CHEMISTRY COMMUNITY

Katie Frei 1L

When can you assume that the work of the system equals zero, or when no work is done?

Katie Frei 1L

When does the change in internal energy equal zero?

Katie Frei 1L

In the solutions manual for problem 4F.11) of the 7th edition of the textbook, they use the formula for change of entropy that delta S = nRln(T2/T1). Is this a formula that we can normally use? I thought it only applied to changes in volume.

Katie Frei 1L

Why in problem 4D.7 of the 7th edition of the textbook, does the solution manual make the temperature equal to 298K even though it was never stated in the original problem? Is there a rule for this assumption?

Katie Frei 1L

In the example given in class, to calculate the net enthalpy change of the reaction of Br2(l) becoming 2Br(g), why is the change of enthalpy of vaporization added to the change of bond enthalpy?

Katie Frei 1L

In problem 4B.1 of the 7th edition of the textbook, it says that a piston compresses the gas, doing 340 kJ of work. Does this mean that the value of work is positive rather than negative?

Katie Frei 1L

In the announcement made about what was going to be covered on the midterm for chem 14B, it said everything we have covered until the end of entropy. Does this mean for thermodynamics (2nd and 3rd laws), sections 4F-4I of the 7th edition of the textbook (Basically, only excluding section 4J in outli...

Katie Frei 1L

Are you sure you input all of your calculations correctly? When i plugged in the equation you provided I got 132 kJ, not 128kJ. Maybe try inputting your values again into your calculator.

Katie Frei 1L

For problem 4A.9 of the 7th edition of the textbook, I got the correct final temperature to be 25 degrees Celsius. However, when I plugged this value back into the equation in which I solved for final temperature, the value was not checking out. I was wondering, is there a way in which to check in t...

Katie Frei 1L

When considering the units for work, are we supposed to give our final answer in J or kJ? Thanks!

Katie Frei 1L

For 6A.19 of the 7th edition of the textbook, why does the answer for part c contain 10^-12 for scientific notation instead of 10^-15? The solutions manual converted 3.1 from mmol to mols, but it was already given in mol so I'm confused. Thanks!

Katie Frei 1L

Can you use an ICE box in essentially the same way whether you are using partial pressure versus molar concentration? Thanks!

Katie Frei 1L

Can I use partial pressure to solve for K if there are only solids, liquids, and gases in the chemical equation since you do not include solids and liquids in the K expression?

Katie Frei 1L

Hello! I'm confused about the answer to problem 5G.1 of the 7th edition of the textbook. In the solutions manual, the answer for part b states the "equilibrium reactions are affected by the presence of both products and reactants" and then for part c states that "the value of the equi...

Katie Frei 1L

Hello! I am slightly confused as to why for part b of problem 5H.1 of the 7th edition of the textbook the K value of 41 from equation 1 is square rooted to find the K value of equation b. If anyone could explain this to me that would be great!

Katie Frei 1L

The question says there are 0.50 mmol of O2, so you need to convert this number to moles and then divide by the volume of the vessel in liters to get (5.0 X 10^-4)/0.500 as the concentration of 02.

Katie Frei 1L

Does anyone know why for problem 5I.35 in the 7th edition of the textbook the p in the numerator of the correct equilibrium relation is squared? Does it have to do with setting up the ICE box?

Katie Frei 1L

Using the ICE box he subtracted the initial molarity from the equilibrium molarity to find the change in molarity.

Katie Frei 1L

it helps if you write out the K values for all of the equations 2BrCl >>> Br2 + Cl2 H2 +Cl2 >>> 2HCl ----------------------- 2BrCl + H2 >>> Br2 + 2HCl K1 = [Br2][Cl2]/[BrCl]^2 K2 = [HCl]^2/[H2][Cl2] K3 = [Br2][HCl]^2/[H2][BrCl]^2 = K1 x K2 Hope this helps! Thank you so much, your explanation really...

Katie Frei 1L

To find Q, or the reaction quotient, you would need to use the same equation used to find K, or the equilibrium constant. Also only include gases and aqueous phases in your equation to find Q.

Katie Frei 1L

Does anyone know why for problem 5H.3 of the 7th edition of the textbook, the answer is the result of multiplying the two equilibrium constants of two chemical equations from the table 5G.2? I am confused why in order to find K of the chemical equation given, I would multiply the K's of the other tw...

Katie Frei 1L

Electronegativity increases across a period and up a group, so it is the same trend as ionization energy.

Katie Frei 1L

For 9c.1 of the 7th edition of the textbook, how do you determine the oxidation number of the metals?

Katie Frei 1L

B is the answer because a strong acid is completely deprotonated in solution, meaning that every acid molecule/ion has lost its hydrogen, and in the image b all of the hydrogens have separated from the Cl.

Katie Frei 1L

Does anyone know if we were asked to determine if a compound was ionic vs covalent, would we be given a chart of electronegativity for test 3?

Katie Frei 1L

Would the presence of a dipole moment contribute to the boiling point being higher?

Katie Frei 1L

Why does CN2H2 have a dipole moment? When drawing the Lewis structure, it looks to be symmetrical when the arrows point toward the two nitrogens, so I'm confused why the molecule has a dipole moment. Thanks!

Katie Frei 1L

P is the central atom because it is the least electronegative in comparison to O and Cl, and it also has the ability to be an expanded octet, which makes the drawing of the lewis structure accurate.

Katie Frei 1L

I believe that option b may have lone pairs because if a lone pair was added to each side of the central atom, the overall shape would appear as depicted and not bent like a.

Katie Frei 1L

For this problem, you have to come up with the shape of a ClO2+ ion. In the solutions manual it says the shape is angular, but that it has an trigonal planar arrangement. Which one of these would be the correct answer/how did the book come up with these answers?

Katie Frei 1L

There must be lone pairs because since the shape is bent, and not linear, you can recognize that lone pairs are causing repulsion and with that, the bent shape.

Katie Frei 1L

Yes, I always use the Lewis structure with the lowest energy by looking at the formal charges because this corresponds to the most likely molecular shape of the compound. And also make sure you satisfy the octet rule and its exceptions!

Katie Frei 1L

I think that the answer the textbook gave corresponds to Cu+ and not Cu2+.

Katie Frei 1L

Oxygen has a lower ionization energy because, even though it is technically further down the period than Nitrogen, its p orbital is half-filled, making it more stable and so harder to remove an electron.

Katie Frei 1L

Yes, two atoms of the same element are bonded as a covalent bond, sharing the electrons equally between the two atoms.

Katie Frei 1L

Yes, I believe that answer would be fine. I also explained in mine how I was able to figure out that the element had 5 valence electrons by totaling the number of electrons in the lewis structure, and then subtracting the valence electrons of the other elements.

Katie Frei 1L

Hello! Could someone please explain to me why for part e) of this question the electron configuration of Ni^+2 is [Ar]3d^8 instead of [Ar]3d^6 4s^2. Thank you!

Katie Frei 1L

The central atom of the lewis structure is the atom with the lowest ionization energy.

Katie Frei 1L

It's because the electron is taken from the outermost shell, which would be 5s orbital, leaving 4d^10 which since it is a full shell, is stable.

Katie Frei 1L

I am not going to study black body radiation because we were told not to study it for test 2, so I'm assuming it would not be on the midterm either.

Katie Frei 1L

I have this problem often as well, so I usually just do the calculations without the powers, then figure out the powers separately, and then finally input them in to the final answer. This also helps me check my work and that I have the correct scientific notation.

Katie Frei 1L

Given the magnetic quantum number you can differentiate the specific orbitals within a subshell. The magnetic quantum number also states the orientation of the orbital.

Katie Frei 1L

The problem would give you the information on whether you are entering the mass of a neutron or proton into De Broglie's equation.

Katie Frei 1L

How is 1 Joule expressed in terms of SI base units? When would we convert J into SI base units in order to solve an equation?

Katie Frei 1L

Yes, you would turn in another seven problems from the quantum world section. For the seventh edition of the textbook, he gave us the following options for homework problems: 1A: 3, 5, 7, 9, 11, 15; 1B: 3, 5, 7, 9, 15, 19, 21, 23, 25, 27; 1D: 1, 9, 11, 13, 15, 17, 19, 21, 23, 25; 1E: 1, 5, 7, 9, 11,...

Katie Frei 1L

The wavelength or the frequency can determine the color of light because of the equation c = wavelength x frequency. The color of light is more commonly identified by wavelength however, because this is seen based on the values on the electromagnetic spectrum in nm.

Katie Frei 1L

Does anyone know if when solving for an initial volume using the formula M(inital)V(inital) = M(final)V(final), would I have to convert the final volume originally given in mL to liters? In other words, when is it necessary to convert mL to liters? Thanks!

Katie Frei 1L

I do not believe that the states of matter have any effect on balancing chemical equations. However when given the states of matter in a problem, it is best if you include them when writing out the chemical equations for the reactions.

Katie Frei 1L

Hello! For part b) of problem E.21 in the 7th edition of the textbook, both of my answers for the amount of moles and molecules of HF included four significant figures because the problem initially gave the mass of HF to be 25.92 mg. However, in the solutions manual, the final answers for part b) ar...

Katie Frei 1L

Does anyone know if we have to put our final answers after solving problems in scientific notation?

Katie Frei 1L

I was curious about this too, because when I checked the molar mass I found it to be 176.12 gmol^-1. I believe the empirical formula is accurate even though the molar mass calculated is .02 off of the 176.14gmol^-1 given. I do not think it has to do with significant figures, but I would appreciate h...

Katie Frei 1L

Does anyone know why you would round to the nearest even number if the number ends in 5? For example if 2.85 was to have two significant figures, why would I write 2.8 instead of round up to 2.9? Thanks!

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