BIEN 300 by me

specific heat at cst volume

the amount of heat required to raise the temperature of unit mass of gas through one degree, at constant volume

0th law of thermodynamics

when 2 bodys are in thermal equilibrium w a 3rd body, they are also in thermal equilibrium w eachother

intensive property of a system

does not depend on mass (temp, pressure)

entropy

disorder of a system

internal energy and enthalpy are functions of only temperature for which substance

ideal gas

1st law of thermodynamics

energy cant be created nor destroyed, only converted from one form to another

compressed liquid

liquid is not about to vaporize

saturated liquid

liquid about to vaporize

saturated vapor

vapor about to condense

superheated vapor

vapor not about to condense

saturated liquid-vapor mix

liquid and vapour are coexsisting

saturation temp

temp at which pure substance changes phase

saturation pressure

pressure at which pure substance changes phase

latent heat

amount of energy absorbed/ released during phase change

latent heat of fusion

amount of heat absorbed during melting (= amount of heat released during freezing)

latent heat of vaporization

amt of heat absorbed during vaporization (=amt heat release during condensation)

closed system

no exchange of mass, energy may cross bounds

isolated system

no exchange of mass nor energy

irreversible process (in terms of heat)

heat is lost

define a heat engine

uses heat transfer from hot reservoir to cold reservoir to extract work

change in enthalpy of a system is the heat supplied at:

constant pressure

throttling

work = 0 ; fluids pressure is reduced by passing it through a restriction

Which of the following processes are thermodynamically reversible and why

• throttling

• cst volume & cst pressure

• free expansion

• isothermic & adiabatic

TThrottling — Irreversible
Large pressure drop, entropy increases.

Free expansion — Irreversible
Expansion into vacuum, not quasi-static, entropy increases.

Constant volume / constant pressure — Not inherently reversible
Usually involve heat transfer across a finite temperature difference → entropy generation.

Isothermal and adiabatic — Reversible (only in the limiting ideal case)
Can be reversible only if no entropy is generated (idealized, quasi-static process).

what should be satisfied in order for a cycle to be reversible

No free expansion or friction-resisted processes
→ These generate entropy and make the cycle irreversible.

• When heat is absorbed, the working substance and hot reservoir must be at the same temperature
→ Heat transfer across a finite temperature difference causes irreversibility.

• When heat is rejected, the working substance and cold reservoir must be at the same temperature
→ Again, no finite temperature difference is allowed.

forced vs natural convection

mechanism of fluid motion

• Natural: relies on buoyancy forces (density diff due to temperature)

• Forced: external mechanical means to move fluid (fans/ pumps)

hfg

enthalpy of vaporization - amt of energy needed to vaporize unit of mass of saturated liq at given press / temp