CHEMISTRY COMMUNITY

LedaKnowles2E

Nope, E naught doesn't change

LedaKnowles2E

A is the frequency factor. It takes into account what percentage of collisions between molecules will actually make the reaction progress (the molecules have to be oriented correctly, etc)

LedaKnowles2E

If the reaction is endothermic and the temperature is increased, the reaction will be pushed towards the products and K will increase.
If the reaction is exothermic and the temperature is increased, the reaction will be pushed towards the reactants and K will decrease.

LedaKnowles2E

In the slides it says a straight line plot of ln[R] vs time means the reaction is 1st-order.

LedaKnowles2E

In acidic solutions, balance half-reactions by adding H2O and H+; in basic solutions, balance by adding H2O and OH-.

LedaKnowles2E

You should probably mix in some kinetics in there.

LedaKnowles2E

It's usually a lower-case n, though.

LedaKnowles2E

A temperature change pushes the reaction to either the left or right depending on whether heat is a reactant or product (depending on whether the rxn is exo or endothermic). This gives the reaction a new equilibrium point, so k changes.

LedaKnowles2E

Pt is sometimes added when one half of the reaction only involves aqueous solutions and a solid electrode is needed.

LedaKnowles2E

Without a salt bridge, charge builds up on either side of the cell and stops transferring. The salt bridge puts ions into solution, keeping them neutral so that charge can keep flowing.

LedaKnowles2E

A half reaction is half of a redox reaction; either the part of the reaction that oxidizes a reactant or the half that reduces a reactant. We separate redox reactions into half reactions because they're easier to balance that way, and then once they're balanced we can add them together to see the wh...

LedaKnowles2E

The oxidation number is the charge on an atom or molecule. O2-, for example.

LedaKnowles2E

When Gibbs free energy is negative the process is spontaneous.

LedaKnowles2E

I'd think the human body must be an open system because we give off heat, and we intake and output substances (O2, CO2, nutrients, waste) all the time.

LedaKnowles2E

A microstate is a specific arrangement of molecules. Degeneracy is the number of possible microstates/arrangements of a group of molecules, and entropy is calculated using degeneracy.

LedaKnowles2E

Enthalpy is the heat transferred in/out of the system, while entropy is the disorder of the system (how many possible positions, vibrations, etc).

LedaKnowles2E

Residual entropy or positional entropy is the entropy that a sample has when you disregard thermal entropy. This residual/positional entropy results from the different positions the atoms can be found in.

LedaKnowles2E

A state property depends on the current state of the system, as opposed to the path it took to get to that state.

LedaKnowles2E

From what I understand from lecture, a microstate is a specific arrangement of molecules, a specific set of positions for each molecule in a sample. The more possible microstates or arrangements there are for a sample, the more entropy that sample has. (If anyone wants to correct/add to that, pls do)

LedaKnowles2E

What's delta U?

LedaKnowles2E

You can use the 5% approximation when K<10^-3 (when the reaction strongly favors the reactants). This means that no quadratic equation solving will be necessary. But if this is not the case and the reaction doesn't strongly favor the reactants, you will end up having to solve a quadratic.

LedaKnowles2E

Initial concentration/pressure, Change in concentration/pressure, Equilibrium concentration/pressure

LedaKnowles2E

The enthalpy of a substance in its gaseous form > enthalpy in liquid form > enthalpy in solid form.
This is because heat is required to change a substance from solid to liquid, and liquid to gas.

LedaKnowles2E

The change in enthalpy of liquid water to water vapor is positive because the phase change from liquid to vapor requires heat to be added to the water. Since heat was added to the water for it to become vapor, the vapor will have higher enthalpy than the water. The change in enthalpy is calculated a...

LedaKnowles2E

If the Kb value is lower than 10^-3 then it's considered a weak base, since the reaction favors the reactants. (This also applies to Ka with weak acids)

LedaKnowles2E

When you double the pressure of the gases in a reaction by halving the volume, it increases the concentration of the gases, which pushes the reaction left or right depending on the moles of gas on either side. However, when you double the pressure by adding an inert gas, it doesn't change the concen...

LedaKnowles2E

Ka*Kb=Kw=10^-14
pKa+pKb=14
and
[OH-][H3O+]=Kw=10^-14

LedaKnowles2E

X is negligible when x is less than 5% of the initial concentration, or when K is less than 10^-3.

LedaKnowles2E

I have the same question, all I got from lecture is that it's unit-less and that the concentrations we use are approximations. Does anyone understand?

LedaKnowles2E

Since R is in Kelvin, use Kelvin. You almost always use Kelvin in chemistry.

LedaKnowles2E

If Q is less than K, it means that there are more reactants and less products than at equilibrium, which means more of the reactants have to react and become products in order to reach equilibrium.

LedaKnowles2E

Wouldn't that mean that it's just bidentate, since it always has the potential to form two coordinate bonds?

LedaKnowles2E

Are there any polydentate ligands we need to know for naming compounds other than edta, en, dien, and oxolato?

Also, am I right in saying that edta is hexadentate, oxolato and en are bidentate, and dien is tridentate?

Thanks

LedaKnowles2E

What is the charge for ethylenediaminetetraacetato? The textbook table of ligands just says it's an anion.

Also, is its formula C10H16N2O8?

Thanks

LedaKnowles2E

What are axial and equatorial atoms? I saw a few posts that mentioned them but don't remember them being mentioned in lecture...?

LedaKnowles2E

Expanded octets are possible for elements in period 3 and greater, because those elements have d-orbitals that extra electrons can occupy.

LedaKnowles2E

Transition metals tend to have multiple oxidation states, because the energy difference between the oxidation states isn't that large. Since they can have multiple oxidation states, and gain and lose elections easily, they're good for electron transfers.

LedaKnowles2E

A seesaw structure happens whenever an atom is surrounded by four atoms and one lone electron pair, or AX4E1.

LedaKnowles2E

If a molecule has a tetrahedral electron pair arrangement with one lone pair, the atom arrangement will be trigonal pyramidal because the lone pair takes up as much (and more) space than an atom in its place would. It repels the atoms into a trigonal pyramidal shape.

LedaKnowles2E

As far as I know they mean the same thing. If anyone knows better please correct me

LedaKnowles2E

Lewis structures are the drawings we've been doing of where the electrons and bonds are in molecules. VSEPR formulas indicate the number of atoms and lone pairs of electrons around the central atom in a molecule, written as AXnEm, where A is the central atom, X are the surrounding atoms, n is the nu...

LedaKnowles2E

I believe bent and angular are different names for the same shape. The VSEPR model predicting things qualitatively but not quantitatively means that the VSEPR model can't predict the exact bond angles between atoms; when the atoms are different or there are lone pairs, it can only predict the relati...

LedaKnowles2E

Dipole moments happen when one atom in a molecule is more polar than another, like H2O. Electrons are pulled toward O, the more electronegative atom. This gives the end of the molecule with O a slightly negative charge compared to the H ends. Dipole-dipole attractions: this is when 2 polar molecules...

LedaKnowles2E

Dipole-induced dipole: this is when you have a polar molecule and a neutral molecule. When they get close enough together, the negative end of the polar molecule repels the electrons in the neutral molecule, causing the neutral molecule to have a positive end and a negative end, called an induced di...

LedaKnowles2E

Dipole-dipole attractions: this is when 2 polar molecules (like H2O) are attracted to each other because each molecule has a positive end and a negative end, so the positive end of one molecule is attracted to the negative end of the other. Dipole-induced dipole: this is when you have a polar molecu...

LedaKnowles2E

Electronegativity is calculated using electron affinity and ionization energy; high electron affinity and ionization energy mean high electronegativity. Electron affinity and ionization energy decrease down a group because as you go down a group, the atoms get larger, and so the electrons are farthe...

LedaKnowles2E

Br2 is a liquid because Br is a larger atom than F and Cl. The larger the atom, the stronger the dispersion force between them. So since F2 and Cl2 are smaller and have less attraction between them, they're held less closely together and are gases at room temperature. Br2 is a liquid because the Br2...

LedaKnowles2E

Hi, I'm pretty sure Prof. Lavelle said that induced dipole attraction is caused when by chance, the electrons of an atom/molecule are condensed more on one side of the atom, making one side negative and the other positive, which attracts them to other atoms/molecules...what I'm confused about is tha...

LedaKnowles2E

In class Prof. Lavelle said that the interaction potential energy of induced dipole--induced dipole attraction was always negative, meaning that it was always attractive. Could someone explain why it being always negative means that it's attractive?

LedaKnowles2E

Hi! I'll try to explain it as far as I understand it... All the lines in the Balmer series result from electrons transitioning from various energy levels down to the n=2 energy level. As the electron drops from higher energy levels, more energy is released from the transition. The more energy, the h...

LedaKnowles2E

Here's my work. What I did makes sense to me but I didn't know where to look for the solution so I don't know for sure that it's right. Hope it helps :)

LedaKnowles2E

As far as I understand, electron density is the probability of finding an electron in a given spot. For example, the 1s orbital has uniform electron density, so there's an equal probability of finding the electron anywhere in the orbital.

LedaKnowles2E

I think what you mean is Dr. Lavelle wanted us to use En= -hR/(n^2) instead of deltaE= hR(1/n1^2 - 1/n2^2). The two equations are closely related; the second one is easily derived from the 1st. Dr. Lavelle used the first because he said it better conceptualized what was happening. My TA said that th...

LedaKnowles2E

It's enough to know 400-700nm :)

LedaKnowles2E

Here's my work, hope it helps

LedaKnowles2E

Why does hamburger yield lower energy than steak?

...because it's in the ground state.

LedaKnowles2E

When we're told that a compound is made of some percentages of elements, like C, O, H, and N, and then we calculate the empirical and molecular formulas, how do we know which order to put the elements in the formula? Like if the ratios are 6 C to 4 O to 1 H to 2 N, how do we know if it's C6O4HN2 or ...

LedaKnowles2E

The Lyman series are the lines that occur from electrons dropping down to the n=1 energy level. The Balmer series is when electrons drop to n=2.

LedaKnowles2E

I had the same question...in high school we used f for frequency and v (nu) for other stuff. But I suppose v (nu) for frequency is the best way to go now to avoid confusion.

LedaKnowles2E

Yes, if I understand what you're asking.
For example, the molar mass of plain oxygen, O, is 16 g/mol.
But the molar mass of oxygen gas, O2, is 2x16= 32 g/mol.
Hope that helps.

LedaKnowles2E

Hi! I did this problem for hw too. I first found what the molarity of the solution would be once it had been diluted to a total volume of 4L (0.050M), and then figured out how many moles of NH4NO3 would be in 100mL of that diluted solution, which ends up being 0.0050 mol. Since there's 2 N atoms in ...

LedaKnowles2E

Hi! The solution manual's solution didn't make much sense to me either. I did the problem a little differently, by figuring out what the final volume of the diluted solution would be after 90 doublings of the volume, and showing that in 10mL of the diluted solution there would be less than a single ...

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