chapter 11 2 how does temperature affect enthalpy and entropy
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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.

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Presentation Transcript
thermodynamics properties
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 (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
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
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
slide6

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
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
homework rest of class
Homework/Rest of Class

Work on problems 9-13 on page 395

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