AP Kinetics Concepts Flashcards
What must molecules do to react?
1) collide
2) collide w/ sufficient energy
3) collide in proper orientation
What affects the rate of the reaction?
- temperature
- concentration
- physical states (size of particles)
- presence of catalyst
When temp goes up, what happens to rate?
Temp goes down?
Increases
Decreases
Does breaking bonds absorb or release energy?
Creating bonds?
absorb
release
True/False: Kinetics can only be determined through experiment
True
What is the only thing that affects K?
temperature
Which molecules are more likely to orient themselves correctly? Why?
Small molecules are more likely to orient themselves correctly because they have less surface area and only have a few ways to orient themselves; whereas larger molecules have multiple ways to orient themselves and have a larger margin to orient themselves incorrectly.
What is the most common way to measure reaction rate?
through a color change
Method to find reaction orders
1) choose two trials where two reactions’ concentrations are the same
2) write out rate equations
3) divide one rate equation by the other
4) write two other rate equations to find other two variables
(note: you usually find k after you’ve found all the reaction orders. Pick one trial and solve for k remembering to solve for k’s units.)
If units for k are:
1) time^-1
2) mol/Ltime
3) mol^2/L^2time
1) first order
2) second order
3) third order
How to find the order of the reaction?
order of reaction = x + y + z
rate of formation equation
rate = delta C/ delta t
where reaction rate is coefficient of molecule
rate of disappearance
rate = - delta A (or B)/ delta t
where reaction rate is coefficient of molecule
If graph of concentration vs time is a straight line…
then reaction order is 0
If graph of ln[M] vs time is a straight line…
then reaction is first order
If graph of 1/[M] vs time is a straight line…
then the reaction is second order
How to remember graph analysis
clnr-
- concentration v time –> 0
- ln concentration v time –> 1
- reciprocal concentration v time –> 2
Equation for decay of first order reactions
ln([A]t/[A]0) = -kt
Equation for half life of first order reactions
t1/2 = .693/k
Equation for second order reactions
1/[A]t - 1/[A]0 = kt
Intermediate
starts on the products side and ends in the reactants
Catalyst
starts in the reactants and ends in the products side; ONLY lowers activation energy by orienting molecules to collide correctly and react
What does a reaction mechanism do?
describes the step-by-step process of an overall reaction
What are the two requirements for a reaction mechanism?
1) rate law that matches the rate-limiting step (slow step)
2) sum of all reactions must equal the total reaction
What is the rate of the overall reaction?
the rate of the slow step (rate-limiting step)
How to write the rate law
find the slow step and multiply k by the reactants raised to their coefficients in the rate limiting step
Can you have an intermediate in the rate law?
NO
To take an intermediate out of the rate law:
1) write the rate law based on the slow step (as you do)
2) use the fast and reversible step (w/ the reactants equaling the products) and solve for the intermediate
3) substitute that expression in for the intermediate in the rate law
How to find enthalpy (delta H)
products - reactants
What is a ___ catalyst?
homogenous
heterogeneous
enzyme
1) same phase as reactants
2) different phase than reactants
3) biological catalyst
