THERMODYNAMICS

additional topic

THERMODYNAMICS

Study of the rate of a chemical reaction

Collision theory

Reaction occurs when reactants “effectively collide"

1. Proper Orientation

2. Sufficient energy

For a collision to be effective and lead to a reaction: (2)

Sufficient energy

to overcome Ea (Activation Energy)

Activation Energy (Ea)

Minimum amount of energy required to start a reaction

Gas

the most reactive state because it possess a very high Kinetic Energy (KE)

Surface area (SA)

○ Small particle size, greater surface area

○ Small particle size – faster chemical reaction (most reactive)

Small particle size

faster chemical reaction (most reactive)

Temperature

High temperature, high kinetic energy (KE)

Catalysts

increasing chemical reaction by decreasing Ea (activation energy)

○ not consumed in a chemical reaction

Concentration of reactants

increasing concentration, increases rate of chemical reaction

THERMOCHEMISTRY

Branch of physical chemistry that describes energy (heat) changes that occurs in a reaction

Enthalpy

(ΔH)

■ Energy of reaction 

■ Measures heat content of a system

■ Heat absorbed / released in a chemical reaction

Entropy

(ΔS)

■ Degree of disorderliness

■ How chaotic the particles are.

Exothermic reaction

○ Release heat

○ Hot surroundings

○ Negative enthalpy (-ΔH)

○ Positive entropy (+ΔS)

○ Spontaneous

■ Can start chemical reaction on their own

Condensation, Deposition, Freezing, Formation of Bonds

Exothermic reaction Examples:

Endothermic reaction

○ Absorb heat

○ Cold surroundings

○ Positive enthalpy (+ΔH)

○ Negative entropy (-ΔS)

○ Non-spontaneous

■ Chemical reaction will only occur when you add external energy or heat

Melting, Evaporation, Sublimation, Breaking of Bonds

Endothermic reaction Examples:

Endothermic

• Heat: absorb

• Surrounding Temp: Cold

• Change in ΔH: +

• Change in ΔS: -

Exothermic

• Heat: release

• Surrounding Temp: Hot

• Change in ΔH: -

• Change in ΔS: +

Second law of thermodynamics

a decrease in temperature (cold) in the surroundings leads to a decrease in the entropy (less disordered) of the surroundings.

non-spontaneous

Melting, evaporation, sublimation, breaking of bonds

spontaneous

Condensation , deposition, freezing, formation of bonds

Gibb’s Free Energy

A thermodynamic potential

ΔG = ΔH - TΔS

Formula to determine Gibb’s Free Energy:

negative

ΔG < 0 (____) = spontaneous

equal

ΔG = 0 (___) = at equilibrium

positive

ΔG > 0 (___) = non-spontaneous

-ΔS & +ΔH

Non-spontaneous ΔG > 0

-ΔS & -ΔH

Spontaneous at low temperature

+ΔS & +ΔH

Spontaneous at high temperature

+ΔS & -ΔH

Spontaneous ΔG < 0

SYSTEMS

★ A specific, well-defined part of the universe that’s being studied. Its separated from everything else, which is called the surroundings, by a real or imaginary boundary.

★ In pharmaceutical sciences is considered as bounded space or an exact quantity of a material substance.

Open (non-conservative)

There is transfer of energy and transfer of matter

Closed (conservative)

There is transfer of energy but no transfer of matter

Isolated (Adiabatic)

○ There is no transfer of energy nor transfer of matter

○ Does not exist in reality

First Law: Law of Conservation

★ Defines the____ or energy

★ “Energy can neither be created nor destroyed”

★ Energy can be interconverted but the sum of energy must remain constant (thermal to mechanical energy).

Second Law: Law of Entropy

★ Entropy of the universe, as an isolated system, will increase in an irreversible process and remains constant in a reversible process.

○ Entropy is ZERO in a reversible process

★ Heat always flows spontaneously from hotter regions to colder regions of matter.

○ Heat will enter the system, not the cold going out.

Third Law

The entropy of a perfect crystal at a temperature of 0K (absolute zero) is always equal to zero.

○ All motion at absolute zero theoretically stops

Zeroth Law

If two systems are in thermal equilibrium with the third one, then the first two systems are in equilibrium with each other.