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?

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

- 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 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

- 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

- 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?

- 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

Work on problems 9-13 on page 395