Chem 113

• Homogeneous system: A system whose properties are the same in all parts, or at least vary continuously from point to point
• Heterogeneous system: A system consists of two or more distinct homogeneous regions (states of matter or phases)
• Solid: A form of matter that adopts and maintains a shape that is independent of the container it occupies
• Liquid: A form of matter that adopts the shape of the part of the container it occupies and is separated from the unoccupied part of the container by a definite surface
• Gas: A form of matter that immediately fills any container it occupies
• Thermodynamics can determine:

  • Work given a quantity of fuel
  • Maximum efficiency
  • Stability of substance
  • Maximum yield
• Thermodynamics cannot tell us the time given for the process to occur
• State of a system is determined by its properties
• State of a substance: When all its properties of interest in a thermodynamic treatment are defined within experimental accuracy
• Two classes of properties:

  • Extensive: Size of system (n, m, V)
  • Intensive: Independent of the size of the system (T, p)
• Thermodynamics applies in equilibrium (state of rest)
• Equilibrium: When a hot object is placed in thermal contact with a cold object, heat flows from the warmer to the cooler object until they are in thermal equilibrium (same temperature, same kinetic energy)
• 0th Law of Thermodynamics: If A is in thermal equilibrium with B, and B in thermal equilibrium with C, then C will be in thermal equilibrium with A. B acts as a thermometer and A, B, and C are all at the same temperature
• Operational definition of temperature:

  • Substance
  • Property that depends on temperature
  • Reference points
  • Interpolation scheme between reference points
• To convert Celsius to Kelvin: Add 273.15
• Pressure is described as the molecules of a gas being in constant motion, having random directions and a distribution of energies, and colliding with each other and the barriers of the vessel
• Equation of state: p = f(T, V, n)
• Empirical laws: Boyle’s, Charles’s, Avogadro’s
• Boyle’s Law: Pressure and volume are inversely related at constant temperature (P1V1 = P2V2)
• Charles’s Law: Volume of a gas varies directly with the absolute temperature at constant pressure (V1/T1 = V2/T2)
• Avogadro’s Law: At constant temperature and pressure, the volume of a gas is directly related to the number of moles (V1/n1 = V2/n2)
• Ideal gas equation: PV = nRT, where R is the gas constant (R = 0.0821 atm L/mol K or R = 8.314 kPa L/mol K)
• Dalton’s Law: The total pressure in a container is the sum of the pressure each gas would exert if it were alone in the container
• Ideal gas: Obeys PV = nRT, has zero molecular volume, zero molecular attractions, and zero molecular repulsions
• Real gas: Does not obey ideal gas laws due to molecular volume, attractions, and repulsions
• Volume correction is used in real gases because the actual volume free to move in is less due to particle size
• Pressure correction is needed in real gases because the pressure on the container will be less than ideal due to molecular interactions
• Van der Waals equation includes experimentally determined constants “a” and “b” for each gas, where “a” depends on size and polarity
• System: The part of the Universe being studied
• Surroundings: The rest of the Universe
• Boundary: The surface dividing the system from the surroundings
• Open system: Mass and energy can transfer between the system and the surroundings
• Closed system: Energy can transfer between the system and the surroundings, but not mass
• Isolated system: Neither mass nor energy can transfer between the system and the surroundings (e.g., a thermos)
• Systems lose energy when they do work or give out heat, and gain energy when work is done on them or heat is transferred to them
• To calculate work: Units are joules, and expansion work occurs when a gas pushes a piston
• Expansion pressure calculation: A = area, h = height, V = volume, w = work, change = final - initial
• A negative sign in work indicates that work is done by the surroundings on the system
• Heat is the quantity flowing between the system and the surroundings, used to change temperatures
• Heat capacity (C) is the heat needed to raise the temperature of a substance by 1 K