CHEMISTRY COMMUNITY

Hannah Thornton 1F

The slowest step determines the rate of the chemical reaction.

Hannah Thornton 1F

If H2O is the solvent, aka in its liquid phase, it will not be included in the rate law.

Hannah Thornton 1F

Catalysts lower the activation energy of both the forward and the reverse reaction and thus increase the rates of both reactions. However, they have no affect on the heat.

Hannah Thornton 1F

Yes, a catalyst lowers the activation energy for both the forward and reverse reactions.

Hannah Thornton 1F

Since C(coulombs) = J/V, both units are interchangeable.

Hannah Thornton 1F

F is Faraday's constant, which is provided on the equation sheet.

Hannah Thornton 1F

the anode is the half reaction being oxidized and the cathode is the half reaction being reduced.

Hannah Thornton 1F

E=E₀-(RT/nF)lnQ or E=E₀-(0.05916 V/n)logQ

Hannah Thornton 1F

To find n, you need to balance the redox reaction as two separate half reactions, which will allow you to see how many moles of electrons are being transferred.

Hannah Thornton 1F

Gibbs free energy is the energy available to do work and is represented by G. We can determine whether or not a reaction is spontaneous by looking at if delta G is negative or positive - if it's negative, then it is spontaneous, if positive, then not spontaneous.

Hannah Thornton 1F

"n" stands for the number of mols

Hannah Thornton 1F

A species is oxidized is when it loses electrons, or when their charge becomes more positive. It is reduced when it gains electrons, or the charge becomes more negative.

Hannah Thornton 1F

Halogens (Group 1) is usually +1, Group 2 is +2, Group 16 is -2, Group 17 is usually -1. These ones you should memorize, whereas for other groups such as transition metals, the numbers vary.

Hannah Thornton 1F

any reaction in which oxidation and reduction are occuring!

Hannah Thornton 1F

any reaction in which oxidation and reduction are occuring!

Hannah Thornton 1F

They both represent internal energy and can be used interchangeably!

Hannah Thornton 1F

Delta U represents the change in internal energy of a system, so a negative delta U would mean that the energy of the system has decreased since it’s initial energy.

Hannah Thornton 1F

In the case that you are given moles, you would use q=nCΔT, while if you are given the mass in grams you can use q=mCΔT

Hannah Thornton 1F

The correct formula is U = q + w !

Hannah Thornton 1F

J/K is its typical units!

Hannah Thornton 1F

Enthalpy is the amount of heat released or absorbed at constant pressure. Entropy is the amount of disorder in the system. Gibbs free energy determines if a reaction will proceed spontaneously; if it is less than 0, it will be spontaneous, and if it’s greater than 0, it won’t be spontaneous.

Hannah Thornton 1F

An open system is one that can exchange both matter and energy with its surroundings.

Hannah Thornton 1F

Isolated systems cannot exchange matter or energy with its surroundings, whereas closed systems can exchange energy.

Hannah Thornton 1F

Yes, delta u can be zero if the net change of internal energy is zero, meaning the initial and final energies are the same.

Hannah Thornton 1F

Work is negative when work is done by the solution, since the system needs to use its energy to do its work and therefore energy is lost, hence the negative sign. Positive work would be work done on a system since energy is being added to it.

Hannah Thornton 1F

Work is negative when work is done by the solution, since the system needs to use its energy to do its work and therefore energy is lost, hence the negative sign. Positive work would be work done on a system since energy is being added to it.

Hannah Thornton 1F

Since our tests are multiple choice based, we don’t really need to worry about sig figs. However they are important to know in general.

Hannah Thornton 1F

Yes, if temperature is not given, we can assume it is under standard conditions of 25 degrees C.

Hannah Thornton 1F

K is the ratio of products to reactants at equilibrium, while Q is the ratio of products to reactants at any point during the reaction. They are calculated using the same formula.

Hannah Thornton 1F

Delta U is the change in internal energy of a system. To calculate this, since energy can be lost or gained through heat and work, we would add heat and work with the equation being Delta U = q (heat) + w (work).

Hannah Thornton 1F

No, you cannot change the energy of an isolated system at all.

Hannah Thornton 1F

Work done on the system means that something outside of the system is doing work on the system, while work done by the system means that the system is doing work on something outside.

Hannah Thornton 1F

No method is specifically preferred, it just depends on what information is given in the question.

Hannah Thornton 1F

An open system is a system that can exchange both matter and energy with its surroundings. One example of this would be a beaker of water.

Hannah Thornton 1F

The difference is that specific heat capacity involves mass. Specific heat capacity is the heat required to raise the temperature of 1 g of a substance by 1 degree C, while heat capacity is the heat required to raise the temperature of an object by 1 degree C and is independent of mass.

Hannah Thornton 1F

A closed system can exchange energy with its surroundings, but not matter. An isolated system cannot exchange neither energy nor matter.

Hannah Thornton 1F

You would choose which method to use depending on the situation, or if the question tells you which to use. If reactions are given, you would use Hess's Law. If the question gives you the bond enthalpy values, then you would use the bond enthalpy method. If the standard enthalpies of formation is gi...

Hannah Thornton 1F

Q is the ratio of the concentrations of the products and reactants during any time of the reaction.

Hannah Thornton 1F

Yes, when Q=K, this means that the reaction is at equilibrum.

Hannah Thornton 1F

K is the measure of the concentrations of the reaction at equilibrium, while Q is the measure of the concentrations at any point in the reaction.

Hannah Thornton 1F

Although pH can be smaller than 0 or bigger than 14, this will never appear in our course.

Hannah Thornton 1F

An exothermic reaction would have a delta H value of less than zero, meaning heat/energy is being
released. An endothermic reaction would be a delta H value of greater than zero, meaning heat/energy is being absorbed.

Hannah Thornton 1F

From here, you need to just turn that equation into a quadratic equation and use the quadratic formula to solve for the value of x. Then, plug this value into 2x to find the final concentration of HI.

Hannah Thornton 1F

K is a very general equilibrium constant, while Kc is specifically using molar concentrations in the ratio to find K.

Hannah Thornton 1F

The reactant side is negative in the case that we are creating more product and the reaction is shifting right. However, it would be positive in the case that we are creating more reactants and the reaction is shifting left.

Hannah Thornton 1F

The total pressure is just the sum of all of the individual pressures, so after finding x, you just need to add up all of the equilibrium pressures together from the ice table, so (x + x + (.0691-x)), in order to find the total pressure.

Hannah Thornton 1F

Le Chatelier's Principle is the idea that when a reaction is in equilibrium, if that equilibrium is affected at all, the reaction will shift in order to counteract that change. For example, if more reactants were added to an equilibrium, the equilibrium will shift to the right and favor the products...

Hannah Thornton 1F

Solids (as well as liquids) would not be included in calculations since the molar concentration is an extremely small amount during reactions, so if it was included in the ratio equation, it would not make a difference.

Hannah Thornton 1F

No, K is a ratio, so it doesn't have any units.

Hannah Thornton 1F

The delta H value determines this - a positive delta H would be an endothermic reaction, while a negative delta H value would be an exothermic reaction.

Hannah Thornton 1F

K is calculated at the equilibrium point of the reaction, while Q can be calculated for any time at all during the reaction.

Hannah Thornton 1F

Yes you should use the same account! It will help to just change your username to your name and discussion section under the "Register Alias" section.

Hannah Thornton 1F

It is only necessary to add -ate to a transition metal if the complex has a negative charge. If it's a neutral or positive charge, do not add -ate.

Hannah Thornton 1F

Chlorido is meant to go before the oxalato, since the ligands are named in alphabetical order, putting aside prefixes.

Hannah Thornton 1F

The formulas to go back and forth from pH to [H+] are: [H+]=10^(-pH) and pH=-log[H+].

Hannah Thornton 1F

Usually, strong bases are made up of Group 1 and 2 metals attached to a hydroxyl group (OH). Weak bases are usually made up of nitrogen atoms with lone pairs. It helps most to just memorize the strong bases and assume anything else is a weak base.

Hannah Thornton 1F

Yes, an amphoteric compound has both acidic and basic character since it can be both a H+ acceptor and a donator.

Hannah Thornton 1F

I believe that quadruple bonds would have the same sigma/pi structure as double and triple bonds, being that a quadruple bond would be 1 sigma bond and 3 pi bonds.

Hannah Thornton 1F

I believe that coefficients must be written in the lowest whole number possible. Fractions are not used.

Hannah Thornton 1F

The reason why we have expanded octets is because of the d-orbital. The octet rule is due to the eight electrons allowed in the s and p orbitals, but when we get to the d-orbital, it can accommodate more than 8 electrons and can form an expanded octet.

Hannah Thornton 1F

In this case, this molecule is tetrahedral with all bonding atoms being the same element, meaning that the dipole moments will cancel. There is also no lone pair electrons on the central atom, so the overall structure would be nonpolar.

Hannah Thornton 1F

To determine sigma and pi bonds, you can look at whether the bond is single, double, or triple. A single bond= sigma bond, double bond= 1 sigma and 1 pi bond, and triple bond= 1 sigma and 2 pi bonds. We can also look into the hybrid plane and see if the overlap is end-to-end (which would be sigma) o...

Hannah Thornton 1F

Sigma bonds are stronger than pi bonds because they connect with a larger overlap of orbitals compared to the lesser side-by-side overlap of a pi-bond.

Hannah Thornton 1F

The main difference between sigma and pi bonds is that sigma bonds interact end-to-end, and pi bonds overlap.

Hannah Thornton 1F

Yes, this is correct. 1 bond is 1 sigma bond, 2 bonds is 1 sigma and 1 pi bond, 3 bonds is 1 sigma and 2 pi bonds.

Hannah Thornton 1F

No, this is not possible. Both double and triple bonds need to have both a sigma and pi bond.

Hannah Thornton 1F

Hybridization only tells us how many regions of electron density we have, which could mean either a single bond, double bond, triple bond, or a lone pair of electrons, but since it doesn't specify bond type, we cannot imply anything about sigma or pi bonds. If the hybridization is sp3, we don't know...

Hannah Thornton 1F

For this question, it's important to look at the geometry of the molecules based off of Lewis structures and the VSEPR models. The VSEPR shapes will tell you if a molecule is polar or nonpolar. In this case, NH3 is polar because it is trigonal pyramidal; BrF3 is polar because it's trigonal bipyramid...

Hannah Thornton 1F

Yes, the final is cumulative.

Hannah Thornton 1F

Yes, it looks like all of the 14B lectures will be in person.

Hannah Thornton 1F

The structure with the least amount of formal charges, ideally being 0, will be the most favorable structure. Stability also comes from having the negative formal charge on the most electronegative element.

Hannah Thornton 1F

CH2Cl2 is tetrahedral and has unequal dipole moments towards the chlorine atom since it is more electronegative than hydrogen. These dipole moments don't cancel and make the molecule polar.

Hannah Thornton 1F

We first need to calculate the number of valence electrons in NH4+. N has 5 e-, and 4 H's means 4 e-, creating a sum of 9e-. However, since NH4+ has a positive charge, we take this into account by subtracting an electron, meaning a total of 8e-. A Lewis structure with N at the center and 4 H's attac...

Hannah Thornton 1F

Other octet exceptions are He, Li, and Be. He can only have 2e, since like H, it only contains electrons in the 1s orbital, and Li and Be can only have 4e, since these elements only contain electrons in the 1s and 2s orbitals.

Hannah Thornton 1F

"Most plausible" is referring to the Lewis structure that is the most favorable and most likely to occur. This would be the structure that minimizes formal charges.

Hannah Thornton 1F

We are unable to determine bond length without knowing the atomic radius. However, we do know that single bonds are the longest, followed by double bonds, and triple bonds are the shortest.

Hannah Thornton 1F

The midterm is not cumulative, so the only quantum topics that would be on Midterm 2 would be the topics we learned about after finishing Midterm 1 material.

Hannah Thornton 1F

Electronegativity is a measure of the tendency of an atom to attract a bonding pair of electrons and depends on the number of valence electrons an element has. Elements closer to a completed octet will have a higher electronegativity, since it wants to attract electrons to bond with and complete its...

Hannah Thornton 1F

Nitrogen appears as N2 in its natural state since its a diatomic molecule, so it needs to be written out like that.

Hannah Thornton 1F

The distribution seems to be the same as most other classes, other than the fact that a C goes down to a 50%.

Hannah Thornton 1F

BaBr2 would be the most ionic because it has the greatest electronegativity. Since electronegativity decreases as we go down a period, and Ba is lower down than Br on the periodic table, this compound would be very electronegative.

Hannah Thornton 1F

It will usually be the element that is the least electronegative, or the atom that appears the least amount of times.

Hannah Thornton 1F

this is great, but I would also add that a covalent bond is atoms sharing a pair of electrons while an ionic bond is one atom donating a electron to another.

Hannah Thornton 1F

the number of electrons in an element is equal to its atomic number.

Hannah Thornton 1F

for b, since you know that l=3, that means ml must be -3, -2, -1, 0, 1, 2, 3. this gives 7 orbitals, and since each orbital can hold 2 electrons, that means 14 electrons.

for c, we have a given ml value so the answer would be 2 since it is once specified orbital with 2 electrons.

Hannah Thornton 1F

the ml quantum number is the magnetic quantum number and it represents the number of orbitals. its based off of the quantum number l, and it ranges of values from negative l to positive l. for example, if l=2, ml could be -2, -1, 0, 1, 2.

Hannah Thornton 1F

using an element in the [ ] brackets represents an abbreviated notation for its electron configuration. since part of the other atom's electron configuration is the same as the bracketed element, it makes it much simpler to represent that section of the configuration with the element's name.

Hannah Thornton 1F

He just sent out an email saying they will be ready in the next few days!

Hannah Thornton 1F

It normally doesn't make a difference whether you begin balancing the reactants or products, but what I would recommend doing is starting with balancing the least occurring element, as this will make it much easier.

Hannah Thornton 1F

The limiting reactant is the one with the least amount of moles since once it's all used up, it "limits" the reaction.

Hannah Thornton 1F

The reason that you have to multiply by 100 is because E=hv only finds the energy of a single photon, so you multiply by 100 to find the overall energy.

Hannah Thornton 1F

I believe that the midterm will include both conceptual questions as well as mathematical ones, but many people have said that it helps to focus on doing practice problems to study.

Hannah Thornton 1F

I like to relax by running and hanging out with my friends.

Hannah Thornton 1F

My favorite comfort movie is Superbad, it always puts me in a good mood. I also love White Chicks.

Hannah Thornton 1F

I personally prefer handwriting out my notes. I feel that for chem, it helps to not be limited to only typing on a computer, it's nice to be able to write out diagrams and equations with symbols. I also like that I can do color coding and highlighting easily with handwritten notes.

Hannah Thornton 1F

my favorite food is sushi! or mexican food.

Hannah Thornton 1F

They have started already! To add onto the other answers, there are some on zoom, but I would recommend going to the in person ones. I went to one last week and it was extremely helpful.

Hannah Thornton 1F

My favorite show ever is How I Met Your Mother! I would recommend it if you want to watch a feel good show. I also have been watching Squid Games, which is a new show on Netflix.

Hannah Thornton 1F

You can convert it to a different unit, but theoretical yield is typically measured in grams, since it is usually used to measure mass and in comparison to the actual yield which is measured in grams.

Hannah Thornton 1F

The number of sig figs you use in an answer should be the same as the sig figs of the values used in the question. If the values each have a different number of sig figs, you should base it off of the value with the least amount of sig figs.

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