Topic 10. Introduction to Energy Balance

Adiabatic system

A system that does not exchange heat with the surroundings during the process.

Isobaric system

A system in which the pressure is constant during a process.

Isochoric system

A system in which the volume is invariant during a process.

Isothermal system

A system in which the temperature is invariant during a process.

Path function

Any function whose value depends on how the process takes place and can differ for different histories.

State function

Any function whose value depends only on the state of the system and not upon its previous history.

Open system

A system where both mass and energy can cross the boundaries.

Closed system

A system where no mass crosses the system boundaries, but energy can cross.

Isolated system

A system where neither mass nor energy crosses the boundaries. Completely cut off from the surroundings.

Law of Conservation of Energy

Energy cannot be created nor destroyed.

Heat or Work

Energy is transferred in the form of either ?

Heat

The form of energy that is transferred between systems or a system and its surroundings due to a temperature difference.

Conduction

It is the transfer of heat through a solid material (or between solids in direct contact) without any movement of the material itself. (Mechanism: vibration of particles)

Convection

It is the transfer of heat through a fluid (liquid or gas) due to the bulk movement of the fluid itself.

Radiation

It is the transfer of heat in the form of electromagnetic waves without the need for a medium.

Q=mc∆T

The common equation for heat.

Work

The energy transferred across the boundary of a system due to a force acting through a distance.

Mechanical Work

The work due to the mechanical (moving) force.

Electrical work

The work due to the moving electrical current through the electrical resistance in the circuit.

Shaft work

The work due to the rotational motion of the shaft against an external mechanical resistance.

Flow work

The work due to the movement of fluid at the system.

Kinetic Energy (KE)

It is the energy due to the motion of the body.

Potential Energy (PE)

A form of energy that the system possessed due to its position in a force field, typically a gravitational or electrical field.

Internal Energy (ΔU)

It is the total energy contained within a system due to the microscopic motions and interactions of its molecules, atoms, and subatomic particles.

∆U=Q-W

The internal energy equation.

Heat Capacity (C)

The amount of heat energy required to raise the temperature of a substance (or system) by one degree.

Sensible heat

It is the amount of heat added or removed from a substance that changes its temperature without causing a phase change.

Latent heat

It is the amount of heat added or removed from a substance that causes a phase change without changing its temperature.

Enthalpy (ΔH)

The total heat content of a system is equal to the sum of its internal energy and the product of its pressure and volume (work).

4.184 J

I cal = ____ J ?

0.1 MPa

I atm = ____ MPa ?