Food Processing Unit Operations Multiple Choice Questions & Answers (MCQs) on “Material and Energy Balances”.
1. What type of energy is considered in enthalpy balance?
a) Heat only
b) Heat and mass only
c) Mass only
d) Heat and potential energy only
Answer: a
Clarification: Enthalpy balances consider only heat energy. It is concept that is based on the first theorem of thermodynamics applied to the flow systems.
2. Which of the following is considered in a continuous process?
a) Mass balance
b) Energy balance
c) Time
d) Mass balance, energy balance and time
Answer: d
Clarification: Mass balances are fundamental to control the processing, particularly in the control of yields of the product. Energy balance is used in examination of each and every stage of a process, even extending over the total food production system from the farm to fork. The time unit is considered in continuous process in three periods. They are startup, continuous processing and close down.
3. A processing unit is producing a product of 100kg which must contain 15% of fat and this is to be made up from component A with 23% of fat and from component B with 5% of fat. What are the proportions in which these should be mixed?
a) 44.4 kg of component A to 55.6kg of component B
b) 67.87kg of component A to 32.13kg of component B
c) 55.6 kg of component A to 44.4kg of component B
d) 32.13kg of component A to 67.87kg of component B
Answer: c
Clarification: Let the proportions be X of component A to Y of component B
Then by a mass balance on the fat,
(X × 0.23)+ (Y × 0.05) = (X+Y) × 0.15
A (0.23-0.15) = B (0.15-0.05)
A (0.08) =B (0.10)
A/B= 5/9
Therefore, 100kg of product will have 55.6 kg of component A to 44.4kg of component B.
4. Are these statements about the mass balance true?
Statement 1: Total mass of the system will remain the same but the constituent’s parts may change.
Statement 2: Chemical and biological changes affect the mass balance of a unit operation.
a) True, False
b) True, True
c) False, True
d) False, False
Answer: a
Clarification: Even though chemical and biological changes occur during a process, the total mass of the system will remain the same but the constituent’s parts may change. For example, in browning reaction, the total sugars may reduce but browning compounds in that product increases leading to mass balance.
5. Which heat energy form is called as hidden energy?
a) Specific heat
b) Latent heat
c) Sensible heat
d) Radiation energy
Answer: b
Clarification: Latent heat is the also known as hidden energy. It can be defined as the heat that is released or absorbed by a system during constant temperature process called as latent heat.
6. Which of the following statements about First law of thermodynamics are correct?
Statement 1: The First Law of Thermodynamics is a statement of energy conservation.
Statement 2: Energy cannot be created or destroyed it can be converted from one form to another.
a) True, False
b) True, True
c) False, True
d) False, False
Answer: b
Clarification: Energy conservation is the main element in the First Law of Thermodynamics where the energy cannot be created or destroyed, it can be converted from one form to another. It can be transferred from body to another. It can occur by heat flow, by transport of mass or performance of work.
7. What type of energy is enthalpy?
a) Internal potential energy
b) Kinetic energy
c) Dynamic kinetic energy
d) It is not a type of energy
Answer: d
Clarification: Enthalpy is a thermodynamic quantity and is not a form of energy. It is a measure of amount of energy stored in a system which is equal to internal energy of the system plus the product of pressure and volume.
8. What are the properties to be considered for designing a unit operation equipment?
a) Only Physical properties and mechanical properties
b) Only Chemical properties and mechanical properties
c) Only Physical properties and chemical properties
d) Physical, chemical, mechanical properties
Answer: d
Clarification: Physical properties, chemical properties, mechanical properties and thermal properties are considered for designing unit operation equipment.
9. How is electric energy calculated in a unit operation?
a) Energy = power × time
b) Energy= power /time
c) Energy = power + time
d)Energy = (power × time) + pressure
Answer: a
Clarification:The total amount of the electrical energy can be calculated by multiplying total power used by the equipment and time of the electricity consumed.
10. Is heat and temperature same?
a) True
b) False
Answer: b
Clarification: Heat is the total energy of motion of molecules in a component and depends on speed and number of particles. Temperature is the measure of average energy of molecular motion in a component. It does not depend on the size or type of particle.