Chemistry- Kinetics & Rate Equations Flashcards
What is a zero order concentration time graph?
IF the order is 0 with resepect to a reactant, then the rate is unaffected by changing the concentration of it.
eg. Rate [A]^0
What is a first order concentration time graph?
If the order is 1 with respect to the reactant, then when the reactant concentration doubles so dows the rate.
eg Rate [B]^1
WHat is a second order concentration time graph?
IF the oder is 2 with respect to a reactant then when the reactant concentration increases by x2, the rate increases by 2^2 = x4.
Eg. Rate [C]^2
What is the general form of rate law for a general cehmical reaction?
Rate = k[A]^m [B]^n
where k= constant
m & n = reaction order.
If any reactant is zero order then it does not appear in the rate equation.
What is the overall oder of a rate equation?
Sum of individual orders
eg. rate = k[B]^1 [C]^2
then overall oder = 1+2
= 3
How do you find units for the rate equation?
Rate =k[A] [B]^2
k= rate / [A] [B]^2
so units = moldm^-3 s^-1 / (moldm-3)(moldm^-3)^2
=mol^-2 dm^6 s^-1
What are the different orders for a reaction?
Order = Effect of each reactant
zero order - Rate unaffected y changing [A]
first order-DIrectly proportional
second order- Rate increases by [A]^2
What are the units for a first order, second order and third order.
1st order - s^-1
2nd order - mol^-1 dm^-3 s^-1
3rd order - mol^-2 dm^6 s^-1
Define Half life.
The time taken for a variable to fall to half the time taken. t(1/2)
Half life decreases with time for 0 order reactions.
Half life is constant for 1st order reactions.
How can you find rate constant using half life?
k= ln(2) / t(1/2)
eg. t(1/2): 3 mins —> 180 seconds
k= ln2 /180 =3.85x10^-3 s^-1
Define the rate determining step.
The slowest step in a multi step reaction that determines the overall reaction.
Define activation energy.
THe minimum energy required by particles for a collisio between them to result in a reaction.
Define kinetics.
Chemical kinetics/reaction kinetics is the study of rates of reactions & factors affect rates.
Define first order Reactions.
A reaction is first order with respect to a particular species if the rate of reaction is directly proportional to the concentration of that species.
Define colourimetry.
A technique that measures the concentration of a coloured solution by measurig the amount of a specific wavelength of light absorbed by the solution.
Define a catalyst.
A substance that speeds up a chemical reaction without being used up in the reaction. It does this by providing an alternative pathway for a reaction to take place with a lower activation energy.
Define zero order reactions.
A reaction is zero order to a particular species if the rate of reaction is independent of the concentration of that species.
Define second order reactions.
A reation is second order with respect to a particular species if the rate of reaction is proportional to the concentration of that species squared.
Define overall oder of reactions
The sum of the powers to which the concentrations have been raised in the equation.
Define rae equation.
An equation that relates the concentration of the substrates involved in the reaction to the rate of reaction.
Define rate of reaction.
The rate at which reactants are consumed or products are formed in a reaction.
What is the rate constant?
The constant of proportinality in the rate equation given the symbol k
Larger k value = faster rate of reaction.
What is the effect of temperature of the rate constant?
Increasing the temperature gives more energy to molecules so the rate increases.
Rate = k[A][B][C]
if the rate increases then so does k
What is the arrhenius equation?
k=Ae^-Ea/RT k= Rate constant Ea= Activation energy R= Gas constant (8.31) T= Temperature in kelvin A= Pre-exponential factor e= Mathematical constant.
Rearrange the arrhenius equation for Ea, A, T
Ea = RT(lnA-lnK)
A= Ke^Ea/RT
T= Ea/ R(lnA-lnK)
What is the initial rate of reaction?
Rate at the start when t=0
How can a clock reaction give initial rate of reaction and what experiment can be used for this?
Some reactions produce visible changes. TIme take for changes to appear is measured.
Rate = 1/t
- Place a piece of paper with a (X) under reacting vessle. Start reaction and timer until (X) is obscured at this point stop the timer.
Initial rate = 1/t
How can you predict a reaction mechanism for RDS (rate determining step) ?
Order tells us number of molecules of each species in RDS.
Only molecules in rate equation are involved in RDS.
