Thermodynamics Quiz-13

Thermodynamics Quiz-13

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. The amount of heat measured for a reaction in a bomb calorimeter is

•  ΔG
•  ΔH
•  ΔE
•  pΔV

Solution:-
Bomb calorimeter measures q_v, which is equal to ΔE.

Q2. The standard heat of formation of NO₂(g) and N₂O₄(g) are 8.0 and 2.0 kcal/mol respectively. The heat of dimerization of NO₂ in kcal is:

•  10.0
•  −6.0
•  −12.0
•  −14.0

Solution:-

Q3. Which reaction is endothermic in nature ?

•  CaCO₃ → CaO + CO₂
•  C + O₂ → CO₂
•  NaOH + HCl → NaCl + H₂O
•  CH₄ + 2O₂ → CO₂ + 2H₂O

Solution:-
Decomposition of CaCO₃ is made on heating.

Q4. The work done in an open vessel at 300 K, when 112g iron reacts with dil. HCl is :

•  102 kcal
•  0.6 kcal
•  0.3 kcal
•  0.2 kcal

Solution:-

Q5. Joule-Thomson expansion is

•  Isobaric
•  Isoenthalpic
•  Isothermal
•  None of these

Solution:-
Isoenthalpic

Q6. Heat of formation of H₂O(g) at 1 atm and 25°C is −243 kJ. ΔU for the reaction,
  H₂(g) + 1/2 O₂(g) → H₂O(g) at 25°C is :

•  241.8 kJ
•  −241.8 kJ
•  −243 kJ
•  243 kJ

Solution:-
  ΔH = ΔU + ΔnRT
  Δn = − 1/2
  ∴   −43 = ΔU + (−1/2) × 8.314 × 298 × 10⁻³
  ∴ ΔU = −241.76 kJ

Q7. Diborane is a potential rocket fuel which undergoes combustion according to equation :
  B₂H₆(g) + 3O₂(g) → B₂O₃(g) + 3H₂O(g)
  Calculate the enthalpy change for the combustion of diborane. Given :

•  +2035 kJ/mol
•  −2035 kJ/mol
•  +2167 kJ/mol
•  −2167 kJ/mol

Solution:-
  For the equation
    B₂H₆(g) + 3O₂(g) → B₂O₃(g) + 3H₂O
  eq.(i) + 3(ii) + 3(iii) − (iv)
  ΔH = −1273 + 3(−286) + 3(44) − 36
  = −2035 kJ/mol

Q8. In a closed insulated container a liquid is stirred with a paddle to increase the temperature, which of the following is true ?

•  ΔU + W ≠ 0 , q = 0
•  ΔU = W = q ≠ 0
•  ΔU = 0, W = q ≠ 0
•  W = 0, ΔU = q ≠ 0

Solution:-
For insulated container, q = 0.

Q9. C(s) + O₂(g) → CO₂(g),   ΔH = −393.5 kJ and
  CO(g) + 1/2 O₂(g) → CO₂(g),   ΔH = −283.5 kJ
  then the heat of formation of CO is :

•  −110.0 kJ
•  +676.5 kJ
•  −676.5 kJ
•  +110.0 kJ

Solution:-
  C(s) + O₂(g) → CO₂(g);     ΔH = −393.5 kJ
  CO(g) + 1/2 O₂(g) → CO₂(g);     ΔH = −283.5 kJ
  On subtracting,   C(s) + 1/2 O₂(g) → CO(g);     ΔH = −110.0 kJ

Q10. Equal volume of 1M HCl and 1M H₂SO₄ are neutralised by dil. NaOH solution and x and y kcal of heat are liberated respectively. Which of the following is true ?

•  x = y
•  x = 0.5y
•  x = 0.4y
•  None of these

Solution:-
  1M H₂SO₄ = 2 eq. H₂SO₄
  1M HCl = 1 eq. HCl
  Thus, for equal volume of two acids to be neutralized separately with NaOH, heat evolved will be twice in case of H₂SO₄ to that of HCl.