New
New
Year 11
AQA
Higher

The rate of a chemical reaction: including graphs

I can describe what happens during a chemical reaction as it progresses over time and interpret graphs showing how the instantaneous rate of the reaction changes.

New
New
Year 11
AQA
Higher

The rate of a chemical reaction: including graphs

I can describe what happens during a chemical reaction as it progresses over time and interpret graphs showing how the instantaneous rate of the reaction changes.

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Lesson details

Key learning points

  1. Most chemical reactions start more quickly and slow down as they progress.
  2. The rate of a chemical reaction is equal to the amount of product formed per unit time (or reactant used per unit time).
  3. The mean rate of a chemical reaction is different to the instantaneous rate that changes throughout the reaction.
  4. Graphs of mass, volume, or concentration vs. time can all represent the changing rate of a chemical reaction.
  5. The gradient of a rate of reaction graph can be calculated from a tangent drawn at a point on the curve.

Keywords

  • Rate of reaction - Rate of reaction is the speed with which a chemical reaction takes place.

  • Mean rate of reaction - The mean rate of reaction is the average rate at which reactants are converted into products over a given period of time.

  • Instantaneous rate of reaction - The instantaneous rate of reaction is the rate at which reactants are converted into products at a specific moment in time.

  • Tangent - A tangent is a straight line that touches a curve at exactly one point without crossing it.

  • Gradient - The gradient on a graph represents the rate at which one quantity changes relative to another.

Common misconception

To calculate the instantaneous rate of reaction by reading values from the graph at a specific time.

Students need to draw a tangent in order to calculate the gradient of the graph at a specific time to work out the instantaneous rate of reaction.

This lesson could be used to practise graph drawing skills. If provided with data, students could plot their own graphs and use these to calculate the mean and instantaneous rate of reaction.
Teacher tip

Licence

This content is © Oak National Academy Limited (2024), licensed on Open Government Licence version 3.0 except where otherwise stated. See Oak's terms & conditions (Collection 2).

Lesson video

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6 Questions

Q1.
Identify the products in this chemical reaction: magnesium + sulfuric acid → magnesium sulfate + hydrogen
magnesium
sulfuric acid
magnesium sulfide
Correct answer: magnesium sulfate
Correct answer: hydrogen
Q2.
What do we call the speed with which a chemical reaction takes place?
speed of reaction
velocity of reaction
Correct answer: rate of reaction
intensity of reaction
Q3.
Which of the following reactions has a relatively low rate of reaction?
combustion of petrol
incomplete combustion of alkanes
Correct answer: rusting of iron
neutralisation of an acid and alkali
Q4.
How do we calculate the gradient of a straight-line graph?
divide the change in time by the change in volume
multiply the change in y-axis value by the change in x-axis value
Correct answer: divide the change in y-axis value by the change in x-axis value
add the change in y-axis value to the change in x-axis value
Q5.
A graph shows the volume of gas produced (in cm³) over time (in seconds). If the graph has a straight line that rises from 0 cm³ at 0 seconds to 40 cm³ at 20 seconds, what is the gradient of the graph
0.5 cm³/s
Correct answer: 2 cm³/s
20 cm³/s
40 cm³/s
Q6.
Given the following data for four different reactions, which reaction has the lowest rate of reaction?
reaction 1 produces 5 cm³ of gas in 10 seconds
reaction 2 produces 10 cm³ of gas in 20 seconds
reaction 3 produces 15 cm³ of gas in 30 seconds
Correct answer: reaction 4 produces 5 cm³ of gas in 20 seconds

6 Questions

Q1.
How do most chemical reactions progress over time?
they start slowly and speed up
they maintain a constant speed
Correct answer: they start quickly and slow down
they stop and start repeatedly
Q2.
What is the rate of a chemical reaction equal to?
the total amount of product formed
Correct answer: the amount of product formed per unit time
Correct answer: the amount of reactant used per unit time
the total time taken for the reaction
the initial amount of reactant
Q3.
Match the keywords with the correct definition.
Correct Answer:mean rate of reaction,the rate in which reactants form products in a given period of time

the rate in which reactants form products in a given period of time

Correct Answer:instantaneous rate of reaction,the rate in which reactants form products at a specific moment in time

the rate in which reactants form products at a specific moment in time

Correct Answer:tangent,a straight line that touches a curve at exactly one point

a straight line that touches a curve at exactly one point

Correct Answer:gradient,represents the rate at which one quantity changes relative to another

represents the rate at which one quantity changes relative to another

Q4.
Why is drawing a tangent useful on a rate of reaction graph?
it shows the total amount of reactant used
Correct answer: it helps find the instantaneous rate at a specific moment
it measures the temperature change over time
it calculates the mean rate of reaction
Q5.
Which of the following can be plotted to represent the changing rate of a chemical reaction?
time versus temperature
Correct answer: mass versus time
pressure versus concentration
Correct answer: concentration versus time
volume versus concentration
Q6.
A chemical reaction produces 0.5 g of gas in 10 seconds. What is the correct rate of reaction?
0.05 grams
10 seconds
Correct answer: 0.05 grams per second
0.05 seconds per gram