibrium will move left in the endothermic direction

###### to reduce the temperature

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