Chemical equilibrium | Chemistry | Quizalize & Oak National Academy

Starter quiz

Physical changes are easily reversible by changing the ______, for example changing the state of water from ice to liquid by heating, and back to ice by cooling.

'conditions' ✓
Why are some reactions reversible?

addition is more easily achieved than decomposition

conditions for forward and backward reactions can easily be met ✓

dehydration is more easily achieved than hydration

reactants and products have comparable stability ✓

the reaction does not involve any energy change
If the forward reaction of a reversible reaction is exothermic, the backward reaction will be ______.

'endothermic' ✓
To carry out the experiment with hydrated and anhydrous copper sulfate, put the steps in order:

1

⇔

Place 5 g of powdered blue copper(II) sulfate in a test tube.

2

⇔

Heat the copper sulfate until the colour no longer changes.

3

⇔

Record any observations during the heating process.

4

⇔

Allow the anhydrous copper sulfate to cool back to room temperature.

5

⇔

Pour the collected water very slowly onto the cooled powder.

6

⇔

Record any observations when the water is poured back onto the powder.
How can reaction conditions be changed so that reaction rates change?

adding a catalyst to the reaction ✓

changing the shape and size of glassware

changing the surface area of a solid reactant ✓

varying the concentration of reactant ✓

varying the temperature of the reaction ✓
Models have limitations. What does this image of the particle model NOT attempt to show?

arrangement of particles

elasticity of particles ✓

forces between particles ✓

movement of particles ✓

Exit quiz

Hot coffee cooling to room temperature is a reversible process. It is a ______ rather than a chemical change.

'physical' ✓
Equilibrium is a state where opposing forces or processes are balanced. Which statements MUST be true at chemical equilibrium?

amounts of reactions and products are constant ✓

amounts of reactants and products are equal

changes in amounts of reactants and products are equal ✓

reaction rates of forward and backward reaction are equal ✓
Dynamic equilibrium occurs in a ______ system when forward and backward reactions occur at the same rate, and the concentrations of reactants and products remain constant.

'closed' ✓
A closed system of a glass container is filled with NO $_2$ under conditions which allows the equilibrium with N $_2$ O $_4$ to be established. Why will you never observe a colourless situation?

N $_2$ O $_4$ can leave the system, which disrupts the balance of equilibrium.

N $_2$ O $_4$ is a light brown gas and NO $_2$ is a dark brown gas.

There is never a full conversion of reactant molecules to product molecules. ✓
Match the following key terms to their definition.

closed system

⇔

system where matter cannot enter/leave, but energy can be transferred ✓

dynamic equilibrium

⇔

opposing processes occur with equal rates; no observable changes ✓

irreversible reaction

⇔

reaction where reactants form products; reaction goes to completion ✓

open system

⇔

system where both matter and energy can freely enter and leave ✓

reversible reaction

⇔

reaction where reactants form products, which revert to reactants ✓
The models of water with food colouring, or of cars entering/leaving a road, are unhelpful for the ‘dynamic’ aspect of equilibrium, as you cannot see that individual molecules are continuously ______.

'changing' ✓

Worksheet

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Lesson Details

Key learning points

At equilibrium, both reactants and products are formed at the same rate.
Amounts of reactants and products remain constant at equilibrium.
Equilibrium can only occur in a closed system.

Common misconception

Equilibrium can occur in an open system; no reactions occur at equilibrium; amounts of reactants and products are equal at equilibrium.

Equilibrium requires a closed system; in an open system, matter exchange disrupts balance. At equilibrium, reactions still occur but at equal rates, leading to constant amounts, not necessarily equal amounts of reactants and products.

Keywords

Dynamic equilibrium - occurs in a closed system when the forward and backward reactions of a reversible chemical reaction occur at the same rate; and the concentrations of reactants and products remain constant.
Reaction rate - is the speed with which a chemical reaction takes place, measured by the amount of a reactant used or amount of product formed in a given time.
Closed system - is one in which matter cannot enter or leave the observed environment, allowing only energy transfer between the system and its surrounding environment.