rates equations Flashcards
the rate of a chemical reaction is related to
the concentration of reactants
rate eqaution form
rate = k[A]^m [B]^n
where m and n are orders of reaction with respect to A and B
k is the rate constant
order of reaction is restricted to
0,1 and 2
the rate constant k varies with
tempertaure
arrhenius equation
Ae ^(-Ea/RT)
k = rate constant (same units as A)
A = arrhenius constant(same units as k)
e= mathmatical constant
Ea= activation energy (J)
R= molar gas constant (J mol-1 K-1)
T= temperature (K)
define rate of reaction
the change in concentration per unit time
mol-1 dm-3 s-1
define activation energy
the minimum amount of energy required to start of reaction
endothermic
what do the differnet orders of reaction mean
zero- changing concentration has no effect on the rate
first- rate directly proportional to the change in concentration of reaction
second - rate proportional to the square of change in concentration
rearrangement of arrhenius eqaution
ln k = ln A -(Ea/RT)
deine the rate constant
the rate of reaction when all concentrations are 1 mol dm-3
specific for every reaction
how to determine order of reaction with respect to each reactant
only determined by experiment
what are the 2 types of experiment that can be done to determine the order with respect to different reactants
continuous monitoring method (following the course of a single reaction)
initial rates method (doing multiple experiments)
how to measure the progress of reaction in continuous monitoring method and its problems+ solutions
by taking samples at regular intervals, much quench the reaction when sampling by adding a large volume of cold distilled water to both cool and dilute the reaction decreasing the rate
OR
by using a visible indicator/ physical properties such as a gas syringe to measure gas volume, this mearsures the amount of product produced and the order of reaction is about reactants so volumes recorded would need converting to reactant concentration
if colour changing reaction use colorimetry
how to use reuslts of continous monitoring to work out orders
CTT graphs (concnetration time and tangent)
plot concenration on y axis and time on x axis, draw tangent at any value of t and the gradient of the tangent will give the rate of reaction at that specific moment in time. do this is different concentration and compare facto of change in conc to factor of change of rate worked out by gradients
graph of zero order reaction
straight line as change in conc does not affect rate