CHEMISTRY COMMUNITY

Daniela Santana 2L

Hi! In order to solve for the half life of something you use the equation t1/2 = ln2/k. ln2 approximately equals .693 so solve for .693/3.7x10^-5. The value you get from this will be in seconds so be sure to convert this value to hours by applying 60 as many times needed. I hope this helps!!

Daniela Santana 2L

Hi! It seems like you just need to add more H20 molecules to the left side of the reaction :)

Daniela Santana 2L

Hi! For this problem you use the equation t = 1/k ln([A]0/[A]t . You are given all the information you need to plug values in to the equation so all you need to do is plug in and solve and you will get the answer. I hope this helped!!

Daniela Santana 2L

Hi! You included the C reactant in your answer. Since it is zeroth-order, it does not get included. I hope this helped :)

Daniela Santana 2L

Hi! The way that I thought about solving this problem was by adding the 1/2 and 3 coefficient where the problem said it should go. I then set up the rate equation that was also given with the new coefficients in their respective places. I multiplied the coefficients together then multiplied this val...

Daniela Santana 2L

Hi! I solved this problem by taking the concentration of the second time given (t=292) and of the first time given (t=0) and subtracting them from each other and then dividing them by the overall change in time (292). I then multiplied the value I got by two since B has a coefficient of 2. This shou...

Daniela Santana 2L

Hi! I solved this question by looking at the reaction and taking note of the coefficients in front of each substance. I would essentially find the reciprocal of the coefficient and put that in instead of the coefficient thats given. For example, the 4 in 4B would become 1/4. I would rewrite the whol...

Daniela Santana 2L

Hi! The main difference between balancing a redox reaction in acidic and basic solution is that for basic solution when balancing the H's and O's of the reaction, you use H2O and OH-. For acidic solutions, you would use H2O and H+. Other than this every other step is essentially the same.

Daniela Santana 2L

Hi! The compound with the higher or most positive reduction potential is the best oxidizing agent.

Daniela Santana 2L

In most of the problems I've seen it is usually stated somewhere in the problem if the reaction is taking place in acidic or basic solution.

Daniela Santana 2L

Hi! When balancing under acidic conditions you use H2O and H+ to balance out the H and O's of the reaction. When balancing under basic conditions you use H20 and OH- to balance out the H and O's of the reaction. If you need more help Organic Chemistry Tutor on Youtube is a great resource for redox r...

Daniela Santana 2L

Hi! I usually first identify which half-reaction is the reduction one and which is the oxidation one. I also write down the oxidation numbers of each side of each half-reaction. Once the half reaction is all balanced and you're deciding how many electrons and where to put them, I revisit the half-re...

Daniela Santana 2L

Hi! I don't think the order matters when balancing a reaction, just make sure to have the correct coefficients and phases for each molecule.

Daniela Santana 2L

Hi! This problem is taking place in a basic solution so you should use OH- molecules to balance the equations instead of H+ ones (you use those in acidic solutions). Also a completely balanced reaction shouldn't have electrons in it, you're supposed to make sure they cancel out when you add the two ...

Daniela Santana 2L

Hi! I had a little trouble figuring this out as well. In order to determine what the half-reactions are I looked at the molecules that had the most in common with each other (element wise) and noticed that they belonged in a half-reaction together. For example, the Au on the reactant side had one el...

Daniela Santana 2L

Hi! Try to revisit your work for calculating the HNO3 --> NO2 half-reaction, the coefficients you put are slightly off from the correct answer. I hope this helped :)

Daniela Santana 2L

In order to solve this problem: Step 1: Identify the oxidation and reduction half-reactions. You do this by calculating the oxidation number for each molecule and seeing how its value changes from reactant to product. Step 2: Start with the reduction half-reaction. (HNO3 --> NO2). Since the N part o...

Daniela Santana 2L

In order to find the enthalpy of this reaction, you should find the sum of the products and the sum of the reactants and subtract them (sum of products - sum of reactants). You can find the respective deltaHf value in the chempendix for each compound and multiply it by their coefficient in the react...

Daniela Santana 2L

The n and m in the formula are referring to the coefficients that are in front of its respective compound. For example, since CCl4 has a coefficient of two you would multiply its deltaGf value by two. I hope this helps!

Daniela Santana 2L

Hi! In order to solve this problem you use the equation deltaS=Cp*ln(T2/T1). First you convert the temperatures given into kelvins and plug them into the equation with Cp being 75.3 and solve. Then add 109 to the answer you get. Next use the the equation deltaS=Cp*ln(T1/T2) (temperatures are flipped...

Daniela Santana 2L

Hi! In order to solve this problem take the heat being generated and divide it by the temperature (in kelvin). Then multiply the answer you get by 60 and then multiply that answer by 60 again. You should get the correct answer to the problem. I hope this helped :)

Daniela Santana 2L

Hi! In order to calculate the standard reaction enthalpy you just find the sum of the products and the sum of the reactants and subtract them. It should look like (sum of products - sum of reactants), this method should help you find the standard reaction enthalpy. I hope this helped!

Daniela Santana 2L

Hi! I struggled with this problem a lot too at first. Since we aren't given an n value I just plugged 1.00 mol into the delta S=nRln(V2/V1) equation. You plug 8.3145 in as the R constant as usual. Then for V2 and V1 I just plugged 1/6 into the equation. Once multiplying all these values together you...

Daniela Santana 2L

Hi! I got the correct answer to this question without converting kPa to atm. I hope this helped :)

Daniela Santana 2L

Hi! After you get your n value and multiplied it by your Cv,m value you should multiply it by ln(T2/T1). The temperatures should be in kelvin, and you should plug ln(1073/298) in your calculator. Once you have this value you can multiply it by .407J/K and the result should be the answer to the probl...

Daniela Santana 2L

Hi! I solved this problem by using R=8.3145. I hope this helps!

Daniela Santana 2L

Hi! q is the energy transferred as heat and when its written as qrev it just means that the energy must be transferred reversibly. I hope this helps :)

Daniela Santana 2L

Hi! The way that I solve problems involving Hess's Law is by noticing what compounds the target reaction contains and then looking for those same compounds in the available reactions given. Then I think about how I can manipulate these reactions into giving me the target reaction in the end. A way t...

Daniela Santana 2L

Hi! A way to solve this problem is by noticing how many moles of gas there are on the reactant and product side of the reaction. If there are more moles of gas on the product side than on the reactant side of a reaction this tells you that the system is doing work on its surrounding. I hope this hel...

Daniela Santana 2L

Hi! I solved this problem by multiplying the amount of heat that is absorbed thats given in the problem by 4 mol CS2. I then divided this by 358.8 (my original delta H value). I then multiplied the value I got from that by the molar mass of CS2 to get the answer of this problem. I hope this helped!

Daniela Santana 2L

Hi! The way that I solved this was by taking 371KJ and multiplying it by 4 mol CS2. I then divided this value by 358.8. Then I multiplied the value I got from that by the molar mass of CS2 and this should be the answer to your problem. I hope this helped!!

Daniela Santana 2L

Hi, I was wondering how you could tell which bonds are breaking and which are forming when dealing with a problem related to bond enthalpy. Thanks!

Daniela Santana 2L

Hi! If you go to the Sapling home page where all the homeworks are listed there will be a resource titled Chempendix. If you click on it, it will have a lot of helpful information. You can also use the search bar near the top right corner to search for strong acids and bases. It will give you a list...

Daniela Santana 2L

Hi! I also had trouble figuring this out. A tip on knowing if its -x or +x in the change row of an ICE table is by noticing which value(s) are given in the problem and which are not. For example, if a problem gives you a value for the HA, its value in the change row will be negative (-x). Say the sa...

Daniela Santana 2L

Hi! If you want to take the anti log of something you just do 10 to the power of a negative value. For example, if you wanted to take the anti log of a pH value, you'd turn that into a negative value and then put it to the power of 10 (10^-pH). I hope this helped :)

Daniela Santana 2L

Hi! The only thing that can effect or change the equilibrium constant, K, is temperature. Nothing else can change K. I hope this helped :)

Daniela Santana 2L

Hi! K and Kc are essentially the same thing. Kc is used when dealing with concentrations and if you want to be specific on notation. You can think of K as just a general way of equilibrium constant notation. I hope this helped!

Daniela Santana 2L

Hi! In order to check if this is an instance where you can approximate you can multiply the initial concentration by 1000. If the value you get is greater than Ka, you can approximate and disregard the x.

Daniela Santana 2L

Hi! Yes it would help you to create a chemical equation. What I wrote out for the equation was HA(aq) + H2O(l) --><-- H3O+(aq) + A-(aq). You then set up the Ka as [H3O+][A-]/[HA]. Then you make an ice table with 0.35 as the initial value for HA and 0 for H3O+ and A-. You then input these values in t...

Daniela Santana 2L

Hi! Basically, you used the equilibrium concentration of amine instead of the initial concentration to calculate percent ionization. if you did an ICE table, the equilibrium concentration of the amine is [ x minus (the [OH-] concentration you calculated)], which is the one you just calculated. x is...

Daniela Santana 2L

Hi! You use the quadratic formula to solve for x. Once you have the value of x you can take your x value and divide it by the initial value of the acid given in the problem. Once you have found this just multiply it by 100 and the value you get is the percent ionization. I hope this helped!

Daniela Santana 2L

How do you know if the value in the 2nd or change row of an ICE table is negative or positive? I know that the value that goes in front of the x is determined by the stoichiometry of the reactions but I don't know how to figure out if they're positive or negative. Could someone explain this to me?

Daniela Santana 2L

Q is the reaction quotient, K is the equilibrium constant. Q can be calculated at any time whereas K can only be calculated at equilibrium. Hope this helps!

Daniela Santana 2L

Hi! Yes you're right, the q value will eventually equal k, when it does this signifies that the reaction is at equilibrium. Yes Q can be calculated at any time, K is only when the reaction is at equilibrium.

Daniela Santana 2L

Hi! Yes you are right about Q and K. Q is the reaction quotient and you can calculate this at any time. K is the equilibrium constant and you can only calculate this at equilibrium.

Daniela Santana 2L

Hi! First you would set up you equation for Q as normal. Put the products on top (in your case NH3 with the exponent of 2) and the reactants on bottom (N2 multiplied by H2 to the power of 3). Then take the values that Sapling gave you for each respective element and put them in. Then solve normally....

Daniela Santana 2L

Hi! When Q > K, this means that the reaction shifts to the reactants or to the left (since the reactants are on the left). When Q < K the reaction shifts towards the products or to the right (since the products are on the right). I hope this helped clear up any confusion!

Daniela Santana 2L

Yes you are correct. Q is used when they are not equilibrium values yet. You can find Q at any time during the reaction but K is only when the reaction is at equilibrium.

Daniela Santana 2L

Hi! Yes when calculating a problem that contains a solid or liquid you should exclude it and only include gases in your answer. I hope this helped!

Daniela Santana 2L

Hi! If you see a post that you want to reply to click on it and then click post reply to type out a reply. Sometimes after I post it tells me the number of posts I have made under my name in the reply I just left. This number is almost usually off by a number for me, make sure to click on your actua...

Daniela Santana 2L

I had a similar problem and to fix it I switched browsers and it worked (Safari to Chrome). If the site ever asks if you want to use credit, select it so you won't have to pay more than what you already have for the class :)

Daniela Santana 2L

When you reverse a reaction, the K value of it is the inverse of the forward reaction. So to find K for the reverse reaction solve for 1/K.

Daniela Santana 2L

You add -ate to the end of the name of the central metal atom when the overall charge of the compound is negative.

Daniela Santana 2L

The number of bonds that are bonded to the central atom determine the shape of the complex.

Daniela Santana 2L

Hi!
A square planar complex has four bonded atoms and 2 electron pairs. A tetrahedral complex only has four atoms bonded to it (no electron pairs). You can distinguish by drawing out the molecule's lewis structure and seeing if the central atom has lone pairs or not. Hope this helps :)

Daniela Santana 2L

The way I think about this is by envisioning a globe. I know that the globe's equator cuts across the middle of it horizontally so the equatorial position must be the atoms that are attached to the sides of the central atom. The globe's axis starts from the top of the globe and cuts its way down to ...

Daniela Santana 2L

What is the difference between [OH-] and pOH? Question 5 on sapling asks for us to list both but I thought that they meant the same thing, are we supposed to put the same thing for both of them on Sapling or are they different. Could someone clarify what the difference between the two are?

Daniela Santana 2L

Hi, can someone explain to me the differences between each type of intermolecular forces and how to differentiate between them? I know that there are some that are the same but just have different names, which are those?

Thanks a lot!

Daniela Santana 2L

Whenever a complex has an overall negative charge -ate is added to the end of the metal's name. If you need more information about this look at Step 7 of Toolbox 9C.1 in the textbook. I hope this helped :)

Daniela Santana 2L

Hi! Step 1: In order to solve this problem I first write out the name of metal and ligands in the formula. You can reference your periodic table for the name of some of the elements or table 9C.1 in the textbook for the names of some ligands. For your problem, this would be cobalt ammine chloride an...

Daniela Santana 2L

Hi, you would arrange the ligands in alphabetical order. Remember to ignore the prefixes while doing this and to focus only on the actual name of the ligand.

Daniela Santana 2L

The en stands for ethylenediamine, its formula is NH2CH2CH2NH2. You can find this in chapter 9C of the textbook in table 9C.1. Hope this helps!

Daniela Santana 2L

Hi, when naming a compound you ignore the prefixes and base the alphabetical order off of the actual name of the ligand. So in this case you would only consider the first letter in ammine and chloro.

Daniela Santana 2L

Hi, the third lewis structure is supposed to have the carbon atoms in a triangular shape. It should look like this:
C
/ \
C=C

And then you would just arrange the H atoms around the C atoms where there is room to bond.

Daniela Santana 2L

Hi, the third lewis structure is supposed to have the three carbon atoms form a triangular shape. Its supposed to look like this:
C
/ \
C=C
And then you just connect the H atoms around the C atoms where there is enough room to bond. I hope this helped :)

Daniela Santana 2L

How does the P atom in the PCl5 molecule have an expanded octet? A P atom only has 5 valence electrons so wouldn't it be full by being bonded to 5 Cl atoms? How does the expanded octet concept work?

Daniela Santana 2L

Hi! You determine the number of sigma and pi bonds in a lewis structure by looking at the types of bonds the atoms are connected with. A single bond has one sigma bond. A double bond has one sigma bond and one pi bond. A triple bond has one sigma bond and two pi bonds. A tip to remember is that pi b...

Daniela Santana 2L

Does anyone have a way of remembering the electron configurations exceptions for the elements in the d-block that don't follow the regular method of filling subshells?

Daniela Santana 2L

Hi! In order to determine this you would calculate the formal charge of each of the structures given and the one with the formal charge closest to zero has the best resonance. Hope this helps :)

Daniela Santana 2L

I find the formal charge with this equation: FC(of certain element in a structure): V(amount of valence electrons it has) - (Lone electrons it has + amount of bonds it shares with another element in the structure divided by 2) I would recommend trying out different ways of calculating the formal cha...

Daniela Santana 2L

Hi! A Lewis acid accepts electrons. A way to help you remember definition wise is Acid=Accepts. A Lewis base donates electrons.

Daniela Santana 2L

Hi! A Lewis acid is defined as a species that accepts an electrons. An example of a Lewis acid is BF3 and H+. A Lewis base is defined as a species that donates electrons. An example of a Lewis base is NH3 and F-. Hope this helps :)

Daniela Santana 2L

Hi! H can never be a central atom because it can only bond with one other atom. Hope this helped!

Daniela Santana 2L

Hi! I've been trying to go back through the lectures to find the formula for formal charge and I can't find it. Based off this post, I think the formula is: formal charge= valence electrons-( (bonds/2) + lone pairs). Is this correct? Yes but just remember that the "bonds" part of the form...

Daniela Santana 2L

I think Sophia made a mistake with the formal charge for phosphorus so I'll just start from the beginning: So phosphite is PO3 with an overall charge of 3-. We would put P in the middle since it has a lower ionization energy. First, we should calculate the total number of valence electrons. In this...

Daniela Santana 2L

Hi, I googled the formula in order to solve the problem but you should try to memorize the formula in case you need it for the future. Hope this helps!

Daniela Santana 2L

Nitrogen cant have an expanded octet. The structure should only have one double bond (the rest should be single). Dont forget to assign the correct charges to the elements when you make this adjustment. Hope this helps!

Daniela Santana 2L

Anna Yang 2A wrote:For this problem how do you figure out the formulas for the nitrate and nitrite, etc ions? Or is it something we are supposed to memorize?

Hi, I just googled the formula for the ions, but you should probably memorize it for the future.

Daniela Santana 2L

Hi! Yes you can find the amount of valence electrons for each element by looking at the periodic table. For example, in the image of the periodic table I attached the underlined value is the number of valence electrons for that specific element. Its usually the last number after the last hyphen. Hop...

Daniela Santana 2L

Lone pairs are the dots that are around an atom. They are not bonded or shared with another atom (represented by a bar in the structure).

Daniela Santana 2L

I'm having a little trouble understanding the octet rule. Could someone explain to me what it means and how to apply it to a problem?

Thanks in advance :)

Daniela Santana 2L

The formal charge would be -1. Hope this helps!

Daniela Santana 2L

The L in the formal charge equation represents the number of lone pair electrons around a specific atom. In order to find its value just count the dots around the specific atom. Also make sure that you only count whats not bonded to another atom. Hope this helps!

Daniela Santana 2L

Do we have to do anything with the 25 degree celsius part of the problem to solve or is it something that is not relevant to the problem's solution?

Daniela Santana 2L

So based on this would n=6 be be n1 or n2?

Daniela Santana 2L

How can we find the maximum number of electrons that can be ejected from metal when given a total energy?

Daniela Santana 2L

Can the work function ever be a negative value?

Daniela Santana 2L

If the frequency of a wave increases by a certain amount, does the wavelength of that same wave decrease by the same amount?

If not what happens?
How does the wavelength and frequency relate to each other?

Daniela Santana 2L

How would you solve this? In the following ball-and-stick molecular structures, dark gray indicates carbon; white, hydrogen; blue, nitrogen; and green, chlorine. Write the empirical and molecular formulas of each structure. Hint: It may be easier to write the molecular formula first. Hi, you would ...

Daniela Santana 2L

Hi, yes the empirical formula shows the relative number of atoms in a molecule. It is a ratio of the molecular formula. The molecular formula shows the actual number of atoms in the molecule. The empirical and molecular formula relate to one another and you can find a factor between the two and use ...

Daniela Santana 2L

Can someone walk me through A.9 in the textbook? I have figured out the order of events and the first two columns but am struggling with the 3rd and 4th column. Could someone walk me through them? Problem: A college student recently had a busy day. Each of the student’s activities on that day (readi...

Daniela Santana 2L

Does anyone know how to convert meters to nanometers? I'm not sure how to convert it and in a lot of the problems I see it seems like you just have to move the decimal place over? Example: 4.2x10^-7 m converts to 420 nm Is there an actual method to convert it or is it just moving the decimal place o...

Daniela Santana 2L

Does anyone know how to convert m to picometer? In a lot of the problems I see it seems like you just have to move the decimal place over and its usually a 3 digit number. Example 1.5x10^-10 m converts to 150 pm. Is there an actual mathematical way to compute it or is it just moving the decimal plac...

Daniela Santana 2L

Hi! We are supposed to have the stoichiometric coefficients as whole numbers when we're balancing a chemical equation. If you were to have a stoichiometric coefficient in fraction form in order to make it a whole number multiply everything in the equation by the fraction's denominator. This will lea...

Daniela Santana 2L

In the problem you gave CO4 would be C=1 and O=4. This is because there is one carbon atom and four oxygen atoms in the compound you listed. If you're confused on whether elements are together or not like if its C and O or CO, look at the periodic table and see if you can find it on there. From what...

Daniela Santana 2L

Hi! You can access the textbook by viewing an email Dr. Lavelle sent out on October 6th. There will be a link to a google doc outlining instructions on how to access the textbook. Remember that it can only be accessed through the Sapling link on the CCLE class website page. Hope this helps!

Daniela Santana 2L

Hi! To solve this problem, you will be using the equation M(initial) x V(initial) = M(final) x V(final). From the information provided in the text, we know that the initial M is 0.20 M and the initial V is 1.0L. We also know that the final V is 4.0 L (1.0 L + 3.0 L = 4.0 L). So, we have to solve fo...

Daniela Santana 2L

In the Question F25 it states: In the following ball-and-stick molecular structures, dark gray indicates carbon; white, hydrogen; blue, nitrogen; and green, chlorine. Write the empirical and molecular formulas of each structure. Hint: It may be easier to write the molecular formula first. It then go...

Daniela Santana 2L

You have to multiply the atomic mass of hydrogen by 2 and get 2.016 in order to divide it to the atomic mass of H2O. You do this because there are two hydrogen atoms in the compound of H20. You are trying to separate the hydrogen atoms from the oxygen atoms in order to figure out the correct amount ...

Daniela Santana 2L

To solve this problem count how much of each element there is. You would count how many H's there are, then O's, then C's. Once you have that you just write it out as you would write any molecular formula. With the amount of each element being in subscript next to it. Then you simply find the atomic...

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