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)
Arrhenius equation with A as the subject
A = K/ e^ -(Ea/RT)
What is the effect of concentration of a solution on. rate?
The higher the conc, the faster the reaction (unless zero order)
Why does rate increase with conc of reactants?
The particles are closer together and so there are more frequent collisions
What is the effect of surface area of a solid on rate?
The greater surface area, the faster the reaction
Why does rate increase with surface area?
There are more particles exposed at the surface that can be collided with, and so there are more frequent successful collisions
What is the effect of pressure of gases (reactants) on rate?
The higher the pressure, the faster the reaction (unless zero order)
Why does rate increase with pressure of reactant gases?
The particles are closer together and so there are more frequent successful collisions
What is the effect of temperature on rate?
The higher the temperature, the faster the reaction
Why does rate increase with temperature?
3
Particles have more energy and so a greater proportion of the collisions are successful.
The particles also move faster and so collsions are more frequent.
Therefore, more frequent successful collisions
What is the effect of a catalyst on rate?
A catalyst increases the rate of a reaction but is not used up
Why does rate increase with a catalyst added?
It provides an alternative route/mechanism with a lower activation energy and therefore a greater proportion of the collisions are successful
