CHEMISTRY COMMUNITY

Xingzheng Sun 2K

The unit of k for a zero-order reaction is mol L-1 s-1; for a first-order reaction is s-1; For a second-order reaction is L mol-1 s-1.

Xingzheng Sun 2K

Intermediate molecules are not included in general rate laws because only reactants are, but they can be included if you break down the reaction mechanism and look into the rate for each step.

Xingzheng Sun 2K

I think E'cell is the standard E which is the same as E°. It is a fast way in my opinion because otherwise, you need to calculate pH from lnQ.

Xingzheng Sun 2K

E and E°can be calculated by the formula E = E°- （RT/nF) lnQ.

Xingzheng Sun 2K

Standard E = 0 only when there is the same material on both sides. Otherwise, you will need to calculate by subtracting the right side by the left side.

Xingzheng Sun 2K

I think the correct equation for this is In3+ (aq) + e- -----> In2+ (aq). This is from my solution manual.

Xingzheng Sun 2K

Because the actual reaction going on is the reverse of formation of Tl3+, resulting in the standard Gibbs Free energy being the opposite.

Xingzheng Sun 2K

For the calculation of Q and K, the equation is that Q = (The concentration x pressure of Products)/(The concentration x pressure of reactants) in the case there are two or more products or reactants which each contains both concentration and pressure.

Xingzheng Sun 2K

When we are asked to put a reaction equation into a cell diagram, how do we know if an inert component such as Pt should be included? Or it will always be mentioned in the question (since some question does not mention Pt but the ask has it)?

Xingzheng Sun 2K

First, you need to write down the half-oxid and half-red equations for the reaction. When you balance it out, I find the electron flow of the reaction which is the number of e- being canceled on each side. Use this number as n to find the △G with △G= -nFE.

Xingzheng Sun 2K

Yes. When an element in reactant is both oxidized and reduced in two products, it is both agents.

Xingzheng Sun 2K

△G determines whether a reaction can happen spontaneously. Negative △G is spontaneous, and positive △G is not. It is also related to which way of reaction can be more stable. The lower △G is, the more stable it is.

Xingzheng Sun 2K

△G with Degree means it is the standard Gibbs free energy. Without a degree is not standard. It can be calculated by △G = standard△G + RTlnQ.

Xingzheng Sun 2K

The conversion from atm L to J is given on the formula sheet for the tests.

Xingzheng Sun 2K

I think the sign of work always depends on if the system does the work or work is done to the system. Once it is determined, the sign of work is figured out.

Xingzheng Sun 2K

During the phase change, the heat is called latent heat. The formula is q=mL (L is latent heat capacity).

Xingzheng Sun 2K

I think since C is in J/g, the final answer should be in J.

Xingzheng Sun 2K

Normally it is told that the system is isothermal if it is important for solving the problem.

Xingzheng Sun 2K

The change in temperature means that the kinetic energy of molecules is changing. While in the phase change, the substance is changing its potential energy. Thus the temperature does not change.

Xingzheng Sun 2K

Can the unit for Pressure be other than atm?

Xingzheng Sun 2K

Because the process of boiling water intakes energy, and when it becomes steam, the steam has more heat than water.

Xingzheng Sun 2K

Simply, an open system means both matter and energy can exchange; A closed system can exchange energy but not matter. An isolated system does not exchange either matter or system.

Xingzheng Sun 2K

There can be graphs of △H △S and △G. I think the graphs will mainly function to show the change of values.

Xingzheng Sun 2K

mC represents the specific heat capacity is measured in per unit of mass; nC means the specific heat capacity is measured per mole.

Xingzheng Sun 2K

If K is not given, we probably can calculate the K using given information such as concentration. If not, we can not compare K vs Q.

Xingzheng Sun 2K

That is what we are supposed to do. The formula to calculate x is given on the formula sheet, and it always works for solving the x.

Xingzheng Sun 2K

When pressure is increased, the reaction wants to do something to reduce the effects. Lowering the number of molecules can decrease the pressure which reduce the effect.

Xingzheng Sun 2K

The questions on the midterm should not be solved using approximations. Also, I think there is a statement by the question saying no approximation allowed.

Xingzheng Sun 2K

For reverse reactions, it is important to calculate the K value, which k=[P]/[R].

Xingzheng Sun 2K

I think we need to know strong acids and bases, and others are just weak.

Xingzheng Sun 2K

I think it simply means that if x (the change) is less than 5% than it is ok. It is important that the formula x=(-b+/-(b2-4ac)^1/2)/2a always work.

Xingzheng Sun 2K

So which one is the right unit for the equation PV=nRT?

Xingzheng Sun 2K

One more thing to know is that rain is normally acidic, and the acid rain is when rain is too acidic (more than normal).

Xingzheng Sun 2K

I understand the number of the bond (single, double and triple) results in the type of bond. Can anyone tell me the relationship between the type of bond (sigma and pi) and its hybridization orbital?

Xingzheng Sun 2K

The pH is the concentration of H3O+ and calculated by -log[H3O+], whereas the pOH is the concentration of OH- and calculated by -log[OH-]

Xingzheng Sun 2K

Yes, because the Tetrahedral shape has 4 bonds, which is 4 regions of electron density, resulting in an sp3 hybrid orbital.

Xingzheng Sun 2K

Yes, the number of regions of electron density include bond and lone pairs, which is equal to hybrid orbitals.

Xingzheng Sun 2K

The tetrahedral shape has 4 bonds, which in order 1, 2, 3, 4 bonds form s, sp, sp2 and sp3 hybridization.

Xingzheng Sun 2K

Because of the existence of a lone pair, the bond angles of seesaw shape should be <120 and <90 degrees. I guess less than 180 degrees will work too.

Xingzheng Sun 2K

For trigonal planer, the bond angle is exactly 120 degrees. For other shapes, since the lone pair has a stronger force, the bond angle can be slightly smaller than the original angle.

Xingzheng Sun 2K

Molecules with one pair of electrons are polar, but as for two pairs or more, it depends on the shape and if the elements are the same. The graph on the textbook of VSEPR type VS polarity would help.

Xingzheng Sun 2K

The interaction potential energy equation is expressed by (-a1a2)/(r to the sixth). Therefore, the determinations would be the charges of molecules and the distance between them. The distance is more significant because of the 6th power.

Xingzheng Sun 2K

Energy is needed to break a bond and is released to form a bond. You also can understand by looking at the energy equation which starts with a negative sign.

Xingzheng Sun 2K

There is no definite determination on which force results in which state of matter because it depends on the element. However, the stronger the intermolecular force is, the more likely it will be solid; the weaker it is, the more to be gas.

Xingzheng Sun 2K

When you are asked to calculate the difference of electronegativity, the values will be given. More importantly, you need to know how to compare each element in a periodic table to figure out, for example, which bond has more ionic or covalent characteristics.

Xingzheng Sun 2K

Because the double bond has a stronger attraction between the atoms, which pulls to form a shorter bond than a single bond.

Xingzheng Sun 2K

In the answer key, I found that when we draw a Lewis structure for an ion, we need to put parenthesis after drawing the diagram and the write the charge on the up right corner. I wonder if it is a necessary step or just a better representation?

Xingzheng Sun 2K

This is a good question because the example given in lecture C6H6 has two possible structures, while indeed they are just one turning around. I believe it is still a resonance for the reason that it can also be seen as the change of single bond and double bond of the Cs in the structure.

Xingzheng Sun 2K

For the Lewis structure, we always choose the atom with the lowest ionization energy as the central atom. Therefore it is C in this case.

Xingzheng Sun 2K

No, because metals tend to form cations and nonmetals tend to form anions.

Xingzheng Sun 2K

De Broglie equation describes the status of a single quantum, which includes the mass and velocity. Therefore, the object has to be in motion.

Xingzheng Sun 2K

Will the concept of Black Body Radiation be tested?

Xingzheng Sun 2K

In the textbook, there is a part in chapter 2 describing spherical polar coordinates, but I do not think our professor covered that in classes. Is it a required material for the test?

Xingzheng Sun 2K

Since electromagnetic radiation acts like particles, E in this equation stands for the energy per photon.

Xingzheng Sun 2K

The question is: Sodium vapor lamps, used for public lighting, emit yellow light of wavelength 589 nm. How much energy is emitted by (a) an excited sodium atom when it generates a photon; (b) 5.00 mg of sodium atoms emitting light at this wavelength; (c) 1.00 mol of sodium atoms emitting light at th...

Xingzheng Sun 2K

In homework problem 1.23, the energy is in the unit of keV. I wonder what is its relation to joules and how often do we use it.

Xingzheng Sun 2K

I would say you do the three reagents together. Find the moles of each one first and figure out which one is the smallest. That is the limiting reagent.

Xingzheng Sun 2K

Yes, they can be the same when the molecule, or the molecular formulas, is at the simplest form, then it is the empirical formula.

Xingzheng Sun 2K

I have the same question that if my discussion is on Friday, can I still do the homework from the previous chapter?

Xingzheng Sun 2K

From my experiences, I usually start with the element that is the least common to the most common or easiest. By meaning the easiest, for example, H2 can be the one because it will be balanced easily so that I leave it for the latest. After you have the fixed number of the least common element, try ...

Xingzheng Sun 2K

I would say scientific notation is not required except the question asks. It is a way to make your answer clear, so it is up to you to use it or not for most questions as long as you get the right result.

Xingzheng Sun 2K

This post is very useful for a biology student like me. Thank you very much!

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