Unit 3 - Reaction Rates

Question 1

What does the steepness of the reaction curve tell us about the reaction rate?

Answer 1

How fast the reaction is proceeding.

Question 2

What is the equation for reaction rate?

Answer 2

reaction rate = change in quantity/change in time

Question 3

What is the equation for the relative rate of a reaction?

Answer 3

Relative rate = 1/t

Question 4

When do reactions take place?

Answer 4

When there are SUCCESSFUL COLLISIONS between reactants.

Question 5

How can you speed up a reaction?

Answer 5

Decreasing the PARTICLE SIZE of any solid. (Increased surface area = increase in the probability of SUCCESSFUL COLLISIONS).

Increasing the CONCENTRATION of a solution. (Increasing the NUMBER OF PARTICLES = increase in the probability of SUCCESSFUL COLLISIONS.)

Increasing the TEMPERATURE of the reaction.
(Increases the amount of energy and the speed of particles = increase in the probability of SUCCESSFUL COLLISIONS.)

Using a Catalyst. (Increases the probability of SUCCESSFUL COLLISIONS.) (Is not used up and can be used again)

Question 6

What do all molecules and atoms have?

Answer 6

Kinetic energy in the form of vibrations,

Question 7

What does collision theory state must happen for a reaction to take place?

Answer 7

Collision theory states that in order for a reaction to take place the particles in the reactants must collide.

Question 8

What molecules will collide successfully in collision theory?

Answer 8

Molecules with more energy than the activation energy that collide in the correct orientation and geometry

Question 9

How can sufficient energy for successful collisions be achieved?

Answer 9

With an increase in temperature the molecules will gain kinetic energy, and more molecules will have the required energy to collide successfully and to react.

Question 10

What is the activation energy?

Answer 10

The activation energy is the minimum energy required by colliding particles to form an activated complex.

Question 11

In exothermic reactions what is the ΔH?

Answer 11

Negative

Question 12

In endothermic reactions what is the ΔH?

Answer 12

Positive

Question 13

What is enthalpy?

Answer 13

A measure of the change in potential energy between the reactants and the products of a reaction.

Question 14

Unless stated on the graph what is enthalpy measured in?

Answer 14

kJmol-1

Question 15

What is an exothermic reaction?

Answer 15

An exothermic reaction involves the reaction RELEASING energy to the surroundings, usually in the form of heat.

Question 16

What is an endothermic reaction?

Answer 16

An endothermic reaction ABSORBS energy (usually in the form of heat) form the surroundings.

Question 17

What does ‘ whether a reaction is fast or slow ‘ depend on?

Answer 17

The height of the activation energy barrier.

Question 18

What does a catalyst provide?

Answer 18

A catalyst provides an alternative reaction pathway with a lower activation energy but does not have an effect on ΔH.

Question 19

Is the reaction rate slower for a reaction with a higher activation energy?

Answer 19

Yes

Question 20

Is the reaction rate slower for a reaction with a lower activation energy?

Answer 20

No

Question 21

What is the activated complex?

Answer 21

The activated complex is an unstable arrangement of atoms formed at the maximum of the potential energy barrier, during a reaction. They are very short lived and have bonds being broken and made at the same time.

Question 22

What happens in regards to activation energy when a catalyst is added?

Answer 22

The activation energy decreases.

Question 23

What are the two types of catalysts?

Answer 23

Heterogeneous and homogeneous.

Question 24

What is a homogeneous catalyst?

Answer 24

A catalyst which is in a different state as the reactants.

Question 25

What is a homogeneous catalyst?

Answer 25

A catalyst which is in the same state as the reactants

Question 26

What is adsorption in catalysis?

Answer 26

Occurs when molecules attach themselves to the catalyst

Question 27

What is desorption in catalysts?

Answer 27

Occurs when the molecules leave the surface of the catalyst

Question 28

What is catalyst poisoning?

Answer 28

Where IMPURITIES PERMANENTLY BLOCK the active site decreasing the efficiency of the catalyst.

Question 29

How do catalysts actually speed up the reaction?

Answer 29

As the molecules are held in a fixed position by the catalyst it is easier for the molecules to collide/there is a higher chance of the molecules colliding.