Rates of Reaction Flashcards
(36 cards)
Rate Of Reaction
Change in concentration of product or reactant with respect to time
Rate Equation
rate=k[A]x[B]y
For A+B->C+D
Rate Constant (k)
the proportionality constant that links the rate of reaction to the concentrations in the rate equation
Order of Reaction
with respect to a particular reactant, is the power to which the concentration of this reactant is raised in the rate equation
Overall Order of Reaction
Sum of the powers to which the concentrated terms are raised in the rate equation
Units in Rate Reaction
rate = mol dm-3 s-1
conc = mol dm-3
Rate Constants For Overall Orders
1 = s-1
2= mol-1 dm3 s-1
3= mol-2 dm6 s-1
4= mol-3 dm9 s-1
5= mol-4 dm12 s-1
When are reactants left out of rate equation
When they are 0 order
How to work out units of k
Treat mol, dm and s seperately
Cancel eachother out
Rate of Appearance / Disappearance
Use ratio of product to reactant in equation
Reactant disappear = product appear
e.g. BrO3- -> 3Br2
ratio 1:3
If 2moldm-3 Bromate (v) ions disappear ever second - 6moldm-3 Bromine appearing every second
Rates relation to concentration?
Rate is directly proportional to concentration
How does Temperature affect rate
increase temp = increase energy of reacting particles = increase number collisions = increase in successful collisions
Increase Rate of Reaction
How does Pressure affect rate of reaction
Increase pressure pushes reacting particles closer together = increase no. collisions and successful in a given period of time
Increase Rate of Reaction
How does concentration affect rate of reaction
Increase conc = increase number of reacting particles = increased collisions and successful
Increase Rate Of Reaction
How does presence of a catalyst affect Rate of Reaction
Provides alternate reaction pathway with lower activation energy - incr successful collisions
Increase Rate of Reaction
high activation energy will have low rate constant
Name of distribution of molecular energies plot
Maxwell-Boltzmann Distribution
Initial Rate
rate at time zero seconds (t=0s)
reaction just started
Rate is dependant on concs of reactants added at t=0s
Progressive Rate
ROR decreases as reaction proceeds and reactants used up
Methods, Measure rates at certain points during reaction and relate directly to conc of reactants at these times
Relies on being able to measure conc of reactants at directly during
Measure rate when Substance is coloured
Colorimeter used to measure conc
Calibration curve used - relating absorbance values to conc of known solutions of coloured substances
Directly proportional relationship
Absorbance values to conc converted to conc value using calibration curve
Measure rate when gas is released
Gas syringe used to measure gas volume
or
Change in mass can be recorded
Measure rate when substance can be titrated
Sample of reaction taken and quenched and titrated to determine conc
Quenching may be chemical (removing another reactant) or by cooling reaction rapidly to stop it at the time the sample was taken
Acid, Alkali and Iodine (using standard solution of Sodium Thiosulfate)
Measure rate when H+ or OH- ions are a reactant or product
Change in pH measured w/ pH meter
Also could be titrated using alkali for H+ or acid for OH-
Method of Measuring Initial Rate
- choose a product that is measurable
*for 1 reactant, set up series of experiments using a range of concs
*Plot graphs of measurable quantity against time
*determine rate at t=0s by drawing a tangent at t=0s and calc its gradient
*gradient=Initial ROR
Rate against Conc Graphs
Repeat experminet for other concs of reactant & plot graphs of initial rate against conc
Zero Order= Straight Line
First Order= Diagonal Line
Second Order=Curved Line
