Hess's law

(noun)

States that, if an overall reaction takes place in several steps, its standard reaction enthalpy is the sum of the standard enthalpies of the intermediate reactions, at the same temperature.

Related Terms

  • law of conservation of energy
  • thermochemical equation
  • enthalpy

(noun)

States that the enthalpy change for a reaction is the same whether it occurs in one step or in a series of steps.

Related Terms

  • law of conservation of energy
  • thermochemical equation
  • enthalpy

Examples of Hess's law in the following topics:

  • Hess's Law

    • Hess's Law sums the changes in enthalpy for a series of intermediate reaction steps to find the overall change in enthalpy for a reaction.
    • Hess's law is a relationship in physical chemistry named after Germain Hess, a Swiss-born Russian chemist and physician.
    • Hess's law derives directly from the law of conservation of energy, as well as its expression in the first law of thermodynamics.
    • Keep in mind that when reversing reactions using Hess's law, the sign of ΔH will change.
    • By Hess's law, we can sum the ΔH values for these intermediate reactions to get our final value, $\Delta H^\circ_{rxn}$.
  • Change in Enthalpy

    • Hess's law addresses how to calculate the enthalpy for the overall reaction.
    • The law states that the enthalpy change for a reaction is the same whether it occurs in one or many steps.
    • Hess's law states that the standard enthalpy change of the overall reaction is the sum of the enthalpy change of all the intermediate reactions that make up the overall reaction.
    • By remembering and employing Hess's Law, the change in enthalpy for the overall reaction can be determined by adding up the enthalpies of the intermediate reactions.
  • Thermochemical Equations

    • This becomes important once we begin working with Hess's law.
  • Introduction to Macro Advantages of Micro-power

    • John Hess, Chairman of the Hess Corporation, agrees.
  • Bibliography

    • Hess. )
  • German Migration

    • The largest group came from the country of Hesse, and the soldiers are often referred to as Hessians.
  • Postmodernist Sculpture

    • Eva Hesse, Sol LeWitt, Jackie Winsor, Keith Sonnier, and Bruce Nauman, among others, were pioneers of postminimalist sculpture .
  • The Uncertainty Principle

    • A more formal inequality relating the standard deviation of position (${ \sigma }_{ x }$) and the standard deviation of momentum (${ \sigma }_{ \rho }$) was derived by Earle Hesse Kennard later that year (and independently by Hermann Weyl in 1928):
  • Gauss's Law

    • Gauss's law is a law relating the distribution of electric charge to the resulting electric field.
    • Gauss's law can be used to derive Coulomb's law, and vice versa.
    • In fact, Gauss's law does hold for moving charges, and in this respect Gauss's law is more general than Coulomb's law.
    • Gauss's law has a close mathematical similarity with a number of laws in other areas of physics, such as Gauss's law for magnetism and Gauss's law for gravity.
    • In fact, any "inverse-square law" can be formulated in a way similar to Gauss's law: For example, Gauss's law itself is essentially equivalent to the inverse-square Coulomb's law, and Gauss's law for gravity is essentially equivalent to the inverse-square Newton's law of gravity.
  • Gender

    • The exhibition, "Inside the Visible," traveled globally and included artists' works from the 1930s through the 1990s, featuring: Claude Cahun, Louise Bourgeois, Bracha Ettinger, Agnes Martin, Carrie Mae Weems, Charlotte Salomon, Eva Hesse, Nancy Spero, Francesca Woodman, Lygia Clark, and Mona Hatoum, among others.
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