# Balbharati solutions for Chemistry 12th Standard HSC for Maharashtra State Board chapter 4 - Chemical Thermodynamics [Latest edition]

## Chapter 4: Chemical Thermodynamics

Exercises
Exercises [Pages 86 - 89]

### Balbharati solutions for Chemistry 12th Standard HSC for Maharashtra State Board Chapter 4 Chemical Thermodynamics Exercises [Pages 86 - 89]

Exercises | Q 1.01 | Page 86

Select the most appropriate option.

The correct thermodynamic conditions for the spontaneous reaction at all temperatures are _______.

• ΔH < 0 and ΔS > 0

• ΔH > 0 and ΔS < 0

• ΔH < 0 and ΔS < 0

• ΔH < 0 and ΔS = 0

Exercises | Q 1.02 | Page 86

Select the most appropriate option.

A gas is allowed to expand in a well-insulated container against a constant external pressure of 2.5 bar from an initial volume of 2.5 L to a final volume of 4.5 L. The change in internal energy, ΔU of the gas will be _______.

• –500 J

• + 500 J

• –1013 J

• + 1013 J

Exercises | Q 1.03 | Page 86

Select the most appropriate option.

In which of the following, entropy of the system decreases?

• Crystallization of liquid into solid

• Temperature of crystalline solid is increased from 0 K to 115 K

• H2(g) → 2H(g)

• 2 NaHCO3(s)  → Na2CO3(s) + CO2(g) + H2O(g)

Exercises | Q 1.04 | Page 87

Select the most appropriate option.

The enthalpy of formation for all elements in their standard states is _______.

• unity

• zero

• less than zero

• different elements

Exercises | Q 1.05 | Page 87

Select the most appropriate option.

Which of the following reactions is exothermic?

• H2(g)  →  2H(g)

• C(s)  →  C(g)

• 2Cl(g)  →  Cl2(g)

• H2O(s)  →   H2O(l)

Exercises | Q 1.06 | Page 87

Select the most appropriate option.

6.24 g of ethanol are vaporized by supplying 5.89 kJ of heat. Enthalpy of vaporization of ethanol will be _______.

• 43.4 kJ mol–1

• 60.2 kJ mol–1

• 38.9 kJ mol–1

• 20.4 kJ mol–1

Exercises | Q 1.07 | Page 87

Select the most appropriate option.

If the standard enthalpy of formation of methanol is –238.9 kJ mol–1 then entropy change of the surroundings will be _______.

• –801.7 J K–1

• 801.7 J K–1

• 0.8017 J K–1

• –0.8017 J K–1

Exercises | Q 1.08 | Page 87

Select the most appropriate option.

Which of the following are not state functions?

1. Q + W
2. Q
3. W
4. H - TS
• 1, 2 and 3

• 2 and 3

• 1 and 4

• 2, 3 and 4

Exercises | Q 1.09 | Page 87

Select the most appropriate option.

For vaporization of water at 1 bar, ΔH = 40.63 kJ mol–1 and ΔS = 108.8 J K–1 mol–1 . At what temperature, ΔG = 0?

• 273.4 K

• 393.4 K

• 373.4 K

• 293.4 K

Exercises | Q 1.1 | Page 87

Select the most appropriate option.

Bond enthalpies of H–H, Cl–Cl, and H–Cl bonds are 434 kJ mol–1, 242 kJ mol–1, and 431 kJ mol–1, respectively. Enthalpy of formation of HCl is _______.

• 245 kJ mol–1

• –93 kJ mol–1

• –245 kJ mol–1

• 93 kJ mol–1

Exercises | Q 2.1 | Page 87

Answer the following in one or two sentences.

Comment on the statement: no work is involved in an expansion of gas in a vacuum.

Exercises | Q 2.2 | Page 87

Answer the following in one or two sentences.

State the first law of thermodynamics.

Exercises | Q 2.3 | Page 87

Answer the following in one or two sentences.

What is enthalpy of fusion?

Exercises | Q 2.4 | Page 87

Answer the following in one or two sentences.

What is standard state of a substance?

Exercises | Q 2.5 | Page 87

Answer the following in one or two sentences.

State whether ΔS is positive, negative or zero for the reaction 2H(g)  →  H2(g). Explain.

Exercises | Q 2.6 | Page 87

Answer the following in one or two sentences.

State second law of thermodynamics in terms of entropy.

Exercises | Q 2.7 | Page 87

Answer the following in one or two sentences.

If the enthalpy change of a reaction is ∆H how will you calculate the entropy of surroundings?

Exercises | Q 2.8 | Page 87

Answer the following in one or two sentences.

Comment on the spontaneity of reactions for which ∆H is positive and ∆S is negative.

Exercises | Q 3.1 | Page 87

Obtain the relationship between ∆G° of a reaction and the equilibrium constant.

Exercises | Q 3.2 | Page 87

What is entropy? Give its units.

Exercises | Q 3.3 | Page 87

How will you calculate reaction enthalpy from data on bond enthalpies?

Exercises | Q 3.4 | Page 87

What is the standard enthalpy of combustion? Give an example.

Exercises | Q 3.5 | Page 87

What is the enthalpy of atomization? Give an example.

Exercises | Q 3.6 | Page 87

Obtain the expression for work done in chemical reaction.

Exercises | Q 3.7 | Page 88

Derive the expression for PV work.

Exercises | Q 3.8 | Page 88

What are intensive properties? Explain why density is an intensive property.

Exercises | Q 3.9 | Page 88

How much heat is evolved when 12 g of CO reacts with NO2? The reaction is:

4CO(g)  2NO2(g) → 4CO2(g) + N2(g), ΔrH° = - 1200 kJ

Exercises | Q 4.01 | Page 88

Derive the expression for the maximum work.

Exercises | Q 4.02 | Page 88

Obtain the relationship between ΔH and ΔU for gas phase reactions.

Exercises | Q 4.03 | Page 88

State Hess’s law of constant heat summation. Illustrate with an example. State its applications.

Exercises | Q 4.04 | Page 88

Although ΔS for the formation of two moles of water from H2 and O2 is –327J K–1, it is spontaneous. Explain.
(Given ΔH for the reaction is –572 kJ).

Exercises | Q 4.05 | Page 88

Obtain the relation between ΔG and triangle "S"_"total". Comment on the spontaneity of the reaction.

Exercises | Q 4.06 | Page 88

One mole of an ideal gas is compressed from 500 cm3 against a constant pressure of 1.2 × 105 Pa. The work involved in the process is 36.0 J. Calculate the final volume.

Exercises | Q 4.07 | Page 88

Calculate the maximum work when 24 g of O2 are expanded isothermally and reversibly from the pressure of 1.6 bar to 1 bar at 298 K.

Exercises | Q 4.08 | Page 88

Calculate the work done in the decomposition of 132 g of NH4NO3 at 100 °C.

NH4NO3(s) → N2O(g) + 2H2O(g)

State whether work is done on the system or by the system.

Exercises | Q 4.09 | Page 88

Calculate standard enthalpy of reaction,

Fe2O3(s) + 3CO(g) → 2Fe(s) + 3CO2(g), from the following data.

Δf H°(Fe2O3) = - 824 kJ/mol,

Δf H°(CO) = - 110 kJ/mol,

Δf H°(CO2) = - 393 kJ/mol

Exercises | Q 4.1 | Page 88

For a certain reaction ΔH° = 219 kJ and ΔS° = –21 J/K. Determine whether the reaction is spontaneous or nonspontaneous.

Exercises | Q 4.11 | Page 88

Determine whether the following reaction is spontaneous under standard state conditions.

2H2O(l) + O2(g) → 2H2O2(l)

if ΔH° = 196 kJ, ΔS° = –126 J/K, does it have a cross-over temperature?

Exercises | Q 4.12 | Page 88

Calculate ΔU at 298 K for the reaction,

C2H4(g) + HCl(g) → C2H5Cl(g), ΔH = - 72.3 kJ

How much PV work is done?

Exercises | Q 4.13 | Page 88

Calculate the work done during the synthesis of NH3 in which volume changes from 8.0 dm3 to 4.0 dm3 at a constant external pressure of 43 bar. In what direction the work-energy flows?

Exercises | Q 4.14 | Page 88

Calculate the amount of work done in the

1) Oxidation of 1 mole HCl(g) at 200 °C according to reaction.

4HCl(g) + O2(g) → 2Cl2(g) + 2H2O(g)

2) Decomposition of one mole of NO at 300 °C for the reaction

2NO(g) → N2(g) + O2(g)

Exercises | Q 4.15 | Page 89

When 6.0 g of O2 reacts with CIF as per

2ClF(g) + O2(g) → Cl2O(g) + OF2(g)

The enthalpy change is 38.55 kJ. What is standard enthalpy of the reaction? (Δr H° = 205.6 kJ)

Exercises | Q 4.16 | Page 89

Calculate the standard enthalpy of formation of CH3OH(l) from the following data:

CH3OH(l) + 3/2O2(g) → CO2(g) + 2H2O(l); ΔrH° = - 726 kJ mol-1

"C"_("graphite") + "O"_(2("g")) -> "CO"_(2("g")); ΔrH° = - 393 kJ mol-1

H2(g) + 1/2 O2(g) → H2O(l); ΔrH° = - 286 kJ mol-1

Exercises | Q 4.17 | Page 89

Calculate ΔrH° for the following reaction at 298 K:

1) 2H3BO3(aq) → B2O3(s) + 3H2O(l), ΔrH° = + 14.4 kJ

2) H3BO3(aq) → HBO2(aq) + H2O(l), ΔrH° = - 0.02 kJ

3) H2B4O7(s) → 2B2O3(s) + H2O(l), ΔrH° = + 17.3 kJ

Exercises | Q 4.18 | Page 89

Calculate the total heat required

a) to melt 180 g of ice at 0 °C

b) heat it to 100 °C and then

c) vapourise it at that temperature.

[Given: ΔfusH° (ice) = 6.01 kJ mol-1 at 0 °C, ΔvapH° (H2O) = 40.7 kJ mol-1 at 100 °C, Specific heat of water is 4.18 J g-1 K-1]

Exercises | Q 4.19 | Page 89

The enthalpy change for the reaction,

C2H4(g) + H2(g) → C2H6(g) is - 620 J when 100 mL of ethylene and 100 mL of H2 react at 1 bar pressure. Calculate the pressure-volume type of work and ΔU for the reaction.

Exercises | Q 4.2 | Page 89

Calculate the work done and comment on whether work is done on or by the system for the decomposition of 2 moles of NH4NO3 at 100 °C
NH4NO3(s) → N2O(g) + 2H2O(g)

Exercises

## Balbharati solutions for Chemistry 12th Standard HSC for Maharashtra State Board chapter 4 - Chemical Thermodynamics

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Concepts covered in Chemistry 12th Standard HSC for Maharashtra State Board chapter 4 Chemical Thermodynamics are Chemical Thermodynamics, Terms Used in Thermodynamics, Nature of Heat and Work, Expression for Pressure-volume (PV) Work, Concept of Maximum Work, Internal Energy (U), First Law of Thermodynamics, Enthalpy (H), Enthalpies of Physical Transformations, Thermochemistry, Spontaneous (Irreversible) Process.

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