UNIT 12 REVIEW

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Write the equilibrium expression for the following reaction:

4 HCl(g) + O2(g) 2 Cl2(g) + 2 H2O(g)

ANSWER: Keq = [Cl2]2 [H2O]2

[HCl]4 [O2]

Write the equilibrium expression for the following reaction:

SO3(g) + H2O(l) H2SO4(l)

Answer:Keq = 1 [SO3]

Write the equilibrium expression for the following reaction:

Cu(s) + 2 AgNO3(aq) Cu(NO3)2(aq) + 2 Ag (s)

Answer:

Keq = [Cu(NO3)2] [AgNO3]2

• CH4(g) + 2 O2(g) CO2(g) + 2 H2O(g)

• Calculate [O2] if: [CH4] = 0.0150 M, Keq = 3,620[CO2] = 0.0824 M, [H2O]= 0.0603 M

• Are the reactants or products favored at equilibrium?

Answer: Keq = [CO2] [H2O]2

[CH4] [O2]2

3,620 = (0.0824)(0.0603)2 (54.3)x2 = 0.0002996 x2 = 0.0000552 (0.0150)(x)2 54.3 54.3[O2] = 0.00235 MProducts are favored because Keq is greater than one.

Write the equilibrium expression & calculate [CH3OH] for this reaction:

CO(g) + 2H2(g) CH3OH(g)

[CO]=0.025M, [H2]=0.080M, Keq = 394

Answers: Keq = [CH3OH]

[CO] [H2]2

[CH3OH]: 394 = x = 0.063 M (0.025)(0.080)2

• Calculate Keq:• PCl5(g) PCl3(g) + Cl2(g)

• [PCl5] = 1.00M, [PCl3]=3.16x10-2M, [Cl2]=7.18x10-3M

• Are the reactants or products favored at equilibrium?

• If you change the temperature, would the Keq be the same?

Answers: Keq = [PCl3][Cl2] = (3.16x10-2)(7.18x10-3) = 2.27x10-4

[PCl5] (1.00)Reactants are favored because Keq is less than 1. No, because temperature affects concentration.

• What 2 types of changes cause a reaction to go to completion?

• If a reaction does not go to completion, what may happen to some of the products?

Answers: •Forms a Gas (g) or a Precipitate ( )•Can reform reactants (Reverse Reaction)

• A reaction that does not go to completion is called a __________________ reaction.

• What part of the equation shows if a reaction goes to completion or not?

Answer: • Reversible • The Arrow (double = reversible, single = completion)

• Why does the word “dynamic” describe equilibrium?

• Define reversible reaction.

• Define completion reaction.

Answers:Dynamic describes equilibrium because the reaction does not stop. The forward and reverse reactions continue at equal rates.A reversible reaction can form products and then reform reactants.A completion reaction can only form products and forms a gas or a precipitate.

• When a system is at ________________________ , it will stay that way until something changes.

• State Le Chatelier’s Principle.

• List three examples of stresses that can change a system at equilibrium.

• 1)

• 2)

• 3)Answers:

• Equilibrium• When a reaction at equilibrium is disturbed, it will shift to eliminate the stress.• Changing temperature, concentration, or pressure/volume (only for gases)

• You can tell if a reaction is endothermic or exothermic by looking at the equation. If heat is on the reactant side, the reaction is ________________. If heat is on the product side, the reaction is ________________.

• Determine if these reactions are endothermic or exothermic.a) 2NO2 ↔ N2O4 + 58.8 Jb) 2AgCl + energy ↔ 2Ag + Cl2

• What direction will the system shift if the temperature in “a” is raised?

• How could you make reaction “b” produce more products? Add energy or remove energy?

Answers: endothermic, exothermica) exothermic b) endothermic•Shift left•Add energy

• When an equilibrium mixture is subjected to a decreased pressure, it will shift to the side with ____________________.

Answer: More Moles

Decrease Pressure = Increase Volume = Shift to Side with MOST Moles

2 NO2(g) N2O4(g) + energy

According to Le Chatelier’s Principle, what direction will the system above shift if the following stresses are applied?

A. Lower TemperatureB. Increase N2O4(g)

C. Decrease NO2(g)

D. Increase PressureE. Increase VolumeAnswer:

A. Right (to replace heat lost on right side)

B. Left (to decrease [N2O4]

C.Left (to replace [NO2])

D.Right (Increase P = Decrease V so shift to side with less moles

E. Left (Increase V so shift to side with more moles)

• What does Ksp stand for?• What does it describe?• Which lead compound below is the least soluble?

• Ksp = PbBr2 = 6.3 x 10-6

• Ksp = PbCl2 = 1.7 x 10-5

• Ksp = PbCrO4 = 1.8 x 10-14

Answers: •Solubility Product Constant•Ksp describes the solubility (ability to dissolve) of slightly soluble substances.• PbCrO4 because it has the smallest Ksp