CHEMISTRY COMMUNITY

Althea Zhao 1B

Do we round the exponent a to the nearest whole number?

Althea Zhao 1B

The document that Dr. Lavelle shared with us says that the final exam questions will come from the homework. Does this mean all questions will be taken from the homework, or will the format be more like the midterm?

Althea Zhao 1B

The starting temperature is T1 and it is associated with K1; the final temperature is T2 and it is associated with K2.

Althea Zhao 1B

I think it will be given but not labeled, so we need to be able to ID it.

Althea Zhao 1B

The equation for E(cell) allows you to use the given reduction potentials for each half-reaction: making E(anode) a negative value accounts for the oxidation sign change.

Althea Zhao 1B

Since E(cell) is equal to E(red)-E(ox) and must be positive for a spontaneous reaction, E(red) should be greater than E(ox). So, the half reaction with the greater reduction potential is reduced.

Althea Zhao 1B

I'm confused as well. Why isn't the answer a positive value?

Althea Zhao 1B

Can someone explain why the oxidation reaction is Au(s) to Au3+(aq) instead of Au+(aq) to Au3+(aq)? I thought that it would make sense to have reactant and product on opposite sides of the reaction...

Althea Zhao 1B

Oxygen should have a 2- charge in ionic aqueous form, as well as in molecules such as H2O. It should have a charge of zero in O2 gas form, where it is most stable.

Althea Zhao 1B

For 6L.7, why is AgBr(s) only used in the reduction half reaction and not in both?

Althea Zhao 1B

How do you know when to use an inert electrode in a cell diagram?

Althea Zhao 1B

For the reaction of H2(g) with Cl2(g) as shown in the diagram, how do you know which half reaction to reverse?

Althea Zhao 1B

How do you determine the value of n for -nFEcell? Is n the number of moles being reduced?

Althea Zhao 1B

Reduction is gain of electrons, so look for the atom whose charge is reduced.

Althea Zhao 1B

I think Dr. Lavelle said it will be on the end of thermo (5G) and electrochem.

Althea Zhao 1B

Oxidation is loss of electrons, so the atom whose charge increases is the one that is oxidized.

Althea Zhao 1B

When is the oxidation number of hydrogen -1? For this course, should we just assume that it is +1?

Althea Zhao 1B

Which elements have only one ionization state? For example, oxygen is always O2-.

Althea Zhao 1B

IN-tensive properties are IN-dependent of quantity.

Althea Zhao 1B

How is the formula for enthalpy with a change in temperature along a heating curve different from the formula for enthalpy at temperature plateaus?

Althea Zhao 1B

For the midterm, do we need to know the values of Cp,m and Cv,m for monatomic gases only, or for linear and nonlinear molecules as well?

Althea Zhao 1B

I'm having a hard time understanding degeneracy and the Boltzmann equation. Can anyone recommend a good Youtube video or link a website that explains it well?

Althea Zhao 1B

When you're under Pressure or Depressed, you'll want to watch TV and get HUGS.

Althea Zhao 1B

I think it would be good to know. An isolated system does not allow for the transfer of heat or matter, a closed system allows for the transfer of heat and an open system allows for both.

Althea Zhao 1B

Not just - it's used primarily to calculate enthalpy when a system's heat changes.

Althea Zhao 1B

Delta H times mass.

Althea Zhao 1B

The universe favors disorder. The textbook has a good example: it's a lot easier for heat to leave a block of metal than enter it because in order for it to enter the block of metal, it has to be concentrated and directional.

Althea Zhao 1B

Standard entropy is found when a substance is in its pure state at 1 bar.

Althea Zhao 1B

In 4F, the textbook says that "the entropy change for or of 1 mol of a substance is reported differently from the entropy change per mole: the units of the former are joules per kelvin (J/K), whereas those of the latter are joules per kelvin per mole (J/K*mol)". Can someone explain why thi...

Althea Zhao 1B

Enthalpy of formation is the enthalpy of change between products and reactants; enthalpy of reaction is the difference.

Althea Zhao 1B

At a constant pressure, enthalpy is equal to change in heat.

Althea Zhao 1B

By definition, at equilibrium forward and reverse reactions occur at the same rates. So, any reaction that is at equilibrium must be reversible.

Althea Zhao 1B

Hess's law states that the total enthalpy change for a reaction is the sum of the enthalpy changes for each step of the reaction. So, you just balance the equations given and add their delta H's.

Althea Zhao 1B

I had a hard time matching the data given to a heating curve because b) and c) look pretty similar to me. Does anyone have tips for interpreting these curves? Will we have problems like this on the test?

Althea Zhao 1B

bond enthalpy is the least accurate, but it really depends on what information its given to you. I would definitely know how to use all 3.

Althea Zhao 1B

SOME solids do have a higher heat capacity than water and the same goes for gases. If you mean in terms of the solid and gaseous forms of water, it is because liquid water is polar and has the ability to expand a little when heated.

Althea Zhao 1B

You need to calculate a reaction's enthalpy when all reactants and products are in the gas phase. If there are solids and/or liquids present, you need to add in the enthalpy it takes to convert them to gases.

Althea Zhao 1B

Just to confirm: do we use 2 decimal places for pH/pOH and follow sig fig rules for constants and concentrations?

Althea Zhao 1B

How can we find the pKa/relative strength for +NH3OH and (CH3)2NH2+, since they aren't listed in the tables we're asked to refer to?

Althea Zhao 1B

If you change partial pressure or concentration, the reaction will shift to maintain the original equilibrium constant. A change in temperature changes reaction rates.

Althea Zhao 1B

By Le Chatelier's principle, a change in partial pressure on one side of the equilibrium equation will cause the other side to adjust to maintain equilibrium.

Althea Zhao 1B

Since the reaction begins with only reactants and moves towards equilibrium as products form, the amount of reactant decreases and the amount of product increases. So, you use +x for products and -x for reactants

Althea Zhao 1B

For part b, why is the equation Na2O+H2O -> 2NaOH instead of Na2O +2H2O -> H3O + OH + 2 Na?

Althea Zhao 1B

When we calculate the pH or pOH for strong acids and bases, do we need to raise [H3O+] or [OH-] to their stoichiometric coefficients? For example, would the pOH of Ba(OH)2 be -log[OH]^2?

Althea Zhao 1B

Solvents aren't really part of the reaction, and their concentrations don't change much from one side of the reaction to the other. So, the product concentration will cancel out that of the reactants.

Althea Zhao 1B

Liquids don't change, so they cancel out.

Althea Zhao 1B

Kc is used for aqueous solutions and Kp is for gases.

Althea Zhao 1B

n/V is the same as (nRT)/V!

Althea Zhao 1B

I saw dates for the midterm and final on CCLE, but does anyone know the dates for Test 1 and Test 2?

Althea Zhao 1B

Why do pi bonds only have p hybridization and not spx?

Althea Zhao 1B

In the textbook answer key, the proton transfer equations for H2SO4 and H2PO4 show only one H+ (not both) being transferred. Why is this? Wouldn't both protons be transferred? Are both answers correct?

Althea Zhao 1B

I think we're supposed to know the ones we reviewed in class.

Althea Zhao 1B

Should we have solubility rules memorized for the final? Will we see any problems with precipitates?

Althea Zhao 1B

I understand what differentiates the Bronsted definition from the Lewis definition, but how will we know which definition to apply? In other words, what kind of situation would you use each definition in?

Althea Zhao 1B

The lone pairs on one atom can't get close enough to bind in two locations; only one pair can align with the binding site.

Althea Zhao 1B

I think you're supposed to do both and turn in two separate HWs.

Althea Zhao 1B

The major contributor is the most stable, where the central atom's charge is close to 0.

Althea Zhao 1B

You usually want 0 charge on the central atom.

Althea Zhao 1B

When strong acids and strong bases deprotonate, they separate into aqueous ions; for example, HCl would become H+ (aq) + Cl- (aq). Weak acids and bases, on the other hand, do not separate fully.

Althea Zhao 1B

Bronsted acids are proton donors and Bronsted bases are proton acceptors. Since H+ represents a proton, you're right that it helps to look for an H at the beginning of the compound when you're trying to identify an acid. Likewise, an OH- attached to the end of a compound indicates that the compound ...

Althea Zhao 1B

How can you tell whether a ligand is polydentate?

Althea Zhao 1B

When naming coordination compounds, how can you tell whether you should use the English name for a transition metal (like Iron (II)) or the Latin name (like ferrate (II))?

Althea Zhao 1B

Oh, that makes sense! I didn't look closely at the structures and missed the fact that in diethyl ether, O is bonded to C and not H. Thank you :)

Althea Zhao 1B

Why is H bonding possible for C4H9OH (butanol) but not C2H5OC2H5 (diethyl ether)?

Althea Zhao 1B

How do you determine whether a molecule exhibits dipole-dipole or dipole- induced dipole interactions? I had believed that H2SeO4 would have dipole-induced dipole interactions, because H2SO4 is polar and O4 is non polar.

Althea Zhao 1B

I don't think H bonds have a direct influence on ionic bonds. They are separate, but what makes them distinct is how strong they are.

Althea Zhao 1B

Lone pairs take up more space - they push away other atoms.

Althea Zhao 1B

As you go down a group, the atoms grow larger. This makes them more polarizable, which in turn makes them more prone to Van Der Waals attractive forces. When atoms are pulled together by these forces, they become liquids.

Althea Zhao 1B

Ion dipole describes the permanent dipole moment between a cation and anion; a dipole-dipole interaction is a Van der Waals force that exists in non-ionic molecules, where one atom is permanently negative (distorting e-) and the other Is permanently positive (being distorted).

Althea Zhao 1B

The shape of the molecule plays a role in determining its polarity. Since the seesaw shape is not symmetrical, the S-F bond energies do not cancel and there is polarity.

Althea Zhao 1B

Yes! Stronger bonds are harder to disturb, so the atoms stay close together - aka in solid state.

Althea Zhao 1B

I've heard that it's possible to take both at once and do well, but it can be helpful to take 14B first. 14B lays the groundwork for 14BL.

Althea Zhao 1B

Yes! No bond is purely one or the other.

Althea Zhao 1B

Pretty much! The bond lengths are the average of bond lengths across all of the structures, so each bond length is the same.

Althea Zhao 1B

For broad understanding, I like Crash Course!

Althea Zhao 1B

I think there is a quicker way, but we haven't learned it yet.

Althea Zhao 1B

Nope! Some molecules have a symmetrical e- distribution, so no resonance.

Althea Zhao 1B

I believe that past the 4s2 elements, you start filling the d orbital first. For the f orbital, you start filling it after 6s2 (Ba).

Althea Zhao 1B

Ionization energy is the energy required for an atom to lose an electron; electron affinity is the energy released when an atom gains an electron.

Althea Zhao 1B

Most noble gases have no electronegativity, with the exception of Kr and Xe. These elements are heavier, so their outermost electrons have more shielding from the nuclear pull and can be ionized by highly electronegative elements.

Althea Zhao 1B

I'd expect it to cover at least the first two weeks of chemical bonds, since we're being given time to study the material.

Althea Zhao 1B

Since you adjust the Lewis structures of ions to reflect the number of additional electrons that they have, why do you still need to put brackets around them and write the charge? Isn't this redundant?

Althea Zhao 1B

For Ti 3+, why is the electron configuration [Xe] 4f14 5d10 instead of [Xe] 4f14 5d8 6s2?

Althea Zhao 1B

For Mn, which has electron configuration {Ar} 3d5 4s2, the textbook says there are 7 valence electrons. Is this because you need 8 electrons to close an octet, so all of the d-subshell electrons are still unstable in this configuration? If so, how do you know when there is a stable d-subshell? Is it...

Althea Zhao 1B

Do we need to understand how the Rydberg equation for other 1-electron ions, -[(Z^2)hR]/n^2 is derived, or can we just apply it?

Althea Zhao 1B

Spins are opposite because electrons repel each other, and you always start up.

Althea Zhao 1B

If it's assigned, I think he'll go over it this week.

Althea Zhao 1B

I think it has to go to 2px first.

Althea Zhao 1B

It's from Quantum World!

Althea Zhao 1B

Speed will remain constant- only wavelength and frequency are inversely proportional.

Althea Zhao 1B

I think they're just a resource that you can use whenever you want to review his lectures! No deadline :)

Althea Zhao 1B

Lines within a series share a principal quantum number, n.

Althea Zhao 1B

Electrons absorb and emit energy in photons, which are basically discrete packets of light. I think of photons like tide pods, and electrons like laundry: I can do a smaller load of laundry with one tide pod, or a larger load of laundry with two. One tide pod is sufficient for a lower range of laund...

Althea Zhao 1B

I found Dr. Lavelle's watering can analogy helpful for understanding this concept. In large quantities, water moves as a wave (continuously). However, we can also think of water jumping out of the (now shrunken to microscopic proportions) mouth of the water can in single molecules, or particles.

Althea Zhao 1B

I think that the term "circular standing wave" just refers to the oscillatory behavior of electromagnetic radiation. It's a standing wave because the wave's amplitude doesn't move, and it's circular because it's continuous. Do you remember Dr. Lavelle's diagram for this concept, where the ...

Althea Zhao 1B

For problem M11, which gives the following information: A reaction vessel contains 5.77 g of white phosphorus and 5.77 g of oxygen. The first reaction to take place is the formation of phosphorus(III) oxide, P4O6: P4(s) + 3 O2(g) --> P4O6(s). If enough oxygen is present, the oxygen can react further...

Althea Zhao 1B

Crash Course is fun but less specific than Khan Academy. A lot of people also like the OChem tutor!

Althea Zhao 1B

For the problem you're referencing, Dr. Lavelle said either unit is fine. I think you don't need to convert unless explicitly asked.

Althea Zhao 1B

You probably read the second half of E16, which asks for chloride. E15 asks: "The molar mass of the metal hydroxide M(OH)2 is 74.10 g/mol. What is the molar mass of the sulfide of this metal?"

Althea Zhao 1B

Not all polyatomic ions dissolve. If the ion is insoluble, you don't distribute the stoichiometric coefficient.

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