Thermodynamics Quiz-15

Thermodynamics Quiz-15

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. Assuming that water vapours are ideal gas. The change in internal energy(ΔU) when 1 mol of water is vaporized at 1 bar pressure and 100°C. (Given molar enthalpy of vaporization at 1 bar and 373 K is 41 kJ/mol and R = 8.3 J mol^-1K^-1) will be:

•  41.00 kJ/mol
•  4.100 kJ/mol
•  3.7904 kJ/mol
•  37.904 kJ/mol

Solution:-

Q2. The heat evolved in the combustion of methane is given by the following equations

    CH₄(g) + 2O₂(g) → CO₂(g) + H₂O(l);   ΔH = −890.3 kJ
  How many grams of methane would be required to produce 44.15 kJ of heat of combustion?

•  4 g
•  8 g
•  12 g
•  16 g

Solution:-
CH₄ required = (445.15 × 16)/890.3 = 8g

Q3. The value of ΔH and ΔS for the reaction
    C_(graphite) + CO₂(g) → 2CO(g)
  are 170 kJ and 170 J/K respectively.This reaction will be spontaneous at:

•  510 K
•  710 K
•  910 K
•  1110 K

Solution:-

Q4. Absorption of gases on solid surface is generally exothermic because

•  Enthalpy is positive
•  Entropy decreases
•  Entropy increases
•  Free energy increases

Solution:-
Due to randomness of particles is reduced since, entropy decreases

Q5. When the change of entropy is greater, then the ability for work is:

•  Maximum
•  Minimum
•  Medium
•  None of these

Solution
The change ΔS will be more and the q or W will be more because ΔS = q/T and work depends on q.

Q6. A container has hydrogen and oxygen mixture in ratio of 4 : 1 by weight, then:

•  Entropy of these gases increase
•  Internal energy increases
•  Internal energy of the gas decreases
•  Entropy of the gases decreases

Solution:-
On mixing gases entropy increases due to increase in disorderness.

Q7. The heat of combustion of methane is −880 kJ/mol. If 3.2g of methane is burnt:

•  −176 kJ of heat is evolved
•  176 kJ of heat is absorbed
•  88 kJ of heat is evolved
•  None of the above

Solution:-
Heat evolved during combustion of 3.2g CH₄
= −(880×3.2) / 16 = −176 kJ

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

•  ΔE = W ≠ 0, Q = 0
•  ΔE ≠ 0, W = Q = 0
•  ΔE = W = Q = 0
•  ΔE = 0,W = 0, Q ≠ 0

Solution:-
As the system is closed and insulated, no heat enter or leave the system i.e. q = 0
∴ ΔE = q + W = W

Q9. A solution of 500 mL of 2M KOH is added to 500 mL of 2M HCl and the mixture is well shaken. The rise in temperature T₁ is noted. The experiment is then repeated using 250 mL of each solution and rise in temperature T₂ is again noted. Assume all heat is taken up by the solution:

•  T₁ = T₂
•  T₁ is two times as larger as T₂
•  T₂ is twice larger as T₁
•  T₁ is 4 times as larger as T₂

Solution:-
No doubt, heat evolved in first process is twice to second but volume absorbing this heat is also twice in comparison to first.

Q10. The enthalpy of formation of ammonia gas at 298 K is −46.11 kJ/mol. The equation to which this value relates is:

•  1/2N₂(g) + 3/2H₂(g) → NH₃(g)
•  N(g) + 3H(g) → NH₃(g)
•  N₂(g) + 3H₂(g) → 2NH₃(g)
•  1/2N₂(g) + 3/2H₂(g) → NH₃(l)

Solution:-