A2 Rate Of Reaction Flashcards
Rate of reaction
Change in amount or come net ration of a reactant or product per unit time
4 factors affecting rate of reaction
1)temperature
2)surface area
3)pressure
4)catalyst
5)concentration
Rate of reaction equation
Amount of reactant used up or amount of product formed /time taken
The change in concentration of reactants or products over time
what does rate depend on
rate is dependent upon the concentration of all the reactant species
each reactant doesnt have the same contribution to rate
the rate expression
the rate expression describes how the rate of reaction at a given temprature depends on the cocnetration of the species involved
a catalyst doesnt appear in the equation
a+b=c if we change a conc there ar three posisble outcomes
a= no effect
a=has an effect eg. double a double rate
a=double a quadruple rate
a has no effect
rate directly proportional [a]0
(1) no effect
change a for a constant
rate = k[a]0
0 order
double a double rate
rate directly proporitonal [a]1
rate= k[a]1
1st order
double a qudruple rate
rate direclty proportional [a]2
rate=k[a]2
2nd order
overall rate equation
rate=k[A]^m[B]^n
k=rate contant the bigger it is the faster the reaction it increases with temperature
A=increases with temp
B=Increases with temp
m+n=order of reaction
co efficents in rate equation
no revelence in rate expression only in chem equation
catalysts which arent in the chemical equation may appear in ate expression
calculating untis for the rate constant- 0 order
units for k very depending on the overall order of the reaction
rate=k
units for rate are mol dm-3s-1
so units for k are mol dm-3s-1
first order units
rate=k[a]
k=rate/[a]
s-1
second order
rate=k[a][b]
k=rate/[a][b]
units= mol-1dm3s-1
third order
rate=k[a][b]2
k=rate/[a][b]2
units = mol-2dm6s-1
the initial rate method
-experiments conducted at constant temperature
-each with a different concentrations of reactants and catalysts
-concentration of one reactant vs time graph drawn
-tangent drawn at t=o , gradient is the initial rate
- at the initial rate the concnetration of all the substances are known exactly at this time
-compare the intial rates for pairs of experiments to find order with respect to each reactant
effect of temperature
-small changes in temp gives large change in rate
-rough rule- for ever 10k increases rate doubles
-rate=k{a}{b}
concnetration doesnt change with temp only k increases with temp
arrhenius equation
how temp affects k
k=Ae^-Ea/RT
e
natural log constant
K
rate constant
A
pre exponential frequency factor
takes into account the frequency of collisions with the correct orientation
A has the same units as K
represents the proportion of molecules that exceed Ea
-Ea
activation energy
if this increases k decreases and then rate decreases
R
gas constant
T
temperature
as temperature increases k increases so rate increases
inverse of arrhenius equation
K= -Ea/RT + ln A
y= m x+ c
