CHEMISTRY COMMUNITY

Bryce Ramirez 1J

Do we need to be aware of any technical changes to the formula if we decide to use Kelvins vs Celcius in the calculations for temperature in both T1 and T2? Or should we just stick with Kelvin to be safe?

Bryce Ramirez 1J

When bonds are being broken/ formed in relation to melting points and freezing points, is energy released when a bond is broken? Or is energy gained? Similarly, is energy released/gained when a bond is formed?

Bryce Ramirez 1J

Remember that the cathode will be on the right and the anode will be on the left. Electrons always flow from left to right because it's commonly accepted that the anode will be left and the cathode will be right.

Bryce Ramirez 1J

Changing the mass of the electrode, whether it be the cathode or the anode, will not affect the Ecell. It could be doubled, halved, or changed by any factor; the overall change will have no affect on the Ecell.

Bryce Ramirez 1J

To find which one is the oxidation half and which one is the reduction half, you subtract the two Ecells and whichever one gives you a positive Ecell is the correct order. Then you analyze which numbers are in which position. The one on the left is the cathode and the one on the right is the anode.

Bryce Ramirez 1J

Reversible expansion means that the expansion is gradual, while irreversible expansion means that the expansion is instantaneous.

Bryce Ramirez 1J

Specific heat capacity will usually use the weight of the molecule that is being used, like grams or kilograms. Molar heat capacity calculates how much the molecule will change by one degree celcius, given the amount of moles.

Bryce Ramirez 1J

For the graphs of first order and zero order reactions, why are they both exactly the same? The first order reaction has the Ln of A while the zero order is just A. The slopes for both of the graphs are -k, but how can they be the same when the equations are significantly different?

Bryce Ramirez 1J

When adding water to either the cathode or anode half of a solution, why does this decrease the overall Ecell? Would the reverse for this apply to, where taking away solution would increase the overall Ecell?

Bryce Ramirez 1J

Changing the size, whether it be an increase or decrease, will have no affect on Ecell. If they try to say the mass of the anode being doubled or halved, nothing will happen to the overall reaction.

Bryce Ramirez 1J

For solving for the concentration of cathodes or anodes, are you able to use the Nernst equation? I know that there is the ln of Q, which is product over reactant, so how would you know if the anode or cathode is the reactant or product in the equation?

Bryce Ramirez 1J

Can someone explain the difference between gibbs free energy and standard gibbs free energy?

Bryce Ramirez 1J

It is easiest to find two experiments where changes in one of the reactants is equal to an even factor, like 2 or 3. Then you can cross that off from the two combinations of tests required, leaving you with fewer possibilities to choose from for the next tests.

Bryce Ramirez 1J

Why does the second part of the reaction count towards the overall rate of the reaction? If the second part is fast, then why would it be counted because the first part is the slow part, which decides how fast the reaction occurs. Step 1 NO + Br2 → NOBr2 (slow) Step 2 NOBr2 + NO → NOBr + NOBr (fast)...

Bryce Ramirez 1J

For the temperature in every calculation using the ideal gas formula, will it always be in Kelvin or will there be times where it is in Celcius? I know that the units have to cancel from the gas constant, but I'm not sure if there is any gas constant that requires celcius instead of Kelvin.

Bryce Ramirez 1J

What formula are you referring to? I think for this problem you just use the given equilibrium and initial conditions to create an ice table which can be set equal to the equilibrium constant. The solution manual shows no ice table, just using straight moles and using the equation for the equilibri...

Bryce Ramirez 1J

In part b of the problem, it asks to find the concentration of NO, a reactant in the chemical equation. But when finding it, it takes out the volume part of the formula because the amount of moles stays the same from the reactants and the products. How do we know when we are allowed to do this and w...

Bryce Ramirez 1J

What are the rules for when Qc is greater than Kc and when Qc is less than Kc? And what happens when the two are exactly equal?

Bryce Ramirez 1J

How do you know when a reaction is favored because it is either endo or exothermic?

Bryce Ramirez 1J

You can determine which one is the cathode and which one is the anode by subtracting one from the other, and whichever order of numbers gives you a positive E cell, then the number on the left was the cathode and the one on the right is the anode.

Bryce Ramirez 1J

When solving for t using the first order integrated rate law, does the other part of the equation have a negative sign? I was looking at the example problem for 7B.3, and it seems to solve the equation without having transferred over the negative sign. [img][/img Screen Shot 2020-03-08 at 11.47.39 A...

Bryce Ramirez 1J

For part a of the problem, it asks to find the order of each reactant. For B, I don't know how to calculate what B equals when setting up the equation. I have (3.02/1.25)^b = 50.8/17.4. When these fractions are simplified, the numbers don't have any common factor. Would I have to use log rules to so...

Bryce Ramirez 1J

Can someone explain how the equation works? The negative inverse times the regular rate of a reactant equals the negative inverse times the regular rate of a product?

Bryce Ramirez 1J

We must add solid platinum so that the electrons have something to bind to. Whenever no solid is present in the equations given, we have to include platinum. In the oxidizing part of the half reaction, I^- changes to I^2 (gas I assume). Does this mean that because there is no solid present, you hav...

Bryce Ramirez 1J

Q is the concentration of product divided by the concentration of reactant. [product]/[reactant]. Lots of questions will give you the concentrations and you'll be able to solve from there. When you say product/ reactant, do you mean that you take the part on the right of the cell diagram and divide...

Bryce Ramirez 1J

Can someone explain what Q is and how to use it in the Nernst equation?

Bryce Ramirez 1J

When setting up the equation for the energy of the cell, the problem gives us the cell diagram with the unknown metal on the left side and the Cu^2+ to Cu on the right side. So when setting up to solve for the unknown metal, I set it as the anode because it was on the left side and the Copper as the...

Bryce Ramirez 1J

For 6L.5 part b, it adds Pt(s) to the Cell Diagram, but how do you know when to add it?

Bryce Ramirez 1J

How do we know when to do the reverse of a reaction. In 6L.3, it reverses the order of the oxidation half reaction. Aren't you able to just write out the reactions based on the order of the cell diagrams? I'm confused why the answer shows a step of having it reversed and then switching it to the cor...

Bryce Ramirez 1J

When calculating for Gibbs free energy, you use the equation Delta G = -n*F*Ecell, but how do you determine the n? It says to use Equation 1a in the textbook, but I don't know what that equation is. Also, do we have to set up an half reactions for solving for this or will we just be able to plug in ...

Bryce Ramirez 1J

For part a, how do you know whether O3 --> 02 is the reduction reaction or oxidizing reaction? Both of them have a 0 charge, and since oxygen has a -2 charge, the left side would have a -6 charge while the right side would have a -4 charge? So would it make this the reduction reaction because it is ...

Bryce Ramirez 1J

For clarification, if the element is undergoing oxidation, this makes it the reducing agent? And if an element is undergoing reduction, it makes it the oxidizing agent? Or is it the other way around?

Bryce Ramirez 1J

Also why is Cl2 the oxidizing agent and S2O3^2- is the reducing agent?

Bryce Ramirez 1J

How do you find how many electrons are being gained and lost, and how do you compare the redox reactions so that you have an equal amount of electrons in each half reaction in order to cancel the electrons out and find the final balanced equation. For 6k.3 part a, it has the equation Cl2(g) + S2O3^2...

Bryce Ramirez 1J

Can someone explain how you would know which half reactions are being oxidized and reduced in 6k.1. Do you have to look at the elements on each side and determine their states to find which one is oxidized and which one is reduced? And how do you know to add H+ for the Carbon but H20 for the Cromium?

Bryce Ramirez 1J

When splitting up a redox reaction into its two separate half reactions, how do you know when you would add H20 or H+ to fix the amount of hydrogens one each side of an equation?

Bryce Ramirez 1J

Because they say its a weak acid, you know that the HA is never going to fully dissociate into H30+, so HA doesnt equal H30+. You can calculate HA and it does not equal approximately 0. You have the pka and to find ka, you just do 10^-pka, giving you ka. Then you set that equal to the concentration ...

Bryce Ramirez 1J

Can someone explain how to set up the calculations for solving the enthalpy using bond enthalpy. In part a of 4E.5 it has 3 C2H2 forms into C6H6, but I don't know how to find which bonds are actually used for calculating the net change.

Bryce Ramirez 1J

Can someone explain the main differences between reversible and irreversible expansion.

Bryce Ramirez 1J

Can someone explain the basics to pKa and pKb. I thought it was the product of the two equals pKw and that their product is equal to 14. And when calculating it, you just need to do the -log of the ja or kb. Is there anything else I should know fundamentally when applying this to a problem?

Bryce Ramirez 1J

On the list of constants, it shows R = 8.206 and also 8.314 with the units of K and mol^-1 and atm^-1 and J. But what is the difference between these two constants; why can’t they both be used?

Bryce Ramirez 1J

When determine whether the energy of a system is increasing or decreasing in energy, can someone explain the difference between when energy (heat) gets added/ removed and what sign that would be.

Bryce Ramirez 1J

In converting the work to L x atm, the answer says to use the conversion of 760 Torr x atm^-1, but we are given that the atmospheric pressure is 750. Can someone explain why this is the conversion for the work?

Bryce Ramirez 1J

The equation for irreversible expansion is q = (mass)(heat capacity)(change in temperature). This will calculate how much energy is required to change the temperature of a substance.

Bryce Ramirez 1J

Lower heat capacity means that the substance will easily heat and cool. Heat transfer will also easily happen when the value for the heat capacity is low.

Bryce Ramirez 1J

What is the change ininternal energy of the system?

The change in U would be equal to be w because no other internal change is happening besides the change in volume, so the answer you get for the work would be equal to U.

Bryce Ramirez 1J

PranaviKolla2B wrote:Can someone please define molar heat capacity?

By definition, the Molar Heat Capacity is the heat capacity divided by the amount (in moles) of the sample. When using it to determine the heat, you would just need to find the value given in table 4A.2.

Bryce Ramirez 1J

When trying to cancel out the units for finding the heat needed to change an amount of moles of a substance, do you have to convert the temperature from Celcius to Kelvin? The units for the molar heat capacity have K in it, so I assumed the heat would have to be used in Kelvin, but I am not sure. Ca...

Bryce Ramirez 1J

If a chemical equation has a stoichiometric coefficient of 2, then when you put the change for that molecule in the ice table, would you add a two in front of that change? And when writing the equilibrium constant, would you put whatever value of concentration you for it and square it because the va...

Bryce Ramirez 1J

The five percent rule is when you are checking to see if your approximation for the equilibrium constant is valid. You apply it by taking the equilibrium concentration and dividing by the initial concentration and multiplying by 100. If less than five percent, then your approximation is valid. But i...

Bryce Ramirez 1J

Make sure to remember that significant figures for logs involves the numbers after the decimal. So if there were two significant figures given in the problem, setting up the equation for pH would involve using two significant figures after the decimal point.

Bryce Ramirez 1J

If the value you get is more than 5%, you would know because the value should be significantly higher so that you are sure that it's not a valid approximation. If it's close around the 5% range, then you should redo the problem and make sure not to round any of the numbers until the final answer.

Bryce Ramirez 1J

I also did the math for this problem and the book said my answers were wrong, though I think the book is wrong. When calculating the pH for part a using 1.5 moles of H30, my calculator gives the pH as -.176. The answer shows it being positive .176, which is wrong. If 1 mole of Hydrochloric Acid (HCI...

Bryce Ramirez 1J

For part c of the question, it asks the molar concentrations of OH when given H30. It gives 3.1 mol of H30, so I divided (1.0 x 10^-14) / (3.1) and got 3.2 x 10^-15 mol/L. But the answer says that it is 3.2 x 10^-12 and writes that the denominator is supposed to be 3.1 x 10^-3. Why is that the value...

Bryce Ramirez 1J

It can be applied, you would just need to have enough information to solve for the unknown. Is there a specific homework question you are referencing?

Bryce Ramirez 1J

For part b of the homework problem, it has the chemical equation of H2O(g) + C(s) <> H2(g) + CO(g). I thought that there are the same amount of moles for reactants and products, but the answer says that reactants are favored. Can someone explain why they are favored and not equal?

Bryce Ramirez 1J

The reaction is occurring in the forward direction, which means the solid NH4HS will yield more of the products -- in this case, the products are NH3 and H2S. In other words, the initial amount of NH3 (0.200 mol) will increase by x because of the reaction of NH4HS. So does this mean that whenever w...

Bryce Ramirez 1J

When writing out the table for the initial, change, and equilibrium concentrations, the problem wants us to calculate the equilibrium concentration for NH3 and H2S. They give us .2mol/L for NH3 and nothing for H2S. So I wrote the initial as .2 for NH3 and 0 for H2S. But for the change, the answer sa...

Bryce Ramirez 1J

For parts b and c, the question asks to determine K from the given chemical equation. Both of them show the exponents to be either halved or doubled, but can someone explain why this would mean that K need to be has to be square rooted or raised to the power of 2. Why couldn't you divide/ multiply K...

Bryce Ramirez 1J

When writing the products and reactants for the equilibrium constant, why do we add P before the formula that is part of the chemical equation? Does this represent the partial pressure?

Bryce Ramirez 1J

Yeah, you just have to change the C to whatever atom it is that is bonded to another atom.

Bryce Ramirez 1J

Yes you would only use it for the atoms that are inside the brackets in a complex.

Bryce Ramirez 1J

When trying to find the conjugates to acids and bases, all you have to do is remove an H or add an H? And this reaction would happen in water.

Bryce Ramirez 1J

I think that it would normally be monodentate because the bond angle between the two oxygens is 120 degrees, meaning it's too small of an angle for two oxygen atoms to bind to a single metal. But in rare cases, it can be bidentate.

Bryce Ramirez 1J

Final Update: Tony made it, everything is good again. He will be going over review until the next session starts for anyone who left early.

Bryce Ramirez 1J

Update: Most people have left, but there are still a few of us staying strong and waiting for Tony.

Bryce Ramirez 1J

Wondering if Tony is still coming to do the review session, I’m sitting here wondering if I should still wait.

Bryce Ramirez 1J

I know that deprotonated acids are supposed to have transfered their proton from one species to another, and that strong acids will be fully deprotonated. But for weak acids, will we need to know the percent of the ions or molecules that are depronated in a solution. Is there any calculations we wou...

Bryce Ramirez 1J

Is a common trend for bases to have an OH or O in the formula? I know for acids that it says that they will give up a hydrogen and that bases will accept something, but do they normally have oxygen or hydroxide in them?

Bryce Ramirez 1J

For J.17, it asks for "Write the chemical equation for the proton transfer reaction of this cation or anion with water" and for part B, it gives KClO, which I know is an acid. But how does combining it with water form the cation/ anion, because these reactions are supposed to form salts an...

Bryce Ramirez 1J

The question gives four pictures and asks "Which of the following images best represents a solution of hydrochloric acid?" The answer is the picture where there are just hydrogen and Cl atoms floating in a space, but not connected to each other. Why does this best represent a solution of h...

Bryce Ramirez 1J

When balancing equations, you usually only know that the products are going to be some form of salt and H20. But how do you know how much of the reactants to use to make the equation balanced? And when certain molecules have an exponent, like potassium phosphate, do they have to be neutral in order ...

Bryce Ramirez 1J

The question asks "Noting that the bond angle of an sp3 hybridized atom is 109.5 and that of an sp2 hybridized atom is 120, do you expect the bond angle between two hybrid orbitals to increase or decrease as the s-character of the hybrids is increased?" Why is the answer to this that if s ...

Bryce Ramirez 1J

When looking at the lewis structure of a molecule, if there are lone pairs on the central atom, do you count that towards the total amount of bonds? Like if an atom had three single bonds and then a lone pair, its hybrid orbitals would be sp^3 because you would be counted as having four atomic orbit...

Bryce Ramirez 1J

What are the different formulas for making arrangements of electron pairs. There are three formulas that involve the S and P orbital with Px and Py but I don't understand how they apply to hybrid orbitals.

Bryce Ramirez 1J

Because there are only three bonds on the central atom carbon, that means that it has to have the hybridization 2p^3. This also means that the number of hybrid orbitals will be 3. When determining the hybridization, you look at the bonds made on the central atoms, not just the amount of central atom...

Bryce Ramirez 1J

Can someone explain how the overlapping of orbitals is significant for sigma bonds and pi bonds. And how this applies to the hybridization of the central atom.

Bryce Ramirez 1J

Why are there only certain VSEPR electron arrangements for determining the hybridization of a central atom? Why isn't angular or See Saw or Square Planar possible VSEPR models that can be used for hybridization.

Bryce Ramirez 1J

Why does Xenon have two double bonds with oxygen and 2 single bonds with fluorine and a lone pair to make the lowest energy level for its lewis structure. I thought that you are only allowed to assign 8 electrons to each atom, but if you were to add it up, Xe would have 14 electrons. Not sure if thi...

Bryce Ramirez 1J

Drawing the Lewis Structure really helps because then you can visually see where the signs are coming from, if there are no charges then you would see it from the molecule being drawn and if there are charges they can easily be labeled on the Lewis Structure and understood why they are there.

Bryce Ramirez 1J

All molecules have LDF, but these are relatively weak compared to the rest of the intermolecular forces. But this is an easy one to remember because nearly all will have it. In terms of remembering the others, knowing why each bond is formed can give insight into how strong or weak it is.

Bryce Ramirez 1J

For part d, there is no opportunity for Hydrogen bonding in C[2]H[4], and Hydrogen bonds are stronger so that is why CH[3]OH would have a higher melting point (hydrogen bonds can occur between the H's and O's). For part b, I am unsure though since there are the same amount of H and O molecules allo...

Bryce Ramirez 1J

Thank you for explaining, this definitely clears it up!

Bryce Ramirez 1J

For C2H4, the hydrogen atoms bond to the two carbon atoms, but there are no lone pairs left on the carbon. If there were lone pairs left on the carbon atom, would this then make it potential for hydrogen bonding? I know as it stands that the molecule doesn't have hydrogen bonding, asking for clarifi...

Bryce Ramirez 1J

When finding which molecule has the higher melting point, how do you determine it from the hydrogen bonding. For part b and d of 3F.5, is says that the reason one molecule has a higher melting point is because of the hydrogen bonding that is present in one molecule but not the other, but I don't kno...

Bryce Ramirez 1J

So does this mean that everything that is a molecule will automatically have LDF?

Bryce Ramirez 1J

Can someone explain the process of finding the answer to part a of this question? It ask "Identify the types of attractive intermolecular interactions that might arise between molecules of each of the following sub- stances: (a) NH2OH". Should I start by drawing the Lewis Structure, and th...

Bryce Ramirez 1J

The interaction that happens between Dipole Moments is what keeps the negative side attracted to the positive side, but will we need to know how they are attracted together, like the force of the two atoms being attracted and how much energy it would take to separate them?

Bryce Ramirez 1J

Will we need to know how to draw the models for each orbital? Or do we just need to know how they are created and the theory behind them?

Bryce Ramirez 1J

For Lewis Structures with different lengths of bonds, will the bond lengths for each always be somewhere in between the length of the longest and shortest bond? I know that single bonds are usually longer than shorter bonds, and triple bonds are even shorter.

Bryce Ramirez 1J

For 12b, you would first calculate the total amount of electrons in ClO^4-, which would be 7e- + 4(6e-) + 1e-, giving you 32e-. Then you would draw the Lewis structure that has these amount of electrons accounted for in the whole structure. For 12c, you would do the same steps as part b. After addin...

Bryce Ramirez 1J

When Delta E is negative, it means that the difference in energy states is a negative value because the first value was smaller than the second. This would be from solving from an energy state that is higher to lower, like n = 3 to n =1. When an electron is being excited, then the change would be po...

Bryce Ramirez 1J

There might be lone pairs instead of adding an extra bond because it helps with the formal charge of the central atom. Because lone pairs count as two and bonds only count as one electron, this could make the difference in an atom being neutral or being negative/ positive. It will always want to hav...

Bryce Ramirez 1J

How do you know when a chemical structure will actually be a radical. For part c of 2C.5, the formula is chlorine nitrate, ClONO2 (the central O atom is attached to the Cl atom and to the N atom of the NO2 group). If N is supposed to have 5 electrons and the formal charge on it is +1, does that effe...

Bryce Ramirez 1J

For part A, it asks "Draw the Lewis structure and determine the formal charge on each atom in (a) NO+. But why are the two triple bonded to each other? I understand that the formal charges would be 0 for the N and +1 for the O.

Bryce Ramirez 1J

When saying how many electrons there are for an element in the d block, how do you know when to write the electron configuration without the s block and transfer those electrons to the d block. For Ru^+3, the electron configuration is [Kr] 4d^5, but this uses the two electrons from the 5s^2 and puts...

Bryce Ramirez 1J

The question asks "Give the number of valence electrons (including d electrons) for each of the following elements: (a) Sb; (b) Si; (c) Mn; (d) B." Why are the answers 5, 4, 7, and 3? For most of them, the only valence electrons were from the p block. For a, I thought it would be 3 valence...

Bryce Ramirez 1J

When writing the electron configuration for rubidium, it goes all the way up to the 5s row. But when writing 4s^2 and 3d^10, would you write the 3d^10 before or after the 4s^2, because both are filled. I think the filled 3d^10 would have more energy, but it also starts with 3 and being consistent wi...

Bryce Ramirez 1J

When solving for orbitals and you are only given that n = 2, why is the answer? Solving for l would give you 1, which corresponds to the P orbital, giving you three. But the answer shows 4. Why is this?

Bryce Ramirez 1J

The problems asks for the number of orbitals given a subshell. Would the answer be finding Ml from L or finding n from L?

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