Exam 1 Lecture 4

Question 1

when does chemical equilibrium occur?

Answer 1

when a reaction and its reverse reaction proceed at the same rate

Question 2

equilibrium constant, K

Answer 2

• reaction is favored if K > 1
• if the direction of a reaction is reversed, the new value of K is simply the reciprocal of the original value of K

Question 3

Enthalpy (H)

Answer 3

the enthalpy change for a reaction is the heat absorbed or released when the reaction takes place under constant applied pressure

• if change H = positive, heat is absorbed and the reaction is endothermic
• if change H = negative, heat is released and the reaction is exothermic

Question 4

Entropy (S)

Answer 4

when a chemical or physical change occurs in a reversible manner at a constant temperature, the entropy change, delta S, is equal to the heat absorbed (q of rev) divided by the temperature (T)

• gas has higher entropy than a liquid, liquid has higher entropy than solid
• if delta S = positive, products have greater entropy than reactants
• if delta S = negative, the products have lower entropy than the reactants

Question 5

Gibbs free energy (delta G)

Answer 5

the arbiter between opposing tendencies of delta H and delta S

at constant temperature (T),
delta G= delta H - (T)(delta S)

Question 6

if delta G is positive and K is less than one,

Answer 6

the reaction is disfavored

Question 7

if delta G is negative and K is greater than one,

Answer 7

the reaction is favored

Question 8

Le Chateliter’s Principle

Answer 8

if a system at equilibrium is subjected to a change or disturbance: the direction in which the system proceeds back to equilibrium will attempt to offset the change

Question 9

if the reaction quotient, Q < K, then?

Answer 9

the system shifts to form more products until Q=K

Question 10

if a reaction is at equilibrium and products are added/reactants are removed…?

Answer 10

the reaction goes to the left

Question 11

if a reaction is at equilibrium and reactants are added (or products are removed)…?

Answer 11

the reaction goes to the right

Question 12

the equilibrium constant of an endothermic reaction (delta H positive)….?

Answer 12

increases if the temperature is raised

Question 13

the equilibrium constant of an exothermic reaction (delta H negative)…?

Answer 13

decreases if the temperature is raised

Question 14

Solubility product (Ksp)

Answer 14

equilibrium constant for the reaction in which a solid salt dissolves to give its constituent ions in solution

Question 15

saturated solution

Answer 15

equilibrium with excess, undissolved solid

Question 16

Common Ion Effect

Answer 16

the application of Le Chatelier’s principle; a salt is less soluble if one of its constituent ions is already present in solution