spontaneous change

(noun)

A spontaneous process is the time-evolution of a system in which it releases free energy (usually as heat) and moves to a lower, more thermodynamically stable energy state.

Examples of spontaneous change in the following topics:

  • Free Energy Changes in Chemical Reactions

    • ΔG determines the direction and extent of chemical change.
    • In a spontaneous change, Gibbs energy always decreases and never increases.
    • $\Delta G > 0$: The reaction will occur spontaneously to the left.
    • where ΔG = change in Gibbs free energy, ΔH = change in enthalpy, T = absolute temperature, and ΔS = change in entropy
    • In particular, notice that in the above equation the sign of the entropy change determines whether the reaction becomes more or less spontaneous as the temperature is raised.
  • Spontaneous and Nonspontaneous Processes

    • There are two types of processes (or reactions): spontaneous and non-spontaneous.
    • Spontaneous changes, also called natural processes, proceed when left to themselves, and in the absence of any attempt to drive them in reverse.
    • This means a release of free energy from the system corresponds to a negative change in free energy, but to a positive change for the surroundings.
    • 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.
    • Spontaneity does not imply that the reaction proceeds with great speed.
  • Free Energy and Cell Potential

    • In a galvanic cell, where a spontaneous redox reaction drives the cell to produce an electric potential, the change in Gibbs free energy must be negative.
    • In a galvanic cell, where a spontaneous redox reaction drives the cell to produce an electric potential, the change in Gibbs free energy must be negative.
    • If E°cell > 0, then the process is spontaneous (galvanic cell)
    • Because the change in Gibbs free energy is negative, the redox process is spontaneous.
    • Calculate the change in Gibbs free energy of an electrochemical cell, and discuss its implications for whether a redox reaction will be spontaneous
  • Concentration of Cells

    • In the late 19th century, Josiah Willard Gibbs formulated a theory to predict whether a chemical reaction would be spontaneous based on free energy:
    • Here, ΔG is the change in Gibbs free energy, T is absolute temperature, R is the gas constant, and Q is the reaction quotient.
    • Gibbs' key contribution was to formalize the understanding of the effect of reactant concentration on spontaneity.
    • The change in Gibbs free energy for an electrochemical cell can be related to the cell potential.
    • When a change in the concentration or activity of reactants occurs, or the temperature or pressure changes, the output voltage changes.
  • Predicting Spontaneous Direction of a Redox Reaction

    • Neither the relative strengths of the oxidizing or reducing agents nor the magnitude of the potential will change.
    • However, what will change is the sign of the standard electrode potential.
    • This means we can convert a spontaneous reaction to an unfavorable one and vice versa.
    • In order to predict if two reactants will take part in a spontaneous redox reaction, it is important to know how they rank in an electrochemical series.
  • Additional Funds Needed (AFN)

    • Since a business that seeks to increase its sales level will require more assets to meet that goal, some provision must be made to accommodate the change in assets .
    • AFN = Projected increase in assets – spontaneous increase in liabilities – any increase in retained earnings.
  • Free Energy

    • Every chemical reaction involves a change in free energy, called delta G (∆G).
    • The change in free energy can be calculated for any system that undergoes a change, such as a chemical reaction.
    • This total energy change in the system is called enthalpy and is denoted as ∆H.
    • These chemical reactions are called endergonic reactions; they are non-spontaneous.
    • Exergonic and endergonic reactions result in changes in Gibbs free energy.
  • Stable Isotopes

    • Stable isotopes are atoms that are not radioactive, in other words, they are not going to lose neutrons and decay spontaneously.
    • This work is especially important due to our current concern with climate change/global warming.
    • Elements of the same name (for example, oxygen) must always have the same number of protons, but the number of neutrons can change.
    • Adding or subtracting neutrons from an atom does not change the elemental properties, but it can alter some of its features (like making it more radioactive).
    • This work is especially important due to our current concern with climate change/global warming.
  • Pneumothorax and Hemothorax

    • There are two types of spontaneous pneumothoraces, a primary pneumothorax and a secondary pneumothorax.
    • Small spontaneous pneumothoraces typically resolve without treatment and require only monitoring.
    • Primary spontaneous pneumothorax (PSP) tends to occur in young adults without underlying lung problems, and usually causes limited signs and symptoms.
    • PSP occurs more commonly during changes in atmospheric pressure and during exposure to loud music.
    • Secondary spontaneous pneumothorax (SSP), by definition, occurs in individuals with significant underlying lung disease.
  • Dispersion Force

    • Temporary dipoles are created when electrons, which are in constant movement around the nucleus, spontaneously come into close proximity.
    • Although charges are usually distributed evenly between atoms in non-polar molecules, spontaneous dipoles can still occur.
    • How does changing the Van der Waals attraction or charging the atoms affect the melting and boiling point of the substance?
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