Thermodynamics Laws and Concepts Quiz

Laws of Thermodynamics

• Zeroth Law: Establishes a temperature equilibrium concept between systems.
• First Law: Energy conservation; the energy change in a closed system is equal to heat added minus work done.
• Second Law: In spontaneous processes, the total energy of the universe increases (ΔSuniverse > 0).
• Third Law: As temperature approaches absolute zero, the entropy of a perfect crystal approaches zero.

Basic Thermodynamic Terms

• System: The part of the universe being studied.
• Surroundings: Everything outside the system.
• Boundary: The division between the system and surroundings.
• Homogeneous System: Uniform composition throughout.
• Heterogeneous System: Composed of two or more distinct phases.
• Open System: Exchanges both energy and matter with surroundings.
• Closed System: Transfers energy but not matter.
• Isolated System: No exchange of energy or matter with its surroundings.

Properties

• Intensive Property: Independent of system size (e.g., temperature, pressure).
• Extensive Property: Dependent on system size (e.g., volume, mass).

First Law of Thermodynamics

• Internal energy change (ΔE) is linked to heat (q) and work (W) through the equation ΔE = q - W.
• For expanding gas, total work done is calculated as W = P × ΔV.
• Energy changes must balance in a closed system—no perpetual motion machines can exist.

Enthalpy

• Defined as total heat content at constant pressure: H = E + PV.
• Change in Enthalpy (ΔH) is represented as ΔH = ΔE + PΔV.
• Substantial for calculations at constant pressure (ΔH = q).

Reversible Expansion

• Isothermal reversible expansion involves gradual changes in pressure.
• Work done during expansion expressed as W = -∫PdV.
• For ideal gases, work can also be represented with logarithmic functions of pressure (e.g., W = -nRT ln(P2/P1)).

Heat Capacity

• Molar Heat Capacity (Cp): dH/dT = Cp at constant pressure.
• Internal Energy Capacity (Cv): dE/dT = Cv at constant volume.
• Relation between heat capacities: Cp = Cv + R, where R is the gas constant (1.987 cal K–1 mol–1 or 8.314 J K–1 mol–1).

Second Law of Thermodynamics & Entropy

• Entropy increases in spontaneous processes (ΔSuniverse = ΔSsystem + ΔSsurroundings).
• Reversible processes maintain constant entropy (ΔSuniverse = 0).
• Entropy quantifies molecular disorder or randomness within a system.