Equilibrium
Le Chatelier's Principle tells us what happens to the equilibrium of a chemical system (reaction) when certain stresses are inflicted onto it.
Temperature
When the temperature of a system is increased, the system moves away from the heat. For instance, for a forward exothermic reaction, it would move to the reactants side, favouring the endothermic reaction. For a forward endothermic reaction, it would however favour the forward reaction with an increase in heat.
The opposite occurs when heat is removed.
Concentration
When the concentration of a reactant is increased, the equilibrium shifts to the right and favours the formation of products. The opposite occurs when the concentration of a product is increased, it shifts to the left.
Pressure/Volume
Pressure and volume are inversely proportional, meaning an increase in pressure leads to a decrease in volume (and vice versa). When pressure is increased/volume is decreased, the system shifts in the direction of least moles/molecules. Count the sum of the coefficients on the reactants and products side to determine which side this is.
Again, the opposite occurs when pressure is decreased or volume is increased; the system shifts to the side with more moles.
Other Things to Note
- Remember, only gases and aqueous solutions affect the equilibrium. Pure substances, such as solids and liquids, are not.
- For instance, if the concentration of a solid substance is increased, it will not have an affect on the equilibrium.
- The addition of a catalyst will have no effect on the equilibrium.
- Temperature is the only thing that affects the equilibrium constant.
Answers
Taking into account all the pieces of information mentioned above, here is what our answers should be to the given question:
A. Increasing [SO2]: shifts right
B. Removing O2: shifts left
C. Increasing temperature: shifts left
D. Decreasing pressure: shifts left
E. Add a catalyst: no effect
