Standard enthalpy of vaporisation $$\Delta $$vapHo for water at 100oC is 40.66 kJ mol$$-$$1. The internal energy of vaporisation of water at 100oC (in kJ mol$$-$$1) is
In which of the following reactions, standard reaction entropy change ($$\Delta $$So) is positive and standard Gibb's energy change ($$\Delta $$Go) decreases sharply with increasing temperature ?
$$\Delta $$So positive means entropy of products is more
than that of reactants. Among the given reactions
only in option (a) the $$\Delta $$So is positive cause products
has 1 mole of gaseous products CO while reaction
have half mole of gaseous O2 and Carbon (C) in
solid state. Thus, reactions have less randomness
than products. Also, the reaction is a combustion
reaction which has a negative value of $$\Delta $$H.
According to Gibbs energy change ($$\Delta $$So).
$$\Delta $$Go = $$\Delta $$Ho - T$$\Delta $$So
$$ \Rightarrow $$ $$\Delta $$Go = -ve - T(+ve)
Thus, on increasing temperature value of $$\Delta $$Go
decreases sharply.
3
AIPMT 2011 Mains
MCQ (Single Correct Answer)
Consider the following processes :
H (kJ/mol)
1/2A $$ \to $$ B
+150
3B $$ \to $$ 2C + D
-125
E + A $$ \to $$ 2D
+350
For B + D $$ \to $$ E + 2C, $$\Delta $$H will be
A
525 kJ/mol
B
$$-$$175 kJ/mol
C
$$-$$ 325 kJ/mol
D
325 kJ/mol
Explanation
H (kJ/mol)
1/2A $$ \to $$ B
+150
3B $$ \to $$ 2C + D
-125
E + A $$ \to $$ 2D
+350
___________________________________
B + D $$ \to $$ E + 2C;
$$\Delta $$H = (300 - 125 - 350) = - 175 kJ/mol
4
AIPMT 2011 Prelims
MCQ (Single Correct Answer)
Which of the following is correct option for free expansion of an ideal gas under adiabatic condition ?
A
q = 0, $$\Delta $$T $$ \ne $$ 0, w = 0
B
q $$ \ne $$ 0, $$\Delta $$T = 0, w = 0
C
q = 0, $$\Delta $$T = 0, w = 0
D
q = 0, $$\Delta $$T < 0, w $$ \ne $$ 0
Explanation
For adiabatic condition, change in heat does
not take place thus, q = 0.
If q = 0 then change in
temperature does not take place thus, $$\Delta $$T = 0.
Also
for a free expansion of ideal gas work done, W = 0
as there is no external pressure on it.
Questions Asked from Thermodynamics
On those following papers in MCQ (Single Correct Answer)
Number in Brackets after Paper Indicates No. of Questions