Topic 4&5 - Reversible reactions, equilibrium and dynamic equilibrium

What is a reversible reaction?

Reactions where the products react to form reactants.

This is an example of a reversible reaction

What is the symbol used in reversible reactions?

Give 3 common reversible reactions

1. heating hydrated copper sulphate

2. heating ammonium chloride

3. making ammonia

What are the word and symbol equations for the reaction of heating hydrated copper sulphate?

hydrated copper sulphate →←anhydrous copper sulphate + water

hydrated meaning

water of crystallisation present

anhydrous meaning

containing no water

What are the word and symbol equations for the reaction of heating ammonium chloride?

NH4Cl (s) →← NH3 (g) + HCl (g)

Ammonium chloride →← ammonia + hydrogen chloride

What is observed to form in the heating of ammonium chloride?

a white solid (NH4Cl) because it is a reversible reaction the condenses very quickly

What are the word and symbol equations for the reaction of making ammonia?

nitrogen + hydrogen →← ammonia

N2 + 3H2 →← 2NH3

What is the difference between ammonium and ammonia?

• Ammonia is NH3 (a compound)

• Ammonium is NH4+ (a cation derived from ammonia)

What state is ammonia at room temp?

gas

What are the features of a reaction at dynamic equilibrium?

1. Rate of the forward reaction equals the rate of the reverse reaction

2. Concentrations of reactants and products remain unchanged

3. The reaction must take place in a closed system

4. dynamic means that the reaction is still continuing, they are still reacting

What are the factors which affect the position of equilibrium?

1. Changing the temp

2. Changing the pressure (when the reaction involves gases)

3. Changing the concentration of reactants or products

What effect does altering certain factor generally have on the position of equilibrium?

It causes equilibrium to shift until equilibrium is re-established

What was the purpose of Le Chatelier’s Principle?

to allow us to make predictions about which way the equilibrium reaction will shift when we change the conditions.

It tells us that equilibrium will shift to the side that will counteract the changes (such as in temp/ pressure/ concentration), and then restores equilibrium

Explain the effect of temperature of the position of equilibrium

Increasing the temperature will cause the equilibrium to shift to the side which will make the temperature decrease

The side which will make the temp decrease is the direction which is endothermic

Finish the sentences:

1.increasing the temperature shifts equilibrium to the …….. direction

2.decreases the temperature shifts equilibrium to the …….. direction

1.endothermic

2.exothermic

For the following reaction explain how an increase in temp will affect the position of equilibrium

• Equilibrium will shifts to the reactants

• because the reverse reaction is endothermic

For the following reaction explain how an decrease in temp will affect the position of equilibrium

• equilibrium will shift to reactants

• because the reverse reaction is exothermic

What affect does pressure have on the position of equilibrium?

the greater the frequency of the collisions. or the greater the energy of the collisions, then the greater the pressure.

What will happen to the position of equilibrium generally if the pressure increases?

equilibrium will shift to the side that will make the pressure decrease

The more particles in the same volume the (greater/ lesser) the pressure

greater

What affect does increasing the pressure have on the position of equilibrium?

• equilibrium shifts to the side with the least moles of gas

What affect does decreasing the pressure have on the position of equilibrium?

• equilibrium shifts to the side with the most moles of a gas

Explain how decreasing the pressure of the reaction above would affect the position of equilibrium

• equilibrium will shift to the products

• because the products have the more moles of a gas

What can pressure be changed by ?

changing the volume of the container

What affect will decreasing the volume of a container have on the pressure?

it will increase the pressure

What affect will increasing the volume of a container have on the pressure?

It will decrease the pressure

Explain how decreasing the volume of the reaction below would affect the position of equilibrium

• decreasing the volume will increase the pressure

• so equilibrium will shift to the products

• because there are less moles of a gas in the products

What affect does concentration generally have on the position of equilibrium?

If you increase the concentration of a reactant or product at equilibrium, the reaction will shift to the opposite side (from which it was added)

What affect does concentration generally have on the position of equilibrium?

If you remove a reactant or product from a reaction at equilibrium, (decreasing the concentration), the reaction will shift towards the side from which it was removed, to try to increase its concentration again, until equilibrium is re-established

What would happen to the position of equilibrium if A is added to the reaction below?

• equilibrium shifts to the products

• to decrease the concentration of A

Explain what would happen to the position of equilibrium if B is removed from the following reaction

• equilibrium shifts to the reactants

• to increase the concentration of B

here is something else to be aware of

Question may also ask you to observe what you might see if you change certain concentrations.

How should you respond to these questions?

In response to these questions you should state what happens to the colour:

• if the change made shifts equilibrium to the side with the coloured substance then the colour would darken.

• if the change shifts equilibrium to the other side the colour would fade
  

What affect does adding a catalyse have on the position of equilibrium?

It has no affect on the position of equilibrium

What is a catalyst?

a substance which:

• increases the rate of the forward and reverse reactions equally/ by the same amount

• by providing an alternative reaction pathway

• so more particles have energy bigger than or equal to the activation energy

catalysts only affect THE RATE OF THE REACTION AND NOT THE POSITION OF EQUALIBRIUM