Entropy, Enthalpy, Gibbs Free Energy

+ ΔS (system), + ΔS (surroundings), + ΔS (universe)

Spontaneous

- ΔS (system), - ΔS (surroundings), - ΔS (universe)

Non-spontaneous (rxn will occur in opposite direction)

+ ΔS (system), - ΔS (surroundings)

Only spont. if ΔS (sys) has a larger magnitude than ΔS (surr)

- ΔS (system), + ΔS (surroundings)

Only spont. if ΔS (sys) has a smaller magnitude than ΔS (surr)

+ ΔH, - ΔS, + TΔS, + ΔG

Non-spontaneous

- ΔH, + ΔS, - TΔS, - ΔG

Spontaneous

- ΔH, - ΔS, + TΔS, +/- ΔG

Spont. at low temps, nonspont. at high temps

+ ΔH, + ΔS, -TΔS, +/- ΔG

Spont. at high temps, nonspont. at low temps

What is enthalpy?

The heat transferred from a particular process

What is entropy?

The change in disorder of a physical or chemical process, measured in J/mol K

Substances with _____ disorder are more likely to interact than substances with _____ disorder

high disorder; low disorder

The universe prefers systems with ____ entropy

with high entropy

Equation for entropy

Sum of entropy of reactants - sum of entropy of products

What happens as you transition from the solid, to liquid, to gas phase?

You increase entropy as disorder increases; delta S >0 (+delta S)

What happens when you transition from a gas, to a liquid, to a solid?

You decrease entropy because disorder decreases; delta S<0 (-delta S)

What is thermodynamically favorable?

Processes that occur without outside intervention or help —> spontaneous reactions

if delta G < 0 (-delta G) then

the reaction is favorable( no external effect is required)

if delta G > 0 (+delta G) then

the reaction is unfavorable (external effect is required)

if delta G = 0 then

the reaction is at equilibrium

First equation for delta G

delta H - T * delta S

Second equation for delta G reaction (given G of each substance)

sum of delta G of products - sum of delta G of reactants

When is a reaction ALWAYS favorable(- delta G)?

When it is exothermic (-delta H) that increases disorder (+delta S)

When is a reaction NEVER favorable(+ delta G)?

when it is an endothermic process (+ delta H) that decreases disorder (- delta S)

When is a reaction favorable only at high temperatures?

When it is endothermic (+ delta H) and increases disorder (+ delta S)

When is a reaction only favorable at low temperatures?

when it is exothermic (- delta H) and decreases disorder (- delta S)

When does temperature matter?

When enthalpy and entropy are in competing directions, as it will then determine the overall charge of delta G( and if reaction is favorable)

What does an unfavorable reaction indicate(- delta G)?

it indicates that the reverse reaction is favored

Define entropy

Entropy is a description of the number of ways atoms can share quanta of energy

If the number of of ways (W) is high, then the system is disordered and the entropy (S) is high

Greater entropy means what

The greater the entropy, the greater the energy is spread out meaning the system is more disordered

What are the entropy levels of the states

1. Solids have smallest entropies

2. Liquids have greater entropies

3. Gases have greatest entropies

What is the entropy value when temperature is 0K

0

What happens to entropy if system changes to become more random

If a system changes to become more random then entropy CHNAGE will be positive and energy is being spread out more

What happens to entropy if system changes to become less random

If system changes to become less random then the entropy CHANGE will be negative as energy is being more concentrated

How can you predict entropy changes

Compare the change in states from reactants to products

How do melting and boiling point affect entropy

1. Melting and boiling point increase the temperature

2. Increasing temperature increase kinetic energy

3. More kinetic energy means particles are more random

4. Energy is spread out more

5. Entropy change is positive

What is standard entropy

Standard entropy is the entropy of one mole of a substance under standard conditions

Standard entropies are always positive

What is the equation of entropy

First Law of Thermodynamics

Energy can be neither created nor destroyed; the energy of the universe is constant.

Spontaneous Processes

Processes that occur without outside intervention, which may be fast or slow.

Entropy (S)

A measure of randomness or disorder; driving force for spontaneous processes.

Second Law of Thermodynamics

In any spontaneous process, there is always an increase in the entropy of the universe.

Positional Entropy

Depends on the number of ways (microstates) an arrangement can be achieved; Ssolid < Sliquid << Sgas.

Exothermic Process

A process where the entropy change of the surroundings is positive due to heat release.

Endothermic Process

A process where the entropy change of the surroundings is negative due to heat absorption.

Gibbs Free Energy (G)

Energy available to perform work, determines whether a process is spontaneous.

Gibbs Free Energy Equation

DG = DH - TDS, where DG indicates spontaneity.

Standard State Conditions

Defined conditions for comparing quantities like S, H, and G; typically at 1 atm and 298 K.

Third Law of Thermodynamics

The entropy of a perfect crystal at 0 K is zero.

Free Energy of Formation (DGf0)

Standard free energy of formation for elements in their standard state is zero.

Equilibrium Constant (K)

Describes the ratio of concentrations of products to reactants when the system is at equilibrium.

Free Energy Change (DG)

DG = DGo + RTln(Q), indicates spontaneity under given conditions.

Enthalpy (H)

A measure of energy in a system that accounts for heat content.

Thermal Energy

Kinetic energy transferred to the surroundings in the form of heat.

Kinetics vs Thermodynamics

Kinetics concerns the speed of reactions, while thermodynamics concerns the initial and final states.

Microstates

The different configurations of particles in a system that contribute to entropy.

Chemical Bonds

The potential energy contained in the connections between atoms in a compound.

DG = 0

Indicates a reaction is at equilibrium, with no net forward or reverse reaction.

Reaction Rates

The speed at which reactants are converted into products in a chemical reaction.