CHEMISTRY COMMUNITY

Samantha Ito 2E

I don't know exactly what specifically we will have to know for electrolysis for the final, but electrolysis is when an electron current is used to drive a nonspontaneous redox reaction (electrical energy -> chemical energy).

Samantha Ito 2E

We never went over organic molecules and naming in lecture, so I do not think that they will be on the final.

Samantha Ito 2E

Yes, t½ = 1 / k [A]o

Samantha Ito 2E

Rusting is spontaneous because it naturally occurs without any outside intervention even though it happens over a long period of time.

Samantha Ito 2E

Samantha Silva 1F wrote:Does anyone know if the TA's passed back the tests? I was unable to attend.

Yes, the TAs passed back the tests during our discussion sections this week.

Samantha Ito 2E

I don't think he does.

Samantha Ito 2E

1. Write the two unbalanced equations for the oxidation and reduction half-reactions 2. Balance all the elements in the half-reactions except O and H 3. In a basic solution, balance O by using H2O; then balance H by adding H2O to the side of each half reaction that needs H and adding OH- to the othe...

Samantha Ito 2E

When using the equation, Eºcell = Eºcathode - Eºanode, you do not need to flip the sign for the standard reduction potential of the anode.

Samantha Ito 2E

I noticed that too and I think it is an error in the solutions manual.

Samantha Ito 2E

For Q in the solutions manual, the partial pressures are in the numerator and the concentrations are in the denominator. Are you allowed to mix partial pressures and concentrations when calculating Q?

Samantha Ito 2E

Can someone please explain #4 on the Gibbs Free Energy worksheet?

Samantha Ito 2E

I find the outlines on his website to be useful guidelines on the main topics we need to know for the tests. Test 2 covers Gibbs free energy and electrochemistry up to the Nernst equation. Homework problems are also very good practice for the types of questions that could be asked on the tests.

Samantha Ito 2E

The correct response would be that the equilibrium constant is large (K = 3*10^4), therefore, the product (SO3) is more stable.

Samantha Ito 2E

Also, the work calculated for an irreversible expansion is w= -P∆V while the work calculated for a reversible expansion is w= -nRTln(V2/V1).

Samantha Ito 2E

A state function is a property that depends only on the current state of the system and is independent of how the state was prepared.

Samantha Ito 2E

Boyle's Law states that P1V1=P2V2 and by rearranging the equation, you are left with V2/V1 = P1/P2.

Samantha Ito 2E

C is the general term for specific heat. Cv is specific heat at constant volume. Cp is specific heat at constant pressure.

Samantha Ito 2E

The C-H bonds of the 3C2H2 are never broken. Therefore, the C-H bonds do not need to be formed again to make C6H6.

Samantha Ito 2E

Hydrochloric acid oxidizes zinc metal in a reaction that produces hydrogen gas and chloride ions. A piece of zinc metal of mass 8.5 g is dropped into an apparatus containing 800.0 mL of 0.500 M HCl(aq). If the initial temperature of the hydrochloric acid solution is 25°C, what is the final temperatu...

Samantha Ito 2E

Calculate the standard enthalpy of formation of dinitrogen pentoxide from the following data:
2NO(g) + O2(g) -> 2NO2(g) ∆H° = -112.1 kJ
4NO2(g) + O2(g) -> 2N2O5(g) ∆H° = -110.2 kJ
Also, the standard enthalpy of NO = +90.25 kJ

How would you solve this?

Samantha Ito 2E

A state function is a property whose value does not depend on the path taken to go from the initial to the final state(Ex: enthalpy). Work is not a state function because work is quantified based on the pathway it takes.

Samantha Ito 2E

The heat gained by the water in the ice cube is equal to the heat lost by the initial hot water in the glass. Therefore, use the heat formula for the water in the ice cube and the water in the glass and set them equal to each other to find final temp. You also need to be aware that the enthalpy chan...

Samantha Ito 2E

We will probably have to know the heat curve and the general concepts that it is indicating. I think it would also be helpful to know the key temperatures where a phase change is occurring in water (0 degrees Celsius and 100 degrees Celsius).

Samantha Ito 2E

You have to compare the number of moles of gas (don't include the solid).

Samantha Ito 2E

Can someone please indicate the main steps to solve worksheet 1 problem #5?

Samantha Ito 2E

So then would the pOH of the solution be above 14?

Samantha Ito 2E

Is it possible to have a negative pH value? It is given that [H3O+] = 1.50 mol*L^-1, but the -log(1.50) = -.176

Samantha Ito 2E

If a reaction is endothermic, then heat is absorbed in the reaction. So if there is an increase in the temperature, the reaction will shift towards the products. If there is an increase in products, then the Kc value will increase.

Samantha Ito 2E

The pH of a solution is the -log of the hydronium ion concentration: pH = -log[H3O+]

Samantha Ito 2E

Lavelle said that if the K value is less than 10^-3, then typically we can use the approximation.

Samantha Ito 2E

I think he was talking about how you can plug in 1.59 for x in the equation x^2 + 1.80x - 5.40 and that equals zero.

Samantha Ito 2E

Decreasing the volume of a contained gas will increase its pressure, and increasing its volume will decrease its pressure.

Samantha Ito 2E

Using table 5G.2, you will notice that K=377 for 2BrCl(g) <-> Br2(g) + Cl2(g) at 300K and K=4.0*10^31 for H2(g) + Cl2(g) <-> HCl(g) at 300K. You are then able to multiple these 2 K values together in order to get the K value of the combined reaction.

Samantha Ito 2E

Bronsted acids donate protons and Bronsted bases accept protons. Lewis acids accept electrons and Lewis bases donate electrons. I would think that there are not anymore we need to know.

Samantha Ito 2E

Can someone explain why CO3^2- serves as a monodentate or bidentate?

Samantha Ito 2E

It has to do with the orientation of overlapped orbitals. Sigma bonds are formed by end-to-end overlapping while pi bonds are formed by lateral overlapping. The extent of overlapping is maximized in sigma bonds and is therefore stronger than pi bonds.

Samantha Ito 2E

Check the formal charges of the atoms when determining the most stable structure. Typically, the structure with the most formal charges of zero on atoms is the more stable Lewis structure. When there must be positive or negative formal charges on various atoms, the most stable structures generally h...

Samantha Ito 2E

Bronsted acids donate protons and Bronsted bases accept protons. Lewis acids accept electrons and Lewis bases donate electrons.

Samantha Ito 2E

It's the end of chemical bonding and all of molecular shape and structure.

Samantha Ito 2E

: Hope this helps you to visualize it!

Samantha Ito 2E

A seesaw structure occurs when the electron geometry is trigonal bipyramidal and there are 4 bonds to the central atom and 1 lone pair to the central atom.

Samantha Ito 2E

Group 13 elements are often exceptions to the octet rule. Since these atoms need to gain 5 electrons to fulfill their octet rule, the octet rule is not reliable in Group 13. Furthermore, elements in Period 3 or later have an expanded valence shell by using their empty d orbital to hold additional el...

Samantha Ito 2E

A sigma bond is the same in all directions around the long axis of the bond with no nodal planes containing the internuclear axis. A pi bond has a single nodal plane containing the internuclear axis.

Samantha Ito 2E

: I find it helpful to look at photos of molecules to understand their shapes, so I hope this helps!

Samantha Ito 2E

An octahedral shape occurs when there are six atoms symmetrically arranged around a central atom. A square planar shape occurs when two of these atoms are replaced by two lone pairs that are on opposite sites of the central atom, leaving a square planar shape.

Samantha Ito 2E

A T-shaped molecule occurs when there are 3 bonds and 2 lone pairs around the central atom in a molecule. The atoms bonded to the central atom have 90 degree angles between them to form a T-shape. The t-shaped geometry is related to the trigonal bipyramidal geometry, but two lone pairs occupy two po...

Samantha Ito 2E

Electronegativity is the ability of a neutral atom to attract electrons towards itself. Electron affinity is the energy released when an electron is added to a neutral atom.

Samantha Ito 2E

The bond electron pair lies further from the atom than the lone pair of an atom (the lone pair is closer to the positively charged nucleus). Therefore, the lone pairs are closer to one another to make a greater repulsion between them.

Samantha Ito 2E

I think that the only molecular shapes that we have to know are the ones we discuss in lectures.

Samantha Ito 2E

Lewis bases donate pairs of electrons (not protons) and Lewis acids accept pairs of electrons.

Samantha Ito 2E

I think of the ml as the integers ranging from -l to +l.

Samantha Ito 2E

I'm going to the as many review sessions as possible, look over all of my notes, and do as many homework problems as possible.

Samantha Ito 2E

I believe that s- electrons have a lower energy than p- electrons within the same shell.

Samantha Ito 2E

I'm not sure whether or not we need to know it, but I think knowing it wouldn't hurt you. Going from shorter wavelength to longer wavelength, it is
gamma ray, x-ray, ultraviolet, visible, infrared, microwave, radio

Samantha Ito 2E

An excited hydrogen atom emits light with a frequency of 1.14*10^14 Hz to reach the energy level for which n=4. In what principle quantum level did the electron begin? I made n2=4 in the equation and solved for n1 but I don't get 6 as the answer. Can someone show me the work for this problem using t...

Samantha Ito 2E

Depending on what is given, it can be used to determine the frequency, wavelength, or the other energy level. I don't know for sure whether or not it will be on the 2nd test, but I think it is likely that it will be.

Samantha Ito 2E

Also, I think that the Rydberg constant can be written in Hz or m^-1 depending on which formula you want to use.

Samantha Ito 2E

I've seen the equation written both ways too and I think that both are correct. This formula is mainly used to determine the wavelength of light emitted by an electron moving between the energy levels of an atom.

Samantha Ito 2E

E stands for energy per photon.

Samantha Ito 2E

E=hv indicates that the energy per photon is equal to Planck's constant times frequency. c=λv indicates that the speed of light is equal to the wavelength times the frequency. A possible relationship between the two equations is that you are able to solve for frequency in both and substitute it with...

Samantha Ito 2E

Since there are 4 moles of oxygen, you just multiply the molar mass of the oxygen by 4. Then, you divide this value by the molar mass of the entire sample.

Samantha Ito 2E

3 more Astatine atoms would be needed to balance the 9 Gallium atoms on the scale because Astatine's molar mass is 3 times more than a Gallium atom.

Samantha Ito 2E

When rounding for sig figs with a number that ends in 5, you would round up. So for your example, 2.65 would round to 2.7 for two sig figs.

Samantha Ito 2E

Since water has a molar mass of 18.02 g/mole, you can divide that by Avogadro's number in order to get g/molecule.
(18.02g/mol)/(6.022*10^23molecules/mol)=2.992*10^-23g/molecule

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