What four things could be done to increase the yeild of SO3 in the following system?2SO2+02 =2SO3 with a change in potential energy of -99kJ/mol.   I understand that it is an exothermic reaction.

Expert Answers
thilina-g eNotes educator| Certified Educator

2SO2+O2 <----> 2SO3

This can be explained by using Le Chatelier's Principle.

Le Chatelier's Principle:

"If a chemical system at equilibrium experiences a change in concentration, temperature, volume, or partial pressure, then the equilibrium shifts to counteract the imposed change and a new equilibrium is established"

Therefore if we change some parameter which will make the equilibrium shift to the forward, we can increase the SO3 yield. Let's find out how we can shift the reaction forward.

1) Increase SO2 concentration of reactant side

The equilibrium constant = Kc

Kc = [SO3]^2/([SO2]^2 [O2])

If we increase SO2 concentration on reactant side, the reaction will produce more SO3 to keep Kc constant.

2)This can be done increasing the O2 concentration also.

3) Decrease the temperature or extract heat out of the system.

If we extract heat out of the system, according to the Le Chatelier's principle, the system will look to produce more heat. Therefore it will shift the reaction forward since the forward reaction is exothermic. Therefore by making more SO2 system counteract the decrease of temperature.

4) Increase the partial pressure by decreasing volume

If we decrease the volume of the system, the total pressure of the system will increase so as the partial pressures of substances. According to Le Chateliers principle, if we increase the pressure of the system, it will try to decrease it. The only way of doing so is shifting the reaction to the side where it has less number of moles. The product side of this reaction has only 2 moles while compared to the 3 of reactant side. Therefore when we increase pressure, the reaction will shift to the forward and will produce more SO2.