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?

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
• 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

Work on problems 9-13 on page 395