7.4 Calculations Involving Equilibrium Constants and 7.5 Explaining Le Chatelier's Principle

Question 1

When working out Kc what concentrations must be used?

Answer 1

Equilibrium concentrations.

Question 2

What calculations do you use for most concentration calculations?

Answer 2

ICE.

Question 3

How can the effect pf changes in concentration of equilibrium be explained?

Answer 3

Using Kc and Q.

Question 4

For the reaction A + B C + D what happens if more of C is added to the reaction mixture so the concentration doubles?

Answer 4

At the moment of addition all other concentrations have not changed so only the increased concentration of C needs to be taken into account, Q is greater than Kc so the system is not at equilibrium.

Question 5

Since Q is greater than Kc for the previous reaction what must happen?

Answer 5

The equilibrium must proceed more tot he eft to reduce the concentration of C and D (on top of the Kc and Q fraction) and so reduces the value of Q until it equals K. There will be more A and B present when equilibrium is established again, which is in agreement with Le Chatelier’s principle - the position of equilibrium shifts to the left to use up the added C.