Module 3Module 3

Lesson 12/13 Reversible Reactions & Dynamic Equilibria

ObjectivesObjectives

MustState that some chemical reactions are reversibleShouldDescribe how reversible reactions reach a state of equilibriumCouldExplain how at dynamical equilibrium the rate of the forward reaction is equal to the rate of the reverse reaction.

MustState that some chemical reactions are reversibleShouldDescribe how reversible reactions reach a state of equilibriumCouldExplain how at dynamical equilibrium the rate of the forward reaction is equal to the rate of the reverse reaction.

Reversible or not reversibleReversible or not reversible

Until now, we were careful to say that most chemical reactions were not reversible –

They could not go back to the reactants once the products are formed.

ExampleExample

ReversibleReversible

• Some chemical reactions, however, will go backwards and forwards depending on the conditions.

• CoCl2·6H2O(s) CoCl2(s) + 6H2O(l) pink blue

How do we write them down?How do we write them down?

• This is the symbol for used for reversible

reactions.

CoCl2·6H2O(s) CoCl2(s) + 6H2O(l)

What is equilibrium?What is equilibrium?

General equationGeneral equation

• This is the equation for a general reaction which has reached dynamic equilibrium:

• How did it reach this balanced state

• Eventually, the rates of the two reactions will become equal.

• A and B will be converting into C and D at exactly the same rate as C and D convert back into A and B again

Dynamic Equilibrium. Dynamic Equilibrium.

Other examplesOther examples

2NO2 N2O4

Briggs Rauscher – an awesome set of 10 competing chemical reactions in equilibrium

Plenary - Examination questionsPlenary - Examination questions

• As a warm up we will use some GCSE level answers.

Mark schemeMark scheme

SummarySummary

State that some chemical reactions are reversible

Describe how reversible reactions reach a state of equilibrium

Explain this using dynamic equilibrium model.

State that some chemical reactions are reversible

Describe how reversible reactions reach a state of equilibrium

Explain this using dynamic equilibrium model.