Laws of Thermodynamics Quiz

Laws of Thermodynamics

• The First Law of Thermodynamics states that energy cannot be created or destroyed in an isolated system. This is also known as the Law of Conservation of Energy.
• The Second Law of Thermodynamics establishes that the entropy of any isolated system always increases.
• The Third Law of Thermodynamics states that the entropy of a system approaches a constant value as the temperature approaches absolute zero.

Key Terms

• Pressure is the force applied per unit area.
• Volume is the amount of space an object occupies.
• Temperature measures the average kinetic energy of the molecules in a substance.
• Absolute Zero is the lowest theoretically possible temperature.
• Entropy is a thermodynamic property that measures a system's thermal energy per unit of temperature that is unavailable for useful work.
• Work is done when the volume changes under pressure.
• Heat is the thermal energy transferred between substances.
• Heat Capacity measures the amount of heat a substance needs to absorb to increase its temperature by a specific amount.
• Internal Energy refers to the total energy of a substance's molecules, excluding interactions with external fields.
• Isothermal processes maintain a constant temperature.
• Isobaric processes maintain a constant pressure.
• Isochoric processes maintain a constant volume.
• Adiabatic processes do not permit any heat absorption or release.
• Isentropic processes maintain a constant entropy.
• Steady-state processes maintain a constant internal energy.
• Quasistatic processes occur slowly enough that the system reaches equilibrium between infinitesimal disturbances.
• Spontaneous processes occur without an energy source.
• Reversible processes are quasistatic and can be reversed.
• Irreversible processes are not quasistatic or involve frictional or dissipative forces.

P-V Diagrams

• Work done in thermal physics can be calculated in two common ways:
  • Expressing pressure as a function of volume and integrating.
  • Finding the area under the curve for a P-V diagram.
• The area under the curve for a P-V diagram represents work done.
  • Positive area indicates an increase in volume.
  • Negative area indicates a decrease in volume.

Thermodynamic Processes

• Isochoric Process:
  • Volume remains constant (∆𝑉 = 0).
  • No work is done (𝑊 = 0).
  • Heat exchange is expressed in terms of specific heat capacity at constant volume.
  • Change in internal energy equals heat exchanged (∆𝑈 = 𝑄).
• Isobaric Process:
  • Pressure remains constant.
  • Work is calculated using the integral 𝑊 = ∫𝑉=𝑉 𝑃𝑑𝑉 = 𝑃 (𝑉 − 𝑉𝑜 ) = 𝑃∆𝑉.
  • Heat exchange is expressed in terms of specific heat capacity at constant pressure.
  • Internal energy change is ∆𝑈 = 𝑄 − 𝑊.
• Free Expansion:
  • Occurs under zero pressure.
  • No work is done (𝑊 = 0) because the pressure equals zero.
  • Change in internal energy equals heat exchanged: ∆𝑈 = 𝑄.
• Isothermal Process:
  • Temperature remains constant.
  • Heat change (𝑄 = 𝑛𝑐𝑉 ∆𝑇) depends on the molar specific heat at constant volume.
  • Internal energy change (∆𝑈 = 𝑄 − 𝑊) can be simplified for different scenarios.
  • For an isochor, ∆𝑈 = 𝑄 = 𝑛𝑐𝑉 ∆𝑇. Internal energy depends only on temperature.
  • For an isobar, 𝑊 = 𝑛𝑅∆𝑇. Heat change depends on the molar specific heat at constant pressure.
  • Internal energy change is ∆𝑈 = 𝑛𝑐𝑃 ∆𝑇 − 𝑛𝑅∆𝑇.
  • For a monatomic ideal gas, 𝑐𝑉 = 𝑅, 𝑐𝑝 = 𝑅, and 𝛾 = 5/3.
• Adiabatic Process:
  • No heat absorption or release takes place.
  • The relationship between pressure and volume can be expressed as 𝑃𝑜 𝑉𝑜 = 𝑃𝑉𝜸 for an ideal gas.
  • This relationship can be derived by combining the ideal gas law and the first law of thermodynamics.