Physical Chemistry Questions and Answers – Thermodynamics Reactions

This set of Physical Chemistry Multiple Choice Questions & Answers (MCQs) focuses on “Thermodynamics Reactions”.

1. What is hydration enthalpy?
a) A reaction which forms a single compound from its constituent elements
b) When a system is in contact with an outside thermal reservoir, the change will occur slowly
c) Heat released when new bonds are made between the ions and water molecules
d) It is the average of enthalpies required to dissociate the bond
View Answer

Answer: c
Explanation: It is the enthalpy change when one mole of ions dissolve in water to give a dilute solution. It is always negative.

2. Thermodynamics is not concerned about the rate at which a reaction proceeds.
a) False
b) True
View Answer

Answer: b
Explanation: Thermodynamics is concerned with heat and temperature and their relation to heat and work. The quantities are governed by four laws.

3. Select the correct statement:
a) The presence of reactant in a thermos flask or any other closed insulated vessel is an example of closed vessel
b) There is an exchange of energy as well as matter between the system and the surroundings in a closed system
c) The presence of reacting species in a covered beaker is an example of open system
d) The presence of reactant in a closed vessel made up of copper is an example of closed vessel
View Answer

Answer: c
Explanation: Matter does not exchange with surroundings in a closed system and isn’t subject to any force whose source is external.

4. An elevator with a mass of 2500 kg rests at 10m above the base of an elevator. It is raised to 100m above the base. The elevator falls freely to the base and strikes a strong spring. Find the potential energy of the elevator, (g = 9.8 ms-2).
a) 245000 J
b) 346780 J
c) 456243 J
d) 878000 J
View Answer

Answer: a
Explanation: Given: mass = 2500 kg, height = 10m and g = 9.8 ms-2. So, by the equation of potential energy: EP1 = mz1g = (2500) (10) (9.8) = 245000 J.

5. Water flows over a height of 100m in height. Take 1kg as the water of the system. After 1kg of water enters the stream below the falls, what change has occurred in its state?
a) 985.99 J
b) 967.99 J
c) 960.59 J
d) 980.66 J
View Answer

Answer: d
Explanation: As 1kg of water strikes the bottom and mixes with other falling water to form a stream, the resulting turbulence has the effect of converting kinetic energy into internal energy. During this process, ΔEP = 0, ΔU + ΔEK = 0 or ΔU = EK2 – EK3, so, ΔU = EK2 = 980.66 J.

6. Calculate the degree of freedom in a liquid solution of alcohol in water in equilibrium with its vapor.
a) 2
b) 5
c) 3
d) 4
View Answer

Answer: a
Explanation: Here N = 2, and π = 2, and F = 2 – π + N = 2 – 2 + 2 = 2. The phase rule variables are temperature, pressure and the phase compositions.

7. For liquid acetone at 20℃ (293.15 K) and 1 bar, β = 1.487 * 10-3, k = 62 * 10-6 bar-1, v = 1.287 cm3g-1. Find the value of ((P/T) * v) at 20℃ and 1 bar.
a) 24 bar℃-1
b) 34 bar℃-1
c) 44 bar℃-1
d) 54 bar℃-1
View Answer

Answer: a
Explanation: The derivative ((P/T) * v) is determined where V is constant and d V = 0: β d T – k d P = 0 or (P/T)V = β/k = (1.487 * 10-3/62 * 10-6) = 24 bar℃-1.

8. How can a state of gas describe?
a) Temperature, amount, pressure
b) Amount, volume, temperature
c) Pressure, volume, temperature
d) Pressure, volume, temperature, amount
View Answer

Answer: d
Explanation: Gases are difficult to observe, they are described through the physical properties such as pressure, volume, temperature and amount or number of particles.

9. The enthalpy of elements at their standard states is zero. What is the enthalpy of formation of a compound?
a) Positive
b) Negative
c) Maybe positive or negative
d) Never negative
View Answer

Answer: c
Explanation: Enthalpy of formation can be positive or negative, since it takes energy to pull to pull atoms apart it is called endothermic (+) and bond formation does release energy therefore exothermic (-).

10. What is the compression ratio for petrol engines?
a) 16 to 22
b) 10 to 15
c) 8 to 10
d) 3 to 6
View Answer

Answer: c
Explanation: The compression ratio for the petrol engine is 8 to 10. The higher compression ratio of an engine has higher thermal efficiency.

Sanfoundry Global Education & Learning Series – Physical Chemistry.

To practice all areas of Physical Chemistry, here is complete set of Multiple Choice Questions and Answers.

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