Chapter 16 Entropy
A process at constant T and P is spontaneous in the direction where free energy decreases - satisfies the second law of thermodynamics
(∆G<0)
Law of Thermodynamics
- Energy can be neither created nor destroyed" - Total energy is constant, but various forms of energy can be interchanged in physical and chemical processes
Entropy
- Thermodynamic function that describes the number of arrangements (positions/energy levels) available to a system existing in a given state - Closely associated with probability - More ways a particular state can be achieved leads to a greater likelihood of finding that state (increased probability!)
positional probability
-Depends on the number of configurations in space that yield a particular state -Gas expands into vacuum in a uniform distribution because expanded state has the highest positional probability (largest entropy)
Achieving the maximum work available from a spontaneous process can occur only via a hypothetical pathway. Any real pathway wastes energy. •i.e. all real processes are irreversible processes
Achieving the maximum work available from a spontaneous process can occur only via a hypothetical pathway. Any real pathway wastes energy. •i.e. all real processes are___
In thermodynamics, it is the change is a certain function that is important
Change in enthalpy determines whether a reaction is exothermic or endothermic •Change in free energy allows us to determine is a process is spontaneous at constant temperature and pressure
heat flow
Entropy changes of surroundings is determined by ___
Entropy changes of surroundings is determined primarily by heat flow
Entropy changes of surroundings is determined primarily by ____
positional probability
Entropy changes of system determined by ___
Entropy is a measure of disorder or molecular randomness
Entropy is a measure of ___ or __
For irreversible processes that is spontaneous, the entropy change is positive (the universe is different after the process occurs) •Work is changed to heat in surroundings and entropy increases •Heat = wasted energy
For ___ processes that is spontaneous, the entropy change is positive (the universe is different after the process occurs) •Work is changed to heat in surroundings and entropy increases•Heat = wasted energy
For a reversible process, the universe is unchanged (entropy change is zero)
For a ___ process, the universe is unchanged (entropy change is zero)
For a non-spontaneous process, the value of ∆G tells us the minimum amount of work that must be expended to make the process occur
For a non-spontaneous process, the value of ∆G tells us the minimum amount of work that ___
Positional probability -Compare # of molecules for reactants vs. products - Fewer molecules means fewer configurations
How do we predict the sign for∆S sys for the system of a chemical reaction?
In any spontaneous process there is always an increase in the entropy of the universe
In any spontaneous process there is always an ___
K=e^-∆G/RT
K formula (rearranged)
First law of entropy
Law of Conservation of Energy, states that energy cannot be created or destroyed in an isolated system
Must take entropy of system AND surroundings into account to determine spontaneity of a process from entropy
Must take entropy of __ AND ___ into account to determine spontaneity of a process from entropy
(products/reactants) don forget the coefficients
Q (in the equation)
Remember that we can describe heat flow using enthalpy,∆H
Remember that we can describe heat flow using ...
molecular motion
Temperature is a measure of ___
The driving force for a spontaneous process is an increase in entropy of the universe
The driving force for a spontaneous process is an increase in ____
The maximum possible useful work obtainable from a process at constant temperature and pressure is equal to the change in free energy
The maximum possible useful work obtainable from a process at constant temperature and pressure is equal to _____
higher
The more freedoms of motion leads to____ entropy
The total free energy decreases as the reaction proceeds spontaneously in the forward direction.
The total free energy decreases as the reaction proceeds spontaneously in the ___ direction. - (When it is mostly reactants)
The total free energy decreases as the reaction proceeds spontaneously in the reverse direction
The total free energy decreases as the reaction proceeds spontaneously in the _____ direction - When is is mostly products
Thermodynamics can tell us the direction a process will occur but will say nothing about the speed
Thermodynamics can tell us the ____will occur but will say nothing about the speed
Thermodynamics considers ONLY the initial and final states, not pathways
Thermodynamics considers ONLY the ____, not pathways
Thermodynamics lets us predict whether a process will occur, but notabout the amount of time required for the process
Thermodynamics lets us predict ____ will occur, but not about the amount of time required for the process
Transfer of energy to surroundings at greater temperature will change the molecular motion by a smaller percentage than transferring the same amount of energy to a system at low temperature
Transfer of energy to surroundings at ____ temperature will change the molecular motion by a ____ percentage than transferring the same amount of energy to a system at low temperature
1. The sign of ∆S surr depends on the direction of heat flow -Exothermic cause heat to flow into the surroundings, increasing random motion thus ∆S surris positive (increase in entropy) - Endothermic reaction causes heat to leave the surroundings, decreasing random motion, thus ∆S surr is negative (decrease entropy) 2. The magnitude of ∆S surr depends on the temperature -∆S surr is inversely dependent on temperature -The tendency for a system to lower its energy is more important driving force a low temperatures
Two key characteristics of entropy changes for the surroundings:
∆S surr =-∆H/T
We can describe entropy of the surroundings in terms of enthalpy
We must consider atoms and molecules not just in the system but also in the surroundings
We must consider _____ not just in the system but also in the surroundings
∆G can tell us whether a particular reaction is spontaneous under standard conditions
What does ∆G tell us?
Temperature and entropy changes in surroundings
___ and _____ changes in surroundings
equilibrium point occurs at the lowest value of free energy available to the reaction system
equilibrium point occurs at the___ value of free energy available to the reaction system
for a spontaneous process ∆G represents the amount of energy that is free to do useful work
for a spontaneous process ∆G represents the amount of energy that is ___
Endothermic
heat flows from surroundings into the system
Exothermic
heat flows into surroundings from system
then K is greater than 1 products are favored
if ∆G is negative then
then K is less than 1 reactants are favored
if ∆G is positive then
Free energy, G
is another thermodynamic function related to spontaneity that becomes especially useful when discussing temperature dependence
Third law of Entropy
states that the entropy of a system approaches a constant value as the temperature approaches absolute zero.
Second law of Entropy
states that the total entropy of an isolated system can never decrease over time. - increasing
∆S univ> 0
the entropy of the universe increases and the process is spontaneous
∆S univ< 0
the process does not have a tendency to occur and the system is at equilibrium
∆S univ
to predict whether a process will be spontaneous, we must know the sign of...
A spontaneous process
without outside intervention (does not require energy input) - can be fast or slow
standard or nonstandard, the free energy change can be found this way:
∆G =∆Gdegrees + RTlnQ
coefficients (products)- coefficient(reactants)
∆G and ∆S using the same formula
∆H-T∆S
∆G formula
The reaction is spontaneous.
∆G< 0
not spontaneous
∆G> 0
For an exothermic process:
∆S surr = + quantity of heat (J)/temperature (K)
For an endothermic process:
∆S surr = - quantity of heat (J)/ temperature (K)
-∆G/T
∆Suniv formula
