FST 111 (2nd LE)

• refers to the transformation of heat into other forms of energy

  Thermodynamics
• Three types of systems and boundaries. Discuss differences.

  Open (permissive wall), Closed (diathermic), and Isolated (adiabatic wall, Q = 0)
• a system is in a definite state when each of the properties (P, V, T) has a definite value; System at equilibrium; state defined by state variables or thermodynamic variables

  State of a system
• completely defined when the initial and final states are specified; Initial state -> final state; P1, V1, T1 -> P2, V2, T2

  Change in state
• any quantity that flows across the boundary of a system during a change in weight somewhere in the surroundings; done when an object is moved against an opposing force; doing work is equivalent to raising a weight somewhere into the surroundings

  Work (W)
• any quantity that flows across the boundary of a system during

  a change in state by virtue of a difference in temperature between system and surrounding

  Heat (Q)
• Heat flows from? (in relation with Temp.)

  Higher temp. to lower temp.
• capacity to do work; sum of the kinetic and potential energies of the

  molecules

  Internal energy (U) of a system
• What contributes to U of a substance? (In relation with PE and KE)


  -KE of the motion of individual molecules

  -PE that rises from interactions between molecules

  -KE and PE of nuclei and electrons within the individual molecules

  -KE and PE contributions: translational, rotational, vibrational, electronic, nuclear, positional and mass contributions
• “If A is in thermal equilibrium with B and B is in thermal equilibrium with C, then A is in thermal equilibrium with C”

  Zeroth law of thermodynamics
• "has the same temperature" (term)

  Thermal equilibrium
• degree of hotness or coldness (term)

  Temperature
• “Energy cannot be created nor destroyed but can only be transformed from one form to another” (The energy of the universe is constant); 


  First Law of Thermodynamics (Conservation of Energy)
• ____ and ____ are equivalent ways of changing a systems internal

  energy.

  Heat and Work
• State sign conventions (ΔU, Q, and W) and what they imply.

  (system ang main character d2)

  
• function that is: path independent, depends only on the initial and final state of the system, ex. Internal energy (U), enthalpy (H), entropy (S), Gibbs energy (G) and Helmholtz energy (A)

  State Function
• function that: depends on the preparation of the state, path dependent, ex. W and Q

  Path function
• Product of an intensity factor (force, P etc.) and a capacity factor (distance, electrical charge etc.)


  Work (W)
• Expansion or compression work; work arising from change in volume

  Pressure-Volume Work (PV work)
• Path dependence of work

  -Free expansion

  -Expansion against constant pressure (irreversible process)

  -Reversible expansion

  -Isothermal, Reversible expansion (at constant T); for ideal and VDW gas

  -No change in volume, dV = 0

  -Work involving phase changes (ex. Gas production); condensed phase (solid/liquid) -> gas
• a change in state of the system implies changes in

  properties of the system such as T and V (these properties

  are measurable) in the initial and final states
• If the volume of the system is constant in the change of state, then dV = O.
• amount of heat needed to raise the T of 1 gram of a substance by 1°C

  Unit: J/g-K or J/g-°C

  Specific heat capacity
• amount of heat needed to raise the T of 1 mole

  of a substance by 1 °C; Unit: J/mol-K or J/mol-°C; an intensive property (molar quantity)

  Molar heat capacity
• When a system is subjected to a constant P and only expansion work can occur, the energy supplied as heat is equal to the enthalpy (enthalpy is the same as heat content)
• a reversible thermodynamic cycle

  Carnot Cycle
• Sadi Carnot (French engineer) investigated the principles governing the transformation of thermal energy (heat) into mechanical energy (work)
• Consider an ideal gas confined in a cylinder fitted with a

  piston. The ideal gas is taken through a sequence of 4

  steps that return to its initial state

  Steps:

  1. isothermal, reversible expansion

  2. adiabatic, reversible expansion

  3. isothermal, reversible compression

  4. adiabatic, reversible compression
• (delta)U is a state function
• Q and W are path functions
• an engine that uses heat to generate mechanical work by carrying a “working substance” through a cyclic process (using the 4 steps in the

  Carnot cycle)

  Heat Engine
• system that has the same temperature everywhere within it

  Heat reservoir
• Heat engine

  • absorbs heat, Qh, from high temperature reservoir
  • rejects heat, Qc, to the low temperature reservoir
  • does work on the surroundings
• A Carnot engine operates between two thermal reservoirs at temperatures T1 and T2 where T1 > T2.
• “The energy of the universe is constant”

  1st Law of Thermodynamics – Law of Conservation of Energy
• “ The entropy of the universe is increasing”

  2nd Law of Thermodynamics – Law of Maximization of Entropy
• measure of the degree of disorderliness/randomness

  Entropy
• 2nd Law statements

  1. A cyclic process must transfer heat from a hot to a cold reservoir if it is to convert heat into work.

  2. Work must be done to transfer heat from a cold to a hot

  reservoir.

  3. No engine can operate more efficient than a Carnot

  engine.

  4. A perpetual motion machine of the 2nd kind (one that

  extracts heat from surroundings at T, does work on the

  surroundings and returns it to the initial state without

  transferring heat to another system at a temp lower than T) cannot exist.

  5. The entropy or randomness of the universe is increasing.
• Closed System - exchanges only energy but not mass with its surroundings
• Open System - exchanges both mass and energy with its surroundings