CHEMISTRY COMMUNITY

Tanya Bearson 2K

The values you found for E naught and n look right to me. I think your calculation for Q is correct as well! Since the other species in the reaction are solids they do not affect Q. When you use these values do you get the right answer?

Tanya Bearson 2K

Austin Aldujaili 2D wrote:Also, you do not need to convert the H2 from a pressure into a concentration, you can find Q by using the given values for [H+] and PH2

Why is it that you don't have to convert the pressure into a concentration?

Tanya Bearson 2K

I was also struggling with this problem! Apparently the way you are supposed to write it is with the anode and cathode in the outermost slots and the other phases in the order in which they are in contact with the salt bridge. For example, the Cl-(aq) should be closest to the || (salt bridge) becaus...

Tanya Bearson 2K

One thing that really helps me deal with my anxiety is to get a good night's sleep. It can often feel like there is so much to do that you do not have enough time to sleep but rest is incredibly important and allows you to be more productive in the long run. I find that the later it gets into the ni...

Tanya Bearson 2K

I also like to use the OIL (oxidation involves loss) RIG (reduction involves gain) acronym. I write it down every time I am considering oxidation and reduction even when I don't think I need to because it is so easy to get confused. Another helpful phrase to remember is "red cat" which ref...

Tanya Bearson 2K

I agree that it can be very challenging to get into a good test taking mindset when taking exams from home. I find that it can be helpful to visualize myself taking the test before hand and think about how I want to act during it (confident, efficient, careful, etc). It may feel a bit ridiculous but...

Tanya Bearson 2K

Ooh banana bread is so good!! I love all foods but a tasty burrito is hard to beat. I'm a big fan of strawberry shortcake and blackberry pie too. All this talk about food is making me hungry...

Tanya Bearson 2K

Yes, I think we can use the two terms interchangeably for this class. Dr. Lavelle did explain that historically a Galvanic Cell refers to a battery that involves the transfer of electrons through a solution (like the diagram given in class) but now we have more advanced batteries that do not do this...

Tanya Bearson 2K

Thanks for asking this because I not sure either but yes, the next Sapling assignment is due the Sunday after week 8 at 11:59pm.

Tanya Bearson 2K

I was confused about this too but your answer Crystal definitely helped me visualize it. To clarify, is the difference that we are talking about the entropy of the world rather than comparing the entropy of individual molecules?

Tanya Bearson 2K

I was able to calculate the standard reaction entropy, but I was wondering how to approach the second part of the question where we interpret the sign of the reaction entropy. The key says that the reaction entropy is negative because the four moles of solid products are more ordered than the four ...

Tanya Bearson 2K

Did you all get 1281.8J for delta H in part b of this question? I don't see it in the answer key and want to make sure I did it right.

Tanya Bearson 2K

I think the main things we are supposed to understand is that the combustion of fossil fuels is an exothermic reaction so burning things like wood, coal, and natural gas is used to produce energy. When burning hydrocarbons, H2O and CO2 are produced which can react together and form acid rain. If the...

Tanya Bearson 2K

Make sure you are factoring in the change in moles and not just the moles of C6H6 because since the question is asking about the combustion of C6H6 the change in moles (products minus reactants) of the whole balanced chemical reaction is significant. I think if you do this you should get the right a...

Tanya Bearson 2K

If a reaction is occurring in an open beaker can you assume it is reversible because the pressure inside and outside the beaker will be constant? Likewise, can you assume that reactions in closed beakers will be irreversible?

Tanya Bearson 2K

You can use the ideal gas law PV=nRT. In this case, you are given the values for temperature and pressure (which are constant) and can solve for the change in moles (n) by writing out and balancing the chemical equation for the combustion of C6H6(l). This will give you delta V which you can plug bac...

Tanya Bearson 2K

I was confused about this question at first too! Systems that do work on the surroundings have negative values for work. If a system expands (delta V = positive) then it will have to push against the surroundings in order to do so. Because the systems are at constant external pressure, we can consid...

Tanya Bearson 2K

In this problem, you are given the heat of combustion of A in KJ/mol so if you solve for the moles of A and multiply this by the heat of combustion that they gave you you will get the overall heat of combustion of the reaction. You want to solve for the heat capacity of the calorimeter which is the ...

Tanya Bearson 2K

One way you can conceptualize this is that combustion reactions will be hot due to the fact that something is being burned. This heat is coming from the large amount of thermal energy released. This is a good indication that it is an exothermic reaction.

Tanya Bearson 2K

Hi! I also have a part time job and am doing research and have definitely found it hard to balance all of my work. There just doesn't seem to be enough time in the day to do everything! I am good about being productive but I think I spend more time than most people on my schoolwork so it adds up. I ...

Tanya Bearson 2K

I agree that the textbook problems and LA worksheets were the most helpful for me. I also think that attending the LA workshops was very beneficial because hearing them go over the questions helped me get a deeper understanding of the concepts. There were multiple topics that I thought I had down bu...

Tanya Bearson 2K

Math 31A/B are single variable calculus and 32A/B are multivariable. My guess is that 31A/B would be the most applicable to the chemistry in this class. Math 33A/B are linear algebra. LS30A/B also cover calculus and it is possible that they are more science related because they are life science clas...

Tanya Bearson 2K

If the bonds of the reactants are stronger than the products it is an endothermic reaction. If the bonds of the products are stronger than those of the reactants it is exothermic. Whether a reaction is exothermic vs endothermic depends on the change in energy of the reaction and so if it takes more ...

Tanya Bearson 2K

You can find heat capacity the same way using either Celsius or Kelvins. In class Dr. Lavelle used the example, 98KJ are required to raise the temperature of ethanol by 2 degree Celsius and calculated the heat capacity to be 49 KJ/C or KJ/K because a raise by 2 degree C is also a raise in 2 degree K...

Tanya Bearson 2K

Does anyone know if Justin's review session was recorded or if there are any more UA review sessions before the midterm?

Tanya Bearson 2K

I do not think we will be expected to know any Ka/Kb values (other than Kw). At the top of the problems for section 6D it says you can use the charts to find the Ka/Kb values. I talked to a TA who said that for problems like this on an exam we will be given Ka/Kb values or a chart similar to how pro...

Tanya Bearson 2K

Could someone explain part b of textbook problem 6D.15? It asks you to calculate the pH of 0.055M AlCl3 (aq). I don't understand how to go about writing the chemical equation for the deprotonation of AlCl3 and I could not find the correct Ka value in the textbook charts. Thank you!

Tanya Bearson 2K

The list of strong acids in our textbook says that HClO3 can be classified as either a strong acid or a weak acid. What are we classifying it as for this class?

https://sites.google.com/site/chempendi ... cids-bases

Tanya Bearson 2K

I also have a TI-84 plus calculator but when I looked up a picture of your calculator it showed both "ln" and "log" on the same button. Maybe your issue is coming from the caluculator using "ln" which is base e instead of "log" which is base 10? If you try pre...

Tanya Bearson 2K

I think this is because all reactions require some amount of energy and release some portion of the energy they use throughout the process. But when we describe a reaction as exothermic or endothermic we are talking about the reaction's change in energy overall energy (final - initial) so we do not ...

Tanya Bearson 2K

We did a Polyprotic Acid problem in my discussion today and the process my TA used was to first treat the acid as a strong acid that fully dissociates from one of its protons. Do this calculation as you would treat any other strong acid in which you say that the concentration of the H+ and its conju...

Tanya Bearson 2K

K = [concentration of the products]/[concentration of the reactants] so if k = 1 this means that the concentration of the products and reactants must be equal because the numerator and denominator of the fraction have to be equal for k = 1. -If k > 1 we know that the concentration of the products is...

Tanya Bearson 2K

If you get two positive values you should try plugging them both in to calculate your final equilibrium values from your ICE table. One of them will leave you with a negative concentration for one of your final equilibrium values which is not possible so you can rule that x value out. I do not think...

Tanya Bearson 2K

In this question, why do we use K = [NO]^2/[N2][O2] instead of its reciprocal with NO as a reactant? I'm confused because I thought that since we are adding NO which makes the reaction shift left we would need to use the K for the reverse reaction.

Tanya Bearson 2K

[H3O+] was not included in the equation because when Ba(OH)2 dissociates, it only dissociates into Ba2+ and OH-. Ba2+ is a spectator ion, so it does not affect our calculations. Then, you can use stoichiometry to see that for 1 mole of Ba(OH)2, there are 2 moles of OH-. Thus, we multiply the concen...

Tanya Bearson 2K

Yes, they are different for every UA. I also didn't take chem 14A with Professor Lavelle but I went to my first UA session earlier this week and found it very helpful. I definitely recommend going!

Tanya Bearson 2K

Thank you all for the tips! Are we allowed to use TI-84 calculators on exams?

Tanya Bearson 2K

I would recommend looking at the products and reactants in the overall equation and comparing the products and reactants in the equations below. If you see similar species, try adding and subtracting (or adding reverse reaction) of multiples of those equations until you get them to equal the equatio...

Tanya Bearson 2K

Anil Chaganti 3L wrote:Adding onto that question, are bars and atm the same thing?

In lecture yesterday Professor Lavelle said that bars and atmospheres are not exactly the same (1 bar = 0.986923 atm) but for our purposes they are used interchangeably.

Tanya Bearson 2K

John Calonia 1D wrote:Q is just the same calculation as K, just at a certain point in time and does not necessarily have to be at equilibrium, correct?

Yes, that is correct. This makes it so the Q and K values are useful to compare like people explained in previous comments.

Tanya Bearson 2K

I think that changes in volume would cause the reaction to shift in order to restore the reaction back to equilibrium. For example, in a reaction with more moles of reactants than products an increase in volume would cause the equilibrium to shift left to favor the reactants. The increase may change...

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