Rates of reaction
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Rate of reaction
• Change in mass or concentration • of reactant or product • per unit time
Order of reaction
the power to which a concentration is raised in the rate equation
First order
concentration of reagent increases the rate proportionately
Second order
rate is proportional to square of concentration of reagent
zero order
increasing concentration of reagent has no effect on rate
rate equation(+units)
rate = k[a]^a moldm^-3s^-1
Rate constant
k is constant of proportionality units s^-1
half life
time taken for concentration of one reactants to fall by half
Rate equation from rds
reactants (+conc) in rds or before will be used in rate equation
Arrhenius equation
k = Ae^-Ea/RT lnk = lnA + (-Ea/RT)
Increased temperature (in Arrhenius)
rate constant increases so rate of reaction increases
Increase Ea in arrhenius
rate constant decreases (less molecules exceed Ea) rate of reaction decreases
Arrhenius straight line
y = lnk m= -Ea/R x = 1/T c= lnA
Rate determining step
• slowest step • highest activation energy • controls rate of reaction
R-C graph 1st order
• straight diagonal line • through origin • rate proportional to concentration
R-C graph 2nd order
• curve • through oririgin
R-C zero order
• straight horizontal line • not through origin
C-T graph 1st order
• curve • equal half lives
C-T graph zero order
• straight line • decreases
C-T graph 2nd order
• curve • unequal half lives
Rate constant from 1st order
k = ln2/ half life
Affect of temperature
• more particles exceed activation energy • rate increases • k increases
Catalyst
• increases rate of reaction • lowers activation energy • more molecules exceed • increased chance of successful collisions
Draw the botlzman graph