Kinetics 2 Flashcards
What does the rate equation describe?
How the rate of reaction at a particular temperature depends on the concentration of the species involved
What is the rate of equation?
rate = k [A]* [B]*
Define autocatalysis
When a catalyst appears in the rate equation
What is an order?
The degree of effect to which change in a reactant has on rate
What does order zero mean?
A change in the concentration of the reactant has no effect on the rate
What does order one mean?
A change in the concentration of the reactant is directly proportional to change in the rate
What does order two mean?
A change in the concentration of the reactant is proportional to change in rate squared
How do the orders appear in the rate equation?
Order zero: does not appear
Order one: [A]
Order two: [B]2
What is the overall order of a reaction?
Sum of all the orders of the species involved in a reaction
How do you determine k from the rate equation?
- Determine the order of the reactants
- construct the rate equation
- rearrange for k
rate/[a][B] - determine units for k
- calculate value for k
Define rate of reaction
Change in concentration per unit time
What is the rate determining step?
The slowest step in a mechanism for a reaction
Are species involved only after the rate determining step in the rate equation?
No
What are the two rules involving the rate equation and the rate determining step?
-only species involved up and to including the RDS appear in the rate equation
- must be enough of each species to fulfil the rate equation
- –> ie: if rate=k[W]2[X] = all reactants up to RDS must have 2x W per X
What is the arrhenius equation?
word
The link between the rate constant, activation energy and temperature
What is the arrhenius equation?
Actual equation
k = Ae ^-Ea/RT
Arrhenius equation: what is the exponential and what does it represent
e ^-Ea/RT
The fraction of collisions with enough energy to react
What is the logarithmic form of the arrhenius equation?
ln(K) = -Ea/RT + ln(A)
Why is the logarithmic form of the arrheius equation used?
It is easier to use the arrhenius equation when you take (natural) logs of both sides to the base e
What does the logarithmic form of the arrhenius equation equate to?
hint: graphs
Equates to the equation of a straight line graph
ln(K) = -Ea/R x 1/t + ln(A)
Y = m x + c
What is the effect of increasing the activation energy on the arrhenius equation and therefore rate of reaction?
- The fraction is larger and more negative
- t/4 the value of the exponential is smaller
- t/4 k is smaller
- t/4 decreased rate of reaction
What is the effect of increasing the temperature on the arrhenius equation and therefore rate of reaction?
- The fraction is smaller and less negative
- t/4 the value of the exponential is bigger
- t/4 k is bigger
- t/4 increased rate of reaction
Arrhenius equation with Ea as the subject
Ea = (ln(A)-ln(K)) (R x T)
Arrhenius equation with T as the subject
T = Ea/ R x (lnA-lnK)
