2.2 Rates of Reaction Flashcards
what are 6 factors which affect the rate of reaction?
- pressure (only gases)
- temperature
- light intensity
- catalyst presence
- concentration
- surface area (only solids)
how does concentration affect the rate of reaction?
the higher the conc, the more reactant particles present per unit vol and so a greater possibility of successful collisions occurring per second therefore the faster the reaction.
how does pressure affect the rate of reaction?
the higher the pressure, the closer the reactant particles are together and so a greater possibility of successful collisions per second and therefore the faster the reaction
describe the rate of reaction in a usual graph and explain
-rate fastest at the start of the rxn since each reactant is at its highest conc
-slows down as rxn proceeds bc conc of reactants decreases
-becomes 0 when rxn stops (1 of the reactants become used up)
how does a high Ea affect rate?
fewer no.of molecules that will have the sufficient energy to react and therefore rate decreases
how do you find the gradient/rate? units?
change in conc/times
moldm-3s-1
Label an exothermic reaction profile (book)
Label an endothermic reaction profile (book)
what must you always use when explaining the effect of changing conditions on reaction rates?
always use the collision theory
Draw a Maxwell-Boltzman distribution graph. Add a line for a lower temperature. Add a line for a higher temperature. (book)
what does a lower temperature on the Maxwell-Boltman distribution graph mean?
fewer molecules with an energy greater than or equal to the activation energy
what does a higher temperature on the Maxwell-Boltman distribution graph mean?
greater proportion of molecules with an energy greater or equal to the activation energy
which molecules are able to react? (in terms of Maxwel-Boltzman graph)
only those with an equal energy to or greater than the activation energy
what is the area under a maxwell-boltzman graph proportional to?
the number of molecules
what are the two types of catalysts?
homogenous, heterogenous
what is a homogenous catalyst, give an example
catalyst in the same physical state as reactants
eg acid catalysed hydrolysis of esters
CH3COOH (aq) + H2SO4 (c) + H2O(l) ⇌ CH3COOH (aq) + CH3OH (aq)
What is a heterogenous reaction and give an example
catalyst in a different physical state to reactants
eg catalytic hydrogenation of an alkene
C2H4 (g) + H2(g) ->Ni(c) C2H6(g) Nickel in the hydrogenation of unsaturated oils in the production of margerine
Give the 7 methods for studying reaction kinetics
- change in colour over time
- change in vol of a gas produced over time
- changes in press over time
- change in pH over time
- formation of a ppt over time
- change in mass of a reactant over time
- chemical analysis
Describe the method of measuring a change in colour over time
give an example
measure the amount of EM radiatoon absorbed by substances in the visible region over time
CuSO4 (blue) + Zn -> ZnSO4 (colourless) + Cu
Describe the method of measuring a change in volume over time
give an example
(in book draw apparatus)
using a syringe measure the change in volume of a gas produced over time
Mg + 2CHl -> MgCl2 + H2(g)
Describe the method of measuring a change in pressure over time
give an example
measure the change in pressure over time using a barometer
2NO2(g) -> 2NO(g) + O2(g)
Describe the method of measuring a change in pH over time
give an example
(in book draw apparatus)
measure the change in pH over time using a pH meter
Any formation of H+ or OH- ions
Describe the method of measuring the formation of a ppt over time
give an example
(in book draw apparatus)
time how long it takes a cross to disppear under the reaction mixture
Na2S2O3 + 2HCL -> 2NaCl + SO2 + H2O + S
Describe the method of chemical analysis
(in book draw apparatus)
(what does quenched mean)
taking samples at regular intervals til the rxn sample is ‘quenched’, the conc of a reactant can be determined by a titration
quenched - put in ice
