18 kinetics
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define rate of reaction
change in concentration per unit of time
what is the equation for rate of reaction?
change in conc/time
why do the majority of chemical reactions start off with a fast rate and then slow down before the reaction stops?
• at first, high conc of reactants so more frequent successful collisions • as reactants use up, less frequent collisions • one or more reactants used up = no successful collisions
what is on the y axis of a maxwell boltzmann distribution?
number of particles
what is on the x axis of a maxwell boltzmann distribution?
kinetic energy
what is an order of reaction?
which species have an influence on the rate and by how much
what is zero order of reaction?
where the change in concentration of reactants have no effect on the rate
what is 1st order of reaction?
where the change in concentration of reactants is directly proportional to the rate
what is the 2nd order of reaction?
[reactants]^2 = proportional to rate
what is the overall order of k[X][Y]^3? explain why
4th order 1. [X] is to the power of 1 so reaction 1st order with respect to X 2. [Y] is to the power of 3 so reaction 3rd order with respect to Y 3. overall order is 4th order
what happens to the order when using a large excess of reactants?
zero order with respect to that reactant as the reactant’s concentration is constant
what is the letter for rate constant?
k
which only factor affects k?
temperature
when is the value of k essentially just the rate of reaction?
1moldm^-3
what 2 experiments can be done to determine the order with respect to different reactants?
1) continuous monitoring method 2) initial rates method
what are the 2 ways to measure the progress of a reaction within the continuous monitoring method?
1) take sample at regular intervals 2) use a visible indicator
what would you do if a reaction mixture is still reacting?
quench reaction by adding large volume of cold distilled water to cool and dilute to reduce rate
what is a problem of the continuous monitoring method using a visible indicator?
volume of gas recorded will need converting into conc
how would you measure the initial rate from a CTT graph?
draw a tangent from 0 seconds and calculate gradient
how do you calculate gradient?
change in y/change in x