The Equilibrium Constant

Question 1

What is Kc?

Answer 1

This is the equilibrium constant.

Question 2

What happens when you have a homogeneous reaction that has reached dynamic equilibrium?

Answer 2

You can work out the equilibrium constant.

Question 3

What is meant by a homogeneous reaction?

Answer 3

This is where all of the reactants and products are in the same physical state.

Question 4

What is the general reaction?

Answer 4

aA+bB=dD+eE

Question 5

What do the lower case letters stand for?

Answer 5

Moles of substance.

Question 6

What does the upper case letters stand for?

Answer 6

Products/reactants

Question 7

What do the square brackets stand for?

Answer 7

Concentration

Question 8

What is concentration measured in?

Answer 8

mol dm-3

Question 9

What is the express ion for Kc?

Answer 9

Kc= ([D]^d X [E]^e)/([A]^a X [B]^b)

Question 10

How do you calculate Kc?

Answer 10

By putting numbers into the expressions.

Question 11

Are the units for Kc always the same?

Answer 11

No

Question 12

How do you find the units for Kc?

Answer 12

Put the units in the expression instead of the number, then cancel out as much as possible.

Question 13

What can you do with the value of Kc?

Answer 13

You can estimate the position of equilibrium.

Question 14

What happens if the value of Kc is high?

Answer 14

The larger the value of Kc, the further to the right equilibrium lies. There are more products relative to the reactants.

Question 15

What happens if the value of Kc is low?

Answer 15

The smaller the value of Kc, the further to the left equilibrium lies. There are more reactants relevant to the products.

Question 16

How can you investigate the equilibrium position with changing temperature using NO2 and N2O4?

Answer 16

Place two sealed tubes containing the equilibrium mixture in water baths, one water bath should be warm and the other should be cool. Observe the colours of the mixtures.

Question 17

What will happen to the tube in the warm water bath?

Answer 17

It will change to a darker brown colour as the endothermic reaction speeds up to absorb the extra heat, pushing equilibrium to the left.

Question 18

What will happen to the tube in the cool water bath?

Answer 18

The solution will lose colour as the exothermic reaction speeds up to replace the heat, shifting the equilibrium to the right.

Question 19

How can you investigate the equilibrium position with changing concentration?

Answer 19

Mix iron(111) nitrate with potassium thiocyanate to produce iron(111) thiocyanate.

Question 20

What colour is iron(111)nitrate?

Answer 20

Yellow

Question 21

What colour is potassium thiocyanate?

Answer 21

It is colourless.

Question 22

What colour is iron(111) thiocyanate?

Answer 22

Blood red

Question 23

What happens when more reactants are added to the experiment?

Answer 23

The forward reaction speeds up to produce more product.

Question 24

What happens when more product is added?

Answer 24

The backward reaction speeds up so more reactants are created.