CHEMISTRY COMMUNITY

Elizabeth Ignacio 1C

Hi! When is it necessary to use steady state approximation to find the rate of a reaction as opposed to just using the slow step? Thanks!

Elizabeth Ignacio 1C

Does it matter which set of numbers is used as k1 and T1, and k2 and T2?

Elizabeth Ignacio 1C

The outline for Chapter 15 says that we should be able to "show how the rate of change of one species in a reaction is related to that of another species." What exactly does this mean (like what equations do we need to know) ?

Elizabeth Ignacio 1C

Why did the hipster get burnt?

Because he touched the beaker before it was cool.

Elizabeth Ignacio 1C

You find the units of k by cancelling out all other known units in the rate law, like all of the different mol/L and the units for time. You can also just memorize them, because they're the same for each rxn order. Zero order: mol/L/s or basically, Molarity/Time First Order: 1/s, or basically 1/Time...

Elizabeth Ignacio 1C

A photon checks into a hotel and is asked if it needs any help with its luggage.

"No," it says. "I'm traveling light."

Elizabeth Ignacio 1C

One of half reactions needed to calculate the overall cell potential in 14.23A is 2Hg -> Hg 2 2+ + 2e- and the cell potential for the reverse reaction in the textbook is listed as +0.79, which the solutions manual uses in the calculations for E o cell. I'm confused why they didn't flip the cell pote...

Elizabeth Ignacio 1C

I heard/read a lot that the anode is conventionally on the left of the cell diagram and the cathode is on the right. However, there's also a rule that mentions that a negative cell potential means that the cathode is actually on the left. Do we have to draw cell diagrams differently when the cell po...

Elizabeth Ignacio 1C

In the homework problem 9.25, the units used in the final answer for residual molar entropy is J/K. Why would the units for residual molar entropy be in J/K and not J/K/mol?

Elizabeth Ignacio 1C

Is there an advantage to using either form of the van't Hoff equation? I know there's the version in the textbook and the version that Lavelle recommended in class, but are there certain times when it's better to use one form or the other? Thanks!

Elizabeth Ignacio 1C

Think of it as though the universe always wants to have more entropy. Just as Lavelle showed in class, a gas will always want to spread out and fill the container it's in. It's never going to want to huddle up densely packed in a corner of a room by itself; it, and everything in the universe, will w...

Elizabeth Ignacio 1C

That is only necessary when the question specifically asks, "What is the Gibbs Free Energy for one mole of _____?" and they will specifically tell you which molecule needs to have one mole. If there is more than one product for the equation, all that matters is that the specific molecule t...

Elizabeth Ignacio 1C

I believe the stability of Fe 3 O 4 and Fe 2 O 3 were mentioned in problem 9.81, and in that problem, it was important to write out the equation that involves the two of them, which is 4Fe 3 O 4 + O2 -> 6Fe 2 O 3 . This Gibbs Free Energy for this forward reaction is negative and the reverse is posit...

Elizabeth Ignacio 1C

We usually don't consider vibrational energy because most molecules don't vibrate under standard conditions.

Elizabeth Ignacio 1C

A good way to define molar entropy is just the amount of entropy in one mole of the given substance. Although it's important to remember that when it's mentioned, it's usually referred to as "standard molar entropy," meaning that it's asking for the molar entropy at standard conditions. Th...

Elizabeth Ignacio 1C

You don't need to do any calculations. You just explain that since Br has a higher atomic mass, it has higher molecular complexity (a fancy way of saying that its electrons have more energy levels that they can jump between), and that gives HBr more entropy.

Elizabeth Ignacio 1C

Is there a specific way to best find W? Other than drawing out the different possible microstates?

Elizabeth Ignacio 1C

A u! Did you take my gold?

A g, never mind, it's just silver.

Elizabeth Ignacio 1C

Why are the units for entropy sometimes J/K and other times J/K/mol?

Elizabeth Ignacio 1C

Do we need to know the equipartition theorem for Test 1? I don't recall learning it in class.

Elizabeth Ignacio 1C

Is heat of combustion the same thing as the heat of formation, except during a combustion reaction? Or is it more similar to the reaction enthalpy?

Elizabeth Ignacio 1C

For 8.53b, which reads The reaction of 1.40 g of carbon monoxide with excess water vapor to produce carbon dioxide and hydrogen gases in a bomb calorimeter causes the temperature of the calorimeter assembly to rise from 22.113C to 22.799C. The calorimeter assembly is known to have a total heat capac...

Elizabeth Ignacio 1C

8.27 reads "Calculate the work for each of the following processes beginning with a gas sample in a piston assembly with T=305 K, P=1.79 atm, and V= 4.29 L: (a) irreversible expansion against a constant external pressure of 1.00 atm to a final volume of 6.52 L; (b) isothermal, reversible expans...

Elizabeth Ignacio 1C

Heat capacity is dependent on temperature, as you mentioned with C v = ΔU/ΔT (equation for heat capacity at a constant volume). To find the molar heat capacity at a constant volume, you take C v and divide it by however many moles of substance you have. You're looking for the heat capacity per unit ...

Elizabeth Ignacio 1C

I'm having a hard time seeing the differences between heat and enthalpy. What happens when calculating heat that leads it to /not/ be a state function?

Elizabeth Ignacio 1C

At constant volume, all work is lost as heat (no work). Therefore, ΔU = q. The equation for heat capacity at a constant volume therefore, C_v = ΔU/ΔT, is derived from ΔU = q and c = q/ΔT.

At constant pressure, ΔH = q. So we substitute that into c = q/ΔT, and we get C_p = ΔH/ΔT.

Elizabeth Ignacio 1C

Never mind haha I got it. For anyone wondering, the coordination sphere is specifically referring to the central atom/ion and the ligands attached to it. So if given an entire molecule consisting of more than just the coordination compound, you disregard the other atoms/molecules attached to to the ...

Elizabeth Ignacio 1C

Hi!

I know it's a bit late, but what exactly is a coordination sphere, and what do we need to know about its geometry? Thanks!

Elizabeth Ignacio 1C

The syllabus for chapter 17 on the website says we need to know "well-known examples of coordination compounds used as chemotherapy drugs." Is this something he mentioned in a lecture or something in the textbook? I can't seem to find anything on it.

Elizabeth Ignacio 1C

How is EDTA a hexadentate?

Elizabeth Ignacio 1C

Unless it's one of the more common coordination compounds where you're expected to know whether it's a bidentate etc, drawing out the Lewis diagram is the best thing to do to figure it out.

Elizabeth Ignacio 1C

Did you have to draw out the Lewis diagrams to figure that out?

Elizabeth Ignacio 1C

Gases are pretty much always as partial pressure, and solutes (aq) more often appear in concentration (mol/L). Usually, the only time gases are written in mol/L are when they give you moles and liters in the equation.

Elizabeth Ignacio 1C

In toolbox 17.1, the name for [Fe(NCS)(OH2) 5 ] ]2+ with an Fe-N bond is thiocyanato( k N)pentaaqua(III) iron. I'm not 100% sure, but are the roman numerals meant to describe iron? And if so, are there any particular rules as to where the roman numerals are placed? I'm more used to seeing them come ...

Elizabeth Ignacio 1C

If the lone pair is axial, it interacts with three atoms instead of the (only) two atoms it would interact with as an equatorial. As an equatorial lone pair, it would just interact with the axial atoms. The molecule prefers this because it takes less energy.

Elizabeth Ignacio 1C

Hi! What exactly makes carbon dioxide non-polar while H2O is polar? I know that it has to do with its dipole moments, but I'm unsure how you can look at the dipole moments and determine polarity. Thanks!

Elizabeth Ignacio 1C

Is there a correlation between electronegativity and bond strength?

Elizabeth Ignacio 1C

Hi guys! I know that the magnetic quantum number can be positive or negative, but which one indicates clockwise or counterclockwise? And how does the electron's orientation change when the magnetic quantum number equals 0?

Elizabeth Ignacio 1C

The above post is correct - 1.5 is the furthest material that the test covers. All the material we are learning this week are part of the next section.

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