Thermodynamics

Question 1

Zeroth Law of Thermodynamics

Answer 1

• Zeroth Law: When one object is in thermal equilibrium with a second object, and the second object is in thermal equilibrium with a third object, then the first and third object are also in thermal equilibrium; no net heat flow occurs between objects in thermal equilibrium.

• Temperature is a measure of the average kinetic energy of the particles within a substance.
• Kelvin is larger than Celcius; K = °C + 273
• Absolute Zero: 0 K = -273°C
• Room Temperature: 298 K = 25°C

Question 2

Systems

Answer 2

• Isolated System: Cannot exchange energy or matter with the surroundings (ΔU = 0); bomb calorimeter or the universe.
• Closed System: Energy can be exchanged with the surroundings, but matter cannot; chamber of gas with moving pistons.
• Open System: Energy and matter can be exchanged with the surroundings; pot of boiling water.

• State Functions: Path-independent properties; Pressure (P), Density (ρ), Temperature (T), Volume (V), Enthalpy (H), Internal Energy (U), Gibbs Free Energy (G), Entropy (S).
• Process Functions: Heat (Q) and Work (W).

Question 3

First Law of Thermodynamics

Answer 3

• States that the change in the total internal energy of a system is equal to the amount of energy transferred to the system in the form of heat, minus the amount of energy transferred from the system in the form of work; extension of law of conservation of energy.

• ΔU = Q - W
• Temperature is directly proportional to internal energy; positive ΔU means increasing temperature, and negative ΔU means decreasing temperature.
• Positive Q means heat flows into system, and negative Q means heat flows out of system.
• Positive W means work is done by the system through expansion; negative W means work is done on the system through compression.

Question 4

Specific Heat and Latent Heat

Answer 4

• Specific Heat: The amount of heat energy required to raise 1g of a substance by 1°C.
• Heat Transfer: q = mcΔT
• ΔT can be given in °C or K.
• Specific heat of water is 1 cal/(g•K).

• Latent Heat: q = mL
• ΔT = 0 during phase change.

Question 5

Thermodynamics Processes

Answer 5

• Adiabatic: No heat exchange (Q = 0).
• Therefore, ΔU = -W.

• Isothermal: Temperature remains constant (ΔT = 0), meaning ΔU = 0.
• Therefore, Q = W.

• Isovolumetric: Volume remains constant (ΔV = 0), meaning W = 0.
• Therefore, ΔU = Q.

Question 6

Second Law of Thermodynamics

Answer 6

• Second Law: Heat transfer occurs spontaneously between objects in thermal contact that are not in thermal equilibrium; materials that have higher temperatures will give off heat energy to materials that have lower temperatures.

• Entropy: Measure of spontaneous dispersal of energy at a specific temperature; can be understood in terms of microstates.
• ΔS = Q/T
• Q is heat that is gained or lost in a reversible process, and T is temperature in Kelvin; units of entropy are J/(mol•K).