CHEMISTRY COMMUNITY

Evelyn L 1H

External pressure is only zero in a vacuum. In a calorimeter, it doesn't matter what Pext is because it's being multiplied by delta V which is zero.

Evelyn L 1H

You have to use deltaG=-nFE because the number of moles of electrons are different in each equation. After splitting up the given equation into the half reactions and finding Enaught, to find the standard potential of the reaction you would use deltaG = -nFE -nFE = -nFE + -nFE -3FE= -1FE - 2FE -- ca...

Evelyn L 1H

The slow step is the rate-determining law, not the fast step. If it is the slowest step, the entire reaction must wait for it, then it is the rate-determining step. Dr. Lavelle used the example of the bottleneck/funnel neck effect to describe this. Here is a helpful analogy I found: The rate determi...

Evelyn L 1H

The most negative cell potential is the anode in a galvanic cell in order to make E positive.

Evelyn L 1H

Why and how exactly does pH give you H+ concentration?

Evelyn L 1H

Is the lewis structure arrangements more important than the molar mass?

Evelyn L 1H

I don't really understand the solutions manual's explanation about why COF2 has a higher molar entropy than BF3, could someone please explain it? I thought the molecule with the higher molar entropy is the one with the highest molar mass but the molar mass of BF3 is higher than COF2. What are the ge...

Evelyn L 1H

I had this same question, I think it means the initial concentration is used. As in [A]₀ aka A not (but i'm not sure that's how you spell "not") because for the first order reaction, half-lives do not depend on concentration while zero and second order half life equations do.

Evelyn L 1H

Those formulas are on the formula sheet! You can see that sheet on Lavelle's website under "Constants and Equations"

Evelyn L 1H

Thank you that was so helpful!!

Evelyn L 1H

This is a question from a practice quiz: A given compound decomposes with a half-life of 8.0 s and the half-life is independent of the concentration. How long does it take for the concentration to decrease to 1/9th of its initial value? How would I solve this? I think it's zero order but there's no ...

Evelyn L 1H

how did avogadro write to his friends?
by e-mole

Evelyn L 1H

chemistry jokes are sodium funny

Evelyn L 1H

Chemistry puts the cation in education

Evelyn L 1H

The solutions manual says the half reactions of Cl2 + H2 --> HCL are Cl2+2e --> 2Cl and 2H+ + 2e --> H2
How can you just split up HCL into H and Cl and then add them together to get HCL?

Evelyn L 1H

When we flip a reaction, for example flipping Ni2+ +2e- --> Ni to Ni --> Ni2+ +2e- to show oxidation, why don't we flip the sign of the reduction half potential?

Evelyn L 1H

Update I figured it out:

it asks for the oxidization/reduction agent not what is being oxidized/reduced.

Evelyn L 1H

The solutions manual says Cl2 is the oxidizing agent and S2O3 is the reducing agent. But I thought since Cl goes from +0 to -2 it is reduced and S2O3 2- is oxidized because it goes from +4 to +12. Is that a solutions manual error or did I do something wrong?

Evelyn L 1H

no, K is the equilibrium constant while Q is when the rxn is not at equilibrium

Evelyn L 1H

Yes, there is no work being performed because there is no opposing pressure in a vacuum. Therefore it is freely expanding without any work being done.

Evelyn L 1H

Monoatomic: 3/2R
Diatomic: 5/2R

Evelyn L 1H

Delta H would be equal to Delta U when there is no work being done.
No work is being done when volume is constant or if there is no external pressure (vacuum)

Evelyn L 1H

q=m1CdeltaT + m2* delta Hfusion

q=234kj
temp: -2.8 --> 0 delta T = 2.8
m1 = 125g
m2= .5*125 = 62.5g (bc half the ice cream melted)

234000 J = 125 * 10 (found in previous problem) * 2.8 + delta H fusion * 62.5
delta H fusion = 3688 J/g --> 3.7 kj/g

Evelyn L 1H

Since G is a state function, only the final and initial states matter, not the path to get there. Since the final and initial states are the same, then delta G is 0.

Evelyn L 1H

1). Delta U is zero because the final reaction was the same as the first reaction, and because internal energy is a state function, only the initial and final state matter. 2). Delta S is also zero because of the same reason and there was no temperature change. 3). q=-w because delta U=0 solve for w...

Evelyn L 1H

To clarify, Isochoric means Isovolumetric which I think you meant but I don't know what isometric is.

Evelyn L 1H

Isobaric means pressure is constant but that doesn't affect the delta U formula.
Isochoric means volume is constant which means work = 0 so delta U = q.

Evelyn L 1H

Reversible reactions take more work than irreversible reactions (remember the graphs in Lavelle's lecture).
Isothermal means temperature is constant.
Isothermal reversible reactions happen very slowly.

Evelyn L 1H

a). when change in entropy is zero, it is a reversible reaction or reaction at equilibrium b). when change in gibbs free energy is zero, the reaction is at equilibrium and doesn't favor the products or reactants c). when change in internal energy is zero, the reaction is isothermal (I think there ma...

Evelyn L 1H

What does the question state?

Evelyn L 1H

This question: Initially, a sample of ideal gas at 323 K occupies 1.67 L at 4.95 atm. The gas is allowed to expand to 7.33 L by two pathways: (a) isothermal, reversible expansion; (b) isothermal, irreversible free expansion. Calculate delta Stot, delta S, and delta Ssurr for each pathway. Why for th...

Evelyn L 1H

Can someone explain and why vibrationally active diatomic molecules have a higher change in entropy than non-vibrationally active diatomic molecules.

Evelyn L 1H

How are we supposed to know to calculate the change in entropy back down to 85 degrees from the way the problem is worded?

Evelyn L 1H

Lavelle also clarified that the Van Hoff Equation in the chemistry text book is actually two Van Hoff equations subtracted.

Evelyn L 1H

Sorry, I just realized that which side the negative sign is on doesn't matter too much because it will end up canceling out and giving you the same answer, but it helps to think of it conceptually and visualize what is actually physically happening.

Evelyn L 1H

It would actually be q_ice= -q_water because the heat used to melt the ice comes from the water so water is losing the energy that the ice gains.

Evelyn L 1H

That's why in problems with isolated systems we can use qice=-qwater

Evelyn L 1H

The kJ/mol describes the enthalpy of formation of a mole of a molecule (like H2O) but when you get the enthalpy of formation for the entire reaction, it's not per mole because it's for the whole reaction. (I think)

Evelyn L 1H

To make things cancel out more easily, you can switch the products and reactants. All you would have to do is switch the sign of delta H.

Evelyn L 1H

I don't understand where they got the target reaction from the two given reactions. Why can't we use Hess's law to find delta H?

Evelyn L 1H

Make sure to have constant units so you could cancel them out if necessary.

Evelyn L 1H

I am confused about how to calculate the standard reaction enthalpies. For example, in 8.63, part a asks to calculate the standard reaction enthalpy for the final stage in the production of nitric acid. 3NO2(g)+H2O(l) --> 2HNO3(aq) + NO(g).
What are the steps to finding the answer?

Evelyn L 1H

Evelyn L 1H

Evelyn L 1H

Lewis acid: Electron pair accepter
Lewis base: Electron pair donor

Bronsted acid: Proton (H+) donor
Bronsted base: Proton (H+) accepter

Arrhenius acid: Proton donor (same as bronsted acid)
Arrhenius base: produces hydroxide ions (OH-) (ie NaOH)

Evelyn L 1H

Oxidation means losing electrons which increases lewis acidity. This is because the more positive charge, the more likely to accept electrons.

Evelyn L 1H

No they are either neutral or negative. They cannot be positive if they are interacting with positive transition metals.

Evelyn L 1H

Be, Al, Ga, Ge, As, In, Sn, Sb, Pb, Bi are elements that will form amphoteric compounds. This closely follows the metalloid band but not completely. Figure 12.7 on page 469 in the textbook shows this.

Evelyn L 1H

Everything that isn't a strong base or strong acid (which were listed above) is considered weak.

Evelyn L 1H

Just make sure the units are correct when using concentration or pressure. Concentration would be measured in moles.L^-1 and Pressure can be in bars or atm.

Evelyn L 1H

What is the difference between K and K with a subscript of c?

Evelyn L 1H

I need clarification on the same question

Evelyn L 1H

On number 4.19, it says that (CH3)2BE is tetrahedral - how is that right if it's VSEPR is sp?

Evelyn L 1H

Evelyn L 1H

@all these jokes

Evelyn L 1H

What do you call a salty fish?
2NA

Evelyn L 1H

single bonds are the weakest and longest, double bonds are stronger and shorter than single bonds, and triple bonds are the strongest and the shortest

Evelyn L 1H

Also, if there must be a formal charge, elements like Oxygen which have a higher ionization energy are more likely than elements that have lower ionization energies (left, down) to have a charge.

Evelyn L 1H

I've heard electronegativity and ionization energy being used interchangeably by multiple different UA's. But either way, isn't it the least highest ionization energy that is the central atom, which in this case is Chlorine. And Chlorine can have an expanded octet.

Evelyn L 1H

In 51, it asks for two Lewis structures with different atom arrangements for HClO and to select the most likely structure by identifying the structure with the formal charges closest to zero. Since Cl has the lowest electronegativity, I thought it was supposed to be in the middle and made a structur...

Evelyn L 1H

This would definitely be something to study because the test covers everything from section 1.5 and all of chapter 2.

Evelyn L 1H

How do you calculate the total number of valence electrons when making a lewis structure.

Evelyn L 1H

Also if you keep your answers in meters it's ok. However you should know the prefixes so you can convert values given in the problem to meters.

Evelyn L 1H

I'm in Rieber hall! evelynluu19@gmail.com

Evelyn L 1H

In the hydrogen atomic spectrum, what is the wavelength of light associated with the n = 4 to n = 1 electron transition? What part of the electromagnetic spectrum is this wavelength? A. 1.03 x 107 m; radio waves region B. 9.73 x 10-8 m; UV region C. -9.73 x 10-8 m; visible light region D. -2.044 x 1...

Evelyn L 1H

Also, to add on, it would be best to save your rounding of sig figs until the last step for the most accurate answer.

Evelyn L 1H

There are 3 sig figs in 0.0450. This is more clearly shown if you write it in scientific notation as 4.50 x 10^-2
The 0s before 450 do not count as sig figs.

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