CHEMISTRY COMMUNITY

TimVintsDis4L

It's pretty much the likelihood of a molecular collision to occur. An H+ and H+ collision is way more likely to occur then an H H O since the molecules have to hit each other at a certain angle in order for the bonds to form.

TimVintsDis4L

You can access the final from the website and it will be open book. However, I do not know if it will be similar to the Audio-Visual Assessments in that it will be multiple choice or free response. I expect it to be free response and fairly simple.

TimVintsDis4L

An Endothermic reaction requires an input of energy to get over the hump that is the Activation Energy, in order to turn Reactants into Products. It makes sense if you think about which one requires more energy. Since an endothermic reaction requires an input, but an exothermic does not, you know th...

TimVintsDis4L

So Kinetics deals with how fast or slow a species react, but Thermodynamics deals with how stable they are in one state or another. That's essentially what the question is asking.

TimVintsDis4L

Mariah wrote:Any word on how long it will be ?

He mentioned that it was going to be pretty short and simple so I would assume no more than 1.5 hours, so half of what the actual final would have been like.

TimVintsDis4L

The only awkward part I had when doing the homework was the way in which they set up the reactions, something my TA also addressed. Other than that its simply finding out which equation to use and what components are needed.

TimVintsDis4L

Galvanic Cell and Electrolytic Cells are essentially opposites

Galvanic Cell = $-\Delta G = spontaneous = +E^{\circ} cell = k<1$

Electrolytic Cell = $+\Delta G = nonspontaneous = -E^{\circ} cell = k>1$

TimVintsDis4L

If you are asking whether or not to change the sign when subtracting the anode from cathode then remember this simple rule. When you are doing E(cell) = E(cathode) - E(anode), then you use the numbers given as is, and DO NOT change the sign based on whether its Oxidized or not. For example If your r...

TimVintsDis4L

Just remember that when balacing basic solutions you balance the O with OH- and the H with H20

TimVintsDis4L

I wouldn't be surprised if we get our tests back on Wednesday as the Ta's might have to work on the final so they get the tests over with first.

TimVintsDis4L

Instead of having to plug in all of those constants you can remember it as something that looks like this
$E=E^{\circ} - \frac{.025693}{n}\cdot lnQ$

Here the RT/F is converted into .025693 to make the equation simpler.

TimVintsDis4L

When we are given a Cell Diagram and concentrations and asked to find the Q what do we use as the Products and Reactants. Would we not use the right side (cathode, reduced) side as the Product and the (anode,oxidized) side as the Reactant?

TimVintsDis4L

First order reactions and second order reactions are way more common than third and forth, those are very unlikely because it requires 3 or 4 separate entities to perfectly come together, which is very unlikely.

TimVintsDis4L

When you write the cell diagram you do not include the balancing stoichiometric number. Essentially, you don't include any coefficients.

TimVintsDis4L

If you are referring to what we learned on Friday in class and the n in the following equation Rate = k[A]^{n} [B]^{m} then you need to do the following You essentially gather all of the data you have in terms of which experiment you are doing and compare the rates at which the equation changes. So ...

TimVintsDis4L

So [censored] electrons flow from the anode to the cathode, essentially leaves a more positive charge on the left side (anode) compared to the cathode. The salt bridge neutralizes that charge by allowing electrons to migrate back to the left via a sort of concentration gradient where solutes will al...

TimVintsDis4L

So essentially there are 2 sets of correlations, if that's a way to put it, but you can remember it as the following.

Galvanic Cell = - $\Delta G$ = Spontaneous = + E knot = K > 1

Electrolytic Cell = $\Delta G$ = non spontaneous = - E knot = K < 1

TimVintsDis4L

One of the rules our TA taught us regarding this was that it's based off what type of reaction you have.

If it's acidic, balance O with water, then balance H with protons

If it's basic, balance O with OH-, and H with H20

TimVintsDis4L

Essentially look at what units you have and what units you need to cancel out so that it makes sense for Gibbs Free Energy. Gibbs Free Energy should be kj.mol^-1

TimVintsDis4L

Within a battery, electrons are pumped away from the anode and into the cathode. I believe the same can be said for electrolytes as they become ions when dissolved in water.

TimVintsDis4L

An electrolyte is something that dissolves into ions when placed in a solution such as water.

TimVintsDis4L

I'm sure if you have a quick question regarding the topic the UA's will be more than happy to help.

TimVintsDis4L

Although it covers the second page of Outline 4 and all of Outline 5, many of the concepts in Outline 4 will be needed for Outline 5 as well as determining concentrations.

TimVintsDis4L

I don't know if this really helps, but if we are given the Internal Energy, q, or things that can be used to find q such as $\Delta S$ and t, then we can find q using $\Delta s = q/t$ . Once you find the q, you can plug it into $\Delta U = q + w$ to get w.

TimVintsDis4L

The type of bond has a constant enthalpy which will always be provided were we to have to solve for it. My advice for calculating these problems is to draw it out first and write out how many of what type of bond you have. Once you have that, you can cancel out duplicates as this will make the calcu...

TimVintsDis4L

I believe that every constant we may ever need will be provided for us on every test and exam. However, some equations may not be and we may have to derive them.

TimVintsDis4L

When Delta G is negative, the reaction is exothermic. This means that it releases heat and does not require an input of energy; hence, it is spontaneous. An exothermic reaction indicates that an input of energy is required. This makes it a non-spontaneous reaction as it needs something else (not spo...

TimVintsDis4L

If the Internal Energy of the System is equal to 0, then q must = - w so that they cancel out and you're left with 0.

TimVintsDis4L

It is the heat required to change 1 mole of a substance, by 1 Degree Celsius

TimVintsDis4L

By $\Delta G$ being Negative, we know that this is an exothermic reaction. As it is an exothermic reaction, we don't need and input of energy for it to proceed. As a result, the reaction is favorable and thus, spontaneous.

TimVintsDis4L

Ya, I would simply draw out the Lewis Structures then compare the bonds. If one structure has 2 C-C bonds and the other has 1 C-C bond, then you can cancel 1 from each side to make the calculations easier.

TimVintsDis4L

One of the ways you can tell if an equation is exothermic or endothermic is using Gibbs Free Energy.
If the $\Delta G$ is negative then it is exothermic, if it is positive then it is endothermic.

TimVintsDis4L

I don't know the first part to your question, but I do know the equation used to calculate enthalpy.

$\Delta H = m s\Delta T$

The Delta H = Change in Enthalpy

The m = mass

The s = heat

and the Delta T = the temperature change

TimVintsDis4L

Open System ( matter & energy can exchange with surroundings) Beaker of Water Water can evaporate & Beaker does not insulate Closed System( energy can exchange with surroundings) Sealed beaker of water Beaker does not insulate Isolated System ( nothing exchanged with surroundings) Combustion...

TimVintsDis4L

The process of steaming converting back into water as it touches your skin releases a lot of heat as a result of the phase change. That transition emits heat which can be seen as heat on top of the pre-existing 100 degrees.

TimVintsDis4L

Can we think of work as either exothermic and endothermic. The work can be in the form of heat so would that be a valid statement.

TimVintsDis4L

Can someone please explain how to do #4 on Test # 1. The questions states

There is an unknown quantity of Xenon in a 25 L container at .50 atm and 27 C. How many grams of Xenon are present?

TimVintsDis4L

Based off last years midterm I would say most of the content will revolve around the new topics. As we have already been tested on Chemical Equillibrium and Acids and Bases expect more Thermodynamics and Thermochemistry. However, I believe that there will be 1 or 2 questions covering the entire sect...

TimVintsDis4L

State property is like the distance between UCLA and downtown. The state property distance will be different from the actual route to take their as you can't go through buildings when driving.

TimVintsDis4L

The midterms/final are similar in the sense that the questions are sandwiched between an equation sheet and a periodic table. However, the midterms are harder overall as the questions require you master the subject or you will get the question wrong, as well as the follow up questions regarding the ...

TimVintsDis4L

∆H tells us the change in temperature so I don't know what else could tell us if its an endothermic or exothermic reaction.

TimVintsDis4L

What should you do if noone laughs at your Chemistry joke.

Keep telling them until you get a reaction

TimVintsDis4L

I've been doing the following problem and I feel like I am doing it right, but the results say it is wrong. I would assume that i is neither since the moles are equal on both sides. The pressure increases with the volume decreasing so the chemical reaction would favor the side with less moles but th...

TimVintsDis4L

It's just an aqueous solution of a weak acid and a conjugate base that helps keep the pH at a constant value.

TimVintsDis4L

Just remember that pH = -log[H30+] and pOH= - log [OH-] so try not to get them confused. If only one is given, then subtract the pH from 14 to get the other.

TimVintsDis4L

I doubt there's any science behind it being 5%. Scientists are lazy so they just choose a good number to go by and stick with that. The 5% is just something for us to follow as to whether or not to use the quadratic formula.

TimVintsDis4L

Temperature is the only thing that affects the constant because even if the concentration changes, the equation will do its best to mitigate the change. Le Chatelier's Principle pretty much explains this.

TimVintsDis4L

He just gave us examples of calculating the pH of a weak acid and its salt ( to make a buffer) as well as just calculating the pH of a salt solution.

TimVintsDis4L

In addition to what everyone else has said regarding Q being used at any point in the equation, it can alos help us solve problems as to which way the reaction is heading. If Q < K, pre equilibrium, then reaction will proceed forward ( too much reactant , or not enough product) Greater Denominator I...

TimVintsDis4L

Will helium always be the inert gas we would add, or what other gases could also work? I'm fairly certain that any inert gas can be added but Helium is the most ideal as it is the least reactive. Helium exists as a single atom so the van der Waals forces are even weaker. This makes it less reactive...

TimVintsDis4L

The professor said that we won't be dealing with cubic expressions when it comes to finding the concentrations. He did however state that the quadratic formula would not work so you would have to find it by hand or via a calculator.

TimVintsDis4L

It can only be the positive number as there is no such thing as a negative concentration

TimVintsDis4L

When HCl and CaO are accidentally mixed in the flask, they will react to form salt and water making the following equation: 2HCl + CaO ---> CaCl2 + H2O. Knowing this, find the limiting reactant that was poured into the the flask. (Its CaO) so that means that HCl will be in excess in the solution. U...

TimVintsDis4L

Can someone please explain how to do #34. I know that you find the moles then use the excess moles and find the pH using that, but my math doesn't add up. When HCl and CaO are accidentally mixed in the flask, they will react to form salt and water making the following equation: 2HCl + CaO ---> CaCl...

TimVintsDis4L

Can someone please explain how to do #34. I know that you find the moles then use the excess moles and find the pH using that, but my math doesn't add up.

TimVintsDis4L

It's amphiprotic because it can act as both an acid and base. The nitrogen atoms with lone pairs can accept two protons. It can also accept a proton to form a conjugate base.

TimVintsDis4L

There are many differences but I think the major difference is that Hemoglobin binds with 4 oxygen molecules while Myoglobin binds with 1.

TimVintsDis4L

I'm fairly certain that almost all of the equations and constants will be provided for the final.

TimVintsDis4L

Does anyone know where the answers to the practice are since its well over the time they were supposed to be posted?

TimVintsDis4L

The readings are there to get a better understanding of what the professor lectures in class. If there are things you don't get in class, look to the textbook to get a better idea.

TimVintsDis4L

I believe the main difference is that bronsted deals with proton donors/acceptors, while Lewis deals with electron donors/acceptors.

TimVintsDis4L

The roman numeral is simply the oxidation number of the central atom that makes the chemical compound neutral

TimVintsDis4L

The oxidation number is vital to the name as it tells us what the oxidation of the central atom must be to make the compound neutral.

TimVintsDis4L

Ligands bond to the central metal atom or ion. The ligands act as the Lewis Bases(donors) and the central atom acts as the Lewis Acid (receiver).

TimVintsDis4L

Sigma and Pi bonds have their own shapes. A sigma bond is more like an oval, while a Pi bond looks like a single macaroni of Kraft Mac n Cheese

TimVintsDis4L

By knowing the coordination number we can then determine the name of the coordination complex.

TimVintsDis4L

The number of ligands are also represented by the X number in the AXE method.

TimVintsDis4L

The X represents the Ligands and the E represents the lone pairs.

TimVintsDis4L

Is test 2 just on sections 2E and 2F, or am I forgetting something?

TimVintsDis4L

The drawing won't ever be quite balanced as it's a 2 dimensional version of the the shape. What matters more is the formal charge of the Lewis structure.

TimVintsDis4L

They can only form with Oxygen, Nitrogen, and Fluorine as this is the greatest difference in electronegativity between them and Hydrogen.

TimVintsDis4L

It's all based on the surface area and how much surface the atoms can cling on to.

TimVintsDis4L

If the difference in electronegativity for the atoms in a bond is greater than 0.4, then it's polar. If the difference in electronegativity is less than 0.4, then it's non polar.

TimVintsDis4L

From what we've learned, Van Der Waals are actually the weakest. That is then followed by Dipole-Dipole which is the 2nd strongest and Hydrogen Bonds which are the strongest. You can look at it like this

Van Der Waals < Dipole-Dipole < Hydrogen Bonds

TimVintsDis4L

Bond Energy can be found by subtracting the sum of all the bonds formed from the sum of all bonds broken.

TimVintsDis4L

Resonance structures are simply alternate Lewis structures for a given ion or molecule.

TimVintsDis4L

A formal charge of 0 simply states that a Lewis Structure is at its lowest energy level. Some structures may not have a formal charge of 0, but the goal is to draw a structure so that it is at its lowest formal charge/ more stable.

TimVintsDis4L

Van Der Waals - the weakest interaction and is present in all compounds, something like Iodine and Argong

Dipole-Dipole - stronger, between more positively charged element and negative. An example being Carbon and Oxygen

Hydrogen Bond- strongest, essentially a super bond between H and C,N,O,F

TimVintsDis4L

The balance between the kinetic energies of the molecules and the inter molecular attractions determines whether something will be a solid, liquid, or gas .The attractive forces between the molecules increase as you go down a group so that explains the change.

TimVintsDis4L

I would do the online modules and go through the problems assigned for homework. I believe all of the questions will be taken from there, so it's almost like an exact study guide.

TimVintsDis4L

I doubt it. Unless it is something we learned in class or from our homework. I believe all of the questions will be taken from the homeworks and Online Modules so it will not be something we have never seen before.

TimVintsDis4L

The electrons are removed from the right most sections of the electron configuration. Electrons are typically removed from the valence shells, which are the highest in s and p orbitals.

TimVintsDis4L

The dipole moment also tells us about the charge. The bigger the difference in electronegativity, the larger the charge and vice versa.

TimVintsDis4L

Shorter Bonds are stronger since the & less reactive, so triple bonds would be the strongest. Longer bonds are weaker and are more likely to be involved in a reaction, so single bonds are the weakest.

TimVintsDis4L

A more stable Lewis structure will have a formal charge of 0. That is why we try to draw the Lewis Structure in different ways to see if we can get the formal charge to 0. In the example provided of (S04^2-), the first Lewis Structure we drew had a final formal charge of (-1); whereas, the second on...

TimVintsDis4L

Ionic compounds transfer dots (electrons) from metal to nonmetal atom.

Non metals do not form cations because their ionization energies are too high sot hey share electrons to form covalent bonds.

TimVintsDis4L

My TA let us write the short form of the electron configuration so I believe this is something one of the mods can clarify. Either way its good to know how to do the whole thing.

TimVintsDis4L

The best way to draw a Lewis Structure is by putting the element with the ionization energy in the middle. This is because all the other atoms will be placed around. You then want to make sure the dots and bonds drawn correlates to the valence electrons calculated from the elements. Also, make sure ...

TimVintsDis4L

Double bonds and triple bonds have more electrons so they exert a stronger attraction force. This pulls the atoms closer together, creating shorter bond lengths.

TimVintsDis4L

The Empirical formula is needed to calculate the molecular formula but cannot be done so without the molar mass. Once you have the molar masses of both the Empirical formula and the Molecular formula you divide the two to get the ration. If E(molar mass)/M(molar mass)= 2, then multiply the Empirical...

TimVintsDis4L

Is it possible to have more arrows pointing in one direction than another. If so, what does that entail?

TimVintsDis4L

Both the Work Function and the Threshold Energy function refer to the energy required to eject the electron. They are fundamentally the same when it comes down to calculating. The work function refers to the energy that needs to be put in and the Threshold Energy function refers to the frequency req...

TimVintsDis4L

Are all of these equations meant to be memorized, or will they be provided on tests?

TimVintsDis4L

I would show all work. I had points taken off my first test for not showing work in some parts. You don't have to show everything step by step, but as long as it shows your calculations you should be fine. If you feel you should have gotten more points for the work you showed you can always talk wit...

TimVintsDis4L

From what I recall, if you get the answer correct, then you are given full credit as long as some work is shown. However, I would still show work in case I get the problem wrong and my work shown will be worth some partial credit.

TimVintsDis4L

I would personally refrain from keeping fractions in the formula because of how easy of a fix it is. All you really have to do is multiply everything by the denominator to remove the fraction. It's an easy fix for something you won't have to worry about later.

TimVintsDis4L

Maybe, but if that's the case then it shouldn't be much harder than finding how much product we can make. We would simply find it by using the remaining moles or even by subtracting what we have from the total

TimVintsDis4L

The professor went over this in class and the way he taught us seems to be working fine for me. The steps are as follows: Give yourself time, be mindful What is the question? What concepts do I know? What model or equation do I know? What is known? What is unknown? Can I express the unknown with res...

TimVintsDis4L

Sig Figs have to do with any number that isn't a 0 or a 0 between two numbers.
So for example:
72345 has 5 Sig figs
72300 has 3 Sig figs
72032 has 5 sig figs

So in your case there are 3 sig figs.

TimVintsDis4L

I'd assume he 'll provide us with a sort of image/ reference. Just how it's ridiculous to have us memorize the periodic table, so he provides us with one on tests. We are learning about the topic and how to find what it is we are looking for, not memorize something that has already been established.

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