CHEMISTRY COMMUNITY

Emily Chirila 2E

For reactions to occur, collisions btwn reactants must occur. The # of reactants in the elementary step gives us the molecularity and thus the order. Also, these collisions must occur at a correct orientation, which is why we use frequency factor A (a constant) in the Arrhenius equation.

Emily Chirila 2E

I believe it won't occur spontaneously unless you add a catalyst to lower the high activation energy.

Emily Chirila 2E

Search "UA Final Review - Kate, Riya, Matthew" for another review packet, it goes over info we learned earlier in the quarter!

Emily Chirila 2E

Given a graph of a straight line, you need to be able to know what order the reaction is based off the y-axis.

Emily Chirila 2E

If the salt contains a basic anion, the dissociation will thus produce OH- instead of H3O+ so you need to use your ice table to find [OH-] and then find pOH.. then convert pOH to pH using the equation pH + pOH = 14

Emily Chirila 2E

My TA instructed us to email him a picture of our homework 10

Emily Chirila 2E

When would we need to use the Arrhenius equation? What is its significance?

Emily Chirila 2E

It is unlikely we would be tested on a reaction with 4 reactants because Dr. Lavelle stated in class that even having a termolecular molecularity (3 molecules) is very uncommon

Emily Chirila 2E

A negative standard reduction potential means that the reduction of a substance is NOT favorable, rather, oxidation is favorable (it is a better reducing agent, as it causes other substances to be reduced)

Emily Chirila 2E

I found this video to be very helpful in visualizing why the units are different for zeroth, first, and second-order reactions.

https://www.khanacademy.org/science/che ... constant-k

Emily Chirila 2E

You know the metal will dissolve in solution if its redox reaction cell potential is more negative than the other reaction's cell potential.

Emily Chirila 2E

I think of the "agent" part as meaning caused. So if something is an oxidizing agent, it caused oxidation of another substance by taking the e- from the other substance (the oxidizing agent is reduced) & vice versa.

Emily Chirila 2E

When they are in acidic solutions, you balance using H2O and H+

For basic solutions, you do the exact same process but at the very end you add OH- to both sides to neutralize the H+

Emily Chirila 2E

I think they are derived in lecture just to help our conceptual understanding, but on homework/exams you can just use the final equation and plug stuff in

Emily Chirila 2E

I find it easier to remember "OIL RIG": oxidation is losing electrons, reduction is gaining electrons
Oxidation half rxns are losing electrons so the e- are a product, reduction half rxns are gaining electrons so e- are a reactant

Emily Chirila 2E

Ecell=0 means the rxn is at equilibrium, but K isn't 0. To calculate K at equilibrium you can do: K=10^(nE°/ 0.0592)

Emily Chirila 2E

Test 2 covers the 2nd page of Outline 4 and all of Outline 5 Some of the major topics are: -Gibbs Free Energy -Van't Hoff Equation -Galvanic/Voltaic Cells -Redox Reactions -Cell Potential -Nernst Equation There are more topics so definitely check out the outlines for the more specific information yo...

Emily Chirila 2E

I took Lavelle last quarter for 14A and there was no extra credit opportunities, although there was a small curve applied to final grades (about 1%). Everything is strictly followed from the course outline on the syllabus, which is the homework, chem community, 2 tests, midterm, and final (the class...

Emily Chirila 2E

I believe he would send an email out.

Emily Chirila 2E

If you increase the concentration of the product > 1.0M, we get a larger value of Q (CONCENTRATIONproducts/CONTENTRATIONreactants) which is used in the equation: E= E(standard conditions) - (RT/nF(lnQ)) Taking the ln of a Q that is more than 1 gives a positive number for lnQ, which is being subtract...

Emily Chirila 2E

These observations come from Le Chatelier's Principle. Increasing concentration of reactants leads to formation of products, thus Ecell will be larger than Ecell at standard conditions Increasing concentration of products leads to formation of reactants, thus Ecell will be smaller than Ecell at stan...

Emily Chirila 2E

sarahsalama2E wrote:also, for an isothermal reaction, is delta u equal to 0?

Yes, internal energy depends on temperature so for isothermal expansion deltaU=0 and thus:
deltaU=q+w ------> 0=q+w ------> q=-w

Emily Chirila 2E

I also am unsure of the equations to use for reversible expansion but I do think it is good to know that for reversible expansion, ΔStotal=0 so ΔSsys+ΔSsurr=0

Emily Chirila 2E

ΔH ---- change in enthalpy ΔH°---- change in enthalpy, at standard conditions ΔH(rxn)°---- standard enthalpy of a given rxn, at standard conditions ΔH(f)°---- standard enthalpy of formation, basically the energy required to change an element into the given phase from its most stable state (O2(g) has...

Emily Chirila 2E

Internal Energy of a monoatomic ideal gas is equal to 3/2nRt

We can't change R because it is a constant, so I believe the only way to change the internal energy is to change moles (n) or temp (t)

Emily Chirila 2E

Could you explain why delta U would equal 0? I'm a little confused about the connection between temperature and delta U. We know that delta U= q + w and delta U=(3/2)nR(deltaT) if delta T=0 then you are multiplying the constants in the 2nd equation by 0, thus you end up with delta U= 0 if delta U= ...

Emily Chirila 2E

I think that generally, irreversible expansion occurs in real life situations, so we assume temp is changing, unless it is a phase change (which are isothermal). Reversible expansion calculations are hypothetical maximums and temp is always kept constant, which we can see in the equation w=-nrTln(v2...

Emily Chirila 2E

805317518 wrote:Conceptually speaking, would an adiabatic system always be an isolated system? Or is there a more specific definition?

I believe it could also be referred to as an insulated system, as there is no heat transfer.

Emily Chirila 2E

I think that if it is explained as occurring in real life, it is safe to assume it is irreversible.

Emily Chirila 2E

Cv and Cp refer to heat capacity of ideal gases. It helps to imagine this in the case of a piston. The constant Cp is greater than the constant Cv at the same temperature because at constant volume, the heat added only goes towards increasing the temperature. So in a piston with a fixed volume, when...

Emily Chirila 2E

Celena Kim 2I wrote:Is it just me or is the link to the review problems not working?

I believed they are inserting the link around 7pm tonight.

Emily Chirila 2E

If the expansion of the gas is isothermal, then this means the temperature remains constant and delta U = 0 Could you explain why delta U would equal 0? I'm a little confused about the connection between temperature and delta U. We know that delta U= q + w and delta U=(3/2)nR(deltaT) if delta T=0 t...

Emily Chirila 2E

Midterm and final tend to have more application based problems, usually with some biological connection. It's good to have a solid understanding of all the concepts learned in class because you'll need to know which one to apply once you get to the exam, where you will most likely encounter a comple...

Emily Chirila 2E

I was stuck on this question too. Can someone explain the difference/relationship between molar energy and stability of a molecule? Is it referring to the energy required to break the bonds so having a higher molar energy means it is less likely to be broken?

Emily Chirila 2E

Equilibrium molar concentration is the same thing as equilibrium concentration, it is just specifying that your answer should be given in M. But you should have your units in M either way, and both are the same ICE table process.

Emily Chirila 2E

1/2kt refers to a certain direction or way of storing energy. We can calculate the ideal gas heat capacity at constant volume by using this concept. Particles/Noble Gases: have 3 possible directions, x, y, and z, so 1/2kt + 1/2kt + 1/2kt = 3/2kt Linear Molecules: the 3 possible directions plus 2 add...

Emily Chirila 2E

Degeneracy is the number of ways of achieving a given energy state. W=2^n where n= # of particles

Emily Chirila 2E

J/K (its the same as R but no mol in denominator)

Emily Chirila 2E

The values are the same in solids and liquids. In gases, Cv is constant volume and Cp is constant pressure so the values will be different. I think Cp may be used because Cp calorimetry gives enthalpy values, whereas Cv calorimetry gives heat capacity of the whole container/all parts

Emily Chirila 2E

This confuses me too because its not like it gives off energy to create a bond, right? Unless it is saying it gives off energy to break a bond. When the bond is formed, energy is given off to the surroundings. When the bond is broken, energy is absorbed by the system. It is really important to clar...

Emily Chirila 2E

The heating curve for water shows this phase change energy as horizontal lines on the graph.

Emily Chirila 2E

Steam causes extreme burns because as the steam hits your skin, lots of energy is released as it condenses to a liquid (phase change). This extra release of energy wouldn’t occur with the same temperature of boiling water hitting your skin because no phase change occurs.

Emily Chirila 2E

More accurate methods include Hess’s Method (adding rxns to obtain net rxn) or using ΔH°values from a table

Emily Chirila 2E

When I attempted 4A,B,& C problems, it was not material we have covered yet in class.

Emily Chirila 2E

Basically all you need to worry about is removing the first proton.

Emily Chirila 2E

You need to make an ice table for the reaction of NH3 reacting with H2O. Once you solve for the equilibrium concentration of OH-, you can find pOH (pOH= -log[OH-]). Then you can convert pOH to pH (pH + pOH = 14). Percentage protonation is calculated by doing ([NH4+]/[NH3]initial) x100%

Emily Chirila 2E

For pH, the sig figs in the given molarity determine how many decimal places we should have. For instance, for a H3O+ concentration of 0.040 the pH should have 2 decimal places since there are 2 sig figs (pH=1.40). I don't know if it's possible yet, but say the H3O+ concentration is a crazy number ...

Emily Chirila 2E

If you go to "Your Posts" you can view the dates and I just count starting at January 2020 to see how many posts I have for the quarter

Emily Chirila 2E

First you need to be able to recognize which parts of a salt don't affect pH (group 1&2 elements, like Na+). Once you recognize what part of the salt WILL affect the pH, you write the reaction for that part of the salt reacting with water to form it's conjugate acid/base and either H3O+ or OH-, ...

Emily Chirila 2E

pH sig figs start to count after the decimal point. So, if you have 2 sig figs in the given information for the problem, then your pH answer should have 2 sig figs AFTER the decimal point.

Emily Chirila 2E

K is a constant for each given temperature. So K values vary dependent on temperature but besides that the K value will stay the same despite any changes.

Emily Chirila 2E

Because the questions are all free response, I have found that the best way to study is doing all of the homework problems for the related chapters, so I would do all of chemical equilibrium hw and all of acids and bases hw

Emily Chirila 2E

The problem: Find the initial concentration of the weak acid or base in each of the following aqueous solutions: (a) a solution of HCLO with pH=4.60 (b) a solution of hydrazine, NH2NH2, with pH=10.20 Is there a way to solve this without Ka values? I looked up the Ka values and used them to solve and...

Emily Chirila 2E

They are inversely related. If one increases, the other decreases. That is why Kw is a constant. When they are equal, that means the solution is neutral.

Emily Chirila 2E

Step 1: write out chemical rxn (balanced) Step 2: fill out ICE table (use the coefficients to know the change, for example if coefficient of the reactant is 2, then it would be -2x, and for a product with a coefficient of 2 it would be +2x) (ALSO you know you don't start with any products so those i...

Emily Chirila 2E

We only use gases and aqueous solutions in K expressions. Solids don't have concentrations so they are not included and pure substances (liquids) will not react enough to make any effect so they are left out as well.

Emily Chirila 2E

Step 1: write out chemical rxn (balanced) Step 2: fill out ICE table (use the coefficients to know the change, for example if coefficient of the reactant is 2, then it would be -2x) Step 3: plug in equilibrium values from the ICE table and the given K value into K expression (make sure to square the...

Emily Chirila 2E

The system will adjust in response to the change and thus produce more product, keeping a consistent ratio.

Emily Chirila 2E

Le Chatelier's Principle is important because it explains why the questions about systems shifting in different directions are important. They are shifting either towards the reactants or towards the products in attempt to minimize the effect of external causes, such as increasing the pressure by de...

Emily Chirila 2E

HI is the stronger acid because the chlorine in HCL is more electronegative than the I in HI. The chlorine pulls in the electrons more and creates a stronger bond that is harder to break. Remember the stronger acid will have the weaker bond-- and strong acids fully dissociate :)

Emily Chirila 2E

A bronsted acid is a proton donor. A Lewis acid is the species that accepts the e- pair. So, a Lewis acid is a broad term for anything that accepts a pair of electrons, whereas a bronsted acid is specifically the proton donor.

Emily Chirila 2E

Test Topics: VSEPR, intermolecular forces, polarizability/polarizing power, sigma/pi bonds

Emily Chirila 2E

Ion ion interactions occur when there are complete charges differences, not partial. So, anytime 2 ions interact it is ion-ion. If it is an ion interacting with a polar molecule (not an ion) it is ion-dipole

Emily Chirila 2E

A hydrogen bond is a dipole-dipole force but not all dipole-dipole forces are hydrogen bonds--- only when a H bonds with a highly electronegative atom (N,O,F). Hydrogen bonds are stronger than normal dipole-dipole forces.

Emily Chirila 2E

Pi bonds are only formed when two atoms are bound by more than 1 covalent bond (in a double or triple bond). Visually, you can think about the sigma bond first forming by 2 orbitals bonding end-to-end, then the pi bonds form after when the orbitals bond side-to-side

Emily Chirila 2E

On my manual it says A must have a lone pair, which is correct. If it is bent it must have at least one lone pair on it. B may have a lone pair because some linear structures allow for that.

Emily Chirila 2E

If total domains surrounding the central atom is less than 5, lone pairs can be placed anywhere. If total domains is 5, lone pairs should be placed in equatorial positions. If total domains is 6, lone pairs should be placed in axial positions.

Emily Chirila 2E

Linear 180 Trigonal Planar 120 Bent (varies based on which formula it is, if its AX2E2 then its less than 109.5, if its AX2E then its less than 120) Tetrahedral 109.5 Trigonal Pyramidal less than 109.5 Trigonal Bipyramidal 90 and 120 See Saw less than 90 & less than 120 T-shaped less than 90 &am...

Emily Chirila 2E

Can someone attending this peer learning session post the worksheet to this thread? I am unable to attend but would like to complete the worksheet.

Emily Chirila 2E

There will always be a sigma bond present, because pi bonds are only formed in double and triple bonds, in which a single bond is always within it.

single bond= 1 sigma bond
double bond= 1 sigma bond + 1 pi bond
triple bond= 1 sigma bond + 2 pi bonds

Emily Chirila 2E

Lone pairs change the bond angles of shapes. For example, a tetrahedral structure (4 bonding pairs, 0 lone pairs) has 4 regions of e- density, and the bond angles are 109.5 degrees. On the other hand, trigonal pyramidal also has 4 regions of e- density, but it has 3 bonding pairs and 1 lone pair, so...

Emily Chirila 2E

Besides for some tetrahedral and trigonal pyramidal bond angles being less than 109.5, are there other molecular shapes we should know for test 2? Also, how would we know the bond angles for more complicated shapes like trigonal bipyramidals? So far we're suppose to know: linear, trigonal pyramidal...

Emily Chirila 2E

It can be determined if a molecule has linear shape by looking at the number of bonding and lone pairs on the central atom. For example, molecules with the VSEPR notation of AX2 and AX2E3 both have linear shapes. AX2E3 is an important one to remember--- even though the central atom has lone pairs i...

Emily Chirila 2E

Intermolecular forces, VSEPR, and sigma/pi bonds (were learning this topic Monday in class)

Emily Chirila 2E

005384106 wrote:Do lone pair electrons have a stronger force of repulsion of atoms compared to the strength of atoms repelling against each other?

These are the relative strengths of repulsion:
lone-lone pair repulsion > lone-bonding pair repulsion > bonding-bonding pair repulsion

Emily Chirila 2E

The instantaneous dipoles in 2 nearby rod shaped molecules are closer than those found in nearby spherical molecules. This is because rod shaped molecules have more surface area that is closer to each other. Because of this, rod shaped molecules have stronger interactions than spherical molecules. T...

Emily Chirila 2E

I would focus my homework for week 7 on intermolecular forces (3F in the textbook) because that is the most recent lecture topic we covered.

Emily Chirila 2E

I would do section 3F because it covers intermolecular forces, and that is what we covered in class this week.

Emily Chirila 2E

I can leave some below from my discussion.

What orbital is consistent with the following quantum #'s?
n=4 l=1. ml=1. ms= +1/2

Give one set of quantum #'s for a 3d e- in Cr+.

What are possible #'s for an e- in a Flourine 2p orbital?

How many e- in an atom can have quantum #'s n=3 l=2?

Emily Chirila 2E

MHz means mega hz. 1MHz is one million hertz: 1 MHz= 1x10^6 Hz

Emily Chirila 2E

You can figure out the chemical formulas using the charges on the PT. You have to make the charges equally balanced. You can do this by swapping the charges and using it as your subscript. Magnesium Arsenide Mg has a 2+ charge, As has a 3- charge, so it would be Mg3As2 Indium (III) Sulfide In is 3+....

Emily Chirila 2E

Nitrogen is an exception because it really wants to have a half-full sub shell. But yes, ionization trend on the PT is increasing up and to the right. Just keep in mind Nitrogen has a larger ionization energy than Oxygen.

Emily Chirila 2E

Energy of the electron would go up because you are increasing energy levels. Value of n would go up because you go from n=1 (the 1 in 1s) to n=2 (the 2 in 2p). Value of l would go up (s=0 and p=1, so 0 to 1 is increasing). Radius of the atom would go up because adding orbitals makes the atom bigger ...

Emily Chirila 2E

Since all that changes is the placement of electrons between resonance structures, I think it would be a good thing to keep in mind, but it wouldn't be too complicated to figure out on a test as long as you know it exists/what it means.

Emily Chirila 2E

Cation size decreases up and decreases to the right. They get smaller as you go up because number of orbitals decrease, and get smaller as you go right as you add more positive charge (holds in electrons tighter). Same trend as atomic radius. The smaller the cation leads to more polarizing power.

Emily Chirila 2E

Yes, that is correct. In the sub-shell 4p, there is 3 orbitals (fitting 6e-, 2e- in each orbital). Sub-shell 3d has 5 orbitals (fits 10e-), Sub-shell 1s has one orbital (fits 2e-), and sub-shell 4f has 7 orbitals (fits 14e-). So just remember: Shell= n value (like 4) Sub-Shell= a section of the shel...

Emily Chirila 2E

Electronegativity is how tight the electrons are held together. Polarizability is the ease to release an electron. High electronegativity= electrons are held very tight together, high polarizability=easier to release an electron (due to it being a larger atom).

Emily Chirila 2E

I think as long as you know the general trend you will be fine. Anything close we will probably be given the values or if its lewis structures, generally you can tell which atom will go in the middle based off other factors like how many of them there are (the atom with the subscript of 1 will go in...

Emily Chirila 2E

Alexis Webb 1B wrote:In the answer key, it says it’s not a radical.

Weird. On my sapling online textbook answer key it said it is a radical:

2C.1 Only (a) and (b) are radicals

But I understand that it isn't a radical.. maybe just a mistake?

Emily Chirila 2E

I think that all you need to know is that the quantum number ms is only valid if its value is + or - 1/2 and that it refers to the spin of the electron, with the 2 electrons in an orbital having opposite spins (one has +1/2 one has -1/2).

Emily Chirila 2E

If all else fails an easy way to remember is that ionization energy, electron affinity, and electronegativity all increase up and to the right, and atomic radius is the opposite (increase down and to the left). It is important to know the meaning behind them but that's a simple way to remember :)

Emily Chirila 2E

I've been trying to do this homework problem and seriously struggling. I understand what a radical is but I cannot seem to figure out why NO2- is a radical. I drew the lewis structure but I don't see any unpaired electrons. Can anyone explain why NO2- is a radical?

Emily Chirila 2E

A covalent bond is formed between nonmetals. Atoms share the electrons in covalent bonds because nonmetals have too high of an ionization energy to form cations.

Emily Chirila 2E

The full electron configuration would be 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p3 :) It helps me to write it by just going in order on the PT and writing it as I go.

Emily Chirila 2E

Personally, in my homework I do not put the (x, y, z) notation to distinguish between subshells, but I think it does help conceptually to think about it that way as it reinforces the idea of Hund's Rule

Emily Chirila 2E

I definitely benefit from looking over my notes from lecture and discussion. Just trying to get a solid basis of WHY things occur makes it a lot easier to conceptually understand the problem. Then, when you get to the test you won't freeze up because you forgot everything you tried to memorize, you ...

Emily Chirila 2E

You should fill the shells in the order they appear on the PT, but write them in order of values of n. So you would fill 4s before 3d, but when you write the configuration, say for titanium, you would write [Ar] 3d2 4s2.

Emily Chirila 2E

The second element in the f-block is Praseodymium

Emily Chirila 2E

I like to think of electron affinity as how much an atom wants an e-. So, when you move to the right on the PT, you are getting elements with almost full shells. They really want to complete the octet rule so they are stable, thus they really want the e-, especially because on the very right, like f...

Emily Chirila 2E

In my opinion, the easiest way to start this question would be to write out the ground state e- configuration, then you can compare the two and see if you find any differences. Any differences would suggest the e- has been excited.

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