Q1.A reaction, A + B → C + D + q is found to have a positive entropy change. The reaction will be
Answer : Option CExplaination / Solution:
ΔG = ΔH -T ΔS
ΔS is positive and ΔH is negative as heat is liberated in the reaction.
so ΔG is negative hence reaction will be spontaneous at all temperature.
Q2.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?
Answer : Option CExplaination / Solution:
ΔU = q + w (1st law of thermodynamics)
q = +701J (heat is absorbed by system)
w = -394 J (work is done by system)
ΔU = 701- 394
= 307J
Q3.The reaction of cyanamide, NH2CN (s), with dioxygen was carried out in a bomb calorimeter, and ΔU was found to be 742.7 kJ mol_1 at 298 K. Calculate enthalpy change for the reaction at 298 K. NH2CN(g) +32 O2(g)→N2(g)+ CO2(g)+H2O(l)
Q4.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 Al is 24 J mol−1K−1
Answer : Option DExplaination / Solution:
q=nC ΔT where n= 60.0/27 mole and ΔT = 20 K and C = 24J/mol K
Q5.Calculate the enthalpy change on freezing of 1.0 mol of water at 10.0∘C to ice at -10.0∘C. Δfus H = 6.03 kJ mol−1at 0∘C.1 Cp[H2O(l)]= 75.3 J mol−1K−1Cp[H2O(s)]= 36.8 J mol−1K−1
Enthalpy of combustion of carbon to CO2is –393.5 kJ mol−1. Calculate the heat released upon formation of 35.2 g of CO2from carbon and dioxygen gas.
Answer : Option AExplaination / Solution: when 1 mole of CO2 is produced energy released is –393.5 kJ mol−1Moles of CO2given =35.2/44 =0.8 moles So energy released = 0.8 x393.5 KJ/mol = 315 KJ/mol
Q7.Enthalpies of formation of CO(g), CO2(g), N2O(g)and N2O4(g) are -110, –-393, 81 and 9.7 kJ mol−1respectively. Find the value of ΔrH for the reaction: N2O4(g)+ 3CO(g)→N2O(g)+ 3CO2(g)
Q8.Given N2(g)+ 3H2(g)→ 2NH3(g);ΔrH0= –-92.4 kJ mol−1 What is the standard enthalpy of formation of NH3gas?
Answer : Option BExplaination / Solution: Standard Enthalpy of formation of NH3 is the energy change that take place when 1 mole of NH3 is formed from elements in standard state. For 2 moles of ammonia formation energy= –-92.4 kJ mol−1. For 1 mole energy =0.5 x–-92.4 kJ mol−1= -46.2 kJ mol−1
Q10.for the reaction at 298 K, 2A + B → CΔH = 400 kJ mol−1and ΔS = 0.2 kJ K−1mol−1 At what temperature will the reaction become spontaneous considering ΔH and ΔS to be constant over the temperature range.
Answer : Option BExplaination / Solution:
ΔG= ΔH-TΔS At equilibrium ΔG=0 then T= ΔH/ΔS =2000K
Total Question/Mark :
Scored Mark :
Mark for Correct Answer : 1
Mark for Wrong Answer : -0.5
Mark for Left Answer : 0