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Objective Type Questions and Answers On Class 11 Chemistry Chapter 6 Thermodynamics

Questions
1 Consider the following reaction between zinc and oxygen and choose the correct options out of the options given below :

2 Zn (s) + O2 (g) → 2 ZnO (s) ; ∆H = – 693.8 kJ mol–1

A The enthalpy of two moles of ZnO is less than the total enthalpy of two moles of Zn and one mole of oxygen by 693.8 kJ.
B The enthalpy of two moles of ZnO is more than the total enthalpy of two moles of Zn and one mole of oxygen by 693.8 kJ.
C 693.8 kJ mol–1 energy is evolved in the reaction.
D 693.8 kJ mol–1 energy is absorbed in the reaction.

Answer:A, C
2 For an ideal gas, the work of reversible expansion under isothermal condition can be calculated by using the expression w = – nRT ln Vf/Vi A sample containing 1.0 mol of an ideal gas is expanded isothermally and reversibly to ten times of its original volume, in two separate experiments. The expansion is carried out at 300 K and 600 K respectively. Choose the correct option.
A Work done at 600 K is 20 times the work done at 300 K.
B Work done at 300 K is twice the work done at 600 K.
C Work done at 600 K is twice the work done at 300 K.
D ∆U = 0 in both cases.

Answer:C, D
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3 The spontaneity means, having the potential to proceed without the assistance of an external agency. The processes which occur spontaneously are
A flow of heat from colder to warmer body.
B gas in a container contracting into one corner.
C gas expanding to fill the available volume.
D burning carbon in oxygen to give carbon dioxide.

Answer:C, D
4 In an exothermic reaction, heat is evolved, and the system loses heat to the surrounding. For such a system
A qp will be negative
B ∆rH will be negative
C qp will be positive
D ∆rH will be positive

Answer:A, B
5 Thermodynamics mainly deals with
A interrelation of various forms of energy and their transformation from one form to another.
B energy changes in the processes which depend only on initial and final states of the microscopic systems containing a few molecules.
C how and at what rate these energy transformations are carried out.
D the system in equilibrium state or moving from one equilibrium state to another equilibrium state.

Answer:A, D
6 Which of the following is not correct?
A ∆G is zero for a reversible reaction
B ∆G is positive for a spontaneous reaction
C ∆G is negative for a spontaneous reaction
D ∆G is positive for a non-spontaneous reaction

Answer:∆G is positive for a spontaneous reaction
7 Enthalpy of sublimation of a substance is equal to
A enthalpy of fusion + enthalpy of vapourisation
B enthalpy of fusion
C enthalpy of vapourisation
D twice the enthalpy of vapourisation

Answer:enthalpy of fusion + enthalpy of vapourisation
8 The enthalpies of elements in their standard states are taken as zero. The enthalpy of formation of a compound
A is always negative
B is always positive
C maybe positive or negative
D is never negative

Answer:maybe positive or negative
9 Consider the reactions given below. On the basis of these reactions find out

which of the algebraic relations given in options (i) to (iv) is correct?

(a) C (g) + 4 H (g) → CH4 (g); ∆rH = x kJ mol–1

(b) C (graphite,s) + 2H2 (g) → CH4 (g); ∆rH = y kJ mol–1

A x = y
B x = 2y
C x > y
D x < y

Answer:x > y
10 On the basis of thermochemical equations (a), (b) and (c), find out which of the algebraic relationships given in options (i) to (iv) is correct.

(a) C (graphite) + O2 (g) → CO2 (g) ; ∆rH = x kJ mol–1

(b) C (graphite) +12 O2 (g) → CO (g) ; ∆rH = y kJ mol–1

(c) CO (g) +12 O2 (g) → CO2 (g) ; ∆rH = z kJ mol–1

A z = x + y
B x = y – z
C x = y + z
D y = 2z – x

Answer:x = y + z
11 The entropy change can be calculated by using the expression ∆S = qrev/T When water freezes in a glass beaker, choose the correct statement amongst the following :
A ∆S (system) decreases but ∆S (surroundings) remains the same.
B ∆S (system) increases but ∆S (surroundings) decreases.
C ∆S (system) decreases but ∆S (surroundings) increases.
D ∆S (system) decreases and ∆S (surroundings) also decreases.

Answer:∆S (system) decreases but ∆S (surroundings) increases.
12 The pressure-volume work for an ideal gas can be calculated by using the expression w= ʃPexdv. The work can also be calculated from the pV– a plot by using the area under the curve within the specified limits. When an ideal gas is compressed

(a) reversibly or

(b) irreversibly from volume Vi to Vf. choose the correct option.

A w (reversible) = w (irreversible)
B w (reversible) < w (irreversible)
C w (reversible) > w (irreversible)
D w (reversible) = w (irreversible) + pex.∆V

Answer:w (reversible) < w (irreversible)
13 In an adiabatic process, no transfer of heat takes place between system and surroundings. Choose the correct option for free expansion of an ideal gas under adiabatic condition from the following.
A q = 0, ∆T ≠ 0, w = 0
B q ≠ 0, ∆T = 0, w = 0
C q = 0, ∆T = 0, w = 0
D q = 0, ∆T < 0, w ≠ 0

Answer:q = 0, ∆T = 0, w = 0
14 ∆fUᶱ of formation of CH4 (g) at certain temperature is –393 kJ mol–1. The value of ∆fHᶱ is
A zero
B < ∆f Uᶱ
C > ∆f Uᶱ
D equal to ∆f Uᶱ

Answer:< ∆f Uᶱ
15 During complete combustion of one mole of butane, 2658 kJ of heat is released.

The thermochemical reaction for above change is

A 2C4H10(g) + 13O2(g) → 8CO2(g) + 10H2O(l) ∆cH = –2658.0 kJ mol–1
B C4H10(g) +13/2 O2 (g) → 4CO2 (g) + 5H2O (g) ∆cH = –1329.0 kJ mol–1
C C4H10(g) +13/2 O2 (g) → 4CO2 (g) + 5H2O (l) ∆cH = –2658.0 kJ mol–1
D C4H10 (g) +13/2 O2 (g) → 4CO2 (g) + 5H2O (l) ∆cH = +2658.0 kJ mol–1

Answer:C4H10(g) +13/2 O2 (g) → 4CO2 (g) + 5H2O (l) ∆cH = –2658.0 kJ mol–1
16 The volume of gas is reduced to half from its original volume. The specific heat will be ______.
A reduce to half
B be doubled
C remain constant
D increase four times

Answer:remain constant
17 The state of a gas can be described by quoting the relationship between___.
A pressure, volume, temperature
B temperature, amount, pressure
C the amount, volume, temperature
D pressure, volume, temperature, amount

Answer:pressure, volume, temperature, amount
18 Which of the following statements is correct?
A The presence of reacting species in a covered beaker is an example of an open system.
B There is an exchange of energy as well as a matter between the system and the surroundings in a closed system.
C The presence of reactants in a closed vessel made up of copper is an example of a closed system.
D The presence of reactants in a thermos flask or any other closed insulated vessel is an example of a closed system.

Answer: The presence of reactants in a closed vessel made up of copper is an example of a closed system.
19 Thermodynamics is not concerned about______.
A energy changes involved in a chemical reaction.
B the extent to which a chemical reaction proceeds.
C the rate at which a reaction proceeds.
D the feasibility of a chemical reaction.

Answer:the rate at which a reaction proceeds.
20 The temperature of the system .decreases in an ______.
A adiabatic compression
B isothermal expansion
C isothermal compression
D adiabatic expansion

Answer:adiabatic expansion

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