mean free path

(noun)

the average distance traveled by a particle between collisions with other particles

Related Terms

Examples of mean free path in the following topics:

  • Gas Diffusion and Effusion

    • For effusion to occur, the hole's diameter must be smaller than the molecules' mean free path (the average distance that a gas particle travels between successive collisions with other gas particles).
    • The opening of the hole must be smaller than the mean free path because otherwise, the gas could move back and forth through the hole.
    • Trace an individual molecule to see the path it takes.

  • Non-Ionic Reactions

    • By this we mean that nucleophilic and electrophilic sites in reacting molecules bond to each other.
    • Furthermore, charged species such as carbocations, carbanions, conjugate acids and conjugate bases are often intermediates on the reaction path, the overall transformation taking place in two or more discrete steps.
    • Here we shall consider two other classes of organic reactions: Free-Radical Reactions & Pericyclic Reactions.
    • One type of "free-radical reaction", alkane halogenation has already been described.
    • Indeed, the study of free-radical polymerization of alkene monomers has opened the door to modern polymer chemistry.

  • Free Energy Changes in Chemical Reactions

    • Conversely, if the free energy of the products exceeds that of the reactants, the reaction will not take place.
    • An important consequence of the one-way downward path of the free energy is that once it reaches its minimum possible value, net change comes to a halt.
    • where ΔG = change in Gibbs free energy, ΔH = change in enthalpy, T = absolute temperature, and ΔS = change in entropy
    • This means that there are four possibilities for the influence that temperature can have on the spontaneity of a process:
    • This means that there is a temperature defined by $T = \frac{\Delta H}{\Delta S}$ at which the reaction is at equilibrium; the reaction will only proceed spontaneously below this temperature.

  • Pressure and Free Energy

    • Gibbs free energy measures the useful work obtainable from a thermodynamic system at a constant temperature and pressure.
    • Just as in mechanics, where potential energy is defined as capacity to do work, similarly different potentials have different meanings.
    • The Gibbs free energy is the maximum amount of non-expansion work that can be extracted from a closed system.
    • When a system changes from an initial state to a final state, the Gibbs free energy (ΔG) equals the work exchanged by the system with its surroundings, minus the work of the pressure force.
    • Therefore, Gibbs free energy is most useful for thermochemical processes at constant temperature and pressure.

  • Free Energy and Work

    • The Gibbs free energy is the maximum amount of non-expansion work that can be extracted from a closed system.
    • As in mechanics, where potential energy is defined as capacity to do work, different potentials have different meanings.
    • The Gibbs free energy is the maximum amount of non-expansion work that can be extracted from a closed system.
    • The appellation "free energy" for G has led to so much confusion that many scientists now refer to it simply as the "Gibbs energy. " The "free" part of the older name reflects the steam-engine origins of thermodynamics, with its interest in converting heat into work.

  • Pericyclic Reactions

    • An important body of chemical reactions, differing from ionic or free radical reactions in a number of respects, has been recognized and extensively studied.
    • In agreement with 1 & 2, no ionic, free radical or other discernible intermediates lie on the reaction path.

  • Odd-Electron Molecules

    • Molecules with unpaired electrons are termed 'free radicals.'
    • While typically highly unstable, and therefore highly reactive, some free radicals exhibit stability of days, months, or even years.
    • These latter compounds are said to be 'metastable,' meaning they will decompose or react if given enough time, but are stable enough for a considerable amount of time, from days to even years, when subjected to only minor disturbances.
    • Nitric oxide (NO) is an example of a stable free radical.

  • Free Energy Changes for Nonstandard States

    • The important principle to understand is that a negative $\Delta G^{\circ}$ does not mean that the reactants will be completely transformed into products.
    • By the same token, a positive $\Delta G^{\circ}$ does not mean that no products are formed at all.
    • This does not mean that each mole of pure A will be converted into one mole of pure B.
    • The physical meaning of $\Delta G$ is that it tells us how far the free energy of the system has changed from G° of the pure reactants (point 1).
    • But because free energy can only decrease but never increase, this does not happen.

  • General Rules for Assigning Electrons to Atomic Orbitals

    • As an example, fluorine (F), has an atomic number of 9, meaning that a neutral fluorine atom has 9 electrons.
    • Though electrons can be represented simply as circling the nucleus in rings, in reality, electrons move along paths that are much more complicated.
    • These paths are called atomic orbitals, or subshells.
    • Lithium (Li) has an atomic number of 3, meaning that in a neutral atom, the number of electrons will be 3.

  • Complex Ion Equilibria and Solubility

    • This means that mixtures containing Fe3+ and SCN− will react until the above equation is satisfied.
    • The Beer-Lambert Law relates the amount of light being absorbed to the concentration of the substance absorbing the light and the path length through which the light passes:
    • In this equation, the measured absorbance (A) is related to the molar absorptivity constant (ε), the path length (b), and the molar concentration (c) of the absorbing species.