250+ TOP MCQs on Thermodynamics – Measurement of ∆U and ∆H: Calorimetry and Answers

Chemistry Multiple Choice Questions on “Thermodynamics – Measurement of ∆U and ∆H: Calorimetry”.

1. Bomb calorimeter is __________ in nature.
a) isothermal
b) isochoric
c) isobaric
d) absolute
Answer: b
Clarification: ABomb calorimeter works at constant volume, so it is isochoric in nature. Here, the heat energy that’s measured is only the internal energy. The work done is zero because of no change in volume.

2. If an exothermic reaction occurs in a Bomb calorimeter then the temperature of the water bath ________
a) increases
b) decreases
c) remains constant
d) cannot predict
Answer: a
Clarification: In a Bomb calorimeter, the reaction occurs in a vessel and that is surrounded by the water bath. If it is an exothermic reaction the temperature rises and if it is an endothermic reaction the temperature decreases. Temperature can be measured using a thermometer.

3. Heat capacity of a Bomb calorimeter is given by _______
a) C_V
b) C_P
c) C_M
d) C_B
Answer: a
Clarification: A bomb calorimeter operates at a constant volume i.e. it is an isochoric process. So the heat capacity is C_V which represents heat capacity at constant volume. While C_P represents heat capacity at constant pressure.

4. Bomb calorimeter is used to determine ____________
a) molar heat capacity
b) heat of combustion
c) rate kinetics
d) affinity
Answer: b
Clarification: A bomb calorimeter is used to measure the heat of combustion of a reaction. It has to withstand a large amount of pressure, in order to determine the heat of combustion. It is an isochoric process and the heat energy is equal to the internal energy.

5. “c” the specific heat capacity of a substance is given by temperature difference is given by ΔT and the heat energy is given by Q then what is the mass of the substance?
a) Q/cΔT
b) cΔT /Q
c) QcΔT
d) QΔT
Answer: a
Clarification: Heat energy of a substance is denoted by Q and is given by the expression mcΔT, where m is a mass of the substance, c is a specific heat capacity and ΔT is temperature difference, so the mass of the substance is Q/cΔT.

6. During the process of conversion of ice into the water, the specific heat capacity is given by _______
a) 0
b) positive
c) infinity
d) negative
Answer: c
Clarification: During the phase change of a substance the temperature change is zero. As we know that specific heat capacity = Q/cΔT which is zero; specific heat capacity becomes infinity, so during the process of conversion of ice into the water, the specific heat capacity is infinity.

7. What is the value of specific heat capacity in the adiabatic process?
a) 0
b) infinity
c) positive
d) negative
Answer: a
Clarification: During an adiabatic process the change in total energy is zero, As we know that the specific heat capacity is given by the total heat required by mass X change in temperature, heat energy is zero the specific heat capacity becomes zero.

8. When 1 kg of water at 373 k, is converted into steam how much amount of heat energy is required?
a) 22600 KJ
b) 226 KJ
c) 2260 KJ
d) 22.6 KJ
Answer: c
Clarification: The latent heat of vaporization of water is 2260 KJ/Kg. The heat that is required to convert water at 373 k to steam is given by Q = mL, where m = mass of the water and L = latent heat vaporization of water; heat energy required = 1 kg x 2260 KJ/Kg = 2260 KJ.

9. The total heat energy utilized for increasing the temperature by 4 degrees Kelvin in a 3 kgs substance is 100 KJ what is the specific heat capacity of that substance?
a) 8.34 KJ/g-k
b) 8.34 KJ/Kg-k
c) 8.34 KJKg-k
d) 8.34 KJ/Kg
Answer: b
Clarification: The formula of heat energy is given by the expression: Q = mcΔT, m is the mass of the substance, c is the specific heat capacity and ΔT is the temperature difference. c = Q/mΔT; c = 100KJ/3kg(4k) = 8.34 KJ/Kg-k.

10. The enthalpy, internal energy during a process and change in volume are 500 units, 400 units, and 2 units. What is the pressure that is exerted on the gas during this process?
a) 20 units
b) 80 units
c) 100 units
d) 50 units
Answer: d
Clarification: We know that ΔH = ΔU + PΔV; ΔH is the enthalpy, ΔU is the internal energy, ΔV is the change in volume and P is the pressure. So by substituting the enthalpy, internal energy during a process and change in volume as 500 units, 400 units and 2 units, we get pressure as 50 units.