Chapter 19: Thermochemistry Flashcards
second law of thermodynamics:
the pervasive tendency for energy to spread out or dissipate when not prevented from doing so
the second law determines…
spontaneous direction of all processes
spontaneous process occurs..
without outside intervention
what is the spontaneity of a reaction?
the direction in which, and the extent to which, a chemical reaction proceeds
a rxn may be thermodynamically spontaneous but kinetically BLANK at a give temp
slow
what effect does a catalyst have on a chemical rxn
the rate of a spontaneous process can be increased by a catalyst, but a nonspontaneous process can’t be made spontaneous by te use of a catalyst
thermodynamics deals with the relative chemical potentials of the BLANK and BLANK
reactants and products
how can a nonspontaneous process be made spontaneous?
by coupling the nonspontaneous rxn to another process that is spontaneous or by supplying energy from an external source
most spontaneous processes are what kind of rxns
exothermic
what type of process do you have when a highly ordered arrangement goes to a disorderly arrangement
spontaneous
entropy:
quantity related to disorder or randomness at the molecular level
sign for entropy
S
what are the units of entropy
J/K
if conditions P,V, and T remain constant, the energy of the system..
also remains constant
microstate:
exact internal energy distribution among the particles at any one instant
microstate in simpler terms:
snapshot of the system at a given instant in time
macrostate:
composed of several microstates, each with a different number of molecules and/or different arrangement of molecules
greater entropy says what about arrangment?
greater entropy means more energetically equivalent ways to arrange the components of a system
if state A is highly dispersed and state B is highly concentrated, which has the higher entropy?
state A
processes that decrease the entropy of the university occur spontaneously or nonspontaneously
nonspontaneously
entropy is what kind of function?
state function
formula for change in entropy:
change in S = Sfinal - Sinitial
chemical system proceeds in a direction that BLANK the entropy of the universe
increases
A gas has more BLANK than a solid
microstates
a change in state is accompanied by an exchange of
heat between the system and surroundings
equation for change in entropy at constant temperature
change in S = (qreverse)/T
All reversible processes are in a constant…
state of equilibrium
formula for entropy of universe:
change S universe = (change in S system) + (change S surroundings)
an exothermic process BLANK entropy of surroundings
increases
an endothermic process BLANK entropy of surroundings
decreases
The greater the temperature, the smaller the BLANK in entropy for a given amount of energy dispersed into the surroundings
increase
the higher the temperature the BLANK the impact
smaller
at low temperatures, the decrease in entropy of the system is BLANK by the large increase in the entropy of the surroundings
overcome
the change in entropy of the surroundings depends on what two things?
(a) the amount of heat transferred into or out of the surroundings
(b) the temperature of the surroundings
first law of thermodynamics:
any heat leaving the system must go into the surroundings and vice versa
A process that emits heat into the surroundings does what to the surroundings?
increases the entropy of the surroundings
A process that absorbs heat from the surroundings does what to the surroundings?
decreases the entropy of the surroundings
exothermic processes have a tendency to be spontaneous at what temperatures
low temperatures
formula for free energy:
change in G = enthalphy - T*entropy
a negative value of G corresponds to :
spontaneous process
what values of for enthalpy and entropy produce a process that is spontaneous at all temperatures?
negative H, positive S… because entropy of both system and surroundings increases
what values of for enthalpy and entropy produce a process that is not spontaneous at all temperatures?
postive H, negative S
negative H and negative S yields a spontaneous process at what temperatures
low temperatures
formula for standard entropy of rxn
Srxn = Sproducts - S reactants
third law of thermodynamics:
the entropy of a perfect crystal at absolute zero (0K) is zero
allotropes
elements that exist in two or more forms within the same state
as molar mass increases, what happens to standard entropies?
increase
allotropes that allow for more freedom of molecules have what kind of standard entropies?
greater entropies
how does increasing molecular complexity affect entropy
entropy increases
The dissolution of a crystalline solid into solution usually results in an BLANK in entropy
increase
