CHEMISTRY COMMUNITY

Hellen Truong 2J

Also, I think it's helpful to remember that standard potentials are based on a cell with the hydrogen reaction as the anode. So if E>0, then the species is oxidizing the hydrogen electrode (since the species gets reduced). It E<0, then the forward reaction is not spontaneous, so the species is being...

Hellen Truong 2J

It's based on the table of standard potentials! If you want the species with highest reducing power, you want the species itself to be the most easily oxidized. That means in order of standard potentials, you order species most positive to least positive (most negative).

Hellen Truong 2J

I used this method! I got points on the calculations for deltaG(1) and (2), but then I am confused about the final calculation for the standard potential. I added the two values, then divided by -(12mol)*(96485C/mol). I got -0.01V. How can I correct this?

Hellen Truong 2J

Is it accurate to use half lives for questions that say something like 1/4 of the reactant is remaining?

Hellen Truong 2J

Is it possible for k to be negative for any order reaction?

Hellen Truong 2J

After you determine what order the reaction is with respect to each reactant, what does it mean conceptually when you get a negative order?

Hellen Truong 2J

How do you indicate that the reaction occurs in basic conditions for a cell diagram?

Hellen Truong 2J

How do you know which side to put H+ on?

Hellen Truong 2J

If there's a single reactant, how do you know which part is the reducing agent and which is the oxidizing agent?

Hellen Truong 2J

Why is the reduction potential for hydrogen 0?

Hellen Truong 2J

How do you know if a metal will dissolve in solution?

Hellen Truong 2J

How do you organize stuff when they're in the same state in a cell diagram? Like oxidized, reduced?

Hellen Truong 2J

Why does an isothermal reaction have no change in internal energy?

Hellen Truong 2J

Can it be considered standard Gibbs free energy if it is given for a temperature other than 25C?

Hellen Truong 2J

So I know that physical states (gas>liquid>solid) affect entropy and molecular size affect entropy (larger means more entropy), but which has more of an effect? As in would a heavy liquid or a light gas have more entropy?

Hellen Truong 2J

Why don't changes in pressure affect change in work?

Hellen Truong 2J

When using C(gr) to solve for reaction enthalpies using the bond enthalpy method, why would you add the atomization or sublimation of carbon (+717kj/mol)?

Hellen Truong 2J

It helps to remember that atoms are more stable when they form bonds, so forming bonds releases energy (exothermic), while breaking them and returning them to a less stable state requires energy (endothermic).

Hellen Truong 2J

Additionally, when exothermic processes release heat, the number of microstates for the surroundings is increased, so entropy still goes up! The second law of thermodynamics stays true.

Hellen Truong 2J

How can an isolated system have a change in temperature but no heat transfer since isolated means no energy or matter exchanged with the surroundings?

Hellen Truong 2J

snehabhargava wrote:The change in entropy of the universe is the same always.

Wait how can this be true? I think my TA said that delta S can be zero for reactions at equilibrium or something like that?

Hellen Truong 2J

Also, the purpose of a bomb calorimeter being an isolated system is so that heat is not lost to the environment and q rxn can be calculated as negative q calorimeter!

Hellen Truong 2J

How do you find deltaH given enthalpies of combustion? I checked with the solution manual and I was confused about its setup of writing out all the combustion equations and then rearranging them to get the final equation so I keep getting positive 312kj/mol instead of negative.

Hellen Truong 2J

what is an example of a conceptual question in terms of internal energy? I think for example he could give you a scenario where the walls between the system and the surroundings are adiabatic. Then, it could be true/false for a series of things like: q=0 True q>0 False delta U = w True delta U = q ...

Hellen Truong 2J

When you compress a system, is that considered the system doing work or work being done on the system? How does that affect internal energy and how can I remember?

Hellen Truong 2J

To convert from Celsius to Kelvin, you just need to add 273.15, so that's why!

Hellen Truong 2J

Why is enthalpy related to heat under constant pressure but not constant volume? What is the difference between enthalpy and heat in general?

Hellen Truong 2J

Are there any other path functions we should know?

Hellen Truong 2J

What is the difference between these two and are there any shortcuts to remember?

Hellen Truong 2J

I think we used enthalpy changes of each step and added them together to demonstrate that enthalpy of a net reaction is additive.

Hellen Truong 2J

Also when you write partial pressures, you don't need the brackets because those indicate concentration!

Hellen Truong 2J

Why don't changes in pressure alter the equilibrium constant?

Hellen Truong 2J

The cutoff value is 10^-3 when determining if the reaction tends toward reactants.

Hellen Truong 2J

Why can units be ignored during equilibrium constant calculations? Can equilibrium constants still be determined for a system with both solutes and gases?

Hellen Truong 2J

There is also conservation of orbitals. Even when carbon orbitals are hybridized into sp or sp2, there are 2 and 1 p orbitals left over, respectively. The total number of orbitals following hybridization stays the same.

Hellen Truong 2J

How do we visualize the hybridization of something like the sulfur in SO4 2-?

Hellen Truong 2J

One example of T-shape is AX3E2, which has a structure of trigonal bipyramidal, so the lone pairs always go on the equatorial plane because they are separated from the bonded atoms by 90 and 120 degrees. If the lone pairs went on the axial plane, it would only be separated by 90 degrees which is uns...

Hellen Truong 2J

So in class we discussed how bond order is the average of the bonds because electrons are delocalized. For benzene, is 1.5 the correct bond order? (I divided 6 sigma bonds and 3 pi bonds by 6 carbons to get 1.5 between each carbon)

Hellen Truong 2J

Are Be2+ and Li+ considered isoelectronic to F-?

Hellen Truong 2J

To determine the Lewis structure for HOCO, I first counted the electrons to get 17. Then, I linked single bonds so the structure looked like H-O-C-O. I added a double bond between C and the second O and then filled in 2 lone pairs for each oxygen. At this point, 16 electrons have been filled in and ...

Hellen Truong 2J

How do we remember the trend for electron affinity if it doesn't really seem to follow the periodic table? For example, I know that higher electron affinities are usually toward the top right of the table, but chlorine and fluorine already contradict that.

Hellen Truong 2J

This is also true for uncertainty in speed! On example 1.7, it shows you that you need to double the uncertainty because it is given as +/- 1.0 m/s, so when you plug it into the Heisenberg equation, it should be 2.0 m/s.

Hellen Truong 2J

Why are electrons removed from the 4s orbital first if it is a lower energy and is filled before the 3d orbital is?

Hellen Truong 2J

To rephrase, ionization energy is the energy an atom needs to form an ion. Ionization energies are specific to elements, but they get higher each successive electron removal because of shielding. After the first electron is removed, all the other electrons experience a stronger pull, so the second i...

Hellen Truong 2J

I remember in class that a complete set of quantum numbers (n, l, ml) is the solution to the wave function, but how do we visualize what that means without the actual equation? Do we have to know the equation or just understand that it models the electron density of an atom?

Hellen Truong 2J

For the wave function, the double derivative helps you understand how either side is related to each other. Because psi is returned on the right side after the equation is performed, you can relate this concept to the way (for example) sinx would return -sinx after you derive it twice. Though the or...

Hellen Truong 2J

I know that the aim of atomic spectroscopy is to measure the energy emitted or absorbed by monitoring photons, and the photoelectric effect studies the kinetic energy contained by electrons after incident light exceeds the work function. Why doesn't the energy added to the atom in atomic spectroscop...

Hellen Truong 2J

Diffraction is when wavelengths of light encounter a narrow opening, and they spread out. This is accompanied by interference if there are multiple narrow openings, causing the new curved wavelengths to hit each other. Destructive interference occurs when the waves are out of phase, or not perfectly...

Hellen Truong 2J

This problem gives percentages anyway, but if a problem were to give me amounts in grams, could I convert to moles and find a ratio that way? Why does the book teach us to find mass percentages and then use a sample mass of 100g?

Hellen Truong 2J

My TA showed us this method for dimensional analysis called a ladder! You can easily convert to different units by writing out your "given," and then matching conversion units to it by just writing the units so that they cancel out. Every unit should cancel out diagonally if you match all ...

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