Rates of reaction flashcards

The rate of a reaction describes how quickly reactants are converted into products. Students must understand how to measure reaction rate using changes in mass, volume of gas produced, or colour change over time. Four key factors affect reaction rate: temperature, concentration (or pressure for gases), surface area, and the use of a catalyst. These factors are explained using collision theory, which states that reactions occur when particles collide with sufficient energy, known as the activation energy. Increasing temperature, concentration, surface area, or adding a catalyst all increase the frequency or energy of successful collisions. Students should also be able to interpret and draw graphs of rate experiments, calculate mean rate from results, and explain the effect of each factor at the particle level.

1. Card 1

   What is the rate of a reaction?

   The rate of a reaction measures how quickly reactants are used up or products are formed, usually expressed as change in quantity divided by time.

2. Card 2

   What is activation energy?

   Activation energy is the minimum amount of energy that colliding particles must have for a reaction to occur successfully.

3. Card 3

   How does increasing temperature affect reaction rate?

   Higher temperature gives particles more kinetic energy, so they move faster, collide more frequently, and more collisions exceed the activation energy, increasing the rate.

4. Card 4

   How does increasing concentration affect reaction rate?

   Higher concentration means more particles in the same volume, so collisions happen more frequently, leading to a greater number of successful collisions per second.

5. Card 5

   How does increasing surface area affect reaction rate?

   A larger surface area exposes more particles of a solid reactant to collisions, so the frequency of successful collisions increases and the reaction speeds up.

6. Card 6

   What does a catalyst do and how does it work?

   A catalyst increases reaction rate by providing an alternative reaction pathway with a lower activation energy, without being used up in the reaction.

7. Card 7

   State collision theory in one sentence.

   Collision theory states that reactions only occur when particles collide with the correct orientation and with energy equal to or greater than the activation energy.

8. Card 8

   How can you measure the rate of a reaction that produces a gas?

   You can measure the volume of gas collected in a gas syringe over time, or measure the loss in mass using a balance if the gas escapes.

9. Card 9

   How do you calculate the mean rate of reaction from an experiment?

   Mean rate = quantity of reactant used (or product formed) divided by time taken. Units are often g/s, cm3/s, or mol/s.

10. Card 10

    Why does a powdered solid react faster than a lump of the same mass?

    Powder has a much greater surface area than a lump, so more reactant particles are exposed and available for collisions at any one time.

11. Card 11

    What does the gradient of a rate-of-reaction graph tell you?

    The gradient (steepness) of the graph shows the rate at that moment; a steeper gradient means a faster rate, and the graph flattens when a reactant is used up.

12. Card 12

    How does increasing pressure affect the rate of a reaction involving gases?

    Higher pressure pushes gas molecules closer together, increasing their concentration, so collisions occur more frequently and the reaction rate increases.

• Many students say a catalyst is 'used up' in a reaction, but a catalyst is not consumed and can be recovered unchanged at the end.
• Students often confuse frequency of collisions with energy of collisions, writing that higher temperature only causes more collisions rather than also increasing the proportion that meet the activation energy threshold.
• When asked to explain the effect of surface area, students frequently write that there are 'more particles' rather than correctly stating that more particles are exposed and available for collisions.

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