Work & Heat

Question 1

Elaborate on the basic energy concepts and the role of the 1st law of thermodynamics

Answer 1

Energy cannot be created or destroyed. It can only be converted from one form to another.

Question 2

Explain how energy is transferred by heat. Is heat a property?

Answer 2

Heat transfer thermal energy from system to its surroundings or from one object to another as a result of a difference in temperature

Question 3

Define an adiabatic process and explain its differences with an isothermal process

Answer 3

Adiabatic process is a thermodynamic process that occurs without any heat transfer between a system and its surrounding

Isothermal has heat trf but adiabatic dont.
Isothermal temp is constant but adiabatic can change temp.
Isothermal work done is due to change in heat content whereas adiabatic work done is due to the change in internal energy

Question 4

Explain how energy is transferred by work. Explain why work is not a property

Answer 4

Work is done by the system when it is used to turn a turbine and thereby generate electricity in a turbine-generator. Work is done on the system when a pump is used to move the working fluid from one location to another.

Work is not a property as it is energy in transit.

Question 5

Derive a relationship for electrical work

Answer 5

Work done, W = QV
P = W/t
P = V/t
V = IR
P = Q/t * IR

Energy = Pt
= I^2 * R * t
= V^2/R *t

Question 6

Explain the general relationship for moving boundary work using a typical piston-cylinder device and a P-v diagram

Answer 6

A

Question 7

Derive the relationship for moving boundary work for the following 
> constant vol
> constant pressure process
> isothermal process for ideal gas
> polytropic proces

Answer 7

H

Question 8

Elaborate on the definition of the 1st law of thermodynamics for a closed system and show the derived energy balance

Answer 8

W