CHEMISTRY COMMUNITY

Valeria Viera 1B

Which should we use on final:
Sum of bonds broken - sum of bond formed
Or
Sum of bonds in reactant side - sum of bonds in product side

Valeria Viera 1B

What do we need to include/label in drawing a concentration cell?
When I google a picture of a cell there’s so much information

Valeria Viera 1B

How is balancing any different if there are acidic conditions (asking on question 3b in Lyndon’s Pork Ramen review)

Valeria Viera 1B

What would be an example of a conductive metal? Should we have some memorized?

Valeria Viera 1B

I attached a graph from Wikipedia if that helps!

Valeria Viera 1B

I believe it’s because it displays a straight line so it’s easier to say more things about its slope since it’s a straight line.
If it was all wiggly I imagine it might be harder to make estimates or assume what K is for example.

Valeria Viera 1B

Activation energy is the energy needed for a reaction to happen (for reactants to turn into products or vice versa) You can show this using graphs by drawing a little hump (if you google activation energy exothermic / endothermic they’ll have all the graphs showing this) If the hump goes from higher...

Valeria Viera 1B

You should use half life if there’s a questions asking how long does it take for the concentration of “A” to get to a certain percentage of its original concentration
Or when a questions asks how much of A concentration is left after certain years if it’s half life is 10 years or so, for example.

Valeria Viera 1B

What does it mean for an electrode to be ion selective?
What’s the difference between an electrode and an electron?
What role do ion selective electrons play in electrolysis?

Valeria Viera 1B

In Friday’s lecture, professor Lavelle explain the difference between the unique rate and the instantaneous rate but I don’t think I understood
Could anyone explain?

Valeria Viera 1B

What does it mean for a reaction to be first or second order? Did we cover this in 14a or 14b?

Valeria Viera 1B

Also the professor also showed us the cell diagram in writing form and omgg I feel like there is so much going on. Could someone explain it please ?

Valeria Viera 1B

How do you know if delta S, H, or G are spontaneous?

Valeria Viera 1B

What is the difference between E and E°?

Valeria Viera 1B

in lecture, the professor showed a cell diagram with a little line labeled circuit
What is this? Like a copper wire that transmits electrons ?

Valeria Viera 1B

What is the relationship between activation energy and kinetic control?

Valeria Viera 1B

There are so many work equations and equations derived from others
How do you know which to use? Do you need to memorize each or know how to derive them?
Thanks in advance

Valeria Viera 1B

What is the relationship between enthpy and exothermic/endothermic reactions?
Can any explain the two graphs we saw in class ? (One has a flat line and the other had a curved line)

Valeria Viera 1B

How do you know if work was done on the system or if system did work on its surroundings? I know it’s a difference of work being negative but I don’t understand why

Valeria Viera 1B

I’ve seen this equation written as q=nCdeltaT and q=mCdeltaT
Should we use moles or grams for this equation on the test?

Valeria Viera 1B

Why is entropy at its maximum when it’s at equilibrium ?

Valeria Viera 1B

Hi I have no idea how to approach this problem: Calculate the heat that must be supplied to a 500g Cu kettle containing 400g of water to raise its temperature from 22°C to 100°C I know heat is q but I can’t seem to find an equation with q and temperature in the lecture notes. Any help is appreciated!

Valeria Viera 1B

What is the difference between constant P calorimetry and constant V calorimetry? How do they work? When would we use them?

Valeria Viera 1B

What is the difference between $\Delta H$ and standard enthalpy of formation $\Delta H_f$ ° ?

How do we know which to use?

Valeria Viera 1B

What is internal energy and how do we find it?

Valeria Viera 1B

Under method two- additional comments from the notes it says “ 2) bond enthalpies of diatomic molecules are accurate (measured for those molecules)” what does this mean? And enthalpies of diatomic molecules are more accurate as opposed to what, exactly?

Thank you!

Valeria Viera 1B

Can anyone show me how to add to reactions together for Hess’s law? Or give an example?

Thank you!

Valeria Viera 1B

In Wednesday’s lecture professor Lavelle said enthalpy has state properties but heat does not
Can anyone explain to me

Thank you!

Valeria Viera 1B

I took 14A a long time ago so I’m really rusty when it comes to writing equations Can someone help me by explaining the steps to writing an equation where a weak base/acid reacts with water to make H3O or OH? Like how do you know where the H/proton is being transferred to? (For example in NH3 + H2O ...

Valeria Viera 1B

Can someone tell me when we would use the ice box, what are the steps to it and also
when is it better to assume x is a really small number instead of just using the quadratic formula? (Like 1.01-x becoming just 1.01 if we assume x is really tiny)

Valeria Viera 1B

In problem 12.35 (6th Ed) they ask us to get Ka from pKa which is fine you just use 10^pKa. However I noticed that the pKa values have numbers right next to them like pKa1=... or pKa2=.... what do they mean by saying pKa2 ? How do you get Ka from that ? (Part d says: give the Ka value for the acid H...

Valeria Viera 1B

What are some of the main differences between K and Q? how are they similar?

Valeria Viera 1B

I don’t understand how the ratio between O2 and O3 is different. How would you predict it just from seeing a equation. Is it because of the molar ratios?

Valeria Viera 1B

How come pressure does not affect Kc? It does affect Kp right?

Valeria Viera 1B

Hello,
I was not able to go to today’s lecture for chem 14B :( could anyone please let me know what happened today? I will appreciate you and thank you for the rest of the quarter!

Valeria Viera 1B

hello, can someone explain to me the difference between lewis acids/bases vs bronsteds? Also, what are some key differences between acids and bases? what is important to remember?

Valeria Viera 1B

Can someone explain to me how to determine hybridization? What are some key things to remember?

Valeria Viera 1B

I get that a single bond has one sigma bond and that a double bond has one sigma and one pi bond but what is the difference between a sigma bond and a pi bond?

Valeria Viera 1B

thanks guys helped a lot!

Valeria Viera 1B

can someone go over important things in determining VSEPR shape? thank you!

Valeria Viera 1B

i found this picture
hope it helps!

Valeria Viera 1B

doesn't this refer to the shape of the electrons like the way they move or something like that? I am also confused on this

Valeria Viera 1B

I think it’s important to have symmetry when drawing structures

Hope this helps

Valeria Viera 1B

Do you mean like a radical?

Valeria Viera 1B

(Is this is about that one question in test 3 ?) I went to a UA and asked and he basically said the slight negative charge of the Two molecules made the nucleus of the atom slightly more positive which would have more of an attractive force pulling in other atoms So maybe this makes the double bond ...

Valeria Viera 1B

How do we show ionic bonds?
In a covalent bond we can draw a line that shows two atoms sharing electrons
but ionic bonds don't share electrons
So like let's say we're drawing the lewis structure for NaCl
Do we just write Na+ Cl- and that shows a bond?

Valeria Viera 1B

I agree with Joanna,
The central atom should I always be the one with the least electronegativity
The trend in periodic table increases going up and to the right
Out of Cl, O, and C in this example C is the most left so it has the least electronegativity

Valeria Viera 1B

I think it's right ( it might just be a matter of structure but I don't think we've learned about that yet)

Also, would this be resonance?

Valeria Viera 1B

The way a UA described it to me was that electronegativity is the ability of a neutral atom to attract electrons towards itself and electron affinity is the energy released when the electron is added to the neutral atom (kind of like a cause and effect I think) hope this helps

Valeria Viera 1B

I believe taking a lone pair of electrons from oxygen to make a double bond between N and O is possible and it would make the formal charges of O and N zero (without the double bond the formal charge of N is +1 and FC of O is -1) So I think creating a double bond would be the way to go \dddot{N}= {\...

Valeria Viera 1B

it's because F it does not follow the rules to have an expanding octet meaning that it is not possible for F to take anymore electrons since it is in the second row (elements from third row and down can get expanding octets from d orbital)

Valeria Viera 1B

A guy went by yesterday in lecture saying there would be a review session Friday from 12 to 1:50 ( I don’t know if he’s from the step up/workshops) I’m not sure if this helps

Valeria Viera 1B

In my step up section someone said that the order is dsp as well (ex: 3d10 4s2 4p6). However they also said that if the d orbitals are not full then the order is actually sdp (ex: 4s2 3d5 instead of 3d5 4s2).

Is that right? If so doesn’t that go against the whole writing from least to highest energy?

Valeria Viera 1B

I understand that Cu and Cr are exceptions when it comes to electron configurations since the d orbital is not full so then electrons in the s orbital go down a level to have a balanced amount of electrons in d. Does this mean that the elements in the same group will behave similarly? Also, is it po...

Valeria Viera 1B

I think what it means is that e- are pulled by the nucleus and therefore can't escape I suppose? Like a particle that is stuck inside a box.

Valeria Viera 1B

gamma rays have a higher energy since they have a higher frequency and a shorter wavelength (it helps to look at pictures of this)

Valeria Viera 1B

I asked my TA about which equation to use and he said that we can derive the same answer from either or so we can use whichever we want

Valeria Viera 1B

section in the textbook? or here on the website? I also have this question

Valeria Viera 1B

I think it's something that we will review later on since hybridization is mentioned in outline 4 "Molecular Shape and Structure"

Valeria Viera 1B

I believe we use them to be as exact as possible. For example, when measuring grams of a compound, one might get different results depending in how they round (sig figs are important in rounding). Other than using them in actual lab, I think we use them so we know how to deal with decimals (there ca...

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