Question

The reaction for industrially producing ethanol, C₂H₂OH, is given below:

C₂H₂(g) + H₂O(g) → C₂H₂OH(g)
AH=-45 kJ per mole

The temperature and pressure can be changed to increase the yield of ethanol at
equilibrium.

The forward reaction is exothermic

The conditions used in the process are:
.
60 atmospheres pressure
200 °C
phosphoric acid catalyst.

Using the equation and your knowledge of reversible reactions, explain why such a
high pressure is used, why a moderate (not too low or too high) temperature are used
and why a catalyst is used.

Consider both yield and rate of reaction in your answer.
[8 marks]

Answer 1

Step-by-step explanation:

There are 2 moles of gaseous reactants that produce one mole of gaseous products. This means that a change in pressure will affect the reactant side more than the product side. Thus, we should increase the pressure to make it so that pressure is higher on the reactant side than the product side. This will cause the reaction to shift to the product side (ethanol) to reestablish equilibrium and increase the yield of the reaction. Also, increasing the pressure increases the number of collisions the reactants will have with each other, thus increasing the rate of the reaction. Thus, a high pressure is used.

A catalyst is a substance that does not get used up in a reaction that provides an alternate reaction pathway with a lower activation energy, thus speeding up the rate of the reaction. Thus, a catalyst is used.

The reaction is exothermic, so heat gets produced in the reaction and is thus a product in the reaction. Thus, we should decrease the temperature of the reaction because it would decrease the amount of heat on the products side and thus shift the reaction to the product side to reestablish equilibrium and increase the yield of the reaction.

However, the temperature of a reaction also affects the rate of the reaction, so making the temperature too low will make the reaction too slow. On the contrary, making the temperature too high increases the amount of heat on the products side and thus shifts the reaction to the reactant side to reestablish equilibrium and makes the yield of the reaction too low. Thus, the temperature used is moderate.