Rates Flashcards
what are units for rates?
moldm-3s-1
change in conc/time
at what time is the initial rate
0s
this is directly related to the initial concentration of the reactant
the rate equation for a general reaction
A + B -> C + D
rate = k [A]m[B]n
m = order of reaction with respect to reactant A
n = order of reaction with respect to reactant B
what is the order of reaction
m + n
the power to which the concentrations of this reactant is raised in a rate equation
zero order
the conc of a zero order reactant has no effect on the rate of reaction
[A]0 = 1
how to work out the rate of a reaction
it can only be found experimentally
first order
rate is proportional to A
so doubling A, doubles the rate of reaction
second order
rate is proportional to [A]2
if we double [A], the rate is quadrupled
what is the order of reaction
the power which [A] is raised with respect to A
what is the rate determining step
the slowest step that holds everything else up
measuring rates of reaction experimentally
Collecting gas
1) gas syringe is attached to a sealed reaction vessel and measure the volume of gas produced
2) measured on a graph against time
3) gradient of tangent shows the rate of reaction
measuring rate of reaction experimentally:
measure colour change using a colorimeter
- if a blue solution you should use a red filter, as the solution is absorbing red light
- amount of red absorbed relates directly to the concentration
- draw a calibration curve, so absorbance can be converted to conc
- several experiment take place with differ conc
measuring rate of reaction experimentally:
quenching and titrating
- The reaction in each of the samples is stopped (quenching)
- Quenching ‘freezes’ the reaction to allow the concentration to be determined by titration
- with collected data, the ror can be calculated by determining the change in concentration with time
measuring rate of reaction experimentally
loss of mass
- measuring mass over a period of time. curve decrease until initial tangent T=0s gives the initial rate
- conc will be changed and initial rate is measured
measuring rate of reaction experimentally
ph monitoring
pH = -log10[H]+, so [H]+ = 10(-pH)
- pH values can be taken over time, they can be directly converted to [H]+ by using the equation
-graph of [H]+ can be drawn
- if [H]+ is a reactant, the curve can give the rate or gradients of tangents at various [H]+ can be taken which equal the rate
