Kinetics

Question 1

What are the 4 factors effecting the rate of reaction?

Answer 1

Temperature
Surface area
Concentration
Presence of a catalyst

Question 2

What does collision theory state?

Answer 2

Particles must collide for a reaction to happen

Question 3

What is activation energy?

Answer 3

Particles collide with the correct amount of energy

Question 4

What is a maxwell Boltzmann distribution?

Answer 4

A plot of the number of molecules with a certain amount of kinetic energy
Curves will only cross each other once
An increase in temperature will increase the number of particles with a higher kinetic energy and so the graph shifts to the right

Question 5

How can rate be measured?

Answer 5

By:
Consumption of reactants or production of product

Question 6

What are the two equations that can be used for measuring rate?

Answer 6

Amount of reactant used OR amount of product formed / time

Question 7

When do chemical reactions happen?

Answer 7

When molecules or particles of reactants collide
These collisions must happen with the correct amount of energy for a reaction to take place which is called activation energy

Question 8

When does no reaction occur?

Answer 8

If a collision happens without particles having activation energy
Instead they just bounce off eachother

Question 9

What do faster reactions mean?

Answer 9

A faster rate of collisions or an increase in the amount of energy that the particles have when they collide

Question 10

What is special about all particles in a reaction mixture?

Answer 10

They all have different amounts of energy
Some have less than activation energy and some have more therefore most collisions don’t result in a reaction

Question 11

What happens if we increase the amount of collisions in a reaction?

Answer 11

We increase the number of successful reactions and so increase the rate if reaction

Question 12

What happens if we increase the amount of energy particles have?

Answer 12

More particles have energy that is more than the activation energy
So more of the collisions taking place will result in a chemical reaction and so it speeds up the rate if reaction

Question 13

How does temperature change the rate if reaction?

Answer 13

Temperature is related to how much kinetic energy particles have
Increasing temp increases energy if particles and so particles are moving faster and with more energy which means a greater frequency of collisions that have more energy
This means a greater proportion of collisions result in chemical reactions

Question 14

What is the overall impact of temperature on rate of reaction?

Answer 14

Two fold
It increases collisions and energy

Question 15

How does concentration or pressure change the rate of reaction?

Answer 15

Pressure is for gases and concentration is for liquids
Increasing the concentration means more particles in the same volume and so particles collide more frequently which in turn increases the rate if reaction

Question 16

How does surface area change the rate if reaction?

Answer 16

This is for when one of the reactants is a solid
Only particles on the surface of the solid are available to react
So if you increase the surface area by breaking the solid into smaller pieces or grinding it into a powder the more particles are available or reaction
This increases frequency of collisions which then increases the rate if reaction

Question 17

How do catalysts change the rate of reaction?

Answer 17

They lower the activation energy by providing an alternative reaction pathway for the chemical reaction
The number of collisions remains the same but more if these collisions will be successful as more of the collisions will take place with greater than activation energy
So the rate of reaction increases

Question 18

How is the rate of reaction increased overall?

Answer 18

By increasing the rate of successful collisions

Question 19

What two things can be altered to change rate?

Answer 19

Energy if the molecules and frequency of collisions

Question 20

Where is activation energy marked on a maxwell distribution curve?

Answer 20

The area to the right of the activation energy line shows the molecules that will react when they collide

Question 21

What are some tips when drawing maxwell distribution curves?

Answer 21

Correct labels for the axes
Start from the origin
Make peak clearly defined
Make curve flatten out near x axis

Question 22

How is a decrease in temperature shown on the graph?

Answer 22

Curve becomes higher and the position is shifted to the left
The peak also becomes narrower

Question 23

How is an increase in temperature shown on the graph?

Answer 23

Becomes lower in height and the position is shifted to the right
The peak of the curve also becomes wider and broader

Question 24

What do maxwell distribution plots show in summary?

Answer 24

The number of molecules and energy

Question 25

What should the curve not do after the origin?

Answer 25

Touch the x axis again

Question 26

What is collision theory?

Answer 26

Chemical reactions occur when particles of substances collide For a reaction to occur collisions must have energy greater than or equal to the activation energy of the reaction Particle orientation must also be correct

Question 27

Define maxwell Boltzmann distribution

Answer 27

Not all molecules in a substance have the same amount of energy Their energies are distributed in a pattern called the maxwell Boltzmann distribution Molecules with energy greater than the activation energy will collide with enough energy to result in a reaction

Question 28

What are the features of a Maxwell Boltzmann distribution curve?

Answer 28

Mean energy line going up Most probable energy line also going up Activation energy line going up Zero molecules have zero energy shown X axis= kinetic energy Y axis=number of molecules

Question 29

How does changing reaction conditions alter the shape of the curve?

Answer 29

Number of particles with energy greater than the activation energy is different Total area under the curve represents the total number of molecules in the sample and this must remain constant

Question 30

What is the effect of temperature on rate of reaction?

Answer 30

When a substance is heated thermal energy is transferred to it This energy is converted to kinetic energy and the molecules of the substance now move faster and further Increase movement of the molecules means collisions will occur more often with greater energy More collisions have energy greater than the activation energy= a reaction

Question 31

What is the effect of concentration and pressure on he rate of reaction?

Answer 31

When concentration of a sample is increased more molecules of a substance occur in the same volume = packed closer together Collisions between molecules are more likely + chances of a collision with greater activation energy increases= rate if reaction increases Increasing pressure has similar effect as molecules are packed closer together into a smaller volume

Question 32

What is the effects of catalysts on rate of reaction?

Answer 32

A catalyst increases the rate if reaction without being used up in the reaction itself It works by providing an alternative reaction pathway that requires a lower activation energy for the reaction to occur Maxwell Boltzmann distribution curve is unchanged in shape but position of activation energy is shifted to the left so a greater proportion of molecules have sufficient energy to react

Question 33

Explain the effect that lowering the temperature would have on the rate of reaction

Answer 33

Exam question Lowering the temperature would mean less thermal energy is transferred to a substance Molecules move slower due to having less kinetic energy Decreased movement means less collisions will occur less often Decreasing temperature decreases rate of reaction

Question 34

How does a decrease in pressure change the rate of reaction?

Answer 34

Amount of gas present has been reduced so the pressure as been reduced Particles are further apart Fewer collisions between gas particles so fewer successful collisions