Chem #6

Question 1

what would adding or removing a catalyst do to the equilibrium of a reaction?

Answer 1

Adding or removing a catalyst would change the reaction rates but it would not change where the equilibrium lies.

Question 2

irreversible reaction

Answer 2

the reaction proceeds in one direction only, the reaction goes to completion, and the maximum amount of product formed is determined by the amount of limiting reagent initially present.

Question 3

reversible reactions

Answer 3

those in which the reaction can proceed in one of two ways: forward (to the products) and reverse (to the reactants)

Question 4

dynamic equilibrium

Answer 4

the forward and reverse reactions are still occurring. The forward reaction rate equals the reverse reaction rate and the concentrations of the products and reactants remain constant.

Question 5

static equilibrium

Answer 5

the forward and reverse reactions have stopped.

Question 6

entropy

Answer 6

the distribution of energy throughout a system or between a system and its environment.

Question 7

for a reversible reaction at a given temperature, the reaction will reach equilibrium when the system’s ____ is at a maximum and the ____ is at a minimum

Answer 7

entropy

Gibbs free energy

Question 8

law of mass action

Answer 8

if the system is at equilibrium at constant temperature, then the ratio is constant (see notes).

deals with equilibrium constant

Question 9

keq or kc

Answer 9

 Subscript c can indicate that it is in terms of concentration.
 Subscript p can indicate it is in terms of pressure.
 When a reaction occurs in more than one step, the equilibrium constant for the overall reaction is found by multiplying together the equilibrium constants for each step of the reaction.

 The concentrations of pure solids and pure liquids do not appear in the equilibrium constant expression (found to be 1)
 Keq is characteristic of a particular reaction at a given temperature.
 The larger the Keq, the further to the right the equilibrium position.
 If the equilibrium constant for a reaction written in one direction is Keq, the equilibrium constant for the reverse reaction is 1/Keq

Question 10

reaction quotient

Answer 10

serves as a timer to indicate how far the reaction has proceeded toward equilibrium.
o Measure of the concentrations of the reactants and products at any point during a reaction.
o Q < K (delta G < 0): more R than at equilibrium, forward reaction will dominate to get to equilibrium
o Q = K (delta G = 0): at equilibrium, the forward and reverse reaction rates are equal, concentrations of the reactants and products will be constant.
 Once a reaction is at equilibrium, any further movement in the forward or reverse direction will be nonspontaneous.
o Q > K (delta G > 0 for the forward reaction): more P than at equilibrium, reverse reaction will dominate to get to equilibrium

Question 11

Q < K

Answer 11

more R than at equilibrium, forward reaction will dominate to get to equilibrium

Question 12

Q = K

Answer 12

at equilibrium, the forward and reverse reaction rates are equal, concentrations of the reactants and products will be constant.
 Once a reaction is at equilibrium, any further movement in the forward or reverse direction will be nonspontaneous.

Question 13

Q > K

Answer 13

more P than at equilibrium, reverse reaction will dominate to get to equilibrium

Question 14

what values are used in equilibrium constant calcuations?

Answer 14

either pressures or concentrations.

Question 15

making the assumption during the ice table making

Answer 15

can only be used if the percentage of reactant that goes to product is very small.

Question 16

LeChatelier’s principle

Answer 16

if stress is applied to a system, the system shifts to relieve that applied stress.
o Concentrations or partial pressures are no longer in equilibrium ratio or equilibrium ratio has changed due to temperature.

Question 17

LeChatelier’s principle: changes in concentration

Answer 17

o Addition or removal of reactants or products.

o Reactants added (or products removed), Q>K, shift toward products until equilibrium is reached again.

Question 18

LeChatelier’s principle: changes in pressure or volume

Answer 18

o Only chemical reactions that involve at least one gaseous species will be affected by changes in the system’s pressure and volume.
o When pressure is increased (or volume is decreased), shift toward the side that has less moles of gas.

Question 19

LeChatelier’s principle: changes in temperature

Answer 19

o Change in temperature is a change in the Keq. Initially the concentrations of reactants and products do not change but the Keq does change, so the Q is has to be readjusted to fit the Keq.
o Treat temperature as a reactant or product.

Question 20

kinetic product vs. thermodynamic product

Answer 20

Kinetic product: formed at lower temperatures with smaller heat transfer (less stable product)
o Forms faster
o Lower activation energy but higher energy product.
Thermodynamic product: formed at higher temperatures with larger heat transfer
o More stable and more negative deltaG
o More spontaneous
• Important for orgo and seeing what the product will be based on the stability after a certain reaction occurs.

Question 21

the concentration of ______ do not appear in the equilibrium constant expression

Answer 21

solids and liquids

aqueous is included

Question 22

the equilibrium constant is ___ dependent

Answer 22

temperature

Question 23

if the equilibrium constant for forward reaction is keq then for the reverse reaction it is ______.

Answer 23

1/keq

Question 24

for solving equilibrium constant value problems, when is the assumption valid?

Answer 24

not valid when the value for keq is within one to two orders of magnitude of 1, or if the reactant that goes to product is within two orders of magnitude of the initial concentration of reactant. OR if the value of keq is very large (more goes to products).

Question 25

the square root of 10^-6 is ___

Answer 25

10^-3

Question 26

Does changing pressure affect the equilibrium of liquids and solids?

Answer 26

not really because they are essentially incompressible.

Question 27

despite proceeding more slowly than the kinetic pathway, the thermodynamic pathway is more _______

Answer 27

more spontaneous (more negative deltaG)

Question 28

if the volume of a container is decreased but the pressure is held constant will this effect the equilibrium position?

Answer 28

no

Question 29

when equilibrium shifts to the products, the forward reaction rate ____ while the reverse reaction rate _____

Answer 29

increases

decreases