Princeton Ch 10 - Equilibrium

Question 1

Equilibrium

Answer 1

When a reaction is at equilibrium (and only at equilibrium), the rate of the forward reaction is equal to the rate of the reverse reaction.

Question 2

Give the eq constant and comment on its properties.

Answer 2

Keq = [C]^c[D]^d/[A]^a[B]^b

1) products are the numerator; reactants denominator
2) solids and pure liquids are NOT included
3) in the reaction is gaseous, we use partial pressures; but then, it is called Kp

Question 3

What happens to the Keq if the temperature is constant.

Answer 3

The value of Keq for a given reaction is a constant at a given temperature. If the temperature changes, the reaction’s Keq changes.

Question 4

What happens in the following scenarios:

Keq<1 or = 1 or > 1?

Answer 4

Keq<1 - favors reactants (more reactants than products at eq)
Keq = 1 roughly equal amounts of reactants and products
Keq>1 - favors products (more products than reactant at eq)

Question 5

If the reaction is not at equilibrium, what is used instead of Keq?

Answer 5

The reaction quotient, Q. Q is only equal to Keq when the reaction is at equilibrium.

Question 6

If QKeq, what happens?

Answer 6

If QKeq , the reaction proceeds in the reverse direction so Q gets closer to Keq.

Question 7

Le Chatelier’s principle.

Answer 7

A system at equilibrium will try to neutralize any imposed change (or stress) in order to reestablish eq. If you add more reactant, the system will favor the forward reaction in order to consume that reactant and reestablish eq.

Question 8

Consider a gaseous reaction at equilibrium with unequal numbers of moels of gas of reactants and products. What happens if the volume is reduced? Expanded?

Answer 8

If the volume is reduced, increasing the pressure, a net reaction occurs favoring the side with SMALLER total # of moles of gas. If the volume is expanded, decreasing the pressure, a net reaction occurs favoring the side with a greater total number of moles of gas. (only for gas).

Question 9

Lowering the temperature favors the (exo/endo) reaction while raising the temperature favors the (exo/endothermic) reaction. This is only specific to systems once it is at equilibrium.

Answer 9

Lowering the temperature favors the Exothermic rxn while raising the temperature favors the Endothermic reaction. In an exothermic rxn, increasing temp at which the rxn takes place once it reaches eq, the reaction will shift left in order to consume the extra heat, thereby producing more reactants.

Question 10

What does adding an inert gas do equilibrium.

Answer 10

The inert gas doesn’t particulate in the reaction (or ANY REACTION). It will change neither the partial pressure or the concentration of the product or reactants when injected into a container with a constant volume.

Question 11

When a solution has water as its solvent, it is known as a:

Answer 11

aquous solution.

Question 12

True or false. A solution only involves liquids.

Answer 12

False. You can have a solution that involves any of the three phases of matter. Solid in a solid = alloy.

Question 13

Electrolytes versus non-electrolytes.

Answer 13

Electrolytes - free ions dissolved in solution. Non-electrolytes - covalent compounds that don’t dissociate into ions.

Question 14

Strong versus weak electrolytes.

Answer 14

Strong electrolytes - solutes that dissociate completely. Weak electrolytes - solutes that remain ion paired to some degree.

Question 15

van’t Hoff (ionizability) factor (i) tells us:

Answer 15

how many ion units of a substance will produce a solution. Ex. C6H12O6 = 1; NaCl = 2

Question 16

Concentrated versus dilute solution.

Answer 16

A concentrated solution has a greater amount of solute per unit volume that a solution that is diluted.

Question 17

Saturated solution.

Answer 17

One in which no more solute will dissolve. At this point, we reached the molar solubility of the solute for the particular solvent, and the reverse process of dissolution, called precipitation occurs at the same rate as dissolving.

Question 18

When a solution is saturated, the solid and dissolved form of the solute is said to be in:

Answer 18

dynamic equilibrium.

Question 19

Solubility.

Answer 19

The amount of solute that will saturate a particular solvent.

Question 20

Phase solubility rules:

1) The solubility of solids in liquids with ^temp.
2) The solubility of gases in liquids with ^temp
3) The solubility of gases in liquids with ^pressure.

Answer 20

1) The solubility of solids in liquids tends to INCREASE with ^temp. Ex. Boiling sugar in water.
2) The solubility of gases in liquids tends to DECREASE with ^temp. Ex. vapor escapes.
3) The solubility of gases in liquids tends to increase with increasing pressure.

Question 21

Salt Solubility Rules:

1) All group 1 (Li+, Na+, K+, Rb+, Cs+) and ammonium (Nh4+) salts are (soluble/insoluble) in water.
2) All nitrate (NO3-), perchlorate (ClO4-, and acetate (C2H3O2-) salts are (soluble/insoluble) in water.
3) All silver (Ag+), lead (Pb2+/Pb4+), and mercury (Hg2+) salts (soluble/insoluble) in wate, except for their nitrates, percholrates, and acetates.

Answer 21

1) All group 1 (Li+, Na+, K+, Rb+, Cs+) and ammonium (Nh4+) salts are soluble in water.
2) All nitrate (NO3-), perchlorate (ClO4-, and acetate (C2H3O2-) salts are soluble in water.
3) All silver (Ag+), lead (Pb2+/Pb4+), and mercury (Hg2+) salt insoluble in water, except for their nitrates, perchlorates, and acetates.

Question 22

Solubility product constant.

Answer 22

The extent to which a salt will dissolve in water.
Ksp = [C]^c[D]^d;
We exclude the denominator, if we begin with a solid.

Question 23

Molar solubility.

Answer 23

The number of moles of the salt that will saturate a liter of water.

Question 24

Ion product (Qsp) versus Ksp. and What happens if it’s less, equal, greater?

Answer 24

The ion product is the reaction quotient for a solubility reaction. Qsp doesn’t have to be at eq.

Qsp>Ksp –> more salt can be dissolved
Qsp = Ksp –> solution is saturated.
Qsp< Ksp –> excess salt will precipitate

Question 25

Common ion effect. q

Answer 25

The molar solubility of the sightly soluable salt is decreased by the presence of another solute that supplies a common ion.
Ex. Mg(OH)2 and NaOH. NaOH causes MgOH2 reaction to reverse because of the increase in OH

Question 26

You want to prepare a saturated solution of a lead compound that contains the greater [ ] of lead II ions. Which should you use:
A) Pb(OH)2 - Ksp = 2.8*10^-16
B) PbCls - Ksp = 1.7 * 10^-5

Answer 26

Since the equilibrium has the form PbX2 Pb2+ + 2X, we have Ksp = [Pb2+][X-]^2. Therefore to maximize Pb2+, you want to maximize Ksp. B has the larger Ksp value.