Thermochemistry Exercises

Q1

Find the amount of heat requires to:

1. raise the temperature of 10 L of water from 23 ˚C to 30 ˚C;
2. associated with a 33 ˚C decrease in temperature in a 6.80 kg aluminum bar (specific heat of aluminum = 0.903 J/(g ˚C)).

Q2

Calculate the final temperature that results when

1. a 13.8 g sample of water at 21.7°C absorbs 679 J of heat;
2. a 2.43 kg sample of aluminum at 69.5 °C gives off 2.04 kcal of heat (\(c_{sp}\) of Al = 0.902 J g^-1 °C^-1).

Q3

A 96.5 g chunk of an unknown metal heated to 98.0 °C is dropped into a coffee cup calorimeter holding 45.0 g of pure water. Before the addition of the metal, the temperature of the water is measured at 25.0 °C. After the addition of the metal, the temperature of the water raises to 33.3°C. What is the specific heat of the given metal?

Q4

Calculate the specific heat of:

1. a 119.5 g sample of zinc that give off 1.02 kJ of heat when it cools from 65.7 °C to 43.5 °C;
2. a 0.893 kg sample of mercury increases in temperature by 21.2 °C when it absorbs 0.69 kcal of heat.

Q5

Calculate the work, in joules, associated with an ideal gas expansion from 3.04 L to 5.60 L against an external pressure of 1.4 atm.

Q6

In compressing a gas, 489 J of work is done on the system, while 239 J escape the system as heat. Calculate \(\Delta U\) for the system for this compression.

Q29

What mass of ice can be melted with the same quantity of heat as required to raise the temperature of 4.5 mol \(H_2O_{(l)}\) by 35.0 °C? [ ∆H°_fusion=6.01 kJ/mol \(H_2O_{(s)}\)]

Q33

If 300.0 J of heat is transferred to a block of dry ice at -80.5°C, what volume of CO₂ gas (\(\rho\) = 1.88 g/L) will be generated? The specific enthalpy of sublimation for dry ice (CO₂) is 581 kJ/kg at -80.5°C.

Q35

A sample gives off 4,678 cal. when burned in a bomb calorimeter which increased its temperature by 10.1°C. Calculate the heat capacity of the calorimeter in kilojoules per degree Celsius.

Q47

How much work is done when a gas expands 3 L against a pressure of 753 mmHg in:

1. \(L \cdot atm\)
2. joules
3. calories

Q67

The standard enthalpy of formation of \(HCl_{(g)}\) is -52.4 kJ/mol HCl. What is \(\Delta H_{rx}°\) for the following reaction?

\[2 HCl_{(g)} \rightarrow Cl_{2(g)} + H_{2(g)}\]

with \(\Delta H_f°=52.4\; kJ/mol\)

Q69

Calculate \(∆H˚\) of the full reaction of

\[2NO(g) + O_3 \rightleftharpoons 2NO_2(g)\]

given knowledge of the thermodynamics of the following reactions?

\[2O_3(g) \rightleftharpoons 3O_2(g) \tag{∆H1= -420 kJ}\]

\[O_2(g) \rightleftharpoons 2O(g) \tag{∆H2= 622 kJ}\]

\[NO(g) + O_3(g) \rightleftharpoons NO_2(g) + O_2(g) \tag{∆H3= -137 kJ}\]

Q73

Find \(ΔH\) for the reaction

\[4 NH_3 (g) + 5 O_2 (g) \rightarrow 4 NO (g) + 6 H_2O (g)\]

by using Hess's law and the following equations with known thermodynamic properties

\[N_2 (g) + O_2 (g) \rightarrow 2 NO (g) \tag{ΔH = -210.2 kJ}\]

\[N_2 (g) + 3 H_2 (g) \rightarrow 2 NH_3 (g) \tag{ΔH = -80.8 kJ}\]

\[2 H_2 (g) + O_2 (g) \rightarrow 2 H_2O (g) \tag{ΔH = -376.2 kJ}\]

Q75

Find the \(ΔH\) for the reaction

\[CH_4(g) + NH_3 (g) \rightarrow HCN(g) + 3 H_2(g)\]

by using Hess's law.

\[N_2(g) + 3 H_2 (g) \rightarrow 2 NH_3 (g) \tag{ΔH = -82.6 kJ}\]

\[C (s) + 2 H_2 (g) \rightarrow CH_4 (g) \tag{ΔH = -90.3 kJ}\]

\[H_2 (g) + 2 C (s) + N_2 (g) \rightarrow 2 HCN (g) \tag{ΔH = 293.3 kJ}\]

Q81

Calculate the \(∆H˚\) for the reaction

\[Cd^{2+} (aq) + SO_4^{2-}(aq) \rightarrow CdSO_4(s)\]

given the following Enthalpies of formation:

• \(∆H_f˚[Cd^{2+}_{(aq)}]=-75.9\; kJ/mol\),
• \(∆H_f˚[SO^{2-}_{4(aq)}]=-909.3 \; kJ/mol\), and
• \(∆H_f˚[CdSO_{4(s)}]= -1473\; kJ/mol\).