Chapter 10 Rates of Reaction and Equilibrium

Question 1

What is meant by rate of reaction

Answer 1

• How fast a reactant is used up
• How fast a product is formed

Question 2

What is the equation for rate of reaction

Answer 2

Change in concentration / Time

Question 3

Describe and explain the curve on a concentration-time graph

Answer 3

1. Here the slope is steepest – the rate is fastest at the start of the reaction (each reactant is at its highest concentration)
2. The curve becomes less steep as the reaction
   progresses – the reactants are being used up and their concentrations decrease
3. Eventually the curve becomes a straight line parallel to the x-axis – the reaction is complete (one of the reactants has been completely used up)

Question 4

What does the gradient of a curve on a concentration-time graph

Answer 4

The rate of reaction

Question 5

What factors affect rate of reaction

Answer 5

• concentration (or pressure when reactants are gases)
• temperature
• use of a catalyst
• surface area of solid reactants

Question 6

What is the collision theory

Answer 6

For a reaction to occur reactant particles must come together and
collide with:
* The correct orientation
* Energy greater than the activation energy, E_a for the reaction

Question 7

Why is there a slower rate of reaction at lower concentrations

Answer 7

Less particles in a given volume so less frequent collisions and therefore slower rate of reaction

Question 8

Why is there a faster rate of reaction at a higher concentration

Answer 8

More particles in a given volume so more frequent collisions and
therefore faster rate of reaction

Question 9

Why is there a faster rate of reaction when gas is compressed into a smaller volume

Answer 9

Gas molecules are closer together and
collide more frequently

Question 10

How can you measure the progress of a reaction

Answer 10

• Monitor the removal of a reactant
• Monitor the formation of a product

Question 11

What is a catalyst

Answer 11

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

Question 12

What does a catalyst do

Answer 12

A catalyst provides an alternative reaction
pathway with a lower activation energy

Question 13

What is a Homogeneous Catalyst

Answer 13

A catalyst that has the same physical state as the reactants

Question 14

What is a heterogeneous catalyst

Answer 14

A heterogeneous catalyst has a different physical state from the reactants.

Question 15

How does a Heterogeneous Catalyst work

Answer 15

1. The reactant molecules form weak bonds with the catalyst surface - absorbtion
2. Bonds within the molecules break
3. New bonds form
4. Product molecules leave the catalyst surface - desorbtion

Question 16

How do Catalysts have a sustainability and economic importance

Answer 16

• Catalysts lower activation energy
• This lowers the temperature needed for the reaction
• Lower temperatures mean less electricity from combustion of
  fossil fuels is used
  Less combustion of fossil fuels results in a reduction emissions from atmospheric pollutants.

Question 17

What does the Boltzmann distribution curve show

Answer 17

The Boltzmann distribution curve shows the spread of molecular energies in a sample of gas molecules

Question 18

How does the boltzman distribution curve change at a higher temperature

Answer 18

At higher temperature, the peak is lower and
shifted to the right

Question 19

How does the boltzman distribution curve change with a catalyst

Answer 19

A greater proportion of molecules exceed the new activation menergy

Question 20

What is equillibrium

Answer 20

• The rate of the foward reaction is equal to the rate of the reverse reaction
• The concentrations of reactants and products remain constant

Question 20

If you increase the concentration of reactants, which way does equilibrium shift

Answer 20

Equilibrium shifts to the right

Question 21

If pressure is increased, which side of the reaction will be favoured

Answer 21

equilibrium position moves to the side with fewer gaseous molecules

Question 22

How does a catalyst affect equilibrium

Answer 22

A catalyst does not affect the
position of equilibrium

Question 23

What is the equation for the equilibrium constant

Answer 23

For the equation:
aA + bB –> cC + dD

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

Question 24

What does K_c tell you

Answer 24

On which side of the equation the position of
equilibrium lies.

Question 25

Where does equilibrium lie if K_c = 1

Answer 25

Equilibrium lies halfway between the reactants and products

[reactants] = [products]

Question 26

Where does equilibrium lie if K_c > 1

Answer 26

Equilibrium lies on the right of the equation
[products] > [reactants]

The larger the value of Kc the further to the right equilibrium lies

Question 27

Where does equilibrium lie if K_c < 1

Answer 27

Equilibrium lies on the left of
the equation
[reactants] > [products]