Chemical Thermodynamics: Chemistry

 

Q.1.  In an adiabatic expansion of ideal gas 

A) W= - E

B) W = E

C) E = 0

D) W = 0

Explanation- 

E = q - W            ( for expansion )

In case of adiabatic expansion q = 0

 

Q.2.  For the reaction of one mole of zinc dust with one mole of sulphuric acid in a bomb calorimeter , U and W correspond to  

A) U < 0 , W = 0

B) U < 0 , W < 0

C) U > 0 , W = 0

D) U > 0 , W > 0

Explanation-

Since the reaction is carried out in closed vessel , ( V = 0 ) so no work of expansion or contraction can be there . 

Hence by   law of thermodynamics U = q 

The reaction is a redox reaction , therefore it must be exothermic i.e., q < 0

So that U < 0 .

Q.3.  The bond dissociation energy of gaseous   and HCI are 104,58 and 103 kcal/mol respectively. Enthalpy of formation of HCI gas is 

A) 59 kcal

B) -265 kcal

C) -22 kcal

D) -29.5 kcal

Explanation-

Formation of HCI can be given as 

 

Q.4.  In an endothermic reaction , the value of   is 

A) Zero

B) Positive

C) Negative

D) Constant 

Explanation-

 

Q.5.  2 mol of an ideal gas at 27 C is expanded reversibly from 2 L to 20 L . Find entropy change ( R = 2 cal/ mol K ).

A) 92.1

B) 0

C) 4

D) 9.2

Q.6.  For melting of a solid at 25 C , the fusion process requires energy equivalent to 2906 J to be added to system considering the process to be reversible at fusion point, the entropy change of the process is 

A) 9.75 J K mol

B) 11.272 J  K mol

C) 2.33 J K mol

D) Insufficient data 

Q.7. Compounds with high heat of formation are less stable because 

A) It is difficult to synthesis them 

B) Energy rich state leads to instability 

C) High temperature is required to synthesis them

D) Molecules of such compounds are disturbed 

Explanation-

More energy results in less stability.

Q.8.  Heat exchanged in a chemical reaction at constant temperature and pressure is called 

A) Entropy change

B) Enthalpy change

C) Internal energy change

D) Free energy change 

Explanation-

Enthalpy change is the heat exchanged at constant temperature and pressure 

Q.9.  In order to decompose 9 g of water , 142.5 kJ of heat is required. Hence enthalpy of formation of water is 

A) -142.5 kJ

B) +142.5 kJ

C) -285 kJ

D) +285 kJ

Q.10.  The value of   is 109  kcal mol .Then formation of one mole of water in gaseous state from  H  and O is  accompanied by 

A) Release of 218 kcal of energy 

B) Release of 109 kcal of energy 

C) Absorption of 218 kcal of energy 

D) Unpredictable 

Explanation-

 forms two O - H bonds .