Chapter 14 and 15 Flashcards
What is the formula for average rate?
Change in concentration over change in time
How do you find instantaneous rate?
Slope of the tangent line
How do you find the order of each of the reactants from experiments?
Concentration doubles as rate increases by 2^1 = first order
Concentration doubles as rate increases by 2^2 = second order
What is the general rate law?
Rate=k[X]^y
What is the first order integrated rate law?
Ln [A]t = -kt + Ln[A]0
What does the straight line graph look like for a first order reaction?
Ln[A] vs t with a slope of -k and a y-intercept of ln[A]0
What is the half-life formula for a first order reaction?
Ln2/k
What is the second order integrated rate law?
1/[A]t = kt + 1/[A]0
What does the straight line graph look like for a second order reaction?
1/[A]t vs t with a slope of k and a y-intercept of 1[A]0
What is the half-life formula for a second order reaction?
1/([A]0 * k)
What are the two tenets of collusion theory?
the reactants must collide with a energy greater than a minimum energy (E>Emin) and with the right orientation
What is the Arrhenius equation that only has one temperature?
Ln k = Ln A - Emin/RT or K = A times e^(-Emin/RT)
What is the Arrhenius equation that relates two temperatures?
Ln (K2/K1) = -Emin/R (1/T2 - 1/T1)
What is the value of R in J/molK?
8.3145J/molK
On an Potential Energy vs Reaction Coordinate Graph, how do you find Ea?
Distance from reactants/products to top of hill
On an Potential Energy vs Reaction Coordinate Graph, how do you find the transition state?
Top of hill
On an Potential Energy vs Reaction Coordinate Graph, how do you find Delta E/H?
Difference between products and reactants
On an Potential Energy vs Reaction Coordinate Graph, how can you tell endothermic/exothermic?
endothermic- +Delta H/E, products are higher, Ea of forward reaction is higher (all opposite for exothermic)
On an Potential Energy vs Reaction Coordinate Graph, what is the role of a catalyst?
to increase reaction rate by reducing Ea
What is the Arrhenius equation relating the rates of a reaction with and without a catalyst?
Include the equation for when temperature is different.
Ln (rate cat/rate uncat) = Delta Ea / RT (same temperature/A)
His-Rate cat/Rate uncat = e^((Ea noncat- Ea cat )/ RT)
DiffTemp-
ratecat/rateuncat = e^(Eanoncat/RTnoncat minus Eacat/RTcat)
How do the forward and backwards Ea relate?
Ea reverse = Ea forward + Delta H or E (Delta H is equal to Delta E)
What is the equation for bond energies and delta H?
Delta H is energy in reactant minus products
What are the three things that prove a reaction mechanism is possible?
Adds up to overall, same rate law, presence of intermediates
How do you get the rate law from a reaction mechanism when one step is slow?
Rate law of the slow elementary reaction is the rate law of overall (may need to substitute to get rid of intermediates)
How do you get started on a rate law for a reaction mechanism when no reactions are slow?
Look at overall products and find something that is only produced once
Describe the steady state approximation
Make an assumption that the intermediate’s concentration never accumulates, and remains steady. It remains steady only if the rate of formation is equal to the rate of consumption.
What can you assume if the rate of a reverse reaction is faster than the forward reaction of the next reaction?
The second one is slow (and therefore the first is at equilibrium)
What is the equation for the equilibrium constant K?
aA+bB->cC+dD
pressure/concentration of C raised to c times D raised to d over A raised to a times B raised to b
How does the equilibrium constant K change when reversing a reaction?
1/K
How does the equilibrium constant K change when multiplying a reaction by a number?
K^n
How does K tell you if products or reactants will be favored?
K>1 favor products, K<1 favor reactants
What is the equation for the new K when adding equations?
K1*K2
What factor will change the equilibrium constant?
Temperature
What is the equation that shows how the equilibrium constant changes with temperature?
Ln (K2/K1) = -Delta H/R (1/T2 - 1/T1)
What is the formula for converting between Kp and Kc?
Kp=Kc(RT)^Delta n
R is .08206 Latm over molesK
Delta n is sum of coefficients of products minus sum of coefficients of reactants
How is Q calculated?
Like Kc, but the values are original, not equilibrium
How can you tell which way a reaction will run if you have Q and K?
Q greater than K, reaction will move right to left
Q less than K, reaction will move left to right
What is the quadratic formula?
-b +/- the square root of b^2 - 4ac all over 2a
What simplification can you make when you are working with ICE tables and K is very small?
You can assume the x’s on the bottom are very small and leave them off (Check simplification by doing a percent error calculation, error should be below 5%)
How do you calculate percent error?
(theoretical-actual) over theoretical
Describe LeChatelier’s principle
If a change in conditions (a “stress”) is imposed on a system at equilibrium, the equilibrium position will shift in the direction that tends to reduce the effect of the change in conditions
Which direction will the reaction head if reactants are added?
Forward, toward products
Which direction will the reaction head if products are added?
Backward, toward reactants
Which direction will the reaction head if temperature is increased?
Whichever direction is endothermic
Which direction will the reaction head if temperature is decreased?
Whichever direction is exothermic
Which direction will the reaction head if pressure is increased?
The side with fewer gas molecules
Which direction will the reaction head if pressure is decreased?
The side with more gas molecules
What is the effect of adding an inert gas when a reaction is at equilibrium?
None, ratio of partial pressures remains the same
What is R in atmL/moleK?
.08206
What can you tell (in a set of elementary reactions that may form a possible mechanism) if the second equation is slow?
The first is at equilibrium
What is R in kJ?
.00831447 or 8.3145x10^-3
What is the conversion between atm and torr?
1 atm = 760 torr
