CHEMISTRY COMMUNITY

Sydney Myers 4I

You would need to find K for whatever step you're considering is at equilibrium. Whatever fast step happens before the slow step with the intermediate.

Sydney Myers 4I

Most reactions only have two molecules involved and not three because there are so many more ways that three molecules can collide than just two, which decreases the likelyhood of the correct orientation occurring and producing a sufficient amount of product to consider it.

Sydney Myers 4I

That equation is simply derived from a different one where the activation energy and gas constant and etc are all to the power of e. In order to make it a linear equation, it can be transformed into the one that you have typed. A is just the pre-exponential factor, its a constant.

Sydney Myers 4I

It must be introduced as a reactant, as opposed to an intermediate, which is produced as a product first, then maybe used as a reactant. Catalysts also must reappear as products in equal amount as was inputted.

Sydney Myers 4I

It is not affected by whatever is in the exponent basically.

Sydney Myers 4I

I think understanding the linear graphs also helps us understand why we write integrated rate laws in point slope form of a line.

Sydney Myers 4I

Often, you can see which step of a reaction is slow by looking at its rate law. If there is a certain reactant in the rate law, you can tell that reactant is involved in the slow step of the reaction because it is the slow step that determines the rate. Whatever isn't involved in the rate is most li...

Sydney Myers 4I

The concentration of A over time changes at a constant rate, k. K is not affected by anything as time goes on, which is why it's a straight line.

Sydney Myers 4I

You have to take into account that the rate of formation of B is not equal to the rate of consumption of A. They are separated by a factor of 2, the coefficient.

Sydney Myers 4I

The equation for the half life of a reaction can be derived from its integrated rate law. The rate of the reaction has a direct effect on the half life of the reaction.

Sydney Myers 4I

The only reason that electrons flow is because of a difference in the concentration of the cells. They have the same species, which makes them generally have a lower E value than regular galvanic cells.

Sydney Myers 4I

It's important to only change the concentration of one reactant at a time in order to isolate that reactant's relationship with the rate.

Sydney Myers 4I

We use the coefficients to make fractions because the relationship is inverse. That's why we need the fraction.

Sydney Myers 4I

The order of the reaction also tells you which integrated rate law to use, so that's useful.

Sydney Myers 4I

The conditions of the reaction will not favor the occurrence of the reaction, even if the reaction is spontaneous thermodynamically.

Sydney Myers 4I

Since both are directly correlated with the spontaneity of the reaction, and they are inversely related, then it makes sense that if one is positive, the other must be negative and vice versa.

Sydney Myers 4I

The purpose of a salt bridge is to allow electrons to flow back to the anode after they are transferred to the cathode. This allows a circuit to form and continuous flow of electrons.

Sydney Myers 4I

There are three separate sections on the right because there are three different phases represented. They are all in contact with each other, just different phases.

Sydney Myers 4I

Instead of balancing hydrogens with H+, you add twice the amount of hydrogens needed in the form of water on the side that need hydrogens, then you balance that with an equal amount of OH- on the other side.

Sydney Myers 4I

You'll know based on the oxidation states of a certain element. If the oxidation state goes up from the left side of the equation to the right, then that element has been oxidized.

Sydney Myers 4I

When the delta S is 0, it doesn't necessarily mean that there's no heat transfer, just that whatever heat is being transferred is being converted to work or being transferred elsewhere. In an adiabatic system, there is no heat transferred.

Sydney Myers 4I

The relationship between delta H and delta S depends on which delta S you're referring to. If it's the entropy of the system, then as delta H increases, then delta S increases with it. If it's the entropy of the surroundings, then delta S would decrease with an increase in delta H. If its the total ...

Sydney Myers 4I

The equation allows us to relate a change in temperature to a change in the K value for a chemical reaction at equilibrium.

Sydney Myers 4I

005324438 wrote:For the most part, O will always be -1, halogens will always be -1, and H will always be +1. Once we assign values to these elements, then the rest we just add up the rest of the molecule to equal the total charge.

I think Oxygen's oxidation states is usually -2, not -1.

Sydney Myers 4I

Why are there three steps to finding the change in entropy at a transition temperature? If entropy is a state function, then how does heating a substance then cooling a substance give us anything other than delta S = 0?

Sydney Myers 4I

Whenever there is a degree symbol next to a delta S, delta H, or delta G, it means that the value was measured under standard conditions. When you say it out loud, its "delta S naught"

Sydney Myers 4I

The values differ because the heat capacity of a gas can be calculated with either a constant volume or a constant pressure. When it's calculated with a constant pressure, the gas can lose energy by doing work on whatever boundary is present, which makes the amount of energy to change its temperatur...

Sydney Myers 4I

Energy can be gained or lost by a system, however, it always is gained or lost by another system in an equal amount, so it is conserved because it was neither created or destroyed.

Sydney Myers 4I

If it's a confusing problem with bonds, you can count up all of the bonds on either side and write them out. For example, 3 carbon-carbon bonds, 2 oxygen-carbon bonds. Do this for the reactants and the products. Then you can easily figure out which bonds are present on both sides and ignore them, si...

Sydney Myers 4I

You will also need to use q=c*g*deltaT in order to deal with the temperature changes in the problem.

Sydney Myers 4I

Kaitlyn Ang 1J wrote:Adding to this, you know work = 0 when $\Delta{V} = 0$ because $w = -P\Delta{V}$ so 0 for $\Delta{V}$ (aka there is no change in volume, aka the volume is constant) makes the entire work equation 0

expanding on this, work is also 0 when pressure is 0, or when the system is in a vacuum.

Sydney Myers 4I

In order to account for the fact that energy is conserved, we must include entropy because some energy will be lost as entropy. Also, whether or a reaction increases or decreases entropy can have a effect on whether or not it is spontaneous.

Sydney Myers 4I

We probably wouldn't have to memorize any values, except to note that the standard enthalpy of formation of an element already in its most stable form is 0.

Sydney Myers 4I

It's simply that the definition of enthalpy is heat at a constant pressure. That's how it's defined as a function.

Sydney Myers 4I

The definition of enthaply is heat at a constant pressure. Q is heat, so the two are highly related. You can tell if delta H and q are the same if q has a subscript of p, meaning that it's the heat at a constant pressure.

Sydney Myers 4I

Enthalpy is the total amount of energy absorbed or released in a chemical reaction. It's made up of two components: one of them is usable energy that is stored in the chemical bonds of whatever molecule is formed (which is called free energy - G), entropy is the energy that is released and is unusab...

Sydney Myers 4I

A factor that may play into which method to use is if the reaction you're trying to find the enthalpy of occurs in standard states. If not, you may not be able to use standard reaction enthalpy of formation.

Sydney Myers 4I

All he meant by that is to just keep in mind that every bond enthalpy is slightly different, so when we are measuring a bond's enthalpy, we only know that its truly accurate if it's being measured from a diatomic molecule. A different bond, such as C-H, is going to be present in many different molec...

Sydney Myers 4I

When you form a bond, you're taking atoms from a state of high energy (free floating) to a more stable state (in a bond). This is a net decrease in potential energy, and the excess is given off as heat and the reaction is exothermic. When you break a bond, you need some form of energy to take the at...

Sydney Myers 4I

Water can only hold so much energy until it is converted to steam, but once it has been converted, it has the capability to hold much more energy, making the burn worse.

Sydney Myers 4I

It's true that breaking bonds releases energy, but only apply this when the breaking of a single bond in a very simple reaction. Otherwise there are too many factors to simplify to just breaking or forming bonds.

Sydney Myers 4I

Conjugates are useful to know for setting up buffer solutions.

Sydney Myers 4I

The reason we haven't dealt with reverse reactions in class is because usually we assign the chemical that we start with to be the reactant, so the reaction will go mostly in the forward direction and we can assume that the initial concentration will decrease be some amount (x).

Sydney Myers 4I

The effectiveness of buffers comes from their ability to both accept protons from any acids added, as well as donating protons to any base added, so that water is unaffected and the concentrations of H+ and OH- stay relatively constant.

Sydney Myers 4I

Adding a molecule that is not in the reaction wouldn't affect the reaction or the equilibrium because it doesn't change the concentration of the reactants or the products.

Sydney Myers 4I

Since the concentration and the pressure can be related by a factor of R*T (using the ideal gas law), the K should be the same whether you use partial pressures of temperature.

Sydney Myers 4I

When it comes to partial pressures, there are two ways that a system at equilibrium can change. Either 1) The entire volume of the container is being reduced. This would increase pressure on all of the molecules in the system and it would respond by shifting the equilibrium to whichever side has a s...

Sydney Myers 4I

We won't be expected to just look at a chemical equation and know which side the heat is on, instead we will get an energy value. If the energy value is negative, then the heat is on the right, it is being lost. If the value is positive, then heat is being added to the system as a result of the forw...

Sydney Myers 4I

Kc is the equilibrium constant calculated using the concentrations of the products and reactants, while Kp is the equilibrium constant calculated using the partial pressures of the products and reactants.

Sydney Myers 4I

K also tells us which of the products or reactants is more stable. If K is large, then the products are favored, which means they are more stable. If K is small, then the reactants are favored, meaning that they are more stable.

Sydney Myers 4I

The electrons would separate to different energy levels when an atom bonds with another atom. This is when hybridization orbitals are used.

Sydney Myers 4I

Would two dipole moments cancel if they are on opposite sides of a tetrahedral molecule? Because they're not exactly in line with each other!

Sydney Myers 4I

I know Lavelle told us that commonly, compounds that can form chelates have two atoms that aren't boding sites in between them. He said that was the most common form, but is it possible to have a compound that can form a chelate with only one atom in between the two atoms that can form a chelate?

Sydney Myers 4I

I know that there's a different set of prefixes to use when a molecule is polydentate, but are there any tricks to use in figuring out if a ligand is polydentate?

Sydney Myers 4I

Are there two a's in pentaammine, or would you just combine it into pentammine?

Sydney Myers 4I

Strong bases fully dissociate in water, while weak bases only partially dissociate, as the strength of the base depends on its ability to fully dissociate. Is this why the balanced equation for strong acids have a one-way arrow while weak acids have a two-way arrow? Technically, even strong bases a...

Sydney Myers 4I

An acid is considered strong if a hydrogen ion is easily separated from it, which then raises the concentration of the hydronium ions in the solution, which lowers pH.

Sydney Myers 4I

805097738 wrote:
Michael Torres 4I wrote:If something is a strong acid, then it will be a weaker base. Weaker acids will also be stronger bases.

how can acids be bases?

I think that is referring to the equilibrium that acid-base reactions can reach. If something is a strong acid, then it is a weak conjugate base.

Sydney Myers 4I

Mariepahos4D wrote:yes, the co2 and so2 would be considered an acid in that reaction because they donate the proton to water to create 2 oh- and a gas

If a proton is donated to water, it would form hydroxide (H30+)

Sydney Myers 4I

There are certain elements that you have to know will form amphoteric molecules. They are near the metalloids but do not correspond exactly to them.

Sydney Myers 4I

He also mentioned that any coordination compound with 6 ligands will be octehedral.

Sydney Myers 4I

It is mainly helpful to know the hybridization when bonding occurs because it can help visualize which bonds are placed where. Like double bonds can be comprised of a hybrid orbital and a regular orbital, because the bond is counted as a single region of electron density.

Sydney Myers 4I

Daniel Martinez 1k wrote:Si2F2

Is this due to the shape? because Si2F2 would have a more linear structure, compared with a round structure of SiF4, and higher surface area makes for higher intermolecular forces, specifically London Dispersion Forces.

Sydney Myers 4I

Not super important, but just know that its VSEPR, not VSEPER

Sydney Myers 4I

It mirrors the order in electron configuration. Since the d orbital is from a lower energy level, even though it fills later, it is put before. Today in class Lavelle said that it doesn't really matter what the order is though.

Sydney Myers 4I

If you wanted to think of it spatially, bonding pairs are being shared with another atom, so they don't take up as much space on an atom because their orbital is larger. Lone pairs tend to stay on one atom, so they would have a higher repulsion force.

Sydney Myers 4I

Yes, it has to do with lone pairs and polarity, so if these charges are present they will repel other elements and cause the bent shape that is observed in water rather than the linear shape present in co2 when there are 2 lone pairs that repel the other elements equally. I'm not quite sure that th...

Sydney Myers 4I

It's not so much a formula as a concept to understand. Essentially, the shape of a molecule is dependent on how many regions of electron density it has. A region can be a bond or a lone pair.

Sydney Myers 4I

It would be the second option because the dipole moments are the most directly lined up.

Sydney Myers 4I

I think it would be better to just memorize the values for dissociation energy for the different interactions we went over in class.

Sydney Myers 4I

Another thing to note is that the bonds get weaker when they get longer.

Sydney Myers 4I

In 2C.9 and 2C.11, there are Lewis structures involving Xenon that have expanded electron shells, but the formal charge in the atom still appears to be zero, even though by all of the rules we have learned, it should be negative? Is there some kind of noble gas exception to the rule?

Sydney Myers 4I

In Outline 2, it says we have to know the difference between atomic and molecular spectroscopy, but I couldn't find anything on molecular spectroscopy in the textbook. Can anyone explain it/know where it is in the text?

Sydney Myers 4I

For the record, anything on that slide will not be included on the midterm.

Sydney Myers 4I

A dipole moment can also affect the shape of a molecule, since a molecule's shape is essentially its electron cloud. If the electrons are shifted or distorted by a dipole moment, then the molecule's shape and properties are changed as well.

Sydney Myers 4I

The polarizing power follows the same trends as electronegativity, because electronegativity is a measure of how much an electron is attracted to an atom. It follows that an atom that attracts electrons will be effective at polarizing them.

Sydney Myers 4I

Resonance only occurs in molecules which could theoretically switch some of their bonds (single vs double) and it would still be the same molecule but in a different orientation. In other words, there several combinations of possibilities of bonding that are equally correct. Only then will resonance...

Sydney Myers 4I

Electrons are delocalized in a resonant structure, meaning they cannot be represented as a part of a single, double, or triple, bond. They are involved with multiple bonds, resulting in a sort of average bond length and strength.

Sydney Myers 4I

Since the formula is Valence electrons minus a value, it would follow that the closer that value is to the number of valence electrons the smaller the formal charge is. The value subtracted from valence electrons is the lone pairs and half of the shared electrons. If you think about it, this value w...

Sydney Myers 4I

It is important to note also that electron affinity can be a negative value. This occurs when it requires energy in order to add an electron to an atom. This happens with noble gases, for example.

Sydney Myers 4I

As long as you understand that two charges interact with each other and we can measure their interaction, and that it affects the energy of electrons in a multi-electron atom, you're good. We don't do calculations with that equation.

Sydney Myers 4I

He did this in order to demonstrate Hund's Rule, that electrons fill each orbital before they are paired in one orbital. He was representing each electron in its own orbital instead of just giving the total number of electrons in the subshell. He said that it's BETTER and more specific to do it in t...

Sydney Myers 4I

One difference between atomic and covalent radii versus ionic radii is that when we measure an ionic radius, it's more complicated than simply dividing the distance between the nuclei of two atoms in the ionic bond because they are of different size. Also, the ionic radius of, for example, chlorine,...

Sydney Myers 4I

Effective nuclear charge is the phenomena of inner electrons shielding the effects of the attraction from the nucleus on outer electrons. Because the outer electrons are more loosely bound, the radius of the atom increases.

Sydney Myers 4I

The reason that each orbital is limited to two electrons is because of electron-electron repulsion. The reason that two electrons can coexist in an orbital is because they have opposite spins, which is the lowest energy state. Since there are only two states that electrons can exist in an orbital, t...

Sydney Myers 4I

Lavelle advised us not to use Rydberg's Equation because it's easier to understand what's going on if you calculate the energies at both the levels (using E= -hR/n^2) then subtract the initial from the final.

Sydney Myers 4I

To answer Leila's question, Δx represents the indeterminacy in position of the e-, or the possible places to find the e-. Since we suppose that the e- is possibly in the nucleus, we would use the diameter of the nucleus to represent the uncertainty in position. It would not have anything to do with...

Sydney Myers 4I

I'm confused about this one as well, particularly on how a one-dimensional box can even exist?? Boxes are two-dimensional right?

Sydney Myers 4I

In general, associate the photoelectric effect with electrons being treated as particles (because the intensity of the electron doesn't change its energy, which is counterintuitive when thinking about a wave) and the three fundamental equations we learned (deBroglie's, Heisenberg's Uncertainty Equat...

Sydney Myers 4I

Lavelle has said that we don't have to know all of the specifics, but know that visible light ranges from 400-700 nm, and radiation with more energy (UV, gamma rays for example) has shorter wavelengths (<400) and radiation with less energy have longer wavelengths.

Sydney Myers 4I

I think that electrons generally only drop one energy level at a time so they would emit one photon when they drop the first level and then emit a second photon when they drop the second level. I'm not 100% sure about this though so if anyone knows for sure, please correct me if I'm wrong Electrons...

Sydney Myers 4I

For atomic spectroscopy, it is necessary to expose an element or molecule to every wavelength of light in the electromagnetic spectrum in order to find all of the wavelengths of light that the element/molecule absorbs/emits. I don't think that UV is given special consideration, but maybe a lot of el...

Sydney Myers 4I

Absorption of a photon will excite electrons to a higher energy level only if the photon contains enough energy to move electrons to energy levels beyond their ground state. When the electrons drop back down to their ground state, a photon will be emitted. This isn't technically correct and is conf...

Sydney Myers 4I

The gaps between energy levels get larger the further from the nucleus you go, so the jumps (or emissions) with the largest energy will have to do with the largest gap because it would require the most energy to jump. Since the largest gap will always involve n=1, it is said to be associated with th...

Sydney Myers 4I

Another thing to note is that there is actually no formula for the work function that we learned. It's a constant that is usually given in a problem (if not, it can be found if you have an electron's excess energy after being removed and the energy that the photon had when it hit the electron)

Sydney Myers 4I

If by molar ratio you're talking about the whole numbers that you get once you've manipulated the number of moles of each substance into a ratio (dividing by the smallest amount then multiplying all of those ratios by a scalar until they're all whole numbers), then yes, they are the same as the atom...

Sydney Myers 4I

In my high school chemistry class we were allowed to truncate, but my teacher said it was a bit ambiguous on what any college professor would want. She also said that rounding is generally safer, so I would get in the habit of rounding.

Sydney Myers 4I

The previous reply is right; in this problem, all you need to know about oxidation is that it occurs during combustion. If you want to understand what oxidation is though, it is what happens when an atom loses some of its electrons during a chemical reaction. Oxygen has a high electronegativity, so ...

Sydney Myers 4I

I think by fundamentals he means more than just the four modules, because there is more than that covered in the fundamentals section of the textbook that he told us to read.

Sydney Myers 4I

So I know that Hertz is the number of oscillations per second, but is there a unit for oscillation? In other words, if we were to break down the unit Hz, it would be *blank*/s. What's the blank?

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