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 with the correct orientation

Question 3

What factors can affect the reaction rate?

Answer 3

• Concentration (pressure)
• Temperature
• Use of a catalyst
• Surface area of solid reactants

Question 4

What effect does increasing temperature have on the reaction rate?

Answer 4

Rate increases

Question 5

Explain why increasing temperature affects reaction rate

Answer 5

• Particles gain more kinetic energy
• So more frequent collisions/more successful collisions
• So rate increases

Question 6

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

Answer 6

Rate increases

Question 7

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

Answer 7

• More particles per unit volume
• So more frequent collisions/more successful collisions
• So rate increases

Question 8

How can progress of a chemical reaction be followed?

Answer 8

Monitoring the removal of a reactant/the formation of a product

Question 9

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

Answer 9

• Monitoring the volume of gas produced
• Monitoring the loss of mass of reactants

Question 10

What is a catalyst?

Answer 10

A substance that increases the rate of a chemical reaction by providing an alternative reaction pathway with a lower activation energy, without being used up in the process

Question 11

What are the main properties of a catalyst?

Answer 11

• Not used up in the reaction
• May react 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 12

What is a homogeneous catalyst?

Answer 12

Has the same physical state as the reactants

Question 13

How does a homogeneous catalyst interact with the reactants?

Answer 13

• Forms an intermediate
• This intermediate breaks down to give the product and regenerates the catalyst

Question 14

Give two examples of homogeneous catalysts:

Answer 14

• Sulphuric acid in the production of esters
• Chlorine radicals in ozone depletion

Question 15

What is a heterogeneous catalyst?

Answer 15

Has a different physical state from the reactants

Question 16

What is the process for heterogeneous catalysis?

Answer 16

• Adsorption - Reactant molecules form weak bonds with the catalyst’s surface
• Reaction - Bonds within reactant molecules break, then new bonds/molecules are formed
• Desorption - Product molecules leave the catalyst’s surface

Question 17

Give examples of heterogeneous catalysts

Answer 17

• Iron (Haber process)
• Platinum/rhodium (catalytic converters)
• Nickel (hydrogenation of alkenes)

Question 18

What are the benefits of using a catalyst?

Answer 18

• Less energy needed (cheaper electricity, less fossil fuels used)
• Product made faster

Question 19

What is autocatalysis?

Answer 19

A reaction product acts as a catalyst for that reaction

Question 20

What are the main features of the 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
• Thus 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

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 formula for Kc of the reaction: aA + bB ⇌ cC + dD

Answer 25

• Where [X] is the concentration of that substance

Question 26

What is different about the equilibrium constant to regular constants?

Answer 26

• Only constant at a given temperature • Units change depending on the reaction

Question 27

What effect does changing the concentration of reactants/products have on the equilibrium position?

Answer 27

• Increase [reactant(s)] - Equilibrium shifts to the right • Increase [product(s)] - Equilibrium shifts to the left • Decrease [reactant(s)/product(s)] - Vice Versa

Question 28

Hess’ Cycle for enthalpies of combustion:

Answer 28

Question 29

Hess’ Cycle for enthalpies of formation:

Answer 29

Question 30

What effect does changing the temperature of the system have on the equilibrium position?

Answer 30

• Increase temperature - Equilibrium shifts to favour the endothermic reaction • Decrease temperature - Equilibrium shifts to favour the exothermic reaction

Question 31

What effect does changing the pressure of the system have on the equilibrium position?

Answer 31

• Increase pressure - Equilibrium shifts to the side with fewer moles of gas • Decrease pressure - Equilibrium shifts to the side with more moles of gas • Note: If the N° moles on either side are equal, then changing pressure has no effect on the equilibrium position

Question 32

What effect does the presence of a catalyst have on the equilibrium position?

Answer 32

• A catalyst does not change the equilibrium position • It only equally increases the rate of the forward and reverse reactions