AQA · GCSE · Chemistry
Course version: 8462 · Version from Sept 2018
If the concentration of a reactant is increased, more products will be…
Full specification wording
The effect of changing concentration (HT only): If the concentration of a reactant is increased, more products will be formed until equilibrium is reached again.
Increasing the concentration of a reactant disturbs an equilibrium by making the forward reaction faster than the reverse reaction.
Checked against the AQA 8462 specification (opens in a new tab) on .
- Point 2 of 4
- 4 key terms
Study notes
From the checked teaching notes for this specification point.
The idea
Increasing the concentration of a reactant disturbs an equilibrium by making the forward reaction faster than the reverse reaction. The system responds by shifting equilibrium to the right, so more products are formed until the rates of the forward and reverse reactions become equal again. For example, in the equilibrium CH₃COOH(aq) + C₂H₅OH(aq) ⇌ CH₃COOC₂H₅(aq) + H₂O(l), adding more ethanoic acid increases the rate of the forward reaction, producing more ethyl ethanoate until a new equilibrium is established. The final yield of product is greater than before the change, although some of the added reactant remains. This is a qualitative prediction: the direction of shift and the increase in product formation are stated without numerical calculation.
What earns the marks
- State that increasing the concentration of a reactant increases the rate of the forward reaction relative to the reverse reaction.
- Explain that equilibrium shifts to the right, so more products are formed.
- Describe that the shift continues until the forward and reverse reaction rates become equal again at a new equilibrium.
- Use a balanced equation to identify the reactant whose concentration is increased and the product whose yield increases.
- Recognise that the new equilibrium has a greater amount of product than the original equilibrium, but not all added reactant is converted.
Common mistakes and how to put them right
Thinking that all of the added reactant is converted into product.
Put it right: Some remains at the new equilibrium.
Believing that the equilibrium constant changes when a reactant concentration is increased.
Put it right: The position of equilibrium shifts but the equilibrium constant is unchanged at constant temperature.
Stating that the reverse reaction stops.
Put it right: Both reactions continue, but the forward reaction is initially faster.
Exam tips
- Name the reactant added and the product whose yield increases, using the balanced equation.
- Use the phrase shifts to the right and link it to more products being formed until equilibrium is reached again.
- Avoid saying the reaction goes to completion; state that a new equilibrium is established.
Try the lesson
The start of the The effect of changing concentration (HT only): If the concentration of a reactant is increased, more products will be formed until equilibrium is reached again. lesson, made from checked teaching notes for this specification point.
Have a go first
In the equilibrium P(aq) + Q(aq) ⇌ R(aq), the concentration of reactant P is increased. What is the effect on the amount of product R?
Listen
Increasing the concentration of a reactant disturbs an equilibrium by making the forward reaction faster than the reverse reaction. The system responds by shifting equilibrium to the right, so more products are formed until the rates of the forward and reverse reactions become equal again. For example, in the equilibrium CH₃COOH(aq) + C₂H₅OH(aq) ⇌ CH₃COOC₂H₅(aq) + H₂O(l), adding more ethanoic acid increases the rate of the forward reaction, producing more ethyl ethanoate until a new equilibrium is established. The final yield of product is greater than before the change, although some of the added reactant remains. This is a qualitative prediction: the direction of shift and the increase in product formation are stated without numerical calculation. A strong answer earns marks for these points. State that increasing the concentration of a reactant increases the rate of the forward reaction relative to the reverse reaction. Explain that equilibrium shifts to the right, so more products are formed. Describe that the shift continues until the forward and reverse reaction rates become equal again at a new equilibrium. Use a balanced equation to identify the reactant whose concentration is increased and the product whose yield increases. Exam tip: Name the reactant added and the product whose yield increases, using the balanced equation.
See it
Put it in order
Put these steps in the order they happen.
- 1. Greater amount of product than before, but some added reactant remains
- 2. New equilibrium reached
- 3. Equilibrium shifts to the right
- 4. Forward and reverse rates become equal again
- 5. Increase concentration of a reactant
- 6. Forward reaction faster than reverse reaction
- 7. More products formed
Key words
Say what each word means before you turn the card.
Effect of concentration on equilibrium
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Forward and reverse reaction rates
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Product yield
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Dynamic equilibrium
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See every definition
- Effect of concentration on equilibrium
- If the concentration of a reactant is increased, more products will be formed until equilibrium is reached again.
- Forward and reverse reaction rates
- Increasing the concentration of a reactant makes the forward reaction faster than the reverse reaction, and the shift continues until the two rates become equal again.
- Product yield
- The final yield of product is greater than before the change, although some of the added reactant remains.
- Dynamic equilibrium
- A new equilibrium is established in which the forward and reverse reaction rates become equal again, and both reactions continue.
Label the diagram
Some boxes have lost their names. Pick the right name for each number.
1Box 1
2Box 2
3Box 3
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