Objective Questions of Thermodynamics

Prob 1. A system is taken from state A to state B along two different paths 1 and 2. The heat absorbed and work done by the system along these paths are Q1 and Q2 and W1 and W2respectively. Then 

               (A) Q1 = Q2                                                  (B) W1 + Q1 = Q2 + W2

               (C) W1 = W2                                                (D) Q1 - W1 = Q2 - W2

Sol.        (D)

Prob 2. In which of the following process does the entropy decrease? 

               (A) dissolving of NaCl in water                (B) evaporation of water

               (C) conversion of CO2(g) into dry ice      (D) none

Sol.         (C)

Prob 3. Calculate the enthalpy change when 50 ml of 0.01 M Ca(OH)2 reacts with 25 ml of 0.01 M HCl. Given that ΔH0neut of a strong acid and strong base is 140 cal/ equivalent

               (A) 14.0 cal                                                 (B) 35 cal

               (C) 10.0 cal                                                 (D) 7.5 cal

Sol.         (B)

Prob 4   In a reversible adiabatic change ΔS is 

               (A) infinity                                                    (B) zero

               (C) equal to CvdT                                       (D) equal to nRln V2/V1

Sol.        (B) 

Prob 5 At constant temperature and pressure which one of the following statements is correct for the reaction?

               CO(g) + 1/2O2(g) ——> CO2(g)

               (A) ΔH = ΔE                                              

               (B) ΔH < ΔE

               (C) ΔH > ΔE                                                                                               

               (D) ΔH is independent physical state of reactant

Sol.        (B)

Prob 6   For the reaction, 

C7H8(l) + 9O2(g) —> 7CO2(g) + 4H2O(l), the calculated heat of reaction is 232 kJ/mol and observed heat of reaction is 50.4 kJ/mol, then the resonance energy is

                (A) – 182.2 kJ / mol                                  (B) + 182.2 kJ / mol

                (C) 172 kJ/ mol                                         (D) None

Sol.        (A) As we know that,

               Resonance energy = ΔH° (observed) – DH° (calculated)

               = (50.4 – 232.6) kJ / mol

               = – 182.2 kJ mol–1

Fill in the Blanks

Prob 7         An isolated system is one which neither shows exchange of ………….. nor ………………. with surroundings. 

Sol.              (heat, mass) 

Prob 8         During fusion, the entropy of the system ……………………. 

Sol.              (increases) 

Prob 9          N2 + O2 ———> 2 NO, shows an ………………….. of heat. 

Sol.        (absorption)  

Prob 10      For spontaneous reaction ΔG is ………………………

Sol.              (negative)  

Prob 11   Bomb calorimeter used for determining change in internal energy at constant…………………… 

Sol.           Volume 

True and False 

Prob 12. Specific heat is an intensive property.                                                            

Sol.           True 

Prob 13. A thermodynamic equilibrium represents the state when all the three equilibrium (i.e. chemical, thermal and mechanical equilibrium) are attained at a time.             

Sol.           True 

Prob 14. The process is isothermal if temperature of the system remains constant throughout the course of studies.                                     

Sol.           True 

Prob 15. Rivers flowing from mountain to field shows decrease in entropy.                       

Sol.           False 

Prob 16. Enthalpy of combustion at a given temperature is defined as the enthalpy change for the compete combustion of 1 gm of substance. 

Sol.           False

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