Chapter 10 - Reaction Rates and Equilibrium

Question 1

What is reaction rate?

Answer 1

The change in concentration of a reactant or product in a given time.

Question 2

What makes an effective collision?

Answer 2

Particles must have sufficient energy

Particles must collide in correct orientation

Question 3

Which factors can change the rate of a chemical reaction?

Answer 3

Concentration
Temperature
Use of a catalyst
Surface area of solid reactants

Question 4

What effect does increasing temperature have on reaction rate?

Answer 4

Reaction rate increases

Question 5

Explain why increasing temperature has its effect on reaction rate

Answer 5

Particles have more energy
Higher speed
Collide more frequently
More successful collisions
Rate increases

Question 6

What is the rule of thumb for reaction rate and temperature?

Answer 6

A 10C increase in temperature doubles the rate.

Question 7

What effect does increasing concentration/pressure have on reaction rate?

Answer 7

Reaction rate increases

Question 8

Explain why increasing concentration/pressure has its effect on reaction rate

Answer 8

Concentration increases
More particles per unit volume
More frequent collisions
More successful collisions
Rate increases

Question 9

How can progress of a chemical reaction be followed?

Answer 9

Monitoring the removal of a reactant.

Following the formation of a product.

Question 10

What are the two methods of determining reaction rate, when a gas is produced?

Answer 10

Monitoring the volume of gas produced

Monitoring the loss of mass of reactants

Question 11

What does a catalyst do?

Answer 11

A substance that changes the rate of a chemical reaction without undergoing any permanent change itself.

Question 12

What are the main properties of a catalyst?

Answer 12

Not used up in the reaction.
May react with a reactant to form an intermediate or provide a surface for the reaction to take place.
The catalyst is regenerated at the end of the reaction.

Question 13

What is a homogeneous catalyst?

Answer 13

Has the same physical state as the reactants.

Question 14

How does a homogeneous catalyst interact with the reactants?

Answer 14

Forms an intermediate

This intermediate breaks down to give the product and regenerates the catalyst

Question 15

Give two examples of homogeneous catalysts

Answer 15

Sulphuric acid in the production of esters

Chlorine radicals in ozone depletion

Question 16

What is a heterogeneous catalyst?

Answer 16

Has a different physical state from the reactants.

Question 17

How does a heterogeneous catalyst interact with the reactants?

Answer 17

Usually solids in contact with gaseous reactants or reactants in solution.
Reactants are adsorbed onto the surface, where the reaction takes place.
After the reaction, the products leave the surface by desorption.

Question 18

Give examples of heterogeneous catalysts

Answer 18

Iron in making ammonia
Platinum or rhodium in reforming
Nickel in hydrogenation of alkenes
Vanadium oxide in making sulphur trioxide

Question 19

What are the benefits of using a catalyst?

Answer 19

Lowers activation energy
Less electricity used
Product made faster and cuts costs and increases profit
Less fossil fuels used cuts emissions of carbon dioxide

Question 20

What is autocatalysis?

Answer 20

A reaction product acts as a catalyst for that reaction.

Question 21

What are the main features of Boltzmann distribution?

Answer 21

No molecules have zero energy
Area under the curve is equal to the number of molecules
No maximum energy

Question 22

How does a Boltzmann distribution curve change when temperature is increased?

Answer 22

The peak is lower and shifted to the right

A greater proportion of molecules can overcome the activation energy

Question 23

How does a Boltzmann distribution show the effect of a catalyst?

Answer 23

Activation energy with a catalyst is lower than normal activation energy.
Therefore a greater proportion of molecules exceed the new lower activation energy.

Question 24

What is a dynamic equilibrium?

Answer 24

The equilibrium that exists in a closed system when the rate of the forward reaction is equal to the rate of the reverse reaction and concentrations do not change.

Question 25

What is le Chatelier’s principle?

Answer 25

When a system in dynamic equilibrium is subjected to an external change, the system readjusts itself to minimise the effect of that change.

Question 26

What is the effect of a catalyst on equilibrium?

Answer 26

Does not change the position

Speeds up the rates of forward and reverse reactions equally

Question 27

If a reversible reaction is shown as:
aA + bB cC + dD
how is Kc worked out?

Answer 27

Kc = [C]^c x [D]^d / [A]^a x [B]^b

Question 28

What is different about the equilibrium constant to regular constants?

Answer 28

Only constant at a given temperature

Units change depending on the reaction