Chemistry

Thermodynamics

Question:

ncert-solutions-for-class-11-chemistry-chapter-6-thermodynamics-31

Answer:

ncert-solutions-for-class-11-chemistry-chapter-6-thermodynamics-32

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Thermodynamics

Q 1.

The difference between Cp and Cv can be derived using the empirical relation H = U + pV. Calculate the difference between Cp and Cv for 10 moles of an ideal gas.

Q 2.

Thermodynamics mainly deals with
(a) interrelation of various forms of energy and their transformation front one from  to another.
(b) energy changes in the processes which depend only on initial and final states of the microscopic system 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.

Q 3.

What do you mean by entropy?

Q 4.

The enthalpy of combustion of methane, graphite and dihydrogen at 298 K are -890.3 KJ mol-1, – 393.5  KJ mol-1 and – 285.8 KJ mol-1 respectively. Enthalpy of formation of CHJg) will be
(i) – 74.8  KJ mol-1   (ii) – 52.27 KJ mol-1
(iii) + 74.8 KJ mol-1 (iv) + 52.26 KJ mol-1

Q 5.

What is a spontaneous change? Give one example.

Q 6.

Define intensive properties.

Q 7.

Define extensive properties.

Q 8.

What is Gibbs Helmholtz equation?

Q 9.

The pressure-volume work for an ideal gas can be calculated by using the expression
ncert-exemplar-problems-class-11-chemistry-chapter-6-thermodynamics-5

The work can also be calculated from the pV

plot by using the area under curve within the specified limits. When an ideal gas is compressed (a) reversibly or (b) irreversibly from 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

Q 10.

Enthalpy is an extensive property. In general, if enthalpy of an overall reaction A→B along one route is ∆rH and ∆rH1, ∆rH2, ∆rH3 …. represent enthalpies of intermediate reactions leading to product B. What will be the relation between ∆rH for overall reaction and ∆rH1, ∆rH2….. etc. for intermediate reactions.

Q 11.

Q 12.

Predict the sign of  âˆ†S for the following reaction  heat
CaCO3 (s) ———> CaO(s) + CO2(g)

Q 13.

What is an adiabatic process?

Q 14.

How are internal energy change, free energy change and entropy change are related to one another?

Q 15.

What are the units of entropy?

Q 16.

1 g of graphite is burnt in a bomb calorimeter in excess of oxygen at 298 K and 1 atmospheric pressure according to the equation C(graphite) + 02 (g) —> C02 (g) During the reaction, temperature rises from 298 K to 299 K. If the heat capacity of the bomb calorimeter is 20.7 kJ/K, what is the enthalpy change for the above reaction at 298 K and 1 atm?

Q 17.

ncert-solutions-for-class-11-chemistry-chapter-6-thermodynamics-31

Q 18.

What is the enthalpy change for an adiabatic process?

Q 19.

Q 20.

Out of diamond and graphite, which has greater entropy?

Q 21.

Predict in which of the following, entropy increases/decreases.
(i) A liquid crystallizes into a solid
(ii) Temperature of a crystallize solid is raised from OK to 115 K
(iii) 2NaHCO3 (s) ———-> Na2 C03 (s) + C02 (g) + H2O (g)
(iv) H2(g)——>2H(g)

Q 22.

Why standard entropy of an elementary substance is not zero whereas standard enthalpy of formation is taken as zero?
Under what conditions will the reaction occur, if
(i) both ∆H and ∆S are positive
(ii) both ∆H and ∆S are negative

Q 23.

A sample of 1.0 mol of a monoatomic ideal gas is taken through a cyclic process of expansion and compression as shown in the figure. What will be the value of ΔHfor the cycle as a whole?

ncert-exemplar-problems-class-11-chemistry-chapter-6-thermodynamics-16

Q 24.

The standard molar entropy of H2O(l) is 70 J K-1 mol-1. Will the standard molar entropy H20(s) be more, or less than 70 J K -1 mol-1?

Q 25.

Expansion of a gas in vacuum is called free expansion. Calculate the work done and the change in internal energy when 1 litre of ideal gas expands isothermally into vacuum until its total volume is 5 litre.

Q 26.

Q 27.

When is bond energy equal to bond dissociation energy ?

Q 28.

State Hess’s law.

Q 29.

Give a relation between entropy change and heat absorbed or evolved for a reversible reaction occurring at temperature T.

Q 30.

What is the condition for spontaneity in terms of free energy change?

Q 31.

Q 32.

During complete combustion of one mole of butane, 2658 kJ of heat is released. The thermochemical reaction for above change is
ncert-exemplar-problems-class-11-chemistry-chapter-6-thermodynamics-1

Q 33.

18.0 g of water completely vapourises at 100 °C and 1 bar pressure and the enthalpy change in the process is
40.79 kJ mol-1. What will be the enthalpy change for vapourising two moles of water under the same conditions? What is the standard enthalpy of vapourisation for water?

Q 34.

At 298 K, Kp for the reaction N204(g)⇌ 2N02(g) is 0.98. Predict whether the reaction is spontaneous or not.

Q 35.

Although heat is a path function but heat absorbed by the system under certain specific conditions is independent of path. What are those conditions? Explain.

Q 36.

The reaction of cyanamide,NH2CN(s) with dioxygen was carried out in a bomb calorimeter and ∆U was found to be -742,7  KJ-1   mol-1  at 298 K. Calculate the enthalpy change for the reaction at 298 K.NH2CN  (S) + 3/202(g) —–>N2(g) + CO2(g) + H20(Z)

Q 37.

Calculate the standard enthalpy of formation of CH3OH. from the following data:
(i) CH3OH(l) + 3/2 02 (g) ———-> CO2 (g) + 2H20 (l); ∆rH = – 726kj mol-1
(ii) C(s) + 02(g) —————>C02 (g); ∆cH = -393 kj mol-1
(iii) H2(g) + 1/202(g) —————->H20 (l); ∆fH = -286 kj mol-1

Q 38.

For an isolated system∆U = 0; what will be ∆S?

Q 39.

For the reaction; 2Cl(g) ———-> Cl2(g); what will be the signs of ∆H and ∆S?

Q 40.

What is free energy in terms of thermodynamics?

Q 41.

Calculate the enthalpy change for the reaction: H2(g) + Cl2(g) ————-> 2HCl(g). Given that  bond energies ofH-H, Cl- Cl and H-Cl bonds are 433, 244 and 431 kj mol-1  respectively.

Q 42.

ncert-solutions-for-class-11-chemistry-chapter-6-thermodynamics-23

Q 43.

Define the following:
(i) First law of thermodynamics.
(ii) Standard enthalpy of formation.

Q 44.

ncert-solutions-for-class-11-chemistry-chapter-6-thermodynamics-25

Q 45.

Give reason for the following:
(a)Neither q nor w is a state function but q + w is a state function.
(b)A real crystal has more entropy than an ideal crystal.

Q 46.

(a)What is a spontaneous process? Mention the conditions for a reaction to be spontaneous at constant temperature and pressure.
(b) Discuss the effect of temperature on the spontaneity of an exothermic reaction.

Q 47.

(a) What is bond energy? Why is it called enthalpy of atomisation?
(b) Calculate the bond energy of C-H bond, given that the heat of formation of CH4, heat of sublimation of carbon and heat of dissociation of H2  are – 74.8, + 719.6, 435.4 kj mol-1 respectively.

Q 48.

Consider the reactions given below. On the basis of these reactions find out which of the algebraic relations given in options (a) to (d) is correct?
(i) C(g) + 4H(g) → CH4(g); ∆rH= kJ mol-1
(ii) C(graphite, s) + 2H2(g) → CH4(g); ∆rH = y kJ mol 1
(a) x = y                                   (b) x = 2y                     (c)x >y         (d)x< y

Q 49.

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.

Q 50.

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 tor a spontaneous reaction
(d) ∆G is positive for a non-spontaneous reaction.