Chapter 5. Chemical Thermodynamics

Class 11 Chemistry Chapter 5. Chemical Thermodynamics Internal Problems and Answers :

Problem 5.1 : Express the change in internal energy of a system when

(i) No heat is absorbed by the system from the surroundings, but work (w) is done on the system. What type of wall does the system have ?

(ii) No work is done on the system, but  amount of heat is taken out from the system and given to the surroundings. What type of wall does the system have?

(iii) w amount of work is done by the system and q amount of heat is supplied to the system. What type of system would it be?

Problem 5.2 : Two litres of an ideal gas at a pressure of 10 atm expands isothermally at 25 °C into a vacuum until its total volume is 10 litres. How much heat is absorbed and how much work is done in the expansion ?

Problem 5.3 : Consider the same expansion, but this time against a constant external pressure of 1 atm.

Problem 5.4 :  Consider the expansion given in problem 5.2, for 1 mol of an ideal gas conducted reversibly.

Problem 5.5 : If water vapour is assumed to be a perfect gas, molar enthalpy change for vapourisation of 1 mol of water at 1bar and 100°C is 41kJ  . Calculate the internal energy change, when 1 mol of water is vapourised at 1 bar pressure and 100°C.

Problem 5.6 : 1g of graphite is burnt in a bomb calorimeter in excess of oxygen at 298 K and 1 atmospheric pressure according to the equation, 

During the reaction, temperature rises from 298 K to 299 K. If the heat capacity of the bomb calorimeter is 20.7kJ/K, what is the enthalpy change for the above reaction at 298 K and 1 atm?

Problem 5.7 : A swimmer coming out from a pool is covered with a film of water weighing about 18g. How much heat must be supplied to evaporate this water at 298 K ? Calculate the internal energy of vaporisation at 298K.  for water at 298K= 44.01kJ .

Problem 5.8 : Assuming the water vapour to be a perfect gas, calculate the internal energy change when 1 mol of water at 100°C and 1 bar pressure is converted to ice at 0°C. Given the enthalpy of fusion of ice is 6.00 kJ heat capacity of water is 4.2 J/g°C

Problem 5.9 : The combustion of one mole of benzene takes place at 298 K and 1 atm. After combustion,  (g) and  are produced and 3267.0 kJ of heat is liberated. Calculate the standard enthalpy of formation,  of benzene. Standard enthalpies of formation of (g) and  are –393.5 kJ   and – 285.83 kJ  respectively.

Problem 5.10 : Predict in which of the following, entropy increases/decreases :

(i) A liquid crystallizes into a solid.

(ii) Temperature of a crystalline solid is raised from 0 K to 115 K.

(iii)   

 (iv)  

Problem 5.11 : For oxidation of iron,  entropy change is – 549.4 J  at 298 K. Inspite of negative entropy change of this reaction, why is the reaction spontaneous? (  for this reaction is –1648 × 10 3 J  )

Problem 5.12 : Calculate   for conversion of oxygen to ozone,  at 298 K. if  for this conversion is  .

Problem 5.13 : Find out the value of equilibrium constant for the following reaction at 298 K.

 

Standard Gibbs energy change,  at the given temperature is –13.6 kJ  .

Problem 5.14 : At 60°C, dinitrogen tetroxide is 50 per cent dissociated. Calculate the standard free energy change at this temperature and at one atmosphere.  

Class 11 Chemistry Chapter 5. Chemical Thermodynamics Exercise Questions and Answers :

5.1 Choose the correct answer. A thermodynamic state function is a quantity

(i) used to determine heat changes

(ii) whose value is independent of path

(iii) used to determine pressure volume work

(iv) whose value depends on temperature only.

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

(i) ∆T = 0

(ii) ∆p = 0

(iii) q = 0

(iv) w = 0

5.3 The enthalpies of all elements in their standard states are:

(i) unity

(ii) zero

(iii) < 0

(iv) different for each element

5.4   of combustion of methane is – X kJ  .The value of  is

(i) 

(ii)  

(iii) 

(iv)   = 0

5.5 The enthalpy of combustion of methane, graphite and dihydrogen at 298 K are  – 890.3 kJ  , –393.5 kJ   and –285.8 kJ  respectively. Enthalpy of formation of   will be

(i) – 74.8 kJ    (ii) – 52.27 kJ   (iii) + 74.8 kJ    (iv) + 52.26 kJ   .

5.6 A reaction,  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

(v) possible at any temperature

5.7 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?

5.8 The reaction of cyanamide,   with dioxygen was carried out in a bomb calorimeter, and  was found to be –742.7 kJ  at 298 K. Calculate enthalpy change for the reaction at 298 K.

  

5.9 Calculate the number of kJ of heat necessary to raise the temperature of 60.0 g of aluminium from 35°C to 55°C. Molar heat capacity of  is 24 J  .

5.10 Calculate the enthalpy change on freezing of 1.0 mol of water at 10.0°C to ice at –10.0°C.  kJ  at 0°C.

 J

 J

5.11 Enthalpy of combustion of carbon to  is –393.5 kJ . Calculate the heat released upon formation of 35.2 g of  from carbon and dioxygen gas.

5.12 Enthalpies of formation of CO(g),  (g),  (g) and  (g) are –110, – 393, 81 and 9.7 kJ  respectively. Find the value of  for the reaction:

  

5.13 Given,  ;   kj . What is the standard enthalpy of formation of  gas?

5.14 Calculate the standard enthalpy of formation of   from the following data:

     ;   kJ

    ;   kJ

      ;   kJ mol-1 

5.15 Calculate the enthalpy change for the process

         and calculate bond enthalpy of  in  .

 kJ

 kJ

 kJ  , Where  is enthalpy of atomisation

 kJ

5.16 For an isolated system, ∆U = 0, what will be ∆S ?

5.17 For the reaction at 298 K,   

∆H = 400 kJ   and ∆S = 0.2 kJ

At what temperature will the reaction become spontaneous considering  and  to be constant over the temperature range.

5.18 For the reaction,  , what are the signs of  and  ?

5.19 For the reaction, 

   kj and  J K-1

Calculate  for the reaction, and predict whether the reaction may occur spontaneously.

5.20 The equilibrium constant for a reaction is 10. What will be the value of  ?    R = 8.314 J  , T = 300 K.

5.21 Comment on the thermodynamic stability of NO(g), given

     ;   kj

     ;    kj

5.22 Calculate the entropy change in surroundings when 1.00 mol of  is formed under standard conditions.  –286 kJ  .