Question 1 Medium
Give two ways to make a reaction between a solid and an acid go faster, without changing the acid.
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Answer: use a powder and increase the temperature
- Use smaller pieces of the solid.
- Heat the mixture.
Rates of reaction and catalysts: GCSE Combined Science Chemistry practice questions
A second set of questions on rates of reaction and catalysts. They are different from the ones on the topic page. Try each, then open the answer and compare your working.
More questions
Question 2 Medium
Why does the rate of a reaction decrease with time?
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Answer: the reactants are being used up
- Reactants are used up.
- Their concentration falls.
Question 3 Medium
A balance shows a mass loss of 3.0 g in 100 s. Calculate the mean rate in g/s.
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Answer: 0.030 g/s
- Rate = 3.0 ÷ 100.
- = 0.030 g/s.
Question 4 Medium
The volume of gas is measured in cm³ and the time in minutes. Give the unit for the rate.
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Answer: cm³/min
- Rate = amount ÷ time.
- So the unit is cm³ divided by minutes.
Question 5 Hard
A tangent to a curve passes through (0, 5) and (20, 25). Calculate the rate of reaction in cm³/s.
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Answer: 1.0 cm³/s
- Gradient = (25 − 5) ÷ (20 − 0).
- = 1.0 cm³/s.
Question 6 Hard
Explain, using collisions, why doubling the concentration of an acid increases the rate.
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Answer: more particles in the same volume so more frequent collisions
- There are more acid particles in the same volume.
- So collisions are more frequent.
Question 7 Hard
Explain why a catalyst increases the rate of reaction.
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Answer: it lowers the activation energy so more collisions are successful
- It gives a different route.
- The route has a lower activation energy, so more collisions are successful.
Question 8 Hard
Two experiments use the same mass of marble and excess acid. In experiment B the line is steeper but ends at the same height as experiment A. What does this show?
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Answer: B is faster but makes the same amount of product
- A steeper line means a faster rate.
- The same final height means the same amount of product.
Quick checks
Short questions with options. Choose one before you open the answer.
Check 1
What is the equation for mean rate of reaction?
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Amount of reactant used or product formed ÷ time taken.
Check 2
What units can rate of reaction have?
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g/s, cm³/s or mol/s.
Check 3
What does a flat line on a rate graph show?
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The reaction has finished.
Check 4
What is collision theory?
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Reactions happen when particles collide with enough energy.
Check 5
What is activation energy?
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The minimum energy needed for a collision to cause a reaction.
Check 6
How does increasing concentration affect rate?
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More particles in the same volume, so more frequent collisions.
Check 7
How does increasing surface area affect rate?
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More particles are exposed, so more collisions per second.
Check 8
How does increasing temperature affect rate?
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More frequent collisions and more collisions with enough energy.
Check 9
How does increasing pressure affect the rate of a gas reaction?
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The particles are closer together, so collisions are more frequent.
Check 10
What does a catalyst do?
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Speeds up a reaction by lowering the activation energy, without being used up.
Check 11
Does a catalyst change the amount of product?
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No.
Check 12
How do you find the rate at one time from a curve?
Show answer
Draw a tangent and find its gradient.
Check 13
Why does a reaction slow down as it goes on?
Show answer
The reactants are used up, so their concentration falls.
Check 14
How can you measure the rate of a reaction that makes a gas?
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Collect the gas in a syringe, or measure the mass lost.
Check 15
What is a biological catalyst called?
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An enzyme.
Check 16
Which catalyst speeds up the decomposition of hydrogen peroxide?
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Manganese dioxide.
Check 17
What is a successful collision?
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A collision between particles with at least the activation energy.
Check 18
What does frequency of collisions mean?
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How often the particles collide.
Check 19
Why do particles collide more often at a higher temperature?
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They have more energy and move faster.
Check 20
Why are more collisions successful at a higher temperature?
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A bigger fraction of particles have at least the activation energy.
Check 21
What does a steeper line on a rate graph show?
Show answer
A faster rate of reaction.
Check 22
What is a tangent to a curve?
Show answer
A straight line that just touches the curve at one point.
Check 23
What does the gradient of a tangent give you?
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The rate of reaction at that moment.
Check 24
Why does powder react faster than lumps of the same mass?
Show answer
It has a larger surface area, so more collisions happen each second.
Check 25
What unit is rate in when you measure mass lost over time?
Show answer
g/s.
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