CHEMISTRY COMMUNITY

sharonvivianv

Can someone help me figure out how to think through this questions. Thnx

sharonvivianv

How do I compare reducing power? Which values have greater or lesser reducing power?

sharonvivianv

If you write the equation out you get

HA +H2O -> A- +H3O+

you know that A- and H3O+ concentrations are equal to x and [HA] was 0.1-x so it can't be

[HA]=[H3O+] or [HA]=[A-]

so the answer is [HA] can't equal [H3O+]

sharonvivianv

Partial Answer:
[HA] = 0
can't be true because they gave you [HA] in the problem already
[HA] = Ka
can't be true because of the relationship between pKa and Ka (pKa = -logKa)

sharonvivianv

For the final if we are asked to find internal energy but are not given conditions for change in temperature, do we just ignore the fact that internal energy is only when there is no constant temperature?

sharonvivianv

This is from my PLF

sharonvivianv

If you look at experiments 1 and 4, you see that concentrations for C change but the initial rates are both 2. This means that C is independent of the rate.

sharonvivianv

Experiments 1 and 2 would help you get the order for [A] but not for [B] because the concentrations are the same in both equations.

sharonvivianv

With ln k2/k1 =Ea/R (1/T - 1/T2) is it assumed that A is 1?

sharonvivianv

What are the units for Activation Energy?

sharonvivianv

You're supposed to refer to Appendix 2B.

sharonvivianv

The reaction quotient Q is set up the same as the equilibrium constant K.

sharonvivianv

Work would not be considered a stat function because the we need the information in between. Work is a path function.

sharonvivianv

I think it's because there was a change in moles from 30 to 36.

sharonvivianv

Don't forget to check midterm solutions on the course website!

sharonvivianv

Make sure you have a good grasp on the conceptual things as well. Lecture notes would be most helpful for this but the book explains a lot as well. The concepts will help putting a lot of things together during the final.

sharonvivianv

I believe that in the example that you provided you would look at Cu to Cu+ etc. The question should help you determine which one to use. Just like in test 2.

sharonvivianv

Why does the shift of a reaction due to a temperature change depend on if the reaction is exothermic or endothermic?

sharonvivianv

For 14.13 part c

After balancing :

the cathode is Cl2 + 2e --> 2Cl-

the anode is H2 --> 2H+ +2e

The book adds these and gets Cl2+H2 --> 2Cl-

I don't understand what happens to 2H+ once this is added or if I am missing some conceptual step.

sharonvivianv

Do we have to know how to balance redox reactions in a basic solution for Test 2?

sharonvivianv

How do we know which value to plug in for n when finding the reaction Gibbs free energy?

sharonvivianv

When should I use deltaS=nRln(t2/t1) as opposed to deltaS=nCvln(t2/t1) in a 2 step problem that had a volume change?

I am comparing example 9.5 from the book and 9.13 in the HW (6th edition).

sharonvivianv

I'm doing 8.31 of the sixth edition and to calculate the Cp and Cv, the solutions manual uses R=8.314 J·K^-1·mol^-1 but writes the Cv and Cp in J·C^-1·mol^-1. How does that work???

sharonvivianv

In 8.31 of the sixth edition they used q=n*Cv*deltaT for calculating at a constant volume.

sharonvivianv

Bond breaking is an endothermic process while bond forming is an exothermic process!

sharonvivianv

We haven't covered work in lecture yet. The answer is actually 28J for a. First, they based the calculations off of w=-P*deltaV To find the volume they used deltaV=-pi(r^2)(d)=-pi(1.5^2cm)(20cm)(1L/10^3cm^3)= -0.14L Volume is negative because it was compressed to a smaller volume. They plug in the d...

sharonvivianv

How do we know which expansion equations to use?

sharonvivianv

Can someone summarize the explanation of the heating curve. I didn't exactly follow everything that was said.

sharonvivianv

How do I test and confirm any approximations from acid and base equilibria pH?

sharonvivianv

How do I compare the strength of two acids?

sharonvivianv

How do I compare the strength of two acids?

sharonvivianv

HW Question: A careless laboratory technician wants to prepare 200.0 mL of a 0.025 m HCl(aq) solution, but uses a 250.0-mL volumetric fl ask by mistake. (a) What would the pH of the desired solution have been? (b) What will be the actual pH of the solution as prepared? For part a I simply calculated...

sharonvivianv

You also have to consider the geometry. You have to visually tell if the molecule will bend to make a chelating structure

sharonvivianv

I have HCl, HBr, and HI in my notes

I also have HF which is considered a weak acid

sharonvivianv

a) tridentate, you can see that there are three nitrogens meaning there are three lone pairs. b) bidentate, usually if there is a charge on an oxygen, a metal will be able to bind. There is a minus 2 charge. c) monodentate, honestly I've asked around and no one has been able to give a good explanati...

sharonvivianv

Does anyone know why the electron configuration of Palladium is [Kr] 4d^10 and not [Kr] 4d^8 5s^2?

sharonvivianv

The book mentions that other structures are possible and more stable. They could've just wanted the easiest to draw on there or soemthing. There is no real reason why they did that.

sharonvivianv

What is the cutoff of visible ot measurable light?

sharonvivianv

How do we know when a salt dissocociates in a reaction? And what exactly does that mean?

sharonvivianv

Which yield are we usually given? And which do we use to make further calculations?

sharonvivianv

I was asked to identify the shortest boxed bond and indicate whether it is stronger. I didn't know how to answer this because they look the same to me. Pls help

sharonvivianv

The difference in electronegativity determines ionic character. If you remember the trend of electronegativity, it increases going up and increases going across. With that in mind, you notice that Mg is higher in the periodic table than Ca so you can assume that Mg is more electronegative than Ca wh...

sharonvivianv

Here is a helpful image I've been using to memorize the names

sharonvivianv

Yes, the AXE notation will tell you the molecular structures.

sharonvivianv

Is the bond strength affected when the overall charge of the molecule is negative?

sharonvivianv

How do you calculate formal charge when considering radicals?

sharonvivianv

Drawing the structure might help

Ex:

sharonvivianv

There is also an easier way to tell. If you get the number of valence electrons and subtract the electrons "directly surrounding it", you will find the formal charge.

Ex: CH4
C: 4 valence electrons - 4 electrons around it = 0
H: 1 valence electron - 1 electron around it = 0

sharonvivianv

They are electrons that are not used while making bonds I don’t think that is totally true. Lone pairs also are electrons that are not used “while making bonds.” But radicals are more specific, like what Emily said above, that radicals involve a single , unpaired valence electron. What I meant was ...

sharonvivianv

A resonance structure is a version of a lewis structure.

sharonvivianv

You should know what the work function means exactly. It is the threshold energy. So when they ask for a minimum amount of energy of the photon to meet the threshold energy, there will be no kinetic energy. The threshold energy will not cause any electrons to bounce off. Any value greater than the t...

sharonvivianv

They are electrons that are not used while making bonds

sharonvivianv

Yes, you can lose a maximum of one point for each page where you don't use the correct sig figs.

sharonvivianv

The trend on the periodic table is a positive slope so as you go across and up the periodic table, the electronegativities are greater.

sharonvivianv

Memorizing the units will be helpful. Dimensional analysis helps a lot when figuring out what units each answers should be in.

sharonvivianv

In the ultraviolet spectrum of atomic hydrogen, a line is observed at 102.6 nm. Determine the values of n for the initial and final energy levels of the electron during the emission of energy that leads to this spectral line? For this question I would think that the final energy level is n=1 since t...

sharonvivianv

What does it mean when the peak of one wave interacts with the trough of another wave?

sharonvivianv

It's easier if you find the molecular formula first. Once you find it, you can try to divide it by the least common denominator that will make it the empirical formula. Sometimes the molecular and empirical formulas are the same. Remember that the molecular formula gives the actual number and the em...

sharonvivianv

Look for which elements are least present and begin placing those coefficients. If there is an odd number of elements for one, multiply by the fraction then cancel that out by multiplying the whole thing by the denominator. Remember that the stoichiometric coefficients should be whole numbers

sharonvivianv

Why was it important for scientists to undergo this experiment? What questions led to their conclusion and what real contribution did they expect to make with their initial hypothesis?

sharonvivianv

Just to confirm,

n is amount in moles
m is mass of a sample which comes in the form of grams
M is mass per mole (g/mol)
N is number of objects, (not quite clear on this)
NA is Avagadro's Constant

Are there any other important variables?

sharonvivianv

The first box below represents the reactants for a chemical reaction and the second box the products that form if all the reactant molecules shown react. Use the following key to write a balanced equation for the reaction. Assume that if two atoms are touching, they are bonded together. Key: ● oxyge...

sharonvivianv

Question: Vanillin is found in vanilla extracted from Mexican orchids. A report on the analysis of vanillin listed the mass percentage composition as 63.15% C, 5.30% H, and 31.55% O. In what atom ratios are the atoms present in vanillin? I started by converting each mass to an amount of atoms and ge...

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