Thermodynamics

Thermodynamics & Thermochemistry

THERMOCHEMISTRY


PART - I : SUBJECTIVE QUESTIONS
Section (A) : Calculation U, H & W for chemical reaction
A-1. For the reaction : C2H5OH() + 3O2(g)  2CO2(g) + 3H2O(g)
ifUº = –1373 kJ mol–1 at 298 K. Calculate Hº
A-2. 2 mole of zinc is dissolved in HCl at 25ºC. Calculate the work done in open vessel.

Section (B) : Basics & Kirchoff’s law
B-1. Diborane is a potential rocket fuel which undergoes combustion according to the reaction
B2H6(g) + 3O2(g)  B2O3(s) + 3H2O(g)
From the following data, calculate the enthalpy change for the combustion of diborane
2B(s) + (3/2) O2(g)  B2O3(s) H = – 1273 kJ mol–1
H2(g) + (1/2)O2(g)  H2O(l) H = – 286 kJ mol–1
H2O(l)  H2O(g) H = 44 kJ mol–1
2B(s) + 3H2(g) B2H6(g) H = 36 kJ mol–1
B-2. Predict the standard reaction enthalpy of 2 NO 2(g)  N2O4(g) at 100°C. H° at 25°C is –57.2 kJ.mol–1
Cp(NO2) = 37.2 J.mol–1 K–1 Cp(N2O4) = 77.28 J.mol–1 k–1.

Section (C) : Enthalpy of formation & combustion
C-1. The heat of combustion of ethyl alcohol is –300 kcal. If the heats of formation of CO 2 (g) and H2O() are
–94.3 and –68.5 kcal respectively, calculate the heat of formation of ethyl alcohol.
C-2. If H2 + 1/2 O2 H2O,    H = – 68 kcal
K + H2O + water  KOH (aq) + 1/2 H2, H = – 48 kcal
KOH + water KOH (aq),   H = – 14 kcal
Find the heat of formation of KOH.
C-3. The standard enthalpy of decomposition of the yellow complex H3NSO2 into NH3 and SO2 is + 40 kJ
mol–1. Calculate the standard enthalpy of formation of H3NSO2. H0f(NH3) = – 46.17 kJ mol–1,
H0f(SO2) = –296.83.
C-4. When 12.0 g of carbon (graphite) reacted with oxygen to form CO and CO 2 at 250C and constant
pressure, 252 kJ of heat was released and no carbon remained. If H0f (CO, g) = – 110.5 kJ mol–1 and
H0f (CO2,g) = – 393.5 kJ mol–1, calculate the mass of oxygen consumed.

Section (D) : Bond enthalpy method & Resonance energy
D-1. Calcualte the bond energy of Cl–Cl bond from the following data :
CH4(g) + Cl2(g)  CH3Cl(g) + HCl(g); H = – 100.3 kJ. Also the bond enthalpies of C–H, C–Cl, H–Cl
bonds are 413, 326 and 431 kJ mol–1 respectively.
D-2. Calculate Hºr for the reaction CH2Cl2(g) C(g) + 2H(g) + 2Cl(g). The average bond enthalpies of
C–H and C–Cl bonds are 414 kJ mol–1 and 330 kJ mol–1.
D-3. Calculate the enthalpy change (H) of the following reaction 2C2H2(g) + 5O2(g) 4CO2(g) + 2H2O(g)
given average bond enthalpies of various bonds, i.e., C–H, CC, O=O, C=O, O–H as 414, 814, 499,
724 and 640 kJ mol–1 respectively.



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, Thermodynamics & Thermochemistry
D-4. Calculate change in enthalpy for the reaction at 27ºC
H2(g) + C2(g)  2H–C(g)
by using the bond energy and energy data
Bond energies of H–H, C–C and H–C bonds are 435 kJ mol–1, 240 kJ mol–1 and 430 kJ mol–1
respectively.
D-5. Estimate the average S–F bond enthalpy in SF6. The values of standard enthalpy of formation of
SF6(g), S(g) and F(g) are : –1100, 274 and 80 kJ mol–1 respectively.

Section (E) : Enthalpy of solution & Born Haber’s cycle
E-1. Calculate the standard enthalpy of solution of AgCl(s) in water Hºf (AgCl,s) = – 127.07 kJ mol–1, H0f
(Ag+, aq) = 105.58 kJ mol–1, H0f (Cl–, aq) = –167.35 kJ mol–1.
E-2. Enthalpies of solution of BaCl2 (s) and BaCl2.2H2O (s) are – 20 kJ/mole and 8.0 kJ/mole respectively.
Calculate heat of hydration of BaCl2 (s).
E-3. Setup of Born-Haber cycle; calculate lattice energy of MgO(s). The given that - enthalpy of formation of
MgO(s) = –602, sublimation of Mg(s) = 148 ; 1st & 2nd ionization energy of Mg = 738 & 1450 respectively.
For Oxygen bond dissociation energy = 498; 1st & 2nd electron gain enthalpy = –141 & 844 respectively
(all unit in kJmole–1).

Section (F) : Enthalpy of neutralization
F-1. 10 mL of each 1 M HCl and 1M H2SO4 are neutralized by 1 M NaOH solution that liberate the heat of
a & b kJ/mol respectively. What is relation between a and b ?
F-2. The enthalpy of neutralization of 1M HCl by 1M NaOH is – 57 kJ/mole. The enthalpy of formation of
water is – 285 kJ/mole. The enthalpy of formation of OH– ion is :
F-3. The standard enthalpy of neutralization of KOH with HCN and HCl in dilute solution is –2480 cal.mol–1
and –13.68 kcalmol–1 respectively. Find the enthalpy of dissociation of HCN at the same temperature.

PART - II : ONLY ONE OPTION CORRECT TYPE
Section (A) : Calculation U, H & W for chemical reaction
A–1. The free energy change for a reversible reaction at equilibrium is :
(A) Positive (B) Negative (C) Zero (D) Cannot say
A-2. Hº for the reaction X(g) + Y(g) Z(g) is – 4.6 Kcal, the value of Uº of the reaction at 227ºC is
(R = 2 cal.mol–1 K–1) :
(A) –3.6 kcal (B) –5.6 kcal (C) –4.6 kcal (D) –2.6 kcal
A-3. Determine which of the following reactions at constant pressure represent surrounding that do work on
the system :
I. 4NH3 (g) + 7O2 (g)  4NO2 (g) + 6H2O (g)
II. CO (g) + 2H2 (g)  CH3OH ( )
III. C (s, graphite) + H2O (g)CO (g) + H2 (g)
IV. H2O (s) H2O ( )
(A) III, IV (B) II and III (C) II, IV (D) I and II, IV
A-4. Consider the reaction at 300 K
H2 (g) + Cl2(g)  2HCl (g) ; Hº = – 185 kJ
If 2 mole of H2 completely react with 2 mole of Cl2 to form HCl. What is Uº for this reaction ?
(A) 0 (B) – 185 kJ (C) 370 kJ (D) – 370 kJ
A-5. A mixture of 2 mole of CO and 1 mole of O2, in a closed vessel is ignited to convert the CO to CO 2. If
H is the enthalpy change and U is the change in internal energy then :
(A) H < U (B) H > U (C) H = U (D) H = 2U

Reg. & Corp. Office : CG Tower, A-46 & 52, IPIA, Near City Mall, Jhalawar Road, Kota (Raj.) – 324005
Website : www.resonance.ac.in | E-mail :
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Toll Free : 1800 258 5555 | CIN: U80302RJ2007PLC024029