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

The catalyst reacts with the reactants to form an intermediate.

The intermediate then 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

Heterogeneous catalysts are usually solids in contact with gaseous reactants or reactants in solution.

Reactant molecules are adsorbed (weakly bonded) onto the surface of the catalyst, where the reaction takes place.

After the reaction, the products leave the surface of the catalyst 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 the making sulfur 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 are the main features of Boltzmann distribution?

Answer 20

No molecules have zero energy

Area under the curve is equal to the number of molecules

No maximum energy

Question 21

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

Answer 21

The peak is lower and shifted to the right

A greater proportion of molecules can overcome the activation energy

Question 22

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

Answer 22

Activation energy with a catalyst is lower than normal activation energy.

Therefore a greater proportion of molecules exceed the new lower activation energy.

Question 23

What is a dynamic equilibrium?

Answer 23

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 24

What is le Chatelier’s principle?

Answer 24

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

Question 25

What is the effect of a catalyst on equilibrium?

Answer 25

Does not change the position

Speeds up the rates of forward and reverse reactions equally

Question 26

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

Answer 26

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

Question 27

Answer 27