Chemistry

8. The reaction of cyanamide,NH₂CN(s) with dioxygen was carried out in a bomb calorimeter and ?U was found to be -742,7 KJ^-1  mol^-1 at 298 K. Calculate the enthalpy change for the reaction at 298 K.

NH₂CN (S) + 3/2O₂(g) → N₂(g) + CO₂(g) + H₂O(l)

7.  In a process, 701 J of heat is absorbed by a system and 394 J of work is done by the system. What is the change in internal energy for the process?        

6. A reaction, A + B—>C + D + q is found to have a positive entropy change. The reaction will be

(i) Possible at high temperature                               

(ii) Possible only at low temperature

(iii) Not possible at any temperature                         

(iv) Possible at any temperature  

5. The enthalpy of combustion of methane, graphite and dihydrogen at 298 K are -890.3 KJ mol^-1, – 393.5 KJ mol^-1 and – 285.8 KJ mol^-1 respectively. Enthalpy of formation of CH₄(g) will be

(i) – 74.8 KJ mol^-1                                         

(ii) – 52.27 KJ mol^-1

(iii) + 74.8 KJ mol^-1                                 

(iv) + 52.26 KJ mol^-1    

4. ΔU^? of combustion of methane is – X kJ mol^–1. The value of ΔH^? is

(i) = ΔU^?

(ii) > ΔU^?

(iii) < U^?

(iv) = 0      

3. The enthalpies of all elements in their standard states are:                       

(i) Unity                   

(ii) Zero

(iii) < 0                     

(iv) Different for each element

2. For the process to occur under adiabatic conditions, the correct condition is:

(i) ?T= 0                           

(ii) ?p = 0

(iii) q = 0                           

(iv) w = 0   

 Although heat is a path function but heat absorbed by the system under certain specific conditions is independent of path. What are those conditions? Explain.