module 5 (p1) Flashcards
what does zero order mean
conc of reactant doesn’t affect the rate
what does first order mean
conc of reactant affects the rate raised by power of 1
what does second order mean
conc of reactants affects the rate raised by power of 2
give the equation for the rate constant
rate = k [A]
how are concentration-time graphs made
plotting using continuous measurements during course of reaction
(continuous monitoring)
how is the gradient of the zero order on a C-T graph different from the other orders
straight line with a downward gradient
what is the half life
time taken from half a reactant to be used up
what does a first order have in terms on half life
exponential decay
the concentration of reactant halves at a constant time
how do we calculate k using a CT graph using the rate
- calculate gradient of tangent
- position where tangent has been in the conc. of the reactant
- rearrange the equation r = k [A]
how do we calculate k using a CT graph using the half life
k = ln2 / half-life
what is the gradient of zero order in a rate-concentration graph
no gradient (horizontal)
what is the gradient of first order in a rate-concentration graph
straight line gradient from the origin
how do we calculate k in zero order R-C graph
the y-intercept
how do we calculate k in first order R-C graph
(rate is directly proportional to conc.)
k is determined by measuring the gradient
how do we calculate k in second order R-C graph
plotting a second graph with conc^2 to give a straight line graph
gradient = k
describe a clock reaction
the time at the start of experiment measured for visual change
what does a clock reaction assume
average rate of r. is the same as the initial rate
initial rate directly proportional to 1/time
define a reaction mechanism
series of steps that make up an overall reaction
what is the rate-determining step
the slowest step
what does the orders in rate equaton show
number of species involved in the R-D step
CH3Br is hydrolysed with a hot aqueous alkali.
r = k [CH3Br]
what is the overall equation and what are the steps?
1) CH3Br –> CH3+ + Br-
2) CH3+ + OH- –> CH3OH
overall) CH3Br + OH- –> CH3OH + Br-
describe the factors affecting the rate constant
increasing temperature shifts the boltzmann distribution to the right, higher proportion of molecules that exceed activation energy
(change in rate mostly determined by this)
particles move faster so they collide more frequently
what is the arrhenius equation
k = A e^-Ea/RT
what is the arrhenius equation in logarithmic form
lnk = -Ea/RT + lnA
