1 )
The value of ∆H (O-H) is 109 k cal / mol . The formation of 1 mole of
water in gaseous state from H(g) and O(g) is accompanied by : -
Solution
: -
H2 + O2
-------> 2 (OH)
So , 2 (109) = 218 .
So , water is liquid
, So energy is released .
So ∆H = - 218 K cal ,
Answer .
. .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . .
2 )
The enthalpies of combustion of carbon and carbon monoxide are - 390 K J / mol and -
278 K J / mol respectively . The
enthalpy of formation of carbon mono oxide ?
Solution
: -
Combustion
of carbon : -
C + O2
----------> CO2 , ∆H =
- 390 . . . . . . . . . . . eq. 1
Combustion
of carbon mono oxide : -
CO + (1/2) O2
----------> CO2 , ∆H =
- 278 . . . . . . . . . . . eq. 2
So , eq. 1 – eq. 2 : -
C + O2 - CO - (1/2) O2
----------> CO2 – CO2 , ∆H =
- 390 – ( - 278 ) .
C - (1/2) O2
----------> CO , ∆H = - 112
K J / mol , Answer .
. .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . .
3 )
Latent heat of vaporization of a liquid at 500 k and 1 atm pressure is 10.0 k
cal / mol . What will be the change in internal energy ∆E of 3 mol of liquid at
same temperature ?
Solution
: -
3 H2O (L)
-------------> 3 H2O (g) .
So , ∆n = 3 .
So , ∆E = ∆H - ∆nRT .
∆E =
( 3 x 10 ) – 3 x 500 x 0.002 = 27 k
cal ,
Answer .
. .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . .
4 )
The bond dissociation energies of H2 , Cl2 and HCl are 104 , 58 and 103 k
cal respectively . The enthalpy of
formation of HCl gas will be ?
Solution : -
. .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . .
