Ch 6- Equilibrium

Question 1

“At equilibrium, the rate of the forward reaction equals the rate of the reverse reaction, entropy is at a _____, and Gibbs free energy is at a _____. This links the concepts of thermodynamics and kinetics.”

Answer 1

Maximum; Minimum

Question 2

“Kc is called the ________ and the subscript c indicates that it is in terms of concentration. When dealing with gases, the equilibrium constant is referred to as _____, and the subscript p indicates that it is in terms of pressure”

Answer 2

equilibrium constant; Kp

Question 3

“For dilute solutions, Keq = ____ and both are calculated in units of concentration.”

Answer 3

Kc

Question 4

“While the forward and the reverse reaction rates are equal at equilibrium, the concentrations of the reactants and products are not usually equal. This means that the forward and reverse reaction rate constants, kf and kr, respectively, are not usually equal to each other. The ratio of kf to kr is Kc. Whats the equation

Answer 4

Kc=keq= kforward/kreverse

“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. ”

Question 5

“if the reaction aA + bB ⇌ cC + dD occurs in three steps, each with a forward and reverse rate, then” Kc =

Answer 5

k1k2k3/k^-1K^-2K^-3=[C]^C[D]^D/[A]^A[B]^B

Question 6

“What can serve as a “timer” to indicate how far the reaction has proceeded toward equilibrium? This role is served by _____

Answer 6

the reaction quotient, Q”

Question 7

What is the significance if Q

Answer 7

-the forward reaction has not yet reached equilibrium.”

• There is a greater concentration of reactants (and smaller concentration of products) than at equilibrium.
• The forward rate of reaction is increased to restore equilibrium.”

Question 8

What is the significance if Q=Keq? ΔG = 0

Answer 8

• the reaction is in dynamic equilibrium”
• The reactants and products are present in equilibrium proportions.
• The forward and reverse rates of reaction are equal.”

Question 9

What is the significance if Q>Keq (ΔG>0)

Answer 9

• the forward reaction has exceeded equilibrium
• There is a greater concentration of products (and smaller concentration of reactants) than at equilibrium.
• The reverse rate of reaction is increased to restore equilibrium

Question 10

“Any reaction in the equilibrium state will continue to react in the forward and reverse directions, but the reaction rates for the forward and reverse reactions will be _____, and the concentrations of the reactants and products will be ______, such that Q = Keq”

Answer 10

Equal; Constant

Question 11

“The concentrations of ______ and _______ do not appear in the equilibrium constant expression.

Answer 11

pure solids and pure liquids

This is because the equilibrium expression is technically based on the activities of compounds, not concentrations; the activities of pure solids and liquids are defined to be 1”

Question 12

“Keq is characteristic of a particular reaction at a given _______;

Answer 12

Temperature

the equilibrium constant is temperature-dependent.”

Question 13

“The larger the value of Keq the farther _____

Answer 13

the farther to the right the equilibrium position.”

Question 14

“If the equilibrium constant for a reaction written in one direction is Keq, the equilibrium constant for the reverse reaction is”

Answer 14

1/Keq

Question 15

“states that if a stress is applied to a system, the system shifts to relieve that applied stress”

Answer 15

Le Châtelier’s principle

Question 16

“ When the pressure of this system is increased, the system will react in the direction that produces _____ moles of gas. In this case, that direction is to the right, and more ammonia will form. However, if the pressure is decreased, the system will react in the direction that produces _____ moles of gas”

Answer 16

Fewer; more

Question 17

“unlike the effect of changing concentrations or pressures, the result of changing temperature is not a change in the reaction quotient, Qc or Qp, but a change in”

Answer 17

Keq

Question 18

“That direction is determined by the enthalpy of the reaction. If a reaction is endothermic (ΔH > 0), heat functions as a ______; if a reaction is exothermic (ΔH

Answer 18

Reactant; Product

Question 19

“These reactants can undergo two different sets of reactions. At lower temperatures (with smaller heat transfer), a ______ product is formed. At higher temperatures (with larger heat transfer), a ______ product is formed”

Answer 19

Kinetic; Thermodynamic

“Note that the free energy that must be added for the kinetic pathway is lower than that of the thermodynamic pathway. Therefore, the kinetic products often form faster than the thermodynamic products and are sometimes called “fast” products. On the other hand, the free energy of the thermodynamic product is significantly lower than that of the kinetic product.”

Question 20

“gives the expression for the equilibrium constant, Keq. The reaction quotient, Q, has the same form but can be calculated at any concentrations of reactants and products.”

Answer 20

The law of mass action

Question 21

“Pure _____ and _____do not appear in the law of mass action; only gases and aqueous species do.”

Answer 21

“Pure solids and liquids

Question 22

“There are three main types of stresses applied to a system: changes in

Answer 22

concentration, pressure and volume, and temperature.”

Question 23

“Increasing the concentration of reactants or decreasing the concentration of products will shift the reaction to the _____

Answer 23

right

Question 24

“Increasing pressure on a gaseous system (decreasing its volume) will shift the reaction toward the side with _____ moles of gas. Decreasing pressure on a gaseous system (increasing its volume) will shift the reaction toward the side with _____ moles of gas.”

Answer 24

Fewer; More

Question 25

“Increasing the temperature of an endothermic reaction or decreasing the temperature of an exothermic reaction will shift the reaction to the _____. Decreasing the temperature of an endothermic reaction or increasing the temperature of an exothermic reaction will shift the reaction to the ______”

Answer 25

Right; Left

Question 26

“Reactions may have both ______ and ______ products that can be regulated by temperature and the presence of a catalyst.”

Answer 26

kinetic and thermodynamic

Question 27

“are higher in free energy than thermodynamic products and can form at lower temperatures. These are sometimes termed “fast” products because they can form more quickly under such conditions.”

Answer 27

Kinetic products

Question 28

Are lower in free energy than kinetic products and are therefore more stable. Despite proceeding more slowly than the kinetic pathway, the thermodynamic pathway is more spontaneous (more negative ΔG).”

Answer 28

Thermodynamic Products