Rates of reaction

Question 1

What are the factors that affect the rate of reaction

Answer 1

Temperature
Pressure
Catalyst
Surface area
Concentration

Question 2

What does the rate of reaction mean

Answer 2

The change in concentration between the reactants and products overtime

Question 3

What are the units for concentration

Answer 3

moldm-3s-1

Question 4

What is the collision theory

Answer 4

In order to react particles must collide with eachother

Question 5

How should particles collide to make it successful

Answer 5

Must have the correct orientation and must have energy equal to or greater than the activation energy

Question 6

What happens when we increase the concentration for rate

Answer 6

When we increase the concentration more particles are in the same unit of volume. This will mean more frequent collision occur. This means more successful collisions occur so the rate of reaction increases

Question 7

What happens when we increase the pressure for rate

Answer 7

When we increase the pressure the same number of particles occur in a smaller volume. This means more frequent collisions occur per unit time hence more successful collisions occur. This means the rate of reaction will increase

Question 8

What happens when we increase the temperature for rate

Answer 8

Most collisions are not successful. This is because they do not have the activation energy. However when we increase the temperature more particles will have energy equal to or greater than the activation energy so more successful collisions occur per unit time

Question 9

If a reaction produces gas what are two ways of reducing the rate

Answer 9

1) Measuring the change in volume or pressure of gas over time
2) The loss in mass of reactants over time

Question 10

What does the rate equal

Answer 10

To the gradient of a concentration time graph

Question 11

Why is volume/time the same as concentration/ time

Answer 11

They are proportional

Question 12

How can you state how the rate changes during the course of a reaction for concentration/time

Answer 12

Initially the gradient is at its steepest so the rate is highest. Overtime however the gradient becomes smaller so the rate decreases. Towards the end the curve flattens which means the gradient becomes 0 and the reaction stops

Question 13

How can you explain why the rate changes with a concentration time graph

Answer 13

Initially the reactants are high and collision frequency is high so there are lots of successful collisions leading to a higher rate. As reactants get used up the concentration decreases which decreases collision frequency therefore the rate. At the end, one of the reactants is completely used up so the reaction stops.

Question 14

What does the position of the curve depend on

Answer 14

The moles

Question 15

What does the steepness of the curve depend on

Answer 15

The concentration

Question 16

How do you draw a tangent at a specific point

Answer 16

Draw a line that only just touches the point where asked
Draw a triangle where it matches
Do change in y over change in x

Question 17

How do you work out the initial rate

Answer 17

Draw a line at the beginning of the graph and do change of y over change of x

Question 18

What does a Boltzmann curve show

Answer 18

The distribution of kinetic energy across all particles. Particles dont all have the same energy

Question 19

How do you describe a general Boltzmann curve

Answer 19

The area under the curve is number of particles
No molecules have 0 energy so the graph must start at the origin
There is no maximum energy as the curve never touches the y axis
The area under the curve after the activation energy shows how many particles energy and can react

Question 20

What is the effect of temperature with a Boltzmann curve

Answer 20

At a higher temperature the area under the curve after the activation energy is larger as more particles have reacted

Question 21

What is the effect of the catalyst with a Boltzmann curve

Answer 21

Using a catalyst the activation energy is lowered so more particles have energy

Question 22

How does the catalyst increase the rate of reaction

Answer 22

By providing an alternate route for the reaction with a lower activation energy. This means the increases the rate of reaction without being used up

Question 23

What are the benefits of catalysts

Answer 23

It has lower temperature and pressure so reduces energy demand, fossil fuel consumption and greenhouse gas emissions

Question 24

What is a homogeneous catalyst

Answer 24

Have the same physical state as the reactants. This forms an intermediate with the reactants which breaks down to regenerate the catalyst

Question 25

What is a heterogeneous catalyst

Answer 25

Have a different physical state as the reactants. The reactants are adsorbed to the catalyst surface where the reaction takes place. The products leave the surface by desorption