CHEMISTRY COMMUNITY

Sheridan Slaterbeck 1J

Yes anything we learned this quarter could be on it.

Sheridan Slaterbeck 1J

delta G is negative as a combustion will increase the entropy S, or disorder, of the system and is therefore spontaneous.

Sheridan Slaterbeck 1J

It should be anything that we learned this quarter, cumulative.

Sheridan Slaterbeck 1J

The more negative the E, the more strong it is as a reducing agent (the thing being oxidized). Another way of saying it is a good donator.

Sheridan Slaterbeck 1J

a solid to a liquid would be a spontaneous reaction so delta G would be negative.

Sheridan Slaterbeck 1J

I don't think so, Lavelle usually doesn't curve any tests.

Sheridan Slaterbeck 1J

Thermodynamics and electrochemistry up to nerst equation.

Sheridan Slaterbeck 1J

When delta G is negative it is exergonic and when it is positive it is endergonic
when delta H is negative it is exothermic and when it is positive it is endothermic.

Sheridan Slaterbeck 1J

It is spontaneous if delta G is negative, if (-TdeltaS) is negative, if deltaS is positive, and if delta H is negative
delta G = deltaH -TdeltaS

Sheridan Slaterbeck 1J

Chapter 9 questions I believe

Sheridan Slaterbeck 1J

My TA said by friday of this upcoming week

Sheridan Slaterbeck 1J

peer learning sessions will break down fewer problems but go slowly and more in depth, a chance to ask more questions
Midterm reviews cover more problems but go really fast and get less explanation , more for practice if you already understand the topic.

Sheridan Slaterbeck 1J

My TA said majority of it will be thermodynamics

Sheridan Slaterbeck 1J

when would you use deltaS=nRln(V2/v1) ?

Sheridan Slaterbeck 1J

I would say look to see what the problem gives you if Kc then use concentration values (mol/L). If "K" or Kp then use partial pressure (bars).

Sheridan Slaterbeck 1J

I would a assume they would give us that conversion if we needed it.

Sheridan Slaterbeck 1J

If it asked for change in enthalpy you would solve for deltaH. If it is asking for heat occurring by the system or on the system solve for q.

Sheridan Slaterbeck 1J

I would say convert it to joules just in case if they don't specify

Sheridan Slaterbeck 1J

if V=0
w=-Pext delta V
w=-P(0) so work =0

Sheridan Slaterbeck 1J

I don't think so Lavelle usually just shows derivatives as a way of understanding where the equations came from.

Sheridan Slaterbeck 1J

An example of isolated system would be soup in an insulated container (assuming insulation is sufficient). An example of open system would be boiling water in an open pan on the stove, matter and energy are transferred. A closed system would be putting a lid on the pan, no matter transfer just energy.

Sheridan Slaterbeck 1J

In a closed system the matter remains constant but energy can be transferred between surroundings and the system.
An isolated system neither energy or matter can be transferred.

Sheridan Slaterbeck 1J

I would say the homework problems, and the extra study guides some of the UA's post like I know Lyndon usually does one.

Sheridan Slaterbeck 1J

Also think about how fast steam phase changes back to liquid on your skin, because the process happens so fast it releases a very large amount of heat energy in a very short amount of time. If it was released over a longer period of time, it wouldn't be nearly as harmful.

Sheridan Slaterbeck 1J

Catalysts change the speed at which the reaction occurs, not the components.

Sheridan Slaterbeck 1J

Lavelle doesn't post them, if you missed one day you could just read the textbook and be fine though.

Sheridan Slaterbeck 1J

+H = endothermic the reactions needs heat
-H = exothermic the reaction gives off heat

Sheridan Slaterbeck 1J

5% rule is a way you can test if you assume x is so small of a number it is negligible in finding x. for example if Kc= x^2 / (.55-x) you could try the assumption and calculate for x like this Kc=x^2 /(.55). Once you get a value you can test if it is less than 5% of the initial concentration given. ...

Sheridan Slaterbeck 1J

How did the NH3 become 11.3* 10^-7 On worksheet 1 4d

Sheridan Slaterbeck 1J

Even though K and Q have the same formula P/R it is the numbers that you plug in that are different. Only once the reaction reaches equilibrium can you plug in for K. But Q is at any point during the reaction. K is only one number, whereas Q can be many different numbers.

Sheridan Slaterbeck 1J

The reasoning is Le Chatelier's Principle= chem reactions adjust so as to minimize the effect of changes.

Sheridan Slaterbeck 1J

It is basically the concept that chemical reactions by nature adjust so as to minimize the effect of changes. When equilibria is changed, like if more reactant was added more product is produced until original P/R ratio is attained. Or if more product is added, more reactant will form until the the ...

Sheridan Slaterbeck 1J

Some of the UAs will post practice Tests before the midterm and final that are really helpful for studying, last quarter Lyndon posted them.

Sheridan Slaterbeck 1J

Dr. Lavelle said they are the same thing.

Sheridan Slaterbeck 1J

The dipole should point to the more electronegative element in a bond of two elements. Example between O and F, the dipole would point to F. If two different dipoles point opposite directions they cancel each other out, if all cancel out the molecule is non-polar. If they have a net dipole moment th...

Sheridan Slaterbeck 1J

I think you have to draw out the Lewis structure for sure, then count electron densities and find subsequent and matching spd number
s=1
sp=2
sp2 =3
sp3 =4
sp3d =5 etc

Sheridan Slaterbeck 1J

The two lone pairs balance each other out on top and bottom, and the four bonds make a plus shape on one plane, each exactly 90 degrees apart.

Sheridan Slaterbeck 1J

Row 2 elements usually never have expanded octet.

Sheridan Slaterbeck 1J

My TA said the test should be similar in number to the other tests, so about 8 questions

Sheridan Slaterbeck 1J

My TA said to use the number given on the equation sheet otherwise rounding may affect your final answer and they can take points off for that.

Sheridan Slaterbeck 1J

The lone pairs push the bonding pairs H-O on both sides to increase the angle between lone pair and the hydrogen oxygen bond, but this decreases the angle between the two bonding pairs to 104.5 instead of 109.5

Sheridan Slaterbeck 1J

If you know the VSEPR model , you should be able to remember the bond angle associated with it like 120, or 109.5, or 90 degrees. Then figure out how the lone pairs push on the bonding pairs and affect the angles ( I find this is easiest by drawing it).

Sheridan Slaterbeck 1J

Lone pairs have a large affect on the shape of the molecule, lone pairs push nearby bonding pairs away creating a greater angle than if it were a bonding pair to bonding pair. Making the other angles decrease.

Sheridan Slaterbeck 1J

I think you should always show your calculations for formal charge, each TA grades differently but my TA said the more work you show the greater chance you will earn more points.

Sheridan Slaterbeck 1J

My TA said you don't have to memorize these just know that it could be possible in periods 3 and on, but not in period 1 or 2.

Sheridan Slaterbeck 1J

One of the TA's said we are not able to tell yet if a structure has resonance, we will learn that later. We will be told when to draw resonance structures as of now.

Sheridan Slaterbeck 1J

I don't think so. If it was not mentioned in class it won't be on the test.

Sheridan Slaterbeck 1J

Someone in a review session today said it could be more than 10, don't think we have to know the specifics.

Sheridan Slaterbeck 1J

In a review session today they said they would not ask us this without giving us values for which one has a higher ionization.

Sheridan Slaterbeck 1J

On the periodic table metals form cations, they have low ionization energy. Which means they have larger size, and electrons are farther from nucleus, so they are easily removed from s and p orbitals and do not require a lot of energy for the process. The p-block nonmetals form anions, meaning they ...

Sheridan Slaterbeck 1J

Essentially the number of protons and electrons equal each other in a neutral atom. And after a neutral atom loses a certain amount of electrons, this new cation now has less electrons in comparison to protons. Now that the positive charge protons outnumber the e-, the e- are pulled in tighter to th...

Sheridan Slaterbeck 1J

Cations lose their outermost electrons causing it to change from a neutral atom to a +positively charged atom. Two cations would repel each other since both would be +positive.

Sheridan Slaterbeck 1J

Chem_Mod wrote:No. All it means it that 250/500 is needed to pass with the class (likely a C- because that is the minimum grade needed to pass the class).

What amount of points would be a B- or A-? Is there a set scale now or only provided by the end of the quarter?

Sheridan Slaterbeck 1J

Does anyone know the range of an A in the class, a B, and C. In terms of points or percentage. I am a little confused because on the syllabus it says a passing grade C- is a 50%... ??

Sheridan Slaterbeck 1J

I think all we need to know is that no two electrons in the same atom have the same four quantum #s. And that spin states can either be+1/2 or -1/2 .

Sheridan Slaterbeck 1J

H bar is just a short hand notation, that is used just to simplify what is written. ( Hbar= h/2 pi) (H bar/2 = h/4 pi)

Sheridan Slaterbeck 1J

My TA said that if you write in pencil on your test he has to write over everything you wrote in pen, so you can't change your answers later. But do whatever makes you feel less stressed and more focused. I use to hate writing in pen but forcing your self to use it more and more will help. Usually a...

Sheridan Slaterbeck 1J

I personally like using benegg.net as my grade calculator. Easy to understand and helpful in giving you a close estimate of your final grade. I agree with others in that writing down your grades on little assignments as you go is the best way to keep track. Sometimes TAs do make mistakes.

Sheridan Slaterbeck 1J

I also find handwritten notes to be the best way for me to take notes. I am a very visual learner, so I often use colors too. I find that if I highlight "too much" information I tend to loose focus of what formulas and topics are the most important. Recently I have been actively working on...

Sheridan Slaterbeck 1J

My Ta said the same thing, homework for outline 2 (quantum) and test will be due on your discussion day. They said the test will be 40 min.

Sheridan Slaterbeck 1J

Also a question about the cutoff, is each week's post due that Sunday by midnight..?

Sheridan Slaterbeck 1J

Are we going to be told what will be on the formula sheet for Test one next week in discussion? Do we even get a formula sheet?

Search found 62 matches