3. CHEMICAL THERMODYNAMICS
AND ENERGETICS
Azeem khan
Maharashtra Board Class 12
Numerical Problems

1) Three moles of an ideal gas are expanded isothermally from a
volume of 300 cm3 to 2.5 L at 300 K against a pressure of 1.9 atm.
Calculate the work done in L atm and joules.
Given- Pexe = 1.9 atm, V2= 2.5 L, V1 = 300 cm3
=300/1000L = 0.3L, W = ? J.
W = -Pex (V2 – V1)
= - 1.9(2.5 – 0.3)
= -4.18L.atm
Now, 1L atm = 101.3J
W = -4.18 x 101.3
= -423.4J
Log 4.18 = 0.6212
Log 101.3 = 2.0056
= 5.6268
A.l(5.6268) = 423.5
Since the
expansion take
place at const P, it
is irreversible
process and
works is given
byh

2) One mole of an ideal gas is compressed form 500 cm3 against a
constant pressure of 1.216 X105 Pa. The work involved in the process
is 36.50 J. Calculate the final volume.

3) Calculate the maximum work when 24 g of oxygen are
expanded isothermally and reversibly from a pressure of
1.6X105 Pa to 100 kPa at 298 K.
n o2 = Wo2 = 24 = 0.75 mol
Mo2 32
Log 1.6 = 0.2041

4) Three moles of an ideal gas are compressed isothermally
and reversibly to a volume of 2L. The work done is 2.983 KJ.
At 22 oC. Calculate the initial volume of thegas.

5)2.8X10-2 kg of nitrogen is expanded isothermally and
reversibly at 300K from 15.15X105 Nm-2 when the work
done is found to be -17.33 kJ. Find the final pressure.

6) A simple of gas absorbs 4000 kJ of heat.
a) If volume remains constant, what is ∆U?
b) Suppose that in addition to absorption of heat by the
sample, the surrounding does 2000 kJ of work on the
sample, what is ∆U?
c) Suppose that as the original sample absorbs heat, it
expands against atmospheric pressure and does 600 k J
of work on its surroundings. What is ∆U?

7) Calculate the work done in each of the following
reaction. State whether work is done on or by the system.
(a)The oxidation of one mole of SO2 at 50oC.
2SO2 (g) + O2  2SO3(g)
(b)Decomposition of 2 mole of NH4NO3 at 100 C
NH4NO3(s)  N2O(g) + 2H2O(g)
Log 0.5= 1. 6990
Log 8.314= 0.9198
Log 323= 2.3092
A.l(3.1280) = 1343.0

7) Calculate the work done in each of the following
reaction. State whether work is done on or by the system.
(a)The oxidation of one mole of SO2 at 50 C.
2SO2(g) + O0  2SO3(g)
(b)Decomposition of one mole of NH4NO3 at 100 C
NH4NO3(s)  N2O (g) + 2H2O(g)
NH4NO3
2NH4NO3 (s)  2N2O (g) + 4H2O (g)
Log 6= 0.7782
Log 8.314= 0.9198
Log 373= 2.5717
A.l(4.2697) = 18610.0

This is work of
compression due
to decrease in
volume.

9) Calculate standard enthalpy of the rection
Fe2O3 (s) + 3CO (g)  2Fe (s) + 3CO2 (g)
From the following data:
∆fH⁰ (Fe2O3 = -824.2 kJmol-1) , ∆fH⁰ (CO) = -110.5kJmol-1 ,
∆fH⁰(CO2) = -393.5 kJmol-1.

10) Calculate the standard enthalpy of formation of C2H6
from the following data:
2C2H6 (g) +7O2 (g)  4CO2 (g) + 6 H2O (l), ∆H⁰ = -3119 k J
∆fH⁰ (CO2) = -393.5 k J mol-1
∆fH⁰(H2O) = -285.8 k J mol-1.

11) How much heat is evolved when 12 g of CO react with
NO2 according to the following reaction,
4CO (g) + 2NO2 (g)  4CO2 (g) + N2 (g),
∆H⁰ = -1198 k J
Heat evolved =?
Heat evolved per mole= 1198/4= 299.5kJ
No. of mole of CO = w/M= 12/28= 0.43 moles.
Heat evolved when 0.43 mole of CO react
= 0.43 x 299.5 = 128.8kJ

12) 38.55 kJ of heat is absorbed when 6.0 g of O2 react with
CIF according to the reaction,
2CIF(g) +O2(g)  Cl2O(g) + OF2(g)
What is the standard enthalpy of the reaction ?
∆H =?
Heat absorbed per mole= 38.55kJ
No. of mole of O2 = w/M= 6.0/32= 0.1875 moles
Therefore, 6g of O2, ∆H = 38.55_
0.1875
= 205.6 kJ

13) Calculate ∆Ho of the reaction
CH4(g) +O2(g)  CH2O(g) + H2O(g)
From the following data:
Bond C-H O=O C=O O-H
Ho /k J mol-1 414 499 745 464

14) Calculate C-Cl bond enthalpy from the following data:
CH3Cl(g) + Cl(g)  CH2Cl(g) + HCl(g)
∆H⁰ = -104 k J
Bond C-H Cl-Cl H-Cl
Ho / k J mol-1 414 243 431 [2 Marks]

(15) Calculate the standard enthalpy of the reaction,
2C (graphite) + 3H2(g)  C2H6(g) from the following ∆H⁰ values:
(i)C2H6(g) + 7/2 O2(g)  2CO2(g) + 3H2O(l), ∆H⁰ = -1560 k J
(ii)H2(g) + 1/2 O2(g)  H2O(l) ∆H⁰ = -285.8 kJ
(iii)C(graphite) + O2(g)  CO2(g) ∆H⁰ = -393.5 kJ

16) Given the following equation calculate the standard
enthalpy of the reaction, [3 Marks]
2Fe (s) + 3/2 O2(g)  Fe2O3(s) ∆H⁰ = ?
(i)2Al(s) + Fe2O3(s)  2Fe(s) + Al2O3(s) ∆H⁰ = -847.6 k J
(ii)2Al(s) + 3/2 O2(g)  Al2O3(g) ∆H⁰ = -1670 k J

17) Given following equeations and H values at 25 ⁰C,
(i)Si(s) +O2(g)  SiO2(s) ∆H1⁰ = -911 k J
(ii)2C(graphite) + O2(g)  2CO(g) ∆H2⁰ = -221 k J
(iii)Si(s) + C(graphite)  SiC(s) ∆H3⁰ = -65.3 k J
Calculate ∆H⁰ for the following reaction,
SiO2 + 3C (graphite)  SiC (s) + 2CO(g) .

18) Given the following equation and ∆H⁰ value at 25 ⁰C,
(i)2H3BO3(aq)  B2O3(s) + 3H2O(l) ∆H1⁰ =+14.4 k J
(ii)H3BO3(aq)  HBO2(aq) +H2O(l) ∆H2⁰ = -0.02 k J
(iii)H2B4O7(s)  2B2O3(s) + H2O(l) ∆H3⁰ =17.3 k J
Calculate ∆H⁰ for the following reaction
H2B4O7(s)+ H2O(l)  4HBO2(aq) ∆H4⁰= ?
∆H4⁰ = ∆H⁰product - ∆H⁰reactant
∆H4⁰ = 4 ∆H2⁰ + ∆H3⁰ - 2 ∆H1⁰
= 4(-0.02) + 17.3 – 2(14.4)
= -11.58kJ

19) Calculate Kp for the reaction,
C2H4(g) + H2(g)  C2H6(g)
∆Go = -100 kJ mol-1 at 25 ⁰C. [2 Marks]

20) Kp for the reaction, MgCO3(s)  MgO(s) + CO2(g) is 9 X
10-10. Calculate ∆Go for the reaction at 25 ⁰C. [2 Marks]

21) Calculate ∆G for the reaction at 25oC
CO (g) + 2H2(g)  CH3OH(g) G⁰ = -24.8 k J mol-1 if
PCO = 4 atm, PH2 = 2 atm, PCH3OH = 2 atm [2 Marks]

22) Calculate Stotal and hence show whether the following
reaction is spontaneous at 25⁰C. [2 Marks]
HgS(s) + O2(g)  Hg(l) + SO2(g) ∆H = -238.6 kJ and S = +36.7K-1

23) Determine whether the reaction with the following ∆H
and ∆S values are spontaneous or nonspontaneous. State
whether they are exothermic or endothermic. [2 Marks]
∆H = -110 k J and S = +40 J K-1 at 400 K
∆H =+50 k J and S = -130 J K-1 at 250 K.

24) For a certain reaction ∆Ho = -224 kJ and ∆So = -153 JK-1.
At what temperature it will change from spontaneous to
non spontaneous? [2 marks]

25) Determine whether the following reaction will be
spontaneous or nonspontaneous under standard condition.
[2Marks]
Zn (s)+Cu2+
(aq)  Zn2+
(aq) + Cu(s) ∆H⁰ = -219 kJ, ∆Sᵒ= -21 JK-1.

26) Determine whether the following reaction is
spontaneous under standard conditions.
2H2O(l) + O2(g)  2H2O2(l) ∆H⁰ = +196 kJ, ∆So = -126 JK-1,
Does it have a cross-over temperature?
H.W

27) Oxidation of propane is represented as [2Marks]
C3H8(g) +5O2(g)  3CO2(g) + 4H2O(g) ,
∆Ho = -2043 k J. How much pressure volume of work is done
and what is the value of ∆U at constant pressure of 1 atm
when the volume change is +22.4 L.
∆Ho = -2043KJ
H.W

28) What is the volume of ∆Ssurr for the following reaction
at 298 K?
6CO2 +6H2O  C6H12O6 + 6O2 ,
∆Go = 2879 k J mol-1 , ∆So =-210 J K-1 mol-1. [2marks]
G
H.W

Ln 2816.42 = 3.4496
____Ln 298 = 2.4742
A.L (0.9754) = 9.450
Surrou

29) Calculate the enthalpy change for the reaction,
H2O(g)  2H(g) + O(g) and hence, calculate the bond
enthalpy of O-H bond in H2O from the following data:
∆vapH(H20) = 44.0 k J mol-1 , ∆fH(H2O) = -285.8 KJ mol-1
∆aH (H2) = 436.0 k J mol-1, ∆aH (O2) = 498.0 KJ mol-1
where ∆aH is the enthalpy of atomization. [2 Marks]
∆fHH2O(g) = ∆vapHH2O(l) + ∆fHH2O(l)
∆H = ∆Hproduct - ∆Hreactant
H.W

30) Calculate ∆Ssurr when one mole of methanol (CH3OH) is
formed from its elements under standard conditions if ∆fH⁰
(CH3OH)= -238.9 k J mol-1. [2 mark]
H.W

31) Calculate the total heat required to melt 180 g of ice at
0⁰C , heat it to 100⁰C and then vaporize it at that
temperature. ∆fusH (ice) = 6.01 kJ mol-1 at 0⁰C , ∆vapH(H2O) =
40.7 k Jmol-1 at 100⁰C. Specific heat of water = 4.18 Jg-1 K-1

32) 6.24g of ethanol are vaporized by supplying 5.89
kJ of heat energy. What is enthalpy of vaporization
of ethanol? [2 Marks]
∆H =?
Heat vaporization per mole= 5.89/6.24 = 0.94
1 of molar mass of ethanol = 46g
Therefore, 46g of ethanol, ∆H = 46 x 0.94
= 43.42 kJ/mol

33) Enthalpy of fusion of ice is 6.01 kJmol-1. The enthalpy of
vaporization of water is 45.07 kJmol-1. What is enthalpy of
sublimation of ice? [2 Marks]