Reaction Kinetics Flashcards
Rate of reaction
defined as a CHANGE IN CONCENTRATION of reactants or products per unit time
rate eqn, order of reaction
For general rxn aA+bB-> products
rate= k[A]^m[B]^n
where [] concentration in mol dm^-3
m and n are order of reaction with respect to reactant A and B
k is the rate constant
order of reaction: shows the extent the rate depends on the concentration of the reactant. order with respect to a reactant is defined as the power to which its concentration term is raised in the rate eqn (cannot be deduced from stoichiometric eqn)
overall order of rxn: sum of m and n
half life of reaction
time taken for the concentration of a reactant to fall to half its orginal value
amt. of reactant remaining/amt. of reactant initially = (1/2)^n=(1/2)^time taken to reach current amt. /half life
n is number of half lives
observation of concentration-time graphs
zero-order: rate of rxn is independent of [A]
rate=k
rate vs [A] graph has a horizontal line, indicating a constant value
first-order: rate of rxn is directly proportional to [A]
rate= k [A]^1
rate vs [A] is linear passing through origin , y=x
constant half life
2nd-order: rate of rxn is directly proportional to the SQUARE of [A]
rate= [A]^2
rate vs [A] is the right half of positive x^2 graph
rate vs [A]^2 is linear through origin
(rxns involving 2 reactants w overall order 2 follows 2nd order kinetics)
how does concentration change the rate of rxn
when concentrations of reactants increase, the reactant particles are closer to one another and thus the frequency of effective collisions increase and rate increases as a result
decreasing volume, increasing pressure is also equivalent to increasing conc.
effect of of temperature change on rate constant and reaction (in terms of collision frequency)
as temperature increases the average kinetic energy possessed by the particles increase and thus the curve’s peak increases and is displaced to the right
more particles thus have energy equivalent or more than activation energy and the frequency of effective collisions increase, rate constant increases
effect of catalyst on reaction (in terms of Ea and and k)
when catalyst is added, alternative reaction pathway with lower Ea is provided hence more particles will have energy Ea and rate constant increases
more catalyst added will not speed up reaction, it is also not consumed in the reactions
heterogeneous catalyst and example
reactants and catalyst are in different phases
solid and undergoes chemical adsorption
adsorption theory: attachment of molecules of gases/liquid to the surface of another substance(solid) at an active site
therefore the increased SA of catalyst will speed up rxn
e.g the catalytic removal of oxides of nitrogens in car exhaust
