Thermodynamics - L6 - Entropy

h gen chem 1

spontaneous change

a change that has a tendency to happen without needing to be driven by doing work

example of a spontaneous change

a hot metal block cooling to reach same temperature as surroundings

reverse of a spontaneous reaction

is non spontaneous

spontaneous does not equal

fast

spontaneous does equal

a natural tendency to occur

a nonspontaneous change in a system can be brought about only by

doing work on the system

entropy

measure of disorder

low entropy

little disorder

high entropy

high disorder

second law of thermodynamics states that 

a spontaneous change is accompanied by an increase in the total entropy of the system and its surroundings

the entropy of an isolated system

increases in the course of any spontaneous change

entropy is

a state function

positional disorder

the disorder related to the location of the molecules

thermal disorder

the disorder arising from the thermal motion of the molecules

normal melting point

the temperature at which a solid melts when pressure is 1 atm

normal boiling point

temperature at which a liquid boils when pressure is 1 atm

when pressure is 1 bar

these transition temperatures are called the standard melting point and the standard boiling point

at the transition temperature

the temperature of a substance remains constant as heat is supplied

at the temperature of a phase transition

the transfer of heat is reversible

because the transition takes place at a constant pressure

the heat supplied is equal to the change in enthalpy of the substance

entropy of vaporization

the change in entropy per mole of molecules when a substance changes from a liquid to a vapor

troutons rule

standard entropies of vaporization of a number of liquids are close together

if a liquid doesnt obey troutons rule

the molecules have a more orderly arrangement, making a greater change of disorder when vaporized