CHEMISTRY COMMUNITY

Eileen Quach Dis 2A

I was wondering for 7D.7 part c, why does raising the temperature increase the rate constant of the forward reaction even more than it does for the rate constant of the reverse reaction?

Eileen Quach Dis 2A

Thank you Dr. Lavelle for being a great teacher for the last two quarters! I really appreciate how much effort you put into making sure we do well with all the office hours/workshops and chemistry community. I'm thankful for how much I've learned in your class and how much I've gained confidence in ...

Eileen Quach Dis 2A

How do we know which half-reaction to use for the other half-reaction that wasn't specified for focus 6.57 and why did the answer key take the square root of Ka to get K? Shouldn't they be the same value?

Eileen Quach Dis 2A

I'd say since each outline has about the same number of questions we should study each outline for an equal amount of time, but there are certain sections within these outlines that are shorter which will probably be tested less on based on last quarter.

Eileen Quach Dis 2A

For problem 6.45, I know that a stronger reducing agent is good at oxidizing and has a low standard E value. However, I don't know which standard e value we use for a given element since there's multiple depending on how many electrons are transferred.

Eileen Quach Dis 2A

For textbook 6N.23 a, we're asked to suggest two metals that could be used for the cathodic protection of a titanium pipeline. I know we're supposed to look for standard reduction potentials smaller than that of titanium. However, when I looked up the titanium reaction in the table I saw that two el...

Eileen Quach Dis 2A

I got the same answer too! I think it's because they used ln instead of log.

Eileen Quach Dis 2A

I got the same answer too! I think it's because they used ln instead of log.

Eileen Quach Dis 2A

The left side of the reaction is the anode side (oxidation reaction), and the right is the cathode side (reduction). These two reactions are separated by the double line, or the salt bridge. We add Pt to whichever half reaction is missing a solid in its reaction. Single lines represent different pha...

Eileen Quach Dis 2A

You would have to write the two half reactions and multiply both by any coefficients necessary to get the same number of electrons to cancel out. This is because the number of electrons lost has to be the number of electrons gained. This number of electrons is the number you should use.

Eileen Quach Dis 2A

They're the same thing. K is the equilibrium constant, and the c just specifies that it's calculated from the concentrations rather than the partial pressure (for gases).

Eileen Quach Dis 2A

Salt bridges help allow the redox reaction to keep occuring. As reduction and oxidation occur, the charges will build up on both sides, which is unfavorable and would cause the reaction to stop. However, since we have a salt bridge that replenishes the ion concentrations on both sides, this keeps th...

Eileen Quach Dis 2A

If k is large, the concentration of products is greater than the concentration of the reactants so product formation is favored.

Eileen Quach Dis 2A

For textbook problem 6N.9, they gave us that the molarity of Sn(NO3)2 was 0.015 M. I was wondering when we calculated Q in the Nernst equation and we had to plug in the value for Sn2+ why we used the same concentration of 0.015 M when they're different compounds.

Eileen Quach Dis 2A

For Textbook Problem 6M.11a, I was wondering how we would be able to write the cell diagram when the phases of the reactants and products aren't given in the problem or in the standard reduction table.

Eileen Quach Dis 2A

For textbook 6M.7 part a, I was wondering how we would know which standard reduction potentials to compare. For example if we were looking for the standard reduction potential of Cu, would we use the potential given when 2 electrons are transferred to form Cu or 3 etc.?

Eileen Quach Dis 2A

I was wondering for 6M.5 part a, why they included Pt on only one side instead of both sides of the cell diagram since both the reactant and product side of the reaction are missing a solid?

Eileen Quach Dis 2A

Write the half-reactions and devise a galvanic cell (write a cell diagram) to study each of the following reactions: Cd (s) + 2Ni(OH)3 (s) → Cd(OH)2 (s) + 2Ni(OH)2 (s), the reaction in the nickel−cadmium cell the half-reactions: anode: Cd (s) + 2 OH- (aq) → Cd(OH)2 (s) + 2 e- cathode: 2 Ni(OH)3 (s) ...

Eileen Quach Dis 2A

Chem_Mod wrote:Which office hour was this?

It was Colin Bertz's Wednesday office hour at 3 and 4 pm.

Eileen Quach Dis 2A

I've tried to go to two different office hour sessions today and I made sure that they were the right day and time but each time zoom tells me to wait for the host to start the meeting even though about 8 minutes have passed. I was wondering if this is happening to anyone else?

Eileen Quach Dis 2A

I was wondering why we don't need to add coefficients in the cell diagram?

Eileen Quach Dis 2A

I was wondering why for textbook problems like 6L.5, the answer key calculates the standard E when it doesn't say to do so in the instructions. Should we do that too?

Eileen Quach Dis 2A

You add Pt(s) if you don't have a conducting solid in the redox reaction. Platinum is a common conducting solid, so it's typically used.

Eileen Quach Dis 2A

Yes, they're the same! d[R] will be a negative value because the concentration of the reactants are decreasing, so we add a negative sign to this result to make it positive like d[P] in d[P]/dt. This makes the rates of change comparable because they would have the same sign.

Eileen Quach Dis 2A

Educated by Tara Westover and Book Thief are really good!

Eileen Quach Dis 2A

Educated by Tara Westover and Book Thief are really good!

Eileen Quach Dis 2A

For 6L.3 part b in the textbook, I was wondering what the gr next to the carbon on the anode half of the cell diagram means.

Eileen Quach Dis 2A

For textbook problem 6K.5, I was wondering why for the O3--> O2 half-reaction we have to add water on the products side. Both sides have the same elements already so I don't know why this is necessary.

Eileen Quach Dis 2A

For acidic redox reactions, if we add water to one side do we have to add H+ to the other side? Or could we add water molecules to the other side instead?

Eileen Quach Dis 2A

For Textbook Problem 6K.3, I was wondering why water was added to the oxidation half of the reaction specifically and not the reduction half? And why was it added in the first place?

Eileen Quach Dis 2A

I was wondering for 6K.1 how we would know carbon was oxidized from -2 to -1 in the redox reaction?

Eileen Quach Dis 2A

Yes because they have more subatomic particles which means that they have a higher degeneracy, and therefore a higher entropy.

Eileen Quach Dis 2A

Could someone explain what standard reduction potentials are?

Eileen Quach Dis 2A

The oxidizing agent is becoming oxidized, so it is losing electrons. The reducing agent is becoming reduced, so it's gaining electrons. I like to think of reduction as reducing a positive charge to become more negative. Hope this helps!

Eileen Quach Dis 2A

I believe it's theoretical because you can't completely prevent energy from entering or leaving a system because of the natural design of the container. We can get close to doing this though using a bomb calorimeter.

Eileen Quach Dis 2A

The salt bridge keeps the reaction on both sides neutral by replacing anions on the anode side and replacing cations on the cathode side. It does this because if the reaction didn't remain neutral electrons would no longer flow to the cathode side since it would be increasingly unfavorable to keep i...

Eileen Quach Dis 2A

I was wondering what particular classes made you interested in medicine/ particular clubs?

Eileen Quach Dis 2A

I was wondering when delta H of formation of a compound should be equal to delta H of the reaction, and when would we have to multiply the moles of a reactant or compound by the delta H of formation to get delta H of the reaction instead.

Eileen Quach Dis 2A

I was wondering why for 4J.5 in the textbook, we can't use the standard gibbs free energy of formation given in Appendix 2A as the answer for the standard gibbs free energy of the reaction since they tell us to use the table in Appendix 2A.

Eileen Quach Dis 2A

For Textbook Problem 4H number 1, I was wondering why HBr has a higher molar entropy than HF, both of which are gases. The answer key said that it's because Br has a larger mass but how does this relate to having a higher entropy?

Eileen Quach Dis 2A

ΔH° is the change in enthalpy under standard conditions, while ΔH is just the change in enthalpy.

Eileen Quach Dis 2A

MnO4- is being reduced and Fe2+ is being oxidized. Oxygen has a oxidation number of 2- since it tends to gain two electrons to complete its valence shell. Therefore O4 has a 8- charge and since the overall charge of MnO4- is 1- that must mean that Mn originally has a 7+ oxidation number. MnO4- becom...

Eileen Quach Dis 2A

For textbook problem 4F.13, I was wondering why cooling the products back to 85 degrees Celsius would be one of the steps that we have to take into account since the question is asking for the standard change in entropy of the vaporization of water at 85 degrees Celsius.

Eileen Quach Dis 2A

For Textbook Problem 4.5, I was wondering why the answer key took the ratio of heat absorbed by the liquid water,3135 J/0.5 hr, and multiplied it by 10 hrs. Shouldn't it be 10.5 hours?

Eileen Quach Dis 2A

For focus problem 4.1, I was wondering why we can use delta H to calculate heat absorbed for each step of the reaction. Why can we assume that heat absorbed was at a constant pressure when it wasn't mentioned?

Eileen Quach Dis 2A

I was wondering why for problem 4D.9, the change in enthalpy of the reaction was made positive by the answer key when it was originally negative.

Eileen Quach Dis 2A

Is standard change in enthalpy kJ per one mol, while change in enthalpy is just in moles?

Eileen Quach Dis 2A

Could someone explain why in Problem 4C.7 in the textbook we calculate the change in enthalpy by finding the heat supplied divided by the moles? I don't remember this being a formula.

Eileen Quach Dis 2A

This was really helpful. Thank you!

Eileen Quach Dis 2A

I was wondering for Problem 4C.3a in the textbook, why the answer key wrote n*Cp*deltaT and replaced Cp with 5/2 *R.

Eileen Quach Dis 2A

Could someone explain how to do 4A.13?

Eileen Quach Dis 2A

For Problem 4A.3 in the textbook, when calculating for the change in volume, the answer key multiplied by 1L=1000cm^3. I was wondering how we would know that 1L is equal to 1000 cm^3 based off of the equation sheet.

Eileen Quach Dis 2A

For Problem 4A.3 in the textbook, when calculating for the change in volume, the answer key multiplied by 1L=1000cm^3. I was wondering how we would know that 1L is equal to 1000 cm^3 based off of the equation sheet.

Eileen Quach Dis 2A

I was wondering what the difference is between dT versus ΔT?

Eileen Quach Dis 2A

Yes, phase does matter in Hess's law. It's not enough to just look for the change in enthalpy of the compound name.

Eileen Quach Dis 2A

On the equation sheet, looking at the multiple possible values for R, you can look at what units are being used and plug that into whatever problem you're solving to see if the units cancel.

Eileen Quach Dis 2A

Compression is an example of work done onto the system because the energy lost from compression is going into the system.

Eileen Quach Dis 2A

A closed system has a fixed amount of matter, meaning that it's sealed off but energy can still go into the system. For example, if you're holding a sealed container, it's a closed system because there's a fixed amount of matter but energy in the form of heat from your hand can still enter the syste...

Eileen Quach Dis 2A

I was wondering why in today's lecture when Professor Lavelle was explaining dS=dq/T that the temperature would be constant if the change in entropy and heat are infinitesimally small?

Eileen Quach Dis 2A

I was wondering why molecules in the gas phase occupy more states than liquids and solids?

Eileen Quach Dis 2A

Could someone clarify what entropy is?

Eileen Quach Dis 2A

I recommend planning to finish your work each day right before office hours. I feel more motivated to do my work when I know that if I get stuck I can get help right away. I also recommend following guided meditations on Youtube for example to help clear your mind for 15 minutes because those really...

Eileen Quach Dis 2A

First, draw the Lewis structure of the reactants and products. Then compare the reactants and products to identify which bonds must have been broken and which must have been formed to get the new molecules. Next, take the bond enthalpies of the broken bonds and the enthalpies of the formed bonds (wh...

Eileen Quach Dis 2A

A closed system has a fixed amount of matter because the system is sealed off, so therefore, substances can't be added or taken away and the volume doesn't change.

Eileen Quach Dis 2A

Work isn't a state function because it's necessary to know the intermediate steps and not just the final and initial. For example, with the two hikers on the mountain in Lavelle's old lecture, even if their change in altitude was the same, one path took more work because the hiker hiked a longer pat...

Eileen Quach Dis 2A

Yes, the internal energy is the energy within the system, not in the surroundings. If the internal energy is decreasing that means that the system is losing heat or doing work by expanding. If the internal energy is increasing, that means that the system is gaining heat or having work done onto it t...

Eileen Quach Dis 2A

In today's lecture, at around 28:33, Professor Lavelle gave an example where there was a closed system but the volume was still changing and I'm still confused about how the volume could still change if the system is closed.

Eileen Quach Dis 2A

Some of my recommendations are Hozier, Riles, Bruno Major,Duckwrth, Still Woozy, and Claire Rosinkraz!

Eileen Quach Dis 2A

I was wondering why the answer key didn't include N2 in the calculations for the standard enthalpy of the reaction for 4D Problem 17 in the textbook?

Eileen Quach Dis 2A

I know Professor Lavelle said that sections 4D and 4E are most relevant to the midterm, but I was wondering if we need to do problems 4A to 4C at all still or if we will come back to them later since they weren't lectured on.

Eileen Quach Dis 2A

The reaction is within the system and the surroundings are whatever is outside the system, or doesn't include the reaction.

Eileen Quach Dis 2A

Ice melting is endothermic because heat is going inside the system, or the ice cube, to melt it. For an exothermic reaction, heat is being released into the surroundings and out of the system so that's why the surroundings are gaining more heat. Hope that helps!

Eileen Quach Dis 2A

Hydronium will be in a higher concentration for an acidic solution, and hydroxide will be in a higher concentration for basic solutions.

Eileen Quach Dis 2A

When the equilibrium constant is less than 10^-4 you can assume x is insignificant and not include it in the denominator. If you really want, you can verify if it was okay to use the approximation for a given problem by checking if the percent ionization is less than 5%.

Eileen Quach Dis 2A

Can someone explain what Professor Lavelle meant in the very beginning of today's lecture that a change in Kelvin is the same as a change in Celsius?

Eileen Quach Dis 2A

For Problem 4A.1 in the textbook, I was wondering if someone could explain parts c and d?
Here's the problem:
Identify the following systems as open, closed, or isolated:
(c) a bomb calorimeter in which benzene is burned
(d) gasoline burning in an automobile engine

Eileen Quach Dis 2A

x is still equal to some value and not zero. If it was equal to zero the numerator and denominator would be zero and the entire fraction would be zero so it wouldn't make sense. I'm assuming we keep x^2 in the numerator bc although x may be a small value, x^2 is large enough to be included.

Eileen Quach Dis 2A

For the compound CH3NH3Cl in problem 6D.13, how do we know if it's a salt or base? I know weak bases contain ammonia in them but I still can't tell if this would be a salt or not.

Eileen Quach Dis 2A

I was wondering if we're supposed to use the tables to solve Problem 6D.5a. I know the pka value was given but when I calculated the ka value from it and then the kb value, it didn't match the answer key.

Eileen Quach Dis 2A

I know what the strong acids and bases are as well as what the weak acids and bases are, but sometimes I can't tell if a compound is a salt or if it's an acid/base. How can I tell the difference?

Eileen Quach Dis 2A

I was wondering for textbook problem 6D.3b how did we know that the compound was a base when writing the reaction? I know we can't just assume that it's a base even when they're asking for the kb value so I was wondering how else would we know.

Eileen Quach Dis 2A

I was wondering if someone could explain why a lower pka means that an acid is stronger and why a lower pkb means that a base is stronger? Also, do higher Ka and Kb values correspond to stronger acids and bases or weaker acids and bases?

Eileen Quach Dis 2A

For Problem 6B.11 part ii in the textbook, I used the M*V of the initial solution=M*V of the final solution equation to try to find the molarity of the original solution. I was wondering why the answer key used the 5 ml that was transferred for the volume of the original solution instead of the volu...

Eileen Quach Dis 2A

Ka and Kb are both equilibrium constants for reactions, but Ka is used when an acid is involved in the reaction, while Kb is used when a base is involved in the reaction. Their equations are both the ratio of the concentration of products over the concentration of reactants.

Eileen Quach Dis 2A

They're always the same in concentration because when H3O forms that means that a water molecule donated a proton to H2O, which also must mean that the water molecule became OH once it donated its proton.

Eileen Quach Dis 2A

It can also sometimes be in bars, and in that case, you wouldn't need to convert any units and can just write the number directly into the ICE table.

Eileen Quach Dis 2A

You only include water in reactions when it's not a liquid. Liquids or solids aren't included in k because they're in so much excess that any change to their concentration doesn't change their overall concentration by much so their concentrations would cancel out in the numerator and the denominator...

Eileen Quach Dis 2A

The conjugate base of a weak acid is a strong base, so they are opposites in strength.

Eileen Quach Dis 2A

I was wondering whenever we form an ICE Table, how do we know which concentrations will increase and which will decrease? At first, I assumed that products' concentrations will always decrease and reactants' concentrations will always increase, but that doesn't seem to always be the case.

Eileen Quach Dis 2A

Can someone explain how to do part a in Number 5.35? I'm confused on how to balance the equation from looking at the graph.

Eileen Quach Dis 2A

In today's lecture for the example that involved the reaction Ba(OH)2--> Ba+2OH, I was wondering why Professor Lavelle wrote Kw as equal to the hydronium concentration multiplied by the hydroxide equation. Why didn't he include Ba in the equilibrium constant when it's not a solid or liquid?

Eileen Quach Dis 2A

We get points for both.

Eileen Quach Dis 2A

Yes, only temperature can change K.

Eileen Quach Dis 2A

Hi! I think breaking up the outline problems in chunks throughout the week makes things a lot more manageable and gives you more time to ask questions if you need to so you can understand the content better, since I personally tended to cram last quarter. I also would recommend to go to workshops to...

Eileen Quach Dis 2A

You use it usually when you want to solve for the concentrations of the reactants and products at equilibrium given the initial concentrations of the reactants and products and the k value.

Eileen Quach Dis 2A

You raise the concentrations of each reactant and each product to the power of that coefficient in the fraction. Make sure that the reaction is balanced first so you have the right coefficients.

Eileen Quach Dis 2A

If a reaction favors the left side/reverse reaction, it means that it will try to create more reactants, while if a reaction favors the right side/forward reaction, it will try to create more products.

Eileen Quach Dis 2A

Yes, but you should also be working on the outline problems on your own since some of them are on the test and they can pile up if you don't work on them throughout the week.

Eileen Quach Dis 2A

For liquids, their concentrations don't change because they are in so much excess that the change is very minimal in comparison to their concentrations. When we write the expression for k, since their concentrations don't change on the reactant and product side, they would cancel out in the numerato...

Eileen Quach Dis 2A

When do we know when to use the ICE table? I'm not sure how to tell if the concentration that's given in a problem is the concentration at equilibrium already or if its a concentration not at equilibrium.

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