CHEMISTRY COMMUNITY

Kate Osborne 1H

you do not have to use an ICE table when working with strong acids/bases because they dissociate completely.

Kate Osborne 1H

when using the approximation (removing x when you are subtracting/adding it to something) you must check to make sure that x is less than 5% of the reactant that it is formed from (x will likely be H or OH- so you would use the acid or base)

Kate Osborne 1H

there are multiple ways to solve this question, it just depends on what information you are given/not given

Kate Osborne 1H

if something can have a concentration you have to include it i believe, gases/aqueous.

Kate Osborne 1H

i think they would have to give you one experiment where the concentration is held constant and then if both change in a different one you would first find the change from the one you already know and then find the change from the other change in concentration.

Kate Osborne 1H

unique rate is always positive i believe so you do not have to cancel out a negative

Kate Osborne 1H

because rate is measured in change in concentration versus time only things that have concentrations can change it, so only gases and aqueous substances are included i believe.

Kate Osborne 1H

if you were finding the forward rate law you would add a negative if using the unique rate for reactants and vice versa.

Kate Osborne 1H

the unique rate is the same for all reactants and products in that unique reaction. so the rate at which the product forms and the reactant is used up must equal each other, so they have to have the same sign.

Kate Osborne 1H

∆G° = ∆H° - T∆S°and ∆G° = - RT ln K are the essential equations for thermodynamics

Kate Osborne 1H

the chemical rxn in rechargeable batteries is reversible while in non rechargeable batteries it is not.

Kate Osborne 1H

the only way to determine reaction order is through experiment so i believe we will always be given initial concentrations and rates

Kate Osborne 1H

they will always be a whole number i believe

Kate Osborne 1H

rate always decreases because as you form products you start to form reactants again

Kate Osborne 1H

k is the rate constant and is what allows for different rates when there is the same concentration of reactants and products

Kate Osborne 1H

the concentration doubled for one of the reactants and the rate doubled so to find the order you use the equation: change in rate = change in concentration ^ order where you are solving for the order

Kate Osborne 1H

gibbs free energy is the energy available to do work

Kate Osborne 1H

standard conditions are a specific ratio of products to reactants and if the ratio is not that then you have to use the nernst equation

Kate Osborne 1H

Work(max) is equal to the negative charge times the max cell potential

Kate Osborne 1H

the electromotive force is Ecell, the max potential when very little current is flowing. When there is no current flowing, that is when the difference is at its maximum.

Kate Osborne 1H

i believe it means that if a reaction is spontaneous (negative delta g) then max cell potential is positive, and vice versa

Kate Osborne 1H

use anything that has a concentration or a pressure (so only aqueous things or gases!)

Kate Osborne 1H

A reaction is spontaneous when delta G is negative. for this to happen either delta H has to be negative, delta S has to be positive, or both are true. these factors creative spontaneity by driving the reaction either by enthalpy or entropy.

Kate Osborne 1H

the K values are the equilibrium constants at the two different temperatures, delta H not is the reaction enthalpy, and R is a constant.

Kate Osborne 1H

In the midterm question the change in entropy of the system was not equal to the change in entropy of the surroundings in the irreversible reaction because the reaction occurred in a vacuum and if there are no molecules in the surroundings then you can't change their entropy. I'm not exactly sure ho...

Kate Osborne 1H

I think the temperature is constant because most reactions occur at a constant external temperature and pressure

Kate Osborne 1H

i think Wrev and Wirr are the only ones that specify!

Kate Osborne 1H

isothermal means that the reaction takes place at a constant temperature and if a reaction takes place at a constant temperature it is reversible, as such they mean the same thing

Kate Osborne 1H

This rule only applies when gases are present, if the system only has solids or liquids then a change in volume would not shift the equilibrium because compressing solids and liquids does not make them react more/less

Kate Osborne 1H

irreversible processes are done under constant pressure while reversible are not, and since w is a product of pressure and volume, work is higher when pressure is not constant because the gas will have to do more work

Kate Osborne 1H

entropy is an extensive property because it depends on the amount of substance present. more of a substance = a higher entropy.

Kate Osborne 1H

i think we are probably equally likely to be tested over any of the three methods for calculating enthalpy

Kate Osborne 1H

bond enthalpies is the least accurate because bond enthalpy is an average value not a standard value

Kate Osborne 1H

to solve this question you use the given equation: q=nC ΔT
you are directly given q, n, and the initial temperature and must use the equations: ideal gas, Cp=(5/2)R and Cv=(3/2)R to find C for parts a and b to find final temperature

hope this helps!

Kate Osborne 1H

molar heat capacity of the same gas is different at a constant pressure vs a constant volume, you can use that equation with both Cp and Cv it would just result in a different answer for Cp vs Cv

Kate Osborne 1H

using bond enthalpies to calculate delta h is the least accurate method, but to do so you would be given the bond enthalpies of the products/reactants and you would plug them into the equation we are given

Kate Osborne 1H

concentration of either the products or reactants do not change the equilibrium constant, they simply shift the reaction

Kate Osborne 1H

You're so hot you could change an equilibrium constant

Kate Osborne 1H

Some of the energy that is used to heat up something is also used to create a phase change, so there could be no measurable change in heat while there was heat absorbed.

Kate Osborne 1H

I would do the questions that relate to the stuff we've learned in class, so skip those two sections and come back to them when we've learned that information.

Kate Osborne 1H

You are right, pressure does not affect the equilibrium constant.

Kate Osborne 1H

Method 2 would possibly be used if the only information you are given is bond enthalpy. I would also make sure you understand why it is the least accurate though as well.

Kate Osborne 1H

I think method 1 and method 3 are both accurate so it depends on what information you are given as to which one you use.

Kate Osborne 1H

They both depend on the path that was taken to get to the initial state to the final state.

Kate Osborne 1H

Reaction enthalpy is the heat given off/absorbed during a reaction while enthalpy of formation is the difference between the elements in their standard state and the compound they form. You will need to use these in the different methods for calculating enthalpy.

Kate Osborne 1H

In method 3 the values of delta H were given.

Kate Osborne 1H

The only thing that effects the equilibrium coefficient is a change in temperature

Kate Osborne 1H

if Q is less than K then the reaction will proceed in the forward direction, while if Q is greater than K the reaction will proceed in the reverse direction.

Kate Osborne 1H

I believe both work but a balanced equation should always have whole number coefficients so I would use whole number ratios.

Kate Osborne 1H

I think we need to know how to use the idea gas law to go from pressure to concentration. We may use it for other applications in the future but at this point I think that’s it.

Kate Osborne 1H

The reaction quotient can be compared to K to find out if the reaction is in pre-equilibrium (Q<K), equilibrium(Q=K), or post-equilibrium(Q>K).

Kate Osborne 1H

H2CO3 is a little less common but CO3 is carbonate and when naming an acid you add -ic to it so it is carbonic acid and H2SO4 is sulfuric acid and Dr. Lavelle has talked about it in class so you should make sure to memorize it.

Kate Osborne 1H

Yes, water is an amphoteric compound because it can both accept and donate a H atom.

Kate Osborne 1H

It should be the reverse. The definition of a Lewis acid/base is more general than Bronstead acid/base.

Kate Osborne 1H

I think the radical is on the carbon because it is only forming 3 bonds

Kate Osborne 1H

I understand (a) and (b) in this question but I am confused as to how to determine the coordination number for (c) [PtCl2(en)2]2+ and (d)[Cr(edta)]-

Kate Osborne 1H

Conjugate acids/bases are the compounds formed from a reaction involving an acid/base. You identify them by figuring out what compound on the reactant side is an acid/base and then finding the compound that looks like it on the product side. Acids form conjugate bases and bases form conjugate acids.

Kate Osborne 1H

I understand that Be, Al, Ga, Sn, Pb, and Sb form amphoteric compounds but how do we tell for other compounds? I know that H2O is amphoteric but it doesn't have any of these elements so how do we tell for other compounds?

Kate Osborne 1H

Acids and bases will be on the reactant side while their conjugate base/acid will be on the product side. You should be able to identify the acid/base by identifying which is the proton donor/acceptor.

Kate Osborne 1H

Although one atom is contributing 2 electrons, these electrons are being shared by the two atom that the bond is between rather than being transferred from one atom to another.

Kate Osborne 1H

In addition, all Bronstead acids are Lewis acids and all Bronstead bases are Lewis acids, but not vice versa. The definition of a Lewis acid/base is more general than Bronstead acid/base.

Kate Osborne 1H

A coordination compound occurs in a compound that has a coordinate covalent bond. This means that one atom has supplied both electrons in the bond.

Kate Osborne 1H

C donates the lone pair because it has the lower electronegativity I believe, you should always show C making the coordinate covalent bond in this structure.

Kate Osborne 1H

Atoms with lone pairs can be non-polar, for example I2.

Kate Osborne 1H

It depends on the arrangement of the atoms, for example CH2Cl2 is polar.

Kate Osborne 1H

Hybridization occurs when an atom uses both its s and p orbitals to bond with another atom. This creates an imbalance in energy levels so hybridization occurs to level out the energy as it combines these orbitals.

Kate Osborne 1H

We got our physical midterms passed back today after class by our TAs so if you didn't get yours I would email your TA to see if you can get it from them.

Kate Osborne 1H

In this case it does result in a linear formula but O3 would be bent, so that is not a rule.

Kate Osborne 1H

In lecture Dr. Lavelle only went over examples where there are no lone pairs, but yes lone pairs do influence shape and I believe we will learn about it on Friday during lecture.

Kate Osborne 1H

If the central atom has either zero or three non bonding electron domains in addition to the two bonding it is linear but any other number would be some other shape.

Kate Osborne 1H

I think it's necessary to learn the names for all the shapes that Dr. Lavelle talks about in lecture. I found it easiest to memorize when I looked at all shapes that have the same number of electron domains and memorized them in decreasing bonding domain order.

Kate Osborne 1H

It does not matter what resonance structure you look at when determining molecular shape using the VSEPR model because it only looks at bonding pairs and not the amount of bonds.

Kate Osborne 1H

Octahedral shape describes a compound with 6 shared pairs of electrons and since there are 6 bonds in SF6 it is octahedral.

Kate Osborne 1H

Because areas of electron density should be spread as far apart as possible and actual molecules do not exist in 2D, bond angles of 109.5 allow this to occur.

Kate Osborne 1H

I think that everything that we have learned that was not tested on the midterm will be on test 2 plus probably drawing lewis structures. (outlines 3 and 4)

Kate Osborne 1H

Does anyone know if there is an answer key to the midterm posted anywhere? I thought Dr. Lavelle mentioned one during lecture today but I can't find it.

Kate Osborne 1H

When drawing lewis structures your goal should not be to have the central element have a formal charge of zero but rather have the most elements have a formal charge of zero and the most electronegative elements carry the negative formal charges.

Kate Osborne 1H

Dr. Lavelle said in class he would give us the formulas for any compounds we have not been exposed to a lot (like he might not give us the formula for water but he'd give us those)

Kate Osborne 1H

In the example Dr. Lavelle gave in class, the carbon held the unpaired electron rather than the hydrogen because carbon only contributed to three bons and as such it has one electron left.

Kate Osborne 1H

In the example Dr. Lavelle gave in class you were able to tell that the carbon held the unpaired electron because in a methyl radical the H has one bond so its formal charge is zero but the carbon does not so it holds the unpaired electron.

Kate Osborne 1H

A radical is any compound with an unpaired electron (such as a methyl radical formed by burning hydrocarbons). They are significant because they are another example of an exception to the octet guideline and are so highly reactive that they can react with DNA and damage it.

Kate Osborne 1H

I think in lecture Dr. Lavelle said that obtaining a formal charge of zero is more important than following the octet rule which is why there are so many exceptions to it. Because having an octet on one element does not mean that the surrounding elements will also have an octet.

Kate Osborne 1H

triple bonds are shorter in length than double, and double than single. This is because these types of bonds are stronger and therefore draw the elements closer. And yes, quadruple bonds exist but they are most stable among transition metals.

Kate Osborne 1H

If each element in a compound has a formal charge of zero than it is the most stable form of that compound, and because a lot of compounds are stable they have a formal charge of zero on all the elements. The sulfur did not have a charge in the example given in class because oxygen is more electrone...

Kate Osborne 1H

I think that the number of resonance structures a compound can form doesn't necessarily mean much about it, I think more the fact that it has multiple resonance structures is a defining characteristic of the compound because it means the electrons are delocalized.

Kate Osborne 1H

Intensity is proportional to a wave's amplitude and it typically refers to the amount of photons being emitted, so it is something completely separate from frequency.

Kate Osborne 1H

If the 3d sub-shell is either half full or full that is more stable so the 4s sub-shell will not be full then!

Kate Osborne 1H

Electrons are removed in the order that you write the configuration, so 4s first.

Kate Osborne 1H

Yeah I don’t think we need to know absolutely everything about it but understanding how it relates to the other things that were mentioned already!

Kate Osborne 1H

As was said above, the equation represents the wave characteristic of electrons, so be squaring it you are able to find out how likely you are to find an electron.

Kate Osborne 1H

Yeah we can do quantum for this week but next weeks homework will be the next unit!

Kate Osborne 1H

I think Dr. Lavelle used the example of constructive and destructive interference in light waves to illustrate the idea of diffraction so that he could show us that because electrons passing through a crystal show diffraction they have wave-like properties. So if you were asked to explain how electr...

Kate Osborne 1H

The Balmer series includes the wavelengths of light emitted when an electron falls from an outer energy level to n=2 and Lyman series is the same except for the electron falls to n=1 instead.

Kate Osborne 1H

Yes, photoelectric effect is correct because if light only had wave properties, increasing the amplitude should eject more electrons, but that was not the case as the only thing that increased the amount of electrons ejected was increasing frequency/decreasing wavelength.

Kate Osborne 1H

Yes, the energy of a photon of light is equal to Planck's constant times frequency, so as frequency increases (as when going from visible light to UV) energy also increases.

Kate Osborne 1H

In addition to what was said already, the speed of light is a constant because as the frequency decreases the wavelength increases proportionally, so speed never changes.

Kate Osborne 1H

The way the diagram is set up is kind of confusing as there are 9 astatine atoms shown, but it is not saying that you need to put all nine it is asking how many you need which is not necessarily all nine as the calculations show.

Kate Osborne 1H

Typically the amount of sig figs you have in your final answer is equal to the amount of sig figs in the given number that has the least sig figs. So if you were given two initial masses, one with 3 sig figs and one with 4, and your final answer was also a mass you would most likely round to 3 sig f...

Kate Osborne 1H

I believe that in the solutions it is telling you how you would do this in a lab situation, and when you are mixing acids and bases you must always add the acid in order to the water and not the other way around so the exothermic reaction that occurs during mixing can be somewhat limited, but the am...

Kate Osborne 1H

The way I was taught to find the limiting reactant is to convert from grams to moles and then to divide the amount of moles you find by the coefficient in the reaction and then compare those numbers so you do not have to go about comparing ratios and the math gives you a more clear answer as to whic...

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