Thermochem Flashcards
Path functions vs state functions
Path = consider route taken (ex heat and work)
state = path is insignificant, only start and end points matter (ex pressure, enthalpy, internal energy)
what is entropy
the measure of disorder/randomness of a system AKA the number of microstates
what are microstates
the given instantaneous combination of position and energy of all molecules among the available energy levels
how do # of microstates and entropy relate
greater # of microstates -> greater entropy of the system
what does # of microstates represent
of unique combinations of molecules in containers/energy states
sign of entropy change
can be positive or negative
- increases come from greater freedom of movement
what is the second law of thermodynamics
for a spontaneous process in a closed system, entropy of the system increases OR entropy of the universe is always increasing
list the phases of matter in order of increasing entropy
solid, liquid, gas
how to increase entropy
phase change, increase temperature of substance or increase # of molecules following a chem rxn
how are entropy and heat related
heat is a disorganized transfer of energy (much more than work)
- entropy is directly related to heat transfer as long as it is reversible
what is standard molar entropy
the absolute entropy of 1 mole of a substance at its standard temp (non-zero for all substances other than pure crystal)
what is a spontaneous change
Occurs without an outside intervention
what must the reverse reaction of a spontaneous process be?
non-spontaneous - can only occur with outside help
how does spontaneity relate to speed
it doesn’t, only describes reaction direction, not speed
how do spontaneous processes relate to entropy change
always increases the dS univerise
dS universe > 0
spontaneous
dS universe < 0
non-spontaneous
dS = 0
at equilibrium and a reversible process
gibbs free energy
energy available/free to do work in a process
- describes spontaneity
dG < 0
spontaneous, exergonic reaction
dG>0
non-spontaneous, endergonic reaction
+dS, +dH
spontaneous only at high temperatures
+dS, -dH
always spontaneous
-dS, + dH
never spontaneous
-dS. -dH
only spontaneous at low temperatures
when is spontaneity entropically driven?
+ dH with a very neg -TdS
when is spontaneity enthapically driven
-ve dH that is too neg to overcome with a positive TdS
what is Q
the reaction quotient = describes relative amounts of reactants and pressure in a mixture
what are coupled reactions
non-spontaneous reactions driven by temperature or pressure changes, using spontaneous reactions to drive the next one
nonspontaneous -> spontaneous -> spontaneous
