MODULE 3: Reaction Rates and Equilibrium

Question 1

What is the equation for rate of reaction?

Answer 1

rate = change in concentration/time

Question 2

What are the factors that can effect rate of reaction?

Answer 2

Concentration, pressure, temperature, catalyst and surface area

Question 3

What is collision theory?

Answer 3

Theory that states that particles must collide in order for a reaction to occur

Question 4

What factors effect collision theory?

Answer 4

Orientation of molecules, temperature, catalysts, concentration

Question 5

What is a catalyst?

Answer 5

A substance that decreases the activation energy by providing an alternative route; therefore increases rate of reaction (does not alter own chemical makeup)

Question 6

What is a homogenous catalyst?

Answer 6

A catalyst that is the same physical state as the reactants

Question 7

What is a heterogenous catalyst?

Answer 7

A catalyst that is a different physical state as the reactants

Question 8

Name an example of a homogeneous catalyst

Answer 8

Ozone depletion (chlorine radicals as catalysts)
2O₃ ⇌ 3O₂

Question 9

Name an example of a heterogeneous catalyst

Answer 9

Haber process (iron as catalyst)
N₂ + 3H₂ ⇌ 2NH₃

Question 10

What are the benefits of using a catalyst?

Answer 10

Lower activation energy (therefore lower temperature and so less fuel used), less carbon dioxide produced

Question 11

What is a Boltzmann distribution graph?

Answer 11

A graph to show the spread of molecular energies in gases

Question 12

What are some of the features of the Boltzmann distribution graph?

Answer 12

Curve starts at origin, no maximum energy, curve stays above zero (area under graph = number of molecules)

Question 13

How does temperature effect the shape of the Boltzmann distribution graph?

Answer 13

Area shifts to the right, lower peak, greater proportion of successful collisions that leads to a reaction

Question 14

How does a catalyst effect the shape of the Boltzmann distribution graph?

Answer 14

Provides an alternate route; so lowers activation energy, proportion of molecules have an energy equal or greater than original activation energy

Question 15

What is equilibrium (dynamic equilibrium)?

Answer 15

When, in a closed, reversible reaction, the reaction rate of the forwards and backwards reaction is the same (concentrations of products and reactants do not change)

Question 16

What is le Chatelier’s principal?

Answer 16

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

Question 17

What factors can effect a system in equilibrium?

Answer 17

Temperature, pressure and concentration

Question 18

Why can’t catalyst effect a system in equilibrium?

Answer 18

Because catalysts speed up the rate that each reaction is going, so therefore only reaches equilibrium faster

Question 19

How does changing the concentration effect a system in equilibrium?

Answer 19

Increasing concentration of reactants on the left decreases concentration of products on the right (and vice versa)

Question 20

How does changing the temperature effect a system in equilibrium?

Answer 20

If forwards reaction exothermic: shifts left

If forwards reaction endothermic: shifts right

Question 21

How does changing the pressure effect a system in equilibrium?

Answer 21

Increasing pressure increases volume of side with less number of moles of gas

Question 22

What is the equation for equilibrium law?

Answer 22

Kc = [C]ᶜ[D]ᵈ/[A]ᵃ[B]ᵇ (products/reactants, superscripted letters is moles of)

Question 23

What does equilibrium law teach us?

Answer 23

Kc = 1: position of equilibrium is halfway between products and reactants
Kc > 1: position of equilibrium is towards products
Kc < 1: position of equilibrium is towards reactants