CHEMISTRY COMMUNITY

Mahnoor_Wani_1I

I don't why but I keep getting this question wrong. The presence of a catalyst provides a reaction pathway in which the activation energy of a reaction is reduced by 67.00 kJ⋅mol−1 Uncatalyzed: A⟶B Ea=137.00 kJ⋅mol−1 Catalyzed: A⟶B Ea=70.00 kJ⋅mol−1 Determine the factor by which the catalyzed reacti...

Mahnoor_Wani_1I

Yeah I think we can use the electrolytic cell to reverse the reaction

Mahnoor_Wani_1I

Yeah make sure you have identified in parenthesis if a compound is in aqueous solution (aq), liquid state (l), solid(s), or gas (g) state.

Mahnoor_Wani_1I

I went to few drop-in session and I think they are worth going to if you have specific questions. I usually go if I need help with specific homework qs, textbook problems, or a concept in class.

Mahnoor_Wani_1I

This is correct but remove the parenthesis and only have the coefficient 2 in front of Fe2O3. I'm not sure why sapling marks this incorrect but your answer is correct

Mahnoor_Wani_1I

First write the reduction half reaction for Fe2+ and Fe3+. Then use the appendix two or the standard reduction potential table provided in spaling to find the reduction potential. Then, Write the relevant reduction half reaction for each of the following molecules in the choices and find their reduc...

Mahnoor_Wani_1I

I agree with the above post. Adiabatic just means there is no heat transfer between system and surroundings. So no heat is lost/gained. Only q(heat) is equal 0. For work we need to calculate to find its value. Work is only zero for isochoric (constant volume) system like bomb calorimeter

Mahnoor_Wani_1I

Anode : metal electrode is losing electrons, more readily to form cations since its being oxidized
Cathode: metal electrode gaining electrons

Mahnoor_Wani_1I

I agree with the post above. Usually, one process is spontaneous while the other is not. Also, reactants --> product is forward while products --> reactants are reverse depending of the info given about what are the products and reactants.

Mahnoor_Wani_1I

The main purpose of a salt bridge is not to move electrons but to maintain charge balance and keep the process running as the electrons are moving from one-half cell to the other. Without a salt bridge, the electrons produced at the anode would build up at the cathode and the reaction would stop run...

Mahnoor_Wani_1I

Reactants: Breaking bonds is often an endothermic processs the value of the enthalpy will be positive because it intakes energy to break the bond. Products: forming bonds is often an exothermic reaction that releases energy aka the value of the enthalpy will be negative if it is forming bonds.

Mahnoor_Wani_1I

Wandavision!

Mahnoor_Wani_1I

Bomb calorimeter is a closed system that allows heat to be exchange. The whole purpose of a bomb calorimeter is to calculate heat. We can calculate the q by taking in account of the change in temperature.

Mahnoor_Wani_1I

Happy Valentine's Day Everyone!

Mahnoor_Wani_1I

We use qrev for isothermal processes. Specifically when we want to find entropy of isothermal process that is not at constant pressure.

Mahnoor_Wani_1I

Hey!
I'm struggling too. I think what you are doing is more than enough to study for the exam. Make sure to take breaks so you are not overwhelmed :)

Mahnoor_Wani_1I

Thank you so much! I forgot that Pressure and Volume are inverse of each other

Mahnoor_Wani_1I

A 0.617 mol sample of SO2(g), initially at 298 K and 1.00 atm, is held at constant pressure while enough heat is applied to raise the temperature of the gas by 19.7 K. Calculate the amount of heat q required to bring about this temperature change, and find the corresponding total change in the inter...

Mahnoor_Wani_1I

Ryan_Page_1J wrote:Check out YouTube videos for thermodynamics. I recommend the organic chemistry tutor. He breaks the concepts and formulas down in a clear and concise way that helped my understanding.

I second this!! Organic chem tutor breaks down everything you need to know about thermodynamics

Mahnoor_Wani_1I

Calculate the change in entropy when the pressure of 1.50mol Ne(g) is decreased isothermally from 15.0 atm to 0.500 atm. Assume ideal behavior. I understand that we need to use the formula nRln(P2/P1). However, I don't understand why 15 = P2 when the pressure is going from 15 to 0.5. So shouldn't 15...

Mahnoor_Wani_1I

does that mean at constant volume there is no work done on the system? So the U must equal to heat

Mahnoor_Wani_1I

Personally, I have heard that it is better to take in person if you plan to work at a lab. The skills that you will learn in in-person lab will come in handy when applying to labs.

Mahnoor_Wani_1I

work and heat are different forms of energy transfers. If q=0 then it means the only form go energy transfer in the system is in terms of work and then internal energy = work

Mahnoor_Wani_1I

Those are really great tips :) To add on, if you are struggling with grasping concepts, watch organic chemistry tutor videos

Mahnoor_Wani_1I

You know q = nCdeltaT is the best equation to use to find heat because we are given moles of a substance and the formula to find molar heat capacity. If we were just given specific heat capacity we would use mCdeltaV instead

Mahnoor_Wani_1I

I have 25/25. Maybe the TAs are counting by the total posts for chem14b you have done so far. Your ta is most likely going to update it after you have 25 total posts.

Mahnoor_Wani_1I

Entropy is the randomness/ disorder in the system. Enthalpy is the measure of overall energy in the system.

I've attached below a great visual that helped me differentiate between these concepts.

Mahnoor_Wani_1I

Bomb calorimeter involves measuring the heat of a fuel sample when burned under stable temperature to evaluate the heating energy of the fuel sample. The sample can be a solid or liquid, but not a gas.

Mahnoor_Wani_1I

I am planning on taking 14c in the spring so I can be prepare for in-person chem 14bl lab. Cem14bl will go over some organic chemistry contents

Mahnoor_Wani_1I

I believe some will come from the textbooks. However, I think we can expect all of them to be similar to the textbook problems or the sapling problems .

Mahnoor_Wani_1I

I agree with the above posts. They are different. However, at constant pressure, the heat capacity = change in enthalpy divided by change in temp

Mahnoor_Wani_1I

I believe it is the same as last quarter: A is 93-96% while A- is 90-92%. However, the scores for midterms and finals may be reevaluated based on the class avaerage like the final last quarter for chem14b

Mahnoor_Wani_1I

I agree with the above posts. It was a little harder than I expected. Time wise, it was manageable. However, there were some questions I did not know how to approach.

Mahnoor_Wani_1I

Heat Capacity aka molar heat capacity is the measure of the amount of heat necessary to raise the temperature of one mole of a pure substance by one degree K. Whereas, Specific heat capacity is a measure of the amount of heat necessary to raise the temperature of one gram of a pure substance by one ...

Mahnoor_Wani_1I

yep they are correct because the pH is lower than the pKa, then the compound will be protonated. If the pH is higher than the pKa, then the compound will be deprotonated. Vice versa for the base

Mahnoor_Wani_1I

I found this website particularly helpful at explaining Hess's law in great detail: https://chem.libretexts.org/Bookshelves/Physical_and_Theoretical_Chemistry_Textbook_Maps/Supplemental_Modules_(Physical_and_Theoretical_Chemistry)/Thermodynamics/Thermodynamic_Cycles/Hesss_Law I agree with Selena! I...

Mahnoor_Wani_1I

Autoprotolysis is when one molecule transfers a proton to another molecule of the same kind. Its a molecule that is amphoteric like water. Water is the most common example of autoprotolysis. The kw is the autoprotolysis constant.

Mahnoor_Wani_1I

Thank you! That make sense

Mahnoor_Wani_1I

I would recommend downloading the solution manual so you can view them at your convenient time without having to log back into sapling

Mahnoor_Wani_1I

I agree with the posts above, doing textbook problems are KEY! The midterm qs are similar to the textbook problems. I also recommend going to UAs session for any clarifying question you may have or do some extra practice problems.

Mahnoor_Wani_1I

Yes, all the pKs and their equilibrium constants have a inverse relationship. pks are just a simplified version to interpret the Ka/b (-logKa) values

Mahnoor_Wani_1I

6C.13 Arrange the following bases in order of increasing strength on the basis of the pKa values of their conjugate acids, which are given in parentheses: (a) ammonia (9.26); (b) methylamine (10.56); (c) ethylamine (10.81); (d) aniline (4.63; see Exercise 6C.12). Is there a simple pattern of strengt...

Mahnoor_Wani_1I

I believe that all the UAs workshops are helpful. They all have a good understanding of the materials and always try their best to help the students. Personally, I liked going to Justin's and Kate's workshop because they do a really good job on teaching the material and answering any questions stude...

Mahnoor_Wani_1I

From chem 14a I learned not to stress over chemistry too much. My advice would be to attend one or two UA sessions per week, do textbook problems, review lecture notes, and make a study guide using the learning outcomes

Mahnoor_Wani_1I

The coefficient on HD is 2 so there are two moles on the reactant side. The coefficient on H2 gas and D2 gas is 1 so there are 2 moles of gases on the product side. I think you are probably miscalculating the number of the moles on each side. I don't see 3 moles of reactants for d. Isn't the H2 on ...

Mahnoor_Wani_1I

The coefficient on HD is 2 so there are two moles on the reactant side. The coefficient on H2 gas and D2 gas is 1 so there are 2 moles of gases on the product side.
I think you are probably miscalculating the number of the moles on each side. I don't see 3 moles of reactants for d.

Mahnoor_Wani_1I

If you want to practice ICE tables with two positive x values, topic 5I has textbook problems that pertains to these types of problems. Usually, one of the positive value, when plugged in, would cause you to have a negative new equilibrium concentration.Therefore, you will be able to eliminate that ...

Mahnoor_Wani_1I

I would say use 10^-3 because this is the value used in the textbook too. The video are few years old and the chemistry community is constantly evolving with new ways to write/identify things. So, I would trust his lecture more since they are newer than the audio visual videos.

Mahnoor_Wani_1I

I understand how to use the ice/rice table to calculate the value of x to find the concentrations. Hypothetically, what if both the values of x we get from the quadratic formula are positive, then which one would we use to calculate concentrations?

Mahnoor_Wani_1I

ATM is the standard unit of measure of pressure so we are most likely dealing with atm in chemistry, but I also agree with Sarah it depends on the units given in the problems.

Mahnoor_Wani_1I

Prioritize mental health over everything and be more productive

Mahnoor_Wani_1I

It is not mentioned in the syllabus so most likely not.

Mahnoor_Wani_1I

Last quarter what helped me the most with applying the concepts we learned in class was to go UAs workshops/step up session (one a week) and do practice problems in the textbook.

Mahnoor_Wani_1I

I know that the equilibrium constant is affected by the temperature, but why is it affected by temperature? Why is it only depended on temperature and not the the concentration of reactant we start off with.

Mahnoor_Wani_1I

spending more time with my family and focusing on finishing my shows

Mahnoor_Wani_1I

https://quizlet.com/462765872/ligand-na ... ds/?x=1jqt
here is another quizlet that someone in chem14a made that you can use!!!

Mahnoor_Wani_1I

we are expected to just write the basic formula for a compound he gives us but are not expected to calculate it

Mahnoor_Wani_1I

Thank you!!! This is really helpful

Mahnoor_Wani_1I

You can rewatch lectures that pertain to the topic that you are struggling at, you can also watch YouTube videos online that explains the topic, do practice problem and compare your answers with solution manual and see what you did wrong

Mahnoor_Wani_1I

Mari Williams 2k wrote:Going over them once or twice on quizlet is always helpful!

I agree with this! memorization is key to understanding common conjugates. There is also many quizlet available online so you do not have to worry about making one

Mahnoor_Wani_1I

Draw the lewis strcuture of the molecule
The ligand must have at least 2 atoms with lone pairs

Mahnoor_Wani_1I

Electron geometry describes the arrangement of electron in a compound. Molecular geometry describes the arrangement of atoms, excluding lone pairs

Mahnoor_Wani_1I

Coordination number is number of bonds (number of ligands) attached to the Transitional Metal. In the square planar complex, there are only 4 ligands attached and 2 lone pairs. So the coordination number is 4. REMEMBER NOT TO CONFUSED COORDINATION NUMBER WITH ELECTRON PAIRS OF TM!

Mahnoor_Wani_1I

[Co(NH3)4Cl2]Cl In naming coordination compounds, ligands are named in alphabetical order first and then the TM with their oxidation number. From the compound above we can see that Cl2 and NH3 are the ligands. Since there are two cl anions it is dichloro and since there are 4 NH3 it is tetraammine. ...

Mahnoor_Wani_1I

I don't think there any past final exams made available. However, in many of the workshops the questions are pulled directly from midterms and finals exams so you should be prepared by attending workshops. Also, you should do textbook problems to study. I think textbook problems are most similar to ...

Mahnoor_Wani_1I

Coordination numbers are the numbers of bonds ligands forms with the transitional metal. Basically, they are the number of ligands bonded to TM. If you are still confused I think you should rewatch the Monday lecture (specifically the coordination compound part), Dr. Lavelle goes into dept about coo...

Mahnoor_Wani_1I

When you draw out the lewis structure of CO3 2- you can see that there are two lewis structures. One structure has one CO double bond and two single CO bond. In this structure the Oxygen is capable of interacting with a transitional metal at two different places so it is classified as bidentate. The...

Mahnoor_Wani_1I

Yes, you are correct. +3 is the oxidation state of the Co. NH3 is neutral and since the charge of two chlorine outside is -2 the compound charge must be +2. Therefore, since Cl inside has a charge of -1 you set this equation: X -1 = +2. The X aka the oxidation of Co is +3

Mahnoor_Wani_1I

There is a lot of pre-made quizlets available that you can use as flashcard to study or as a practice test. I recommend this method because you can use quizlet on any browser anywhere

Mahnoor_Wani_1I

I'm not really sure if we can find most favorable structure if there is no resonance. They all have equal net charges of 0 too so I think they are all favorable.

Mahnoor_Wani_1I

They are really helpful! I try to go to at least two workshops per week. I think the workshops problems are very similar to the structure. And they go step-by-step to make sure you understand the concept/problems

Mahnoor_Wani_1I

Lone pairs have a stronger repelling effect than electrons in bonds. This is because lone pair have a larger electron cloud whereas bonding pair are being held in place by the two atom. Thus, to have the lowest energy/stable shape we need to have lone pairs as far away from other electron density re...

Mahnoor_Wani_1I

Is there a possibility that the finals are going to be curved?

Mahnoor_Wani_1I

Pi bonds are bonds formed by overlapping two parallel unhybridized p orbitals. If there are more than one adjacent orbitals the central atom can overlap with then its called a delocalized pi bonds. You can easily identify a delocalized pi bond if there is more than one adjacent atom from which a dou...

Mahnoor_Wani_1I

Here are my tips: ATTEND UAs Sessions!! They go over previous years midterm/final questions so you get used Dr. Lavelle exam structure. Make a study guide using the unit outlines, lecture notes, and textbook I think textbook problems + UAs session problems are the most similar to the exam so priorit...

Mahnoor_Wani_1I

From what I heard Chem 14B material is harder. The textbook is same. Based on the syllabi for 14B there are Two 50 minute tests, One 2 hour midterm exam.
One 3 hour final exam.

Mahnoor_Wani_1I

I always have test anxiety right before any test. The best thing to do in my opinion is finding a study routine that works best for you (aka not procasinate and divide things up for study) and clearing your mind by doing what you like the most (watching movies, talking a walk, or sleeping)

Mahnoor_Wani_1I

What is the difference between unhybridized and hybridized orbitals? How do we determine how many unhybridized orbitals a molecule have?

Mahnoor_Wani_1I

Lone pairs have a stronger repelling effect than electrons in bonds. This is because lone pair have a larger electron cloud whereas bonding pair are being held in place by the two atom. Thus, to have the lowest energy/stable shape we need to have lone pairs as far away from other electron density re...

Mahnoor_Wani_1I

I don't think so since it was only briefly mentioned in the textbook. Calculating it is a really complicated procedure that is beyond the scope of chemistry 14A so you don't have to worry about it Also, in order to analyze it we just look at the different colors. Since each color represent either th...

Mahnoor_Wani_1I

Based on the textbook and lectures, we should know that homonuclear diatomic molecules, benzene, methane, ethylene, and most organic molecules are non polars.

Mahnoor_Wani_1I

http://www.chem.ucla.edu/~harding/IGOC/ ... oment.html
I was also struggling with understanding what dipole moments are and the website above helped me understand them better. I hope It can help!

Mahnoor_Wani_1I

When I was looking up examples of sigma and pi bonds on google for a reference, I saw that there exist something called a delta bond. What exactly is a delta bond and how do we determine if a covalent compound has a delta bond? Also, are we expected to memorize delta bond for this course?

Mahnoor_Wani_1I

If you are struggling with memorizing the molecular shapes, watch this video: https://www.youtube.com/watch?v=r2XmaiEC0Vw!

Mahnoor_Wani_1I

Review your lecture notes, attends workshops/step sessions, practice problems from the book + homework, and if you are unsure about a topic don't be afraid to ask in the chemistry community !

Mahnoor_Wani_1I

Your TA will tell you when to start after making sure your desk is clear. After you are done, I am pretty sure you can just leave the zoom.

Mahnoor_Wani_1I

Basing of the problems in book about radicals, we should know that radicals have unpaired spins, be able to draw radicals/determine which structure is a radical, know that radicals are highly reactive/ can't be stored

Mahnoor_Wani_1I

Least formal charges = more favorable. More electronegative atom should have the negative charge since it attracts electrons. If mot electronegative atom doesn't have the negative charge then its not favorable

Mahnoor_Wani_1I

I have the same question about part c. How do we determine which atom bonds with which when we have three different atoms ?

Mahnoor_Wani_1I

How does resonance lowers energy and make molecules stable?

Mahnoor_Wani_1I

I'm also enrolling in 14B In second enrollment because there is usually enough seats because it is in such a high demands

Mahnoor_Wani_1I

one of the LA mentioned that oxidation states will not be tested. I think we just need to have a general understanding of them

Mahnoor_Wani_1I

What is the difference between temporary and permanent dipole moments? How are they both formed?

Mahnoor_Wani_1I

I think it is both. They can occur between two ions in an ionic bond or between atoms in a covalent bond

Mahnoor_Wani_1I

"E stands for three things: Electronegativity, Electron affinity, and ionization Energy. All of these E’s increase going up and to the right of the periodic table." from MCAT mnemonics Periodic Trends

Mahnoor_Wani_1I

Why is the electron affinity for Carbon greater than nitrogen? Doesn't carbon occupying an orbital outside a closed shell means it farther from nucleus and requires energy.
Also, is the Nobel gas and C&N are the only exceptions in electron affinity?

Mahnoor_Wani_1I

Just out of curiosity, If it is more than 5 orbitals, do we go by alphabet order or is there a specific order you need to go by

Mahnoor_Wani_1I

Would the TA office hours and UA sessions will also be cancelled then?

Mahnoor_Wani_1I

Hi ! I agree with you that studying at home has been really challenging for many. I think the best tip is to make a schedule and stick to it. Schedule for when you are going to do homework, study, or attend UA sessions. Also when studying follow the 45 min rule. Study for 45 min and take a 10 min br...

Mahnoor_Wani_1I

While watching today's lecture, I was confused about the concept of delocalization vs localization. Can someone explain to what each terms means in terms of resonance structures. Also, why does the delocalization of electrons increases a molecule or compound stability?

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