OIA1011 THERMODYNAMICS: HEAT, WORK & LAWS

What is thermodynamics?

The study of energy transformations, particularly the conversion of heat into work and vice versa

Define a system in thermodynamics.

The part of the universe under study, separated from its surroundings by a boundary

What are the three types of systems?

Open (exchange matter and energy), closed (exchange energy only), and isolated (no exchange)

What is an isothermal process?

A process where the temperature remains constant, with heat exchange occurring

What is an adiabatic process?

A process where no heat is exchanged between the system and its surroundings

How is work defined in thermodynamics?

w=−Pext.ΔV, where PextP_{\text{ext}} is external pressure and ΔV\Delta V is the change in volume

What is the sign convention for work?

Work done by the system is negative; work done on the system is positive

What is the formula for work in an isothermal reversible process?

w=−nRTln⁡(P1P2)

State the first law of thermodynamics.

Energy cannot be created or destroyed, only transformed; ΔU=q+w

State the second law of thermodynamics.

The entropy of an isolated system always increases in spontaneous processes

What is the third law of thermodynamics?

The entropy of a perfect crystal approaches zero as the temperature approaches absolute zero (0 K)

Define heat capacity (C).

The amount of heat required to raise the temperature of a system by 1°C or 1 K

Differentiate between Cv and Cp

Cv: Heat capacity at constant volume; Cp: Heat capacity at constant pressure

What is enthalpy (H)?

A state function representing the heat content of a system at constant pressure; ΔH=ΔU+PΔV

State Hess's Law.

The enthalpy change of a reaction is the same, regardless of the number of steps

What is the heat of formation?

The enthalpy change when 1 mole of a compound is formed from its elements in their standard states

Define entropy (S).

A measure of the disorder or randomness of a system

What is Gibbs free energy (GG)?

A thermodynamic potential that predicts the spontaneity of a process; ΔG=ΔH−TΔS

When is a process spontaneous based on ΔG?

When ΔG<0

How is work calculated for expansion against a vacuum?

w=0 because Pext=0

How does work differ for reversible and irreversible processes?

Reversible processes do more work due to gradual pressure changes

What is the work done when 1 mole of gas expands reversibly from 5 atm to 1 atm at 300 K?

w=−nRTln⁡(P1P2)=−5740 J.

Why is the work done during reversible expansion greater than in irreversible expansion?

In reversible processes, the system constantly adjusts to maintain equilibrium with external pressure

Give a pharmaceutical example where thermodynamics is applied.

The solubility and dissolution rate of drugs like paracetamol

How does thermodynamics explain the miscibility of liquids?

By predicting the entropy and Gibbs free energy changes during mixing

What is the effect of compression on work?

Work is positive as it is done on the system

How is enthalpy related to heat in a constant pressure process?

ΔH=qp, where qpq_p is heat exchanged at constant pressure

What determines the direction of a reaction?

The sign of ΔG; negative ΔG indicates spontaneity

How does temperature affect ΔG?

Higher temperatures can make an endothermic reaction spontaneous if TΔS>ΔHT

What is the significance of ΔG=0

The system is at equilibrium