1. The heat change associated when one mole of H+ is neutralized by one mole

of OH– is called heat of neutralization, ΔHoneutralization.

H+(aq) + OH–(aq) → H2O(l) ΔHoneutralization

(a) Calculate ΔHoneutralization from ΔHo

f

(b) The ΔHoneutralization can be experimentally determined by measuring the heat

involved when a strong acid is reacted with a strong base. A 40.00 mL of 1.0

M HCl was mixed with 60.00 mL of 1.0 M NaOH in a coffee cup calorimeter.

The temperature of the solution increased by 5.35 oC. Calculate ΔHoneutralization.

(c) On a separate experiment, a 40.00 mL of 1.0 M unknown weak base was

mixed with 60.00 mL of 1.0 M HCl. The temperature of the solution increased

from 27.2 oC to 32.1 oC. Calculate ΔHoneutralization of the unknown base.

(d) Compare the ΔHoneutralization obtained in (c) to that obtained in (b) and suggest

reasons for any difference. (Hint: Does the result show the strength of the

base? Is the dissociation of the base exothermic or endothermic?)

2. Answer the following:

(a) Calculate the enthalpy change for the combustion of 1 mole of pentane,

C5H12(l) from ΔHfo data.

(b) How much heat (kJ) can be obtained from the complete combustion of 23.5

kg of liquid pentane?

(c) Calculate the enthalpy change using bond energy data (Section 9.4 in your

text).

(d) Is the calculated ΔHcombustion equal to the value in (a)? Explain any

discrepancy.

3. Determine the lattice energy of RbCl by constructing a Born-Haber cycle.

Construct an energy diagram.

4. The graph below shows how ΔG° varies with temperature for three different

oxidation reactions: the oxidations of C(graphite), Zn, and Mg to CO, ZnO, and

MgO, respectively. Such graphs as these can be used to show the

temperatures at which carbon is an effective reducing agent to reduce metal

oxides to the free metals. As a result, such graphs are important to

metallurgists. Use these graphs to answer the following questions.

(a) Why can Mg be used to reduce ZnO to Zn at all temperatures, but Zn cannot

be used to reduce MgO to Mg at any temperature? (Hint: Write the overall

equation for the reduction of ZnO by Mg to form Zn and MgO and calculate

the ΔG° at a particular temperature.

(b) Why can C be used to reduce ZnO to Zn at some temperatures but not at

others? At what temperatures can carbon be used to reduce zinc oxide?

(c) Is it possible to produce Zn from ZnO by its direct decomposition without

requiring a coupled reaction? If so, at what approximate temperatures might

this occur?

(d) Is it possible to decompose CO to C and O in a spontaneous reaction?

Explain.

(e) The slopes of the graph for the formation of ZnO and MgO from Zn and Mg,

respectively is positive, while that for the formation of CO from C is negative.

Explain why this is so, that is, explain the slope of each line in terms of

principles governing Gibbs energy change.

5. For each of the following reactions, determine whether the reaction is

spontaneous at all temperature, nonspontaneous at all temperature,

spontaneous only at high temperature, or spontaneous only at low

temperature. If it’s either of the last two cases, determine the temperature

above/below which the reaction will be spontaneous.

6. Use thermodynamic data from you book to determine the values of ΔHo ΔSo

and ΔGo