Friday, January 27

Today, Mr. Henderson began class by announcing that it would be dedicated to preparing for Thursday's chapter test. He then highlighted the main ideas/sections this test will cover:

1. pp. 1-2

- Heat vs. Temperature (heat is energy)

- 0th Law of Thermodynamics (where the temperature of the system and the surroundings approach each other)

- Thermal Equilibrium

- Energy (differentiating between exothermic and endothermic reactions)

2. pp. 3-4

- Calorimetry (candle labs, etc.)

- Q=mC∆T

- Concept: Energy lost by one thing must be gained by another

- Lab

3. pp. 7-8

- Enthalpy change (∆H)

- Thermal Stoichiometry (how much heat gained/lost)

- 3 rules of Thermal Chemistry (I didn't catch all of them; one was that you have to multiply the moles given by the coefficients to get the proportional amount of heat gained/lost)

4. pp. 9-10

- Heat of Formation (∆Hf)

- Heat of reaction = sum of the heat of the products - sum of the head of the reactants

5. pp. 11-12

- Hess's Law

- The thing where we add, multiple, and cancel multiple chemical equations in order to figure out the amount of heat gained/lost for a given reaction

6. pp. 13-15

- Solids, liquids, gases (differentiating between them)

- Phase changes (melting, boiling, sublimation, etc.)

- Phase diagrams

7. pp. 17-18

- Spontaneity

- ∆H

8. -Entropy.

-Entropy ∆ (∆S)

These are the concepts that will be covered on the test Thursday. Mr. H warned us that this test tends to be challenging for the reason that it covers material from both semesters; and we'll have to remember things we learned before finals. Then, he reminded us that we have a Delicious assignment (a particularly IMPORTANT one, according to Mr. H) due Wednesday morning. For those of you that have forgotten, the tags are: hcp3y1011 unit7 nameL (separated by spaces not commas). We next reviewed Kon's blog and the demo. We spent good part of the class on pages 18 and 19 of our packets.

Page 18 discusses enthalpy, the amount of energy stored in the bonds of chemicals. We talked about how to increase a chemical's stability. Some ways the teacher listed are: a drop in energy, a negative enthalpy change, and as a result the opposite wasn't true, reactions which have an increase in energy generally do NOT increase the chemical's stability or occur naturally/spontaneously. We then reviewed the difference between exothermic and endothermic reactions. For the EN or EX? section, the answers are as follows: ex, en, ex, ex, en, ex, ex, ex. Letter "g" of that section involves calculating the heat of formation, and using the fact that it is negative to deduce that it is an exothermic reaction. Question 7 of the packet deals with diagrams which depict reactions (they mainly just tell us if the reaction is endothermic or exothermic), and Mr. H said that it "looks good for a question on the test".

We then moved on to packet page 19 and began to discuss entropy, which is a measure of the amount of energy dispersion. High entropy is a condition in which energy is NOT concentrated. We then tried to answer the question "What types of processes have an increase in entropy?" The first type is gas diffusion like this:

When the gas is diffused, or spread out, the molecules become less orderly, and less concentrated, which is an increase in enthalpy. The second type is dissolving. Again, this is the energy dispersing and becoming less orderly, so the entropy increases. Also, a note on spontaneity: this type of reaction is spontaneous, things dissolve naturally but this would never happen in reverse. The third type is cooling. The heat energy from a system disperses into the surroundings and spreads out, therefore increasing the entropy.

Mr. Henderson ended the class by reminding us that we have a Webassign reading sheet on chapters 17.1 and 17.2 due Monday.