CHEMISTRY COMMUNITY

Kevin ODonnell 2B

Good question. The only thing I can think of is it would tell you the units of the equation as seen in the table below.

Kevin ODonnell 2B

Hopefully this diagram will help depict it better than any words. The two solutions are separated by a porous barrier that prevents them from rapidly mixing but allows ions to diffuse through. https://chem.libretexts.org/Bookshelves/General_Chemistry/Book%3A_Chem1_(Lower)/16%3A_Electrochemistry/24.0...

Kevin ODonnell 2B

A catalyst can be an intermediate in an equation, but not all intermediates are catalysts. I believe to be able to tell if it is a catalyst you would have to be given that it is a catalyst or that the activation energy was lowered.

Kevin ODonnell 2B

That is because the entire reaction must wait for the slowest step to proceed. That's why this would be the rate-determining step.

Kevin ODonnell 2B

The units of kr depend on the overall order of the reaction and ensure that kr x (concentration) a has the same units as the rate, namely, concentration/time. Thus, when the concentration is expressed in moles per liter and the rate is expressed in mol*L -1 *s -1 , the units of kr are a follows: 1st...

Kevin ODonnell 2B

I am also led to believe that these values have to be experimentally found, and are not just based off of something you can look at a chemical equation and tell. For example, if you have 1 mol of x that produces 1 mol of product then you have 2 mol of x that produces 2 mol of product you can see thi...

Kevin ODonnell 2B

For thermodynamic favorability: ΔG>0, the reaction is nonspontaneous in the forward direction, not thermodynamically favorable ΔG<0, the reaction is spontaneous in the forward direction, thermodynamically favorable However, a reaction can be thermodynamically favorable yet still wont proceed due to ...

Kevin ODonnell 2B

For very easy problems typically involving just one element turning into an ion of itself where you can instantly tell if it was reduced or oxidized by balancing the charge by adding e- to one of the sides. Other than that you have to calculate the oxidation states of the molecules using the oxidati...

Kevin ODonnell 2B

I know you are referring to the example where 2NO2 -> 2NO + O2 turned into - d[NO2]/dt = d[NO]/dt = 2d[O2]/dt. However, it is much easier to just use fractions for more complicated problems where this problem and the unique rate would be -(1/2)d[NO2]/dt = (1/2)d[NO]/dt = d[O2]/dt where the 1/2 comes...

Kevin ODonnell 2B

Basically we can just use Gibbs to relate all three terms and determine if something is spontaneous or not Remember the Gibbs equation is (delta)G = (delta)H - T(delta)S Gibbs Free Energy = if it is negative it is spontaneous Spontaneous = a reaction that favors the formation of products under the c...

Kevin ODonnell 2B

In half reactions we just find the sum of the two halves (the reduction half-reaction + the oxidation half-reaction). First make sure all of the equations are balanced. Make sure in molecule compounds as well that you are taking note of the sign. For example, let's pretend that FeO 2 -2 is a thing. ...

Kevin ODonnell 2B

The standard hydrogen electrode is a measurement of the oxidation-reduction potentials for the thermodynamic scale. Basically it s a very good introduction to oxidation-reduction reactions. Here's a picture to help visualize the oxidation taking place on the left (Lose Electron Oxidized) and the red...

Kevin ODonnell 2B

Temperature should always be given for any Gibbs Free Energy problem, unless you have to solve for the temperature in the problem.

Kevin ODonnell 2B

The only reason I can think of is because O2 is already in its most standard state so this would be counted as 0 for those calculations. The textbook goes more into detail on which calculation to use standard state of elements = 0 for.

Kevin ODonnell 2B

This graph helps demonstrate the point if you are more visual or mathematical. Where you can see the forward and reverse reaction meet at a minimum. This minimum is equilibrium in this reaction and shows why since it is a minimum equilibrium would be 0.

Kevin ODonnell 2B

Thank you for the great review session!

Kevin ODonnell 2B

They relate because through this molecular motion in each one is how the molecule can store energy. This motion results in the greater the number of possible microstates which then leads to higher the entropy.

Kevin ODonnell 2B

The equations are used for the same thing where q = mCT is used to find the heat of a particular substance with a mass, change in temperature, and specific heat capacity. The only difference is in a bomb calorimeter the mass is not that relevant for finding q so you can negate it and just use q (cal...

Kevin ODonnell 2B

From the trend I believe there is a decrease in the entropy as the forces between the atoms, molecules, or ions increases. A good example is the three solid compounds NaF with the molar entropy 51.5, MgO at 26.8, and AlN at 20.2

Kevin ODonnell 2B

Just to give some evidence to what everyone else is saying. A carbon-carbon single bond has a length of 154 and energy of 348, a carbon-carbon double bond has a length of 134 and energy of 614, while a carbon-carbon triple bond has a length of 120 and energy of 839. Here we can see that a double bon...

Kevin ODonnell 2B

This is because the open beaker is open to the entire atmosphere which is much bigger than the beaker so it makes the beaker's pressure irrelevant to any change and that is why pressure is constant. It is just like when you add a bucket of water into the Ocean it really does not make a difference on...

Kevin ODonnell 2B

I would assume so yes just based off the assumption that you can't create heat without any work being done. So any heat released from the breaking of molecules would be from the exact energy stored in those bonds.

Kevin ODonnell 2B

Here is a graph that could help supplement what everyone else is saying. Here, you can see that more energy is needed in order to make a gas a gas, so when it comes into contact with skin it releases the more heat it has stored.

Kevin ODonnell 2B

Yes the state of matter will affect the enthalpy. A liquid of a substance will have a different enthalpy than a gas of the same substance.

Kevin ODonnell 2B

An increase in pressure will cause the reaction to trend towards the side with less moles so lets say we have a reaction that is 2A + 3B -> 2C then an increase in pressure will cause more products to form. This is true unless the pressure is increased by adding an inert gas (a gas that is random and...

Kevin ODonnell 2B

I know what graph you are talking about, and hopefully this one can help explain Q and K with respect to equilibrium.

Kevin ODonnell 2B

So here is everything I have found p in front of anything means -log, so pKa = -log(Ka) pKb = -log(Kb) pH = -log(H+) pOH = -log(OH-) Other relationships at 25 degrees C… pH + pOH = 14 Kw (1 x 10^-14) = Ka * Kb pKa + pKb = 14 (this is a similar equation to the one above but by finding the -log we can...

Kevin ODonnell 2B

I'd say to try and use as many as possible of Dr. Lavelle's provided resources. Since they are created by him and he oversees them I am sure that they are all geared toward the subjects that he sees are most important for our success in the class. I'd definitely recommend going through the video mod...

Kevin ODonnell 2B

This table may help to visualize it all, and is an example that uses Molarity.

Kevin ODonnell 2B

Water is the only thing that I know can possess this power, since it can act both as an acid and a base which is why it can form both hydroxide and hydronium ions. This also explains why it is such a powerful solvent.

Kevin ODonnell 2B

Square brackets [] denotes concentration and it is only used for Kc. Gases (Kp) however use parentheses (). So no they are not interchangeable. This is because Kc is used as an equilibrium constant, while Kp stands for partial pressure.

Kevin ODonnell 2B

Hopefully this visual will help to see where the bond angles are 180, 120, and 90 degrees.

Kevin ODonnell 2B

Some of the trends we see to tell the differences is stronger acids have lower pKa values, strong acids lose H+ easily and the resultant anion must be stable. With weaker (larger) bonds it is easier to remove the H+. Short bonds are stronger where we can see the smaller elements trend towards the up...

Kevin ODonnell 2B

Lewis acids accept pairs of electrons. Electronegativity is a measure of how strongly atoms attract bonding electrons to themselves. Therefore we can assume that if an atom is more electronegative than an atom then it will be the acid since it will be more likely to accept the pairs of electrons.

Kevin ODonnell 2B

Some of the trends we see to tell the differences is stronger acids have lower pKa values, strong acids lose H+ easily and the resultant anion must be stable. With weaker (larger) bonds it is easier to remove the H+. Short bonds are stronger where we can see the smaller elements trend towards the up...

Kevin ODonnell 2B

A Lewis acid is an electron -pair acceptor as shown in the diagram

Kevin ODonnell 2B

Looking at the picture we can see that is is a bronsted-lewis acid

Kevin ODonnell 2B

This should help distinguish between all of the shapes. I often find it's easier to see a visual for these kinds of problems.

Kevin ODonnell 2B

For drawing them either structure should be fine, but you should be able to know the name of the structure that is made from either of the drawings.

Kevin ODonnell 2B

London forces are the weakest of all intermolecular forces, and they increase in strength as the total number of electrons increase.

Kevin ODonnell 2B

A sigma bond is always the first bond between two atoms, while pi bonds are always the second

Kevin ODonnell 2B

Something to keep in mind as well is when lone pairs are involved it changes the bond angle from the expected amount. For example NH3 has bond angles of 107 degrees instead of the expected 109.5 degrees. There is no way to know this since it needs to be tested in the lab since it's unique to each mo...

Kevin ODonnell 2B

The dipole charge has to do with electronegativity. The more electronegative atom has a partial negative charge since it pulls the electrons closer to itself. While, the less electronegative atom is partially positive since the other atom is holding the electrons more tightly.

Kevin ODonnell 2B

Basically to sum it up on how I see it is more electrons = greater ablity to bond and form stronger bonds.

Kevin ODonnell 2B

Here's a post from 2016 that I think does a very good job of explaining the concept: Electron distortion is when the electrons of the anion are attracted to the cation, which causes the shape of the electron density to change slightly. When we talk about ionic bonds, we usually think it means a bond...

Kevin ODonnell 2B

A TA told me that going up a column (group) means it is more electronegative than just going across a row. So in this case Na would be more electronegative than Ca. I would still ask a TA for a further explanation on why this occurs though.

Kevin ODonnell 2B

We use resonance in order to show the different options for different bonding molecules. For example, in NO3 Nitrogen can form a double bond with oxygen on any of the 3 oxygen molecules. This gives us three different possibilities for which one Nitrogen can be bonding too. Since we do not know which...

Kevin ODonnell 2B

This is typically because the elements with lower ionization energies have more open spaces (have more opportunity) for bonding. For example, Carbon can form 4 bonds and has a lower ionization energy than Fluorine who can only form 1 bond (we get these numbers by looking at how many valence electron...

Kevin ODonnell 2B

Here are some numbers to give some of the reasons above some more concrete evidence. For Al it takes 577.6 kJ/mol to remove the 1st electron, 1816.6 for the second, 2744.7 for the third, and 11,577 for the fourth. Looking at these numbers it makes sense why it is a lot easier to gain 4 electrons tha...

Kevin ODonnell 2B

Emmaraf 3K wrote:Are you referring to a specific question? Looking at a chart online for ionization energies, it says the ionization energy for sulfur is less than oxygen.

Here is the chart they were referring to. It may help to have a visual to better understand the concept:

Kevin ODonnell 2B

Sixteen sodiums walk into a room. Who's next? Na - Na - Na - Na - Na - Na - Na - Na - Na - Na - Na - Na - Na - Na - Na - Na - BATMAN

Kevin ODonnell 2B

Losing four electrons would require a large amount of energy. The ionization energies for 4 electron removals with the elements of the group 14 would be very high. This way it would be more likely for them to gain 4 electrons to reach a stable state. That is a very good point. It is especially true...

Kevin ODonnell 2B

This video does a pretty good job of explaining it and is nice since it includes animations: https://www.youtube.com/watch?v=VQJx6JAq_po

Kevin ODonnell 2B

Thank you! That makes a lot more sense and will definitely come in handy! I was wondering the same thing.

Kevin ODonnell 2B

Hopefully he will be uploading a module for it. However in the mean time Khan academy is a great resource for learning Chemistry since they often provide examples and have a video on the topic here: https://www.khanacademy.org/science/physics/quantum-physics/quantum-numbers-and-orbitals/v/heisenberg...

Kevin ODonnell 2B

I don't believe a constant would effect the number of sig figs you should round to in your answer, but rather it should be a given number such as 5.0g since that is a number that the person asking the question can change based off how many significant figures they are looking for in the answer. Ther...

Kevin ODonnell 2B

I believe it's important to know that visible light is in the range between 400-700 nanometers. I would also know that higher energy waves (gamma ray/x-ray/ultraviolet) have shorter wavelengths and higher frequencies. While lower energy waves (radio/microwave/infared) have longer wavelengths and low...

Kevin ODonnell 2B

Example #6 on this website does a great job of explaining it with a practice problem:
https://www.chemteam.info/Stoichiometry ... agent.html

Kevin ODonnell 2B

You should be given the actual yield, and have to calculate for the theoretical yield. This is because we can't calculate for the disruptions that take place during an experiement (side-rections, molecules stuck to the side of the beaker, etc). The actual yield is also done in an experiment setting....

Kevin ODonnell 2B

I believe it's important to know that visible light is in the range between 400-700 nanometers. I would also know that higher energy waves (gamma ray/x-ray/ultraviolet) have shorter wavelengths and higher frequencies. While lower energy waves (radio/microwave/infared) have longer wavelengths and low...

Kevin ODonnell 2B

Dr. Lavelle provides a lot of great resources for studying. I'd definitely reccomend going through the video modules on the website, and reading the chosen sections in the book. Do the practice problems for homework and choose a wide range not just all from one section/topic. If you are confused on ...

Kevin ODonnell 2B

I don’t believe we need to know this quite yet, but if you want a head start here’s a few that have to do with polyatomic ions: -ate means it has more oxygen -ite means it has less oxygen Per- means it has one more oxygen Hypo- means it has one fewer oxygen These are from the video at https://www.kh...

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