TermodinamikaKimia (Part III)

TRIANNISA RAHMAWATI, S.PD., M.SI.

Beberapa Topik Termodinamika

01. Menjelaskan

Hukum Permana

Termodinamika

02. Menerapkan

perubahan energi

dalam dan perubahan

entalpi dalam system

kimia pada berbagai

keadaan

03. Menjelaskan

makna entropi dan

hukum kedua

termodinamika

04. Menjelaskan makna energi

bebas Gibbs dan hubungannya

dengan kespontanan pada proses

fisika dan kimia

2 Annual Review September 29, 2021

SPONTANEITY OF PHYSICAL AND CHEMICAL CHANGES

Another major concern of thermodynamics

is predicting whether a particular process

can occur under specified conditions to give

predominantly products.

The concept of spontaneity has a very

specific interpretation in thermodynamics.

3 Annual Review September 29, 2021

“Which would be more stable at the given conditions—the reactants or the products?”

SPONTANEITY

A change for which the collection of products is thermodynamically more stable than the collection of reactants under the given conditions is said to be product-favored, or spontaneous, under those conditions. A change for which the products are thermodynamically less stable than the reactants under the given conditions is described as reactant-favored, or nonspontaneous, under those conditions.Any spontaneous change has a natural direction, like the rusting of a piece of iron, the

burning of a piece of paper, or the melting of ice at room temperature.

THE TWO ASPECTS OF SPONTANEITYMany product-favored reactions are exothermic. For instance, the combustion (burning) reactions of hydrocarbons such as methane and octane are all exothermic and highly product-favored (spontaneous). The enthalpy contents of the products are lower than those of the reactants.

Not all exothermic changes are spontaneous, however, nor are all spontaneous changes exothermic.Disorder of reactants and products, also plays a role indetermining spontaneity.

Proses Eksotermik

Reaksi pembakaranhidrokarbon → spontan

Pembekuan air

Spontan (diawah 0 ºC)

Tidak spontan (diatas 0 ºC)

THE SECOND LAW OF THERMODYNAMICS

The effect of one factor, the enthalpy change, is that spontaneity is favored (but not required) by exothermicity, and nonspontaneity is favored (but not required) by endothermicity.

The Second Law of Thermodynamics is based on our experiences. Some examples illustrate this law in the macroscopic world. When a mirror is dropped, it can shatter. When a drop of food coloring is added to a glass of water, it diffuses until a homogeneously colored solution results.

The reverse of any spontaneous change is nonspontaneous, because if it did occur, the universe would tend toward a state of greater order.

ENTROPY (S)• The thermodynamic state function entropy, S, is a measure of the disorder of the

system.• The greater the disorder of a system, the higher is its entropy. For any substance,

the particles are more highly ordered in the solid state than in the liquid state.

THIRD LAW OF THERMODYNAMICS

9 Annual Review September 29, 2021

As the temperature of a substance increases, the particles vibrate more vigorously, sothe entropy increases.The standard entropy change, S0, of a reaction can be determined from the absolute entropies of reactants and products.

Factors that Change Entropy

1. Phase changes

2. Temperature changes

3. Volume changes

4. Mixing of substances

5. Increasing the number of particle

6. Changes in the number of gaseous substances

September 29, 2021Annual Review10

September 29, 2021Annual Review11

September 29, 2021Annual Review12

Latihan Part III81, 83, 84, 86, 87, 89, 90, 91.

THANK YOU