CHEMISTRY COMMUNITY

Joshua Xian 1D

We aren't given info on whether the activation energy for step 1 or step 3 is higher, so as long as both are different to each other and less than the activation energy for step 2, it should be ok.

Joshua Xian 1D

The x axis is reaction progression and y axis is potential energy (organic chemists use ∆G). It's probably good to know how to find ∆G using the reaction profile in addition to the activation energy and to be able to compare a catalyzed reaction profile vs. a non-catalyzed one.

Joshua Xian 1D

It's probably a good idea to be familiar with the functional groups and how to draw line structures.

Joshua Xian 1D

You use stoichiometry (3 mmol H2 consumed for every 2 mmol NH3 produced), so (1.15 mmol NH3/Lh)(3 mmol H2/2 mmol NH3) = 1.72 mmol H2/Lh

Joshua Xian 1D

Since final concentration is 10% of the initial, dividing initial by final would result in 10. Therefore, you get ln(10)/k.

Joshua Xian 1D

Since final concentration is 10% of the initial, dividing initial by final would result in 10. Therefore, you get ln(10)/k.

Joshua Xian 1D

When will we know whether we need to calculate the rate vs. the unique average rate? What would the problem say to indicate that it is looking for one vs. the other?

Joshua Xian 1D

We won't need to know how to do calculations, but we need to be familiar with what they are.

Joshua Xian 1D

You can use 150 mg as the "concentration" since volume is constant and the conversion from mass to moles is constant.

Joshua Xian 1D

KOH is used as an arbitrary strong base that contains OH- (could be NaOH, OH-, etc).

Joshua Xian 1D

It should be Sn^4+, Sn^2+ because the one that gets reduced should be on the left and the one that gets oxidized should be on the right (higher positive charge on the left).

Joshua Xian 1D

There shouldn't be three reactions (and I don't believe there are in 14.11).

Joshua Xian 1D

In what situations (cost aside) would it be better to use graphite instead of platinum?

Joshua Xian 1D

Typically for balancing redox reactions, O will be the element you need to balance using water, OH-, and H+ (depending on whether the environment is acidic or basic).

Joshua Xian 1D

∆S(system) = ∆H(system)/T since (assuming constant pressure) ∆H(system)=q(system), and if heat were added to the system, then entropy would increase. (+q(system) --> +∆S(system)). ∆S(surroundings) = -∆H(system)/T since if heat from the surroundings were added to the system, then the entropy of the s...

Joshua Xian 1D

Was "Reduction: 8H^+ + MnO4^- + 5e- --> Mn^2+ + 4H2O" the equation? If so, water (and H+) are needed since MnO4^-, which is being reduced, has O in it, so to balance the equation in terms of substances, H2O must be included in the reaction to account for the oxygens in MnO4^-. Also, I beli...

Joshua Xian 1D

∆G = ∆H - T∆S ∆S ∆H Reaction/Physical Change + - Spontaneous at all T + + Spontaneous at high T - - Spontaneous at low T - + Not spontaneous at any T When ∆G < 0, the reaction is spontaneous (and when ∆G > 0, the reaction is nonspontaneous). Given a positive ∆S, if the ∆H is negative, then ∆G will b...

Joshua Xian 1D

What types of salts are typically used for a salt bridge? Are there any salts that are more effective?

Joshua Xian 1D

You can think of entropy as energy dispersion or degeneracy.

Joshua Xian 1D

The negative sign in ∆S = -∆H/T is there because the ∆S is of the surroundings, while ∆H is of the system. Heat lost by the system is gained by the surroundings (and vice versa), so there needs to be a negative sign to account for that difference.

Joshua Xian 1D

Do we need to be familiar with the exact steps to derive the equations (using integrals) for work of irreversible and reversible processes as well as entropy?

Joshua Xian 1D

C in C∆T is heat capacity, while C in mC∆T is specific heat (Cs). C = mass x Cs, so those two equations are essentially equivalent.

Joshua Xian 1D

Is the difference between adiabatic and isolated systems that adiabatic systems can have energy transferred as work while isolated systems can have no energy transfer at all?

Joshua Xian 1D

If we are provided with ∆H values, do we assume they have an infinite amount of significant figures (i.e. are exact values)?

Joshua Xian 1D

Up to what concentration can we assume that the density of aqueous solutions is the same as that of pure water? Do we assume a density of 1 g/mL for all aqueous solutions?

Joshua Xian 1D

Since Dr. Lavelle said that bond enthalpies are the least accurate form of calculating reaction enthalpies, should we avoid using bond enthalpies to do our calculations on exams, or is there usually not a significant enough discrepancy in accuracy?

Joshua Xian 1D

Usually when solving for something involving joules/work/energy, you would use 8.314 J/mol•K. If it involves pressure (or if you need to use PV=nRT), you would use the other R constants with pressure units.

Joshua Xian 1D

At what temperature does vibrational energy contribute significantly?

Joshua Xian 1D

Why does Cp,m = Cv,m + R?

Joshua Xian 1D

If light (or some other form of energy) is released/absorbed rather than heat, would the reaction still be considered exothermic/endothermic?

Joshua Xian 1D

Acids tend to be stronger with higher bond polarity (when comparing acids with central atom elements in the same period) and with weaker bond strength (when comparing acids with central atom elements in the same group). Oxoacids are stronger if the central atom element is more electronegative and if...

Joshua Xian 1D

ClF3 could act as a Lewis base because it has lone electron pairs that can be donated (definition of a Lewis base).

Joshua Xian 1D

Trigonal pyramidal occurs when tetrahedral electronic geometry has a lone e- pair as one of its four regions of e- density. T shape occurs when a trigonal bipyramidal electronic geometry has lone e- pairs as two of its five regions of e- density or when an octahedral electronic geometry has lone e- ...

Joshua Xian 1D

There isn't a particular reason that it's in parentheses (and diaqua should be before bisoxalato even though the book says otherwise).

Joshua Xian 1D

I believe it's because the formal charges are better (closer to 0) if the Sn in SnCl2 has only one lone pair and two single bonds to each Cl2. The formal charges would all be 0, vs. having 2 lone pairs of electrons and the Sn having a -2 formal charge.

Joshua Xian 1D

Assuming that the frequency is already high enough for an electron to be ejected, higher frequency light would emit electrons with higher kinetic energy. However, for the midterm question, you can't make this assumption (and therefore the statement is not true).

Joshua Xian 1D

Beryllium actually has just 2 regions of electron density (its two bonds with the two carbons), but relative to the carbon atoms (with carbon as the central atom), the molecular shape is tetrahedral since it has 4 regions of electron density (its three bonds with the three hydrogens and one bond wit...

Joshua Xian 1D

For molecular geometries that are both called the same thing but have different origins in terms of electronic geometry (e.g. bent molecular geometry can be from 3 or 4 regions of electron density, trigonal planar and tetrahedral electronic geometries respectively), do we need to specify which elect...

Joshua Xian 1D

For LiI, the difference in electronegativity between Li and I is less than 2, so would it be considered polar covalent instead of ionic?

Joshua Xian 1D

In the Lewis Structure for hyposulfurous acid (H2SO2), why are the H atoms attached to the O atoms instead of the S atom? (both attaching the H atoms to the O atoms or the S atom can result in a formal charge of 0 for all the atoms). Hypophosphorous acid (H3PO2) has an H atom attached to the P in it...

Joshua Xian 1D

The general guideline should be rough and not absolute

Joshua Xian 1D

For writing out the electron configuration of noble gases (and ions that have the same electron configurations as noble gases), can we just put the shorthand (e.g. for neon, [Ne]) or do we need to write out the electron configuration from the previous noble gas (e.g. for neon [He]2s2 2p6), or are bo...

Joshua Xian 1D

Would helium be considered part of the s-block since its electron configuration is 1s2 even though it's attached to the p-block elements?

Joshua Xian 1D

Also, why are most of the 4d elements exceptions, and why is platinum an exception?

Joshua Xian 1D

For the electron configuration exceptions in the d-block, why is tungsten not an exception (it is [Xe]4f14 5d4 6s2 instead of [Xe]4f14 5d5 6s1) while elements in the same group (chromium and molybdenum) are?

Joshua Xian 1D

Where does the 4π come from? (Why is it 4π and not some other number?)

Joshua Xian 1D

Why is the ms quantum number ±1/2? (How did people decide on the number 1/2 and not some other number?)

Joshua Xian 1D

Does a photon have a mass?

Joshua Xian 1D

When the textbook shows the range of wavelengths that fall into each type of EMR, which category do the ones in between belong to (e.g. x-ray is 10 nm - 1 pm, gamma ray is 1 pm - 0.1 pm, is radiation of wavelength 1 pm considered an x-ray or gamma ray)?

Joshua Xian 1D

For conversion factors (including molar masses provided by the periodic table e.g. 12.01 g/mol C), should we assume that they have infinite significant figures and base the number of significant figures in the answer on those of the measured values (e.g. 17.3 m)?

Joshua Xian 1D

During a combustion reaction of an organic compound, is water vapor usually produced, or are there situations in which liquid water is produced instead?

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