Reaction rates

Question 1

define rate

Answer 1

change in conc of reactant or product per unit time

Question 2

rate of reaction can be calculated by measuring the gradient of which type of graph

Answer 2

concentration-time graph

Question 3

effect of increasing temperature on rate of reaction

Answer 3

• increases ke of particles
• frequency of successful collisions increases as more particles have sufficient energy to overcome Ea
• ror increases

Question 4

effect of increasing surface area on rate of reaction

Answer 4

• more reactant particles are exposed at the surface
• freq of successful collisions increases
• ror increases

Question 5

effect of increasing concentration on the rate of reaction

Answer 5

• increases number of particles in a certain volume
• particles are closer together and the frequency of successful collisions increases
• ror increases

Question 6

effect of increasing pressure (on gases)

Answer 6

• same number of particles in a smaller volume
• particles are closer together
• freq of successful collisions increases
• ror increases

Question 7

how can the rate of reaction be determined experimentally

Answer 7

• by monitoring the removal of a reactant or the formation of a product per unit time
• if product is a gas you can measure mass loss of reactants over time at regular intervals using a balance or measure the volume of gas produced at regular intervals using a gas syringe

Question 8

steeper curve on rate graphs shows the ror is

Answer 8

faster

Question 9

why does ror rapidly decrease once a reaction has started

Answer 9

• at start, all particles present are reactants
• reaction begins, reactants used up quickly. High freq of successful collisions
• reaction continues, lower frequency of successful collisions between particles. Slower rate
• all reactants have been used up, no more successful collisions, rate is zero

Question 10

what are catalysts

Answer 10

• substance that increases the ror by providing an alternative pathway with a lower Ea without being used up in the process

Question 11

effect of catalysts on freq of successful collisions

Answer 11

• as Ea is reduced, the proportion of molecules with E > Ea in increases.
• increased freq of collisions

Question 12

define homogenous catalyst

Answer 12

catalyst is the same physical state as the reactants

Question 13

define heterogenous catalyst

Answer 13

catalyst is in different physical state as reactants

Question 14

what does the Boltzmann distribution show

Answer 14

shows a range of possible kinetic energies for gaseous particles in a reaction container

Question 15

parts of Boltzmann distribution

Answer 15

1: No articles have 0 energy
2: few particles have E > Ea
3: most particles have intermediate energies to the right of the peak

Question 16

effect of increasing temperature on the Boltzmann distribution curve

Answer 16

• flattens and shifts to the right, increasing proportion of molecules with E > Ea, hence the number of successful collisions and rate increases
• part where curve levels of is higher

Question 17

effect of catalyst of Boltzmann distribution

Answer 17

• no change to freq of collisions as it has no effect on the ke of particles however more successful collisions occur - greater proportion of particles have E > Ea
• line for Ec will come before Ea line

Question 18

what goes on the x and y axis of Boltzmann distribution graphs

Answer 18

x - energy
y - number of particles

Question 19

what are the benefits of using catalysts

Answer 19

• lower temperatures needed
• higher atom economy of reactions
• increased rate means products are made faster
• fewer pollutants produced

Question 20

impact of lower temperatures needed on environment/industry

Answer 20

• reduces the energy demand from combustion of fossil fuels
• reduction of CO2 emissions
• reduces global warming

Question 21

impact of higher atom economy on environment/industry

Answer 21

• reduced waste
• higher % of useful products made from raw materials

Question 22

impact of faster reactions on environment/industry

Answer 22

• uses less energy
• cuts costs and increases profits

Question 23

impact of fewer pollutants produced on environment/industry

Answer 23

• reduces number of pollutants released into the environment