Chapter 11 2 how does temperature affect enthalpy and entropy
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Chapter 11-2: How does temperature affect enthalpy and entropy?. Thermodynamics Properties. Thermodynamics deals with energy transformation of several different kinds The three properties that affect the relationship between energy and matter are: Entropy Enthalpy Gibbs Energy.

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Chapter 11-2: How does temperature affect enthalpy and entropy?

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Chapter 11-2: How does temperature affect enthalpy and entropy?


Thermodynamics Properties

  • Thermodynamics deals with energy transformation of several different kinds

  • The three properties that affect the relationship between energy and matter are:

    • Entropy

    • Enthalpy

    • Gibbs Energy


Enthalpy (H):

  • Enthalpy can be thought of as heat or thermal energy = as something is heated the increase in enthalpy is equal to the thermal energy it receives

  • A change in enthalpy can be measured when a substance is heated and cooled, however enthalpy itself cannot be measured. So scientists have decided to assign all elements under standard conditions a molar enthalpy of zero


Properties

  • Extensive Properties – a property that depends on the amount of material present

    • Mass

    • Volume

    • Heat capacity

    • Enthalpy

    • Entropy

  • Intensive Properties – a property that does not depend on the amount of material present

    • Density

    • Pressure

    • Temperature

    • Concentration


Temperature Affects Molar Enthalpy

  • Enthalpy increase is equal to the heat input

    • So molar enthalpy can be found by dividing the enthalpy increase by the number of moles

  • Temperature also affects entropy because entropy can be directly measured


How much does the molar enthalpy change when a 92.3g block of ice is cooled from -0.2⁰C to -5.4⁰C?


Things to Notice about that Problem

  • Mass was given, and not needed

    • Scientists often find themselves with more information than needed

  • ΔT = Tf – Ti --- Gives the same result whether or not you change Celsius to Kelvin

    • In thermodynamics problems it doesn’t always work out this way so getting into the habit of changing the temperature to kelvin


Changes of State


Homework/Rest of Class

Work on problems 9-13 on page 395


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