module 5 Flashcards
define rate of reaction
change in conc. of a product or reactant over a certain time
how can you calculate rate of reaction
change in conc/time (s)
what does it mean if a reactant is in zero order?
changing conc. had no effect on the rate
what does it mean if a reactant is in first order?
the rate is directly proportional to the concentration
what does it mean if a reactant is in second order?
change in rate = change in conc. squared
what is the generic rate equation
rate = k [X]^x [Y]^y
do zero order reactants appear on the rate equation? why?
no, as they do not affect rate
how is overall order determined
adding all of the orders
when the overall order is 3 what would the units of the rate be?
dm^6 mol^-2 s^-1
how can you measure rate experimentally?
use colorimeter at suitable intervals and see if colour changes
if gas involved use a gas syringe to collect or use a scale to measure mass lost
what is a half life
time taken for concentration of a reactant to reduce by half
what is the symbol for a half life
t1/2
what is the relationship between first order reactants and half life?
they have a constant half life
which equation is used to find rate constant using the half life in a first order reaction?
k = ln2/ t1/2
what is the relationship between rate and time
rate is directly proportional to 1/t
how to find rate constant from a rate conc. graph of first order
k = rate/conc.
what is the rate determining step?
the slowest step in a reaction with multiple steps
how does the rate determining step relate to the species involved in the rate equation?
any species involved in the RDS appear in the rate equation - species only involved after RDS do not appear in rate equation
for a reactant in the rate equation, what indicates how many molecules of that reactant are involved in the RDS?
the order of the reactant
what conditions affect the value of the rate constant
temperature
what is the effect of a 10 degree increase in temp on the rate of reaction
double
what is the Arrhenius equation? what does each term mean?
k = Ae^-Ea/RT k = rate constant A= pre-exponential factor e= mathematical quantity Ea = activation energy (j) R = gas constant T = temp (in kelvin)
how can you convert the Arrhenius equation into a useful form to plot a graph? how can you find each term?
Lnk = -Ea/RT - LnA
graph of Lnk against 1/T
gradient = -Ea/R and y Intercept is Ln A
what does it mean when a reaction is in equilibrium
the rate of the forward reaction is equal to the rate of the backward reaction