CHEMISTRY COMMUNITY

christabellej 1F

I think he was just explaining how there were multiple ways to approach seeing whether certain reaction mechanisms are valid.However, we don't have to know them except for the preequilibrium approach.

christabellej 1F

Yes, it just has to do with stoichiometric coefficients.For part a for example, the rate of consumption of N2 is 1/3 times the rate of consumption of H2 because H2 is consumed three times as much as N2.

christabellej 1F

Integrated rate laws allow you to consider how time relates to the reaction. As opposed to only knowing initial time/concentration, the integrated rate law lets you know what is going on in the reaction at any point in time.

christabellej 1F

rates would be equal to the rate constant multiplied by the reactant concentrations to the power of what order they are (whether they are zeroeth, first, or second order). At equilibrium, the rates of forward and reverse reactions are equal, but the rate constants don't have to be equal.

christabellej 1F

For natural logs, when you make something a negative, you flip the fraction. This is why, instead of dividing by -k, you can first divide by - first, which would make the natural log fraction 1/0.15. Then, you can also divide by k, which would give you t.

christabellej 1F

You have the equations delta Go= -nFEo, and delta G0 = -RTlnK (at equilibrium). You could calculate the equilibrium constant from standard potential by setting these two equations equal to each other.

christabellej 1F

When calculating the cell potential, you could reverse the voltage sign of the oxidation reaction.

christabellej 1F

Gibbs free energy is related to cell potential by the equation G = -nfE. When you rearrange this equation, you can also get E = -G/nf. When you multiply a chemical reaction by a factor, G is also changed by that factor. However, n is also changed by that factor (since it is the electrons in the bala...

christabellej 1F

K also correlates to cell potential too. If the cell potential is large and positive, then delta G would be a large negative. Since delta G is also equal to -RTlnK, K would also be a large number.

christabellej 1F

I think the note is because the cell potential is negative. When the cell potential is negative, deltaG (free energy) is positive. This means it would be non spontaneous in the forward reaction, but spontaneous in the reverse reaction.

christabellej 1F

The electrons in the half reaction would go on the left side of the reaction because you want to make sure the charges on both sides are balanced. Since Hg2 2+ has a charge on 2+, adding 2 electrons to that side would make the net charge 0, which is what 2Hg on the right side is.

christabellej 1F

The Van't Hoff Equation is used to calculate K at different temperatures. In finding the K, you would assume that the delta S and delta H are not significant.

christabellej 1F

n stands for the moles of electrons transferred in the equation. One example you could use is the reaction where Zn is oxidized to Zn2+ and Cu2+ is reduced to Cu. Since each reactant is oxidized/reduced by 2, the n would be 2.

christabellej 1F

I think that Dr. Lavelle was talking about how he usually likes to write the cell diagram by writing what species is getting reduced in order, and what species is getting oxidized in order. However, this is just how he likes to write it but it is not part of required notation.

christabellej 1F

The enthalpy is a state function, but it doesn't mean that it isn't dependent on amount there. A state function just means that the enthalpy value calculated from the reaction is independent of how the reaction got there.

christabellej 1F

Hw 8 can probably be anything covered since the midterm, such as the second half of thermodynamics or the electrochemistry he talked about in class.

christabellej 1F

For irreversible and reversible problems, the work calculated would be different because work is a state function. For entropy change, entropy is a state function, and so the same equation can be used for calculating the irreversible and reversible entropy of the system.

christabellej 1F

The entropy increases with temperature. In the Van't Hoff Equation though, you are using change of entropy and not entropy, and you are assuming that change of entropy is constant under temperature increase.

christabellej 1F

It is used to find the entropy of both and can be used for everything because entropy is a state function (so it doesn't matter how you get there, and thus how you calculate it). If you are finding entropy of the surroundings though under constant pressure, entropy of the surroundings would be oppos...

christabellej 1F

I think that in general, we just need to know the general entropy trend that entropy increases with the complexity of the molecule because it can occupy more positions. I'm not sure how in depth we would have to know though, such as if we need to know specific molecules by name.

christabellej 1F

The number of orientations is the number of orientations where a molecule would be in a position with equal energy. W would be the number of positions to the power of however many molecules the question says.

christabellej 1F

You would ignore the second deprotonation if it is not significant, and doesn't really affect the pH overall. This usually happens when the second deprotonation has a K value super small, letting you know that not much H3O+ dissociates.

christabellej 1F

delta U is equal to 0 for an isolated system when it is isothermal and reversible.

christabellej 1F

I'll just use hypothetical temperatures of 50 degrees and 120 degrees. You would want to calculate the the delta h of the reaction using q=mcdeltaT, where delta T is the difference in temperature from 50 to 120 degrees. You would then want to use the delta H of the temperature they give you, such as...

christabellej 1F

U would equal 0 because it is an isothermal reversible equation, as the internal energy of the system does not change overall.

christabellej 1F

There isn't one, but you can also use the one with a volume change. The reason the equations don't really matter is because entropy is a state function, whereas work isn't.

christabellej 1F

I think he showed us the curves to help us understand how the amount of work is equal to the area under the curve (since it was an integral). The curves showed that reversible expansions are able to do a greater amount of work than irreversible expansions.

christabellej 1F

Usually you would be given bond enthalpies. Calculating the enthalpy change in general though is the bond enthalpies of the bonds broken (in reactants) - bond enthalpies of the bonds formed (in products).

christabellej 1F

I think it could also be when a gas is in a system that has constant volume, and so there can be no change in volume

christabellej 1F

Cv and Cp would change calculations when it relates to work. When a gas is under constant pressure, it can do work against that constant pressure and experience a change in volume. You can use the equation work = -Pex * delta V. For something that has constant volume, since the volume can't change, ...

christabellej 1F

Yes, you would want to convert the pressure from Torr first so that the units can match and cancel when you use the internal energy change equation.

christabellej 1F

Autoprotolysis is the reaction of 2 H2O --> OH - + H3O+. Like any reaction, you can write the K expression (products over reactants), and get Kw = [OH-][H3O+], since H2O is a liquid and so isn't counted in the K expression. Now , you can use the properties of logs, and do logKw = log[OH-] + log[H3O+...

christabellej 1F

Usually the pH scale runs from 0 -14. However, it can sometimes have a negative pH if there is such a high concentration of hydronium ions that the pH of it becomes negative. I think these are called superacids.

christabellej 1F

I think that the reason only some of the C-H bonds were shown to break or form was based on the lewis structure. When he drew CH2=CH2, most of the C-H bonds remained in the "same" place, and so there was no need to show the bond breaking or forming. However, the = definitely broke as the p...

christabellej 1F

The path is not relevant in enthalpy as you can still calculate delta H without knowing what happens in between as long as you know what happens in the initial and final state.

christabellej 1F

I think you would use K, although since q = mc(delta T) is the change in temperature, the change itself would be the same number whether you use celsius or K. For example, if something changed from 0 to 2 celsius (which is 273 to 275 K), the delta T would still be 2 no matter what you use.

christabellej 1F

I believe that they should give us the exact value of the Ka values, such as Ka1 = "" and Ka2 = "". Good luck on your test too!

christabellej 1F

A salt is composed of a positively and negatively charged ion. It shouldn't be different from calculating other acid/base pH. Usually, one part of the salt will influence the pH - for example, in NaC2H3CO2, C2H3CO2 is negatively charged and will make for a basic solution. You would just do the ICE t...

christabellej 1F

I think that you would just want to know that CO2 when dissolved in water makes carbonic acid, which is H2CO3, which is responsible for all the environmental and biological examples listed in the outline below.

christabellej 1F

Do we have to know how to calculate buffers and titrations for test 1?

christabellej 1F

If a K is that small (less than 10^-3), then at equilibrium, there will be way more reactants than products, indicating only a small amount of product was formed before the reaction reached equilibrium. This is because the reactant state has greater stability, so the reactants will want to stay reac...

christabellej 1F

Changing the temperature would change the K. This is because if a reaction is exothermic, then increasing temp will cause the reaction to shift towards the reactants, so K would be smaller. The opposite would be true for endothermic reactions, where an increase in temp would result in an increase in...

christabellej 1F

I think that you would ignore it if the second deprotonization or third (etc.) does not affect the pH of the solution. In the textbook, it says that for most polyphonic acid, the 2nd or more Ka is so small that pH of the solution isn't really affected. However, for H2SO4, this is an exception where ...

christabellej 1F

I think it would be equilibrium and acid/base, and will probably cover up to what we do Friday

christabellej 1F

I believe the solutions used an approximation for this, and so took off the -2x and -x so that calculating would be easier. This is because x is believed to be so small (less than 5%) that it wouldn't really matter if you included the -2x/-x or not.

christabellej 1F

How does a reaction shift when the pressure of a system is decreased?

christabellej 1F

Q can be calculated at any point during the reaction, whether the reaction is at equilibrium or not. As such, the value of Q could indicate that a reaction is not yet at equilibrium (such as Q<K or Q>K) or that it is at equilibrium (Q=K).

christabellej 1F

if K is between 10 ^-3 and 10^3, the reaction is neither strongly favoring the products or the reactants. If K is greater than 10^3, it strongly favors products, and if K is less than 10^-3, the reaction strongly favors reactants.

christabellej 1F

Basically, the ICE table is a way to calculate the predicted quantitative values of a reaction at equilibrium. You would start by balancing the reaction first, and then in the first row (I), writing down the initial concentration or partial pressures of the reactants and products. You would then exp...

christabellej 1F

The rules for calculating both the reaction and equilibrium constant would be the same. You would calculate the equilibrium constant when the reaction is at equilibrium and calculate the reaction quotient at any other point of the reaction.

christabellej 1F

You also would not have to use variables if any part of your equation includes species that are not in aqueous or gas states. Since a pure solid or liquid would be the same, you would only use variables when determining changes in aqueous/gas reactants and products.

christabellej 1F

You would use Kc when you are given molarity/concentrations of the reactants and products. If you are given partial pressure values, you can use Kp.

christabellej 1F

To find the equilibrium constant here, you would want to use the partial pressures given. The K would be equal to the partial pressures of the product over the reactant. After balancing the equation, you would find K by multiplying the partial pressures of N2 and H2 (with H2 raised to the 3rd) over ...

christabellej 1F

For this question, you could use the K values of 2 different equations, one that includes BrCl and another that has H2 in the equation. You can then find the overall K value of the equation in question by multiplying the K of the first equation with the K of the second equation.

christabellej 1F

In class, Dr. Lavelle talked about how cisplatin works as a chemotherapy drug while translation does not. Why is this, and could someone explain how cisplatin interacts with DNA?

christabellej 1F

Another common example would be H3PO4. In polyprotic acids, the first Ka, which measures the strength of the acid when it donates its first proton, is usually the strongest. The subsequent Kas, which measure the strength of the acid as it donates its second (or third) proton is weaker because it is ...

christabellej 1F

You would use a Latin name for Fe. When writing the coordination compound name, you would write ferrum (or ferrate) instead of iron.

christabellej 1F

You would also want to look at the single and double bonds in the molecule too since single bonds (sigma) allow for rotation but double bonds (with pi bonds) do not. Sometimes, even though there is a lone pair on an atom, it cannot be a binding site because the double bond does not allow the atom to...

christabellej 1F

For both, you would want to look at the difference in electronegativities. The one with a greater difference in electronegativity would make the O-H bond weaker by pulling electron density away, making the acid with the greater electronegativity difference stronger. For example, in the first one, th...

christabellej 1F

In class, it was mentioned how a coordination number of 4 could mean that the molecule is either tetrahedral or square planar complex. How can you determine when a coordination sphere is a tetrahedral complex or square planar complex?

christabellej 1F

For example, a metal atom with four ligands attached would have a coordination number of 4. An atom with six ligands attached would have a coordination number of 6.

christabellej 1F

A complex would be tetrahedral if it has four regions of electron density and none of them are lone pairs. A shape would be sure planar if there are six regions of electron density but only four atoms around the central atom (since two of the electron densities are lone pairs).

christabellej 1F

Sigma bonds also allow for rotation. Pi bonds do not allow for rotations. Pi bonds are also broken first and are weaker because the side-to-side overlap does not allow for as much overlap as the end-to-end overlap found in sigma bonds.

christabellej 1F

I think you can check how many posts you've done under quick links and then "your posts." I believe each week is five points.

christabellej 1F

Brackets are used when writing the formula for the coordination sphere, which includes the metal atom and the ligands attached to it.

christabellej 1F

Yes, AX2, AX3, AX4, AX5, and AX6 are non polar if there are no electron pairs and if X is all the same.

christabellej 1F

You would also want to take from the equatorial position and not the axial position because a lone pair in the equatorial position results in the molecule having lower energy. Lower energy is what most molecules strive for too.

christabellej 1F

In an sp3 hybrid, there is around 25% s character since there is one part s and three parts p. For sp2, there is about 33% character. Since the bond angle for sp2, which has greater s character, is a bigger angle than sp3, you could expect the bond angle to increase as the s character of the hybrids...

christabellej 1F

I believe that this equation shows the the strength of the interaction is dependent on the distance between molecules. For 1/r^6, it means that the strength of the interactions drops quite quickly as the distance between the molecules become greater. Not sure if we'll need to know this for the test

christabellej 1F

The size of the atom is usually related to polarizability, and greater polarizability usually makes interactions stronger since London dispersion forces would increase. As the size of the atom gets bigger, usually there are more electrons. Since there are more electrons, the nucleus doesn't have as ...

christabellej 1F

Sigma and pi bonds are also relevant as part of the valence bond theory, which takes into account the wave nature orbitals. It is also significant because it helps understand the concept of hybridization.

christabellej 1F

I think it helps to draw the lewis structures of these molecules to see if they are polar or non polar. Generally, if the net dipole moments cancel out and the molecule is non polar, it would have London dispersion forces (induced dipole-induced dipole). If it is polar, then I believe dipole dipole ...

christabellej 1F

Hydrogen bonds form when there is a lone pair on the N, O, and F atom. This can be seen in HNO2 too and makes the intermolecular forces between the molecules strong.

christabellej 1F

For some molecules, drawing the structure and arranging them according to the VSEPR model could help determine bond angle. For example, if a molecule is linear, then the bond angle will be 180 degrees. If a molecule is trigonal planar, the bond angle will be 120 degrees and if it is tetrahedral, the...

christabellej 1F

To find which has a higher melting point, you would want to find out what types of IMFs each molecule or compound has, and determine which compound has the stronger IMF. For example, in a) HCl is a covalently bonded molecule while NaCl is an ionic compound. NaCl will have a higher melting point beca...

christabellej 1F

In these types of questions, it could be helpful to first draw the Lewis structures. CCl4 and CH4 are symmetric and are non polar structures overall since the net moments cancel out; they will have London dispersion forces. CH3Cl, CH2Cl2, and CHCl3 will also have dipole dipole interactions, so those...

christabellej 1F

The Aufbau principle is the building up principle that combines both Pauli Exclusion principle and Hunds rule. Pauli Exclusion principle states that there can be a max of two electrons per orbital and that the two electrons must be spin paired. Hunds rule states that the electrons should be placed o...

christabellej 1F

The magnetic spin of an electron can only be +1/2 or -1/2. This is because of the Pauli exclusion principle where there can only be two electrons per orbital, and that the electrons must be spin paired. So, one electron must go in an upwards spin (+1/2) and the other in a downwards spin (-1/2). As f...

christabellej 1F

Formal charge can also help you predict which structure is the lowest energy structure (and thus which structure contributes more to the hybrid) as the closer the formal charges are to 0 on the atoms gives you the lowest energy structure.

christabellej 1F

You generally use this equation when dealing with atomic spectra problems, where calculating the energy difference (or wavelength and frequency) absorbed or emitted by an element that has gone from one energy level to another. For example, if you want to know the change in energy from the emitted ra...

christabellej 1F

This question is a photoelectric effect questions, and gives you the minimum frequency needed to eject an electron from the molybdenum metal surface. This means that any frequency lower than this will not eject any electrons and that with this particular frequency, there won't be any excess kinetic ...

christabellej 1F

The quantum number ms is the magnetic spin of the electron. In the Pauli Exclusion principle, it states that there can only be a maximum of two electrons per orbital, and that the two electron spins must be paired. That basically means that one electron will spin in an upwards direction and one in a...

christabellej 1F

hi! the mass of the electron, as well as the masses of neutrons/protons are on the constants and equations sheet that is on Dr. Lavelle's website. It should also be provided on the test!

christabellej 1F

As someone mentioned above, l= 0 is the s orbital, l=1 is p, l=2 is d, and l=3 is f. Because of that, the number of orbitals in subshells for s will be 1, p is 3, d is 5, and f is 7.

christabellej 1F

In order to find what metal with a 3+ state would have the ground state configuration, I find it helpful to first write what configuration the metal would have if it were not an ion. For the first one, for example, if the 3+ state is [Ar] 3d6, then the configuration for the unionized version would b...

christabellej 1F

In general, the central atom would be the one with the lower ionization energy. In class, Dr. Lavelle also mentioned that because H can only form one bond, it will never be the central atom.

christabellej 1F

Generally, the octet rule will be followed for lewis structures that have resonance. However, as someone mentioned above, some atoms can form more than four bonds because they are big enough and have the ability to fill the d orbitals. This only starts after the 3 p level though, and so some atoms i...

christabellej 1F

Hi! So in this problem, you know that you should use the Heisenberg equation in order to find uncertainty of speed of the electron. Since Delta p * delta x = h/4pi, and delta p can be substituted by m * delta v (velocity), you can rearrange and solve for the minimum uncertainty in a particle's veloc...

christabellej 1F

Both are the same equation. This is because the h is actually h bar and stands for h/2pi. 1/2 (h bar) would then be the same as the first equation as it is h/4pi.

christabellej 1F

The last quantum number, the electron spin, only has two types of spin . It's notated by +1/2 and -1/2. There should only be two types as the Pauli Exclusion Principle states that there should only be 2 electrons per orbital, and that if there are 2 electrons, the spins should be paired up (one up a...

christabellej 1F

Yes, you could use the De Broglie equation, where the wavelength is equal to Planck's constant divided by momentum (which is mass times velocity).Since h is a constant and m is nearly the same, the only thing that could be variable is the velocity. However, in this problem, it states that the proton...

christabellej 1F

Yes, since it says lowest frequency possible, we can assume that the KE is 0. We could then use the equation where the energy of the incident light is equal to the work function plus the KE (which is 0). You could then work backwards to find the energy of the light since you know what the work funct...

christabellej 1F

The kinetic energy is related to the frequency of the incoming light because the frequency of the incoming light, by the equation E = hv, can be used to find the incident light's energy. This energy, by the conservation of energy, is equal to the work function (the energy needed to eject an electron...

christabellej 1F

Hi, 1D4 talks about the probability of finding electrons depending on the shapes of the orbitals. In this class, we would be discussing the orbitals s, p, and d. As far as the probability of finding an electron goes, s orbitals are said to be spherically symmetrical, meaning that the probability is ...

christabellej 1F

KeV is a unit of energy. It is equivalent to 1000 eV because of the prefix kilo. From there, you can convert this unit to another energy unit - Joules by using the constants and equations sheet. 1 eV is equivalent to 1.6022*10^-19 J, so you can then use stoichiometry to convert KeV to Joules. After ...

christabellej 1F

The probability density, symbolized by psi squared, is the probability that something will be found in a space divided by region volume. For example, if psi squared is 0, then there is a probability of 0 that the electron will be found in that space in that region's volume. Probability has no unit b...

christabellej 1F

These two expressions are actually the same. This is because the h/2 is not h, but h bar. H bar is equal to h/2pi. Thus, this would make it the same as h/4pi because 1/2hbar = 1/2(h/2pi) = h/4pi. Hope this helps a bit

christabellej 1F

In addition, the radius of a cation is usually smaller than its regular atom. The radius of an anion is larger than what the neutral atom would normally be because of the increased electron repulsion effects (since anions have more electrons). For atomic radius, the atomic radius increases as you go...

christabellej 1F

Hi, usually a metal and a nonmetal together will form an ionic bond. In an ionic bond, an electron is basically donated.Metals are usually atoms, or elements found in group 1 or 2 of the periodic table. Covalent bonds generally consist of two nonmetals together.In a covalent bond, the electron is us...

christabellej 1F

The theoretical yield actually doesn't have to depend on information on percent or actual yield. Theoretical yield just means the maximum yield that a product can be based on a chemical equation. So, the theoretical yield is can purely be based on calculations, stoichiometry, and molar ratios from t...

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