CHEM 2P03 Test 1

0th Law of Thermodynamics

0th Law of Thermodynamics

if two thermodynamic systems each are in thermal equilibrium with a third, then they are in thermal equilibrium with each other

temperature

a property that determines the direction of heat flow when an object is in contact with another object

internal energy (U)

kinetic energy + potential energy

ideal gases

have no interactions between particles; the internal energy is only a function of temperature and not a function of pressure or volume

variables of state

depend on the state of the system and not how the system arrived at that state

variables of state examples

pressure, volume, temperature, internal energy

work (w)

ordered kinetic energy, no entropy component, high quality

heat (q)

disordered kinetic energy, entropy component, low quality

transfer of internal energy

delta U = q + w

exothermic process

q < 0; heat leaves the system

endothermic process

q > 0; heat enters the system

1st Law of Thermodynamics

energy is conserved; the total energy of the system and the surroundings is constant

isothermal

constant temperature (delta T = 0)

isochoric

constant volume (deltaV = 0, w = 0)

isobaric

constant pressure (deltaP = 0)

adiabatic

no heat is transferred (q = 0)

cyclic

no change in state variables (final state = initial state)

intensive variables of state

independent of the amount of material (eg. pressure, temperature, specific and molar heat capacity, density)

extensive variables of state

proportional to the amount of material (eg. volume, mass, internal energy, entropy, heat capacity)

isothermal expansion of ideal gases

qT OR wT

Cv

heat capacity at a constant volume

Cv of a monoatomic gas

3/2R

Cv of a diatomic gas (small)

5/2R

Cv of a diatomic gas (large)

7/2R

Cv of a linear polyatomic gas

5/2R

Cv of a non-linear polyatomic gas

3R

isobaric expansion of ideal gases

qP OR wP

liquid/solid energy and enthalpy

deltaU approx. equal to deltaH; Cp

standard enthalpy per mole

the enthalpy of formation of 1 mol of the compound at 1 bar pressure from its elements in their standard states

adiabatic reversible expansion

use Cvln(T2/T1) = -Rln(V2/V1)

real gas law A term

accounts for attractive forces between molecules

real gas law B term

accounts for the intrinsic volume of gas molecules

Joule-Thomson Experiment

measuring the temperature of a gas (T1, T2) before and after it expands from P1 to P2 through a porous plug

Joule-Thomson coefficient for ideal gases

0

Joule-Thomson coefficient for real gases

depends on changes in internal energy during expansion caused by intermolecular interactions

Carnot Cycle 1 to 2

isothermal reversible expansion; top left-right curve

Carnot Cycle 2 to 3

adiabatic reversible expansion; right up-down curve

Carnot Cycle 3 to 4

isothermal reversible compression; bottom right-left curve

Carnot Cycle 4 to 1

adiabatic reversible compression; left down-up curve

efficiency

1 - (Tcold/Thot)