Page 53 - Basic physical chemistry for the atmospheric sciences

Chemical thermodynamics J9

done by (or on) a system s a function of state, but the
i
s
difference between these two quantitie , namely, the
change in the internal energy of a system, is a function
of state.
(j) When a system undergoes a transformation, the change
.
in its entropy can be computed from Eq. (2 1 7) by tak­
ing the system from its initial to its final state by a
reversible path. However, entropy is a state function
and therefore does not depend on the path taken. Ex­
plain this apparent paradox.
(k) By measuring the equilibrium radius (r) of a droplet in a
given environment, the relative humidity (RH) of the
environment could be derived from E . (2. 5 6). What
q
would be the practical problems in utilizing this tech­
nique as a sensitive measure of RH?
2. 1 1 . Use E . ( . 1 3 ) to show that:
2
q

where , and K are the equilibrium constants at tempera­
K
2
tures T1 and T2, respectively, and 11/lix is the molar stan­
dard enthalpy (heat) of reaction. Assuming that 11/lix i s
independent o f temperature, show that the predictions of
this relationship with respect to the variations of K P with
temperature for exothermic and endothermic reactions are
consistent with deductions based on LeChatelier's prin­
ciple.
2. 1 2 . If the equilibrium constant fo r a chemical reaction i s
2 .20 x 1 0 -2 at 0°C and the molar standard enthalpy (heat) of
1
reaction i s - 3 . 0 1 x 1 0 5 J mo1- , what is the value of the
equilibrium constant for the reaction at 20°C?
2. 1 3 . Calculate the molar standard enthalpies (or heats) of reac­
tion 11Jl?:x for the reactions :
(a) Nz(g) + 02(g) � 2NO(g)
(b) 0 (g) + NO(g) � N02(g) + 0 2(g)
3
( c) 2S02 (g) + 0 2(g) � 2S0 3(g)
Are the reactions endothermic or exothermic at 1 atm and
25°C?