8.3 THERMO

• What type of thermodynamic processes occur in nature?

  Irreversible processes
• How do irreversible processes behave in terms of direction?

  They proceed spontaneously in one direction
• What does the Second Law of Thermodynamics determine?

  The preferred direction of thermodynamic processes
• What are reversible processes characterized by?

  They are idealized, quasi-equilibrium processes
• What happens to systems undergoing reversible processes?

  They are near thermal equilibrium with environments
• What is the simplest statement of the Second Law of Thermodynamics?

  Spontaneous change occurs from order to disorder
• What is the preferred direction of nearly all thermodynamic processes?

  From order to disorder or randomness
• What does the conversion of mechanical energy to heat involve?

  An increase in randomness or disorder
• What is a heat engine?

  A device transforming heat to work
• What processes does a heat engine undergo?

  Inflow and outflow of heat, expansion, compression
• What must heat engines do with heat absorbed from a hot reservoir?

  Perform mechanical work and discard heat
• What is the relationship between heat absorbed and discarded in a cyclic process?

  ΔU = 0
• What is the formula for work done by a heat engine?

  W = QH - QC
• What is the thermal efficiency of a heat engine?

  e = W/QH
• If a heat engine absorbs $QH =$$9000 \text{ J}$ and discards $QC =$$-6400 \text{ J}$, what is the work output?


  $2600 \text{ J}$
• What is the thermal efficiency of the engine with $QH =$$9000 \text{ J}$ and $QC =$$-6400 \text{ J}$?


  $0.29 \text{ or } 29\%$
• How does a refrigerator operate?

  It takes heat from a cold place to a warm place
• Why is work needed for a refrigerator?

  Heat does not flow naturally from cold to hot
• What is the Coefficient of Performance (COP) of a refrigerator?

  COP = QC/W
• What happens if you leave a refrigerator door open?

  It won't cool the room effectively
• What does the Kelvin-Planck statement of the 2nd Law state?

  No process can transfer heat from cold to hot
• What is the Clausius statement of the 2nd Law?

  It is equivalent to the Kelvin-Planck statement
• What did Sadi Carnot develop regarding heat engines?

  A hypothetical engine with maximum efficiency
• What characterizes a reversible thermodynamic process?

  Both system and surroundings return to original state
• What must be avoided for maximum efficiency in heat conversion?

  Irreversible processes like heat flow
• What are the steps in a Carnot cycle?

  Isothermal absorption, adiabatic expansion, isothermal exhaustion, compression
• How is the efficiency of a Carnot engine calculated?

  e = 1 - QC/QH
• What does the efficiency of a Carnot engine depend on?

  The temperatures of the two reservoirs
• What is Carnot's theorem regarding engine efficiency?

  No engine can be more efficient than a Carnot engine
• What is the significance of the Kelvin temperature scale?

  It defines an absolute temperature scale
• What does the Third Law of Thermodynamics state?

  Absolute zero cannot be reached in finite steps
• What happens to the internal energy at absolute zero?

  It is at its minimum
• What does entropy measure?

  The disorder of a system
• How is the change in entropy calculated for reversible processes?

  ΔS = ∫(dQrev/T)
• What is the change of entropy when 1 kg of ice melts at 0°C?

  $+$$1.22 \times 10^3 \text{ J/K}$
• What does the Second Law of Thermodynamics state about total entropy?

  No process can decrease total entropy
• What happens in reversible processes regarding total change in entropy?

  Total change in entropy is zero
• What occurs in irreversible processes regarding total change in entropy?

  Total change in entropy is greater than zero
• What is the total change in entropy for an irreversible cyclic process?

  ΔSsys = 0, ΔSsurroundings > 0