To go through the different effects, let's look at an example reaction at equilibrium
A(g) + B(aq) <--> C(g) + D(g)
We can think about disturbing an equilibrium reaction like an elevataor. When there are 2 people on an elevator and a third person gets on, the first 2 adjust their position. Their "equilibrium" has been disturbed and they are trying to minimize the effects of that disturbance (i.e. they don't want to be too close to the third person)
We see the same thing with an equilibrium reaction. A system at equilibrium is disturbed and the reaction responds to minimize that disturbance.
1) addition of a substance - If we add more of a substance, the reaction will respond by moving away from the formation of that substance. In our example above, if we add A, the reaction will proceed to the right.
2) removal of a substance - Removing a substance will cause the reaction to shift to make more of that substance. If we we remove A, the reaction will shift to the left.
3) changing the pressure by changing the volume - If we decrease the volume of the reaction vessel which will result in an increase in the pressure, the reaction will proceed towards the side with fewer moles of *gas*. Increasing the volume and decreasing the pressure will result in the opposite effect. If there are equal moles of gas on both sides, there will be no change.
4) Changing the pressure by addition of an inert gas will *NOT* have any affect on the equilibrium.
5) Changing the temperature - When we change the temperature, we need to look at whether the reaction is endothermic or exothermic. Let's look at exothermic as an example. For an exothermic reaction, heat is being given off so we can consider heat as a product. Increasing the temperature (i.e. adding heat) will result in the reaction shifting to the left to minimize the production of more heat). Decreasing the temperature will result in the reacting shifting to the right to make more heat as cooling a reaction is like taking heat away. For endothermic reaction, we treat heat as a reactand and would see the opposite effect for increases and decreases in temperature.