PPFA- Order and disorder , Entropy the arrow of time

What is a non - spontaneous change?

Non-Spontaneous Changes (Require External Work to Occur)

examples-

Gas compression - apply a force

Heating of cool objects- apply heat

What is a spontaneous change?

Spontaneous Changes (Occur Naturally Without External Work)- can't reverse without work

Examples-

ice melting, cooling ,gas expansion ,ink diffusion

What are some spontaneous changes in Pharmacy?

-Medicines slowly break down on the shelf

-A drug spreads through the body after injection

-Tablets break apart and dissolve when they come into contact with fluid

Why do spontaneous reaction only go in one direction( not reverse)?

-both matter and energy spread out naturally this powers spontaneous processes

Explain the gas expansion example?

Gas molecules initially crowded in one area will spread throughout the container on their own — their random motion makes returning all together extremely unlikely

Explain the heat flow example?

A hot object cools down because its energetic (fast-moving) atoms bump into cooler surroundings, transferring energy until everything's at the same temperature.

What are the Two core tendencies in spontaneous reactions direction ?

Two core tendencies:

-Matter tends to spread out

-Energy tends to spread out

What is entropy generally ?

a measure of disorder/degree of freedom of molecules

How does Phase changes effect entropy?

A change in state = increases entropy

-melting of a solid molecules change from ordered arrangement to a chaotic liquid

What is the second law of thermodynamics and how does it relate to entropy?

The Second Law of Thermodynamics states that the entropy of an isolated system increases in any spontaneous process.

example-

Beaker of ice and room = isolated system because you didn't apply any additional heat

What is a universe in terms of thermodynamics ?

universe= system + surroundings

- we assume universe is isolated because there is nothing outside to exchange energy /matter with

Note - internally sytsem can change

ΔS_(Universe ) ⩾ 0

How can entropy predict spontaneous changes ?

According to the Second Law of Thermodynamics:

ΔS_universe = ΔS_system + ΔS_surroundings

-If ΔS_universe > 0 → the process is spontaneous.

-If ΔS_universe = 0 → the system is at equilibrium.

-ΔS_universe < 0 → the process is impossible without external intervention( heat etc..).

How does second law relate to irreversible, reversible changes?

Basic Statement of the Second Law:

-The entropy of the universe increases in an irreversible (spontaneous) process

-in a reversible process entropy remains constant (non-spontaneous)

NOTE- the second law is about predictions of which processes will occur spontaneously

What is the mathematical definition of entropy ?

Entropy change (ΔS) is defined as the reversible heat absorbed (q₍rev₎) divided by the absolute temperature (T):

ΔS = q(rev)/T

What is q(rev) ?

q(rev) : energy transferred reversibly between system and surroundings

EXAMPLE- the heat transferred in the room and the beaker

T: temperature at which the transfer takes place

What does the Temperature tell us/show?

Temp - reflect the level of random motion of molecules

-transfer heat to hot system level of random motion is less but if transferred to cold more entropy

-greater entropy increase to a lower temperature- bigger differnce

Why do we use heat and not work in the entropy equation?

work is more uniform in a direction but temperature is spontaneous/random motions

Why does temperature matter ?

Temperature reflects the existing level of random motion in the system

What is happening at a molecular level in entropy ?

Entropy also has a microscopic meaning

⟶ it's related to the number of ways particles can be arranged — microstates (Ω)

what is a Microstates in entropy ?

microstates- the number of possible configurations

- this is due to increase in disorder of a system

What is the relationship between microstates and the number of molecules?

-The number of possible configurations (Ω) grows rapidly as the number of molecules increases

-By doubling volume , number of particles = more configurations/

arrangements

What is the equation used for working out probability of the molecules position ?

P =(Vi/Vf )^N

vi= initial volume ( no of chambers

vf= final volume ( all the chambers )

NOTE- for a larger number of molecules= extremely small proability

What is the link between entropy (S) and microstates?

entropy is related to the number of possible arrangements (microstates) of molecules in a system

What is the mathematical explanation of Boltzmann linking entropy and the number of microstates ?

S = k ln Ω

S = entropy

k = Boltzmann constant (1.38 × 10⁻²³ J/K)

Ω = number of possible microstates

What is the correlation between microstaes and entropy ?

Positive correlation between increase in the entropy of system and the number of molecules

More microstates → higher entropy

Describe entropy in relation to randomness?

-Entropy is related to the number of ways (microstates) the particles in a system can be arranged without changing its macroscopic properties

- A highly ordered system ⟶ fewer microstates/configurations ⟶ (low entropy)

A disordered system ⟶ has many possible microstates ⟶ (high entropy)

Describe entropy in relation to gas/liquids and gases?

Gases → molecules move randomly in many configurations → highest entropy.

Solids → Perfect crystal → atoms fixed, few possible arrangements → low entropy

Liquids → molecules move more freely → higher entropy.

A clinical scenario- Why do medicines expire ?

A patient brings in an insulin vial that expired two months ago.

They ask: 'It looks fine — can I still use it?'

No ,

Entropy naturally increases with time — proteins tend to move toward more disordered states

The unfolded state of insulin has more possible molecular arrangements (microstates) than the tightly folded, active form

Even if the vial looks clear, unfolding or subtle aggregation may have already occurred, reducing potency and safety

Which phase has a longer expiry date and why ?

Liquid expire first - already more disordered as solid fixed particles take longer to increase the entropy

Why does refrigeration slow down entropy - driven changes?

lower kinetic energy due to lower temperature ,slower movement

First law vs the second law of thermodynamics

first law:

-energy conserved

-tells us how much energy you have

Second law:

-tells us the direction in which natural processes occur

- tells us how useful energy is

Summary

The quantity of energy is always preserved during an actual process — that's the first law

But the quality of energy is likely to decrease — that's the second law

This decrease in quality is always accompanied by an increase in entropy