rates of reaction 4.1 Flashcards
what’s the name of the amount of energy that particles need to react?
activation energy
what two things affect the rate of reaction?
collusion frequency, how often do the particles collide with each other
percentage success
how to work out the rate of collisions?
rate = collusion frequency x percentage success
what four factors affect the rate of success?
solid surface area
solution concentration
temperature
catalysts
what’s the model answer for collision with surface area?
higher solid surface area increases rate:
- more of the solid is exposed to the other particles
- so collision frequency is higher
- so there are more successful collisions per unit time
what’s the model answer for collision in higher solution concentration/ gas pressure?
higher solution concentration/gas pressure increases rate:
- more particle per unit volume
- so collision frequency is higher
- so there are more successful collisions per unit time
what’s the model answer of collusions with a higher temperature?
higher temperature increases rate:
- particles have more kinetic energy
- so percentage of collisions with enough energy is higher
- so there are more successful collisions per unit time
what’s a model answer for collisions with catalysts?
catalysts increases rate:
- provide an alternative route with lower activation energy
- so percentage of collisions with enough energy is higher
- so there are more successful collisions per unit time
how can you increase surface area?
cutting or grinding up a solid
what’s the marble chip experiment?
the effect of surface area on rate is demonstrated by reacting calcium carbonate chips with hydrochloric acid
calcium carbonate (s) + hydrochloric acid (aq) > calcium chloride (aq) + water (l) + carbon dioxide (g)
input - sizes of CaCO3 chips
output - the volume of CO2
control - mass of CaCO3
- volume and concentration of HCl
- temperature
measure the volume of CO2 with a gas syringe
steeper start - rate has increased, volume of CO2 increasing faster
same final volume - amount of reactants hasn’t changed
how is rate calculated for the disappearing cross experiment?
rate = 1/ time taken
what’s the disappearing cross experiment?
the effect of concentration on rate can be demonstrated by reacting sodium thiosulphate solution with hydrochloric acid
in the reactuon, a solid sulphur is slowly produced
therefore after a while you can’t see through the mixture any more
this is measured by observing a black cross under the mixture
input - concentration of sodium thiosulphate
output - the time taken for the cross to disappear
control - the volume of solution
- concentration of HCl
- temperature
graph shows straight, directly proportional line through the origin:
- double concentration = double the rate
- triple the concentration = triple the rate
etc
what’s the magnesium and acid experiment?
the effect of temperature on rate can be demonstrated by reacting magnesium with hydrochloric acid
in this reaction magnesium disappears
input - the temperature of HCl
output - the time taken for Mg to disappear
control - mass and surface area of Mg
- volume and concentration of HCl
it’s not a straight line as rate isn’t proportional to temperature
doesn’t go through origin as rate isn’t 0 at 0 degrees
what are catalysts?
substances which increase rate and remain chemically unchanged
what’s the hydrogen peroxide experiment?
the effect of catalysts on rate can be demonstrated using the decomposition of hydrogen peroxide
this reaction is normally very slow, however it is catalysed by maganese oxide which is a black solid causing reaction to take place much faster
input - which catalysts is being used
output - volume of O2
control - volume and concentration of H2O2
- temperature
- mass and surface area of catalyst
more effective catalyst increases rate more effectively - steeper line
