3.2.2 Reaction rates

Question 1

Define rate of reaction

Answer 1

how fast a reactant is being used up or how fast a product is being formed

Question 2

Give the equation for rate of reaction

Answer 2

change in concentration / time

Question 3

What four factors affect rate of reaction?

Answer 3

• concentration (pressure if reactants are gases)
• temperature
• catalysts
• surface area of solid reactants

Question 4

What is collision theory?

Answer 4

• particles collide at the correct orientation
• sufficient energy to overcome the activation energy

Question 5

How does increasing concentration affect rate of reaction?

Answer 5

• more particles in same volume
• particles are closer together and collide more frequently
• higher frequency of effective collisions and increased rate of reaction

Question 6

How do you calculate the gradient from a tangent?

Answer 6

change in Y / change in X

Question 7

Define catalyst
- what 2 aspects make up a catalyst

Answer 7

increases the rate of a chemical reaction by providing an alternate reaction pathway with a lower activation energy
- not used up
- regenerated at the end of the reaction

Question 8

Define homogeneous catalyst
- how do they work?

Answer 8

same physical state as the reactants
- reacts with the reactants to form an intermediate
- immediate breaks down to form the product (and catalyst is regenerated)

Question 9

Define heterogeneous catalyst
- how do they work?

Answer 9

different physical state to the reactants
- reactant molecules are adsorbed (weakly bonded) to catalyst surface
- reaction occurs
- product molecues leave surface via desorption

Question 10

Why are catalysts important in terms of sustainability and economics?

Answer 10

• reduce temperature required = cheaper
• less energy = less fossil fuels = reduced emissions
• increased rate of reaction = greater production and profits

Question 11

What are the key components of a Bolzmann distribution curve?

Answer 11

1. curve ALWAYS starts at the origin (no molecules have zero energy)
2. area under the curve is equal to the total number of molecules
3. curve does not reach the x-axis (there is no maximum energy)

Question 12

How does changing** temperature** impact the Bolzmann distribution curve?

Answer 12

• peak is LOWER and shifted to the RIGHT
• more molecules have energy greater than or equal to the activation energy
• more collisions , and more with sufficient energy so increased rate of reaction

Question 13

How does a catalyst impact the Bolzmann distribution curve?

Answer 13

• lowers the activation energy
• increased number of molecules with sufficient activation energy
• increased successful collisions so rate of reaction increases