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AQA A Level Physical Chemistry > 5. Kinetics > Flashcards

Flashcards in 5. Kinetics Deck (45)
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1

What must happen for a reaction to occur between two substances?

Particles must collide with each other, with enough energy during the collision

2

Do all collisions result in a reaction?

No - most do not

3

What does the energy of a collision depend on?

• the orientation at which they collide

• the speed at which they are moving

4

Which molecules have energy?

All molecules have some energy

5

What is activation energy?

The minimum energy with which particles need to collide to cause a reaction

6

What is the symbol for activation energy?

Eₐ

7

On a graph showing an exothermic reaction, is the energy of the reactants or the products higher?

Reactants

8

On a graph showing an endothermic reaction, is the energy of the reactants or the products higher?

Products

9

In a sample of liquid or gas where molecules are colliding with each other and the container, are the collisions elastic or inelastic?

Elastic because there is no loss of energy

10

In a sample at a given temperature, what will be the energy of each molecule?

• small fraction will have high/low energies

• however most will be between the two extremes about the most probable energy

11

What is the graph showing the spread of energy of molecules?

A Maxwell-Boltzmann Distribution curve

12

What are the axes on a Maxwell-Boltzmann distribution curve?

Number of particles against energy

13

What is the most probable energy?

The energy that most particles have around, at any given time

14

For the average energy on a Maxwell-Boltzmann graph, how should the area be underneath the graph?

If a vertical line is drawn at the point of average energy, the energy either side of the line should be equal

15

What does the area underneath a Maxwell-Boltzmann graph distribution curve represent?

The total number of particles in the sample

16

How is the activation energy of a sample represented on a Maxwell-Boltzmann curve?

When Eₐ is marked on the x-axis of the graph, the area to the right of it represents the number of particles with at least this energy

17

Why is there an asymptote on a Maxwell-Boltzmann distribution curve?

Few particles have that high energy, however there is no limit on how high the energy of these particles can have - so it doesn't touch the x-axis

18

How can the rate of reaction be calculated?

• rate = product formed / time

• rate = reactant used up / time

19

How does an increase in temperature affect the rate of a reaction?

It increases the rate of a reaction

20

In many reactions, what does a rise of 10°C mean for the rate of reaction?

It causes the rate of reaction to approximately double

21

Why does an increase in temperature increase the rate of reaction?

• at higher temperatures, particles have higher energy

• meaning they move faster and are more likely to collide with other particles

• when particles, collide, they do so with more energy, increasing frequency of collisions with Eₐ

22

What happens to a Maxwell-Boltzmann distribution curve when temperature is increased?

The energy distribution moves to the right as average energy of the molecules increases

23

Why does the shape of a Maxwell-Boltzmann distribution curve change when temperature is increased?

The spread of energies increases

24

How does an increase in temperature affect the area underneath a Maxwell-Boltzmann distribution curve?

Doesn't change as the number of particles stays the same

25

How does an increase in temperature affect the most probable energy on Maxwell-Boltzmann distribution curve?

Increases due to having more energy at higher temperatures

26

How does an increase in temperature affect activation energy on a Maxwell-Boltzmann distribution curve?

The activation energy will stay the same for both temperatures, so if a vertical line was drawn on x-axis where it is, it would stay in the same place

27

How does an increase in temperature affect the number of molecules with energy greater or equal to Eₐ on a Maxwell-Boltzmann distribution curve?

A greater number of molecules with energy greater/equal to Eₐ for higher temps.

28

How does increasing the concentration of a reagent affect the number of particles in a given volume?

It increases the number of particles

29

How does increasing the concentration of a regent affect the rate of reaction?

It increases the rate of reaction

30

Why does an increased concentration increase rate of reaction?

• ↑ chance of successful collision

• so ↑ frequency of collisions

• so ↑ frequency of collisions with required Eₐ