CHEMISTRY COMMUNITY

MichaelRaad_1F

You would need to have an equal amount of electrons on the products and reactants side of the two half equations in order to have them cancel out when writing the final equation.

MichaelRaad_1F

We do not consider the concentrations of solids when calculating Q and K for a reaction.

MichaelRaad_1F

The anode should be in the first box, in this case being Pb(s) and the cathode should be in the last box, in this case being Ag(s). The chloride ions should be on the either side of the salt bridge. The phase changes change as you go through the shorthand notation.

MichaelRaad_1F

That looks good to me. Maybe try removing the parenthesis.

MichaelRaad_1F

Cp-Cv=R and delta U=nCdeltaT are the two equations I used for this problem.

MichaelRaad_1F

Heat capacities cannot be negative and if you get a negative value just take the absolute value of it.

MichaelRaad_1F

For this problem convert the given value of grams to moles and multiply by the heat of combustion. Divide that value by the change in temperature and take the absolute value for part a. For part b, calculate delta T and multiply it by the value you got for part a. Divide that value by the grams of s...

MichaelRaad_1F

For part b you would use the equation w=PexdeltaV and then convert to the proper units.

MichaelRaad_1F

I used q=mcdeltaT and I had to multiply the constant R by three.

MichaelRaad_1F

First covert from Kcal to KJ and subtract that number by the heat given off to solve for deltaE

MichaelRaad_1F

You should use q=mcdeltaT and choose the correct constant based of the shape of the molecule.

MichaelRaad_1F

We first use the equation mcdeltaT to find the final temperature for ice and then we would use that value as the initial temperature value for the second equation in which we set mcdeltaT =-mcdeltaT and then solve for the final temperature.

MichaelRaad_1F

You would first convert the value of grams to moles and multiply it by the heat of combustion and then divide it by the change in temperature. Take the absolute value of that number for the first part. Second, calculate delta T and multiply the value you found in the first part. Divide that number b...

MichaelRaad_1F

Cv-Cp = R Cp being the molar heat capacity of a gas at constant pressure and Cv being the molar heat capacity of a gas at constant volume.

MichaelRaad_1F

It would based of the units given n being moles and m being mass in grams.

MichaelRaad_1F

Cp is the molar heat capacity of a gas at constant pressure.

MichaelRaad_1F

I also think that Professor Lavelle meant NET because he also mentioned that heat spontaneously moves from the hotter object to the cooler object.

MichaelRaad_1F

Can someone please explain the difference between work done along a reversible pathway compared to an irreversible pathway?

MichaelRaad_1F

Can someone please explain the difference between work done along a reversible pathway compared to an irreversible pathway?

MichaelRaad_1F

It is the sum of the products - the sum of the reactants. The H2g and Cs have values of zero because they are in their standard states.

MichaelRaad_1F

I first set up a chemical equation being NH4+ + H2O yields NH3 + H30+. I then calculate ka using the equation ka x kb=10^-14. I set the initial concentration of NH4 to the given M in the question. I then set up my equilibrium equation and solve for x. Calculate the pH by using -log. That is what I ...

MichaelRaad_1F

Water cooling on a surface is an exothermic process because in order for the water to have a phase shift from vapor to liquid, it must be cooled and therefore release heat.

MichaelRaad_1F

I was just wondering how it's possible that we can use either use J/K or J/C when finding specific heat capacity.

MichaelRaad_1F

I was just confused on how to calculate the change in temperature for this problem because I know delta T is equal to final temperature - initial temperature but Im not sure how to find the final temperatures for this problem.

MichaelRaad_1F

Set up an ice chart and use the given molarity of CH3CH(OH)COOH as the initial concentration. Set up an equilibrium equation using the given ka value and solve for x. Use negative log to calculate pH and subtract pH from 14 to find pOH. The x value divided by the initial concentration of lactic acid...

MichaelRaad_1F

I first set up a chemical equation being NH4+ + H2O yields NH3 + H30+. I then calculate ka using the equation ka x kb=10^-14. I set the initial concentration of NH4 to the given M in the question. I then set up my equilibrium equation and solve for x. Calculate the pH by using -log.

MichaelRaad_1F

I first wrote the chemical reaction being NH4+ + H20 yields NH3 + H3O+. From there I make an ice chart and put the given M of NH4Cl for my initial concentration of NH4+. I then find the ka value by using the equation ka x kb = 10^-14. Set up an equation for ka and then use negative log to find the pH.

MichaelRaad_1F

Alexis Sanft 1E wrote:What does it mean to be a "predominant" species?

I'm pretty sure it just means that there is more of it or it is the most basic/acidic in solution.

MichaelRaad_1F

It is important to differentiate between weak and strong acids and bases because strong acids and bases completely dissociate in solution.

MichaelRaad_1F

I first calculate concentration of OH and BH using the given pH and inverse log. I set these values as final concentrations for OH and BH on my ice chart and B reactant is x-the final concentration of OH. I then would solve for x after setting up my expression for kb.

MichaelRaad_1F

You could always check just to be sure by putting the value you get for x divided by the initial molarity given.

MichaelRaad_1F

We do not typically include water in our expressions for k

MichaelRaad_1F

This is because strong acids and strong bases dissociate completely in solution.

MichaelRaad_1F

I think if k is smaller than 10^-5 then we can assume it is 0 when calculating equilibrium.

MichaelRaad_1F

Yes, a change in temperature is the only thing that changes K I believe.

MichaelRaad_1F

When Q is less than K it means that there are more reactants than products and therefore the forward reaction is favored due to the excess of reactants in the chemical reaction.

MichaelRaad_1F

The K of a reverse reaction is the inverse of the K for the forward reaction.

MichaelRaad_1F

The concentration has to be positive because any concentration less than 0 does not exist, 0 concentration means we do not have anything.

MichaelRaad_1F

Q is calculated at any time during the reaction before it has reached equilibrium and the value of q varies as the reaction approaches equilibrium while the k is when equilibrium is reached.

MichaelRaad_1F

You would look at the reaction as a whole and see if there are more than one phase in the reaction. Such as gas and liquid or all gas.

MichaelRaad_1F

I think the question was just trying to show us that the more oxygen atoms present in the molecule, the higher the strength of the acids because the more oxygen atoms, the weaker the bond to hydrogen is in the molecule.

MichaelRaad_1F

At equilibrium, both H and OH have 1x10^-7 so if either H or OH has a higher concentration than 1x10^-7 then the solution is either basic or acidic.

MichaelRaad_1F

It depends on the initial charge of the molecule. For example the third question on sapling is asking us what the conjugate base of HSO4- is and the answer would be SO42-.

MichaelRaad_1F

An example of an Amphoteric compound is H2O because it can both lose and accept protons. If the molecule can both lose and accept protons it is amphoteric.

MichaelRaad_1F

We can look at bond length and electronegativity of the central atom of the molecule.

MichaelRaad_1F

To find the pOH, we would take the negative log of the value we have for out OH concentration.

MichaelRaad_1F

We know that [OH-]([H+]=1x10^-14. We can use this information to determine pH based off of concentration of either OH or H. We know that at equilibria, we have both H and OH having 1x10^-7 concentrations so if OH has a concentration less than that number, then it is more acidic.

MichaelRaad_1F

A Bronsted Acid is a proton donor, it donated an H+ while a lewis acid accepts an electron pair. You can think of H+ being a lewis acid because it cannot donate an electron pair and must instead accept an electron pair because it has no electrons to donate.

MichaelRaad_1F

pKa is the pH value at which there are equal quantities of acid and conjugate base.

MichaelRaad_1F

Dipole Arrows are simply the vectors we draw on the structure of a molecule from the slightly positive charged element to the slightly negative element. if these arrows are equal in magnitude and opposite in direction, then they cancel out rendering the molecule nonpolar.

MichaelRaad_1F

I think formal charge is the only way to check which resonance structure is ideal unless the question tells you the determined bond lengths the elements form. You would then need to choose the structure that most accurately has bond lengths similar to the experimentally determined ones.

MichaelRaad_1F

I write out the number of valence electrons and learn how to recognize the number of bonds elements tend to form. For example carbon tends to form 4 bonds while oxygen tends to form two bonds based off of the electrons in their valence shell.

MichaelRaad_1F

Dipoles cancel out if the vectors drawn are in opposite directions and equal in magnitude. For example an H2O will have a stronger dipole moment than that of CaS.

MichaelRaad_1F

A delocalized pi bond is essentially a pi bond of a molecule that has resonance. If the molecule has resonance (as can be determined by the Lewis structure), then it can have a delocalized pi bond.

MichaelRaad_1F

An easy way to determine hybrid orbitals is to count the number of electron density regions around the central atom and choose the answer that provides the accurate number of orbitals for the electron density regions.

MichaelRaad_1F

You can do this by checking the difference in electronegativities of the elements in the molecule. For example, HO would have a higher dipole moment than a CH bond.

MichaelRaad_1F

An easy way to determine if a molecule is polar or nonpolar is by drawing out vectors on the Lewis structure of the molecule. Keep in mind that if the central atom on a molecule has a lone pair but the vectors cancel out, the molecule is still polar.

MichaelRaad_1F

Once the central atom has a lone pair, other bonds are pushed down changing the bond angles of the molecule.

MichaelRaad_1F

An atom can have an expanded valence if it has space in the d orbital. Elements period 3 and below can have expanded valence shells.

MichaelRaad_1F

The lone pair on the sulfite pushes all the other bonds down changing the bond angle of the molecule.

MichaelRaad_1F

In this scenario Arsenic can form 6 bonds because the molecule is a cation with a -1 charge.

MichaelRaad_1F

This is because Carbon is not as electronegative as Nitrogen, Oxygen, and Fluorine

MichaelRaad_1F

In choice A, the hydrogen is bonded to carbon while in choice C, the hydrogen is bonded to an Oxygen. In order for a Hydrogen bond to form, the hydrogen has to be bonded with a Nitrogen, Oxygen, or Fluorine atom. Therefore choice C is correct because the hydrogen involved in the hydrogen bond is bon...

MichaelRaad_1F

We would need to count the number of valence electrons and if atoms that are not capable of having expanded octets are full, then we would assign the extra electrons to atoms that can have expanded octets. We can also count the number of bonds we need by counting the valence electrons available and ...

MichaelRaad_1F

The Lewis Structure would have two Oxygen Carbon single bond and if we added two protons (two Hydrogens), they would bond to the two Oxygens because Oxygen wants to form two bonds in order to have a formal charge of 0.

MichaelRaad_1F

Boron and Aluminum (group 13 elements) can also be exceptions to the octet rule. Boron has 3 valence electrons that can bond and therefore Boron can form three bonds. Boron can complete its octet if another atom provides both electrons forming a coordinate covalent bond.

MichaelRaad_1F

Is there any way to easily determine the oxidation number of a bonded element?

MichaelRaad_1F

I calculate the formal charge of each element in a bond and try to get the charge to be as close to 0 as possible using the formula Valence electrons-(lone pairs+ shared electrons/2).

MichaelRaad_1F

I don't understand how ionic bonds have covalent character and how covalent bonds have ionic character.

MichaelRaad_1F

I don't understand on the sapling homework how to determine which Lewis structure is more plausible based off of the experimentally determined bond lengths. Do we just see which bond length is closest in length to the bond length experimentally determined?

MichaelRaad_1F

For n=3 you can have 18 electrons because the s subshell can hold 2 electrons, the p subshell can hold 6 electrons, and the d subshell can hold 10 electrons. For n=5,l=0 you can have 2 electrons because l=0 represents the s subshell and the s subshell can hold two electrons. For n=7,l=1,ml=-1 you ca...

MichaelRaad_1F

I think it means that the inner shell electrons shield the electrons in the outer shell because the nucleus is positively charged and the electrons are negatively charged so they attract. The inner shell electrons repel the outer shell electrons because both are negatively charged. The inner electro...

MichaelRaad_1F

I watched some Khan Academy videos about quantum numbers but he goes very in depth into the subject but they were helpful nonetheless.

MichaelRaad_1F

In the n=2 level we know that there are s and p subshells and we know that the s subshell can hold 2 electrons and the p subshell can hold 6 electrons. So the n=2 level can hold a total of 8 electrons.

MichaelRaad_1F

I'm pretty sure an electron just emits light when it moves from the excited state back to its ground state.

MichaelRaad_1F

I used the Rydberg equation but the version that uses the constant 1.097*10^7 for R and instead of frequency the equation is equal to 1/wavelength. This way you don't have to do an extra conversion but I'm sure both methods work.

MichaelRaad_1F

I'm just doing as many practice problems as I can and I'm also trying to form a study group where I can explain what I know and learn what I don't from others.

MichaelRaad_1F

I think the main takeaway from the Schrodinger Equation is that we can find the areas where an electron is most likely located and it gives us the energy of the electron.

MichaelRaad_1F

I think to measure uncertainty in real life we would compare our calculated (theoretical data) with our experimental data. There is also an equation that allows us to find percent error and if I'm not mistaken it was experimental/theoretical *100. Hope this helps!

MichaelRaad_1F

I don't think we would need to memorize all of them but I'm not too sure.

MichaelRaad_1F

Why are we given the degrees Celsius in the question? Is it because at higher temperatures electrons move faster?

MichaelRaad_1F

We know that blue light is part of the Balmer Series because it is under visible light and in the Balmer series n1=2. I used the Rydberg formula to solve this problem by manipulating the equation for n2^2. I used the version of the equation that says 1/wavelength is equal to as opposed to the v is e...

MichaelRaad_1F

I'm not sure if this question made sense so I can clarify if need be.

MichaelRaad_1F

I was going through the sapling homework and I got the right answer by using the same equation (Rydberg Formula) except instead of using frequency is equal to, I used 1/wavelength instead and the units on the Rydberg constant I used were 1/m. Is this fine or should I stick to the frequency is equal ...

MichaelRaad_1F

Are the different lengths between n=1 n=2 and so on measured in nanometers. I don't understand how visible light has larger wavelength but appears to be shorter on the model shown in lecture number 6.

MichaelRaad_1F

I simply counted the number of atoms in the picture and added all their masses

MichaelRaad_1F

Every zig zag has a carbon and hydrogen atoms are used to fill the valence shell of the carbon atoms. The carbon atoms on the far right and left of the image are bonded to three hydrogen atoms.

MichaelRaad_1F

This is because solids and liquids have an activity series of 1 so we don't include them in the calculation.

MichaelRaad_1F

Doesn't it have to do with the amount of energy an electron gives off as it moves from a higher to lower state?

MichaelRaad_1F

Does anyone know how electron density is measured?

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