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
• $∆H_f˚[CdSO_{4(s)}]= -1473\; kJ/mol$.