Rates of Reaction How Fast Flashcards
what do catalysts do
speeds up a reaction but is chemically unchanged at the end of the reaction
provides an alternative route with a lower Ea
units for rate
mol dm-3 s-1
what is dynamic equilibrium
quantities remain constant, although reactions still continuing- rates of forward and backward reactions equal
Closed system only
state Le Chateliers principle
position of equilibrium moves to counteract change
how to calculate rate
change in conc/change in time
what is first order
rate is proportional to the concentration of A
if you double conc A, rate doubles
rate = k[A]
what do [ ] mean
concentration
what is second order
rate is proportional to the square of the conc of A
if conc doubles, rate goes up by 4 times
rate= k[A]2
what is zero order
if the conc of A changes there is no change on rate
rate= k
what is the overall rate of reaction
adding up the individual orders
eg-
rate= k[A]2[B]
order= 3
rearrange the rate equation to find k
k= rate/ [A] [B]2
k units for
first, second and third order
first- s-1
second- dm3mol-1s-1
third- dm6mol-2s-1
what monitoring is concentration-time graphs
continuous monitoring
how to find rate of reaction from concentration-time graph
gradient
change in y over change in x
what is a zero order conc-time graph like
diagonal
rate of reaction is the same
k=gradient
what are the axis of conc time graph
x- time
y- concentration
what is a first order conc- time graph like
curved downwards
decreasing gradient over time (slowing down)
half life constant
what is a second order conc-time graph like
steeper at start
downwards curve
no constant half life
how to calculate k from half life
ln2/half life
rate conc graph axis
x- conc
y-rate
what is a zero order rate-conc graph like
horizontal line
rate= k
what is a first order rate-conc graph like
diagonal line
k= gradient of line
what is a second order rate-conc graph like
upward curve
k=plot graph of rate against conc squared and gradient would be k
how to find initial rate from conc-time graph
draw tangent at T=0
how to find initial rate
1/t
limitation of clock reaction
assumes initial rate is constant up to where the measurement is taken
what is a rate determining step
slowest step in a multi-step reaction
fast step cant happen until the slow reaction has finished
what makes up the Arrhenius Constant
k= rate constant Ae= frequency of collisions Ea= activation energy (joules) r- gas constant t- temperature (kelvin)
if there was no activation energy in the Arrhenius Constant what does A tell you
rate
log of Arrhenius Constant
ln(k)= -Ea/R x 1/t +ln(A) y= mx + c (y intercept)
rearrange y=mx+ c
c= y-mx
