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Lon-Capa. 4 th HW assignment due Friday, 10/10, 5 pm. It is open now. 3 rd Quiz due Sunday, 10/12 by 10 pm. It will open Friday, 10/10 at 5 pm. Clicker Question. The following chemical reaction is exothermic: A 2 + B 2  2AB. This means: more stable higher average bond energies

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Lon capa
Lon-Capa

  • 4th HW assignment due Friday, 10/10, 5 pm. It is open now.

  • 3rd Quiz due Sunday, 10/12 by 10 pm. It will open Friday, 10/10 at 5 pm.


Clicker question
Clicker Question

The following chemical reaction is exothermic: A2 + B2 2AB. This means:

more stable higher average bond energies

a) Reactants Reactants

b) Reactants Products

c) Products Products

d) Products Reactants

e) I do not know.





Some big ideas
Some Big Ideas

  • Low energy  low in potential energy  more stable.

  • If a system absorbs energy, the natural tendency is to release it.

    • That is, achieving low potential energy is “natural”.

    • Ground state preferred over excited state.

  • Energy is converted from one form to another but is NOT created nor destroyed.

    • First law of thermodynamics.

    • Energy is a state function (heat and work are not).



Determining h rxn
Determining Work On the SurroundingsHrxn

  • Since H = qp, measure the heat given off or required at constant pressure. This is termed calorimetry.

  • Since energy is conserved, we can often determine Hrxn for one reaction given values of Hrxn for others. Uses the principle in Hess’s Law.

  • Use standard enthalpies of formations for reactants and products (we have tables of these).



Clicker question1
Clicker Question Work On the Surroundings

You drop 50.0 g of 100.0C metal into 100.0 g of 22.0C water. The final temperature of the water is 29.5C. Identify the metal.

c(water) = 4.18 J/g C

a) aluminum (c=0.89J/gC)

b) iron (c=0.45J/gC)

c) copper (c=0.20J/gC)

d) lead (c=0.14J/gC)

e) I do not know how to do this.


Constant pressure calorimetry
Constant-Pressure Calorimetry Work On the Surroundings

  • Can determine enthalpy change for chemical reactions that occur in solution. See Example 9.3 on page 376 of your text.

  • Can calculate ΔE and ΔH when PV work occurs. See Example 9.4 on page 378 of your text.


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