CHEMISTRY COMMUNITY

Maria Poblete 2C

To solve this question, you need to determine the rate law for each student's reaction and see if it matches with the overall experimentally determined rate law. To do this, you should determine the rate law for each elementary reaction, as well as the equilibrium constant. As you can see in the sol...

Maria Poblete 2C

I'm getting confused between the different k variables in this problem. How exactly does the observed rate k equate to k₂K₁? I understand how to derive the rate for both students, but I don't understand why Student B's k₂K₁ is equivalent to the overall k.

Maria Poblete 2C

Why don't you multiply the cell potential by 2 in the reduction half reaction?

Maria Poblete 2C

For the reversible, one-step reaction A + A <-> B + C, the forward rate constant for the formation of B is 265 L/mol*min and the rate constant for the reverse reaction is 392 L/mol*min. The activation energy for the forward reaction is 39.7 kJ/mol and that of the reverse reaction is 25.4 kJ/mol. (a)...

Maria Poblete 2C

The slowest step determines the rate because the reaction cannot proceed until the slowest step has gone to completion. Essentially, if you think about it like a group on a hike, the slowest person determines the pace of everyone because the group cannot go on without them.

Maria Poblete 2C

I don't think we'll have to sort the order of the intermediate steps, but we should know that the sum of the elementary steps is equivalent to the overall reaction, and that its mechanism agrees with the determined rate law.

Maria Poblete 2C

In a reaction, Gibbs free energy is the energy available to do work.

Maria Poblete 2C

K is a constant, and when calculating K, the units of molarity or partial pressure actually cancel out.

Maria Poblete 2C

The term isothermal refers to a constant temperature. Irreversible free expansion is the expansion of a gas. If you think about it logically, it is irreversible because it is not a natural process for a gas to condense to a smaller volume. Because irreversible free expansion is a spontaneous process...

Maria Poblete 2C

Like someone said before, it's essentially an all or nothing kind of behavior. Someone explained it to me in a helpful analogy: if you're hiking with a group of people, the slowest person in the group determines the pace of their hike. The other people, no matter how fast they are, must keep the pac...

Maria Poblete 2C

The anode is the part of the cell that performs oxidation, so the element/compound inside loses an electron. This electron transfers over to the cathode, which performs reduction and adds the electron to the corresponding element/compound inside.

Maria Poblete 2C

The default setup typically ensures that the anode is on the left and cathode is on the right for standard cell notation.

Maria Poblete 2C

The degree symbol means that the variable is the standard variable in that state. The standard value can be considered the default value to use in calculations, like for the standard enthalpy of formation, or the standard entropy of reaction.

Maria Poblete 2C

Yes, the flow of electrons is what causes a current, therefore causing electricity. This can be used interchangeably.

Maria Poblete 2C

Potassium nitrate dissolves readily in water, and its enthalpy of solution is +34.9 kJ/mol. (a) Does the enthalpy of solution favor the dissolving process? Can someone explain this conceptually? For a, I don't really understand the solution manual's reasoning. It says that because deltaH system is p...

Maria Poblete 2C

Use the information in Table 4C.1 to calculate the changes in entropy of the surroundings and of the system for (a) the vaporization of 1.00 mol CH 4(l) at its boiling point. Would delta S and delta S surr be equivalent (but opposite signs) in this case? I know that you use deltaS surr = -de...

Maria Poblete 2C

I can confirm that it's a typo, it really should be 2Cl^-_(aq) instead of Cl_2(g)

Maria Poblete 2C

A good acronym to remember is LEO: losing electrons - oxidation. A compound undergoes reduction if it gains electrons, and undergoes oxidation if it loses electrons. You can tell by looking at the oxidation number of the element in the compound; if the oxidation number increases, then its charge bec...

Maria Poblete 2C

Work is done on a system if its value is positive; this is because the system absorbs energy from its surroundings.
The opposite should in turn make sense: if the system is doing work, its value is negative because energy is leaving the system to go to the surroundings.

Maria Poblete 2C

What would the half reactions of this redox be? In part b, bromine reacted with itself, so it was the reactant in both reactions, but the description doesn't specify that for part d:
P_{4 (s)} --> H₂PO₂^-_(aq) + PH_{3 (aq)}

Maria Poblete 2C

The following redox reaction is used in acidic solution in the Breathalyzer test to determine the level of alcohol in blood: H + (aq) + Cr 2 O 7 2- (aq) + C 2 H 5 OH (aq) --> Cr 3+ (aq) + C 2 H 4 O (aq) + H 2 O (l) Balance the half-reactions to produce...

Maria Poblete 2C

Half reactions don't necessarily mean the reaction is split in half exactly. Oxidation and reduction reactions are two halves of a redox reaction. So, when you're breaking the reaction up, you're breaking the redox reaction into one oxidation and one reduction reaction.

Maria Poblete 2C

Electrochemistry, as it sounds, is the study of the relationship between electricity and chemistry. What we mostly discussed on Friday is the transfer of electrons in electrons. Oxidation involves the loss of electrons, and reduction involves the gaining of electrons in reaction. A redox reaction is...

Maria Poblete 2C

He just broke the reaction up into two half reactions; it is not necessarily an end result, but a breakdown of what is going on in one redox reaction.

Maria Poblete 2C

A redox reaction is a reaction that includes both a reduction and oxidation reaction. They can be separated into two half reactions: one oxidation and one reduction reaction. An oxidation reaction involves the loss of electrons, and reduction involves gaining electrons. I think that splitting the tw...

Maria Poblete 2C

Can someone please explain the difference between delta S and delta S_tot? The problems I'm reviewing ask for these and I don't know the difference between the two.

Maria Poblete 2C

In a reversible reaction, there is a decrease in pressure, making its slope negative. Since there is constant pressure in an irreversible reaction, the slope is 0. The graphs' slopes correlate with whether or not the pressure is changing in reaction.

Maria Poblete 2C

No work occurs under free expansion, because there is no external pressure applied under a vacuum state.

Maria Poblete 2C

The midterm is from 6-8, I'm pretty sure there's no class that day either.

Maria Poblete 2C

I don't think it would hurt to memorize, the reversible curve expresses a large change in pressure with a negative slope, and the irreversible curve is simply a straight horizontal line.

Maria Poblete 2C

If x is less than 10^-3, it can be considered negligible.

Maria Poblete 2C

As you can see, the R constants use different units. When you're solving a problem, it is important to consider the units you are using when utilizing the gas constant. You can't use the two interchangeably because the units are different in either situation. However, they carry the same value, just...

Maria Poblete 2C

It is important to look at the units of what the problem includes. All of the R constants will be provided on the equation sheet, so when you need to use the R constant, consider what units you are using and use the constant that aligns with these units.

Maria Poblete 2C

Someone correct me if I'm wrong, but I don't think you can do work on an open system because nearly everything is included within the system. For example, an open beaker that has water added to it is an open system, consisting of the old and new water. Work is not done because the mass of the water ...

Maria Poblete 2C

W is found using integrals because integrals add up the tiny increments of change in volume during expansion.

Maria Poblete 2C

It can't really go the other way. If mass is interchangeable, this would make the system open.

Maria Poblete 2C

I usually read the sections that we just finish covering in lecture. I don't think there's a chronological order to the readings he lists on the syllabus, especially because we are covering thermochemistry before thermodynamics (but the textbook sections list in the opposite order).

Maria Poblete 2C

The midterm includes everything we have learned up until that date, which includes material from Test 1 and up until the midterm date. The final is cumulative. Tests 1 and 2 only test on certain topics, so they aren't cumulative.

Maria Poblete 2C

What everyone else said above is correct. Something to keep in mind is that if you are calculating for a weak acid/base, the change in molarity at equilibrium can be considered negligible because they do not 100% dissociate in solution. So, even though you have a change in X, the change is still clo...

Maria Poblete 2C

In the equation sheet we're provided with, there are a number of different values to use for the R constant. It's important to look at which units are being used, which will tell you which one is appropriate to use.

Maria Poblete 2C

X is approximated because weak acids do not 100% dissociate in solution. Because of this, we can assume that the value of change is so small that it is negligible.

Maria Poblete 2C

I'm not sure if I'm answering your question entirely but work is energy leaving or entering a system. Because of this, work done can affect the amount of available energy in a system.

Maria Poblete 2C

Yes, if you think about it, the higher the pressure is, the less room there is for particles to move around.

Maria Poblete 2C

The ideal gas law always uses Kelvin when calculating temperature. Like everyone said, K = 273 + C.

Maria Poblete 2C

Either should be fine, just make sure the units are correct when you're converting and coming up with your final answer!

Maria Poblete 2C

Use the information in Table 5G.2 to determine the value of K at 300 K for the reaction 2 BrCl(g) + H₂(g) = Br₂(g) + 2 HCl(g).
I can't quite find this exact reaction in the table. Is there something additional that I should be doing to find K?
This is what Table 5G.2 looks like:

Maria Poblete 2C

Le Chatelier's Principle applies whenever an external change is added to the system. This can occur in the form of altering concentration, pressure, or temperature. An exception to this is if an inert gas is added to the reaction, which has no impact on the reaction.

Maria Poblete 2C

When you don't know the quantitative change in concentration, you can replace the value with variable X. For example, CO and H 2 O would decrease X amount in reaction, while CO 2 and H 2 would increase X amount. By doing this, you can mathematically figure out the actual numerical value of X by usin...

Maria Poblete 2C

Le Chatelier's Principle is helpful in understanding that changes in concentration or pressure within the system will not affect K, and that the reaction will act accordingly so in order to keep K intact.

Maria Poblete 2C

If the solutions to the problem are the direct concentrations of a substance, there is no way the answer can be negative, as you cannot have negative concentration. I'm not really sure if this would ever come up, but the solution could be negative if this results in the desired concentration is stil...

Maria Poblete 2C

Will we ever have to convert between K and Kc? I'm reading Focus 5H in the textbook and I'm kind of confused.

Maria Poblete 2C

When there is chelation in a coordinate compound, the ligand attaches multiple times to the central atom. It essentially forms a ring of atoms including the central metal atom. Ligands typically bind at one site of the central atom, making them monodentate. A ligand that binds at two sites is bident...

Maria Poblete 2C

I also don't have a mnemonic but quizlet is actually very helpful! When memorizing CN, NC, SCN, and NCS, I realized that the complementing compound beginning with N will always begin with iso-. For example, CN is cyanate, and NC is isocyanate. SCN is thiocyanate, and NCS is isothiocyanate. Hope this...

Maria Poblete 2C

I think that it wouldn't hurt to know the ligand names of each structure. While reviewing, I've done past final exams and I've been asked to identify ligands like ethylenediamine (en) and oxolate.

Maria Poblete 2C

A chelate is a compound with a ligand bonded to a central atom at two or more points. This looks like a ring structure attached to the central atom. A polydentate molecule has multiple ligands of this nature attached to the central atom. So, a chelate can be monodentate, bidentate, tridentate, polyd...

Maria Poblete 2C

I know that Lewis acids accept electron pairs from Lewis bases, but how exactly do you know what the final product looks like? For example, what does the product of Cl - + SO 2 look like, and why? I know that Cl - is the Lewis base, and SO 2 is the Lewis acid, but I'm not exactly sure how the two in...

Maria Poblete 2C

I think it would be really helpful to know the simpler ligands, since I'm pretty confident that we're going to be asked to name some coordination compounds on the final. For the insanely long ligand names, I think it's okay if we don't memorize those haha.

Maria Poblete 2C

I was just wondering why phosphoric acid is weaker than sulfuric acid. When I tried looking at this online, most sources just listed the pKa's, and I don't think that is a sufficient way to answer my question.

Maria Poblete 2C

To add onto this, a more visual representation is this:
p[H] = -log₁₀[H₃O⁺]

So, for example, if [H₃O⁺] = 1.0 * 10^-7 mol/L, the pH would equal 7.

Maria Poblete 2C

Visually, you can tell if chelation occurs in a molecule if one of the ligands forms a ring of atoms that includes the central atom. In a Lewis structure, it would look like a ring on one of the ligands.

Maria Poblete 2C

The Community Programs Office in the Student Activities Center on campus has a test bank of previous finals and tests that students may have previously submitted in past quarters. I'm not sure if Lavelle's tests are there, but I feel like there's a good chance especially because this class has been ...

Maria Poblete 2C

Someone else can add onto this, but I think it's helpful to know their exact function and role when reacting with other substances. For example, Bronsted acids are proton donors and Bronsted bases are proton acceptors. Also, it'd probably be helpful to recognize what makes up a strong/weak acid or b...

Maria Poblete 2C

Yes, induced dipole-induced dipole forces can also be considered London forces. They can also be referred to as dispersion forces, or van der Waals forces.

Maria Poblete 2C

Let's take a molecule with tetrahedral electron geometry, for example. If 4 bonded atoms are connected to the central atom, the molecular geometry will also be tetrahedral with bond angles measuring approximately 109.5 degrees. However, if only 3 bonded atoms and one lone pair of electrons are conne...

Maria Poblete 2C

Does BrF₆ have a net dipole moment? I know that F is more electronegative, so the dipole moment travels from the central Br to each F atom. When I draw all of these vectors out, I think they sum up to be 0. Is this correct? Is there another way to look at this?

Maria Poblete 2C

Let's say we have an ionic compound like ICl 2 - . If you draw the Lewis structure for this, it has two bonded pairs and 3 lone electron pairs, which gives it a linear molecular geometry. Why will the bond angles be 180 o degrees? I thought that lone electron pairs typically repel the bonded atoms' ...

Maria Poblete 2C

The number of regions of electron density help determine the shape of the molecule, concerning both electron and molecular geometry. For example, if the molecule's central atom has 4 regions of electron density surrounding it, you can infer that its electron geometry is tetrahedral. Its amount of lo...

Maria Poblete 2C

Yes, you should treat a single electron as one full region of electron density. However, because there is only one electron compared to two in a lone pair, it most likely has a lower magnitude of electron repulsion.

Maria Poblete 2C

This was really helpful! Thanks for the resource, I'll definitely use this method when memorizing. :)

Maria Poblete 2C

I am not sure if it is required to memorize all of the shapes, but I think it would certainly be extremely helpful. Honestly, bond angles and molecular structure/shape are a large part of the content we learned after the midterm, so I would recommend memorizing them just to be safe before the test.

Maria Poblete 2C

Yes! One lone pair counts as one region of electron density. Molecular shape should always take into account how many regions of electron density surround the central atom, whether this be a bonded atom or a lone pair.

Maria Poblete 2C

I don't think we will have to calculate any values concerning dipole moments on a test, but I am pretty sure that we will have to recognize and identify which molecules participate in dipole moments with each other by determining relative electronegativity within their atoms.

Maria Poblete 2C

Test 2 should cover everything from after the midterm (around Focus 2D) up to the VSEPR model and bonding angles. Hope this helped!

Maria Poblete 2C

I believe Prof. Lavelle said that Test 2 covers everything after the midterm (beginning from Focus 2D) up until the content we learned this Friday, which is the subject of bond angles and the VSEPR model. If I am wrong, someone correct me!

Maria Poblete 2C

The VSEPR model is only able to qualitatively determine the measure of bond angles, but never quantitatively. Because molecules with lone pairs tend to push atoms farther away, the bond angles will always be smaller compared to normal geometric structure. However, it is impossible for us to actually...

Maria Poblete 2C

Hi everyone,
From which section on the syllabus does the homework problems begin for the homework due week 7?

Maria Poblete 2C

Hi, this should be relatively simple but I'm struggling to understand the reasoning behind the correct answers for this problem: Give the ground-state electron configuration expected for each of the following ions: a) Cu + b) Bi 3+ c) Ga 3+ d) Tl 3+ I got [Ar] 4s 2 3d 8 for both a and c, and [Xe]4f ...

Maria Poblete 2C

I don't think we'll ever need to calculate the value of an atomic radius, but we should know the trends of increasing/decreasing atomic radii across periods or groups of the periodic table. For example, the atomic radius gets smaller as you go from left to right in a period because the higher positi...

Maria Poblete 2C

Like Jennifer said, quantum numbers detail the state of an electron. They tell you the overall environment of the orbital, like size/energy (n), shape (l), orientation (ml), and spin state (ms).

Maria Poblete 2C

I believe that gallium's electron configuration is [Ar]4s 2 3d 10 4p 1 . To do this, you count the row that the element is in. Gallium is in period 4, so the s-orbital is in the 4th shell with all of its electrons filled (2). Then you enter the 3 d-block, where the maximum number of electrons in the...

Maria Poblete 2C

I think it's important to keep in mind what you are solving for. For example, if you are solving for E, the units for E are Joules, which translates to kg*m 2 *s 2 . Therefore, it's helpful convert your constants and variables to match units of kg and m so that you don't get confused or end up with ...

Maria Poblete 2C

Hi, can someone please define for me what n actually means in the Rydberg equation? Is it correct that it is the principal quantum number? What does that actually mean?

Maria Poblete 2C

The formation of ionic compounds involve transferring electrons from a metal to a nonmetal atom, resulting in cations and anions. Covalent bonds bind nonmetal atoms to form molecules. The ionization energies of these atoms are too high to transfer electrons from one atom to another, so they simply s...

Maria Poblete 2C

I don't believe there is a concrete study guide for the exams in this class. However, the Community Programs Office has a test bank of exams completed by students who took the course in previous quarters. If you're a first-year, you can print out a test without having to turn anything in. But after ...

Maria Poblete 2C

Correct; because every element has a unique atomic number that corresponds to their generic number of electrons (no exceptions are stated in this problem), finding the number of valence electrons and identifying the element in the table would get you to your answer.

Maria Poblete 2C

Yes! The periodic table is actually structured based on these similarities. As you can see in the middle section of the periodic table, all of those elements contain d-orbitals.

Maria Poblete 2C

Yes, because the d-orbitals in elements in period 3 or higher are capable of holding up to 10 atoms.

Maria Poblete 2C

Yes, I believe this can only be applied to hydrogen atoms just because multi-electron atoms are more complex in nature and require deeper-level analysis.

Maria Poblete 2C

Yes, all three orbitals can be generalized together, but like Ethan said, all three must spin up in the same direction before being paired.

Maria Poblete 2C

Thank you everyone! This was really helpful.

Maria Poblete 2C

Hi! I had a similar problem because I also only have the 6th edition. If you go to Powell Library, you can check out the 7th edition and the solutions manual for 2 hours; the homework problems begin on page 9. I cross referenced the two books and I don't think that the 6th edition has the problems t...

Maria Poblete 2C

I'm having trouble with this problem: In the ultraviolet spectrum of atomic hydrogen, a line is observed at 102.6 nm. Determine the values of n for the initial and final energy levels of the electron during the emission of energy that leads to this spectral line. To be quite honest I'm not even sure...

Maria Poblete 2C

Yep, and each metal requires a different amount of energy to remove an electron from the surface. I am assuming that if you are solving for another variable like wavelength or the photon energy, the work function will be given but can be calculated manually using the equation @dtolentino4H provided.

Maria Poblete 2C

Thank you everyone! I should have been more clear but I am using the 6th edition and am still struggling to find the questions. I think I'm going to visit the library soon to see how the questions line up.

Maria Poblete 2C

I was also wondering the same thing. I have an easier time deriving formulas for telltale compounds (ex. dihydrogen monoxide, haha) but am not sure if I should remember the methods of deriving for acids or oxides.

Maria Poblete 2C

I believe that De Broglie's Equation can only be used for particles with a mass. I don't think light has a mass, so it wouldn't make sense to use the equation when mass is needed as a variable.

Maria Poblete 2C

I'm having trouble finding the exercises assigned in the syllabus under the Quantum World. One of the first sections of problems is Problems 1A: 3, 5, 7, 9, 11, and 15, but I can't seem to find them in the textbook. Can someone direct me to a page number, please? It would mean a lot! Also, just to c...

Maria Poblete 2C

Essentially, formula units unnamed variables. There are always 6.022 * 10²³ units in one mole of something. This could be atoms or molecules. I would say that you should just know that one mole converts to a quantity of Avogadro's number units.

Maria Poblete 2C

Ok so to answer part a, you want to start with the information they give you (1 molecule water) and you're trying to get to grams of H2O. To get there, you have to convert the 1 molecule of water to moles of water by dividing by Avogadro's number (6.022 x 10^23), since 1 mol = 6.022 x 10^23 molecul...

Maria Poblete 2C

Are you talking about side reactions that are given, or side reactions that occur by chance? I would probably only utilize information that is given in the problem.

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