CHEMISTRY COMMUNITY

Verity Lai 2K

You only add OH- if you are dealing with a basic solution, otherwise you add H20 or H+.

Verity Lai 2K

It's not, but you are required to know how to derive it, but the equations necessary to derive it are on the equations sheet.

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You use the van't Hoff equation to relate the equilibrium constant to a change in temperature. This can help you find a new equilibrium constant for the same reaction at a different temperature.

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To cancel out ln from both sides, you raise the entire other side to the power of e.

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It's the same rate. The decomposition and composition rates of a reaction are inverse. The more a recant decomposes, the more a product with compose.

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To find n you balance the redox reaction to determine the number of moles of electrons being transferred during the reaction.

Verity Lai 2K

n is the moles of electrons being transferred during a redox reaction. You find it by balancing the redox reaction and I'm not sure about if you can find n by plugging in numbers and solving for n. I think the best method is using the redox reaction.

Verity Lai 2K

There is no effect on the cell potential if you increase/decrease the mass of the electrodes.

Verity Lai 2K

Q is just the reaction quotient which is from the equilibrium portion of 14b. You use it to connect the molarity of the two solutions with the cell potential.

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You use the rate laws to find the slowest one.

Verity Lai 2K

You should know how to derive it and you can use equations provided on the equation sheet to figure it out. It’s used to find the equilibrium constant (K) when the temperature changes.

Verity Lai 2K

The equation relates K with temperature and it isn’t on the equation sheet. However, the equations you need to derive it are on the equation sheet.

Verity Lai 2K

Could someone please remind me how to derive the Nernst equation??

Verity Lai 2K

It doesn’t matter because Lavelle showed us the conversion from log to ln. But in class he told us that biological sciences are more likely to use the log version, however I don’t think it matters in our case.

Verity Lai 2K

Concentration cells have the same solution in each compartment, but they have different concentrations, hence the name. Galvanic cells have different metals in each compartment which transfer electrons from one solution to the other.

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I think platinum is the most common metal used as an electrode. It's used when there is no solid aspect of either the oxidation or reduction reaction. It is used to facilitate the reaction because otherwise the reaction would not be able to transfer the electrons.

Verity Lai 2K

Pt (platinum) is used in examples like the one Lavelle discussed in class on friday where the redox reaction has two aqueous solutions that change charge without a solid, such as Fe. The platinum helps facilitate the reaction because otherwise there would be not way for the electrons to be transferr...

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The oxidation number is the charge of the element which you can find from patterns on the periodic table. For example, group 1 has an oxidation number/charge of +1.

Verity Lai 2K

I think the only time its okay to keep temperature in Celsius is when the units are in celsius or when you are calculating delta t because the change in Celsius is the same as the change in kelvin.

Verity Lai 2K

It doesn't matter what order the reactants and products because it all produces the same reaction. All that matters is that the coefficients are correct.

Verity Lai 2K

I always look at the units of the information given to me and find the value of R that has most of the same units.

Verity Lai 2K

Depending on what information is given, you can decide which heat capacity to use, and you want all your units to match so they can cancel out.

Verity Lai 2K

There are no entropies given on the constant sheet, so they will provide any entropies you need in the question.

Verity Lai 2K

This equation is used to find entropy when the temperature is constant. If the temp or volume change, you use the equations delta S= nRln(V2/V1) or delta S= nCln(T2/T1).

Verity Lai 2K

Volume and pressure are related inversely, so V=1/P. So when you use the delta S equation, you can replace V with the inverse of P, which results in nRln(P1/P2).

Verity Lai 2K

The integrals I think are meant to understand that work of expansion is very small changes in the system but all together, the sum of the changes makes the work done on the system. This is essentially what reversible expansion is which is why the integral is necessary but luckily it all simplifies s...

Verity Lai 2K

In one of the review sessions today, the TA gave a good example on how to differentiate. He said imagine two scales each with a pile of rocks on them. Irreversible expansion would be like removing all the rocks all at once and recording the difference of the scale in the instant. For reversible expa...

Verity Lai 2K

Yeah, for reversible expansion, the equation for work is w=-nRTln(v2/v1) and for irreversible expansion, the equation is w=-PexdeltaV. They are both essentially the same, except the irreversible expansion has constant pressure, while reversible expansion has change in pressure.

Verity Lai 2K

delta u is the change in internal energy

Verity Lai 2K

It depends on the information given and you can also use the unit its given in.

Verity Lai 2K

If they give you the moles, use q=nCdeltaT, if they give you grams, use q=mCdeltaT. It depends on the information given.

Verity Lai 2K

If the problem uses either J or kJ when giving you information I would use which ever one is given, other than that I don’t think it matters because they are essentially the same.

Verity Lai 2K

It depends on what the information gives you. If there is a table of bonds and their enthalpies, that indicates a bond enthalpy problem, if it gives you the delta H for multiple reactions, you will probably will have to use Hess’s law and for standard enthalpy of formation it will probably ask for t...

Verity Lai 2K

An example of when standard enthalpy of formation is 0 is N2—>N2. Its 0 because N2 is already the most stable form of nitrogen so there is no change in standard enthalpy of formation.

Verity Lai 2K

They are pretty much the same. Just like you said, qp is under constant pressure and qv is under constant volume but they are both calculated the same, q=nCdeltaT.

Verity Lai 2K

Both work, it depends on what information is provided in the problem. If the units aren’t provided I wouldn’t worry about it or maybe use either one but make it clear your using it.

Verity Lai 2K

Changing the stoichiometric coefficient is not the same thing as changing the concentration. By changing the stoichiometric coefficient, you are also changing the power of the concentrations when you are finding K. For example aA+bB—>cC+dD, the K is [C]^c*[D]^d/[A]^a*[B]^b, but if you were to double...

Verity Lai 2K

The temperature only changes once the substance has reached solid/liquid/gas. The transition between them doesn’t increase or decrease in temperature because it is using the energy being put into the system to change the phase and only focuses on that before increasing or decreasing the temperature.

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Inert gas is usually noble gases or very stable gases which are not likely to react with the contents in the reaction vessel. Although by adding inert gas, it is increasing the pressure of the reaction vessel, the gas being added isn’t going to effect the reaction but just exist around it instead.

Verity Lai 2K

Could someone please summarize what Lavelle was talking about buffers please??

Verity Lai 2K

If you increase the pressure, often times by decreasing the volume, the reaction will go to the side that has fewer moles and if you decrease the pressure, by increasing the volume, it will go towards the side with more moles. If they has an equal amount of moles on each side, it should remain the s...

Verity Lai 2K

If it gives the value of K and the initial concentration of either the reactants or products it will require an ice table. If you just set up an ICE table for a problem your unsure about and use the information your given to try to fill it in, you can quickly realize if it is an ICE table or not.

Verity Lai 2K

In a peer review session, the UA suggested that we should use Kc unless it specifically tells us to find Kp or gives information using atm or bars.

Verity Lai 2K

If you multiply all the the coefficients in the reaction, although the ratio of coefficients is the same, it changes the equilibrium constant because it changes the power to which the concentrations or partial pressures are raised to. For example, if you double all the coefficients, it will increase...

Verity Lai 2K

The pH can be negative or above 14 but its not common and I don’t think we will have to deal with any pH outside of 1-14.

Verity Lai 2K

Ice tables help you find out the concentration of the reactants and products when the reaction is at equilibrium. You start out with the initial concentrations, find the change in concentrations to ultimately find the equilibrium concentrations.

Verity Lai 2K

Yes, Q and K are calculated the exact same way. K is just when the reaction is at equilibrium and Q can be calculated anytime during the reaction.

Verity Lai 2K

I think if it asked for the Kp, they would have to been all gases because the partial pressure only applies to gases. So aqueous solutions would not be included.

Verity Lai 2K

In all the examples he has done with us so far, he has included the state of the products and reactants so I’m sure he will include it one tests. Plus we need to know the state so we can determine if they should be included in the equilibrium constant.

Verity Lai 2K

They generally all mean the same thing, they are the equilibrium constants. The p or c denotes if it is based on partial pressure or the concentration of reactants and products.

Verity Lai 2K

Water is monodentate because the lone pairs are too close together to be able to bond more than once.

Verity Lai 2K

You add -ate to metal if the overall charge of the compound is negative. Its not very common though so its meant to stand out and won't occur very often. So be weary about this on the final.

Verity Lai 2K

The coordination number is just the number of bonds on the central atom so I would draw the lewis structure so you have a visual and can easily identify the coordination number.

Verity Lai 2K

They pretty much are the same thing, their definitions are just slightly different. Bronsted acids are proton donors and bronzed bases are proton acceptors. Lewis acids accept the electron pair and Lewis bases donate the electron pair.

Verity Lai 2K

Do we need to know any of the the stuff he discussed on Wednesday for the final?

Verity Lai 2K

You distinguish if its a strong or weak acid/base depending on how much is dissociates in solution but I don't think there's any way for use to know that unless its given to us. I would memorize the ones from the book and you should be set.

Verity Lai 2K

A Lewis acid accepts an e- pair and a Lewis base donates an e- pair. We only need to know about Lewis and Bronsted acids/bases. Strong acids/bases are going to be completely dissociate in solution but it can still be an acid/base if it doesn't completely dissociate, its just weaker than ones the dis...

Verity Lai 2K

The first row of transition metals are the most important for this class, but transition mentally can have multiple oxidation states which is good for e- transfer. I would know the significance of Cr, Fe, Co, Mn, Zn, Ni, and Cu for the final.

Verity Lai 2K

Also maybe study vit B12

Verity Lai 2K

You should know the rules on how to name ligands. Lavelle spent a lot of time in lecture going over it so I would memorize it for the final.

Verity Lai 2K

Strong acids have longer bonds are are usually more electronegative, thus they are more likely to break their bonds and there isn't a very strong force holding the atoms to it compared to elements with smaller radii and higher electronegative values.

Verity Lai 2K

Yeah the pH can be negative and it can go past 14 but I don't think we need to worry about anything but what's between 1-14 for this class.

Verity Lai 2K

Thanks! This helps a lot!

Verity Lai 2K

Could someone please summarize the idea of hybridization? I'm still confused how to determine if an element can be hybridized and how to go about finding the hybrid orbitals.

Verity Lai 2K

All bonds have at a sigma bond, which is just a single bond. Any bonds after the first one are pi bonds, such as double or triple bonds.

Verity Lai 2K

Since Lavelle didn't discuss it in class I don't think we have to know it. I think molecules with more than 6 areas of electron density are pretty rare.

Verity Lai 2K

I don't think we need to learn anything beyond AX6 because any molecules with more atoms or lone pairs is going to be really rare but I would memorize all the shapes between AX and AX6.

Verity Lai 2K

I think your right, the lone pair-bonding pair electron repulsion is stronger than the bonding pair-bonding pair electron repulsion so the bond angles are slightly smaller than if it was all atoms.

Verity Lai 2K

This is a random question but does anyone know if we have lecture on the Wednesday before Thanksgiving? Thanks!!

Verity Lai 2K

I think its always a tetrahedral shape if there are four electron regions because they want to be as far away from each other as they can be which produces the tetrahedral shape.

Verity Lai 2K

If all of the outer atoms are the same except one which has more electrons, the other atoms will be pushed slightly towards each other because the electron repulsion from the atom with more electrons is stronger than the other atoms. Thus some bond angles will be slightly larger and some will be sli...

Verity Lai 2K

In lecture, Lavelle said that double and triple bonds have no effect on the shape of the molecule so it doesn't matter what resonance you use to determine the shape because it will be the same shape no matter where the double or triple bond is.

Verity Lai 2K

Could someone remind me what the bond angles are for each VSEPR shape?? Thanks!

Verity Lai 2K

Delocalized electrons refer to lewis structure resonance while polarizability refers to an atoms likelihood that there will be distortion in the electron cloud.

Verity Lai 2K

The ionic radius trend is the same as the atomic radius trend. It decreases across the period and increases down the group.

Verity Lai 2K

It's when elements or ions have the same electron configurations. For example Na+, Ne and O2- are all isoelectronic.

Verity Lai 2K

The standard is 8 valence e- in the outer orbital but after the 3rd period, the elements have access to the d-orbital which means they can have more than 8 valence e- in the outer orbital.

Verity Lai 2K

How do you know which element in a radical has the lone electron when drawing their lewis structures?

Verity Lai 2K

All elements past row three because they have the extra d-orbital space. P, Cl and S were the beginning of this exception and I think these are the most important ones to remember. And then boron and aluminum can be stable without a full octet.

Verity Lai 2K

Today in the lecture, he said it would be on all the content from lectures up to Friday, November 1. Which covers fundamentals, quantum and almost all of chemical bonds.

Verity Lai 2K

Usually the center atom is the one with the most unpaired electrons in the valence shell because then they can make more bonds and it's just easier for drawing the lewis structure.

Verity Lai 2K

It doesn't matter but in the end the ion should have a full shell of valence electrons (8 dots/bonds).

Verity Lai 2K

You would want to fill the d-shell so that the element is more stable. It is like the exceptions he discussed in the lecture, chromium and copper. You fill the d-shell half full or completely full before completing s-shell because they have lower energy than the s-shell.

Verity Lai 2K

I think we will always be given the atomic radius and I think the 2r was to help us understand how the atomic radii was calculated.

Verity Lai 2K

The atomic radii decreases because since there is more protons, there is a stronger pull on the electrons towards the nucleus. All of the elements in that period have the similar electron configurations so the added protons attract the electrons more, creating a smaller atomic radii.

Verity Lai 2K

I would use the one provided on the constant sheet and it probably have the units for it on there as well.

Verity Lai 2K

Do the different types of wave interaction create different diffraction patterns or do they all result in the same pattern?

Verity Lai 2K

I don't think we have to know the equation but instead just understand how it impacted the orbitals.

Verity Lai 2K

The fancy h just means h/2pi and they wrote it that way in the book so it would be shorter and maybe easier to remember but either way works. If you do use the fancy h, you have to remember to put it over an extra 2 so it equals h/4pi.

Verity Lai 2K

We don't need to know how to use Schrodinger's equation for the exam. As for the orbitals, they show the likelihood that an electron would be present at a certain spot around the nucleus. So for a p-orbital, there is a low chance that there will be an electron near the nucleus but a higher chance th...

Verity Lai 2K

I don't think we've learned about that yet. The photoelectric experiment is about emitting electrons from metals specifically.

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Large objects do have wavelengths which can be demonstrated by De Broglie's equation, but the wavelength is so small that there is no way to measure if there is any properties of waves. The wave length is so small that we just treat it like a particle.

Verity Lai 2K

I think we need to know the general placement of UV, Xray, visible, micro, infrared, etc, on the spectrum, like if they have shorter or longer wavelengths. I think we also have to know the range of wavelengths for visible light (400 to 700 nm).

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Hydrogen atoms only have once electron so there is a very limited amount of things that one electron could do. The equation we learned about in the lecture only accounts for one valence electron so this equation could theoretically also be used on other elements with one valence electron. But most e...

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The electron detector has a positive charge to attract the electrons with no kinetic energy. There is also an electrical current connecting the detector to their piece of metal which transfers electrons back to the metal which prevents the metal from becoming positively charged and then it wouldn't ...

Verity Lai 2K

Formula units is used for ionic compounds, but it uses the same avagadro's number as if you were finding the number of atoms. When a problem asks for the formula units, it is essentially asking for the number of atoms.

Verity Lai 2K

This is really helpful! Thank you so much!

Verity Lai 2K

I would start writing the states of the reactants and products because when we begin to learn about acids and bases, its going to become very important. It all has to do with the aqueous state like the people above me mentioned. Its a good habit to start and it will be beneficial in the future.

Verity Lai 2K

I usually use three sig figs if I'm not given any numbers to base the sig figs on, but the more sig figs you use, the more acurate your values are generally going to be.

Verity Lai 2K

This week the textbook homework is due on friday, but normally it is due in your discussion. I'm not sure about the chemistry community homework. I think its also usually due in your discussion.

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