Thermo Ch. 3 - Properties of Pure substances

pure substance

matter with homogenous and invariable chemical composition throughout

three phases

• solid

• liquid

• gaseous

solid phase

• closely bound and dense

• not easily deformed

• geometric in metals and amorphous in nonmetals

liquid phase

• closely bound and dense

• unable to expand to fill space

• no longer rigid - free to move

gaseous phase

• not attracted to one another

• low- variable densities

• move randomly - not fixed

phase change process

• liquid to vapor (gas)

• assuming constant pressure at all times

process of phase change from liquid to gas

1. sub-cooled/compressed liquid

2. saturated liquid

3. mixture of saturated liquid and saturated gas

4. saturated gas

5. superheated gas

critical point

saturated liquid and saturated vapor states are identical

saturation pressure

the pressure at which the liquid and vapor phases are in equilibrium at a given temperature

saturation temperature

the temperature at which the liquid and vapor phases are in equilibrium at a given pressure

pressure graph - temp and pressure

• the higher the temperature - the higher the line of constant temperature

• the lower the saturation pressure - the lower the boiling point of the saturation temperature

process to find a property not given

1. always look for 2 properties

2. determine if in liquid phase or in mixture phase or in super heated phase - then determine the phase

3. Then go to the table to get the property

reading the table - left of saturated liquid

is a liquid

reading the table in between

is a mixed liquid

reading the table - right of saturated gas

superheated

interpolation formula

y = y1 + ( (y2 - y1) / (x2 - x1) ) (x - x1)

properties of superheated gas are found

• with the tables

  • likely to have to interpolate

quality of saturated liquid - vapor mixture properties from tables

• look for pressures from temperatures

• look for temperatures from pressure

when to use the quality

when you have a mixture

volume of mixture equation

V = Vf + Vg = mf x Vf = mg x Vg

specific volume of mixture equation

• v/m = mf/m Vf + mg/m Vf

• ν = (1 - x) ⋅ Vf + x ⋅ Vg

quality of specific volume given equation

x = ( ν - Vf) / ( Vg - Vf)

quality for internal energy equation

u = (1-x) uf + x ⋅ ug

sub-cooled/ compressed liquid properties

• by temperature

• v ~= vf @ T

• u ~= uf @ T