Chemical equilibrium
I can explain the concept of chemical equilibrium and the characteristics of a system in which equilibrium is established.
- Year 11•
- Edexcel
Chemical equilibrium
I can explain the concept of chemical equilibrium and the characteristics of a system in which equilibrium is established.
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.
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.
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.
Equipment
Beakers, plastic pipettes, food colouring, glass rods.
Content guidance
- Risk assessment required - equipment
Supervision
Adult supervision required
Licence
Lesson video
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Prior knowledge starter quiz
6 Questions
Q1.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.
Q2.Why are some reactions reversible?
Q3.If the forward reaction of a reversible reaction is exothermic, the backward reaction will be .
Q4.To carry out the experiment with hydrated and anhydrous copper sulfate, put the steps in order:
Q5.How can reaction conditions be changed so that reaction rates change?
Q6.Models have limitations. What does this image of the particle model NOT attempt to show?
Assessment exit quiz
6 Questions
Q1.Hot coffee cooling to room temperature is a reversible process. It is a rather than a chemical change.
Q2.Equilibrium is a state where opposing forces or processes are balanced. Which statements MUST be true at chemical equilibrium?
Q3.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.
Q4.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?
Q5.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
Q6.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 .
