L.12 Gibbs Free Energy

Question 1

How is a system classified?

Answer 1

It is the matter being observed and it is based on

what is or is not being exchanged with the surroundings

Question 2

Isolated System

Answer 2

NO EXCHANGE in HEAT WORK or MATTER

Question 3

Closed System

Answer 3

Exchange in HEAT & WORK

but

NOT MATTER

Question 4

Open System

Answer 4

Exchange of Work Heat and Matter

Question 5

Definition of undergoing a process

Answer 5

When a system undergoes a change in one or more of its properties

Concentration, Temperature or Pressure

also known as,

CHANGE OF STATE of SYSTEM

Question 6

First Law of Thermodynamics

Answer 6

The total energy of an isolated system is constant;

energy can be transformed from one form to another but can be neither created nor destroyed.

∆U = Q - W

The internal energy of system = heat added to the system - work done BY the system

W = work = changes in pressure and volume

Question 7

Four processes characterized by a single constant property.

Answer 7

1. Isothermal
2. Adiabatic
3. Isobaric
4. Isovolumetric (isochoric)

Question 8

Isothermal Process

Answer 8

∆U = Q - W

Temperature is Constant

The total energy of the system is constant

∆U = 0, then Q = W

The heat added to the system is equal to the work done by the system

Question 9

Adiabatic Process

Answer 9

∆U = Q - W

Constant heat/ no heat exchange with the environment

Q = 0, then ∆U = - W

The change in internal energy is equal to the work done ON the system

Question 10

Isobaric Process

Answer 10

∆U = Q - W

No change in pressure/pressure is constant

The slope of Line = 0 in the pressure-volume graph

Question 11

Isovolumetric Process

Answer 11

∆U = Q - W

Volume is constant, gas neither expands or compresses

W = 0, the ∆U = Q

The change in internal energy is equal to the heat added to the system

Question 12

What is a State Function?

Name all 8 State Functions & 2 Process Functions

Answer 12

State Function

1. Density
2. Pressure
3. Temperature
4. Internal Energy U
5. Gibbs Free Energy
6. Entropy
7. Enthalpy
8. Volume

Process Function

1. Work W
2. Heat Q

Question 13

Standard Conditions

vs

STP

Answer 13

Standard Conditions

1 atm, 25C/ 298K/ 77F

Gibbs free energy, Enthalpy & Entropy

(Kinetics, Thermodynamics & Equilibrium)

STP for IDEAL GAS Problems

0C/273/32F

Question 14

The Standard State of an Element

Answer 14

is its most prevalent form under standard conditions; standard enthalpy, entropy and free energy are all calculated under standard conditions.

H2 gas

H2O liquid

NaCl solid

O2 gas

C solid, graphite

Question 15

Temperature

Answer 15

Temperature: Scaled measure of the Average Kinetic Energy of molecules of a substance

Question 16

Fusion & Freezing

Answer 16

Fusion/Melting &

Freezing/Crystalization/ solidification

Occur at the interface of solid and gas phase

Question 17

Vaporization & Condensation

Answer 17

Vaporization

• Occurs only above boiling Point
• The ambient pressure is equal to the pressure of the liquid

Condensation

• Forcing gas back into the liquid phase

Question 18

Sublimation & Deposition

Answer 18

Sublimation = Solid into Gas

Deposition = Gas into Solid

Question 19

Critical Point & Triple point

Answer 19

At temperatures above the critical point, all three phases are indistinguishable

At the triple point, all three phases of matter exist in equilibrium

Question 20

Amorphous solid

Answer 20

In condensed matter physics and materials science, an amorphous or non-crystalline solid is a solid that lacks the long-range order that is characteristic of a crystal.

Melts at large range of Temperatures

Question 21

Phase Diagram

Answer 21

Question 22

Heat

Answer 22

Heat is the transfer of energy that results from differences of temperature between two substances

Heat Q

Endothermic = Absorbs Heat

Exothermic = Releases Heat

∆H = Q at Constant Pressure

Heat Is transferred From Warmer Substances —-> To Cooler Ones

Question 23

Enthalpy

Answer 23

Is a measure of the potential energy of a system found in intermolecular attractions and chemical bonds

Heat changes at Constant Pressure (state function)

∆H rxn = ∆H products - ∆H reactants

Positive Change = Endothermic

Negative Change = Exothermic

The heat content of a system undergoing heating, cooling, or phase changes is the sum of all the respective energy changes.

Question 24

Hess’s Law

Answer 24

States that the total change in potential energy of a system is equal to the changes of potential energies of the individual steps of the process.

Enthalpy changes of a reaction are additive

(switch signs when adding reactions/flipping them)

Enthalpy can also be calculated using heats of formation, heats of combustion, or bond dissociation energies.

Question 25

Entropy

Answer 25

Is a measure of the degree to which energy has been spread throughout a system or between a system and its surroundings.

• is a ratio of heat transferred per mole unit Kelvin
• is maximized at equilibrium

∆S = Qrev / T

Question 26

Second Law of Thermodynamics

Answer 26

The Second Law of Thermodynamics is commonly known as the Law of Increased Entropy.

Energy is spontaneously dispersed if it’s not hindered - at a specific Temperature.

∆Suniverse = ∆Ssystem - ∆S surroundings > 0

While quantity remains the same (First Law), the quality of matter/energy deteriorates gradually over time.

How so? Usable energy is inevitably used for productivity, growth, and repair. In the process, usable energy is converted into unusable energy. Thus, usable energy is irretrievably lost in the form of unusable energy.

Question 27

Third Law of Thermodynamics

Answer 27

The Third Law of Thermodynamics refers to a state known as “absolute zero.” This is the bottom point on the Kelvin temperature scale. The Kelvin scale is absolute, meaning 0° Kelvin is mathematically the lowest possible temperature in the universe. This corresponds to about -273.15° Celsius, or -459.7 Fahrenheit.

Nothing can exist after this point

Question 28

Standard Heat of Formation

Standard Heat of Reaction

Answer 28

• Enthalpy required to form 1 mole of compounds from its elements under standard conditions
• Enthalpy changes of a reaction carried under standard conditions

Question 29

Bond Dissociation Energy

Answer 29

Breaking a particular bond between atoms in the gas phase

Bond Breaking = Endothermic

Bond Forming = Exothermic (becoming more stable)

KJ/mol of bonds broken

Question 32

Gibbs Free Energy

Answer 32

The change is Gibbs free energy determines if a process will be spontaneous or non-spontaneous.

∆G = ∆H - T∆S

∆H ∆S OUTCOME

+ + Spontaneous at HIGH T

+ - Non-spontaneous at ALL T

• • Spontaneous at ALL T
• • Spontaneous at LOW T

Question 33

Kinetics vs Thermodynamics

Answer 33

Sometimes the thermodynamically favored/stable product will have high activation energy, therefore will have slower kinetics.

Question 34

Standard Gibbs Free energy from Equilibrium Constant

Answer 34

∆G* rxn = -RT ln K_eq

Standard free energy change = - ideal gas constant ln (equilibrium constant)

When in Process

∆G rxn = ∆G* rxn​ + RT ln Q = RT ln Q/Keq

Q/Keq < 1 (spontaneously move forward)

Q/Keq > 1 (spontaneously move backward)

Q/Keq = 1 (equillibrium)

Question 35

Equations for

Heat Transferred during phase change

Heat Transferred during no phase change

Answer 35

q = mc∆T

q =mL (latent heat)