CHEMISTRY COMMUNITY

Jessa Maheras 4F

KElviN!!!!

Jessa Maheras 4F

For this one, I used conceptual reasoning that because A is the only rxn with all reactants and products as solids, it will have very small changes in S, therefore dG and dH should be similar. :)

Jessa Maheras 4F

For a closed system, heat can be exchanged but volume remains constant. An open system has constant pressure yet a changing volume. An isolated system has no energy exchange whatsoever (eg. bomb calorimeter). So, in an isolated system, if it has no exchange of energy, can work be done? What would t...

Jessa Maheras 4F

Robin Cadd 1D wrote:
Jessa Maheras 4F wrote:In the book, it says that in order to use the Van't Hoff Eq for runs involving gases, you have to convert from K too Kc. What is the difference between the two terms?

For gases, you automatically assume that K is Kp. Converting K to Kc is just converting K to Kp

Oh alright, thanks!

Jessa Maheras 4F

Julie_Reyes1B wrote:In the book, K without a subscript refers to Kp, whereas in Dr. Lavelle's class, both terms will be identified using the subscripts.

Thank you Julie that makes sense!!

Jessa Maheras 4F

Adsorption and Absorption differ in how they function and the state of the species involved. The above answers explain it well! But, why is it important to understand the difference between the two? In the last lecture he mentioned that reactants sit on the surface of a catalyst (adsorption) becaus...

Jessa Maheras 4F

Because entropy is a state function, you can calculate the change in entropy (of the system) as though the expansion occurred reversibly! You would calculate the change in entropy from a change in volume, assuming constant temperature (∆S = nRlnV2/V1), and the change in entropy from the change in t...

Jessa Maheras 4F

Because entropy is a state function, you can calculate the change in entropy (of the system) as though the expansion occurred reversibly! You would calculate the change in entropy from a change in volume, assuming constant temperature (∆S = nRlnV2/V1), and the change in entropy from the change in t...

Jessa Maheras 4F

An isolated system will be under constant pressure because by definition nothing will change within the system: Internal energy is constant. Hope this helps!

Jessa Maheras 4F

Actually, closed systems don't prevent volume changes! A system can change in volume and still be closed, as long as no matter is exchanged between the system and surroundings. (Think of a piston)

Jessa Maheras 4F

Deena Doan 2F wrote:It's most likely going to cover all concepts, but there probably is going to be a heavier emphasis on kinetics and thermo.

I also think we should expect to see a lot of thermo especially since it wasn't covered much on the midterm!

Jessa Maheras 4F

I believe that there is a negative sign due to the loss of energy.

Jessa Maheras 4F

We won’t be needing to use steady state to solve problems in 14B, from my understanding!

Jessa Maheras 4F

To determine the balanced reaction for a basic solution just start with adding as many H2O are needed to balance H, then Twice as many OH on the same side and twice as many H2O on the opposite side.

Jessa Maheras 4F

Manav Govil 1B wrote:This is a helpful link if you're confused!

https://www.khanacademy.org/science/che ... r-small-kc

Thank you this link is very helpful!

Jessa Maheras 4F

These are just from his unit outlines (I included industrial and environmental as well): Unit 1 (Chemical Equilibrium): ATP hydrolysis, osmotic pressure Unit 2 (Acids and Bases):Carbon dioxide reacts with water to form carbonic acid, which makes carbonated drinks acidic, acidic rain, rivers, and la...

Jessa Maheras 4F

Adsorption and Absorption differ in how they function and the state of the species involved. The above answers explain it well! But, why is it important to understand the difference between the two?

Jessa Maheras 4F

Jessica Booth 2F wrote:Correct, they should be replaced using the equilibrium equation solved for the intermediate.

Can you explain how this works? This process is a bit confusing. Thank you!

Jessa Maheras 4F

dG = max work possible ! This is because ideally, all energy released in the reaction would be used to do work. This is not realistic in nature however, because energy dissipates, etc.

Jessa Maheras 4F

Yes, there's usually a pattern you can follow: anything with an OH- is usually a strong base (ex. KOH), and any compound preceded with an H and from the halogen group is usually a strong acid (HBr, HCl, etc.). But any compound with an NH3 is usually a weak acid, and others you can just memorize, li...

Jessa Maheras 4F

I believe it would be B because there is a greater concentration of reactants colliding! Because there are more reactants colliding, more energy will be released and a larger dT will result. :)

Jessa Maheras 4F

Delaney Smith 1C wrote:Wait, how do you solve for k if you don't have [A]t?

Just use the other formula including k! The half life equation:)

Jessa Maheras 4F

Half life equations are given in the equation sheet, but they will not tell you which half-life equation corresponds to which order of reaction. You can also derive them using the standard half life equation, solving for t when the concentrations are half of the initial. That’s really helpful, than...

Jessa Maheras 4F

Yes, the units of the rate constant are representative of the order of the reaction because the units of the rate constant must cancel out with tge units of the rate law.

Jessa Maheras 4F

Why does the slow step determine rate law ? The slow step determines the overall rate law because the overall rate of the reaction can only be as fast as the slowest step. If that makes sense. It's kind of like how a chain is only as strong as its weakest link. Hope that helps? :) That makes lots o...

Jessa Maheras 4F

ALegala_2I wrote:Are zero order reactions common?

Yes I think they are less common than 1st order but definitely more common than third. That’s a good q for dr. Lavelle!

Jessa Maheras 4F

The one with ln has been rearranged so that you can create a graph of certain values that will result in a straight line, something that can't be done with the previous equation. Yes, the reason is important to consider! But a question: why would we want to plot it in a straight line? Is it to see ...

Jessa Maheras 4F

Shannon Asay 1C wrote:I believe you could use the equation ln(k2/k1)=-Ea/R*(1/T2-1/T1). Just plug in all your variables and solve for Ea.

Yes, I agree! All you do is rearrange the equation and plug in values.

Jessa Maheras 4F

Change in activation energy: Ea increases, k decreases and vice versa

Jessa Maheras 4F

He means that the forward and reverse rxns follow the same pathway, this is assumed in order to say k/k’ =K.

Jessa Maheras 4F

The pre-eq method is mentioned in Dr. Lavelle’s notes! You can also find it in section 7C. Essentially, it is when a step that comes before another and equilibrium is met in the prior elementary rxn. You can use this info to verrify if a rxn mechanism is appropriate.

Jessa Maheras 4F

A shorter version of putting the above, in order for AgBr to show up in the balanced redox rxn, you have to include it in one of your half runs. :)

Jessa Maheras 4F

O3 is being reduced, but the half reaction should not be going from O3 --> O2. Rather, it should be going from O3 to BrO3-. Here, the oxidation number of oxygen goes from 0 to -2, which is why this the reduction half reaction (as electrons are being gained). I think so too! It is important to consi...

Jessa Maheras 4F

I think it's always easier to simplify first! Saves some time. Just be careful to make sure you balance electrons when writing the net equation!

Jessa Maheras 4F

You need an inert conductor in order to complete the cell. Pt is most commonly used to do this, and is also known as a Standard Hydrogen electrode! I found the textbook helpful in explaining this:)

Jessa Maheras 4F

The states will remain the same, as long as you are consistent in carrying them through.

Jessa Maheras 4F

I hope this was helpful!! Let me know if anything was confusing.

Jessa Maheras 4F

Yes, there are various ways to determine Anode vs. Cathode depending on informational you are given. By reduction potentials, the Anode has a more negative potential. In a cell diagram, the anode is on the left. Given a redox rn, the anode will be the half run that you identify as oxidation. The cat...

Jessa Maheras 4F

I hope this is helpful!

Jessa Maheras 4F

Yes! Always use the order balance main elements, balance H/O, then balance charge.

Jessa Maheras 4F

First, you have to write the reduction half reactions using the non- H/O elements (find these in the appendix - they are helpful!). Then, balance these in order of non-H/O elements, then H/O, then for charge. Then depending on which is the anode and which is the cathode, reverse the anode run to mak...

Jessa Maheras 4F

Daniela Shatzki 2E wrote:this might be a helpful guideline: https://socratic.org/questions/how-do-y ... a-compound

Thank you Daniela this is really helpful!

Jessa Maheras 4F

Why does the textbook note pH when discussing electrolytic calls? What impact does pH hav on determining at which electrode reduction/oxidation will occur?

Jessa Maheras 4F

Hey, I'm confused on the acknowledgement in the textbook that in order to express a reaction in half reactions, the reaction doesn't have to be redox. How is this so? How can you express non-redox reactions as half reactions?

Jessa Maheras 4F

Hi guys. The solutions manual doesn't explain how 6L.3 is worked out and E standard values are given for each half rxn. I'm a bit confused can someone explain?

Jessa Maheras 4F

The C should be a graphite electrode! You can tell this because it is on the far end of the cell diagram.

Jessa Maheras 4F

Why does run Gibbs Free Energy change when multiplied by a factor and Ecell does not? I understand this can be explained by deltaG=-nFEcell, however, I don't understand the explicit connection.

Jessa Maheras 4F

Hi Jasmine! FIrst, I found Dr. Lavelle's walkthrough on balancing redox runs very helpful, you can fin these in a recent email of his. But, he doesn't include how to figure out Oxidation #'s, which is necessary to start the problem. Figure out the oxidation #'s: O and H have #'s that stay the same, ...

Jessa Maheras 4F

Can someone explain how hydrogen electrodes work? I think my key confusion is how the hydrogen and platinum function to act as an electrode.

Jessa Maheras 4F

Edit to my question: Why can we assume that Cl2 is going to be reduced to form 2Cl-?

Jessa Maheras 4F

Can someone explain how to write this problem as an oxidation half rxn? I don't understand why there can be a net charge of 2- on the last side and a neutral charge on the right. Further, how can Cl2 act as both a reducing and oxidizing agent. Thank you!

Jessa Maheras 4F

When you balance a redox reaction in basic solutions, you use H20 and OH- on each side of the half reaction, whereas when in an acidic solution, you use H20 and H30+. To determine whether to use H20 vs. its protonated/deprotonated form, see whether you need more O or more H on either side of the equ...

Jessa Maheras 4F

In the book, it says that in order to use the Van't Hoff Eq for runs involving gases, you have to convert from K too Kc. What is the difference between the two terms?

Jessa Maheras 4F

I think that the heat capacity is used in the equation \Delta S=\frac{q}{t} , where the heat capacity is used to calculate the value of q using the equation q=mc\Delta T Yes that makes lots of sense thank you! From what I understand now, C=q/mdeltaT , and you can solve for q and use that to find mo...

Jessa Maheras 4F

I think they mean that there is a point where the Gibbs free energy of ice and Gibbs free energy of water are equal, so there is no change in it and it is at equilibrium. There is a graph in the section that has a diagram of temperature vs molar Gibbs free energy where the liquid and solid states i...

Jessa Maheras 4F

At a constant volume, deltaV is zero, so there is no expansion work occurring (w=0) and deltaU overall will only equal q. At a constant pressure, since there may be expansion work occurring, the heat given off can only be interpreted as deltaH or q, since the overall internal energy includes the en...

Jessa Maheras 4F

How can you identify when you need to break the reaction down into 3 steps of heating, vaporization, then cooling? In the situation like described in my question! If you need to find entropy of transition at a temperature other than the boiling/melting point, then you need to break the process into...

Jessa Maheras 4F

Approach a problem in calculating the entropy of transition the same as you would in calculating the qtotal of a substance being raised from a non-boiling-point temperature to its boiling point and transition. Set up two separate components for the entropy for the system and add them: 1) the entrop...

Jessa Maheras 4F

For a closed system, heat can be exchanged but volume remains constant. An open system has constant pressure yet a changing volume. An isolated system has no energy exchange whatsoever (eg. bomb calorimeter). So, in an isolated system, if it has no exchange of energy, can work be done? What would t...

Jessa Maheras 4F

In the textbook 4J: If DeltaG=0 for such a process, then you know at once that the system is at equilibrium. For example, when ice and water are in equilibrium with each other at a particular tempera- ture and pressure, the Gibbs free energy of 1 mol H2O(l) must be the same as the Gibbs free energy ...

Jessa Maheras 4F

The textbook says that you can use heat capacity data to determine the standard molar entropy of a substance and discusses this in 4H.1, but I don't understand how this is done. Can someone explain how or the connection between heat capacity and molar entropy?

Jessa Maheras 4F

Equations 5 and 6 give the entropy change at the transition temperature. To find the entropy of transition at another temperature, the calculation has to be broken down into three steps (1). For example, to find the entropy of vaporization of water at 25 8C and 1 bar: 1. Heat the liquid from 25 8C t...

Jessa Maheras 4F

In 4D, the textbook says: A constant-pressure calorimeter and a constant-volume calorimeter measure changes in different state functions: at constant volume, the heat transfer is interpreted as DeltaU; at constant pressure, it is interpreted as DeltaH (Topic 4C). Why is this so? From my understandin...

Jessa Maheras 4F

For A.13, A constant-volume calorimeter was calibrated by carrying out a reaction known to release 3.50 kJ of heat in 0.200 L of solu- tion in the calorimeter (q 5 23.50 kJ), resulting in a temperature rise of 7.32 8C. In a subsequent experiment, 100.0 mL of 0.200 m HBr(aq) and 100.0 mL of 0.200 m K...

Jessa Maheras 4F

From Textbook: If the external pressure were to be increased even infinitesimally at any stage of the expansion, the piston would move in instead of out. Therefore, the work done during a reversible expansion of a gas is the maximum expansion work possible. This is a very important general point: Th...

Jessa Maheras 4F

I understand the difference between open, closed and isolated systems, but what is the significance of recognizing and understanding what type of system a reaction is when answering problems and doing calculations? Does the type of system affect what must stay constant in a reaction? What informatio...

Jessa Maheras 4F

Still don’t fully understand what we need to know about titrations with their relation to acids and bases, plz help!

Jessa Maheras 4F

In lecture, Dr Lavelle mentioned similarity of doing salt calculations to doing titrations. How are titrations related to equilibrium, what was he referring to? How is calculating the pH of a salt solution like a titration? Thank you!

Jessa Maheras 4F

For 5.35, how can we tell what the molar ratios are? 2A —> B+ 2C

Jessa Maheras 4F

We haven't discussed that, so I think we shouldn't worry about it!

Jessa Maheras 4F

Polydentate ligands are chelating, because if a ligand bonds to a transition metal at multiple locations it will inherently form a ring around it.

Jessa Maheras 4F

At this point, I think it would be helpful to look over homework problems and make sure you understand them, do a few that you identified that were previously difficult for you, and do the same for the past exams.

Jessa Maheras 4F

Yes! The only exception is when you have a radical, but those are very unstable and you won't draw one unless it is indicated.

Jessa Maheras 4F

We don't cover equilibrium so I also don't think we need to worry about it!

Jessa Maheras 4F

https://www.youtube.com/watch?v=011Bj5USal8 here you go! If you just search ligands or coordination compounds on youtube there are more helpful videos.:)

Jessa Maheras 4F

There must be an alternate arrangement of double and single bonds for there to be resonance! Therefore, you must need at least 3 terminal atoms.

Jessa Maheras 4F

Pi bonds only form between unhybridized p orbitals. Hybridization explains the orbitals that atoms use to form single bonds.

Jessa Maheras 4F

The textbook writes, "The acidic, amphoteric, or basic character of the oxides of the d-block metals depends on their oxidation state." How does oxidation state of the metal affect the character of the d-metal oxide?

Jessa Maheras 4F

Hi Doreen, what question is this on the homework?

Jessa Maheras 4F

We are given the Lewis and Bronsted definitions of acids in class. Each definition makes sense on its own, but how are the two definitions related? Does the classification of acid or base change depending on how you define it? Or is a Lewis acid also a Bronsted acid? (Even though it seems like this ...

Jessa Maheras 4F

Note: When I say "Linear combination", I mean "linear combination of atomic orbitals", just to clarify!

Jessa Maheras 4F

How are hybrid orbitals a result of linear combination? For example, an sp orbital is written to be h1= s + p and h2= s - p. It gets more complicated for sp2 and sp3 orbitals (all of them are written in the textbook). Can someone explain how this works? Also - what is the significance of understandi...

Jessa Maheras 4F

Hi guys, why does bond angle increase as s character increases? There was a homework problem that asks about this, but I don't understand how s character influences bond angle. Thank you!

Jessa Maheras 4F

Does each unpaired electron in a hybridized orbital represent a potential bond the atom can form? Why?

Jessa Maheras 4F

How can you tell if promotion is possible in an atom? How does it relate to hybridization?

Jessa Maheras 4F

The textbook describes sigma bonds as having no nodal planes containing the internuclear axis - what does this mean? How does it compare with pi bonds?

Jessa Maheras 4F

Thank you so much!!

Jessa Maheras 4F

I believe that there is a degree of interrelatedness! The clear distinction between Brontead and Lewis is the part of the atom the theory focuses on.

Jessa Maheras 4F

I know Dr. Lavelle said to seek out additional resources regarding this! I think it goes beyond what we see in lecture and that you can ask some UA's or Dr. Lavelle himself. :)

Jessa Maheras 4F

The textbook provides an example of a weak acid as acetic acid, on pg. F75. After providing a chemical equation for the Acid-Base reaction, the textbook claims that "only a small fraction of its molecules undergo deprotonation". Why does only a small fraction of acetic acid undergo deproto...

Jessa Maheras 4F

Can someone explain the concept of protonation? What exactly is it that determines how protonated a base is, or how deprotonated an acid is? It sounds like, "the number of molecules that have gained/lost a proton" (respectively) but in the example the textbook provides it seems like how pr...

Jessa Maheras 4F

Can someone explain the difference between Lewis and Bronsted acids and bases? Thank you!

Jessa Maheras 4F

In what ways can a pi bond result in a molecule being polar? Why does this occur? Examples of this situation? Thank you!

Jessa Maheras 4F

What does it mean for electron density to be spread along the nuclear axis rather than on each side of the internuclear axis? Which corresponds to sigma and which to pi bonds?

Jessa Maheras 4F

Hi guys, can sigma bonds and pi bonds only form between atoms with specific orbitals? Why are some atoms able to form pi bonds and others unable to?

Jessa Maheras 4F

Why is a lone pair present on the electronegative atom necessary for hydrogen bonding to take place?

Jessa Maheras 4F

In the formula for intermolecular energy, the value for Ep is always negative. How is this interpreted conceptually?

Jessa Maheras 4F

Even though we don't need to know the particular distinction between van Der Waal interactions, London forces, dispersion forces and induced-dipole induced-dipole interactions, can anyone explain the how they are different and what the connections between them are? Just for funsies haha thank you!

Jessa Maheras 4F

When talking about the inter ionic forces and boiling points of ionic compounds, are we talking about between +/- ions or between ionic compounds? From what I understand, we are talking about the interaction between ions - can someone clarify this?

Jessa Maheras 4F

Hi guys, I'm having trouble understanding the rule regarding strength of inter-ionic forces. How does the strength of an inter-ionic force vary with changing factors?

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