rates of reaction 4.1
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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