phychem, First Law

• Thermodynamics is the general study of energy and its interconversions. The laws of

  thermodynamics are among the most fundamental in all of science, governing virtually

  every process that involves change.
• The Law of Conservation of Energy is just another statement of the First Law of

  Thermodynamics. Energy is neither created nor destroyed in ordinary chemical

  reactions and physical changes.
• The first law of thermodynamics is the law of energy conservation, which we

  state as follows: The total energy of the universe is constant
• The First Law may be written: ΔU = q + w
• where ΔU is the change in internal energy of the system,
• q is the heat given to

  the system,
• and w is the work done on the system.
• The internal energy of a system is the sum of the kinetic and potential

  energies of all of the particles that compose the system.
• Internal energy, U, is a state function, that is, its value depends only on the

  current state of the system and is independent of how the system has been

  prepared.
• Because energy must be conserved, a change in the energy of the system is always

  accompanied by an opposite change in the energy of the surroundings.
• Increases in internal energy (endergonic) may result in a

  − temperature increase – phase change

  − chemical reaction starting
• Decreases in internal energy (exergonic) may result in a

  − a decrease in temperature

  − phase change
• The total energy of the universe is constant. ΔUsystem − ΔUenvironment = 0
• • For an isolated system, ΔUisolated system = 0 when energy is conserved. Thus

  ΔUsystem = − ΔUsorroundings
• Equipartition Theorem: For a sample at thermal equilibrium the average value

  of each quadratic contribution to the energy is 1

  2

  kT
• Energy transfer outward from the system or inward from the surroundings can

  appear in two forms, heat and work.
• q and w are NOT state functions.
• q + means system heat
• WORK (w), is simply a force acting over a distance, which can be mathematically

  expressed as follows if considering the displacement in the x direction: dw ≡ Fx dx
• Reversible change in thermodynamics is a change that can be reversed by an

  infinitesimal modification of a variable.
• Reversible work means that the entire system (including the surrounding

  system) can be returned to the starting state.
• Irreversible work means that we

  can only bring the piston back to the starting state if we change the surrounding

  system.
• HEAT (or thermal energy, symbol (q) is the energy transferred between a system and its

  surroundings as a result of a difference in their temperatures only.
• Enthalpy, a thermodynamic quantity equivalent to the total heat content of a system. It

  is equal to the internal energy of the system plus the product of pressure and volume.

  H = U + PV
• Enthalpy (H) is a state function, thus we cannot measure the enthalpy of a system,

  but we can look at changes in enthalpy.

  ΔH = ΔU + PΔV
• Heat Capacity, the amount of heat required to raise the temperature of any substance

  by 1 K (which of course is the same as 1°C, and is given the symbol C; its SI unit is J K

  −1

  .
• Heat capacities are extensive properties. However, molar heat capacities, CV,m are

  intensive properties. This is the heat capacity per mole of a substance.
• The Joule–Thomson effect describes the change in temperature that accompanies expansion of a gas without production of work or transfer of heat. At ordinary temperatures and pressures, all real gases except hydrogen and helium cool upon such expansion;
• The Joule–Thomson effect this phenomenon often is used in liquefying gases
• isenthalpic process is one that proceeds without any change in enthalpy (𝐻) or specific enthalpy (ℎ). There will usually be significant changes in pressure and temperature during the process.
• Radiant energy comes from the sun and is earth’s primary energy source
• Thermal energy is the energy associated with the random motion of atoms

  and molecules
• Chemical energy is the energy stored within the bonds of chemical

  substances
• Nuclear energy is the energy stored within the collection of neutrons and

  protons in the atom
• Potential energy is the energy available by virtue of an object’s position