Chapter 16 Entropy

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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


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