CHEMISTRY COMMUNITY

Tahlia Mullins

Thank you for this, you definitely make the world a better place! I hope you can finally get some rest now that the online final is over!

Tahlia Mullins

Dear Dr. Lavelle, Thank you for all of your amazing efforts the past two quarters! The amount of time you put into creating recourses for your students is greatly appreciated, especially considering the change that has recently taken place. Your immense consideration for your students’ success and y...

Tahlia Mullins

I always just look at the units given, and it’s usually pretty easy to tell. Sometimes, temperature might need to be changed to Kelvin though!

Tahlia Mullins

Yes it is, it’s just a way to make it clear what the change in gibbs free energy is due to.

Tahlia Mullins

Also, if there is a liquid or solid in either the products or the reactants, they would just be included in Kc as 1, so obviously they can be disregarded. I like to include this just for clarity.

Tahlia Mullins

The rate law shows the rate of the reaction plotted against time while the integrated rate law shows the actual concentration at certain times. If you think about it in terms of calculus and the definition of an integral, this makes sense.

Tahlia Mullins

I think its more helpful to know the derivation for comprehension purposes, but it is pretty unlikely he will ask us to derive one of these equations on the test.

Tahlia Mullins

I believe that knowing the derivation of the rate laws and even the half lives is important to develop a proper understanding, however, Dr. Lavelle did not go over the derivation of the Arrhenius equation in class.

Tahlia Mullins

Either inert metal can be used when either the cathode or the anode has no solid conductor, but platinum is the most common.

Tahlia Mullins

This means the the activation energy, the hump in the reaction profile, is very high.

Tahlia Mullins

I believe that most of the time, the cell will have this layout, but there are instances where it can be the other way around, so it’s important to pay attention to what is being oxidized and what is being reduced in each individual case instead of assuming.

Tahlia Mullins

Like the other students said, redox reactions are not always acid or base reactions, I just think the examples used are often acid or base because it is more complicated to balance the half reactions, which allows us to practice more!

Tahlia Mullins

If n is not given, you can go through the process of balancing the half reactions for oxidation and reduction, eventually finding the number of moles of electrons being transferred!

Tahlia Mullins

In practice, I have only ever seen platinum being used as the inert metal in the electrolytic cell, so I just like to play it safe and use that!

Tahlia Mullins

K is used when the reaction is specified as being at equilibrium while Q is used when the reaction is not at equilibrium.

Tahlia Mullins

Considering the constant F in electrochemistry, it can be concluded that n refers to the number of moles of electrons being transferred and this is easy to remember since redox reactions come down to an exchange of electrons reducing or oxidizing an atom or molecule.

Tahlia Mullins

It simply comes down to E being an intensive property, meaning that the difference in voltage will not change if the reaction takes place more than once whereas gibbs free energy, for instance, will change.

Tahlia Mullins

Two are given since one refers to standard conditions, 25 degrees C and 1 atm while the other can refer to any condition separate from standard.

Tahlia Mullins

In order to counteract the build up of charge in a galvanic cell, the salt bridge essentially contributes free ions that will not interfere with the redox reaction that is already taking place, it is simply meant to neutralize each side.

Tahlia Mullins

I think it’s always helpful to know how to derive the equation because once you are able to do that, you know you have a proper grasp of the concepts. However, we are not expected to do this on an exam!

Tahlia Mullins

In a vacuum, the external pressure is equal to 0, so during free expansion, work is also equal to 0.

Tahlia Mullins

My TA last quarter checked at the very end to make sure we made 50 posts, but that could vary depending on your TA.

Tahlia Mullins

Sadly, no curve for individual tests since there is a curve at the end of the quarter depending on how students do overall. To pass the class, you only need 50% of points.

Tahlia Mullins

These are interchangeable!

Tahlia Mullins

Yes you can, make sure the R value is the correct one though!

Tahlia Mullins

Yes, W would be the correct notation.

Tahlia Mullins

Yes, I agree! I remember it being mentioned in lecture that it would be meaningless to try to actually measure free energy alone, so the equation must be used in order to find the value of the standard change in Gibbs free energy.

Tahlia Mullins

Degeneracy relates to thermodynamics in that it is used to calculate the change in entropy. The way I remember it is that Lavelle mentioned that he was purposefully avoiding the word disorder in regards to the topic of entropy because degeneracy is a better way to describe what entropy is and what i...

Tahlia Mullins

I agree! I see more of a connection to quantum mechanics as well, but the way I see it in terms of thermodynamics is when considering entropy. Rather than using words such as "disorder" when describing entropy, degeneracy is a more thorough explanation.

Tahlia Mullins

A calorimeter is also a perfect example of an isolated system, and the heat capacity of the calorimeter must be taken into account along with the heat capacity of the solution inside of the calorimeter.

Tahlia Mullins

For reversible expansion, the external pressure can change, which is proven by the integral used to calculate q. For irreversible expansion, external pressure remains constant, which is the reason that the calculation of q is much more simple.

Tahlia Mullins

Insulation is the main difference between the two systems. For an isolated system, a calorimeter is a great example because it is insulated, ensuring that heat will not be exchanged between the system and the surroundings.

Tahlia Mullins

In AP chemistry, we did an experiment where we made our own calorimeter using double foam cups to make sure that neither matter nor energy can be exchanged between the system and the surroundings.

Tahlia Mullins

A closed system has the ability to exchange energy with the surroundings, but not matter, while an isolated system cannot exchange either, such as a calorimeter.

Tahlia Mullins

The purpose of the integral is to account for the infinitesimally small steps in reversible expansion, so you would use it in that context. If you were confused at all in lecture, the textbook explains it pretty well also.

Tahlia Mullins

I remember method 4 being used a lot in AP Chem, so that might mean that it will be coming up pretty often.

Tahlia Mullins

I agree! This association makes sense, but I am not completely sure.

Tahlia Mullins

To verify that the approximation is valid, divide x by the initial value and multiply by 100, and if the value is less than 5%, then it is valid.

Tahlia Mullins

It all depends on the information given. You would use Kp when the partial pressures are given, but you use Kc when the concentration or moles or grams are given even when the reactants and products are gases.

Tahlia Mullins

I find it helpful to add the plus sign just to reinforce the fact that there is a positive change in enthalpy, but I do not think it is absolutely necessary.

Tahlia Mullins

The 5% rule is used to verify that assuming x to be negligibly small is a correct assertion. It is simply the calculation of percent protonation.

Tahlia Mullins

Since both solids and liquids are pure substances, they do not change either.

Tahlia Mullins

To determine if an ICE table is necessary, look at the information given. Such as, if the initial concentration(s) are given along with a Ka or Kb value, then an ICE table is the correct method in finding the equilibrium concentrations and other information.

Tahlia Mullins

To determine if an ICE table is necessary, look at the information given, such as the initial concentration of a weak acid or base and the ka or kb value rather than the equilibrium concentration.

Tahlia Mullins

Since pH is determines by the concentration of H3O+ ions in the solution, the greater protonation yields a lower pH, and strong acids are known to be 100% dissociated, meaning a higher concentration of H3O+.

Tahlia Mullins

I often study by doing several if not all of the problems outlined in the syllabus and reading the given chapters in the textbook. Also, if time permits, the peer learning sessions could be extremely helpful.

Tahlia Mullins

Removing some product would in turn lead to the reaction proceeding to the right and more products being formed.

Tahlia Mullins

The combination of K being a measurement of activity as well as the fact that it is a constant, means that it does not have ay units.

Tahlia Mullins

The reaction quotient is basically the ratio of concentration of products to the concentration of reactants at any point in a reaction, which is used to compare to the equilibrium constant, K, the same ratio but only at equilibrium, in order to determine the future behavior of the reaction(whether i...

Tahlia Mullins

A large K value indicates that the products of the reaction are more favorable and the reaction lies to the right, whereas a small K value indicates that the reactants are more favorable and the reaction lies to the left at equilibrium.

Tahlia Mullins

I remember learning this before too! I believe it was 10^-3 as well! I remember always proving that x was negligibly small in order to make it clear why that simplification is possible as well.

Tahlia Mullins

From my understanding, I believe he curves the class at the end based on the class average, but I am not too sure how.

Tahlia Mullins

I like to think of it this way as well, and when you practice naming coordination compounds, it becomes more and more familiar.

Tahlia Mullins

Basically, a compound that can give or receive protons, amphiprotic, can act as either an acid or a base, amphoteric.

Tahlia Mullins

I like to think of this in terms of the equations used to find pH which is in terms of the logarithm of the concentration of H+ or OH-, which makes sense conceptually for this question.

Tahlia Mullins

Also, in addition to this, enzymes usually perform under a vital pH, and when the environment is functions in is not this pH, the enzyme may become denatured, which changes its active site.

Tahlia Mullins

I like using both definitions simultaneously because they complement each other well and can be depicted in an actual acid-base reaction.

Tahlia Mullins

This is a great example of how the interaction works and how the definitions of lewis and bronsted acids/bases can be applied to a real scenario.

Tahlia Mullins

Basically, they are viewed differently in respect to the protons and electrons being gained or lost. A Bronsted acid is a proton donor while a lewis acid is an electron acceptor and the bases of each reflect the same pattern but are relatively opposite.

Tahlia Mullins

When determining relative melting points, consider the strength of the IMFs involved.

Tahlia Mullins

I like to think of it as since lone pairs affect shape, they also affect hybridization, since they are electrons too, just not shared electrons!

Tahlia Mullins

A bent molecule will have one or two lone pairs with VESPR functions AX2E and AX2E2

Tahlia Mullins

A Bronsted acid is a proton donor while a Lewis acid is a proton acceptor.

Tahlia Mullins

A higher electronegativity difference indicates a stronger bond, which can be exemplified with hydrogen bonds when considering that hydrogen has a very small electronegativity.

Tahlia Mullins

A lone pair should always change the angle at least slightly, so the actual angles would be less than 90 and 120.

Tahlia Mullins

Bronsted acids donate protons whereas Lewis acids take in protons, or rather, accept them. Do not confuse protons with electrons here!

Tahlia Mullins

Inorganic compounds can lose their hydrogen ions more easily, which makes them stronger as an acid.

Tahlia Mullins

I like to think of arrangement and shape as two separate things, where the shape is determined by the geometry and the arrangement is depended on electrons, which includes the electron configuration.

Tahlia Mullins

I found it extremely helpful to make a chart with the steric number as the “y-axis” and the number of lone pairs as the “x-axis” for the molecular shapes. This would make the difference between shapes more obvious.

Tahlia Mullins

A bent shape will have only one or two lone pairs, with VESPR functions AX2E or AX2E2.

Tahlia Mullins

I like to remember that fluorine is the most electronegative, and this gives a hint as to which direction electro negativity increases/decreases.

Tahlia Mullins

Sigma bonds overlap end to end while pi bonds overlap side to side, and sigma bonds are able to rotate do to the way they overlap generally.

Tahlia Mullins

I found it useful to create a chart of shape with the steric number being the "y-axis" and the number of lone pairs being the "x-axis", and this would show that for AX2E3 and AX2E, the shape is linear and the angle is 180.

Tahlia Mullins

Larger molecules are typically more polarizable than smaller ones, meaning that polarizability decreases from left to right and increases as you go down the periodic table.

Tahlia Mullins

If the dipole moments cancel each other out, the molecule is no longer polar, it is non-polar, and there is no dipole moment. I like to consider this in terms of electronegativity and the relative charges on molecules, instead of just memorizing facts.

Tahlia Mullins

N, O, and F each have very high electronegativity, with F being the highest, which allows for the dipole moment to be created when they bond with hydrogen, which is not very electronegativity.

Tahlia Mullins

I do not think it is absolutely necessary every time, but it is a good way to check that the lewis structure is the best possible for the molecule.

Tahlia Mullins

Since atoms are most stable when they share their valence electrons equally in bonding, and valence electrons is the first term in the formal charge formula, if the formal charge is 0, the previously stated will be fulfilled, making it more stable.

Tahlia Mullins

Especially when dealing with resonance, finding the formal charge of each lewis structure is essential to determining the most stable structure, with a formal charge of 0 or as close to 0 as possible.

Tahlia Mullins

Shorter bonds are stronger. Double and triple bonds are shorter than single bonds, so these types of bonds are stronger.

Tahlia Mullins

When the bond length is shorter, as with double and triple bonds, which involve more electrons being shared between atoms, the atoms are closer together, and there is a stronger energy due to the atomic radii in relation to the distance between the nuclei of each atom being shorter, making the pull ...

Tahlia Mullins

I agree that it is best to think of the drawing of lewis dot structures as similar to electron configurations, following Hund's rule in the distribution of dots/arrows.

Tahlia Mullins

I agree with the responses already given, but I would also like to add that I find it easier to think of delocalized as a synonym for mobile, meaning the electrons can move around, hence resonance.

Tahlia Mullins

Compounds with resonance are more stable because their electrons are delocalized, or more mobile, which leads to a lower overall energy since the electrons occupy a greater volume.

Tahlia Mullins

Yes, and I agree with what has already been said. Just wanted to add that I find drawing the lewis dot structures helps tremendously with understanding the exact exchange/sharing of electrons that is occurring with each bond!

Tahlia Mullins

Drawing Lewis dot structures definitely helps in depicting both of these types of bonds. In an ionic bond, between a metal and a nonmetal, one atom gives up an electron to make both atoms more stable, and this is shown with anion and cation depictions(+/-). In a covalent bond, between nonmetals, two...

Tahlia Mullins

It can also be added that electronegativity has an inverse relationship with atomic radius, therefore has an opposite periodic trend. This is because a larger atomic radius usually means more shielding experienced by the nucleus, giving it less affinity for attracting electrons from other atoms.

Tahlia Mullins

A good way to remember what this is would be to relate its trends to the trends in atomic radius since the larger the atomic radius, the greater the ionization energy, so their trends line up since they are in direct relationship with one another.

Tahlia Mullins

I'm in! My email is Tahlia.rose46@gmail.com.

Tahlia Mullins

The Pauli Exclusion Principle basically states that each orbital can only have two electrons, and since they are in the same orbital, these electrons must have opposite spins, which is shown by the arrows pointing in the opposite direction.

Tahlia Mullins

I think it is important to stress theft that the electrons are being added to the same shell when moving from left to right, therefore the atomic radius does not increase too drastically. At the same time, there are more protons in the nucleus, pulling the electrons in closer, decreasing the atomic ...

Tahlia Mullins

This is also consistent in observing the atomic radius. The more shielding of electrons/the more orbitals, the larger the atomic radius.

Tahlia Mullins

Both Hund's Rule and Pauli Exclusion Principle provide the guidelines of the ground state electron configuration for a given atom. Singularly, Hund's Rule provides that each orbital must include one arrow before doubling up. The Pauli Exclusion Principle states that two electrons in the same orbital...

Tahlia Mullins

Since the 2s orbital is closest to the nucleus, the 2p orbital experiences shielding from the nucleus, increasing the diameter of the atom.

Tahlia Mullins

A longer wavelength has a lower frequency, since they have an inverse relationship, and a higher frequency is more effective in reaching the required threshold energy to emit an electron from a given metal surface, which would mean the wavelength is shorter.

Tahlia Mullins

A good way for me to remember it is that the energy of the photon has to be equal to the or greater than the energy required, calculated by the work function, to emit the electron.

Tahlia Mullins

Just a note, Avogadro’s number is actually 6.022*10^23 while planck’s constant is 6.626*10^-34, not to be mixed up! However, these are provided on tests since they are constants.

Tahlia Mullins

Planck’s constant is a vital component of the e=hv equation because it relates the amount of energy emitted to the speed, is with units J.s

Tahlia Mullins

h is planck’s constant, which is 6.626*10^-34, and I like to remind myself that it is an extremely small number when I am making calculations.

Tahlia Mullins

When showing work, I always include units from beginning to end, which makes it easier for the grader to follow as well as serves as a way to check if I got the right answer based on getting down to the right units.

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