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## PowerPoint Slideshow about ' Lon-Capa' - makaio

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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

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

- 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).

The Piston, Moving a Distance Against a Pressure P, Does Work On the Surroundings

Determining Work On the SurroundingsHrxn

- 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).

A Coffee-Cup Calorimeter Made of Two Styrofoam Cups Work On the Surroundings

Clicker Question Work On the Surroundings

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

c(water) = 4.18 J/g C

a) aluminum (c=0.89J/gC)

b) iron (c=0.45J/gC)

c) copper (c=0.20J/gC)

d) lead (c=0.14J/gC)

e) I do not know how to do this.

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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