CHEMISTRY COMMUNITY

madisondesilva1c

Can someone explain to me how the Reverse and forward K are related. I was told today that forward is not always 1/reverse, similar to how we learned during equilibrium. Can someone clarify this please?

madisondesilva1c

Can someone explain to me how the Reverse and forward K are related. I was told today that forward is not always 1/reverse, similar to how we learned during equilibrium. Can someone clarify this please?

madisondesilva1c

The two will have the same unique rate but the k forward and k reverse will not be the same value. The rate of formation of b is 1/2 decomposition of A given your provided example. Check the book problems such as 15.1 in 6th edition, I believe this could clarify this topic for you.

madisondesilva1c

Half life and k are related differently upon what order the reaction proceeds in. The most common half life problems use first order reactions and this is simply .693/k=t1/2. Therefore you can see the inverse relationship that exists.

madisondesilva1c

You use these values when the question involves an ideal gas in thermodynamics. Therefore for a change in entropy question when volume is changing, you can hold pressure constant and use the Cp value in the equation.

madisondesilva1c

amogha_koka3I wrote:Will we be required to know how to derive half-life equations for each order of reaction

I believe this is on the syllabus, and was gone over in lecture so I feel that we are responsible for knowing how to do this.

madisondesilva1c

The prefix simply denotes how many elements one begins with in the elementary step. I believe Dr. Lavelle, went over this in a chart during the last lecture.

madisondesilva1c

The average rate can be found by looking at change in concentration over change in time, and can describe the general change in rate. While instantaneous change can be found by solving for the derivative as time approaches zero. This will be the rate change at a specific time.

madisondesilva1c

In lecture, we finished by going over how the 1st order reaction rate can appear as a exponential if you take the exponentiate the rate equation for half life. Does this pattern still apply for second order reactions in a similar manner, since exponential is decreasing as a function of initial conce...

madisondesilva1c

Should the convention of rate laws always include moles vs mmol? The textbook often gives mmol when giving concentration, but should we convert this to moles to stay in SI conventions?

madisondesilva1c

Is the order of reaction solely determined by how many reactants are in the reaction? How high of an order should we be prepared to be able to find rates for etc?

madisondesilva1c

Dr. Lavelle posted Math assistance sheets on the website which I feel are indicative of the extent of calculus worth reviewing since he pointed them out today near the end of class.

madisondesilva1c

Given any example that is not intuitive or a reaction in everyday life such as a diamond going to graphite in a very slow manner, how is one to predict whether thermodynamics or kinetics is able to control that said reaction given the details of both?

madisondesilva1c

The in class examples had coefficients that were 1 and 2, however what is the best way to approach a reaction where the stoichiometric coefficients do not divide out in a neat fashion?

madisondesilva1c

Even though a unique rate is the same for all concentrations of products of reactants, does it still change with time. Therefore can a unique rate at the beginning of the reaction be different than the unique rate at the end since it is a function of time?

madisondesilva1c

If Q<K does this imply that delta G is negative, meaning that it will progress in the forward direction or must be still consider temperature, enthalpy, and entropy values as well?

madisondesilva1c

When solving for G using H and S, if the H is given in J/mol, should we covert the value to KJ so that our final answer is in the SI unit is in KJ or just be consistent with the units?

madisondesilva1c

Are there any trends to predict whether a compound is acting as a reduction or oxidation agent? Or can all act as either depending on the reaction?

madisondesilva1c

Can someone explain how to solve 10 and 11? For 11, I used the mol(cv)(ln(t2/t1)) and am not getting the correct answer. Can someone please outline the steps to solve?

madisondesilva1c

Delta U is also 0 when there is no temperature change throughout the process.

madisondesilva1c

Is a calorimeter always isolated? Therefore, does delta U always equal work, assuming no heat can enter or leave the system?

madisondesilva1c

It is always best to go with what is given, if OH is formed, then solve for pOH and then 14-pOH to find pH. If H+ is a product of the disassociation, then solve for pH and then use 14-pH if they are asking for pOH?

madisondesilva1c

Is is correct if given a pKa value, to the raise 10^ -pka to find the ka value, then use the expression for ka to solve for H+ concentration, x, to then take the -log of the H+ concentration, to then find the pH?

Are the pKA value and PH related through the Ka constant?

madisondesilva1c

Why is the work quantity in a isobaric process negative, in physics we have learned that w= +pdeltav... Can someone explain where the confusion comes from? Is this due to the fact we are using pressure external?

madisondesilva1c

If the work is negative, how would the isobaric work equation change? Would the integral now be of a positive quantity instead of a negative one?

madisondesilva1c

Will Standard enthalpies be given on exam, or are there certain reactants and products that we should know specifically?

madisondesilva1c

Is there a way to know when to use each enthalpy value, if so can someone please summarize them? I know that one must use the standard enthalpy when solving for the enthalpy of the reaction, but what are the conditions for using the variation notations of enthalpy ie. reaction and formation enthalpy?

madisondesilva1c

The piston either expands or minimizes the volume of your system. Therefore, the gas exerting work on a piston will increase the volume of the closed system. However if the environment does work on the system, the volume will decrease which is explained by the piston of the system compressing.

madisondesilva1c

When figuring out what bonds to break to then reform, is it necessary to draw out the lewis structures? Are we expected to remember and draw out lewis structures in the way that we did in 14A?

madisondesilva1c

In lecture, Professor Lavelle talked about Standard States of pure substances and I was a bit confused on how people knew these so easily. Is this something we should memorize? Or are certain blocks of elements all in the same standard state?

madisondesilva1c

As the Q and K value approach each other, does the rate at which products and reactants are converted ever decline or is the reaction a constant rate?

madisondesilva1c

Is there any type of system that does not fit into this, has qualities of both open and closed say? If this is the case, how to you classify the system?

madisondesilva1c

What are some common examples of ideal gases being added to a reaction? I am having trouble imagining this happening but feel that a real world example may be able to help me understand this better.

madisondesilva1c

Is it equivalent to write mol.L^-1 and M given that molarity is the moles of solute per liter?

madisondesilva1c

I personally can not make all of the Worksheet guided UA sessions, but see they are posted online with solutions but no work. Is there anyway we could coordinate making a more detailed solution guide for students that cannot make the given session?

madisondesilva1c

X is negligible if the K value is below 10^-3. Therefore it would not change the initial concentration of the given reactant, so it is able to be disregarded in these cases.

madisondesilva1c

Is there a list somewhere that indicates strong bases and strong acids that we should know in order to properly execute skills on exams? Are there any biological compounds that we are also expected to know the chemical formula for?

madisondesilva1c

If we encounter a problem where pH is negative, are we supposed to note that this is a super acid? Or is notation not required?

madisondesilva1c

When computing the value of x in ICE tables, using the moles of products and reactants: do subscripts matter? Or does x strictly come from the stoichiometric coefficient?

madisondesilva1c

If there is a solid for a reactant, do you assume that the solid is added to a flask containing water, therefore it really is in aqueous form. Dr. Lavelle mentioned in lecture that you assume the water is present, but are there any cases where assuming water is present incorrect and could lead you t...

madisondesilva1c

Since the molecules of X and X2 do not change in quantity between flask 3 and 4, you must assume that the beaker was at equilibrium at flask 3, but not flask 2 because the quantities change between flask 2 and flask 3.

madisondesilva1c

Is there a maximum equilibrium constant that exists, and or a minimum? IF so how does this affect calculations of reactions?

madisondesilva1c

What is the correct notation for computing the partial pressure of gases, is it more correct to use brackets versus parenthesis when doing a problem of this sort?

madisondesilva1c

During lecture, Dr. Lavelle noted that endothermic reactions require heat. Therefore, in order to proceed they will need heat due to requiring energy due to products from reactants having a positive enthalpy value. Looking at graphs of endothermic vs. exothermic could help you understand a visual.

madisondesilva1c

If there is an oxygen molecule with two hydrogen atoms bonded to it, but the lone pairs are not shown, do you assume the lone pairs still exist? Therefore would this oxygen atom have a hybridization of sp3?

madisondesilva1c

There is a question on the modules that I cannot seem to get correct. If a electron is going from an energy level n to energy level n2 where n2 is less than n, the value of the change in energy will be negative. Is this always the case due to electron emitting energy to enter a lower energy level?

madisondesilva1c

If you are given the pH of a solution, do you simply subtract the pH from 14 to find the pOH concentration value?

madisondesilva1c

I think there are a few exceptions that are not in perfect order of the trend, but relatively the most electronegative elements are on the top and to the right of the periodic table. Therefore, I feel that for exam purposes this trend should be sufficient and if there would be exception, or close di...

madisondesilva1c

Are there any specific workshops that you have found very helpful or specific TA office hours that have really helped you grasp the material? I am trying to decide how to split up my time and want to attend the sessions that people have great past experiences with! Thanks!

madisondesilva1c

How are the orbitals of d level supposed to be arranged when drawing out the sigma / pi bonds? Can the bonds happen between any two orbitals in the d orbitals or are there certain orientations which are more preferred?

madisondesilva1c

During lecture, Professor Lavelle began to what makes a Lewis base different than a Bronsted base and mentioned that Lewis bases are more general. What does general mean in this case?

madisondesilva1c

I believe that in discussion, we drew the arrows toward the net negative charge on the molecule, therefore where the stronger electronegativity is pulling the electrons, the arrow would point.

madisondesilva1c

Are there other circumstances other than lone pairs that would make bond angles "slightly less than" or are these the cases that we are supposed to understand?

madisondesilva1c

A double or triple bond affects the shape in the VSEPR model the same way that a single bond affects the shape. The type of bond does not matter, but what matters is the number of regions of electron density, therefore one single bond is a region, one double bond is also one region. The fact that it...

madisondesilva1c

Will there be the same workshops on the weekend after this upcoming holiday or are these canceled? If so is there extra practice we can see before the Test 3?

madisondesilva1c

I am pretty sure that this question will be specific for the atoms involved in forming the cation or anion. Depending on the number of VE and then the bonds formed as well as the Lone pairs present, this will determine the bond angles, not the pure fact that the structure is a cation or anion. You m...

madisondesilva1c

I am confused how to differentiate whether a hydrogen bonding or a dipole-dipole bonding would be more likely or when one would occur versus the other since they have similar characteristics. When would a dipole-dipole occur over hydrogen bonds?

madisondesilva1c

Is Test 3 Cumulative of material before the midterm? And if so, where does the material that will be tested go up until from lecture?

madisondesilva1c

I think that this means the lewis structure with the correct bond angles and the correct number of bonds to lone pairs. Sometimes the central atom will have a formal charge that is non-zero in order to satisfy the other atoms that is bonded to.

madisondesilva1c

I had this question as well and from other students I have heard that the oxygen is more electronegative therefore it prefers to have the negative charge compared to Nitrogen if one of them has to have it.

madisondesilva1c

How can one distinguish between polar covalent bonds and other forms of covalent bonds. Is there exceptions on the periodic table that would seemingly have a covalent bond but instead form ionic bonds?

madisondesilva1c

Electron affinity decreases down a group, and increases across a period. Therefore the trend is that higher up elements and further right elements have greater electron affinity. The trend is the same trend as ionization energy.

madisondesilva1c

From my knowledge and TA comments, I have the impression that the octet is the first thing to satisfy when drawing a lewis structure. Then once each octet is full, you can rearrange the electrons to create the closest formal charge to zero.

madisondesilva1c

Even though there is a formal charge equation, I find myself coming up with the incorrect formal charge often after drawing the lewis structure and my error is aways in the 1/2(shared) portion of the calculation. Is there any helpful tips or tricks to correctly calculate formal charge or any common ...

madisondesilva1c

You can figure out which would be the central atom due to the formation with the atom that will make the most bonds, or share the most electrons. You can always use the formula charge formula to access and see that placing O as the center atom would give a formal charge closest to or at the optimal ...

madisondesilva1c

Todays lecture ended with the introduction of Dipole, how do you represent dipole with an arrow if two atoms are very similar in electronegativity? Will this ever be the case or will one always be more electronegative than the other?

madisondesilva1c

When determining the 4 quantum numbers that represent a wave function, is there a way to distinguish whether the 4th quantum number will be negative versus positive? Will you have to give two options for the quantum number sequence for each wave function indicating plus or minus 1/2 or is there a wa...

madisondesilva1c

I believe that we need to know the trends up to the lecture Wednesday therefore the ones that would be included are atomic radius, ionization energy, electronegativity, and electron affinity. I find it helpful to think about how the trends are related to each other and then you will have a better id...

madisondesilva1c

I have found that within the text book the side notes help and if there is a topic that you are unsure of, there are many videos on youtube that focus on the keywords related to each topic which helps me to prepare for exams. I hope this helps!

madisondesilva1c

Will there be section held during the week of Thanksgiving? I have a section on tuesday but am trying to coordinate travel plans back home and am wondering if our discussion will meet during this week?

madisondesilva1c

Are there any exceptions in atomic radius, ionization energy, or electronegativity trends on the periodic table that would affect the orientation of the Lewis structure that do not follow the observed patterns learned in class?

madisondesilva1c

Due to hunds rule, the orbitals of the atoms will fill based on that, therefore if you know what block the atom is located in you can figure out how the orbitals are going to fill with one electron in each orbital before filling both spots. You will have to back track the element based on location o...

madisondesilva1c

metals tend to to lose electrons forming cations which are located on the left side of the periodic table. Non metals tend to gain electrons to fill their outer shell forming anions. These nonmetals are found toward the right side of periodic table.

madisondesilva1c

When an electron transitions from n=4 to n=2, or from any higher level to a lower level, should the change in energy by negative always?

madisondesilva1c

I think that the same formula sheet that was given on test 1 will be used for test two which does have those constant provided. You may want to double check with your TA though!

madisondesilva1c

I believe I would only study up to friday lecture. I think that outline two is continuous therefore we may have not finished the entire outline. As long as you know what he discussed about electron configuration on friday, I think that is most important.

madisondesilva1c

I know that during class we derived many equivalent equations using the aspects of the De Broglie Equation, is there certain indicators in questions or certain red flags that would better direct me figure out when you use certain versions of the De Broglie Equation?

madisondesilva1c

On the cover page of the last exam, there were given constants, so that is a possibility. However, if you practice many practice problems and do the homework you will find that it is easy to remember the constants without too much effort, but just due to common use and application in this chapter! I...

madisondesilva1c

When computing the frequency of waves or working with frequency, do you simply either use Hz or s^-1 depending on what other quantities you are working with at the moment? OR / AND is it more correct to leave the final computed frequency in Hz versus s^-1 or vice versa?

madisondesilva1c

If electrons exhibit wave properties, is it possible for an electron to move from n=1 to n=3 while another moves from n=3 to n=1, therefore emitting no photon? Do we view this as a similar property such as destructive interference?

madisondesilva1c

Can someone please explain why as one increases energy level, the distance between the levels decreases? E.g Energy level 3 and 4 are closer together than Energy level 2 and 3. Also, is there a way to calculate the energy of the photon emitted per transition of energy level?

madisondesilva1c

I also asked my TA about the amount of molecules or compounds we should have memorized, and she said that basic diatomics and common ionic compounds are good to have memorized in order to successfully take the tests.

madisondesilva1c

From asking around and from Dr. Lavelle, the only material provided for the test is a periodic table that gives the atomic mass and the symbol, the periodic table is a basic version and there is no other material that is allowed to be used during the test.

madisondesilva1c

Given the g within one molecule, you must multiply this by avogadros constant, 6.022 x 10^22 mol^-1. This comes from the idea that in order to find the mass of one molecule of anything, you take the molar mass of the substance from its composition, and then divide it by Avogadro's number to find the...

madisondesilva1c

Yes. To clarify, you are correct. g/mol is equivalent to writing g.mol^-1. The power of negative 1 refers to the fact that the g/mol has moles within the denominator.

madisondesilva1c

In order to end up with the correct quantities, especially when using dimensional analysis it is much easier to convert all mL to L and all kg to g, in order to properly convert to mol.g-1 (etc.). Therefore I recommend converting units in the beginning so you do not have trouble canceling out units ...

madisondesilva1c

If there are two compounds going into a solution, how do you calculate the molarity? Would it be correct to find the moles of the total solute (adding the moles of solute 1 and solute 2 together found from the molecular mass) and then proceed as normal?

madisondesilva1c

I think potentially there could be a situation where two of the reactants may "run out" faster than the third, but out of these two, there would likely be a reactant that is "more limiting" in a sense that one reactant will still run out first. Therefore, you would continue the p...

madisondesilva1c

In order to compute dilations correctly, you will need to convert the volume of the given quantities to Liters, however if the known volumes in the question are given in milliliters then I would convert back to the unit of mL at the end of the answer. This is the format that the online Video Module ...

madisondesilva1c

I think that either asking or answering a question is sufficient. You must interact three times per week with Chemistry Community according to the syllabus starting week 1 if there are 10 weeks in the quarter.

madisondesilva1c

Within the SI Units, when converting is there a helpful reminder to remember the order of units, and is it sufficient to multiply to convert g to kg by multiplying by 10^-1 or must you simplify what the value truly is using the new units?

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