CHEMISTRY COMMUNITY

Robin Cadd 1D

Abigail Menchaca_1H wrote:How does a concentration cell work?

In a concentration cell, the driving force is the difference in concentrations (as opposed to a regular galvanic cell, in which the driving force is the flow of electrons). Ions flow from one cell to the next to balance out these concentrations

Robin Cadd 1D

nshahwan 1L wrote:How would you define gibbs free energy in laymens terms?

I would define it as the amount of energy free to do work in a system.

Robin Cadd 1D

MaryBanh_2K wrote:When solving for k, do both of these derivations mean the same thing: (ln([Ao]/[[A]))/t AND (ln[A]/[Ao])/-t? The book uses the first equation but I'm not sure if the two equations mean the same thing because I am getting a different answer.

Yes, they’re equivalent expressions.

Robin Cadd 1D

On test 2 someone explained to me that on one of the questions you had to know your solubility rules but I don't remember any of that so does anyone have a good source where I could learn them? I don’t think you needed to know solubility rules for this exam; however, you did need to be able to pred...

Robin Cadd 1D

The textbook defines molecularity as the number of reactant moles, atoms, or ions taking part in a specified elementary reaction.

Robin Cadd 1D

Nick Lewis 4F wrote:What is the difference between zero, first and second order reactions?

Zero, first, and second order reactions also differ in their mechanisms, which Lavelle will talk about later in the course.

Robin Cadd 1D

Marni Kahn 1A wrote:do we have to know the graph of [A] vs time or just ln[A] vs time for the first order rate law and integrated rate law?

I think that we should know both graphs, considering that Lavelle discussed both of them in class.

Robin Cadd 1D

My TA said the exact same thing as your TA did. I think if you follow what the TA said, you should be fine.

Robin Cadd 1D

Reaction order is essentially the power to which a reactant concentration is raised in order to give an accurate relationship between it and the rate of the overall reaction. how do you find this number You could also look at plots of the concentration v. time. This link provides helpful visual ima...

Robin Cadd 1D

One of the important takeaways from the lecture is that kinetics deals with how fast a reaction occurs. As a result, we’re concerned a lot with rates in this chapter.

Robin Cadd 1D

TanveerDhaliwal3G wrote:What is the galvanic/voltaic cell and how is it different from an electrochemical cell?

The phrase “electrochemical cell” is an umbrella term, including galvanic/voltaic cells. For the purpose of this course, electrochemical cells also include electrolytic cells.

Robin Cadd 1D

No, we don’t need to know about how rechargeable batteries work, but the textbook does mention it in passing. Basically, when a rechargeable battery is being used, it works like a galvanic cell. When it is being charged, it functions as an electrolytic cell.

Robin Cadd 1D

805097738 wrote:
Kate Osborne 1H wrote:standard conditions are a specific ratio of products to reactants and if the ratio is not that then you have to use the nernst equation

are you referring to K? what else would a specific ratio be

I’m pretty sure standard conditions are just 1 M and 25°C.

Robin Cadd 1D

If you are referring to n in the equation \Delta G=-nFE , then n is the number of moles of electrons in the balanced redox reaction. Also, if it’s properly balanced, the number of moles of electrons will be the same on both sides, so you don’t have to worry about selecting between the number of ele...

Robin Cadd 1D

Platinum is introduced into the cell diagram when there are no solid metals as part of the anode or cathode of the cell diagram. It serves as an inert electrode (provides a surface for the transfer of electrons, but does not affect or participate in the redox reaction). Another important point to n...

Robin Cadd 1D

In an equation, you can also look at oxidation numbers. Oxidized elements will have an increased oxidation number in the products. Reduced elements will have a decreased oxidation number. To add on, you can determine oxidation numbers by using a set of rules. This links provides some helpful inform...

Robin Cadd 1D

Marni Kahn 1A wrote:Why do larger, more complex molecules possess larger standard entropies than simpler, smaller molecules in the same phase?

You could also think of more complex molecules having greater disorder, as there are more particles that make up the molecules (protons, electrons, etc.)

Robin Cadd 1D

G is the general term; G knot refers to G under standard state conditions (usually 1 atm and 25 degrees Celsius).

Robin Cadd 1D

Test 2 will be all new material covered after the midterm.

Robin Cadd 1D

605110118 wrote:What is the difference between k1 and k2?

K1 is the equilibrium constant for the first dissociation; K2 is the equilibrium constant for the second dissociation. K1>>>K2

Robin Cadd 1D

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

Robin Cadd 1D

For constant pressure the Cv would actually be switched to CP. Is this actually true? I thought that this equation for delta U only works with Cv. For example, in an isobaric process, q = nCp(delta T) and w = -P(delta V) = -nR(delta T). Thus delta U = q + w = n(Cp - R)(delta T). Since Cv = Cp - R, ...

Robin Cadd 1D

I don't think it matters.

Robin Cadd 1D

If the system does the work, the work is negative.

Robin Cadd 1D

Delta S refers to the entropy of the system, and Delta Stotal refers to the total entropy (entropy of the system + entropy of the surroundings).

Robin Cadd 1D

Katie Kyan 2K wrote:Using the Ideal Gas Law we know that PV=nRT where P and V have an inverse relationship. This is why we can use P1/P2 in place of V2/V1.

This is called Boyle's Law.

Robin Cadd 1D

Could someone please explain how to find the stoichiometric coefficents for the balanced equation in problem 5.35?

Robin Cadd 1D

Correct! Just remember work = -Pdeltav.

Robin Cadd 1D

Ashley Fang 2G wrote:The Boltzmann Equation is: S = K_BlnW
It shows the relationship between entropy and the number of ways the atoms or molecules of a thermodynamic system can be arranged.

Accordingly, the Boltzmann equation can be used to solve for entropy.

Robin Cadd 1D

Whenever there's no change in volume, delta v = 0.

Robin Cadd 1D

In addition to what everyone else has posted, it's also important to know why Hess's Law works. Because enthalpy is a state function, you don't have to consider the processes that it took to go from the reaction's final to initial state.

Robin Cadd 1D

Basically, an isolated system can't exchange matter or heat with its surroundings. The cloud-like drawing around the flask represents insulation, and it's meant to convey that heat isn't being exchanged with the surroundings.

Robin Cadd 1D

Either works! Choose whichever one is most convenient for the problem.

Robin Cadd 1D

Micah3J wrote:What are some other examples of extensive properties?

Examples of extensive properties include mass and volume.

Robin Cadd 1D

In general, if heat is used in the reaction, the reaction is endothermic. If heat is released by the reaction, the reaction is exothermic.

Robin Cadd 1D

Either works, since a change in 1 degree Celsius is equivalent to a change in 1 Kelvin.

Robin Cadd 1D

chari_maya 3B wrote:Is a bomb calorimeter an isolated system?

It is a closed system, since heat can be exchanged.

Robin Cadd 1D

AKatukota wrote:What should we know about the activity of a reaction?

We talk about activities when we talk about K. When we use partial pressures and concentrations to calculate K, we're actually using approximations. In reality, K is calculated by using activities.

Robin Cadd 1D

Although rare, what you have described is entirely possible. I think they're called superbases or superacids.

Robin Cadd 1D

We will not cover the Van't Hoff Equation for this section of the course, and we're not expected to know it for any exams. Beyond it being useful to solve problems involving ICE boxes and chemical equilibrium, I'm not entirely sure what it's used for either. It relates changes in temperature to chan...

Robin Cadd 1D

Look at the units of pressure to differentiate between the R constants. Whichever R constant contains the same units of pressure as the data you have is the one you should choose to make further calculations.

Robin Cadd 1D

K refers to the equilibrium constant. Kc is the equilibrium constant calculated by using concentrations. Basically, Kc is a subset of K.

Robin Cadd 1D

In addition to what everyone else has mentioned, make sure the temperatures you are comparing to those listed in the equilibrium constant table are in Kelvin.

Robin Cadd 1D

If K is smaller than 10^-4, you can use the shortcut.

Robin Cadd 1D

ELu 1J wrote:It occurs naturally and emphasizes the amphoteric nature of water (the ability to both give and accept a proton).

One important point to add: autoprotolysis can occur between molecules other than water.

Robin Cadd 1D

If I understand your question correctly, the answer is no. Like any other chemical reaction, there will be times when a given acid-base reaction is at equilibrium and times when the reaction is not at equilibrium.

Robin Cadd 1D

Lyndon doesn’t post his worksheets. Your best bet is to get photos of them from a friend or fellow classmate.

Robin Cadd 1D

Yes. In sum, you can use partial pressures, moles, or concentrations in your ICE box.

Robin Cadd 1D

Yes, because what you’re given corresponds to solving for Kc.

Robin Cadd 1D

In addition to what everyone else has already mentioned, it means that the products are much more stable than the reactants in the chemical equation provided.

Robin Cadd 1D

Bars are pressure units. For the purposes of this class, we assume 1 bar = 1 atm. This is an approximation.

Robin Cadd 1D

A homogenous equation includes substances where all of the phases are the same, for example all gases, and a heterogenous equation has a mixture of different phases. Here's a couple of examples that I think illustrate this well: homogeneous: N2 (g) +3 H2 (g) -> 2 NH3 (g) heterogeneous: CaCO3 (s) ->...

Robin Cadd 1D

Could someone please explain the difference between Kc and K to me? I read about it in the textbook but I'm still a bit confused. Thanks!

Robin Cadd 1D

Do we include data concerning solids and liquids in our "ICE" box calculations? I know such data is excluded from calculations of the equilibrium constant, so is it also omitted from our "ICE" box calculations?

Robin Cadd 1D

I don't have the textbook on me at the moment, but I'd assume it probably has something to do with the strength of the acid.

Robin Cadd 1D

Eesha Sohail 1J wrote:Will we have to deal with any questions about Q vs K and le Chatelier's principle on the final?

No - I believe Dr. Lavelle said we would not be doing any calculations with the equilibrium equation.

Robin Cadd 1D

If the compound can act as both an acid and a base, the compound is amphoteric. The most common example is H2O. It can gain a proton to become a hydronium ion (H3O+) or lose a proton to become a hydroxide ion (OH-).

Robin Cadd 1D

Here's a video that will give you the basics on how to determine oxidation states/numbers. Hope this helps!
https://youtu.be/-a2ckxhfDjQ

Robin Cadd 1D

Depending on the solvent, the amount of dissociation will differ. Since pH depends on the concentration of H+ in a solution, the identity of the solvent will play an important role in the pH.

Robin Cadd 1D

Megan_1F wrote:What is the order of naming coordination compounds?

1) ligands first, then metal ion or atom
2) ligands are named in alphabetical order, disregarding their prefixes

Robin Cadd 1D

Those are abbreviations for ligands. Their chemical formulas can be found in the textbook.

Robin Cadd 1D

This isn't comprehensive, but may help you:
- tetrahedral, trigonal planar, octahedral: non-polar if all atoms surrounding central atom are the same; polar if different atoms surround the central atom

Robin Cadd 1D

A polydentate ligand is a ligand that can attach to multiple bonding sites. They're asking which of the ligands can attach to multiple bonding sites.

Robin Cadd 1D

When it is common for an element to have more than one possible charge (i.e. it's common that Fe has either a charge of 2+ or 3+), Roman numerals are used. These Roman numerals help to identify the compound.

Robin Cadd 1D

Angeline 3E wrote:
alex_4C wrote:Does that mean that our discussions are cancelled this week?

Discussions aren't canceled for the week.

Robin Cadd 1D

As others have said, the answer to your first question is yes. A molecule is non-polar when the dipole moments of the molecule cancel out. A molecule is polar when the dipole moments of that molecule do not cancel out.

Robin Cadd 1D

Based on previous threads I've seen on Chemistry Community, people generally advise to take Chem 14B before taking Chem 14BL. There's no rule, but it may make your workload and studying a bit easier to manage!

Robin Cadd 1D

It is a way of expressing the number of lone pairs and bonding pairs surrounding the central atom of a molecule.

Robin Cadd 1D

In Friday's lecture Lavelle said that only the first slide's material on Monday would be tested on the exam. Anything after that point would not be.

Robin Cadd 1D

One lone pair is first placed in one of the three equatorial positions surrounding an atom in a trigonal bipyramidal electron arrangement because the lone pair will cause the least repulsion there. If placed in an axial position, the lone pair will repel the three equatorial atoms strongly, as oppos...

Robin Cadd 1D

Yes, all molecules have London forces.

Robin Cadd 1D

I'm pretty sure it's okay to turn in homework relating to chemical bonds.

Robin Cadd 1D

I think you should be fine if you submit homework on chemical bonds.

Robin Cadd 1D

I assume it will be everything covered on the midterm + whatever additional material is covered before the date of the test.

Robin Cadd 1D

In short, as polarizability increases, induced dipole-induced dipole interactions grow stronger. Polarizability can be described as how much an electron cloud can be distorted; therefore, greater electron cloud distortion should correlate with stronger dipole interactions.

Robin Cadd 1D

Are you referring to unequal electron contribution? I'm pretty sure they're drawn like any other resonance structure.

Robin Cadd 1D

Anything past the 3d block we don't need to know.

Robin Cadd 1D

Use de Broglie's Equation.

Robin Cadd 1D

They do have a 3d subshell, it's just not filled.

Robin Cadd 1D

The only elements that hold stead-fast to the octet rule are C, N, O, F, and Ne. Hydrogen and helium will always have less than an octet (precisely, 2 electrons) because of the number of electrons their orbitals are able to accommodate. As a general rule, elements in the p-block with shell n=3 or gr...

Robin Cadd 1D

I'm not 100% sure, but if I remember correctly, I think my TA said that it would be both multiple choice and free response.

Robin Cadd 1D

Also, an important conceptual point to add: the possibility of an expanded octet continues for the atoms below Cl, P, and S within the p-block.

Robin Cadd 1D

A good starting point is to recognize that the diameter of 350 pm is your delta x in Heisenburg's indeterminacy equation.

Robin Cadd 1D

I think your TA just used the textbook's equations. B stands for the number of bonding electrons on the atom.

Robin Cadd 1D

I'm pretty sure bonding will also be on the midterm.

Robin Cadd 1D

Considering that Lavelle tends to write noble gas electron configurations and that the solutions manual of the textbook writes solutions with noble gas configurations, I think shorthand notation should be fine. Like others have said, I'm sure he will specify which type of electron configuration he w...

Robin Cadd 1D

The concept of a "standing wave" addresses the wave-like properties of an electron. Basically, it's just saying that an electron behaves somewhat like a wave. This property of an electron affects the electron's movement within an atom.

Robin Cadd 1D

There are only two electron spins, denoted as +1/2 or -1/2 (qualitatively, "spin up" or "spin down"). I don't believe you'll ever see atoms that have multiple electron spins, unless you're talking about "spin up" or "spin down". I hope this answers your questi...

Robin Cadd 1D

We're supposed to post five times a week by Sunday. I don't believe your posts roll over.

Robin Cadd 1D

We're supposed to post five times a week by Sunday. I don't believe your posts roll over.

Robin Cadd 1D

The only reason why these configurations do not follow the original rules is that if they did, the energy would not be distributed symmetrically. The d subshell has 5 orbitals that hold 2 electrons each. It helps to think about it visually. Draw out the 5 orbitals for the d shell and fill it in and...

Robin Cadd 1D

It could be used in either of the situations that you described. I don't have a definitive answer for your last question, but I'd assume we should know how to answer problems pertaining to both situations.

Robin Cadd 1D

I think that this may be of interest to you:
http://chemed.chem.purdue.edu/genchem/t ... l#hydrogen

Robin Cadd 1D

It means that light can behave like a wave, or light can behave like a particle. Depending upon the situation, one of these behaviors may emerge more prominently than the other. This is illustrated by Justin's experimental examples.

Robin Cadd 1D

I'm almost certain finals will not occur where our discussion happens, but the study list says the official location of the final is TBD.

Robin Cadd 1D

I'm not sure if it's because you're using the sixth edition, but the problems should just be at the end of the reading section for 1A. If it helps, the problems for section 1A mainly cover atomic spectra and electromagnetic radiation.

Robin Cadd 1D

The following link may be helpful in answering your question: https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=3&cad=rja&uact=8&ved=2ahUKEwjm9fDx6Y_lAhVTMH0KHZZnA5YQFjACegQIDRAG&url=http%3A%2F%2Fonlinestatbook.com%2Fglossary%2Fdiscrete_variables.html&...

Robin Cadd 1D

The net ionic equation would look like this: Cu+2 + 2OH- = Cu(OH)2 I hope this helps Just a bit of clarification that I thought might be useful - the OH comes from NaOH; the Cu2+ comes from the copper (II) nitrate. Therefore, if you have 2 moles of OH- in your net ionic equation, you will have 2 mo...

Robin Cadd 1D

Adding/Subtracting --> round to the least precise # (i.e. 4.23+4.542 = ? ; Your answer should have 2 decimal points)
v.
Mutiplying/Dividing --> # of sig figs in answer = least # of sig figs in whatever you're multiplying (i.e. 4.0*2 =8)

Robin Cadd 1D

Yes, that's fine.

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