Thermodynamics Quiz-16

Thermodynamics Quiz-16

Dear Readers,

Thermodynamics is a very important branch of both chemistry and physics. It deals with the study of energy, the conversion of energy between different forms and the ability of energy to do work. Thermodynamics is an important chapter for JEE Mains, JEE Advance NEET and many others exams. As this chapter is present in both chemistry and physics and there is only a minor difference between them hence it becomes more important topic. It is not a tough topic, it only requires practice. This topic has been given good weightage in all engineering exams. So don't skip this and prepare well. All the best !.

Q1. Given that C(g) + 4H(g) → CH₄(g);   ΔH = −166kJ. The bond energy C − H will be:

•  −416 kJ/mol
•  −41.6 kJ/mol
•  832 kJ/mol
•  None of these

Solution:-
Bond-energy of C − H bond = −166/4
  = −41.5 kJ/mol

Q2. If S° for H₂, Cl₂ and HCl are 0.13, 0.22 and 0.19 kJ K⁻¹ mol⁻¹ respectively. The total change in standard entropy for the reaction, H₂ + Cl₂ → 2HCl is:

•  30 J K⁻¹ mol⁻¹
•  40 J K⁻¹ mol⁻¹
•  60 J K⁻¹ mol⁻¹
•  20 J K⁻¹ mol⁻¹

Solution:-
ΔS = S_P − S_R
  = (2×0.19)−0.13−0.22 = 0.03 kJ K⁻¹ mol⁻¹
  = 30 J K⁻¹ mol⁻¹

Q3. Hess law is applicable for the determination of heat of

•  Reaction
•  Formation
•  Transition
•  All of these

Solution:-
All of these

Q4. The Kirchhoff’s equation gives the effect of ...... on heat of reaction.

•  Pressure
•  Temperature
•  Volume
•  Molecularity

Solution:-
Kirchhoff’s equation is : ΔH₂ − ΔH₁ = ΔC_p(T₂ − T₁)

Q5. The enthalpy change for the following reaction, NaOH(aq) + HCl(aq) → NaCl(aq) + H₂(l) is −57 kJ. Predict the value of the enthalpy change in the following reaction : Ba(OH)₂ + H₂SO₄(aq) → BaSO₄(s) 2H₂O(l)

•  −57 kJ
•  −76 kJ
•  −114 kJ
•  −228 kJ

Solution:-
Two equivalent of each are used.

Q6. From the reaction P_white → P_red; ΔH = −18.4 kJ it is following that :

•  Red P is readily formed from white P
•  White P is readily formed from red P
•  White P cannot be converted to red P
•  White P can be converted into red P and red P is more stable

Solution:-
Energy of red P is lesser than white P and thus, red P is more stable.

Q7. Heat evolved in the reaction, H₂ + Cl₂ → 2HCl is 182 kJ. Bond energies of H − H and Cl − Cl are 430 and 242 kJ/mol respectively. The H − Cl bond energy is :

•  245 kJ/mol
•  427 kJ/mol
•  336 kJ/mol
•  154 kJ/mol

Solution:-
ΔH = −2×e_H−Cl + e_H−H + e_Cl−Cl
∴   182 = −2×a + 430 + 242
∴     a = 245 kJ/mol

Q8. Heat of neutralization of a strong acid and a strong base is equal to ΔH of :

•  H⁺ + OH⁻ → H₂O
•  H₂O + H⁺ → H₃O⁺
•  2H₂ + O₂ → 2H₂O
•  CH₃COOH + NaOH → CH₃COONa + H₂O

Solution:-
Heat of neutralisation is also defined as the heat of formation of H₂O from H⁺ and OH⁻ ions.

Q9. The enthalpy of vaporization of a liquid is 30 kJ/mol and entropy of vaporization is 75 J/mol. The boiling point of liquid at 1 atm is :

•  250 K
•  400 K
•  450 K
•  600 K

Solution:-
T_b = ΔH / ΔS = 400 K

Q10. The apparatus generally used for measuring heat changes is:

•  Voltameter
•  Voltmeter
•  Calorimeter
•  Coulometer

Solution:-
Heat measurements are made in calorimeter usually made of copper.