ch6: rates of chemical reactions

Question 1

what are the requirements for successful reaction?

Answer 1

• collision
• enough activation energy (greater or equal to)
• orientation of reactants

Question 2

what impact does a catalyst have on activation energy?

Answer 2

The catalyst lowers the activation energy of a reaction by providing an alternative reaction pathway.

Question 3

what factors affect the rate of reaction?

Answer 3

• temperature
• concentration (or pressure for gases)
• surface area (solids/liquids)
• presence of a catalyst

Question 4

how does surface area increase the rate of reaction?

Answer 4

• surface area increases when particle size decreases
• therefore, more exposed particles are able to react

Question 5

how does a high concentration increase the rate of reaction?

Answer 5

• more particles in a given volume
• higher frequency of collisions with appropriate conditions
• more successful reactions occur

Question 6

how do you increase the concentration with a gas?

Answer 6

• increasing the pressure increases the concentration
  (same particles as before, they’re just all closer so the concentration is higher)

Question 7

why does the rate of reaction increase if concentration is increased?

Answer 7

• as concentration is increased, the number of particles increases
• the same percentage of them will be above the required activation energy, so more particles will have energy equal to or greater than the required activation energy
• greater frequency of collisions
• so number of successful collisions increases
• therefore rate of reaction increases

Question 8

why does the rate of reaction increase if surface area is increased?

Answer 8

• as surface area is increased, the number of particles available increases
• the same percentage of them will be above the required activation energy, so more particles will have energy equal to or greater than the required activation energy
• greater frequency of collisions
• so number of successful collisions increases
• therefore the rate of reaction increases

Question 9

why does the rate of reaction increase if temperature is increased?

Answer 9

• as temperature increases, kinetic energy also increases
• the number of particles is the same, but the percentage of particles with energy greater or equal to the required activation energy increases
• the frequency of collisions increases
• the number of successful collisions increase
• therefore the rate of reaction increases

Question 10

why does the rate of reaction increase if a catalyst is added?

Answer 10

• the catalyst lowers the required activation energy, providing an alternative reaction pathway
• number of total particles is the same, but now more particles have the required activation energy
• the frequency of successful collisions increases
• therefore the rate of reaction increases

Question 11

what is the rate of reaction defined as?

Answer 11

the rate of reaction is defined as the change in concentration of a reactant/product over time.

rr= conc/t

Question 12

what’s the difference between a homogenous or heterogenous catalyst?

Answer 12

homogenous -> same physical state as the reactants and products
heterogenous -> different physical state to the reactants and products

Question 13

are homogenous or heterogenous catalysts preferred in industry, and why?

Answer 13

• heterogenous catalysts are preferred in industry
• can be easily separated from products of a reaction
• easier to reuse
• able to be used at high temperatures