CHEMISTRY COMMUNITY

Annie Lieu-1H

can someone explain in simple terms what this is asking for and how i would use resonance to solve it

Annie Lieu-1H

why don't we account for the hf of oxygen in the end reaction?

Annie Lieu-1H

I was wondering the same thing.

Annie Lieu-1H

Did you know protons have mass?

I didn't even know they were Catholic!

Annie Lieu-1H

Money Has Recently Been Discovered To Be A Not Yet Identified Super Heavy Element

The proposed name is: Unobtainium.

Annie Lieu-1H

Everything on the syllabus will be on the final ( so yes everything but 15.9).

Annie Lieu-1H

I believe K is only affected by change in energy (heat) and activation energy.

Hope this helps :))))))

Annie Lieu-1H

I believe that will always be given in the problem (whether explicitly states in directions, or derived from the rates given). Hope this helps :)

Annie Lieu-1H

Yes, any substance that is cancelled out and not in the final reaction is an intermediate (whether it appears a product or reactant first).

Annie Lieu-1H

Anode is always listed first.

Annie Lieu-1H

Like in the test, you will be given the standard reduction potentials and you must judge from there. For context: The more positive the potential is the more likely it will be reduced. (So it's the oxidizing agent because it has higher oxidizing power) So using deductive reasoning, the more negative...

Annie Lieu-1H

The overall charge of a molecule is the number charged to it and the end (if there's nothing there, set the charge equal to zero). Then we would use set oxidation values (O = -2, H= 1) and add it to X (or times it by a coefficient) of the oxidation charge we DON't know. Then we set that to the overa...

Annie Lieu-1H

Like in the test, you will be given the standard reduction potentials and you must judge from there. For context: The more positive the potential is the more likely it will be reduced. So using deductive reasoning, the more negative the potential, the less likely it will be reduced (and more likely ...

Annie Lieu-1H

It's an open system

Annie Lieu-1H

No, unless the problem specifies. When given just "closed" or "isolated" that deals with energy exchange (or lack thereof).

Annie Lieu-1H

Work does not occur in a vacuum, so no I think.

Annie Lieu-1H

Yes, they are the same. Just remember deltau=q+w.

Annie Lieu-1H

The ideal gas constant! Like everyone said, make sure to look at the equations sheet and look at the right units to use for numbers in a particular problem.

Annie Lieu-1H

R refers to the gas constant.

Annie Lieu-1H

The problem deals with molecular complexity regarding heat capacities. Heat capacities are always higher for more complex molecules because it takes more energy to break more bonds/etc. In this particular problem, we can see butane contains much more molecular complexity than H2, who only has one bo...

Annie Lieu-1H

As of now, the universe is the ultimate surrounding that contains everything. So there is nothing outside to exchange with.

Annie Lieu-1H

You should always account for phase changes for "calculating heat" problems because there's an energy change between phases we need to account for in the ultimate result.

Annie Lieu-1H

You would use common knowledge to understand if something is heating up or not. And using that, we can determine if something is endothermic (takes heat), or exothermic (loses heat) in regards to each term in a reaction.

Annie Lieu-1H

It would probably just include the environmental impact (surroundings and such) as context for a problem, but I doubt we would need to memorize how to deal with a complex problem dealing specifically in it.

Annie Lieu-1H

We would use specific heat of ice when H20 is presented in the problem as a solid and undergoing a fusion reaction in the reaction, and use specific heat of water when H20 is being presented in the problem as a liquid.

Annie Lieu-1H

The heat (energy) is being used to break or form bonds for phase changes instead of changing the temperature of the reaction. In addition, as Lavelle said in class: " If the system (reaction) is small compared to the surroundings then the temperature of the surroundings does not change. Tonight...

Annie Lieu-1H

I got part a of this question without using the answer solution method by simple logistics (A decreases at 1/3 rate of B because of coefficients so subtract that from initial A) but part b requires we use that method and I don't understand it. Why do we substract (1molA/2molB) in the first place for...

Annie Lieu-1H

NUMBER 5 ON THE MID TERM AMIRITE LADIES??

Annie Lieu-1H

My bad, misread my own handwriting.

Annie Lieu-1H

For the first part of the question, do we not calculate the standard formation change in enthalpy of Fe and C because they're pure elements?

Annie Lieu-1H

Hi, I was wondering on the mid term/future exams, would the problem state if a certain process is reversible or irreversible? I understand that to be reversible you have to ; the temperature of system and surroundings have to be small change and constant but what does that mean realistically and how...

Annie Lieu-1H

Hi, for "Do you expect there to be a difference between your answer in part (a) and part (b)? " I put that there is an expected difference because mean bond enthalpies are more accurate than ΔHf ways. I got the question right but shouldn't it be the other way around because it's a MEAN bon...

Annie Lieu-1H

Hi could someone please explain in simple terms the equipartition theorem and how we would use it in calculations..

THank you

Annie Lieu-1H

Hi, I understand that The heat capacity at constant pressure is greater than that at constant volume because at constant pressure not all the heat supplied is used to raise the temperature: some returns to the surroundings as expan- sion work and C q/ T is larger (because T is smaller) than at const...

Annie Lieu-1H

Hi, I understand that it's important to understand the derivations and how we find a quantitave relation between the Gibbs free energy and the maximum non expansion work that a system can do.. I remember that Professor Lavelle went over this in class but I don't remember him saying we were going to ...

Annie Lieu-1H

Hi, I'm very confused by what Figure 9.25 in the textbook is trying to tell us.

And the attached paragraph is really confusing and convoluted..

Would anyone be able to summarize the information the graph is trying to tell in regards to Gibbs free energy and phase changes??

Annie Lieu-1H

Can someone explain to me why, when you cool the water back down, you use Cp (constant pressure)? Instead of standard heat capacity..

Annie Lieu-1H

I understand that it's a 2 step process that we end up adding all together. But why do we use constant volume for the temperature equation? The volume is changing, so how is it heat capacity at constant volume?

Annie Lieu-1H

Why is q/t for 800 K negative but q/t for 200k is positive?

Annie Lieu-1H

Delta H deals with internal energy at a constant pressure versus delta U is just change in internal energy.

Annie Lieu-1H

@Hannah

so then please explain why for 8.11 the more negative work answer "does more work"...

Annie Lieu-1H

Hi could someone please explain why for question 8.3 b (which asks if the work with respect to air in the pump is positive or negative) the answer is positive?

If the work is positive because you need more work to compress air (not sure if this is why), in which instances would work be negative?

Annie Lieu-1H

i love chemicals

Annie Lieu-1H

State properties depend solely on final and initial states but heat depends on the path taken.

Annie Lieu-1H

H is enthalpy, and DeltaH is simply the change in enthalpy. However, we are interested in DeltaH because that is how we can measure the change in temperature (and subsequently, internal energy) because a change in the enthalpy of a system is equal to the heat released or absorbed at constant pressure.

Annie Lieu-1H

Lavelle mentioned this in lecture but I'm still confused.

How can exothermic reactions be a reaction with constant temperature?

Annie Lieu-1H

The smaller the pKB, the stronger the base is.

Annie Lieu-1H

Sorry this might be in the completely wrong category. In chemistry, what is the difference between an "empirical" relationship and a "theoretical" relationship. And how do you determine if a formula was derived or not. Like conceptually. I just noticed this on a past final questi...

Annie Lieu-1H

The smaller the Pka, the stronger the acid. But the larger the Ka itself, means it's a stronger acid. (This can be seen in the relationship pka=-log[ka].

Annie Lieu-1H

Knowing the basic trends is enough. But remember the exception with noble gases too. Like Lavelle said, the only chart we need to memorize is the ligands chart!:)

Annie Lieu-1H

No. Titrations and Salts will not be covered on the final.

Annie Lieu-1H

Sorry but what is delocalized bonding? And how will I be able to determine it when given the Lewis structure of a compound. Like what are its distinctions. I understand that its supposed to make it so that electrons are delocalized and spread across a compound, but I'm not really sure how I would se...

Annie Lieu-1H

I think the selected values will be given if needed in the question, I don't remember Lavelle saying anything about memorizing.

Annie Lieu-1H

Typically, non metal oxides are acidic. Metal oxides are basic. And semi metal oxides are amphoteric. If you can't determine it from that, then it's always a safe bet to draw the Lewis Structure and see if there are any lone pairs available (base), if it's an incomplete octet (acid). If it could go ...

Annie Lieu-1H

Typically, non metal oxides are acidic. Metal oxides are basic. And semi metal oxides are amphoteric. If you can't determine it from that, then it's always a safe bet to draw the Lewis Structure and see if there are any lone pairs available (base), if it's an incomplete octet (acid). If it could go ...

Annie Lieu-1H

Liquids don't affect the equilibrium CONSTANT because their effective concentrations stay constant throughout the reaction. BUT, In terms of shifting the reaction itself, H20 is still viewed as a reactant. If you add more H20 concentration, that's not a constant value. When you add more reactants, t...

Annie Lieu-1H

The reaction will shift left to maintain equilibrium because of the excess amount of product. Concentration RATIOS must be maintained during and for equilibrium at all times.

Annie Lieu-1H

Can someone explain the difference between axial lone pairs and equatorial lone pairs ?How can you tell what type of lone pair a given molecule has? And based on these pairs/shape, that's how we determine bond angles right?

Thank you!

Annie Lieu-1H

Just realized you're trying to get to a noble gas configuration, nvm.

Annie Lieu-1H

I understand the concept behind oxidation states (how much you can lose and gain to become an octet). But for the chlorine atom, how does an oxidation charge of (+7) which means it loses 7 electrons, get to a full octet when Chlorine already has 5 electrons, so losing 7 would get it to a full d orbi...

Annie Lieu-1H

^^, also don't forget that l also represents the rate of rotation.

Annie Lieu-1H

I agree with Angelica! But in regards to the grouping, I remember Lavelle saying in class that groups in the periodic table are grouped together because of similiar properties, and so yes the groups did have more exceptions besides Chromium and Copper. But in regards to this particular test, and in ...

Annie Lieu-1H

Basically, yes it is. There can only be two electrons in an orbital, and some subshells like d can contain more orbitals (so basically more electrons) than other subshells like p. D has five orbitals, or 10 electrons.

Annie Lieu-1H

Yes, divide the Avogrado's constant in the dimensional analysis so you can convert the energy/sodium mole to energy/sodium atom

Annie Lieu-1H

The units for the work function will be given in either J or J/mol (or kJ or kJ/mol), but never kg/mol. When you are given the energy/mol, multiply by Avogrado's number to convert the work function in terms of energy/atom. I am so ashamed that I misread my own handwriting. It was in kj/mol this who...

Annie Lieu-1H

The question asks for the energy required to remove an electron from the sodium atom. But the work function is given in units of kg*mol^-1. I know that a joule's SI base units is ‎kg⋅m2⋅s−2. How would I convert that??

Thank you!

Annie Lieu-1H

For the Rydberg equation, you're missing the frequency. So first, you need to find the frequency using the given wavelength. Find this using the c=wavelength*frequency formula. You can then use the calculated frequency for the Rydberg equation! (Remember that for these type of problems, if they don'...

Annie Lieu-1H

They're the same thing basically. Both represent the amount of energy needed to eject an electron. I think for test purposes though they use the term work function!

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