thermodynamics

Examples of thermodynamics in the following topics:

• The Three Laws of Thermodynamics

  • The laws of thermodynamics define fundamental physical quantities (temperature, energy, and entropy) that characterize thermodynamic systems.
  • In order to avoid confusion, scientists discuss thermodynamic values in reference to a system and its surroundings.
  • The first law of thermodynamics, also known as Law of Conservation of Energy, states that energy can neither be created nor destroyed; energy can only be transferred or changed from one form to another.
  • The second law of thermodynamics says 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.

• Comparison of Enthalpy to Internal Energy

  • Internal energy and enthalpy are both measurements that quantify the amount of energy present in a thermodynamic system.
  • A thermodynamic system can be any physical system with a well-defined volume in space.
  • In thermodynamics, the total energy contained by a given thermodynamic system is referred to the internal energy (U).
  • From a thermodynamic perspective, work can be done on or by the system; similarly, heat can be lost or gained by a particular system.
  • Because the internal energy encompasses only the energy contained within a thermodynamic system, the internal energy of isolated systems cannot change.

• Thermodynamics of Redox Reactions

  • The thermodynamics of redox reactions can be determined using their standard reduction potentials and the Nernst equation.
  • In order to calculate thermodynamic quantities like change in Gibbs free energy $\Delta G$ for a general redox reaction, an equation called the Nernst equation must be used.

• Changes in Energy

  • In classical thermodynamics the entropy is interpreted as a state function of a thermodynamic system.
  • The entropy of a system is defined only if it is in thermodynamic equilibrium.
  • In a thermodynamic system, pressure, density, and temperature tend to become uniform over time because this equilibrium state has a higher probability (more possible combinations of microstates) than any other.
  • The entropy of the thermodynamic system is a measure of how far the equalization has progressed.
  • The second law of thermodynamics shows that in an isolated system internal portions at different temperatures will tend to adjust to a single uniform temperature and thus produce equilibrium.

• The Third Law of Thermodynamics and Absolute Energy

  • The third law of thermodynamics states that the entropy of a system approaches a constant value as the temperature approaches absolute zero.
  • The third law of thermodynamics states that the entropy of a system approaches a constant value as the temperature approaches zero.

• Elimination

  • Because E1 reactions are performed under thermodynamic control (at high temperature), the most thermodynamically stable product is favored.
  • Also as a result of E1 being under thermodynamic control, production of the e-alkene isomer, which experiences lesser steric hindrance than the z-isomer, will be favored.
  • As with E1, E2 favors production of the most thermodynamically stable product, so the most substituted double bond possible will be formed, and if possible the e-alkene isomer will be favored.

• Spontaneous and Nonspontaneous Processes

  • The sign convention of changes in free energy follows the general convention for thermodynamic measurements.
  • The laws of thermodynamics govern the direction of a spontaneous process, ensuring that if a sufficiently large number of individual interactions (like atoms colliding) are involved, then the direction will always be in the direction of increased entropy.
  • The second law of thermodynamics states that for any spontaneous process, the overall ΔS must be greater than or equal to zero; yet, spontaneous chemical reactions can result in a negative change in entropy.

• Microstates and Entropy

  • In classical thermodynamics, the second law of thermodynamics states that the entropy of an isolated system always increases or remains constant.
  • Thermodynamic entropy has the dimension of energy divided by temperature, which has a unit of joules per kelvin (J/K) in the International System of Units.

• Interpreting Phase Diagrams

  • The critical point, which occurs at critical pressure (Pcr) and critical temperature (Tcr), is a feature that indicates the point in thermodynamic parameter space at which the liquid and gaseous states of the substance being evaluated are indistinguishable.
  • With a knowledge of the major components of phase diagrams and the features of phase plots, a phase diagram can be used to understand how altering thermodynamic parameters influences the states/phases of matter a sample of a substance is in.
  • The thermodynamic properties of mothballs, made of 1,4-Dichlorobenzene, are used to repel insects. 1,4- Dichlorobenzene sublimates (transitions from solid to gas) at room temperature.

• Properties of Aldehydes and Ketones

  • Curiously, relative bond energies influence the thermodynamics of such addition reactions in the opposite sense.
  • This suggests that addition reactions to carbonyl groups should be thermodynamically disfavored, as is the case for the addition of water.