CHEMISTRY COMMUNITY

Brandon_Tran_2E

I would try to do it before the final because I remember last quarter we couldn't make posts after it.

Brandon_Tran_2E

Concentration cells are galvanic cells with same components (AgNO3 the example Lavelle gave us) but it only works when concentrations are different. The standard cell potential is always zero because the conditions of standard cell potential requires the concentrations to be at 1M, so the voltage is...

Brandon_Tran_2E

Does anyone know why “A reaction with a negative standard reduction potential favors oxidation of the reactant” is True? What is the “reactant” in this case.

And also why for “A reactant in a reaction with a very positive standard reduction potential is a powerful reducing agent” is False?

Brandon_Tran_2E

Since the electrons flow from anode to cathode, the anode side of the reaction will become more positive and there will be a build up of negative charge in the cathode which slows the reaction/flow of e-. To balance the charges and allow the reaction to keep continuing there has to be a salt bridge/...

Brandon_Tran_2E

I don't understand the second part of your question but when free energy (deltaG) is negative, the reaction is spontaneous therefore the reaction's products are stable and will occur without an input of energy. Therefore a reaction with a positive free energy change means the reaction requires energ...

Brandon_Tran_2E

Salt bridge or porous disc to allow negative ions to flow back to the anode side or else the reaction will stop.

Brandon_Tran_2E

because the negative is in front of the charge.

Brandon_Tran_2E

Most of the time anode is left and cathode is right.

Brandon_Tran_2E

Because enthalpy is heat at constant pressure. You can only calculate deltaG when the reaction occurs at constant pressure and temperature.

Brandon_Tran_2E

Another tip is to figure out the oxidation numbers of each molecules first and then figure out which one loses/gains electrons with OIL RIG acronym. Oxidation numbers are basically the charges of an atom, ex) H is always 1+ Oxygen is usually 2- etc, the oxidation number of an ion is its charge... etc.

Brandon_Tran_2E

Gibbs free energy is defined as the energy available to do useful work.

Brandon_Tran_2E

A galvanic cell is basically the diagram that Lavelle showed in lecture where the reactants are divided in two containers and the cathode pulls electrons from the anode due to cell potential.

Brandon_Tran_2E

Brandon_Tran_2E

After you find out what temperature it is to make deltaG zero, the following assumption is made that for every temperature above the "equilibrium" temperature, your delta G will therefore be negative.

Brandon_Tran_2E

You add H2O to balance the amounts of oxygen on the sides of reaction. Since you add H2O you then would at H+ on the other side of the reaction to balance it from the added H2O you just put in.

Brandon_Tran_2E

for electrochemistry up to but no including Nernst equation

Brandon_Tran_2E

To answer the second part of your question, Delta U = 0 in isothermal systems because one of the equations Lavelle showed us is that
delta U = 3/2nR(delta T) and if there is no change in T then there is no change in U.

Brandon_Tran_2E

Remember that PV=nRT or P1V1=P2V2, that is, pressure and volume are inversely related so an increase in volume for example leads to a decrease in pressure.

Brandon_Tran_2E

Actually reversible/isothermal systems are most efficient at doing work considering the area under the curve of reversible expansion vs irreversible expansion on Lavelle's outlines.

Brandon_Tran_2E

I don't know about physics portion of work but Lavelle said the negative sign is because its related to the work of the gas. For example imagine a gas system with a piston, and when the gas expands, delta V would be positive and therefore the work is negative meaning the gas DID work. When the delta...

Brandon_Tran_2E

Since temperature is constant in isothermal reactions, the internal energy is 0 because internal energy is dependent on temperature.

Brandon_Tran_2E

Irreversible expansion uses the equation w = -PexΔV where you would plug in for pressure. For reversible expansion you would use w = -nRT x ln(vf/vi)... one of the TA's said that questions will almost always tell you what type of expansion it is, therefore you would use whatever equation is linked t...

Brandon_Tran_2E

q is the same as delta H, enthalpy when the pressure is constant.

Brandon_Tran_2E

Because it is an open system the system also is at a constant pressure because the system's pressure is the same as the outside pressure.

Brandon_Tran_2E

No need for that equation since it's not on the outline

Brandon_Tran_2E

Thanks Joyce

Brandon_Tran_2E

Think of entropy as disorder, gas molecules and more dispersed and disordered in an aqueous solution whereas a solid is a literal solid and ordered.

Brandon_Tran_2E

Brandon_Tran_2E

Temperature changes K because temperature (average kinetic energy) of the molecules are increased/decreased which means the rate of collisions of the molecules are affected which ultimately affects the K equilibrium constant because the rates of both forward and reverse reactions are now changed bec...

Brandon_Tran_2E

Thanks Joyce.

Brandon_Tran_2E

This questions isn't included in Lavelle's syllabus so it's not something he wants us to master.

Brandon_Tran_2E

Cis-platin , cis means that the constituents are on the same side in the structure, in this case there are 2 Cl's on one side. This is effective in chemotherapy because when cisplatin interacts with DNA, Nitrogen from the DNA takes place of Cl causing the DNA to lose its structure and function and s...

Brandon_Tran_2E

If it has multiple lone pairs. NH2CH2CH2NH2 there is 1 lone pair on each NH2 group in this structure so a total of 2 = bidentate.

Brandon_Tran_2E

Nope, he taught it last year but not to our year. Don't worry about weak acid calculations

Brandon_Tran_2E

Check how many valence electrons there are and if your structures is over or under the amount of total valence electrons you can use.

Brandon_Tran_2E

Usually there will only be 1 metal and everything else is a ligand, also for coordination compounds, the metals are always transition metals.

Brandon_Tran_2E

The physical state of the chemicals (aq) indicates that the reaction occurs with water as the solvent. Therefore when the dissociation occurs, the water accepts the protons from Ba(OH)2 and becomes H3O+.

Brandon_Tran_2E

Yes, because it is a strong acid. When H2O interacts with HCl, the interaction is strong enough for water to take the H+ and become H3O+ , leaving Cl-.

Brandon_Tran_2E

The main reason N is the central atom is because it is the least electronegative out of the 3 atoms (it does not want electrons as much as oxygen therefore oxygen is by itself because its selfish). Also considering formal charge N-N-O is the most stable.

Brandon_Tran_2E

The aufbau diagram for a sp2 hybridized carbon. Would be like sp2 _ _ _, then the other p orbital _. One trick to hybridization and pi bonds is that sigma bonds are formed by hybridized orbitals (sp, sp2, sp3) while pi bonds are formed with the unhybridized orbital. For sp2 hybridization , there is ...

Brandon_Tran_2E

When you comment or something it tells you how many posts you have, that's how TA's will check most likely near the end of the quarter.

Brandon_Tran_2E

It's both.

Brandon_Tran_2E

Although it is linear, oxygen is more electronegative than nitrogen therefore it pulls on the electrons more to its side , creating a dipole moment and making oxygen slightly negative.

Brandon_Tran_2E

Not for lewis structure

Brandon_Tran_2E

I think it just means write out the electron configuration

Brandon_Tran_2E

One easy way is at the top of the periodic table, the last digit of the group numbers is usually the amount of valence electrons... Group 1 and 2 have 1 and 2 valence electrons respectively, 13, 14, 15, 16, 17, 18 have 3 , 4 , 5, 6, 7, 8 valence electrons.

Brandon_Tran_2E

You would calculate the wavelength using de Broglie's equation: lambda = h/(m * v). Where m is the mass and v is the velocity. Make sure units cancel out.

Brandon_Tran_2E

So why did Dr. Lavelle include ... after the L quantum numbers for s,p,d,f,... if theres only four blocks??

Brandon_Tran_2E

We didn't learn those yet in lecture

Brandon_Tran_2E

Yea the correct answer on the solutions manual is 150pm.

Brandon_Tran_2E

Yes energy of each light photon is dependent on the frequency of the wave.

Brandon_Tran_2E

The right idea, basically changing the subscripts of any reactant/product in a chemical equation will change the chemical formula and ultimately the substance.

Brandon_Tran_2E

Hey, so an aqueous solution means a solution that has water. (lol) So if they ask you to prepare a 510. gram solution containing 5.45% KNO3 by mass, you first would solve for the grams of KNO3 in the 510. solution (using the mass percent). This gets you 0.0545 x 510grams =27.8 grams of KNO3. The oth...

Brandon_Tran_2E

Hey, this question is a bit tricky and I figured it out after Lavelle showed me through his office hours. First you would take your 2.111 grams of Na2CO3 and convert it to moles using the molar mass. Then take the moles and divide it by .250L to get the concentration of Na2CO3. The question is askin...

Brandon_Tran_2E

Hey, mole ratio is from a chemical reaction for example: 2A + B -> C + D Say you are told that you have 8 mols of A. Using the mole ratio from the chemical equation, for every 2 moles of A the reaction produces 1 mole of D. So you predict that with 8 moles of A, you expect to get 4 moles of D produc...

Brandon_Tran_2E

Interchangeably. :)

Brandon_Tran_2E

Hey, if you are referring to part a, the question says "What volume of .788 M Na2CO3 (aq) [initial molarity] should be diluted to 150.0mL (final volume) with water to reduce its concentration to .0234M Na2CO3 (aq) [final molarity]. (.788mol/L)(V1) = (.0234mol/L)(.150 L) Solve for initial volume.

Brandon_Tran_2E

The limiting reactant is A since the molar ratio of the reaction is 2A : 1B. You have 1 B for the reaction but only 1A so A limits the amount of product that is produced.

Brandon_Tran_2E

Usually limiting reactant questions will ask you how much of a product will be produced when ____ grams of Reactant A reacts with ____ grams of Reactant B. (For example A + B --> C + D). After finding the limiting reactant, use that reactant to calculate for the amount of product asked from the ques...

Brandon_Tran_2E

Yes if the question gives you mL instead of liters.

Brandon_Tran_2E

The multiplication sign with the H2O just means that that is a hydrate compound (special type of compound with water). To do this question I believe you convert grams to moles first. (Molar mass of Na2CO3 x 10H2O is 286 grams/mol). Using the molar mass, with 2.00 grams of the compound you get .00699...

Brandon_Tran_2E

Yes it is necessary to find the mass % in order to solve the question unless it is given to you. For that particular question you would have to subtract 339.2 grams of Cobalt from the 996.08 grams of the compound to get 656.88 grams of the Fluorine gas. Then you would divide the Cobalt and Fluorine ...

Brandon_Tran_2E

Hey Kylie, the net moles of gas means the overall moles gas produced from the reactants. There are 36 moles on the product side and 30 moles on the reactant side. The net change is 36 - 30 = 6

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