2.8.14 - Equilibrium

Equilibrium

In class last Monday, we did a Metacognitive lab on equilibrium, that look a little something like this.

(except on it's side).












This showed us that when we add more on one side, the other side increases as well. The graph that would represent these changes would look like this:

Additionally, we spent time on Friday looking at a real experiment with NO2 and N2O4. The NO2 is a brown gas. In this experiment, we saw that adding pressure (or decreasing volume) shifts the equilibrium so that there are less molecules, in this case, more N2O4. When pressure is released, more NO2 forms. So, in our experiment, we saw that adding pressure instantly  makes the gas darker, but becomes lighter because more N2O4 is being formed. When the pressure decreases, the gas instantly becomes lighter, but soon turns darker because more NO2 is being formed. 

In addition to these experiments/metacognitive logs, we worked on three worksheets, Equilibrium 1, 2, and 3. These helped us with the equilibrium constant expressions, how to figure out the constants for different reactions, which way equilibrium shifts, etc.

Main Ideas

I think I'm beginning to understand the concepts. It was difficult at first because I didn't understand what it meant to shift to the product/reactant side, or under what conditions it shifted. I think the ConcepTests really help me because I'm able to think about the question and get immediate results. That way, I can fix my misunderstandings in class, rather than having to think about it, answer the question, think about whether I would get it right or wrong, and then checking back on moodle for answers. I also like taking notes on demos like the two we did this week. To see it visually really helps me understand what's going on. After I work on the equilibrium worksheets, I feel pretty confident with mastering the material :)

1.20.14 - Gasses

Gasses

This is a quick summary of the concepts we kept in mind this week:

Boyle's Law: volume of a fixed quantity of gas at constant temperature is inversely proportional to pressure.

         P1V1=P2V2

Charles's Law: volume is directly proportional to temperature

         V1/T1=V2/T2

Gay-Lussac's Law: Pressure and temperature is directly proportional to pressure

         P1/T1=P2/T2

--->Combined gas law: P1V1/T1=P2V2/T2

Avogadro's Law: volume of gas at constant temperature and pressure is directly proportional to the tnumber of moles (n) in a gas

        V1/n1=V2/n2

---> Ideal gas law: PV=nRT

Standard temperature and pressure (STP)

• 0C and 1.000atm
• 1 mole of gas = 22.4L

Molar Mass: M=m/n  (M=Molar mass, m=mass, n=moles)

         PV=nRT ---> PV=(m/M)RT

Density is mass over volume

         PV=(m/M)RT--->m/v=PM/RT

Effusion

        Grahm's Law of Effusion: r1/r2=Square root of (M2/M1)

Ideal Gasses v. Real Gasses

Ideal gasses are volume-less masses. They ignore attracting/repelling force as well. However, in real gasses, these are all taken into account. 

Corrected ideal Gas equation (+ Van der Waals)

         (P+n^2a/V^2)(V=nb)=nRT

a represents interaction part of molecules. b represents volume component of molecules.

General trends:

• Pressure is usually less than expected
• volume is usually greater than expected
• Ideal: small, nonpolar molecules, high temperatures, low pressure
• Non-ideal: low temperature, high pressure.

In class, we worked on ConcepTests as well as worksheets to become familiar with the concepts.

Main Ideas

I felt it was difficult to understand the different concepts because of the lack of time (at least for me, even though I only lost three days). The white boarding helps me (I think) because I learn best with examples and worked out problems. I also was disappointed because I had to rush through the task chains tonight. I hope you'll have them up again before the test! Other than that, I feel comfortable with the general trends and relationships between volume, pressure, and temperature.

12.16.13 - Thermodynamics and upcoming lab

Thermodynamics

This week, we focused on Thermodynamics. We learned that entropy is the number of the most probable discernible microstates (or degrees of freedom) in a system which tended to be the most probable. Boltzmann's equation of entropy is S=klnW

Laws of Thermodynamics
1. energy contained in the universe is constant
2. the entropy of the universe is increasing

Basically, if delta S is positive, the particles in the system are moving faster (more randomness), or there are more particles in the product than the reactants. If delta S is negative, the particles are slowing down, or there are less particles in the product than the reactants.

In class, we worked on several worksheets, Thermodynamics II and Thermodynamics III, in order to understand the concept. We were also given some equations and changes in heat (or heat of formation) in order to find the enthalpy change of the system.

upcoming lab

There is a lab due next week on Friday. We are given a couple of reactions, in addition to the materials we need to find the heat of combustion for the reaction. We determined the equations for this in class. There will be more on this on next week's blog.

Main Ideas

This unit is probably the hardest unit for me. I understand the material whenever we go over it in class, but it takes me a while to understand the concepts of this unit, such as change in heat, enthalpy, and entropy. I still feel that I don't quite understand the general concepts of the topics I've mentioned, but I think it'll become more familiar when I review for next week's test. I was also confused on how the lab is going to work. How do we find the heat of combustion by doing the experiment? How do we get the measurements, let alone the accuracy of the combustion? For one of the steps, how do we create water from hydrogen and oxygen atoms? In summary, I don't feel confident about this unit, although it is starting to make a little bit more sense.

11.11.13 - Liquids, solids, Vapor Pressure, Lattice Energy, and Conductivity

Liquids

We had a lecture quiz on solids and liquids. Viscosity depends on the strength of the intermolecular forces. As force increases, viscosity increases. As temperature increases, the viscosity decreases. Cohesives v. Adhesive: cohesive forces happen when similar molecules bind together. Adhesive happens when intermolecular forces bind a substance to a surface. For example, water's adhesive forces between the H2O and glass are greater than the forces between the h2o molecules (creating a meniscus).

Solids

There are two groups of solids: crystalline (highly ordered arrangement) and amorphous (no particular arrangement). Covalent-Network solids, like diamonds have a high melting point and are often times hard. In order to vaporize this, the covalent bonds must be broken. Molecular solids are when atoms are held together with van der Waals forces, such as graphite. These tend to have lower melting points.

We had a lecture quiz on this to help us understand the material. We also had a worksheet called Intermolecular Forces 11 Worksheet to put together what we learned so far.

Vapor Pressure

Vapor is what we call a gaseous substance that is usually liquid at room temperature. Dynamic equilibrium occurs when the liquid molecules evaporate at the same rate as the vapor molecules condense.

Temperature affects vapor pressure. As temperature increases, more and more molecules at the surface have enough kinetic energy to escape the surface, therefore making the vapor pressure increase. When vapor pressure of a liquid reaches the atmospheric pressure, it boils. That's why water boils at a lower temperature when the elevation is high. Also, higher boiling point equals a lower vapor pressure. vapor pressure decreases with the molecular weight increases.

We had a lecture quiz to become comfortable with the material.

Lattice Energy

A quick review: There are three types of bonds. Ionic (electrostatic attraction between ions), Covalent (sharing of electrons), and Metallic (Metal atoms bonded to several other atoms. Cation surrounded by a sea of electrons). 

Lattice energy - The energy required to completely separate a mole of a solid ionic compound into its gaseous ions.

Smaller ions lead to increased lattice energy. Greater charge leads to increased energy. The effect of charge is greater than the effect of distance.

Conductivity

We worked on a small lab on conductivity. We tested several substance's conductivity. Here are the results:

We understand that in order for a substance to be conductive, there must be a sea of electrons that conduct the electricity from one wire to the other. In the case of NaCl, solids does not conduct because the atoms are in place. however, in it's liquid state, we are able to loosen the atoms and conduct the electricity through the substance.

Main Ideas

This week, I generally understand the main ideas. However, I still have trouble understanding vapor pressure and Lattice Energy. What exactly is Lattice energy, and where does it come from? What exactly is vapor pressure, what does it measure, and what are it's effects on a substance's properties? I feel quite secure on viscosity and the sea of electrons concept, however I feel I need more help on understanding the characteristics of all the other properties, such as why graphite is soft while diamonds are extremely hard.

11.4.13 - Intermolecular forces v. Intramolecular forces, and Water

Intermolecular Forces v. Intramolecular forces

This week, following out ionic and metal worksheets, we worked on understanding Intermolecular forces and intramolecular forces. Intermolecular forces are the forces between the molecules, while the intramolecular forces are between the actual atoms. For example, intermolecular forces hold together the H and O atoms in H2O, while the intermolecular forces hold together the molecules so that it stays together to form solids, liquids, or gas, depending on the temperature of the environment.

There are three types of intermolecular forces: induced dipole-induced dipole (London dispersion forces), Dipole-dipole, and Hydrogen bonding.

London dispersion force occurs between any two molecules because there is a momentary concentration of electrons on one side of the atom, causing a momentary dipole in the molecule. This is what holds molecules with no dipole moment. London dispersion force occurs in all molecules.

The next strongest intermolecular force is the dipole-dipole force. Molecules with this have attraction between the molecules due to the partial charges on the molecules from the dipole moment.

The strongest force is called the Hydrogen bond. This occurs between any molecule that has a Hydrogen atom bonded to either Nitrogen, Oxygen, of Florine atom.

To help learn the material, we went over two worksheets: Intermolecular Fores and Intermolecular Forces 1 Worksheet.

Water

We also went over a pogil about Water. We learned a little about why Salt (NaCl) dissolves in water. The hydrogen bonds override the ionic bond between the Na and Cl, breaking the ions apart. 

Main Ideas

This week, the main ideas connected because we need to know the characteristics of the intermolecular forces and intramolecular forces in order to understand why salt dissolves in water. The model with the molecules helped me because it was easy to understand which side attracted to which molecule. It also helped me understand why ice is less dense than liquid water, something I have been wondering for a very long time. I am becoming unsure, however, about the materials we covered in this weekend's lecture quizzes, "Liquids and Solids". I don't think I quite understand why liquids have surface tension.

10.28.13 - Test on Covalent Bonding, Hydrogen Bonding, Ionic bonding, and Metals

Testing on Covalent Bonding

This Tuesday, we had a test on Covalent bonding.

                     

Overall, I felt better about this test than the last test on Stoichiometry. I haven't looked back at my test yet so I don't know what I got wrong.

Hydrogen Bonding

We also got introduced to hydrogen bonding this week. We read an article about the osmosis of paintballs and the reason behind it. It turns out that there are small attractions called hydrogen bonding between the hydrogen and the oxygen atoms because of the positive polarity on hydrogen and negative polarity on oxygen.

To help understand the material, we wrote an essay on a Paintball essay by Brian Rohrig called "Paintballs"

Ionic bonding

We started our next unit on ionic bonds. In an ionic bond, the electrons are freely moving within the material, unlike covalent bonds where they are sharing electrons. The ionic bond is between a Cation (positive) and an Anion (negative). In NaCl, the sodium ion is smaller than the chlorine atoms because it looses one row of electrons to the Cl.

To help understand this, we did a pogil on Ionic Bonding. 

We also learned that those with an anion or cation with a higher charge has more force between their attraction. The smaller the ionic compound, the larger the melting point. Melting point depends on how much energy it takes to break or spread the bonds between the ions.

Metals

There is a lecture quiz due this Sunday on Metals.

Characteristics of metals include:

• conductivity
• malleable (able to be pressed into different shapes)
• ductile (able to be drawn into wire)
• metals aren't as brittle as other solids

They are not covalently bonded, but they have extremely strong bonds between the ions.

Electron-Sea Model is a representation of how electrons on the outermost valance swims around freely inside the sample. The rest of the ions are structured like this

This explains its conductivity.

Alloys are mixtures of elements that have property characteristics of metals. This can be a metal within a metal, or can be a non-metal within a metal (they are located in the staircase on the periodic table). Solution alloys are solutions such as Steel (Carbon and Iron). They can be substitutional alloys where solute particles take the place of the solvent metal atom, or an interstitial alloy where the solute particles are so small they can fit into the holes between the solvent metal ions. Therefore they are usually more dense than substitutional alloys.

Main Ideas

The main idea that was new this week was the introduction to ionic bonds and metals. I feel relatively comfortable with these ideas because a lot of this material has been gone over last year in SG Chem 1. The only think that I'm wondering about is what is the charge on these atoms measured in? (what is the unit of charge? Coulomb?)

10.21.13 - WebMO, hybridization, sigma/pi bonds, test next week

WebMO

This week, we've mostly worked out building our VSEPR balloon models on WebMO. To build a model on WebMO, we first placed out elements on the program and submitted it to clean up the shape of the structure. Then, by creating the structure, we were able to determine the angle measures, the dipole moment, the charges of the elements, and we were able to build the space filling models.

Here are some examples:

By building these models, we were able to understand the dipole moments, polarity, electron domain geometry and the molecular domain geometry. This activity really helped me with determining the different domain geometries and the angles that correspond to each molecule.

Hybridization

I believe we were introduced hybrid orbitals in one of the lecture quizzes, however this week we went over some examples for homework. sp corresponds with two hybrid orbitals, with angle measures of 180 (linear). sp2 corresponds with three hybrid orbitals with angle measures of 120 (trigonal planar). sp3 has four hybrid orbitals with angle measures of 109.45 (tetrahedral). Although there use to be a theory that the d orbitals also exist, we no longer learn this in class because there is doubt in the theory. So, anything above four hybrid orbitals does not have a hybrid orbital.

sigma/pi bonds

On Friday, we went over a little about sigma and pi bonds to clear up some confusion we had since out lecture quiz. A single bond is always a sigma bond. When there is a double bond, there is a sigma and pi bond.

Here is a picture of a diagram of CO

In this way, there are one sigma bond and two pi bonds that make the CO molecule covalent.

Test Next Week

We have a test next week on Tuesday. We will be tested on drawing Lewis structures, calculating formal charges, resonance structures, bond length and strength, VSEPR models, bond order, bond angles and their reasons, shapes of the Electron Domain Geometry and Molecular Domain Geometry, hybridization, polarity, and other material we have covered in this unit.

Main Ideas

This week, the main idea was to become comfortable with the uncertainties we had since our lecture quizzes. Practicing the electron domain geometry and the molecular domain geometry on the WebMO really helped me because I got more practice and understanding to why the molecules take the shapes they take. I'm still unsure about fully understanding the material for this unit. For example, what is the difference between a sigma bond and a pi bond? I understand that there are two different types of bonds in a double bond or triple bond, but I don't know what the differences are. I would like to relearn the unit with a deeper understanding if I ever have time before the AP exam. I still need to work on understanding the general ideas of all the topics (under Test Next Week) because I mix up a lot of the concepts we've learned over the past few weeks, like hybridization and polarity. However, my ideas have changed about atoms: I know they are much more complicated than what I assumed they were like!