Reaction Rates

Question 1

What is the definition of rate of reaction?

Answer 1

The rate of a reaction is the change in concentration of reactant or product per unit time. The standard units of rate are moldm-3s-1. We will also express rate as gs-1or cm3s-1

Question 2

Which factors may affect the rate of a chemical reaction?

Answer 2

-Temp
-Presence of a catalyst
-Pressure
-SA
-Conc

Question 3

What is collision theory used to do?

Answer 3

explain how some of the factors can change the rate of a chemical reaction

Question 4

what does the collision theory state?

Answer 4

for a chemical reaction to occur, particles must collide in the correct orientation, with sufficient energy (the activation energy).

Question 5

when does concentration affect the rate of reaction?

Answer 5

for an aqueous solution reacting with another reactant

Question 6

what happens at a higher concentration?

Answer 6

-there are more reactant particles in a given volume
-means that there will be more frequent collisions and therefore more successful collisions per unit time; the reaction rate increases.

Question 7

what happens when the pressure of a gas is increased (by decreasing volume of a container)?

Answer 7

molecules are pushed closer together, number of molecules remains the same but less is space occupied meaning that there are more frequent collisions and therefore successful collisions per unit; resulting in an increase in the rate of reaction.

Question 8

how can the pressure of gas also be increased?

Answer 8

by having more molecules/particles in the same space

Question 9

what is the experiment of monitoring the production of a gas using gas collection? (rate of reaction for decomposition of hydrogen peroxide)

Answer 9

1. Hydrogen peroxide is added to the conical flask and the bung is replaced.
2. The initial volume of gas in the measuring cylinder is recorded.
3. Manganese dioxide, MnO, catalyst is then quickly added to the conical flask and the bung is replaced. A stop clock is started.
4. The volume of gas produced in the measuring cylinder is recorded at regular intervals until the reaction is complete.
5. The reaction is complete when no more gas is evolved.

Question 10

what is activation energy (Ea)?

Answer 10

Activation energy (Ea) is the minimum energy required to break bonds, thus allowing a reaction to start.

Question 11

What do reactions with a large activation energy have?

Answer 11

very slow rate, or do not take place at all.

Question 12

When does the decomposition of calcium carbonate take place?

Answer 12

-not at RTP
-Requires large amount of energy input in order to occur

Question 13

What happens to reactions with very small activation energy?

Answer 13

Take place very rapidly

Question 14

why can’t the increase in the rate of reaction with increased temperature be fully explained by collision theory?

Answer 14

If we increase the temperature of a gas phase reaction by 10 K the rate approximately doubles. The increase in frequency of collisions would be relatively small and would not double with this energy increase, therefore there must be another explanation.

Question 15

what is the maxwell Boltman distribution?

Answer 15

A plot of the number of particles having each particular energy; vanity as well as kinetic energy although particles can also vibrate and rotate

Question 16

what are the rules of the Boltman distribution curve?

Answer 16

-The line must meet the origin
-The line must not touch that X axis

Question 17

what is the area under the curve on a boltman distribution curve?

Answer 17

A measure of the total number of particles present

Question 18

what happens when the majority of the particles don’t have enough energy to react when they collide?

Answer 18

we have to change the shape of the curve or move activation energy further to the left

Question 19

What happens a high temperature?

Answer 19

Particles have activation energy or greater

Question 20

How do catalysts affect the rate of reaction?

Answer 20

-increase the reaction rate without being used up by the overall reaction
-speeds up the rate of reaction by providing a lower energy pathway; decreases activation energy for a certain reaction

Question 21

what is the addition of a catalyst mean?

Answer 21

more particles have the activation energy or greater

Question 22

what doesn’t happen to catalysts?

Answer 22

they are not consumed by the overall reaction

Question 23

What do catalysts affect?

Answer 23

-The conditions needed, often requiring lower temperatures and reducing energy demand and therefore CO2 emissions from burning fossil fuels
-This leads to reduced waste and more economic reactions (including better atom economy)

Question 24

What are the 2 types of catalyst?

Answer 24

homogeneous and heterogeneous

Question 25

What happens in homogeneous catalysis?

Answer 25

-the catalyst is in the same state (phase) as the reactants.
-A homogeneous catalyst forms an intermediate with the reactants.
-The intermediate then breaks down to give the product and regenerates the catalyst.

Question 26

What happens in heterogenous catalysis?

Answer 26

The catalyst is in a different phase from the reactants

Question 27

what is an example of homogeneous catalysis?

Answer 27

Depletion of ozone-
The chlorine radical (CI) and ozone are in the same (gas) phase. Cl reacts with ozone to make an intermediate ClO which then is reformed afterwards.

Question 28

What is an example is Heterogeneous Catalysis?

Answer 28

Haber process-
The iron catalyst is in a different phase (solid to nitrogen and hydrogen.

Question 29

Why are catalysts used in industrial process

Answer 29

-have great economic importance.
-used in many industrial processes because they speed up processes which would be too slow without them. They increase sustainability by allowing lower operating temperatures to be used. This then reduces energy demand needed, from the combustion of fossil fuels. Thus reducing COz emissions.

Question 30

What are examples of catalysts used in industrial process?

Answer 30

-Petroleum processing
-Margarine Manufacture
-Ammonia Manufacture