CHEM 191 Lecture 13 Flashcards
(21 cards)
what are the two important things to know about a reaction
how far it goes (thermodynamics)
how fast it goes (kinetics)
the two are not related
do we need experimental kinetics data
we need experimental data to feed into the theory - we can’t listen to the theory if it is different from the experimental data
what is the unit for rate
moles per litre per second
what is rate
the speed of a reaction - how concentration changes with time
what is the formula of rate (for a general reaction)
where the reaction is:
aA + bB —> cC + dD
rate = -(1/a)(d[A]/dt) = -(1/b)(d[B]/dt) =
(1/c)(d[C]/dt) = (1/d)(d[D]/dt)
what factors affect reaction rate
chemical nature of reaction, physical states of reactants and products, concentration of reactants, temperature, catalysts, inhibitors
what is the rate law
rate = k[A]^x[B]^y
where k is the rate constant
x is the order with respect to A
y is the order with respect to B
x+y is the overall order of the reaction
k is the rate constant
what does 0 order mean
this concentration has no effect on the rate
that does first order mean
what ever you do to the concentration you get the same change in rate
what is second order
if you change the concentration the rate change by that value squared
does the rat claw include the products
never - just the reactants
what is a pseudo first order reaction
a reaction in which the concentration of A is much greater than the concentration of B (or vice versa). if both reactants are first order the reaction would normally be second order but when the concentration of A change the concentration of B doesn’t change very much. therefore the concentration of B is approximately constant which means rate = k’[A]
what is the unit for k when the reaction order is 0 (k=rate/[A][B])
molL-1s-1
what is the unit for k when the reaction order is 1 (k=rate/[A][B])
s-1
what is the unit for k when the reaction order is 2 (k=rate/[A][B])
Lmol-1s-1
what is the unit for k when the reaction order is 3 (k=rate/[A][B])
L2mol-2s-1
is rate constant dependent on concentration
no
does rate constant increase with time
yes
how do you find x
measure initial rates for different values of [A]0 while holding [B]0 constant
how do you find y
measure initial rate for different values of [B]0 while holding [A]0 constant
what is the equation for k
k= initial rate/[A]0x [B]0y (0 indicates time)
