C6 Le Chatelier's Principle (pg 148)

Question 1

What is Le Chatelier’s Principle mean?

Answer 1

it is the idea that if you change the conditions of a reversible reaction at equilibrium, the system will try to counteract that change.

Question 2

What can the Le Chatelier’s Principle be used to predict?

Answer 2

it will predict the effect of any changes you make to a reaction system, such as changes to temperature, pressure or concentration.

Question 3

finish the sentence…

All reactions are exothermic in one direction and endothermic…….

Answer 3

in the other direction.

Question 4

What will happen if you decrease the temperature regarding the equilibrium?

Answer 4

the equilibrium will move in the exothermic direction to produce more heat. This means you’ll get more products for the exothermic reaction and fewer products for the endothermic reaction.

Question 5

what will happen if you raise the temperature regarding the equilibrium?

Answer 5

the equilibrium will move in the endothermic direction to try and decrease it. You’ll now get more products for the endothermic reaction and fewer products for the exothermic reaction.

Question 6

explain what this reaction means?

N2 + 3H2 &raquo_space;»>
««&laquo_space; 2NH3

Answer 6

Here the forward reaction is exothermic - a decrease in temperature moves equil rium to the right (more NH3)

Question 7

Changing the pressure only affects an equibilibrium involving what?

Answer 7

involving gasses.

Question 8

What happens if you increase the pressure, regarding the equilibrium?

Answer 8

it tries to reduce it - it moves in the direction where there are fewer molecules of gas.

Question 9

What happens if you decrease the pressure regarding the equilibrium?

Answer 9

the equilibrium tries to increase it - it moves in the direction where there are more molecules of gas.

Question 10

Why can you use the balanced symbol equation for a reaction?

Answer 10

to see which side has more molecules of gas.

Question 11

Explain this reaction:

N2 + 3H2 &raquo_space;»»>
«««< 2NH3

Answer 11

There are 4 moles on the left (1 of N2 and 3 of H2) but only 2 on the right. So, if you increase the pressure, the equilibrium shifts to the right (more NH3)

Question 12

What will happen if you change the concentration of either the reactants or the products?

Answer 12

the system will no longer be at equilibrium, so the system responds to bring itself back to equilibrium again.

Question 13

What happens if you increase the concentration of the reactants?

Answer 13

the system tries to decrease it by making more products.

Question 14

What happens if you decrease the concentration of the products?

Answer 14

the system tries to increase it again by reducing the amount of reactants.

Question 15

Explain this reactant?

N2 + 3H2 &raquo_space;»
«&laquo_space; 2NH3

Answer 15

The more N2 or H2 is added, the forward reaction increases to produce more NH3

(reversible reactions don’t like being messed around - so if you change something, the system will respond to undo the change.

Question 16

For each of the following reactions, state the effect of an increase in pressure on the amount of products at equilibrium?

a) CO2(g) + H2O(l) &raquo_space;»>
««< H2CO3(aq)

b) NH4Cl(s) &raquo_space;»>
««< NH3(g) + HCl(g)

c) 2CO(g) + O2(g) &raquo_space;»
«&laquo_space; 2CO2(g)

Answer 16

a) more H2CO3(aq) would be produced (1 mark)

b) Less NH3(g) and HCl(g) would be produced (1 mark)

c) More CO2(g) would be produced (1 mark)

(you do one thing and the reaction does another. on the face of it, that sounds like it’d be a pain, but in reality it’s what gives you control of what happens in a reversible reaction. And in industry, control is what makes this profitable).