Chemical Engineering Thermodynamics - Study Mode

[#251] For an ideal solution, the value of activity co-efficient is
Correct Answer

(B) 1

Explanation

Solution: For ideal solution the value of activity co-efficient is 1. Definition: activity co-efficient is defined as the ratio of fugacity at existing conditions to fugacity in ideal solution.

[#252] The freezing point of a liquid decreases when the pressure is increased, if the liquid __________ while freezing.
Correct Answer

(A) Contracts

Explanation

Solution: FROM the P-V-T diagram we can say that if the freezing point decreases with increase in pressure than liquid should contract during freezing.

[#253] A/an __________ system is exemplified by a vessel containing a volatile liquid in contact with its vapor.
Correct Answer

(C) Open

Explanation

Solution: Since the vessel containing liquid is transferring both mass and heat (energy) with its vapor we can consider it as open system.

[#254] During Joule-Thomson expansion of gases
Correct Answer

(A) Enthalpy remains constant

Explanation

Solution: During, joule-thomson effect basically the change in internal (inter-molecular) energy and change in pressure energy will be equal to zero hence, enthalpy will remain constant. $$eqalign{
& dU + dleft( {PV}
ight) = 0 cr
& Rightarrow dleft( {U + PV}
ight) = 0 cr
& Rightarrow dleft( H
ight) = 0 cr
& { ext{or }}H = { ext{constant}}{ ext{.}} cr} $$

[#255] The entropy change in a reversible isothermal process, when an ideal gas expands to four times its initial volume is
Correct Answer

(A) R log e 4

Explanation

Solution: For an isothermal process change in internal energy is equal to zero. So, from first law $$eqalign{
& q = - w = - 2.303,RT,{ ext{lo}}{{ ext{g}}_{10}}left( {frac{{v2}}{{v1}}}
ight) cr
& Rightarrow q = - RT,{log _e}4 cr
& Rightarrow { ext{We know for reversible isothermal process }}ds = - frac{{delta q}}{T} cr
& Rightarrow { ext{So, }}ds = R,{log _e}4. cr} $$