Important questions based on NCERT syllabus for Chapter 6 - Thermodynamics:
Question-1: Enthalpy of combustion of carbon to carbon dioxide is – 393.5 J mol-1 Calculate the heat released upon formation of 35.2 g of C02 from carbon and oxygen gas.
Solution: The combustion equation is:
C(s) + 02 (g) —–> C02(g); AcH = – 393.5 KJ mol-1
Heat released in the formation of 44g of C02 = 393.5 kj
Heat released in the formation of 35.2 g of C02=(393.5 KJ) x (35.2g)/(44g) = 314.8 kj
Question-2: What is the condition for spontaneity in terms of free energy change?
Solution: If ∆G is negative, process is spontaneous.
If ∆G is positive, the process is non-spontaneous.
If ∆G = 0, the process is in equilibrium.
Question-3: What is Gibbs Helmholtz equation?
Solution: ∆G = ∆H – T∆S
Where ∆G = free energy change.
∆H = enthalpy change.
∆S = entropy change.
Question-4: Define the following:
(i) First law of thermodynamics.
(ii) Standard enthalpy of formation.
Solution: (i) First law of thermodynamics: It states that energy can neither be created nor be destroyed. The energy of an isolated system is constant.
∆u = q + w
(ii) It is defined as the amount of heat evolved or absorbed when one mole of the compound is formed from its constituent elements in their standard states.