Rates of Reaction – Lecture Review

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These flashcards cover collision theory, factors affecting reaction rate, definitions and calculations of rate, experimental methods for measuring rate, interpretation of rate graphs, and the role of catalysts.

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26 Terms

1
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What does collision theory state must happen for a reaction to occur?

Reactant particles must collide with the correct orientation and with sufficient energy (≥ activation energy).

2
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Which two criteria make a collision successful according to collision theory?

Correct particle orientation and enough kinetic energy to overcome the activation energy barrier.

3
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How does increasing the concentration of reactants affect the rate of reaction?

It raises the number of particles per unit volume, increasing collision frequency and therefore the reaction rate.

4
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Why does raising the temperature speed up a reaction?

Particles gain kinetic energy, collide more frequently, and a larger proportion of collisions have the required activation energy.

5
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How does increasing the surface area of a solid reactant influence reaction rate?

More particle surfaces are exposed, boosting the frequency of collisions and speeding up the reaction.

6
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What is the effect of increasing gas pressure on the rate of a reaction involving gases?

Gas particles are forced closer together, raising collision frequency and increasing the reaction rate.

7
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What role does a catalyst play in a chemical reaction?

It provides an alternative reaction pathway with a lower activation energy, so a higher percentage of collisions are successful.

8
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Define activation energy (Eₐ).

The minimum amount of energy that reacting particles must possess for a successful collision leading to reaction.

9
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Give the chemical definition of the rate of a reaction.

The speed at which reactants are converted into products, often measured as change in concentration, mass, or volume per unit time.

10
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Name two ways of determining reaction rate according to the notes.

(1) Measure the time taken for reactants to be used up. (2) Measure the time taken for products to form.

11
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State the general equation for mean rate of reaction.

Mean rate = (quantity of reactant used OR quantity of product formed) ÷ time.

12
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What are the units of rate when mass change is measured?

Grams per second (g s⁻¹).

13
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What are the units of rate when gas volume is measured?

Cubic centimetres per second (cm³ s⁻¹).

14
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Calculate the mean rate if 120 g of reactant are lost in 30 s.

4 g s⁻¹.

15
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Calculate the mean rate if 20 cm³ of gas are produced in 40 s.

0.5 cm³ s⁻¹.

16
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Which experimental method measures rate by tracking mass loss?

Measuring the decrease in mass when a reaction produces a gas that escapes.

17
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When can rate be measured by collecting gas volume produced?

Only when the reaction forms a gas, using a gas syringe or inverted measuring cylinder.

18
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Describe the ‘disappearing cross’ method for rate measurement.

Timing how long it takes for a precipitate to obscure a mark beneath the reaction vessel.

19
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What is a precipitate?

An insoluble solid that forms when two solutions react and can be seen as a solid appearing in the mixture.

20
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How can a light sensor and data logger improve the disappearing-cross experiment?

They detect the drop in light passing through the mixture, giving precise times for when the precipitate forms.

21
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Describe how reaction rate typically changes over time on a graph.

It is steep (fast) at the start, gradually becomes less steep as reactants are used, and flattens when the reaction ends.

22
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Why does the rate of reaction decrease as the reaction progresses?

Reactant concentrations fall, leading to fewer collisions per second and therefore a slower rate.

23
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What is meant by the ‘mean rate of reaction’ on a graph?

The average slope between two chosen time points, often from t = 0 until the curve becomes flat.

24
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How do you determine the rate at a specific moment on a curved rate graph?

Draw a tangent at that point and calculate its gradient (Δy/Δx).

25
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What is the ‘initial rate’ method?

Finding the slope of a tangent drawn at t = 0 to obtain the reaction rate at the very start of the reaction.

26
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How does a catalyst change the proportion of successful collisions?

By lowering activation energy, it increases the fraction of particle collisions that possess enough energy to react.