CHEMISTRY COMMUNITY

AngieGarcia_4F

If it's endothermic you can treat heat like a reactant and if its exothermic you can treat heat like a product and apply Le Chatlier's principle like that.
Ex. 3H2 + N2 -> 2NH3 + Heat (exothermic). If you add heat to this reaction it'll shift left.

AngieGarcia_4F

You use kinetics when you are observing the speed/rate of a reaction and use thermodynamics to tell if the reaction is favored or not

AngieGarcia_4F

Zero order - rate doesn't depend on concentration
First order - depends on one concentration
Second order - depends on two concentrations or the square of one

AngieGarcia_4F

Does anyone know how we are going to get our test 2 back since in-person classes got cancelled?

AngieGarcia_4F

Are our review sessions going to be cancelled too?

AngieGarcia_4F

We'll probably get them back week 10 in section but i'm not 100% sure

AngieGarcia_4F

How in the world do you do 6.73. Am I looking at the wrong appendix or something?

AngieGarcia_4F

Can anyone explain why for 6.57 the given rxn is the anode?

AngieGarcia_4F

Can anyone explain the difference between E* and E in terms of the homework problem 6.43? Like how do we know what effects/changes their values?

AngieGarcia_4F

Can anyone explain why in the cell diagram for 6L.5(b) the solid I2 is written before the I- (aq)?

AngieGarcia_4F

Can anybody help me with balancing the cathode/reduction reaction in 6L.3(d)?
The cell diagram for the cathode is II OH-(aq) I O2(g) I Pt(s)

AngieGarcia_4F

When we use deltaG=-nFE, how do we know what n to use?

AngieGarcia_4F

The degree symbol indicates that the reaction you are observing was done under standard conditions (298K, 1 bar)

AngieGarcia_4F

On tests for example, will the cathode always be on the right and the anode always on the left?
If not, how do I tell which is the anode and which is the cathode?

AngieGarcia_4F

Can kinetics tell you if a reaction is favorable or not? And if so, how?

AngieGarcia_4F

They are synonymous. However, we do need to know the difference between a galvanic and electrolytic cell; galvanic converts chemical energy into electrical energy and an electrolytic cell turns electrical energy into chemical energy.

AngieGarcia_4F

We're not going to be tested on kinetics in test 2 right?

AngieGarcia_4F

You need a solid to act as an electrode and Pt is an effective and common one bc it is resistant to oxidation, so if there is no solid we just assume it is Pt

AngieGarcia_4F

What do we need to know about the Vant Hoff equation? Like will we need to ever calculate it? And what concepts about the equation should we know?

AngieGarcia_4F

I looked it up and i found "Platinum is used in electrochemical cells because it is resistant to oxidation- it will not easily react, which makes in excellent as an electrode as it will not take part in the Redox reactions occurring in electrochemical cells."

AngieGarcia_4F

Yes, I believe they were both aqueous so you wouldn't separate them with a 'I'

AngieGarcia_4F

I think the only important difference for us to know is that when you write cell diagrams you put one 'I' between the anode and cathode for a disk and 'II' when there's a salt bridge between them

AngieGarcia_4F

What of thermodynamics do we need to know for test 2?

AngieGarcia_4F

Does anyone know what values we assume if told something happens under STP?

AngieGarcia_4F

I think what equation you'd use would depend on what info the question provides

AngieGarcia_4F

You relate these two with the Nernst equation: E=E*-RT/nF x lnQ. (the * is a knot, I just can't find one on my keyboard) So, if Q (concentration) increases then the term RT/nF x lnQ increases meaning you subtract a larger amount from E* and E is smaller. So I believe concentration and cell potential...

AngieGarcia_4F

Does anyone know what day our test 2 get pushed back to?

AngieGarcia_4F

Does anyone know what equations we will need to know on the midterm that won't be on the formula sheet?

AngieGarcia_4F

Does isothermal mean the same thing as reversible?

AngieGarcia_4F

Monatomic compounds are composed of single atoms, and diatomic compounds are composed of molecules containing two atoms. what-are-the-seven-diatomic-elements-606623-v3-5b562dab46e0fb0037fee8c7.png Difference-Between-Monatomic-and-Diatomic-Comparison-Summary.png I don't know why the C s values are 3...

AngieGarcia_4F

In the midterm review today Matthew said that S(sys)=-S(surr) when a process is reversible, but how do S(sys) and S(surr) relate when a process is irreversible?

AngieGarcia_4F

Since we did not finish all the Gibbs free energy topics is the only equation we need to know for the midterm G=H-TS?

AngieGarcia_4F

What does mono and diatomic mean and why are the Cs for them 3/2R and 5/2R?

AngieGarcia_4F

Can anyone explain what makes an expansion reversible versus irreversible?

AngieGarcia_4F

Can anybody explain the difference between heat and temperature?

AngieGarcia_4F

What does it mean when someone says something is an extensive property? Like how is heat capacity an extensive property and specific heat capacity is not?

AngieGarcia_4F

I had to leave early from Lyndon's step-up today, does anyone have the answers to the worksheet?

AngieGarcia_4F

Can anybody explain what it means for a reaction to be reversible/irreversible?

AngieGarcia_4F

I doubt we will, that would suck, but maybe ask your TA for confirmation

AngieGarcia_4F

I think technically all reactions can be reversible when put under certain conditions, but if you mean when we double-arrow a reaction I believe it is because it doesn't fully dissociate or the reverse reaction is likely to occur

AngieGarcia_4F

In an exothermic reactant you can treat heat like a product so if you "added product" (increased heat) the equilibrium would shift left towards the reactants

AngieGarcia_4F

Because you are subtracting a very minuscule amount from a much larger initial amount so the subtraction becomes negligible. Like if I have $10,000 and I give away $1 I would basically still have $10,000.

AngieGarcia_4F

The [H3O+] is 1.5M

AngieGarcia_4F

For this problem I keep taking the -log of [H3O+] to find the pH and getting -0.176 but the answer book says it's +0.176, what am I doing wrong?

AngieGarcia_4F

Why does adding an inert gas not effect an equation?

AngieGarcia_4F

I think it's because K is an activity and activities don't have units.

AngieGarcia_4F

Can anybody explain how to do 6D.3?

AngieGarcia_4F

Can anyone help me with the first two rows of 6B.9?

AngieGarcia_4F

What does it mean if a pH is negative?

AngieGarcia_4F

When am i supposed to use Kc rather than Kp and vice versa? Because i heard that you use Kp for gasses but in an example problem during one of the step-ups we used Kc for an equation with just gasses.

AngieGarcia_4F

What is an inert gas?

AngieGarcia_4F

I think it would depend on the information given in the question (concentration or pressure). The units for pressure are usually atm or bar.

AngieGarcia_4F

Ka x Kb = 10^-14 so if you have Kb and are asked to find Ka then you do 10^-14/Kb.
I am not sure how to find the pH though.

AngieGarcia_4F

I think you use ICE tables when you're given K and an initial concentration and are asked to find a final concentration.

AngieGarcia_4F

On question 6.21 in the textbook why can't the Oxygen on the Thymine accept protons?

AngieGarcia_4F

Can anyone explain 6.5 part c from the textbook?

AngieGarcia_4F

(N2p, N2p) because pi bonds happen when p orbitals overlap. does this mean that pi bonds can only be formed in p orbitals only? Yeah i'm pretty sure by definition pi bonds form between the overlapping of p orbitals. There could be exceptions I don't know of but when you look it up it says overlappi...

AngieGarcia_4F

I'm not sure but I know that having an octet is the most important thing when drawing lewis structures and then usually from making sure each atom has an octet you can figure out how to best balance the formal charges. What if there is more than one way to make all atoms have eight electrons? Then ...

AngieGarcia_4F

(N2p, N2p) because pi bonds happen when p orbitals overlap.

AngieGarcia_4F

Either will work, but on Dr. Levelle's pdf the ones in the starred column are what he will usually use i believe.

AngieGarcia_4F

I think you could relate it to chelating ligands because a ligand cant create a ring around a metal if it cant rotate meaning it would have to have the right type of bond (single vs double) in the right places.

AngieGarcia_4F

I'm pretty sure it can get up tp 6.

AngieGarcia_4F

I thought that polydentate ligands were put in parentheses when there is multiple of them and that explains 9C.4 but not 9C.3 so i'm confused too

AngieGarcia_4F

On a test though when writing out hybridization i think it doesn't matter if you write the 2 in front as long as the sp^2 part is correct.

AngieGarcia_4F

Chelation is when a polydentate ligand forms a ring around its central atom. All polydentate ligands are said to be chelating.

AngieGarcia_4F

I'm not sure but I know that having an octet is the most important thing when drawing lewis structures and then usually from making sure each atom has an octet you can figure out how to best balance the formal charges.

AngieGarcia_4F

At the review session we were told that when going from name to formula the order of the ligands does not matter.

AngieGarcia_4F

14A-1, 10am class: Last name A-L in CS 50.
Last name M-Z in Lakretz 110.
14A-3, 12noon class: Last name A-G in CS 24.
Last name H-M in CS 76.
Last name N-Z in Franz 1178.
14A-4, 2pm class: Last name A-Z in Moore 100.

AngieGarcia_4F

For acids you look at either:
1. Bond length
2. Resulting anion stability.
i'm not sure about bases though

AngieGarcia_4F

Chelates form a ring around the central atom, whereas polydentate ligands allow more than one of its binding sites to be occupied. I think that a polydentate ligand can be a chelate, but they are not necessarily a chelate. In the review session i'm pretty sure Matthew said all polydentate ligands c...

AngieGarcia_4F

Polyprotic acids can donate more than one proton and polyprotic bases can accept more than one proton. For example, H2SO4 is a polyprotic acid and its conjugate base SO4^2- would be a polyprotic base.

AngieGarcia_4F

It's hexadentate and it is also a chelating ligand.

AngieGarcia_4F

Chelates form a ring around the central atom, whereas polydentate ligands allow more than one of its binding sites to be occupied. I think that a polydentate ligand can be a chelate, but they are not necessarily a chelate. In the review session i'm pretty sure Matthew said all polydentate ligands c...

AngieGarcia_4F

If one of the ions in a salt comes from a weak acid or base then the salt will change the pH.

AngieGarcia_4F

A strong acid or base will completely dissociate in water, leading to a higher concentration of [H+] or [OH-] in the solution which contributes to a more extreme pH or pOH.

AngieGarcia_4F

Probably the 7 main strong & weak acids he went over in class, and we will probably have to know bases too, but i'm sure Dr. Lavelle will tell us as we get closer to the final.

AngieGarcia_4F

If you were given a Hydrogen concentration of [H+]=0.1M, for example, and asked to find the pH, you would plug the concentration into the formula pH=-log[H+]; pH=-log[0.1M], and just plug it into your calculator.

AngieGarcia_4F

They are the same thing but the definition of an Acid can be defined as both a Lewis Acid (accepts e- pair) or Bronstead Acid (proton donor).

AngieGarcia_4F

Any site where a Hydrogen atom bonds to a Nitrogen, Oxygen, or Fluorine atom.

AngieGarcia_4F

I believe they are all just synonyms of each other

AngieGarcia_4F

The proton acceptor is the Bronstead Base/ e- pair donator (Lewis Base), and the proton donor is the Bronstead Acid/ e- pair acceptor (Lewis Acid).

AngieGarcia_4F

Clean coal contains more carbon and less sulfur meaning it is better or "cleaner" for the environment whereas dirty coal is the opposite.

AngieGarcia_4F

I think it would be a weak acid/base still because the definition of a strong acid/base is it completely ionizes in water, so I would assume that if an acid or base did not completely ionize in water, even if it did for a notable percentage, it would still be a weak one just because it does not fit ...

AngieGarcia_4F

Heres a joke for you too:
Ya'll wanna hear a joke about chemistry or Na?

AngieGarcia_4F

Linear has no lone electrons so it would be AX but a bent shape has a lone pair so it would be AXE.

AngieGarcia_4F

If he never went over it in the lecture i'd read it in the textbook just in case.

AngieGarcia_4F

Since Test 2 will only be on topics covered in the last 3 lectures i'd assume it's going to be mainly concept based.

AngieGarcia_4F

According to an email from my TA test 2 will include: -Use the Valence-Shell Electron-Pair Repulsion Model (VSEPR) to determine the shape of inorganic, organic, and small biological molecules, cations, and anions. -Use bond dipole moments and shape to determine if a molecule is polar or non-polar. -...

AngieGarcia_4F

We are going over Sigma & Pi bonds on Monday 11/18.

AngieGarcia_4F

Emily_4B wrote:Do you guys know if we’ll get the midterm back or be able to look at it in office hours to review this question?

My TA went over the midterm during discussion so maybe yours will too.

AngieGarcia_4F

Ionic because the electronegativity difference between the two atoms in an ionic bond are usually greater than the electronegativity difference between atoms in covalent bonds.

AngieGarcia_4F

Nitrogen has symmetry in it's 2p orbital (1 e- in each sub shell) and no electron-electron repulsion whereas Oxygen has one more electron than Nitrogen meaning its 2px orbital has electron-electron repulsion so its easier to ionize the fourth electron in the 2p orbital.

AngieGarcia_4F

If they have a d orbital they can expand their octet

AngieGarcia_4F

I think this week we covered topic 2D

AngieGarcia_4F

According to the textbook, the atomic radius is half the distance between the centers of neighboring atoms and the ionic radius is the contribution of an ion to the distance between neighboring ions in a solid ionic compound. You can find out which isoelectronic ion has a larger radius by taking nuc...

AngieGarcia_4F

Since Cl is in the third period it can hold electrons in its d shell (3d) and form an expanded octet. I googled it and found the example: ClF3

AngieGarcia_4F

When atoms have d shells they can hold more than 8 electrons

AngieGarcia_4F

Atomic radius

AngieGarcia_4F

Atoms are isoelectronic when they have the same number of electrons. For example, N2-, O-, and F are isoelectronic.

AngieGarcia_4F

I don't think it matters, as long as you follow the octet rule and put the bracket and the ion's respective charge around the lewis structure.

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