Basic Energy Concepts

Question 1

What is the First Law of Thermodynamics?

Answer 1

Energy can neither be created nor destroyed, only altered in form.

Question 2

What is the Second Law of Thermodynamics?

Answer 2

No engine, actual or ideal, when operating in a cycle can convert all the heat supplied it into mechanical work-heat must be rejected.

Question 3

What is Entropy?

Answer 3

S
Measure of a system’s inefficiency for doing work for a given amount of heat transferred.

Amount of energy that is wasted and unusable.

Delta S=delta Q/T(abs)

Delta s=Delta q/T(abs)

Question 4

What is the State of a substance?

Answer 4

Unique condition of a substance any every specific point. Takes into account pressure, temperature, internal energy, specific volume etc.
Any variation of any of these properties will change the state to some degree.

Question 5

What is the Phase of a substance?

Answer 5

Solid
Liquid
Gas

Question 6

Define Enthalpy.

Answer 6

H
Energy of a system that takes into account Internal energy and Flow energy.

H=U+P•V

Specific enthalpy
h=u+P•v

Question 7

List some Specific Enthalpy changes.

Answer 7

Increase in specific Enthalpy:
SG process
Pump process

Decrease in specific Enthalpy:
Turbine process
Condensing process

Processes with no change in specific Enthalpy:
Throttling-(PORV, turbine control valves)
Pressure reducing valves.

Question 8

Define Specific Heat.

Answer 8

Cp
Heat capacity of a substance is the amount of heat added/removed per unit change in temperature.

Cp=Q/delta T

c(p)=q/delta T (specific, per unit mass)
Or c(p)=Q/(m•delta T)