CHEMISTRY COMMUNITY

JT Wechsler 2B

The half life is the amount of time that it takes for half of a sample to die off. This can be taken with respect to radioactive isotopes or even (like in our case) the amount of time for a certain reactant to decrease by half.

JT Wechsler 2B

No, the rate constant will not be negative.

JT Wechsler 2B

I believe it is the frequency of collisions between two molecules that are at the correct orientation. If they collide with an incorrect orientation, no reaction will occur.

JT Wechsler 2B

You must calculate this by using experimental data as shown in class on Friday. This is found by comparing the reaction rates at different initial concentrations for the same reaction.

JT Wechsler 2B

k is unique for each individual reaction as it changes with temperature.

JT Wechsler 2B

First order reaction graphs are only straight lines when the graph is time vs. ln[A]

JT Wechsler 2B

Typically this is the case. To have a reaction occur, you have to meet a set amount of energy (the activation energy) to have a reaction proceed. Typically the higher the activation energy is, the more energy will be needed to be put into the system.

JT Wechsler 2B

No, coefficients do not because cell potential is an intensive property. This is like how density of a substance is not determined by the actual amount that you have.

JT Wechsler 2B

The fact that they are aqueous implies that water is there.

JT Wechsler 2B

Yes, you heard Lavelle correctly. Basically, when E is positive, the equation, deltaG = -nFE is negative. When deltaG is negative, the reaction is spontaneous.

JT Wechsler 2B

At the anode, there is a buildup of positively charged ions and at the cathode, there is a buildup of negatively charged ions. To prevent this buildup of charge from being too great and stopping the reaction, a salt bridge adds positively charged ions to the cathode and negatively charged ions to th...

JT Wechsler 2B

Entropy always increases as substances go from the solid to the liquid phase. This is because the IMFs between the molecules break and the molecules are now able to occupy more positions than before.

JT Wechsler 2B

deltaU can equal 0 when there is no temperature change or q is equal to -w.

JT Wechsler 2B

Irreversible reactions occur at constant pressure.

JT Wechsler 2B

I believe that it needs to be calculated in Kelvin.

JT Wechsler 2B

Area times distance is considered a change in a volume. Depending on how long the distance is that the area is going through, your volume will be different.

JT Wechsler 2B

If work is done on the system it is positive. If work is done by the system it is negative. This is kind of like temperature changes in a system being endothermic and exothermic. If heat is being given into a system it’s positive and if heat is leaving the system it’s negative.

JT Wechsler 2B

It is considered isolated because there is no matter transfer between it and the environment. Since the water bottle is insulated that means that no heat would be able to be transferred.

JT Wechsler 2B

The reverse reactions would be exothermic because you would be losing heat to go from liquid to solid.

JT Wechsler 2B

Bond enthalpies are less accurate because they are a general average of the bond enthalpies taken from many different molecules for that specific type of bond.

JT Wechsler 2B

Strong acids completely dissociate in solution. Because of this, their Ka value would be so large that for this class we just approximate that to be infinity.

JT Wechsler 2B

Buffer equations are mentioned on the second outline under calculations with salts so I'd know them just to be safe for the test.

JT Wechsler 2B

Basically, if there is an acid base reaction, the base (on the reactants side) will have a conjugate acid (on the products side), and vice versa. Since this is the case, it may be necessary to convert Ka to Kb (or the other way around) depending on what way you are looking at the reaction.

JT Wechsler 2B

Either can be used, however, it should be consistent throughout the entire problem.

JT Wechsler 2B

The Ka or KB should be less than 10^-3 in a reaction just to be safe and apply the 5% approximation.

JT Wechsler 2B

Since we know KaxKb = Kw that is what should be used to be safe.

JT Wechsler 2B

I don’t know if we will for this class but basically what you’d do is balance the equation first. Second in the ice table you will want to add/subtract the stoichiometric coefficient times x from your initial value.

JT Wechsler 2B

You should convert all of the concentrations or partial pressures to whatever you have more of. This can be done with the Ideal gas law.

JT Wechsler 2B

You will use Kc when asked about concentrations (molarity) and Kp when asked about the partial pressures of gases.

JT Wechsler 2B

Brackets are used for concentrations and will be used to calculate Kc. Parentheses are used for the partial pressures and will be used to calculate Kp.

JT Wechsler 2B

He never said if we were going to be required to know this in class. However, I would still be familiar with the concept in case it does come up since he did do an example of this in class.

JT Wechsler 2B

Monodentate is when a ligand only binds to the metal in one location. Polydentate is when a ligand binds in more than one location.

JT Wechsler 2B

I think we need to the Lewis definition and the Bronsted definition. Also, we need to know strong acids and bases and how to calculate the pH. This would include using it for a neutralization reaction.

JT Wechsler 2B

The presence of H-bonding increases both the melting and boiling points.

JT Wechsler 2B

For this course, we assume that strong acids and bases completely ionize in water for calculations.

JT Wechsler 2B

I don't think that we are going to have to memorize the polyatomic ions for the final as up to this point Professor Lavelle has not given off that impression. Also, on all of the past tests we have taken this has not been the case.

JT Wechsler 2B

A lewis base donates electrons while the lewis acid accepts electrons.

JT Wechsler 2B

Double bonds have both a sigma bond and a pi bond. The way that this works is that the first bond (the single bond) in the molecule is a sigma bond. All bonds after that are pi bonds.

JT Wechsler 2B

The presence of a hydrogen bond will increase the melting point and boiling point of a substance because there is a stronger attraction between the molecules of the substance.

JT Wechsler 2B

In a bond, usually there will be characteristics of both a covalent and ionic bond. Despite this, the bond will usually have a character of one type of bond more so than another.

JT Wechsler 2B

The geometric shape of this molecule would be called "T-shaped".

JT Wechsler 2B

Sigma bonds must occur first before a pi bond will form. This has to do with the orientation of the electrons in the bonding pairs.

JT Wechsler 2B

When a molecule has two elements that are bonded together with an electronegativity difference, the electrons will tend to "hang around" the atom with the higher electronegativity. This means that the area around that atom will be slightly more negative and will thus create a dipole. In th...

JT Wechsler 2B

At this point in time, the placement of atoms in the Lewis Structures doesn't matter. It will in the future though.

JT Wechsler 2B

This would require you to draw the lewis structures and to calculate the formal charge. This way you can take a look and see if the structure has resonance. It is tough to know the exact bond lengths though without doing experiments.

JT Wechsler 2B

The first four elements and group 13 elements all can have less than a completed octet. If an element is in period 3 or lower on the periodic table, then they can have greater than 8 electrons because of the d suborbital.

JT Wechsler 2B

The octet rule is a guideline where each atom in a covalent bond should have 8 electrons (noble gas configuration) connected to it either through lone pairs or through bonds. There are exceptions to this rule.

JT Wechsler 2B

The octet rule is more of a guideline because there are exceptions to the rule like the first 4 electrons and the expanded octet if elements are in the third period or higher.

JT Wechsler 2B

V is the valence electrons that can be known by looking at the periodic table L is the number of lone pair electrons S is the number of electrons involved in bonding For H2O, Oxygen is bonded to hydrogen with two single bonds. Oxygen (from the periodic table) has 6 valence e- It has 2 bonds (each wi...

JT Wechsler 2B

Today in class, Professor Lavelle was saying that the electron configurations for the elements copper and chromium are abnormal and will take an electron from the 4s level to fill some of the 3d level. Does this have something to do with the energy levels of the elements?

JT Wechsler 2B

Since there are so many electrons for this electron configuration I don't think that it will be necessary to draw out. Rather I believe what you did and what is written in the back of the textbook should be okay. I would ask your TA if this question comes up on the test.

JT Wechsler 2B

Soyoung Park 1H wrote:The pictures that Professor Lavelle had on the presentation on Friday about d orbitals had cones and planes surrounding the orbitals while pictures in google images don't include them. What do they mean?

This just means that these are the nodal planes, or where there is no electron density.

JT Wechsler 2B

We are still in the Quantum section for homework. My TA said to do homework questions that were relevant to the topics that are currently being addressed in class so that your practice would be most beneficial to what is being taught in the course.

JT Wechsler 2B

The threshold energy is the minimum amount of energy that is required to remove an electron from the surface of the metal.

JT Wechsler 2B

When an electron is still around the nucleus, the system is more stable and at a lower energy than if it were to not be there at all. Because of this, there is a negative sign in the equation.

JT Wechsler 2B

Something that is quantized can only have discrete values or quantities of something. In our case, that would be energy.

JT Wechsler 2B

The way that electrons take in energy is that they must have a specific amount of energy taken in in order to go from one energy level to the next. My high school chem teacher explained it to me like an elevator that automatically took you to the desired floor. You can go from one floor to the next ...

JT Wechsler 2B

Depending on the experiment and on the situation, light has the ability to act both as a wave and as a particle. It can get cloudy and confusing at times, but light is able to do both depending on how you are collecting the data.

JT Wechsler 2B

Quanta basically means that energy is going to be released or gained in discrete "whole numbers." In other words it is not a continuous spectrum.

JT Wechsler 2B

You can use Avogadro's number to convert between molecules and moles.

JT Wechsler 2B

To solve this, you are first going to use the given conversion of 1.00 pounds to grams (454g). Make sure that the equation they give you in the book is balanced (if not balance it). Then, you will want to convert the grams of the fat to moles by using the molar mass of the fat. Once you do this you ...

JT Wechsler 2B

I believe that you should be fine. The textbook only says this because when you count up everything that is the whole number. I personally would have simplified it to be the lowest whole numbers as well.

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