Lakeland Heat/Equilibrium Review

Lakeland Heat/Equilibrium Review

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Given the system at equilibrium: N2O4(g) + 58.1 kJ 2 NO2(g)What will be the result of an increase in temperature at constant pressure?

A) The equilibrium will shift to the left, and the concentration of NO2(g) will decrease.

B) The equilibrium will shift to the left, and the concentration of NO2(g) will increase.

C) The equilibrium will shift to the right, and the concentration of NO2(g) will decrease.

D) The equilibrium will shift to the right, and the concentration of NO2(g) will increase.

Question 1

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• Heat is a reactant so the addition of it should shift the equation away from that side

Correct!

• The addition of heat, a reactant, will shift the equilibrium right and cause the amount of NO2 to increase

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Given the reaction: AgCl(s) Ag+(aq) + Cl–(aq) Once equilibrium is reached, which statement is accurate?

A) The concentration of Ag+(aq) is greater than the concentration of Cl–(aq).

B) The AgCl(s) will be completely consumed.

C) The rates of the forward and reverse reactions are equal.

D) The entropy of the forward reaction will continue to decrease.

Question 2

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• Think about what is equal at equilibrium

Correct!

• Equilibrium means the rate of the forward reaction equals the rate of the reverse reaction

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Given the reaction: 2 H2(g) + O2(g) → 2 H2O(_) + 571.6 kJWhat is the approximate ΔH for the formation of 1 mole of H2O(_)?

A) -285.8 kJ B) -571.6 kJ

C) 285.8 kJ D) 571.6 kJ

Question 3

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• The heat is a product in the reaction, so it is exothermic. There are two moles of H2O in the equation but the question is asking about one mole.

Correct!

• 2 moles of H2O produce -571.6 kJ of heat, so one mole of H2O produces -285.8 kJ

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Which statement best describes a chemical reactionin which energy is released?

A) It is exothermic and ΔH is negative

B) It is endothermic and ΔH is negative

C) It is exothermic and ΔH is positive

D) It is endothermic and ΔH is positive

Question 4

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• Endo means in to and exo means out of

Correct!

• An exothermic reaction is always a release of energy and ΔH will be negative

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Given the reaction at equilibrium: A(g) + B(g) C(g) + D(g)The addition of a catalyst will

A) Shift equilibrium to the right B) Shift equilibrium to the left

C) Increase the rate of the forward and reverse reactions equally

D) Have no effect on the forward or reverse reaction

Question 5

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• The addition of a catalyst lowers the activation energy

Correct!

• The addition of a catalyst lowers the activation energy which increases the rate of both the forward and reverse reactions

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Which equilibrium constant indicates the highestconcentration of product?

A) Keq = 1 x 10-1 B) Keq = 2 x 10-2

C) Keq = 3 x 10-3 D) Keq = 4 x 10-4

Question 6

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• Remember that Keq = products/reactants

Correct!

• 1 x 10-1 is the largest number so must contain the highest ratio of products to reactants

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Given the reaction: H2O(l) + 68.3 kcal H2(g) + O2(g)Which statement describes the reverse reaction?

A) It is endothermic and absorbs 68.3 kcal of heat

B) It is exothermic and absorbs 68.3 kcal of heat

C) It is endothermic and releases 68.3 kcal of heat

D) It is exothermic and releases 68.3 kcal of heat

Question 7

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• The reverse reaction goes from right to left so the heat is going to be a product

Correct!

• The reverse reaction has heat as a product which is exothermic.

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A potential energy diagram of a chemical reaction is shown below.

What is the difference between the potential energy of the reactants and the potential energy of the products?

A) 20 kcal B) 40 kcal

C) 60 kcal D) 80 kcal

Question 8

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• The heat of the reaction is found by finding the difference between the heat of the products (end of the graph) and the heat of the reactants (start of the graph)

Correct!

• The heat of the products (40 kJ) minus the heat of the reactants (20 kJ) is equal to 20 kJ

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Given the potential energy diagram for a chemicalreaction:

Which statement correctly describes the energy changes that occur in the forward reaction?

A) Activation energy is 10 kJ and it is endothermic

B) Activation energy is 10 kJ and it is exothermic

C) Activation energy is 50 kJ and it is endothermic

D) Activation energy is 50 kJ and it is exothermic

Question 9

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• Activation energy is the energy added to the reactants to get the reaction going. Endothermic is a gain of energy, exothermic is a loss.

Correct!

• The reactants gained 10 kJ of energy at the start and overall the reaction lost energy which is exothermic

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How much heat is produced when 4.56 g of oxygen react with excess hydrogen according to the following equation?

2H2(g) + O2(g) 2H2O(g) ΔH = -571.6 kJ

A) +651.6 kJ B) -651.6 kJ

C) +81.45 kJ D) -81.45 kJ

Question 10

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• Convert grams to moles and then moles to heat using the balanced equation

Correct!

• 4.56 g O2 x 1 mol O2 x -571.6 kJ = -81.45 kJ 32 g O2 1 mol O2

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Given the system at equilibrium: PbCO3(s) Pb2+(aq) + CO32–(aq)

How will the addition of Na2CO3(aq) affect [Pb2+](aq) and the mass of PbCO3(s)?

A) [Pb2+] (aq) will decrease and the mass of PbCO3(s) will decrease.

B) [Pb2+] (aq) will decrease and the mass of PbCO3(s) will increase.

C) [Pb2+] (aq) will increase and the mass of PbCO3(s) will decrease.

D) [Pb2+] (aq) will increase and the mass of PbCO3(s) will increase.

Question 11

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• PbCO3 adds CO32- ions which are a product.

Equilibrium should shift left

Correct!

• Adding PbCO3 adds CO32- ions which shifts

equilibrium left. This should reduce the amount of products and increase the amount of reactants

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2SO2(g) + O2(g) 2SO3(g) + heat Which change will shift the equilibrium to the right?

A) increasing the temperature B) increasing the pressure

C) decreasing the amount of SO2(g)

D) decreasing the amount of O2(g)

Question 12

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• Shifting equilibrium to the right will require addition of reactants, removal of products or a change in pressure(depends on number of moles)

Correct!

• Increasing pressure shifts equilibrium to the right since there are fewer number of moles of gas on the right

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How much heat will be produced when 6.34 g of nitrogen react with excess hydrogen according the following reaction?

N2(g) + 3H2(g) 2NH3 ΔH = -91.8 kJ

A) +20.79 kJ B) -20.79 kJ

C) +97.0 kJ D) -97.0 kJ

Question 13

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• Convert grams to moles and then moles to heat using the balanced equation

Correct!

• 6.34 g N2 x 1 mol N2 x -91.8 kJ = -20.79 kJ 28 g N2 1 mol N2

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Given the reaction at equilibrium: 2CO(g) + O2(g) 2CO2(g)What is the correct equilibrium expression for this reaction?

Question 14

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• Products/reactants

Correct!Products over reactants raised to their coefficients

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Which arrow represents the activation energy of the forward reaction?A) A B) B

C) C D) D

Question 15

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• Activation energy is the energy added to reactants to get the reaction to begin

Correct!

• B represents the change in energy needed to start the reaction

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