Kinetics and Equilibrium Flashcards
What is the reaction rate defined as?
The reaction rate is defined as the rate of change in the concentration of reactants or products. ie. how fast a reactant gets used up, and how fast a product gets produced.
If this reaction:
aA + bB → cC + dD
was the rate-determining step, then what is the overall rate order of the reaction?
If the above reaction is the rate-determining step of a multi-step reaction, then the rate of the multi-step reaction = k[A]a[B]b
Given this data, determine the rate law:
From this table, a 2x increase in [A] corresponds to a 4x increase in the rate. 2x = 4, so x = 2.
A 2x increase in [B] corresponds to a 2x increase in the rate. 2y = 2, so y = 1.
A 2x increase in [C] corresponds to 1x (no change) in rate. 2z = 1, so z = 0.
r = k[A]2[B]1[C]0
Given reaction speeds, how do you determine the rate determining step of a reaction?
The slowest step of a multi-step reaction is the rate determining step.
What is the activation energy?
The activation energy is the energy it takes to push the reactants up to the transition state.
Draw a reaction coordinate diagram, indicating where the transition state is, the activation energy, and the change in enthalpy for the forward and reverse reaction.
What does the Arrhenius equation (k = Ae-Ea/RT) tell us?
Low Ea, High T → large k → faster reaction.
When activation energy approaches zero….
When activation energy approaches zero, the reaction proceeds as fast as the molecules can move and collide
When temperature approaches absolute zero…
When temperature approaches absolute zero, reaction rate approaches zero because molecular motion approaches zero.
What is the difference between a kinetic and thermodynamic product?
- Kinetic product = lower activation energy, formed preferentially at lower temperature.
- Thermodynamic product = lower (more favorable/negative) ΔG, formed preferentially at higher temperature.
What factors favor the spontaneinty of a reaction?
Being exothermic (-ΔH) and increasing in entropy (+ΔS)
What do catalysts do?
Catalysts speed up a reaction without being used up. They act by lowering the activation energy to speed up the forward and reverse reaction. They increase “k” but do not affect “Keq”
How can you obtain Keq from a chemical equation?
Keq = [C]c[D]d/[A]a[B]b
Using thermodynamics, how can you obtain Keq?
ΔG° = -RT ln (Keq)
If Keq > 1, what does this mean?
If Keq is much greater than 1 (For example if Keq = 103), then the position of equilibrium is to the right; more products are present at equilibrium.
If Keq = 1, what does this mean?
If Keq = 1, then the position of equilibrium is in the center, the amount of products is roughly equal to the amount of reactants at equilibrium.
If Keq < 1, what does this mean?
If Keq is much smaller than 1 (For example if Keq = 10-3), then the position of equilibrium is to the left; more reactants are present at equilibrium.
If Q < Keq, what does this mean?
If Q < Keq, then the reaction is at a point where it is still moving to the right in order to reach equilibrium.
If Q > Keq, what does this mean?
If Q > Keq, then the reaction is too far right, and is moving back left in order to reach equilibrium.
When REACTANTS are added, where does the reaction go?
FORWARD
When PRODUCTS are added, where do the reactants go?
REVERSE
DECREASING pressure moves the reaction where?
FAVORS THE SIDE WITH MORE MOLES
DECREASING volume moves the reaction where?
FAVORS THE SIDE WITH THE FEWEST MOLES
