Rates of reaction - TN Flashcards
equation for rate of reaction
rate of reaction = change in concentration or mass or volume / time
describe the effects of changes in surface area on the rate of a reaction
- more/less solid accessible
- more/fewer collisions per unit time
- more/less successful collisions per unit time
describe the effects of changes in concentration/pressure on the rate of a reaction
- more/less particles per unit volume
- more/fewer collisions per unit time
- more/less successful collisions per unit time
describe the effects of changes in temperature on the rate of a reaction
- particles have more/less energy
- proportion of collisions that are successful is higher/lower
- so more/less successful collisions per unit time
describe the effects of a catalyst on the rate of a reaction
- catalyst provides an easier route for the reaction which lowers the activation energy
- higher proportion of collisions successful
- more successful collisions per unit time
what is activation energy
the minimum amount of energy needed for the particles to react when they collide.
- if they do not have this they will bounce off each other and won’t react
how do catalysts work
they provide an alternative route with a lower activation energy
what happens to the particles that collide with less energy than their activation energy
they will just rebound and remain unchanged
what is the equation to find: rate of reaction
rate = collision frequency x percentage success
what two factors affect the collision frequency of a reaction
- surface area
- concentration
what two factors affect the percentage success of a reaction
temperature
catalysts
what practical would you use to show how rate is affected by concentration
React sodium thiosulphate solution with hydrochloric acid. this creates sulphur so that after a while you can’t see through the mixture to the cross at the bottom. rate = 1 / time taken (for the cross to disappear)
what practical would you use to show how rate is affected by surface area
Calcium carbonate chips with hydrochloric acid. Measure volume of CO2 output over period of time. more CO2 output = higher rate
what practical would you use to show how rate is affected by temperature
reacting magnesium with hydrochloric acid.
input: temperature of HCl
output: time taken for Mg to disappear
rate = 1/time taken
what practical would you do to show how rate is affected by catalysts
decomposition of hydrogen peroxide, catalysed by manganese oxide. rate = volume O2 produced / time
