CHEMISTRY COMMUNITY

Alex Tchekanov Dis 2k

Boltzmann's' constant can also be expressed in this way:
Kb * Avogadro's number = R

Alex Tchekanov Dis 2k

I know that at constant pressure delta H = qp
Is there anything specific that delta H is equal to for constant temperature? Or constant volume?

Alex Tchekanov Dis 2k

Can someone please explain why in the practice problem today in class we set delta G equal to zero to find out at what temperature the reaction will be spontaneous?

Alex Tchekanov Dis 2k

Yes, but most of the time I believe the question will refer to Cv

Alex Tchekanov Dis 2k

At constant pressure q = delta H

Alex Tchekanov Dis 2k

A closed system means that the matter can not leave and matter can not come in. However, energy in the form of heat can leave/enter. That's probably why you said does not insulate, because the temp can change.

Alex Tchekanov Dis 2k

In the case of isothermic reversible reactions, the pressure decreases thus is not constant. That is why you have to use this equation: -nRTlog (V2/V1)

Alex Tchekanov Dis 2k

Could someone please organize all the equations that are specific to a system that has constant Pressure, a system that has constant volume and an isothermal (constant temperate) system. I feel like there are so many equations that get mixed up and I'm not sure when to use which one.

Alex Tchekanov Dis 2k

When the standard Gibbs free energy of formation is considered thermodynamically stable when it is negative because the pure compound is then considered to have a lower Gibbs free energy than the Gibbs free energy of the pure elements which would mean that the pure element would have the tendency to...

Alex Tchekanov Dis 2k

I believe that the "end" of each week for the chemistry community is on Sunday.

Alex Tchekanov Dis 2k

They are not equal values, however, they are proportional

Alex Tchekanov Dis 2k

You can look at it as the sum of Bonds Broken - the sum of Bonds Formed
This will get you the delta H value.

Alex Tchekanov Dis 2k

You can think about it like this. K is the products over reactants, so therefore anytime the reactants are waayyyyyyyy more than the products it is weak, more specifically when the ratio makes the K value less than 10^-3. This is regardless if it's an acid or base. so Ka>10 3 is a strong acid? Yes ...

Alex Tchekanov Dis 2k

When you are calculating the difference of energy used to raise the temperature, why does the expansion of the volume change the amount of heat change?

Alex Tchekanov Dis 2k

When would we have to know which one of the two to use?

Alex Tchekanov Dis 2k

When you are using a calorimeter to find temperature change, do you have to account for the amount of heat absorbed by the calorimeter? Or would this value be negligible?

Alex Tchekanov Dis 2k

When gas is allowed to expand reversibly and isothermally, it uses the most amount of work because of the infinitely small change.

Alex Tchekanov Dis 2k

In the phase change of water, there is a plateau point when the temperature isn't changing but the ice turns to water or the water turns to steam, but does that also occur for other molecules? And if so, would they have similar looking graphs?

Alex Tchekanov Dis 2k

Can someone please explain why for a closed system the energy is able to be released? Isn't it logical to think that because the system is CLOSED, it is closed off from the surroundings and isn't affected by it?

Alex Tchekanov Dis 2k

In the example he gave in class, the value for the concentration of H3O+ would have been so low that it would be lower than the standard concentration in normal water. Therefore, since it logically doesn't make sense for acid to make the solution more basic, we just regard the addition of the molecu...

Alex Tchekanov Dis 2k

You can think about it like this. K is the products over reactants, so therefore anytime the reactants are waayyyyyyyy more than the products it is weak, more specifically when the ratio makes the K value less than 10^-3. This is regardless if it's an acid or base.

Alex Tchekanov Dis 2k

there are many possible equations to illustrate a proton transfer. A proton is just an H+ atom and so it is common to see this transferred from an acid to a water molecule to make H3O+ in an acid equilibrium equation.

Alex Tchekanov Dis 2k

This equation has many uses, however, the one that Lavelle talked about in class is when you want to convert pressure to concentration as the following:
PV=nRT
P=(n/V)RT
P=concRT
Conc=P/RT

Alex Tchekanov Dis 2k

You are correct that that the concentration change is insignificant. You definitely need some of the solid and liquid to make the product, but the concentration difference is negligible.

Alex Tchekanov Dis 2k

I think in the case of calculations we say the temperature increase from the neutralization reaction (from the formation of a O-H bond) is negligible and therefore, the K doesn't change

Alex Tchekanov Dis 2k

It's also good to mention that if the pressure is increased by making the volume half it will not shift the reaction either way IF there is an equal amount of moles of gas on both sides

Alex Tchekanov Dis 2k

You also do this because the activity of water is said to be one and thus when you multiply by one, it does not change the K value

Alex Tchekanov Dis 2k

For this question, I keep getting my answer to be 3.9... in my calculator but the answer in the book is 3.88. I didn't round any of my answers but I'm not getting the same number, does anyone know what I might be doing wrong?

Alex Tchekanov Dis 2k

If you want to convert from concentration to partial pressure you have to use the ideal gas law: PV=nRT
P=(n/V)RT
P=ConcRT
Cont=P/RT

Alex Tchekanov Dis 2k

We don't include solids or liquids because, in the grand scheme of the reaction, only a negligible amount is used and therefore doesn't affect the equilibrium constant.

Alex Tchekanov Dis 2k

When you are doing the ice tables, the number in front of the x is equal to the stoichiometric coefficient. Here's an example with different coefficients: N2 + 3H2 = 2NH3 x 3x 2x And now when you are writing the equilibrium constant, K, you have to use those stoichiometric coefficients to raise to t...

Alex Tchekanov Dis 2k

So to understand this, you have to understand the equation. K is the product over the reactant at equilibrium. Q is also the product of the reactant.. but not at equilibrium. Therefore when Q<K, how could that be? Well if you look at the formula, it means that Q must have more reactants because it's...

Alex Tchekanov Dis 2k

Because the oxygen molecule is very small and cannot reach far enough to make bonds. The reason why other molecules are polydentate is because they have long chain structures or are at least more spaced out and can reach closer to make more bonds.

Alex Tchekanov Dis 2k

Dirty coal has sulfur in it and clean coal has very minimal, almost negligible amounts.

Alex Tchekanov Dis 2k

It can either mono bi dentate. This depends which oxygen on molecule is making the bond. Because it is trigonal planar, if the transition metal cation is in-between two of the oxygens, it can make two bonds, however, if the cation is directly across from an O, it will only be able to make one bond.

Alex Tchekanov Dis 2k

I don't think you would be considered wrong, but to be safe, you should make sure to have the O be the one that binds to the coordination compounds. So depending on what side of the transition metal it is on, will determine if you write H2O or OH2

Alex Tchekanov Dis 2k

Yes, if one of the attached atoms is different, it is polar.

Alex Tchekanov Dis 2k

The HOCl bond is longer than the HOF bond. Therefore, since the stability and thus electronegativity doesn't matter, it is the length of the bond that does.

Alex Tchekanov Dis 2k

For problem 6.21 in the homework, it says that the given molecule can only accept two protons. My first guess would be that it could accept 6 because of the two lone pairs on each oxygen and then the one lone pair on the two nitrogens. Why can't the oxygens accept protons?

Alex Tchekanov Dis 2k

When he said negatively charged, he basically meant that the acid was dissociated. This is because for example when HCl dissociates, the Cl is negative

Alex Tchekanov Dis 2k

Why is SO3 considered acidic in water? What properties make this so? I know that it creates H2SO4 in water, but how does this make it a lewis acid?

Alex Tchekanov Dis 2k

For question 6A.13, it asks you to draw the lewis structure or symbol for Ag+. How do you know how many valence electrons to draw for the transition metals? For instance, for O, you know it has 6 valence electrons because it is in row 16, but how does this work for the middle elements?

Alex Tchekanov Dis 2k

Is a molecule that is considered a lewis acid also considered a Bronsted acid and vice versa?

Alex Tchekanov Dis 2k

The polydentate ligand binds to a central metal cation. Because polydentate ligands are normally long stands with multiple binding sites, the long molecule can bend and naturally arrange itself around the central atom, thus forming the chelate or ring-like structure.

Alex Tchekanov Dis 2k

Search up "The Organic Chemistry Tutor" on youtube. He literally has everything and is one of the best online resources for chemistry videos

Alex Tchekanov Dis 2k

When a molecule is reduced that means it is gaining electrons. A way to remember this is through Oil Rig. Oxidation Is Losing (electrons) Reduction Is Gaining (electrons)

Alex Tchekanov Dis 2k

We have only gone over the equation pH=-log(H+) and pH=-log(OH-) so I believe these are the only calculation (at least so far) that we will have to do regarding pH

Alex Tchekanov Dis 2k

The most important thing to know is that it always results in the formation of H2O and often results in the formation of a salt.

Alex Tchekanov Dis 2k

Hybridization in a way is the combination of two orbitals. For example, the S orbital and the P orbital in SP3 hybridization. The S orbital has a spherical shape while the P orbital has a 3D infinity sign shape (sorry I don't have a better name for this but you can google a picture). Thus, when hybr...

Alex Tchekanov Dis 2k

No, because the formula doesn't change based on the concentration. This would just result in a negative pH, which is possible for some superacids

Alex Tchekanov Dis 2k

I don't think we necessarily have to memorize any strong acids and bases because Lavelle said that if it is a weak acid or base then we will get a Ka or Kb in the problem and that will be an indicator that it is weak. Otherwise, if there is no equilibrium constant in the equation, then we assume it ...

Alex Tchekanov Dis 2k

The way that you can deduce this formula from the name is that first it starts with potassium - K, you don't know how many yet, but you know the first atom is K, and because K is a positive cation, it is outside of the brackets. Then for hexacyanido - hexa means 6 and cyanido means CN-. Then you hav...

Alex Tchekanov Dis 2k

I believe that it can either be one lone pair or two lone pairs that make a linear shape. Because a molecule with three lone pairs and two atoms would give you a linear geometry.

Alex Tchekanov Dis 2k

For part a and c the metal atom is changed to end in "ate" , but in part b and d, it is not. Can someone please explain why this is?

Alex Tchekanov Dis 2k

I know that we don't have to be able to identify if a coordination compound is one or the other, but were there any compounds that were discussed in lecture that the shapes were specifically given as square planar or tetrahedral?

Alex Tchekanov Dis 2k

The pdf that is on Lavelle's website has two columns for the names of ligands. Are we supposed to know the "Name" column or the "New IUPAC Name Convention"?

Alex Tchekanov Dis 2k

In the lewis structure for CN-, both the C and the N have a lone pair. So why is it the C that donates the lone pair when forming a coordination compound? Would it be wrong to show the N making the coordinate covalent bond?

Alex Tchekanov Dis 2k

Could someone please explain the answer to this homework question? Also, what does it mean by the "s-character" or the hybrid? Question: "Noting that the bond angle of an sp3 hybridized atom is 109.5 degrees and that of an sp2 hybridized atom is 120 degrees, do you expect the bond ang...

Alex Tchekanov Dis 2k

Also, sometimes when adding a different, more electronegative atom, the bond angles can change. For example, CCl4 and CCl3F have the same molecular geometry but slightly different bond angles.

Alex Tchekanov Dis 2k

Polarity is a combination of the molecular geometry and the electronegativity. For example, a linear molecule such as BeH2 is not polar because the central atom has two atoms of equal electronegativity on either side and the dipole moments cancel each other out. However for a linear molecule such as...

Alex Tchekanov Dis 2k

For Lewis Dot structures, both would be technically correct. So not it doesn't matter. However, the structure with the hydrogen atoms drawn diagonally helps show the molecular geometry of the molecule.

Alex Tchekanov Dis 2k

I think the exact answer is 107, however, for this class, I believe we only need to know that it is slightly less than 109.5. So I wouldn't worry about that

Alex Tchekanov Dis 2k

In the homework, it asks what is the expected bond length in ClO2+ I thought that since it is a bent molecule with one lone pair that the answer would be less than 180 degrees because it is less than linear, and also in the example of H20, the angle is 120 degree and H2O has two lone pairs so, there...

Alex Tchekanov Dis 2k

The shape matters because of the available surface area. For example, two rod shaped molecules will be able to have more of their surface area (more of their electron clouds) near each other and this will strengthen the interaction. On the other hand, two spherical shaped molecules will have less of...

Alex Tchekanov Dis 2k

Coordinate Covalent Bonds are also important in relation to lewis acids and lewis bases. A lewis base is a molecule that gives both of its electrons away to form the coordinate covalent bond while a lewis acid is a molecule that accepts both of the electrons.

Alex Tchekanov Dis 2k

The energy to separate two atoms isn't a value you will have to memorize. Rather if it is needed in the context of a problem, it will most likely be given to you.

Alex Tchekanov Dis 2k

You know a molecule has a dipole moment when there is an unequal sharing of the electron. The dipole moment is larger when the difference in electronegativity is greater. The reason why the arrow points towards the partially charged atom is because that is the direction that the electron is being pu...

Alex Tchekanov Dis 2k

In topic 2A.3 in the book, it talked about lattice energy. Do we need to understand this concept for the midterm?

Alex Tchekanov Dis 2k

This is because the electron configuration for neutral Co is [Ar]3d74s2 and when you take off electrons, you take them from the 4s level instead of the 3d because the 4s is technically in a lower energy state. For these problems, it always helps to write the neutral configuration first and then take...

Alex Tchekanov Dis 2k

The trend for electronegativity is increasing upwards and to the right. Florine is thus the most electronegative element on the periodic table. Therefore, if you are ever comparing the ionic character of a single element (carbon for example) with various other elements, fluorine will thus have the g...

Alex Tchekanov Dis 2k

You know that the unpaired electron is on the oxygen atom because oxygen is more electronegative and thus wants the electron more.

Alex Tchekanov Dis 2k

"Describe the interpretation of atomic orbitals in terms of probability"
Can someone please explain this?

Alex Tchekanov Dis 2k

Can someone please explain why the C-F bond is stronger than the C-Cl bond? Is it because of electronegativity?

Alex Tchekanov Dis 2k

I just placed the potassium atoms floating outside of/around the central phosphorous atom and then bracketed each atom to show the individual charges. How do you know that the potassium ions do not covalently bond to the phosphorus atom? What is the clue that tells you that the 3 K atoms are merely...

Alex Tchekanov Dis 2k

When there are electrons in the 3d block and the 4s block, you typically take away the 4s electrons first. This is because 4s is in a slightly higher energy state than the 3d block. Because the 4s electrons have higher energy, they are the first to go when losing electrons, since they are further fr...

Alex Tchekanov Dis 2k

Because they are isoelectronic, the shielding effect will be different and the strength of the positive nuclear pull will be less on the P atom because the proton to electron ratio is lower. And thus, because there is a weaker relative positive charge pulling on the electrons in the atoms with fewer...

Alex Tchekanov Dis 2k

I agree with the above response, that most of the time you want to draw the one with the lowest formal charge. One kind of short-cut that I've noticed from doing problems that helps me is that when Oxygen has two covalent bonds and 4 lone pairs, it formal charge is zero and when carbon has four cova...

Alex Tchekanov Dis 2k

The question is the same as asking you to find the electron configuration of an ion with a 2+ charge... but backward. So, in this case, you have to see what element lines up with the [Ar]3d7 and then identify the ion that it would be. In the case of a) the answer would be the Co 2+ ion -- this is be...

Alex Tchekanov Dis 2k

Benzene is a unique, ring-like structure that is very common in organic chemistry. I think the reason he showed us the "resonance hybrid" is to illustrate to us that the double bonds don't actually belong to any single pair of atoms. However, for other molecules that have resonance, specif...

Alex Tchekanov Dis 2k

I believe that one of the most important factors is the distance the valence electron is away from the nucleus. This is because this affects not only the atomic radius but also the ionization energy and electron shielding. Otherwise, I think that ionization energy and the nuclear charge would be the...

Alex Tchekanov Dis 2k

When there is a double bond, there are more electrons being shared between the two atoms, thus the attraction between the nucleus of the atoms (the positively charged regions) are pulling on two negatively charged electrons instead of one. This is a stronger attraction than a single bond with one el...

Alex Tchekanov Dis 2k

The constant R in the Rydberg equation can have multiple different numbers depending on the units that it is used in, however in the Rydberg Equation the units Hz is used. The constant that is used in the equation is 3.29 x 10^15 Hz. If you google this constant you might find different numbers but o...

Alex Tchekanov Dis 2k

The reason why you draw the dots (lone pairs) of electrons is because it gives a more clear representation since there are expections to the octet rule. However, in the case for Hydrogen atoms since there are only 2 electrons you won't see any dots, only the single covalent bond.

Alex Tchekanov Dis 2k

the units are in pm which means that the x would be 350 x 10^-12 m not 10^-10
Otherwise, yes, the other steps you said would be correct

Alex Tchekanov Dis 2k

In the lecture, I believe he explains that this experiment is done with a slightly positively charged detector that, although the electron has 0 Kinetic energy, will slowly draw the electron towards it, away from the atom.

Alex Tchekanov Dis 2k

Another keyword in the problem is "the lowest frequency" this means that it is the bare minimum to remove an electron and therefore will not have any excess energy to transform into Kinetic energy and thus Ke = 0

Alex Tchekanov Dis 2k

The energy is related to the frequency because of the formula E=hv The intensity of the light only changes how many photons are being released, it does not affect the amount of energy of the photons Thus, you can see the relationship between kinetic energy and the frequency in this equation: Ke= hv ...

Alex Tchekanov Dis 2k

Also, the only reason that the expectations of Cr and Cu "take" electrons from the S orbital for the D orbital is because of the stability. For instance, in the case of Cr, taking an S electron and putting it into the D subshell makes it so that there is one electron in each of the 5 orbit...

Alex Tchekanov Dis 2k

So the most important thing to remember is that if a certain wavelength of light does not cause electrons to be emitted, increasing or decreasing the intensity will not change the fact that electrons are not emitted. This is because the relationship between wavelength and energy. The equation E= hv ...

Alex Tchekanov Dis 2k

All electrons, protons, and neutrons have wave-like properties. This is because according to the de Broglie equation, all objects with momentum have wave-like properties. However, electrons, protons, and neutrons all have extremely small masses that allow for their wave-like properties to be measured.

Alex Tchekanov Dis 2k

Also, if the amount of energy from the photon does not exactly match the amount of energy to excite the electron to a new energy level, it will not be absorbed. Even if the energy of the photon is greater, if it is not exact, it will not be absorbed. This is because it can't absorb only part of the ...

Alex Tchekanov Dis 2k

Absorb and emit are not interchangeable terms. When an electron falls down from a higher energy level to a lower energy level, it will emit specific energy -- the same amount of energy needed to elevate it. For example, if a certain wave length excited an electron from n=2 to n=4, the amount of ener...

Alex Tchekanov Dis 2k

From what I understand, the reason why this proves light acts as a photon in this situation is because of the "photon-electron" interaction. The energy of the individual photon must be equal to that of the energy required to have an electron "jump" to a higher energy level. Thus,...

Alex Tchekanov Dis 2k

What you have to take into account is the new molar mass of the CuSO4*5H20. So what you do is add the molar mass of CuSO4 and the molar mass of 5 H20 molecules and then do the same calculation from part a.

Alex Tchekanov Dis 2k

What I was taught was that in chemistry you always want to make sure you are using the proper sig fig rules and then don't round your answer until the very end of the problem. Waiting to round to the end will prevent the slight rounding difference from each step from adding up into the wrong answer....

Alex Tchekanov Dis 2k

From what I understand, the coefficients mean the ratio between the about of NaCl and H20 is 1 mole to 1 mole. Therefore, in your example, if you have 0.018 moles of NaCl, you would need 0.018 moles of H20 to ensure that there is no limiting reactant. However for example, if it was NaCl + 2H20, you ...

Alex Tchekanov Dis 2k

It is a liquid when the element is in a liquid form - for example a melted metal is liquid. However, aqueous means it is dissolved in water - for example the salt (NaCl) dissociates and is surrounded by water molecules. And make sure you remember aqueous solutions are only in water.

Alex Tchekanov Dis 2k

I agree with both other answers above, but the way I think about the 100g concept is that rather than the actual mass being 100g, it is a comparison. Because of the mass percentage of an element in a given molecule will be the same whether you have 10g of the molecule or 1000g. Thus, we use an easy ...

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