CHEMISTRY COMMUNITY

Te Jung Yang 4K

I don't understand why the equation is change in U is equal to q + w. Why is it not change in U is equal to the change in q + the change in w?

Te Jung Yang 4K

An ideal gas is a man-made notion about a "perfect" gas to simplify calculations. It refers to a gas in which the molecules don't have any volume and don't interact with one another, which of course does not exist in real life. All our equations are assuming that the gas is ideal, and in q...

Te Jung Yang 4K

It depends on the system at hand. If the system is isolated, heat cannot come into the reversible expansion and replace the additional energy loss, so the first law of thermodynamics tells us that in the case that both systems (reversible and irreversible) are isolated, the irreversible one would in...

Te Jung Yang 4K

W= F*d is the more general definition of work which is good to know, but I don't think we will ever need to calculate anything using that definition. It would lean more toward physics.

Te Jung Yang 4K

An intensive property is does not depend on the system size or the amount of material in the system.
An extensive property does depend on the system size or the amount of material in the system.

Te Jung Yang 4K

Basically if you look at the phase change curve, you can see that it takes energy to heat up the liquid to a gas at the same temperature. So that additional energy goes into burning your hand if it's steam that's hitting your hand.

Te Jung Yang 4K

If you're referring to heat energy (which is enthalpy) then yes.
If you're referring to temperature, then also yes.

Te Jung Yang 4K

In lecture, Dr. Lavelle said that bond enthalpies were the least accurate way of finding a reaction's change of enthalpy as they are average values.

Having said that, I would assume that the other two are preferable as they are more specific to the reaction you are trying to solve.

Te Jung Yang 4K

They are not the same thing.

Heat capacity is the number of heat units needed to raise the temperature of a body by one degree, while enthalpy is heat energy.

Te Jung Yang 4K

If the answer is 0.25, then here is what I did. You figure out how much BrCl at eq by 3.312 * 10^-5 * 0.18. Set up your eq constant equation (with concentrations). Subtract the initial amount of BrCl with eq amount of BrCl and divide that difference by 2 to get the amount of both Cl2 and Br2 at eq a...

Te Jung Yang 4K

I'm assuming you are using the equation PV=nRT, which is the ideal gas law. As the name implies, the equation is only for gases.

Te Jung Yang 4K

Strong Acids: Group 17 Acids: HCl - hydrochloric acid. HBr - hydrobromic acid. HI - hydroiodic acid. Others: HNO3 - nitric acid. H2SO4 - sulfuric acid (HSO4- is a weak acid) HClO4 - perchloric acid. HClO3 - chloric acid. Weak Acids (usually organic): Formic HCOOH Acetic CH3COOH Hydrocyanic HCN Hydro...

Te Jung Yang 4K

Would it be possible for someone to help me on 11.7 part c. I got the answer but I'm not quite sure if my reasoning is right. Thanks!

Te Jung Yang 4K

To answer this question, there needs to be an understanding of the thermodynamics behind it. G = H – T*S, where G is the change in Gibb's Free Energy, H is the change in enthalpy, T is the temperature, and S is the entropy. Before dissecting this equation and using it to explain why an increase in t...

Te Jung Yang 4K

You are correct when you say you need to find K so that you can compare it with Q.

You need Gibbs Free Energy (G) as K and G are linked with the following equation (which we didn't see in class yet):
G = - R*T*ln(K)

You use this equation to find K, which you can use to answer the question.

Te Jung Yang 4K

A conjugate base is the compound that is formed when an acid loses its hydrogen.

For example, Cl- would be the conjugate base of HCl.

Te Jung Yang 4K

I'm pretty sure it was S02 (g) + H20 (l) -> H2S04 (aq).

Te Jung Yang 4K

I don't think it matters.

Te Jung Yang 4K

Interactive potential energy is the energy required to break the interactive forces between molecules/atoms. Polarizability is the how easily electrons from an atom is distorted (displaced away from the nucleus of the atom). Interactive potential energy is always negative as it is always attractive ...

Te Jung Yang 4K

It really depends on what Sn is bonding with. In your case, Cl can only accept 1 lone pair. Putting a double bond onto the Sn is not good as the formal charge of Cl will become +1 and Sn will become -1. Usually, it comes down to formal charge.

Te Jung Yang 4K

Polarizability is the how easily the electrons in an atom can be distorted (moved away from the nucleus) with higher polarizability being electrons more easily displaced from the nucleus.
Polarizing power is how good an atom is at polarizing another atom.

Te Jung Yang 4K

I would think it is just the electronegativity. In your example, the bonds in H2S are the same, namely H - S bond. Since they are the same, they do not add to the ionic character.

Te Jung Yang 4K

S-character refers to how prevalent the s-orbital is in the hybrid orbital.
For example, sp3 is made up of 4 different atomic orbitals, one of which is the s-orbital. So the s-orbital can be seen as 25% of the hybrid orbital.
sp2 = 33%
sp = 50%

sp3>sp2>sp: increasing s-character.

Te Jung Yang 4K

Some parts of our body are more flexible in terms of pH levels. The digestive tract can handle varying levels of pH, while the inside of the skin cannot.

Te Jung Yang 4K

I don't understand how to make the I3- lewis structure. The correct lewis structure puts the formal charge -1 on the center I, while I put the formal charge -1 on the side I (via a double bond, creating a resonance structure). I did this because I figured that the formal charge would be the best fur...

Te Jung Yang 4K

If there are no questions in the HW or past midterms about those properties, I would guess not. It would be safer to make sure with Professor Lavelle himself though.

Te Jung Yang 4K

The ionic structures are the models of Cl2 on the far left and right (with - and + charges assigned to a Cl, right above your quoted sentence). Resonance describes delocalization of electrons. From these notes, the sentence seems to be implying that, since in the Cl2 molecule the electrons in the co...

Te Jung Yang 4K

You would have 3 hydrogens on each carbon. But, the carbons are not attached to each other. Instead, the Be is bonded to each C.

H3CBeCH3

Te Jung Yang 4K

In class, professor Lavelle said that orbitals are wave functions, but when he pointed to the graphical representation of the orbitals, he kept using the term probability density/distribution. I know that the probability density is the square of the wave function, but I just wanted a clarification o...

Te Jung Yang 4K

Usually you would first make a Lewis structure and see if there are lone pairs that way, but I'm assuming that you want to know to tell if there are lone pairs solely given the bond angles of a molecule. But, in this case, you would not even know the elements comprising the molecule in question as i...

Te Jung Yang 4K

Differences in strength polarizability mean that the intermolecular (molecule to molecule interactions) forces differ in strength. Intermolecular forces determine the state of matter. Gaseous state means that the intermolecular forces between molecules have been broken, usually by temperature/heat. ...

Te Jung Yang 4K

The octet rule is basically a guideline for bonding which says that elements (with atomic number below 20) should have 4 bonding pairs of electrons (8 e- total - the noble gas configuration). The first 4 elements do not follow this guideline as they do not need 8 e- to reach a noble gas configuratio...

Te Jung Yang 4K

Resonance gives the single bonds partial multiple bond properties by delocalization. Multiple bonds are stronger than single bonds, so the single bonds are strengthened.

Te Jung Yang 4K

The first equation is simply an example of a species gaining an electron, which relates to electron affinity as it is defined as the energy difference between the energy of a gaseous atom and the energy of the anion of the gaseous atom. X(g)+ e- -> X- (g) This second equation is the definition of el...

Te Jung Yang 4K

Can someone please explain to me why anions are larger than their neutral atoms? Thank you!

Te Jung Yang 4K

Hey there, there was a problem that I didn't understand the concept behind. A particle (6.644 * 10^-34 kg) and textbook (2.18 kg) travel the same speed. Which will have a smaller wavelength? I know it is the textbook, but what is the concept behind it? Is it that the larger the mass, the smaller th...

Te Jung Yang 4K

I think you have a misconception here. Firstly, the quantum numbers do not describe atoms. They describe individual electrons within an atom. So when you say atoms have quantum numbers, you are actually talking about the outermost electron, in your case 4s1. Now, to answer your question, the electro...

Te Jung Yang 4K

It means to use the energy you got from part b of the exercise.
So, on the previous exercise, you would have for one absorbtion 7.2 * 10^-20J.
For the answer to part c, you would need to multiply that energy by Avogadro's constant.

Te Jung Yang 4K

In lecture, Dr. Lavelle told us that when given a measurement of a length (ie 10m +-1m), the uncertainty would be 2m in this measurement as the range of values can be 9m - 11m. However, in the solution manual 6th edition for problem 1.45, it uses the value immediately after the +- for a calculation ...

Te Jung Yang 4K

I think you might have misread the manual. It uses the h with a dash on top (ħ), this is not Planck's Constant, which does not have the additional stroke. ħ = h / 2pi So, the solution manual is correct, if you simply used the substitution on top for the formula used in the manual, you would get the ...

Te Jung Yang 4K

It's possible. First, recall that the Balmer series corresponds to the transitions of electrons in higher quantum levels to the 2nd quantum level. Knowing this, you need to find out which transition corresponds to 410.2nm, the shortest wavelength given to us by the question. We want to use this one ...

Te Jung Yang 4K

The common aspect of each of these series is that the energized (excited electron) falls down to the same quantum level (n=X). For example, the Balmer series is the result of electron transitions from higher levels down to the energy level with principal quantum number 2. This definition causes the ...

Te Jung Yang 4K

What symbol for frequency should we use in homework assignments and exams? The letter f or the greek letter nu? Or perhaps it doesn't matter at all and the correcter will allow both? I know that we've only used nu so far, but I'm used to the letter f from high school.

Te Jung Yang 4K

If this is for tests and what not, I'm fairly certain that a formula and constants sheet will be included for every test so we won't need to rote memorize anything (at least here was one for this week's test). If this is for general use, I'd suggest just understanding the formulas rather than memori...

Te Jung Yang 4K

I just can't help but notice that the title is misspelt.

Te Jung Yang 4K

Oh hey, quick reply guys! Thanks. To catch you guys here, is the reason why it is 1 / (6.022 x 10^23) moles because of the need to cancel out the units via dimensional analysis?

Te Jung Yang 4K

I'm stuck on the first part of the question in title. How do you convert 1 H20 molecule to moles?

Te Jung Yang 4K

To find the number of water molecules in 1.00 kg of water, you would have to convert the 1.00 kg of water to moles of water (using the molecular mass of water and the relevant equation - don't forget to convert kg to g when using the equation!). Then, once you have the moles of water in 1.00 kg of w...

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