Thermodynamics CBSE Questions & Answers

A reaction, \({\text{A }} + {\text{ B }} \to {\text{ C }} + {\text{ D }} + {\text{ q}}\) is found to have a positive entropy change. The reaction will be

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?

The reaction of cyanamide, N\({{\text{H}}_2}\)CN (s), with dioxygen was carried out in a bomb calorimeter, and \(\Delta {\text{U}}\) was found to be 742.7 kJ \({\text{mo}}{{\text{l}}^{\_1}}\) at 298 K. Calculate enthalpy change for the reaction at 298 K. N\({{\text{H}}_2}\)CN(g) +\(\frac{3}{2}\) \({{\text{O}}_{\text{2}}}\left( {\text{g}} \right){\text{ }} \to {\text{ }}{{\text{N}}_{\text{2}}}\left( {\text{g}} \right){\text{ }} + {\text{ C}}{{\text{O}}_{\text{2}}}\left( {\text{g}} \right){\text{ }} + {\text{ }}{{\text{H}}_{\text{2}}}{\text{O}}\left( {\text{l}} \right)\)

Calculate the number of kJ of heat necessary to raise the temperature of 60.0 g of aluminium from 35\(^\circ {\text{C}}\) to 55\(^\circ {\text{C}}\). Molar heat capacity of Al is 24 J \({\text{mo}}{{\text{l}}^{ - {\text{1}}}}{{\text{K}}^{ - {\text{1}}}}\)

Calculate the enthalpy change on freezing of 1.0 mol of water at 10.0\(^\circ {\text{C}}\) to ice at -10.0\(^\circ {\text{C}}\). \({\Delta _{{\text{fus}}}}\) H = 6.03 kJ \({\text{mo}}{{\text{l}}^{ - {\text{1}}}}\)at 0\(^\circ {\text{C}}\).1 \({{\text{C}}_{\text{p}}}\left[ {{\text{H2O}}\left( {\text{l}} \right)} \right]{\text{ }} = {\text{ 75}}.{\text{3 J mo}}{{\text{l}}^{ - {\text{1}}}}{{\text{K}}^{ - {\text{1}}}}\) \({{\text{C}}_{\text{p}}}\left[ {{\text{H2O}}\left( {\text{s}} \right)} \right]{\text{ }} = {\text{ 36}}.{\text{8 J mo}}{{\text{l}}^{ - {\text{1}}}}{{\text{K}}^{ - {\text{1}}}}\)

Enthalpy of combustion of carbon to \({\text{C}}{{\text{O}}_{\text{2}}}\)is –393.5 kJ \({\text{mol}}{ - ^{\text{1}}}\). Calculate the heat released upon formation of 35.2 g of \({\text{C}}{{\text{O}}_{\text{2}}}\)from carbon and dioxygen gas.

Enthalpies of formation of CO(g), \({\text{C}}{{\text{O}}_{\text{2}}}\left( {\text{g}} \right)\), \({{\text{N}}_{\text{2}}}{\text{O}}\left( {\text{g}} \right)\)and \({{\text{N}}_{\text{2}}}{{\text{O}}_{\text{4}}}\left( {\text{g}} \right)\) are -110, –-393, 81 and 9.7 kJ \({\text{mo}}{{\text{l}}^{ - {\text{1}}}}\)respectively. Find the value of \({\Delta _{\text{r}}}{\text{H}}\) for the reaction: \({{\text{N}}_{\text{2}}}{{\text{O}}_{\text{4}}}\left( {\text{g}} \right){\text{ }} + {\text{ 3CO}}\left( {\text{g}} \right){\text{ }} \to {\text{ }}{{\text{N}}_{\text{2}}}{\text{O}}\left( {\text{g}} \right){\text{ }} + {\text{ 3C}}{{\text{O}}_{\text{2}}}\left( {\text{g}} \right)\)

Given \({{\text{N}}_{\text{2}}}\left( {\text{g}} \right){\text{ }} + {\text{ 3}}{{\text{H}}_{\text{2}}}\left( {\text{g}} \right){\text{ }} \to {\text{ 2N}}{{\text{H}}_{\text{3}}}\left( {\text{g}} \right){\text{ }};{\text{ }}{\Delta _{\text{r}}}{{\text{H}}^0}\)= –-92.4 kJ \({\text{mol}}{ - ^{\text{1}}}\) What is the standard enthalpy of formation of \({\text{N}}{{\text{H}}_{\text{3}}}\)gas?

Calculate the standard enthalpy of formation of \({\text{C}}{{\text{H}}_{\text{3}}}\)OH(l) from the following data: \({\text{C}}{{\text{H}}_{\text{3}}}{\text{OH }}\left( {\text{l}} \right){\text{ }} + {{\text{O}}_{\text{2}}}\left( {\text{g}} \right){\text{ }} \to {\text{ C}}{{\text{O}}_{\text{2}}}\left( {\text{g}} \right){\text{ }} + {\text{ 2}}{{\text{H}}_{\text{2}}}{\text{O }}\left( {\text{l}} \right);{\text{ }}{\Delta _{\text{r}}}{{\text{H}}^0} = {\text{ }} - {\text{726 kJ mo}}{{\text{l}}^{ - {\text{1}}}}\)C (graphite) + \({{\text{O}}_{\text{2}}}\left( {\text{g}} \right){\text{ }} \to {\text{ C}}{{\text{O}}_{\text{2}}}\left( {\text{g}} \right){\text{ }};{\text{ }}{\Delta _{\text{c}}}{{\text{H}}^0} = {\text{ }} - {\text{393 kJ mo}}{{\text{l}}^{ - {\text{1}}}}\) \({{\text{H}}_{\text{2}}}\left( {\text{g}} \right){\text{ }} + {{\text{O}}_{\text{2}}}\left( {\text{g}} \right){\text{ }} \to {\text{ }}{{\text{H}}_{\text{2}}}{\text{O }}\left( {\text{l}} \right);{\text{ }}{\Delta _{\text{f}}}{{\text{H}}^0} = {\text{ }} - {\text{286 kJ mo}}{{\text{l}}^{ - {\text{1}}}}\)

Calculate the enthalpy change for the process \({\text{CC}}{{\text{l}}_{\text{4}}}\left( {\text{g}} \right){\text{ }} \to {\text{ C }}\left( {\text{g}} \right){\text{ }} + {\text{ 4 Cl }}\left( {\text{g}} \right)\) and calculate bond enthalpy of C-- Cl in \({\text{CC}}{{\text{l}}_{\text{4}}}\) (g). \({\Delta _{{\text{vap}}}}{{\text{H}}^0}\left( {{\text{CC}}{{\text{l}}_{\text{4}}}} \right){\text{ }} = {\text{ 3}}0.{\text{5 kJ mo}}{{\text{l}}^{ - {\text{1}}}}\). \({\Delta _{\text{f}}}{{\text{H}}^0}\left( {{\text{CC}}{{\text{l}}_{\text{4}}}} \right){\text{ }} = {\text{ }} - {\text{135}}.{\text{5 kJ mo}}{{\text{l}}^{ - {\text{1}}}}\). \({\Delta _{\text{a}}}{{\text{H}}^0}\left( {\text{C}} \right){\text{ }} = {\text{ 715}}.0{\text{ kJ mo}}{{\text{l}}^{ - {\text{1}}}}\), where \({\Delta _{\text{a}}}{{\text{H}}^0}\) is enthalpy of atomisation \({\Delta _{\text{a}}}{{\text{H}}^0}\left( {{\text{C}}{{\text{l}}_{\text{2}}}} \right)\)= 242 kJ \({\text{mo}}{{\text{l}}^{ - {\text{1}}}}\)

For an isolated system, \(\Delta {\text{U}}\) = 0, what will be \(\Delta {\text{S}}\)?

for the reaction at 298 K, \({\text{2A }} + {\text{ B }} \to {\text{ C}}\)ΔH = 400 kJ \({\text{mo}}{{\text{l}}^{ - {\text{1}}}}\)and \(\Delta {\text{S}}\) = 0.2 kJ \({{\text{K}}^{ - {\text{1}}}}{\text{mo}}{{\text{l}}^{ - {\text{1}}}}\) At what temperature will the reaction become spontaneous considering \(\Delta {\text{H}}\) and \(\Delta {\text{S}}\) to be constant over the temperature range.

For the reaction, \({\text{2 Cl}}\left( {\text{g}} \right){\text{ }} \to {\text{ C}}{{\text{l}}_{\text{2}}}\left( {\text{g}} \right)\) , what are the signs of \(\Delta {\text{H}}\) and \(\Delta {\text{S}}\)?

for the reaction \({\text{2 A}}\left( {\text{g}} \right){\text{ }} + {\text{ B}}\left( {\text{g}} \right){\text{ }} \to {\text{ 2D}}\left( {\text{g}} \right)\) \(\Delta {{\text{U}}^0} = {\text{ }} - {\text{1}}0.{\text{5 kJ and }}\Delta {{\text{S}}^0} = {\text{ }} - {\text{44}}.{\text{1 J}}{{\text{K}}^{ - {\text{1}}}}\). Calculate \(\Delta {{\text{G}}^0}\)for the reaction, and predict whether the reaction may occur spontaneously.

The equilibrium constant for a reaction is 10. What will be the value of \(\Delta {{\text{G}}^0}?{\text{ R }} = {\text{ 8}}.{\text{314 J}}{{\text{K}}^{ - {\text{1}}}}{\text{mo}}{{\text{l}}^{ - {\text{1}}}}\), T = 300 K.