CHEMISTRY COMMUNITY

Sierra Cheslick 2B

No, you would use the equation k = Ae^(-Ea/RT) to find the new activation energy.

Sierra Cheslick 2B

Why does deltaG depend on pressure and the equilibrium constant?

Sierra Cheslick 2B

How do we use equilibrium constants to predict solubility?

Sierra Cheslick 2B

Zeroth order is linear with a negative slope when time is graphed versus concentration of A. First order is linear with a negative slope when time is graphed versus ln[A]. Second order is linear with a positive slope when time is graphed versus 1/[A].

Sierra Cheslick 2B

The speed of the reaction depends on how much reactant is left, so it is not directly proportional to a quarter of the half-life.

Sierra Cheslick 2B

I think he just assumed a=1 to keep the derivation simple, rather than having to deal with another constant in the equation.

Sierra Cheslick 2B

Yes, T is always in kelvin in this equation.

Sierra Cheslick 2B

Oxidation states are usually determined by which column an element is in in the periodic table, if it is not a transition metal. For example, elements in the first column usually have an oxidation state of +1, elements in column 2 usually have an oxidation state of +2, elements in column 13 usually ...

Sierra Cheslick 2B

They are the same thing, just with two different names.

Sierra Cheslick 2B

When calculating cell potentials using standard cell potentials, why don't you switch the sign of the anode potential since the equation is reversed compared to that given in the list of standard cell potentials?

Sierra Cheslick 2B

I think it means that one of the products/reactants in the redox reaction is hydrogen gas.

Sierra Cheslick 2B

After balancing a redox reaction, do we include H2O, H+, and OH- in the final equation if they cancel out in the products and reactants? For example, if a final balanced redox equation read: 6H2O + 3O3 +6OH- + Br- + 6e- yields 3O2 + 6OH- + BrO3- + 6H2O + 6e- do we include the H2O and OH- in the fina...

Sierra Cheslick 2B

Why does having a negative deltaG make a compound unstable with respect to decomposition?

Sierra Cheslick 2B

What does the subscript "r" mean when used in relation to either deltaH or deltaS? This is used in the solutions manual for 9.67 in the 6th edition.

Sierra Cheslick 2B

The question reads: Which of the following compounds become less stable with respect to the elements as the temperature is raised: (a) PCl5(g); (b) HCN(g); (c) NO(g); (d) SO2(g)? In the solutions manual, it shows that for each compound, you have to use the deltaS for each of the elements in the comp...

Sierra Cheslick 2B

For this question, you have to first calculate the delta S as the water is heated from 85 degrees to 100 degrees using the formula delta S = Cp*ln(T2/T1), then calculate the delta S during the phase change (given in the problem as 109J/K*mol), and then calculate the delta S as the vapor cools back d...

Sierra Cheslick 2B

Since this calculation only involves a change in temperature, and celsius and kelvin have the same scale, 80K is equivalent to 80 degrees celsius in the context of this problem.

Sierra Cheslick 2B

Reversible expansion is slower, and therefore more work is done since less energy is lost as heat.

Sierra Cheslick 2B

In order to see which bonds are being broken, you can draw out the structures and see which ones would need to break in order to form the new structure. However, I think you can also just subtract the energy needed to break all the bonds from the energy released from forming all the bonds, which mig...

Sierra Cheslick 2B

I think you would also want to know that a bomb calorimeter has a constant volume.

Sierra Cheslick 2B

It would depend on the substance you were heating, and you would have to look up the amount of heat needed for each phase change (for the horizontal lines) and the temperature at which each phase change occurs (to determine the steepness of the lines).

Sierra Cheslick 2B

He said that when steam comes into contact with skin, it condenses since the skin is at a lower temperature. The process of condensation releases energy (as heat) which causes the burn. Since the water is going through a phase change at this point, the temperature of the steam is not getting lower e...

Sierra Cheslick 2B

Temperature is the measure of the average kinetic energy of a substance, whereas heat is thermal energy transferred between substances of different temperatures. I believe that a transfer of heat would always lead to an increase in temperature. Since both energy (specifically thermal energy) and hea...

Sierra Cheslick 2B

Yes, this applies to bases as well. A Kb of 10^3 or greater would be considered a strong base and a Kb of 10^-3 would be considered a weak base.

Sierra Cheslick 2B

You may have forgot to convert from mmol to mol, since m=10^3

Sierra Cheslick 2B

This is a salt, and it dissociates in water. Since Cl- is the conjugate base of a strong base, it is very weak and therefore considered to not affect pH and can be left out of the equation. Al3+, however, can pull water molecules towards it and form coordinate covalent bonds, since it is a small and...

Sierra Cheslick 2B

Polyprotic acids have more than one hydrogen that can be removed. Usually, these hydrogens are written together in the formula and are not bonded to a carbon. For example, H2SO4 is a polyprotic acid while CH3OOH is not. Although CH3OOH has multiple hydrogens, three of them are bonded to C, and there...

Sierra Cheslick 2B

No, more ammonia would not be formed because the equilibrium constant at the higher temperature (700K) is smaller so the equilibrium would sit to the left, favoring the formation of reactants

Sierra Cheslick 2B

Kp is K specifically in terms of partial pressures. When referring to a reaction that includes exclusively gases, K is inferred to mean Kp. Kc is K in terms of molarity, and can also be used for gases, but if a question is referring to or asking for Kc, it will specify that this is the K it is askin...

Sierra Cheslick 2B

K(p) is the equilibrium constant in terms of partial pressure. This constant is used when all products and reactants in a reaction are in the gas phase. I'm not sure what K(eq) but I'm guessing you might be referring just to K, which is used for reactions with products and reactants that aren't all ...

Sierra Cheslick 2B

The pH formula is -log[H+]. I believe we would need to know how to derive it.

Sierra Cheslick 2B

A conjugate base is just the acid without one of the hydrogens. For example, the conjugate base to H2SO4 is HSO4-.
A conjugate acid just the base with an additional hydrogen. For example, the conjugate acid to CN- is HCN.

Sierra Cheslick 2B

I think my TA said that she would be returning our tests this week, so I'm assuming it would be the same for other sections as well.

Sierra Cheslick 2B

It it uncommon for the concentration of H3O+ ions to exceed 1M or be less than 10^-14M in solution.

Sierra Cheslick 2B

The structure given in the answer key is favorable because of formal charge.

Sierra Cheslick 2B

Since the electrons are overlapped side by side in pi bonds, if you rotated one of the atoms, the bond would be forced to break.

Sierra Cheslick 2B

I think hybridization occurs whenever there is covalent bonding.

Sierra Cheslick 2B

If the molecule is symmetrical around the central atom (for example CCl4) then the polar qualities of the bonds cancel each other out, as all the partial charges are "pulling" in different directions. However, this is only true if the atoms surrounding the central atom are all the same and...

Sierra Cheslick 2B

Yes, sigma bonds allow bound atoms to rotate (as they are only bonded with a single bond) whereas pi bonds do not allow bound atoms to rotate (as they are bonded with a double bond). Since pi bonds don't allow atoms to rotate, these bonds are more rigid.

Sierra Cheslick 2B

Yes, single, double, and triple bonds are all treated the same. But you do treat lone pairs differently.

Sierra Cheslick 2B

Both H2O and H2S have covalent bonds between their hydrogen atoms and their oxygen or sulfur atoms, but in H2O there are also hydrogen bonds between the hydrogen atoms and oxygen atoms of different molecules. These hydrogen bonds between molecules, in addition to the covalent bonds within each molec...

Sierra Cheslick 2B

Yes, I think that's correct.

Sierra Cheslick 2B

I think that dissociation energy values are usually given to you in a problem, and then used to solve for other values. In other words, I don't think we'll have to actually calculate them since I think they're experimentally derived.

Sierra Cheslick 2B

Why is the molecular shape of I3- described as linear with bond angles of 180 degrees when the central iodine atom has 3 lone pairs in addition to the two bonds? Why isn't it trigonal bipyramidal?

Sierra Cheslick 2B

A Hz is equal to one cycle per second (s^-1)

Sierra Cheslick 2B

The SI unit for distance is meters, the only SI unit that has a prefix is that for mass (kg)

Sierra Cheslick 2B

"n" describes the energy level
"l" describes the type of orbital (ex: s, p, d, f) and its values can range from 0 to (n-1)
"ml" describes the orientation of the orbital (ex: px, py, pz) and its values range from -l to +l

Sierra Cheslick 2B

Yes, helium has the highest ionization energy since it's in the upper right corner of the periodic table.

Sierra Cheslick 2B

You use de Broglie to find the wavelengths of subatomic particles (electrons, protons, and neutrons) but you use lambda = hc/energy for photons since they do not mass.

Sierra Cheslick 2B

Cr and Cu are more stable with 5 and 10 electrons in the 3d orbital, respectively, for symmetry reasons. The 3d shell is either half full (with 5 electrons) or full (with 10) and therefore more stable than if some of these electrons were placed into the 4s orbital instead.

Sierra Cheslick 2B

Boron does not provide both electrons - one electron is from boron and one is from fluorine in each of the three bonds in BF3. Boron is satisfied with only 6 valence electrons because since it only has 3 valence electrons, it can only form a maximum of three bonds, unless there is another atom that ...

Sierra Cheslick 2B

For an ion, for example SO4 2-, do you want the overall formal charge to be zero or 2-? I'm confused because I remember Dr. Lavelle mentioning that compounds are most stable with a formal charge of zero, but I also remember something about how you have to maintain the charge of the ion.

Sierra Cheslick 2B

Ammonium sulfate is a compound made of two ions that are bonded together because of charge, whereas glycine is an organic molecule.

Sierra Cheslick 2B

The number of valence electrons in the d orbital is determined by the element. However, it's important to remember that the 3d orbital has a lower energy level than the 4s orbital, and therefore is filled first. For example, Ni would have an electron configuration of [Ar]3d^10 rather than [Ar]3d^8 4...

Sierra Cheslick 2B

The equation is used to show that we can never know the exact position of an electron, and that the certainty of the momentum and the location are inversely related. For example, if the location of an electron is known without much uncertainty, than the momentum of the electron is only known with lo...

Sierra Cheslick 2B

How/when is the Schrodinger equation used, or is it just concept we should understand but don't have to apply using calculations?

Sierra Cheslick 2B

Before adding the work function to the energy of the emitted electron, you must first divide the work function by 6.022 x 10^23, as the work function is given in moles and you are looking for the threshold energy to remove a single electron. You must also then convert this number into joules from kJ...

Sierra Cheslick 2B

The h is Planck's constant, which is equal to 6.63 x 10^-34

Sierra Cheslick 2B

Your answer could just be an issue of not using enough sig figs throughout the problem, but I'll walk you through the steps I did to get 8.8 nm regardless. I used the equation: KE(of electron) = energy(of photon) - threshold energy. I first solved for the KE of the electron by converting the velocit...

Sierra Cheslick 2B

You can turn in homework questions for either topic.

Sierra Cheslick 2B

First, solve for the limiting reactant by converting grams of both of your reactants (HA and XOH) into moles of reactants using the molar masses given. Then, using the mole ratio (which in this case is 1:1 so it can be disregarded) solve for the limiting reactant, in this case HA. Convert the moles ...

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