CHEMISTRY COMMUNITY

Ryan Troutman 4L

The Ecell value never changes and is set, so we do not multiply it by the coefficient we multiply the whole equation by.

Ryan Troutman 4L

From what everyone else has said, there's a few different tricks to remember which has which such as
RedCat (Reduction - Cathode)
and
AnOx (Oxidization - Anode)

Ryan Troutman 4L

Balancing in acidic and basic conditions is so important to redox reactions. If we're balancing using acidic conditions, add water to the side without the correct # of oxygens and then balance the other side with H+ ions. For basic solutions, do the same as acidic but add the same number of OH- to t...

Ryan Troutman 4L

I can't seem to find them on the website, but I'll look around and let you know if I find anything! Maybe just ask friends in the class who have the answers !

Ryan Troutman 4L

Atm's are the most widely used ones, but if we're given units in bars there's no reason to convert them at the end. This just creates more possibility for error and work.

Ryan Troutman 4L

It's unlikely we'll have to draw graphs as data points would be difficult to interpret for T.A's and take too much time, however being able to understand what each graph means is important for the final.

Ryan Troutman 4L

Do we know how much of what we learn for kinetics in the next week will be on the final? Thanks :)

Ryan Troutman 4L

There are two ways we can determine this: If we're given a graph with a negative slope (-k) and a y-axis labelled as [A] (not ln[A] as that would be first order). In addition to this, if we are given a table, and a molar concentration of one of the reactants changes, but the initial rate does not ch...

Ryan Troutman 4L

The midterm average was an 80% I believe.

Ryan Troutman 4L

k quantifies the rate at which the chemical reaction occurs and allows us to determine the overall rate using the formula given. We multiply k to the molar concentrations of the reactants to their order number to find Rate.

Ryan Troutman 4L

Why do we not multiply the E by 2 when we balance the iron equation? Is it because its an intensive property?

Ryan Troutman 4L

When you split the equation into its two half reactions, you can tell which is the reducing agent by looking at the oxidizing reaction. If Fe+2 is going to Fe and Cu is going to Cu+2, then Cu is being oxidized, meaning that Fe is the oxidizing agent since its the element taking the electron. On the ...

Ryan Troutman 4L

Yiting_Gong_4L wrote:You mean test 2? test 3 will not include gibbs free energy, but test 2 will.

Ahhh thank you!! Sorry for the mistake haha. Thanks for clarifying that Angela!

Ryan Troutman 4L

Will Test 3 include Gibbs free energy?

Ryan Troutman 4L

e^ln simply cancels out leaving K= K. The E value is ~2.71

Ryan Troutman 4L

Gibbs free energy equation relates entropy and enthalpy in deltaG = deltaH - T*deltaS. It allows us to determine whether the reaction is endothermic or exothermic

Ryan Troutman 4L

If work is done ON the system, then work will be positive and internal energy will increase as a result. On the other hand, if work is done by a system (so expanding outward if you think of a piston), then work is negative and the internal energy of the system will decrease as a result. (Based on th...

Ryan Troutman 4L

Henry_Phan_4L wrote:https://www.youtube.com/watch?v=TnDCxw0y6YM The first 10 minutes gives a good explanation of the equations you need.

Thank you very much!! This is so helpful :)

Ryan Troutman 4L

So I mostly understand which equation has to be used where, however an explanation of when to use which equation would be very helpful! If someone could take the time to explain each and what they do that'd be so helpful going into the Midterm!

Ryan Troutman 4L

A reversible expansion happens in very small steps (think infinitesimal) toward the final product. An irreversible expansion happens all at once. Dr. Lavelle had a wonderful picture of two graphs showing the difference in Energy of the two expansions. In the end, the two both end up at the same prod...

Ryan Troutman 4L

If the problem states there is no change in internal energy, then delta U is equal to 0. Therefore, you can either subtract q or w and get q= -w or w=-q.

Ryan Troutman 4L

Only the problem can tell exactly which type of reaction it is without calculating delta G (Gibbs free energy). If there are many many changes (as stated by Chloe) then reversible is the way to go, however if it is sudden and drops quickly then it is irreversible.

Ryan Troutman 4L

Dr. Lavelle stated on Friday that the Midterm will only cover up to the end of Entropy, so knowing Gibbs Free Energy will not be necessary for our midterm.

Ryan Troutman 4L

Usually the problem will say "In a closed system" or "In an open system..., however if you're trying to find exactly what it is, then you have to know how energy is transferred between the two! An open system can interact with both matter (say liquid) and energy with the surrounds. Fo...

Ryan Troutman 4L

The derivation can be useful for the knowledge of what we're doing, however I believe the equation itself if more important. As long as you understand the equation and what to plug in / what it will be used for, you should be fine.

Ryan Troutman 4L

Path functions are properties whose values depend on the specific path the system takes in its transition from its initial to final state. For example, Dr. Lavelle gave the example of the altitude change in the hikers, where altitude was not a path function(instead it is a state function) because in...

Ryan Troutman 4L

Latent heat is only used when transitioning from one phase to the other. For example, if you are trying to transition from a solid to a liquid, that transition is the energy required to change from the solid state to the liquid state. Specific heat is the energy required to raise the temperature of ...

Ryan Troutman 4L

Work can only be done on both open and closed systems, because both heat and movement can occur in these types of systems. For example, in an open and closed system you can transfer heat through your hand to the system, causing it to become warmer. In an isolated system, this cannot occur because he...

Ryan Troutman 4L

We did cover a small example in class based on HS204, but its good to know just in case! It's important to know that when H2S04 and water combine, it dissociates completely, so it is not in chemical equilibrium, however when HS04- and H20 combine, it will be in chemical equilibrium to form S04-2 and...

Ryan Troutman 4L

I understand that n/v is equal to concentration, but what exactly do we use the ideal gas law for in chemical equilibrium? Also, if we have to find P, will we be given R and T?

Ryan Troutman 4L

Using the word shifted assumes we're already at equilibrium and it's shifting in favor of either products or reactants. Instead, using the word "favors" is much more accurate of what we're trying to state.

Ryan Troutman 4L

Solids and liquids are pure substances, so their concentrations do not change during the duration of the reaction,. Therefore solids and liquids are negligible when calculating Kc, Kp, and Q since they won't have any influence on the final answer to the equilibrium problems.

Ryan Troutman 4L

K values will not have units because they are "active" or "activities." Page 400 in the 7th Edition explains how activities are pure numbers and are unit less. More importantly, if you solve for K, you have (mol/L) / (mol/L), which cancel out leaving no units. So Kc and Kp will a...

Ryan Troutman 4L

Q is crucial in finding which way the reaction is moving, whether that be toward the product or the reactants. When we find K we compare that to 1 in order to see whether there are more products or reactants at that moments in the equilibrium state. On the other hand, Q is found at any time before t...

Ryan Troutman 4L

Yes! The wavelength is the distance from one peak of the wave to the other peak. A lower wavelength (100) has a higher frequency and a higher wavelength has a lower frequency (since they are inversely proportional).

Ryan Troutman 4L

Is it possible to determine the strength of an oxoacid compared to others through math or just general knowledge?

Ryan Troutman 4L

How do you tell which bonds have greater ionic character if they have the same two atoms. For example, if you have C02 and CS2 which one has the greater ionic character?

Ryan Troutman 4L

If you have atoms that are linear, trigonal planar, octahedral, tetrahedral (basically all the bond angles are the same), are they all non-polar molecules since they have equal angles? I was doing some practice problems and was confused by this concept.

Ryan Troutman 4L

s-character is the contribution of the sigma type bond in hybridization So, if you have sp, it is a 50-50 percent s-p character ratio, while sp2 has a ratio of 33-66 and sp3 has a ratio of 25 to 75 s character to p character. It's simply the percent that the s takes up in hybridization.

Ryan Troutman 4L

The bond angles is directly correlated to the atom and its VSEPR formula. If we use the question from 2E7, the molecule SOCl2 has a VSEPR formula of AX3E, which is trigonal pyramidal. The bond angle is less than 109.5 degrees, and technically only has one bond angle value since they're all the same....

Ryan Troutman 4L

Hello :) I just wanted to clarify: Is then number before the hybridization the period the element is in? So if we have Carbon it would be 2sp3 and if we had silicon it would be 3sp3 correct? Thanks so much!

Ryan Troutman 4L

Thank you all so much! I completely overthought the process of hybridization and you all made it much more simple.

Ryan Troutman 4L

T-shape models can be 90 and 180 degrees, but if a lone pair is acting upon the molecule (so AX3E2) the bond angles can be decreased to "less than 90" and "less than 180."

Ryan Troutman 4L

When you compare a single bond to a double bond, multiple bonds (double and triple) have a higher electron density region. If you think of it as a small circle, a single bond only has a small circle which can influence around it, and double bonds have a larger circle and a triple bond would be even ...

Ryan Troutman 4L

How do you know when to use sp2 or sp3 when doing hybridization? Can we also use sp4 and sp1?

Ryan Troutman 4L

Drawing out the example can be an indication of what the bond angle may entail, but it's best to just memorize the bond angles for each VSEPR arrangement. In addition to this, you can visualize the model in your head and think of all the different angles. However, I don't believe there is a way to s...

Ryan Troutman 4L

The AXE formula can be very helpful when doing problems since each AXE formula in VSEPR is unique. For example, you can draw an AX3 molecule and know that it's trigonal planar which would make the problem much easier. In general though, you don't need to know each one, but it can be very helpful on ...

Ryan Troutman 4L

My TA said that it's okay to say "Less than 90 degrees or less than 180 degrees" on a test, so I think it's testing our knowledge on the concept that lone pairs alter bond angles.

Ryan Troutman 4L

I'm confused on the aspect of how the number of bonds influences the length. In the case of a single and a triple bond, is the single bond longer than the triple bond(and why)? When we use resonance do we assume that the bond lengths are the same? Thanks :)

Ryan Troutman 4L

Responding to Milena: Hydrogen bonding is so strong because of the positive delta in the hydrogen of one water molecule and the high electronegativity in the delta negative in oxygen. This "bond" between the two are much stronger than dipole-dipole and London dispersion, but very weak comp...

Ryan Troutman 4L

Van Der Waals is the general term used to describe intermolecular forces between atoms which encompasses both strong dipole-dipole moments and the weaker london dispersion forces. Therefore, london dispersion is a sub category of Van Der Waals interactions.

Ryan Troutman 4L

Lone pairs on neighboring atoms repel one another since they are all negative (electrons). Since they repel they want to be as far away from each other as possible as well.

Ryan Troutman 4L

Angular Nodes are dependent on the l value in the (n,l,ml,ms). When l is = 0 (s) there are 0 angular nodes since it is in the S state and its a circle. For every following l value, there will be 1 for p (so when l=1 there is one angular node) and for l=2 there will be 2. Therefore, we can deduce tha...

Ryan Troutman 4L

I believe knowing the exact bond length is outside the scope of the course, but knowing that bond length exists and how resonance is tied in with it is enough to know for the course (as of now).

Ryan Troutman 4L

The best way for the answer to be most correct is if all formal charges are equal to 0 unless it is a cation or anion which it would then either need a +1 charge or -1 charge. Since we haven't learned how to draw structures or calculate angles, I don't think the general shape matters so much as long...

Ryan Troutman 4L

Hydrogen and Helium are exceptions to the octet rule since a full shell is only 2 electrons (1s1,1s2). Lithium and Beryllium are more likely to lose electrons instead of gain them and become cations (Li+1) and (Be+2). Hope this helps :)

Ryan Troutman 4L

When you remove the first electron it is fairly easy since the pull isn't too strong, however the ionization energy increases due to the pull from the positive protons in the nucleus on the electrons that are left, which it doesn't want to let go anymore.

Ryan Troutman 4L

Hello! When placing the dots (electrons) around the element, does it matter where we place them first? For example in Carbon do we go clockwise from the left side or does it really not matter when placing the dots? Thanks!

Ryan Troutman 4L

Hello! When placing the dots (electrons) around the element, does it matter where we place them first? For example in Carbon do we go clockwise from the left side or does it really not matter when placing the dots? Thanks!

Ryan Troutman 4L

Excited electrons are higher in energy levels, so like the energy picture Dr. Lavelle drew, an excited electron could be in the n=4 or n=7 energy level rather than n=1.

Ryan Troutman 4L

I understand that s will be Px, and that p will be px,py,pz, but what happens in the d orbital for ml? I'm quite confused on how you would write the p(?) in the 5 spaces.

Ryan Troutman 4L

The - comes from the jump in electrons from higher energy levels to lower energy levels since electrons must be emitted in order to reach from say n=3 to n=1.

Ryan Troutman 4L

So this guy said that particles can emit wavelike properties, but is it only seen in very small ones? We obviously don't see a baseball doing wavelike things, but is it still emitting the properties a wave would, or is it only in tiny particles? Thanks :)

Ryan Troutman 4L

So the En equation is the simplified version of the full Rydberg equation. To use it in a problem you should be given integer values (so n=2 and n=1) and you solve for whatever the problem asks for. The top numbers are constant (Plancks and Ryberg) divided by the energy level given squared, which wo...

Ryan Troutman 4L

Dr. Lavelle answered this during lecture 3, which he said that if you start at a high energy level and you keep going down the different levels, energy is being lost until you get to n=0 where the electron is separated completely. So the negative stems from the loss of energy that occurs as you go f...

Ryan Troutman 4L

To add to the other comment, if the value you obtain is below the work function, then an electron will not be emitted since it does not have enough energy to do so. So as long as it's larger than work, an electron will bounce off, which is why higher wavelengths (violet) will zoom off rather than sl...

Ryan Troutman 4L

With the formula we used in class, the biggest Energy gap or jump is from n=1 to n=2 (or vice versa). This happens because as energy increases the distance between the energy levels decreases. so n=2 to n=3 is smaller than n=1 to n=2 but larger than n=3 to n=4. So as energy goes up, the space betwee...

Ryan Troutman 4L

C is the constant for the speed of light, which is 3.00 x10^8.

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