10 Reaction rates and equilibrium

Question 1

What is meant by rate of a chemical reaction?

Answer 1

It measures how fast a reactant is being used up or how fast a product is being formed.

Question 2

What makes a collision effective?

Answer 2

• The particles collide with the correct orientation.

- The particles have sufficient energy to overcome the activation energy barrier of the reaction.

Question 3

How does increasing the concentration affect the rate of reaction?

Answer 3

• An increase in concentration increases the number of particles in the same volume.
• The particles are closer together and collide more frequently.
• In a given period of time there will be more effective collisions and an increased rate of reaction.

Question 4

How does increasing the pressure of a gas effect the rate of reaction?

Answer 4

• The concentration of the gas molecules increases as the same number of gas molecules occupy a smaller volume.
• The gas molecules are closer together and collide more frequently, leading to more effective collisions in at the same time.

Question 5

What is a catalyst?

Answer 5

• A catalyst is a substance that increases the rate of a chemical reaction without being used up in the process.
• It provides an alternative reaction pathway of lower activation energy.

Question 6

What are the two types of catalysts?

Answer 6

• Homogeneous catalyst

- Heterogeneous catalyst

Question 7

What is a homogeneous catalyst?

Answer 7

• A homogeneous catalyst has the same physical state as the reactants.
• The catalyst reacts with the reactants to form an intermediate.
• The intermediate then breaks down to give the product and regenerates the catalyst.

Question 8

What is a heterogeneous catalyst?

Answer 8

• A heterogeneous catalyst has a different physical state from the reactants.
• Reactant molecules are adsorbed (weakly bonded) onto the surface of the catalyst, where the reactant takes place.
• After reaction, the product molecules leave the surface of the catalyst by desorption.

Question 9

What happens during autocatalysis?

Answer 9

The reaction product acts as a catalyst for that reaction.

Question 10

What are some features of the Boltzmann distribution?

Answer 10

• No molecules have zero energy.
• The area under the curve is equal to the total number of molecules.
• There is no maximum energy for a molecule- the curve does not meet the x axis.

Question 11

What happens at a higher temperature?

Answer 11

• More molecules have an energy greater than or equal to the activation energy.
• Therefore a greater proportion of collisions will lead to a reaction, increasing the rate of reaction.
• Collisions will also be more frequent as the molecules are moving faster.

Question 12

What happens when there is a catalyst?

Answer 12

• A catalyst provides an alternative route with a lower activation energy.
• A greater proportion of molecules now have an energy equal to, or greater than the lower activation energy.
• On collision, more molecules will react to form products.
• The result is an increase in rate of reaction.

Question 13

In an equilibrium system:

Answer 13

• The rate of the forward reaction is equal to the rate of the reverse reaction.
• The concentration of reactants and products do not change.

Question 14

Equilibrium systems are…

Answer 14

dynamic

Question 15

For a reaction to remain in equilibrium, the system must be…

Answer 15

closed

Question 16

What is le Chatelier’s principle?

Answer 16

It states that 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 effect does changing the concentration of reactants or products have?

Answer 17

• If there are more products formed, the position of the equilibrium has shifted to the right.
• If there are more reactants formed, the position of the equilibrium has shifted to the left.

Question 18

What effect does changing the temperature have?

Answer 18

• An increase in temperature shifts the equilibrium position in the endothermic direction.
• A decrease in temperature shifts the equilibrium position in the exothermic direction.

Question 19

What colour does the solution of cobalt chloride change when there is an increase in temperature?

Answer 19

Blue

Question 20

What colour does the solution of cobalt chloride change when there is a decrease in temperature?

Answer 20

Pink

Question 21

What colour does the solution of potassium dichromate change when you add sulfuric acid?

Answer 21

Orange, as there is an increase in concentration of H+ ions (Shifts right)

Question 22

What colour does the solution of potassium dichromate change when you add sodium hydroxide?

Answer 22

Yellow, as there is a decrease in concentration of H+ ions (Shifts left)

Question 23

What happens when you increase the pressure of the system?

Answer 23

The equilibrium position will shift to the side with fewer molecules, reducing the pressure of the system.

Question 24

What does the Kc value of 1 tell us?

Answer 24

It indicates a position of equilibrium that is halfway between reactants and products.

Question 25

What does a Kc value of >1 tell us?

Answer 25

Position of equilibrium towards products.

Question 26

What does a Kc value of <1 tell us?

Answer 26

Position of equilibrium towards reactants.