Chemical Engineering Thermodynamics - Study Mode

[#156] For a constant volume process
Correct Answer

(B) dE = C v dT

Explanation

Solution: Since, under constant volume process the expansion work is zero, and by the definition of $${C_V}$$ we can write $${C_V} = mathop {lim }limits_{delta T o 0} {left( {frac{{delta Q}}{{delta T}}}
ight)_V}$$ By first law of thermodynamics $$eqalign{
& delta Q = dU cr
& Rightarrow dU = CvdT. cr} $$

[#157] Which of the following equations is obtained on combining 1 st and 2 nd law of thermodynamics, for a system of constant mass?
Correct Answer

(A) dE = Tds - PdV

Explanation

Solution: By second law of thermodynamics we can write $$TdS = delta Q$$ Which is valid only for reversiable process but once it is connected to state variable by using first law of thermodynamics we can say it is valid for both reversible and irreversible process and the relation is: $$dU=TdS-PdV.$$

[#158] For an exothremic reaction
Correct Answer

(C) Both ΔH and ΔE are negative

Explanation

Solution: During exothermic reaction since the heat is given out by the system the thermal energy decreases and therefore the internal energy decreases leading to a decrease in enthalpy.

[#159] For an ideal gas, the enthalpy
Correct Answer

(C) Is independent of pressure

Explanation

Solution: The enthalpy of a substance is given by $$dH = {C_P}dT + left[ {V - T{{left( {frac{{partial V}}{{partial T}}}
ight)}_P}}
ight]dP$$ For ideal gas $$T{left( {frac{{partial V}}{{partial T}}}
ight)_P} = V$$ So, $$dH = {C_P}dT$$ So, it is dependent on temperature only.

[#160] Refrigerants commonly used for domestic refrigerators are
Correct Answer

(A) Ethyl chloride or methyle chloride

Explanation

Solution: Domestic refrigerants are ethyl chloride or methyl chloride.