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.

Monday, November 8

Mr. Henderson started class today by examining what the rest of this week looks like. We will be learning a new topic for the next couple of days preceding the test, followed by the test Friday. He told us that the test Friday will be composed of: 14 multiple choice questions, 1 double-sided page of writing and balancing equations, no math work, and a section on identifying the reaction type. Mr. H said that what is going to make this test difficult is that it requires a lot of unit 2 work -- writing equations and such. But, we have a very resourceful tool to help us review, this blog! Mr. H walked us through Brooke's blog and talked about how helpful it will be to study for the test. To review, we can also use the Delicious websites created by the class (which, reminder, are due on Thursday!).

We then moved on to the new topic of today, Dissociation and Hydration. He begun this by doing page 11 in our packets. The first small section of this page was identifying a compound as being either ionic or molecular. An ionic compound is one which consists of a cation (metal) and anion (nonmetal), while a molecular compound consist of, normally, two anions. A good, common example of a molecular compound are those hydrocarbons Mr. H keeps talking about. These are the answers to the first part of page 11 ("i" for ionic and "m" for molecular):

1.

a. NaCl I

b. CO2 M

c. NaNO3 I

d. D2H5OH M

e. NH4Cl I

f. C6H12O6 M

If you need extra help distinguishing between the two types of compounds, this is very helpful: http://www.buzzle.com/articles/ionic-compounds-vs-molecular-compounds.html

The following section of the packet introduces a new topic to us, dissociation/hydration. We were supposed to find what the compound looked like after it had dissolved in water (after being broken up into individual ions by the water). The first few problems/answers are:

a. KF(s) -> K+(aq) + F-(aq)

b. CaCl2(s) -> Ca2+(aq) + 2Cl(aq)

c. Na2SO4(s) -> 2Na+(aq) + SO42-(aq)

One of the most difficult things to remember is that Uncle HONClBrIF does not apply to these ions because they're not considered to be "by themselves", but "with" water.

As should be obvious by now, all we are doing is splitting the compound into the ions of which it is made up. But then it gets a little more trickey; we are asked to perform the same type of equation, they give us the name and expect us to derive the formula from that. For example the first question asks what happens when you put lithium phosphate in water:

First, we figure out that the formula for lithium phosphate is Li3PO4

Next, we figure out that the ions of which it is mad up are Li+ and PO43-

Then, we balance the equation to get something which looks like this -- Li3PO4(s) -> 3Li+ + PO43-

After doing a couple more problems like this one, we moved onto yet another new topic. This is the topic of electrolytic (E) and non-electrolytic (NE) solutions. What makes a solution electrolytic is if it is created by ionic compounds, a cation and an anion.

Answers to the last section:

a. NaCl E

b. SO3 NE

c. C2H5OH NE

d. KF E

e. BaCl2 E

f. C12H22O11 NE

He demonstrated this concept through a conductivity test. If, when the wires were placed in the solution, it caused the lightbulb to light, then the solution is electrolytic. This also implies that it contains an ionic compound. He used a video (from the blog) to demonstrate this:

http://g.web.umkc.edu/gounevt/Animations/Animations211/StrongWeakNonElelytes.swf

After this, we moved on to Lab CR2, the Chemical Dropout Lab. We mixed various substances, observing whether or not they each created a precipitate. If a solid developed, or the mixture became cloudy, we knew that a precipitate had been formed.

This picture shows perfectly what precipitates look like.

Overall, today was a very intense day. We were introduced to many new concepts, but luckily Mr. Henderson is explaining them very well and we have many review tools at our fingertips.

Tuesday, September 7

Today in Chemistry, we mainly focused on measurements. We began the class by reviewing the assignments. Mr. Henderson reiterated that Labs 1-4 and packet pages 3 and 4 are due tomorrow, Wednesday September 9; and the Intro to Measurement Lab is due on Wednesday. He then proceeded to discuss the lab from yesterday, the MM4 Separating Mixtures Lab. He used a similar (example) lab about coins to demonstrate how to find the percent composition of each element in a mixture. First it is needed to find the total mass of the mixture, and then the mass of the element whose composition you wish to find. Then, you divide the mass of the element by the total mass, and you have the percent composition of that element. Mr. Henderson multiplied the number present of each coin by the mass of that type of coin, then divided the total mass of the coin mixture to find the percent of coins which make up the mixture. He then gave us time to This link describes how to find the percent composition:
http://www.chem.tamu.edu/class/majors/tutorialnotefiles/percentcomp.htm


Next, we began the Intro to Mixtures lab, which taught us about the precision of different instrument (with some divisions), and a graduate (with many divisions). Then we had to measure the length of a blue pen with multiple rulers that had various degrees of divisions. Through these two experiments, we found out that the instruments with less divisions force you to estimate more, and therefore be less precise. After that, we weighed the mass of a penny using three different mass balances, which gave slightly varying numbers. We then discussed significant digits, which are important when communicating the precision of our measurements. Mr. Henderson stated that in regards to significant figures, one figure is one that is always estimated. In other words, it can be assumed that all of the digits are exact up until the last one (and it is important to do this when measuring something yourself in order to communicate it to others).
This link is very helpful in understanding the concept of the degree of uncertainty:
http://www.tutorvista.com/content/chemistry/chemistry-iii/chemistry-concepts/uncertainty-measurement.php

^^These are the different instruments we used to measure the volume of water.

Mr. Henderson today emphasized the importance of the difference between mass and weight. He clarified that mass is the amount of matter one object has, and gravity is the force which acts on that amount of matter. He gave the example that if a person were to go to outer space, they would have a different weight (because different planets have different amounts of gravity), but his/her mass would remain the same. He also pointed out that our scales in Chemistry calculate mass, whereas typical scales calculate weight.
This is a really good link that describes the difference between mass and weight:
http://www.colorado.edu/physics/2000/periodic_table/mass.html

Overall, today was a very informative day in Chemistry; and we learned much about measurements. Don't foget about the pop quiz on Friday!