CHEMISTRY COMMUNITY

Elias Ruben 1O

The name of the organic molecule in the course reader is 1,5,5,6-tetramethylcyclohex-1-ene. Shouldn't the name be 2,3,4,4-tetramethylcyclohex-1-ene though, since it has lower numbers?

Elias Ruben 1O

I just want to make sure I know the difference between axial and equatorial bonds. So axial are either vertically up or down, and equatorial are diagonal in order to form the 109.5 degree bond angles for the sp3 carbons in cyclohexane?

Elias Ruben 1O

What exactly is a gauche conformation? Can molecules have multiple gauche conformations?

Elias Ruben 1O

In one of the course reader examples for cycloalkanes (around pg. 93 of the course reader), it shows 1-tert-butyl-4methylcyclohexane. Why is there a "tert" before the butyl? I don't understand why it isn't just called "butyl"

Elias Ruben 1O

In #29, how do you know that the reaction is exothermic? Is there a way to tell?

In #30, how do you approach this problem? How do you know whether or not a reaction will occur at room temperature if you're given the activation energy?

Elias Ruben 1O

Are the homework problems that Chem_Mod listed in the first post the only ones we should do to prepare for the quiz?

Elias Ruben 1O

I believe you are right about nucleophiles starting reactions since they are the ones that provide electrons to the electrophiles. In contrast, electrophiles have a positive charge, so they don't have electrons to give like nucleophiles do.

Elias Ruben 1O

When we are determining the order with respect to each reactant, can we only take the ratio of the data of consecutive experiments (for example, experiment 3/ experiment 2)? Or can we make a ratio from any of the experiments (like experiment 4/ experiment 1, or experiment 5 over experiment 2, etc.)?

Elias Ruben 1O

Do we only have to use this method if the slow step comes after a fast step? All of the homework problems have a fast step following a slow step, so I was just wondering if this can still be used. Also, will the quiz directly tell us to use the pre-equilibrium method?

Elias Ruben 1O

Are we always supposed to include the H+ in the cell diagram then? Because in other homework problems, they usually don't.

Elias Ruben 1O

My bad. It's #7 on Midterm 2013. But here is the equation: Mn2+ + Br2 ----> MnO4- + Br- The corresponding balanced half reactions are: MnO4- + 8H+ 5e- ----> Mn2+ + 4H2O E= 1.49 V Br2 + 2e- ----> 2Br- E= 1.07 V In the solutions, the first equation was reversed to be oxidized. But since it has a large...

Elias Ruben 1O

What is the difference between the equation with ln Q and the equation with log Q? How do we know when to use which?

Elias Ruben 1O

How come the H+ is included in the right side of the cell diagram for this problem?

Elias Ruben 1O

I don't understand why the half-reaction with Mn2+ was reversed instead of the half reaction with Br2. Wouldn't you reverse the Br2 equation since it has a lower reduction potential than the other half-reaction, or am I missing something?

Elias Ruben 1O

How come the first equation was reversed instead of the second one? Since the second equation has a lower reduction potential, shouldn't that be the equation that gets oxidized? Also, how come the square root of K was taken to find Ka?

Elias Ruben 1O

For part d., the cell diagram has solid gold as an electrode on the left side. Shouldn't this be Platinum, though? Can someone explain the answer to me please? I'm confused

Elias Ruben 1O

I got the correct numerical answer for #9a, -2.08 x 10^-5 J, but the book says the units are J/mol. Shouldn't the moles in Faraday's constant cancel out with the moles of electrons n, leaving only joules as units? Is it just a mistake in the textbook, or am I missing something?

Elias Ruben 1O

Is change in internal energy equal to 0 only for ideal gases in isothermal conditions, or for any system in isothermal conditions?

Elias Ruben 1O

For #12, should the units of free energy be in kJ, not kJ/mol, because you had to multiply by the number of moles of each reactant and product in the calculation?

Elias Ruben 1O

I know that in an isothermal reaction, the temperature doesn't change. But does this mean that q=0 (adiabatic) since there is no temperature difference so no heat flows?

Elias Ruben 1O

For this one, I know that for constant pressure, you would use (5/2)R for heat capacity, and for constant volume it would be (3/2)R. For constant pressure, I used the equation (1.00 mol)(20.785 J/mol x K)[ln(157.9/37.6)]. I got that the change in entropy was 29.8 J/K, but the book says it's 6.80 J/K...

Elias Ruben 1O

For this one, I used this equation:

(moles of ice)(enthalpy of fusion for ice)= -(mass of water)(specific heat of liquid water)(T_final-45.0)

My answer was 35 degrees Celsius, but the answer in the book is 31. Am I forgetting a step?

Elias Ruben 1O

For this problem, I tried using the specific heat equation using the specific heat capacity of ice and 20.0 celsius as delta T, but I didn't get the answer in the solutions manual. What am I doing wrong?

Elias Ruben 1O

For part b, I tried an integral since it is a reversible reaction, but I didn't get the answer in the solution manual. I did -nRTln(v2/v1), but I don't know what I'm doing wrong.

Elias Ruben 1O

How would you approach this problem? I don't understand how the first and second reactions described are connected

Elias Ruben 1O

How do you find the total heat change, though?

Elias Ruben 1O

I know how to find the heat in part a, but for part b, it asks for the percentage of heat that was used to increase the temperature of the water. How would you calculate that?

Elias Ruben 1O

Generally, the enthalpy you solve for in a problem will be in kJ. However, it can vary depending on the what the problem asks for. For example, if it asks you to find the standard enthalpy of formation, it will be in kJ/mol since standard enthalpy of formation is in kJ/mol by definition. Pay attenti...

Elias Ruben 1O

Since only the initial and final values matter for a state function, you can calculate exactly how much change there was by subtracting the initial value from the final value. If you do this for each step of a multi-step reaction, you can add them to find the total change of the entire reaction. Non...

Elias Ruben 1O

How exactly do you calculate the pH of a titration at the endpoint? And also, does the word "endpoint" refer to the end of the titration, or to something else?

Elias Ruben 1O

So in a problem where they give us the concentration of both a weak acid and its conjugate base and asked to find pH, we will most likely use the Henderson-Hasselback equation?

Elias Ruben 1O

Can you only assume X is small for weak acids/base, or can you also assume it is small for strong acids/bases. It makes sense that you can do it for weak acids/bases, since they don't dissociate well. But I'm unsure about strong acids/bases.

Elias Ruben 1O

The Bronsted definition of an acid/base and the Lewis definition of an acid/base just describe two different aspects of the concept of acids and bases. Whenever a problem describes protons being accepted or donated, it has to do with the Bronsted definition; likewise, if it mentions electron pairs b...

Elias Ruben 1O

In the course reader, it gives examples of strong acids and bases, along with weak acids and bases. But how do you tell if something is a strong acid or base, or a weak acid or base? Is there some type of trait that strong acids and bases share that can be used to identify them?

Elias Ruben 1O

Do we need to know the new IUPAC names for the ligands, or do we just need to know the old names? Also, do we need to memorize all of the Latin names for the cations in case they are part of an anionic complex?

Elias Ruben 1O

Why do we draw different diagrams when Z<8 and when Z>8 or equal to 8? What causes that difference? Also, what is the concept of antibonding? What exactly is an antibond?

Elias Ruben 1O

So sigma bonds can form with s and p orbitals between two atoms, but pi bonds can only form with p orbitals? I just want to make sure because on one of the practice midterms, there was a question that asked you to denote all of the sigma and pi bonds.

Elias Ruben 1O

In the course reader around page 73, there is an example of resonance for sulfur dioxide (SO2). It is a set of three resonance structures. In the first one, all three atoms have a formal charge of 0, but in the second and third structures, oxygen has a formal charge of -1 and sulfur has a formal cha...

Elias Ruben 1O

Formal charge is the charge of a certain atom when it is bonded with other atoms in a molecule. A positive formal charge means that there are less electrons than there are protons in an atom, while a negative formal charge means there are more electrons than there are protons. In either case, the at...

Elias Ruben 1O

What does the question mean when it asks how many orbitals are in subshells with an l-value. I know what n, l, and m_l mean, but the wording is confusing me. Could someone please break it down for me?

Elias Ruben 1O

How do we do calculations with inverted centimeters if the units of Planck's Constant are J times s? It doesn't give a conversion from cm-1 to J.

Elias Ruben 1O

What does it mean when it says to model the atom as a one-dimensional box with a length equal to the diameter of the atom?

Elias Ruben 1O

I got the correct wavelength for part a and the correct energy for part b, but for part c I got 12 nm, while the solution in the back is 8.8 nm. I don't know what I did wrong. I set the energy I got in part b equal to hc/lamba in order to find lambda. Is that correct? Please help!

Elias Ruben 1O

The homework problems from Chapter 1. Sorry I forgot to specify the chapter in the original post.

Elias Ruben 1O

I am confused about the answer in #11. It says that for the Lyman series, the lowest energy level is n=1, and for the Balmer series the lowest is n=2. What does that mean? Can someone please explain it to me? Also, for #15, I know you have to do the problem in reverse, first by finding change in ene...

Elias Ruben 1O

There is no reason why the answer only had one significant figure since the two given values both had three significant figures. I believe your answer is correct and the solution has an error. Don't worry about it.

Elias Ruben 1O

Hi, Ashlyn! Accuracy is how close a measured value is to the true value, while precision is how close measurements are to each other. I have an example that really helped me understand the distinction between the two, but it's unrelated to chemistry. If you're playing a game of darts and you hit the...

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