Thermodynamics - Chem Exam 3

spontaneous

happens by itself, without energy input

q_system

-q_surroundings

exothermity and spontaneity

exothermity is not a condition for spontaneity

if q_system is exothermic

q_surroundings must be endothermic, but both are spontaneous

product favorability and spontaneity

product favorability is not a condition for spontaneity

spontaneous processes lead to

dispersal of energy, increase in entropy of the universe

entropy (s)

measure of dispersal of energy, how random something is

∆S =

Q_rev / temp

Q_rev

the heat exchanged with a system during a process where the system remains in thermal equilibrium with its surroundings at every single moment

reversible process

can return to original state without altering surroundings

microstates

possible outcomes for energy distribution

order

all of the energy remaining on the original atom

disorder

the energy becomes spread over more atoms

more microstates

more energy dispersal, more entropy in the system

s =

K * ln(w) . k is constant, w is number of microstates

gases increase volume

leads to more microstates

irreversible processes examples

mixing gasses, mixing liquids that are miscible, dissolving a soluble solid in a liquid

at 0 degrees K, a pure, perfect crystal has (third law of thermodynamics)

s = 0

S°

standard molar entropy (entropy gained by converting 1 mol of perfect crystal at 0°K to standard conditions)

larger molecules S°

larger than smaller molecules

more complex structures S°

larger than less complex

states of matter S°

solid < liquid < gas

∆S > 0 for:

dissolving solutes in a solvent, increasing volume of a gas, increasing temperature, increasing number of moles of gas, going to a more random state (not solid)

S is a ___ function

state (only beginning and ending points matter)

∆S° of a reaction =

Σ n S°_products - Σ m S°_reactants (m and n are the coefficients)

∆S_universe

∆S_system + ∆S_surroundings

∆S_universe =

-∆H/t + ∆S°

∆H° < 0, ∆S° > 0

spontaneous at all temperatures, ∆_Suniverse is always positive

∆H° < 0, ∆S° < 0

spontaneous at low temperatures, ∆S_universe is positive at low temperatures

∆H° > 0, ∆S° > 0

spontaneous at high temperatures, ∆S_universe is positive at high temperatures

∆H° > 0, ∆S° < 0

never spontaneous, ∆S_universe is always negative