CHEMISTRY COMMUNITY

lauren chung 2f

For #4a, how do you know that you would use w=-PdV instead of w=-nRTln(V2/V1)?

lauren chung 2f

Were A and B both correct for this question? I seem to remember being told that either would have been given credit, but I'm not sure.

lauren chung 2f

No. Activation energy is the minimum energy required to start a chemical reaction, and since the higher the temperature the more energy present, the more likely the reaction is to reach the activation energy. But the temperature does not change the activation energy.

lauren chung 2f

I do not have a copy of the winter 2011 midterm, but on a previous post on chemistry community, Chem_Mod has responded to a question about #2b saying "The diatomic molecules in containers B and C, which are two atoms from container A bound together, will have to have a greater molar mass than t...

lauren chung 2f

When you look at table 8.7, you can see that there are mean bond enthalphies for C-C and C=C, but also another category for the bonds between carbon atoms in benzene. If you find the sum of the mean bond enthalpies for the 3 single bonds and 3 double bonds in benzene, not considering the resonance, ...

lauren chung 2f

Do you mean electronegative? I don't think I understand how to tell by looking at a periodic table which elements have more reducing power. Thanks!

lauren chung 2f

Chem_Mod has previously stated on chemistry community that the equation is already balanced. However, you are correct in that the oxygens have not been balanced yet, so hopefully Lavelle can clarify whether the solutions manual is incorrect or if we should ignore the oxygens.

lauren chung 2f

Maybe not, but I would still try to learn everything that is on the practice final since it was made to prepare us for the final.

lauren chung 2f

That's a typo in the solution manual. It is supposed to say =0.59.

lauren chung 2f

The temperature and volume is given at a pressure of 1 atm, so you have all of the elements that you need to plug into PV=nRT and find n. When the temperature changes, you don't know if the pressure is constant. So you cannot use the final temperature because you don't know what the final pressure i...

lauren chung 2f

How do you know which elements are increasing in reducing power? (referring to test 2, question 5, which asks to rank the following elements in order of increasing their reducing power)

lauren chung 2f

Can you explain why you don't flip the signs of the cell potential?

lauren chung 2f

The following redox couple forms a galvanic cell which generates a current under standard conditions: Cr+3/Cr+2 and I3-/I- Identify the oxidizing and reducing agent, and complete the following cell diagram. When they present the ions in the galvanic cell, can we not supposed to assume that Cr+3 is g...

lauren chung 2f

On Test 2, it asks to calculate the standard potential for the galvanic cell, U (s)| U+3 (aq) || V+2 (aq) | V (s) Since U+3 + 3e- --> U E= -1.79 V+2 + 2e- --> V E = -1.18 but U is the anode, so I made the equation U --> U+3 + 3e- E= +1.79 Then I wrote Ecell = Ecathode - Eanode = -1.18 - (1.79) = -2....

lauren chung 2f

Yes, water would be liquid in the product side.

lauren chung 2f

It'll probably be easier to understand the concept of state functions rather than memorize a list. Since a state function is something that doesn't depend on the path taken to get from the initial to final state, you can see why temperature and volume etc can be considered state functions.

lauren chung 2f

I do not think you will be required to know the environmental impact of burning fossil fuels for the final since Lavelle hasn't covered it. I think that he included it because it's an important and relevant concept to understand especially in today's society, but we will not be tested on it.

lauren chung 2f

Because pure substances, like diatomic molecules, do not have an enthalpy of formation.

lauren chung 2f

Thank you so much for this!

lauren chung 2f

Could you post the question you're referring to? I don't know if my test 3 question 5 is the same as yours.

lauren chung 2f

k and k' would only equal each other if K=1, which we know isn't always the case. so the rate constants of the forward and reverse reactions are not always equal.

lauren chung 2f

This is a typo in the solutions manual. It should say =0.59

lauren chung 2f

The rate constant of the reaction between CO2 and OH- in aqueous solution to give the HCO3- ion is 1.5 x 10^10 L*mol-1*s-1 at 25 C. Determine the rate constant at blood temperature (37 C), given that the activation energy for the reaction is 38 kJ*mol-1. I looked at the solution manual for help with...

lauren chung 2f

Do zero order, first order, or second order rate laws change depending on if you are considering the products or the reactants?

lauren chung 2f

On page 621 in the textbook, it discusses negative orders and gives examples of rate laws with the concentration of the products in the denominators. How do you know when you write the rate law with both the reactants and products?

lauren chung 2f

But on the same page it says "A negative cell potential indicates that the right-hand electrode in the cell diagram is the anode (the site of oxidation, where electrons leave the cell)", but isn't the right-hand electrode being reduced in the example?

lauren chung 2f

At the top of page 575 in the textbook, for the reaction Cu(s)|Cu2+(aq)||Zn2+(aq)|Zn(s), it says that Cu(s) is the cathode and Zn (s) is the anode. But shouldn't it be the other way around since Cu is being oxidized and Zn is being reduced?

lauren chung 2f

You wouldn't add H+ since it is in basic solution. You would have to balance with OH- and H20.

lauren chung 2f

For problem #14.3d, since Cl2 is both the oxidizing and reducing agent, would there still be two half reactions? Or only one?

lauren chung 2f

Yes, he wrote on his website that the test will only have material covered in weeks 1 and 2.

lauren chung 2f

Does formal charge affect dipole moments and polarity?

lauren chung 2f

Because a large net dipole means a stronger bond, that would also mean a weaker acid.

lauren chung 2f

Are Bronsted acids and bases only found in the reactant side of an equation or is it possible to have one on the product end as well?

lauren chung 2f

In diatomic acids, the stronger acids are the larger compounds. Because Br is larger, there is a longer bond which is easier to break.

lauren chung 2f

There is no dipole moment because PO4^3- has a tetrahedral shape and therefore the electrons are distributed evenly around the phosphorous.

lauren chung 2f

The "-x" is eliminated because the Ka is so small that the change in initial concentration is insignificant.

lauren chung 2f

A compound with a square pyramidal shape like IF5 doesn't have resonance because all of the bonds are single bonds.

lauren chung 2f

You get the equation by cross multiplying (x^2)/(0.0237-x)=6.28*10^-5. You solve the equation by multiplying either side with (0.0237-x) to get x^2= -6.28*10^-5 x + 1.48836*10^-6. Then you move everything onto one side to get 0=x^2+6.28*10^-5 x - 1.48836*10^-6.

lauren chung 2f

At the same concentration, strong acids have a higher concentration of hydrogen ions than weak acids. Even though the acids are at the same concentration, the concentration of hydrogen ions differs.

lauren chung 2f

No we were not required to use the work function for #7b

lauren chung 2f

Why is there a dipole moment in O3 when there is only one element?

lauren chung 2f

For part c, K = (partial pressure of X)^2/(partial pressure of X2)

You find the partial pressure of X by using the formula listed above, (12 molecules/17 molecules)x0.10 bar= 0.071
The partial pressure of X2 is (5 molecules/17 molecules)x0.10 bar= 0.030

K= (0.071)^2/(0.030)
= 0.017

lauren chung 2f

Electron density is a representation of the probability of finding an electron in a specific location around an atom or molecule. In general, the electron is more likely to be found in regions with high electron density.

lauren chung 2f

ml is found by using -l...l. so if l=2, ml=-2, -1, 0, 1, and 2. electrons fill the orbitals from lowest to highest.

lauren chung 2f

since the unit is cm^-1, you would have to multiply 3600 by 100 to get m^-1.

lauren chung 2f

You only have to use kilograms as your units when you are doing an equation that has joules in it since a joule is equivalent to kg^2m^2/s^2.

lauren chung 2f

This conversion would be provided if you needed it. It's on the constants and equations sheet on the Chem 14A website.

lauren chung 2f

If the question specifies which units to use, then you have to put your answer in that form. But if it doesn't specify, it shouldn't matter much whether you write your answer in nm or pm.

lauren chung 2f

No, you just need to find the mass of each by calculating 5.45% of 510 g to find the mass of the substance (27.8 g) and then you subtract that from the 510 g to get 482.2 g H2O.

lauren chung 2f

You pay attention to the number with the fewest decimal places when adding and subtracting. So if you were doing 10.026 + 0.4, your answer would be 10.4 since 0.4 has one decimal place.

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