CHEMISTRY COMMUNITY

Erik Khong 2E

I just remember that the agent is opposite of what it is doing:

A species being oxidized is the reducing agent.
A species being reduced is the oxidizing agent.

Erik Khong 2E

For the set up for this problem, how did you get 16675.91565 for the first part of the equation? You're supposed to get the deltaH of fusion from the formula sheet and multiply it by the grams of ice, which you convert into moles: (50g H2O/18.02 g/mol H20) * (6.01 kJ/mol) = 16.6759kJ or 16675.91565J.

Erik Khong 2E

An ideal cooler won't allow matter to escape if it's closed. Moreover, it won't allow heat to escape because it is insulated. Thus, it is an isolated system.

Erik Khong 2E

No, bomb calorimeters are not vacuums.

Erik Khong 2E

The x10^12 is correct if you convert the units from mmol to mol, but they seemed to have made a typo in the textbook since they kept the answer in mmol.

Erik Khong 2E

I am getting the same answer. I have no idea how they managed to get x10^12 in the answer. It's most likely a typo since they kept the unit as mmol.

Erik Khong 2E

If a species has a negative order, it means that the more concentration it has, the slower the reaction is. An example given in the book is the decomposition of ozone, O3, in the upper atmosphere. Its rate law is: Rate = k[O3]^2*[O2]^-1 or k[O3]^2/[O2] This means that the reaction of decomposition i...

Erik Khong 2E

The average rate of a reaction is the change in concentration of a species over some time. The unique average rate is just said average rate divided by the stoichiometric coefficient of the species being monitored.

Erik Khong 2E

Overall order and their units of k:

1: 1/s
2: L/mol*s
3: L^2/mol^2*s

Erik Khong 2E

0.44 m/Ls represents the rate of C2H4's reaction. This would be the unique rate of reaction, and you can use it and the other reactants or products' coefficients to find their own rate of reactions. For example, for every one mole of C2H4 being reacted, 3 moles of O2 are being formed. So to find O2'...

Erik Khong 2E

The best reduction agent has the most negative or lowest potential energy. The best oxidation agent has the most positive or highest potential energy.

Erik Khong 2E

Yes, in the textbook it says that Reduction, which is the cathode, is Right to maintain clarity.

Erik Khong 2E

Yes, you need to work out both half reactions and balance them properly to get the same amount of electrons being gained and lost in both half reactions. The mutual number of electrons in both half reactions is the number for n.

Erik Khong 2E

I am sure it doesn't really matter for this class, but I personally like to keep them in the order of importance. I tend to have them in the order of the species being reduced, the species being oxidized, then H2O and/or H+.

Erik Khong 2E

There is actually a toolbox section in the textbook that you can use to easily follow along the steps and see them in action on page 563.

Erik Khong 2E

You need to balance both half reactions in order for them to have equal amount of electrons being gained and lost, so they can cancel out for the final redox reaction.

Erik Khong 2E

Yes, even if there's multiple of the same molecule, their charges add up.

Erik Khong 2E

As for part b, it is much simpler than it looks. All you need to do is make: 6 Fe(3+) --> 6 Fe(2+) From here, the charges on both sides are +18 vs +12. Just add 6 electrons to the left side, and you'll have equal charges. This means that n for this part is 6. There is no real need to focus on the ot...

Erik Khong 2E

In my opinion, it's easier to start with the Br part of the question first. It'll end up being the oxidation half of the reaction, and you can just assume that the O3 part will be the reduction half.

Erik Khong 2E

I just remember the difference by noting that the agent is the opposite of what's happening to them

e.g. The reducing agent is getting oxidized.

Erik Khong 2E

You may need to make the exponent Avogadro's number when there is 1 mole of particles involved--changing the exponent to n * Avogadro's number if there are n moles involved. However, I don't think it will be necessary on the midterm. (I hope)

Erik Khong 2E

I think we might be focusing on closed systems more because we should be focusing on work/heat and not just matter.

Erik Khong 2E

The bond enthalpies are positive when the bonds are being broken because they require energy. However, they are negative when the bonds are being formed again because they release energy.

Erik Khong 2E

The formula requires the delta V because we are trying to calculate how much the system changed overall.

Erik Khong 2E

I think the only real way to tell is if it's a concealed system or not. Then if it's thermally-insulated or the like. It's hard to determine it with any "specific way" or any tricks.

Erik Khong 2E

In an adiabatic process, energy is transferred to its surroundings only as work while an isolated system cannot transfer energy at all.

Erik Khong 2E

The entropy of an isolated system must remain constant or increase because of the number of possible states/configurations it has can only increase or remain the same, never decrease. This is because the system cannot lose energy or matter, so no molecules or energy are being lost; thus, no possible...

Erik Khong 2E

If you want specific examples, there are some in the textbook:

Open: an open flash
Closed: a flask with a cork
Isolated: a plugged flask in a thermally-insulated material

Erik Khong 2E

While a closed system can exchange heat with its surroundings, an isolated system cannot exchange energy. Of course, both cannot exchange matter either.

Erik Khong 2E

Yes. I think a very easy example to think of would be the universe itself. There is no exchange of heat with any surroundings because there are no surroundings.

Erik Khong 2E

No. No work can be done with an isolated system. Also, its internal energy is constant, which is the First Law of Thermodynamics.

Erik Khong 2E

The strength of an acid increases across the periodic table with electronegativity but also downwards with the size of elements.

Erik Khong 2E

It also relates to the fact that the ions of elements on the right and lower side of the periodic table grow progressively larger and result in longer, weaker bonds with H. Hence, HF is a weaker acid than HCl and HI. The strength of acidity increases across with electronegativity but downwards with ...

Erik Khong 2E

I am certain we will be drawing the arrows pointing towards the negative δ. A good rule of thumb is to remember that Lavelle taught us that beginning side of the arrow can be drawn with a "+" symbol to represents that it is δ+.

Erik Khong 2E

Keep in mind that the arrows for dipole moments should be labeled accordingly. If the dipole arrow is pointing towards one atom, that atom should have δ-. Meanwhile the base of the arrow, which is labeled for the bonding atom, should have δ+.

Erik Khong 2E

The superscript states how many orbitals of that subshell is hybridized.

Erik Khong 2E

Pretty sure you accidentally wrote the wrong number. It's supposed to b 2sp^3.

Erik Khong 2E

There can't be two sigma bonds because one sigma bond is already very strong and causes too much repulsion for another sigma bond, which is along a internuclear axis, to be possible. Two atoms cannot be arranged in a way that two sigma bonds are possible.

Erik Khong 2E

Lone pairs have a stronger repulsion than bonding pairs because bonding pairs are farther away from the central atom since it needs to be connected to the sharing atom. Meanwhile, lone pairs are closer to the nucleus as it doesn't need to be shared with any other atoms, so they will give off more re...

Erik Khong 2E

I don't think Lavelle expects us to know how to calculate or remember the bond angles, but try to at least remember how to work out every AXE formation. Also keep in mind that lone pairs, E, will repel electron densities more, which will make their bond angles lesser than usual since they are gettin...

Erik Khong 2E

Hybridization involves the promotion of electrons and making multiple orbitals from different subshells "equal" in energy (such as 2s and 2p), so that electrons can follow the Hund's rule in their newly-created hybridized-subshell to form more bonds. Basically, hybridization involves promo...

Erik Khong 2E

Yes because the first bond is always a sigma bond and any other subsequent bonds are pi bonds.

Erik Khong 2E

So does that mean that if there is a sigma bond, there will always be a pi bond as well? No this is not the case. In fact, it's backwards. If there is a pi bond, there is always a sigma bond. This is because sigma bonds are ALWAYS the first bond to be made between two atoms. Any others will result ...

Erik Khong 2E

The first bond between two atoms IS ALWAYS a sigma bond. Any other extra bonds are pi bonds.

Erik Khong 2E

A bond is nonpolar if the total dipole moment in a bond is zero. For example, CO2 is a nonpolar molecule. A polar molecule is one that has a nonzero dipole moment. For example, H2O. Both hydrogens have equal dipole moments, but they aren't exactly opposite, so the molecule still has a nonzero dipole...

Erik Khong 2E

Why is it that carbon has a higher affinity than nitrogen when nitrogen is at the right of the carbon? I thought that as you go more right, there is a higher electron affinity. What is the exception with carbon that makes it have a higher electron affinity? Carbon has a higher electronic affinity t...

Erik Khong 2E

Ar has lower electron affinity because it's a noble gas with 8 full valence electrons. It would require energy to add another electron since its full and repulsion will play a factor.

Erik Khong 2E

I was a bit confused at first myself, but I think I understand why now after some research. It's due to the fact that carbon has an empty orbital for an electron to enter in the p-subshell, which means there will be no repulsion when trying to add an electron to its last orbital. Meanwhile, nitrogen...

Erik Khong 2E

So one meter fits 1,650,763.73 wavelengths. This means that it's a very high frequency wave (there's a LOT of squiggles in one meter). To find the wavelength of krypton-86 radiation, you just need to simply divide 1 meter by 1,650,763.73. This equals to 6.058 x 10^-7 m (simplified to 605.8 nm). So o...

Erik Khong 2E

Combustion always uses O2 from the atmosphere, so with butane, the equation would be something of the sort:

C4H10(g) + O2(g) --(delta for "heat")--> CO2(g) + H2O(l)

This equation is unbalanced, so don't forget to balance with stoichiometric coefficients!

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