CHEMISTRY COMMUNITY

Elisa Bass 4L

Higher equilibrium constants indicate higher rates of solubility because for a solubility reaction, the products are the dissolved ions and the reactants are the undissolved solute.

Elisa Bass 4L

There is no lecture on Friday (it is a review day) and there are only two slides on Wednesday, but all that is covered up to and including the information given on Wednesday IS fair game for the final generally.

Elisa Bass 4L

The rate constant is represented by a lowercase k. Being a constant, it does not change if the concentrations of the reactants change; it is constant for the reaction at that temperature. On the other hand, the rate of the reaction is what k times concentrations of reactants equals. In other words, ...

Elisa Bass 4L

This notation is just a technicality because in an electrolytic cell, the electrons in the anode are being drawn towards the positive external charge of what is supplying energy to the chemical reaction. Meanwhile, electrons are being pushed towards the cathode on the other side, so they write it as...

Elisa Bass 4L

Why can the value of k be different for two versions of the same reaction with the same concentration and temperature?

Elisa Bass 4L

Differential rate law is where the rate is a function of [R]. Integrated rate law is where rate is a function of time.

Elisa Bass 4L

Remember that a metal having a more negative (or less positive) reduction potential means it is a stronger reducing agent (which means it is the species that is doing the reducing). For the first part of the problem, all the metals except Cu have negative reduction potentials, so compare those value...

Elisa Bass 4L

When writing the cell diagram for a galvanic cell, the convention is to put the cathode on the right and the anode on the left, if that’s what you’re referring to. That would influence which half reaction goes where.

Elisa Bass 4L

Standard Gibbs Free Energy is the value of Gibbs Free Energy at standard conditions. It does not change as the reaction proceeds, which is nice because Gibbs Free Energy does. When calculating standard Gibbs Free Energy, use standard cell potential.

Elisa Bass 4L

∆G, ∆S, and ∆H are all expressed in terms of one mole of reaction. You already account for the number of moles involved when you used the S°m, ∆H°f, and ∆G°f for each reactant/product, so the result you calculate is in terms of the reaction as a whole.

Elisa Bass 4L

I think it’s essentially the same thing as a Galvanic/electrochemical cell, just another name for it.

Elisa Bass 4L

An electrochemical cell, also known as a Galvanic cell, converts chemical energy into electrical energy. An electrolytic cell does the opposite, converting electrical energy into chemical energy.

Elisa Bass 4L

No work is done in free expansion because there is no pressure against which the gas expands and does work. But you don’t need to figure out IF it’s free expansion because the problem will always indicate this, as this one has.

Elisa Bass 4L

In this case, I think because the reaction occurs at 25°C, H2O is a liquid because it condenses after it is formed.

Elisa Bass 4L

Because ∆S = qrev/T, if you’re looking for change in entropy due to temperature change, you can substitute out q for nC∆T, then simplify to get ∆S = nCln(T2/T1).

Elisa Bass 4L

They might give you the basic equation, ∆S = q/T and expect you to evaluate for the changing value specified in the problem, but as long as you have the formulas or the relationships between variables (like q = nC∆T) memorized, you should be able to work backwards to show the integration/get the for...

Elisa Bass 4L

It is important to know that there’s a slight difference between bars and atm (1.013 bar = 1 atm) but from the homework problems it seems rare that they give something in terms of bars and you need to convert to atm. Atm is also helpful because of the useful conversion 101.325 J/L*atm.

Elisa Bass 4L

Open systems can exchange both matter and energy with the surroudings. I think of it like an open, uninsulated container. Closed systems can exchange just energy. So no matter can be added to change the system, but energy can be exchanged with the surroundings, so basically any closed container. Iso...

Elisa Bass 4L

The system has internal energy, ∆U, which is q + w. Therefore, the system has the capacity to do work. In the particular problem I believe you are referring to, we are letting the system do work on surroundings, meaning it is pushing the piston out. Were the piston to be compressed, the volume would...

Elisa Bass 4L

Yes, they are both given in terms of mol, so you have to multiply by the stoichiometric coefficients if you want to find the enthalpy of the reaction based off of bond enthalpies or standard enthalpies of formation.

Elisa Bass 4L

For the slopes I believe. At the slopes, increasing heat will actually cause the substance to change temperature, whereas at phase changes (the flat portions), increasing heat does not change the temperature, which would make it difficult to determine heat capacity because it is based on temperature...

Elisa Bass 4L

The value of Ka will probably be given to you on the test. Also you will probably need to know how to write a reaction similar to this. Basically, whenever a salt with a highly charged small cation is dissolved, the cation surrounds itself with the maximum number of water molecules, 6, which is what...

Elisa Bass 4L

Salt is a product in a neutralization reaction. However, the same salt formed from a neutralization reaction, or another other acidic/basic salt for that matter, can be dissolved in water and may affect pH.

Elisa Bass 4L

pKa is the negative log of the Ka, which is just the K value but for a weak acid.

Elisa Bass 4L

According to the textbook, technically if you are asked for K and everything is in gas phase, you’re supposed to write it with partial pressures. However, the problem will likely specify which they are looking for, or will give values in concentration or partial pressure. In the event they give you ...

Elisa Bass 4L

No. Therefore, if it tells you to calculate the reaction quotient, Q, and compare it to a given K for example, make sure you use partial pressure or concentration depending on if you’re given Kp or Kc.

Elisa Bass 4L

In pure water, the H3O+ and OH- concentrations are equal. Therefore, because they gave you Kw, you can find each of the concentrations by square rooting the given value.

Elisa Bass 4L

Just make sure the units are the same if you are given a gas and an aqueous solution.

Elisa Bass 4L

You would have to convert one of the given values to match the units of the other. Because an aqueous solution does not have a partial pressure, you should convert the partial pressure of the gas to a concentration.

Elisa Bass 4L

It is a ratio of the equilibrium concentrations.

Elisa Bass 4L

H20 is polar because O has a delta negative partial charge. This causes it to have attraction to delta positive atoms, such as the metal atom it binds to.

Elisa Bass 4L

Some common examples of polyprotic acids are: H2SO4, H2CO3 and H3PO4. These can donate more than one proton.

Elisa Bass 4L

Dentate refers to the number of places the ligand can attach to the central atom. Water has two lone pairs, but because they are both on oxygen, it cannot bind in two places, only on one atom.

Elisa Bass 4L

When you draw the Lewis structure, the molecule is shown to have two lone pairs on Br in addition to the three bonds Br forms with the three F. Because each lone pair represents another region of electron density, five hybridized orbitals are needed and there are five sp3d orbitals.

Elisa Bass 4L

Polarizability refers to how easily an atom’s electrons can be distorted by polarizing atoms. The lower the electronegativity, the higher the polarizability, because the atom’s electrons are not held as tightly. Likewise, the larger the atom, the higher the polarizability.

Elisa Bass 4L

S-character basically refers to what fraction of the hybridized orbital is made up from the s-orbital. For example, sp has greater s-character than sp^2. Because there are fewer sp hybridized orbitals than there are sp^2 hybridized orbitals, 2 versus 3, as the s-character increases and the number of...

Elisa Bass 4L

I remember either hearing or reading that the breaking of pi bonds is important in vision, but that’s the only specific example I can recall. The presence of pi bonds is important in determine the shape of a molecule because it is stiffer than a sigma bond, which is likely important for proteins, as...

Elisa Bass 4L

This question is asking for how the hybrid orbitals would likely be arranged three dimensionally around the nucleus. You can determine this by looking at the number of regions of electron density and then determining what shape a molecule in which all the regions had bonds would be. For example, the...

Elisa Bass 4L

In some cases, you can look at the number of electrons an atom has and where those electrons are located to determine how many regions of electron density there can be.

Elisa Bass 4L

As a side note, there are both intermolecular and intramolecular hydrogen bonds, in that there are interactions involving hydrogen between separate molecules and within molecules. Intramolecular hydrogen bonds are just covalent bonds involving hydrogen.

Elisa Bass 4L

This seemed like a good explanation!
viewtopic.php?t=1250

Elisa Bass 4L

Due to electron repulsion, the presence of lone pairs alters the shape of the model. They push the atoms away from them, which causes the angles between the atoms to be different. You can tell whether or not the central atom has any lone pairs from the resulting angle between the atoms, so it’s more...

Elisa Bass 4L

The actual structure of the molecules tends to be a hybrid of multiple resonance structures because it is the most stable.

Elisa Bass 4L

Dipole-dipole occurs between two molecules that are polar on their own. Dipole-induced dipole occurs between a polar and non-polar molecule in which the polar molecule causes the non-polar molecule to exhibit polar character.

Elisa Bass 4L

The 3d orbital is closer to the nucleus than the 4s orbital, making the electrons harder to remove once they have been put in there. This is why the 3d is written before the 4s in the atoms that have a 3d shell and why electrons in 3d do not move to the 4s orbital when it is vacant. Therefore, in th...

Elisa Bass 4L

This has to do with the orbitals. All three of N’s p orbitals already have one e- each in them. C has one open p orbital, so it has a higher electron affinity because it has space to put another e-. N does not have the space unless it pairs electrons, which would cause it to have higher energy due t...

Elisa Bass 4L

I’m not sure if this is what you’re asking, but for the second part of your question, a molecule is negative when it has more electrons than it does positive charge from protons to even it out and positive when it has fewer electrons than it does protons as a whole.

Elisa Bass 4L

The problem is asking you to find the metal 3+ ion with the given electron configuration. In the case of the first problem, [Ar]3d^6, you can see that the ion has lost both electrons from the 4s orbital, as the 4s orbital fills before the 3d but has not been written on the ground state configuration...

Elisa Bass 4L

Nothing with rest mass can have a higher velocity than the speed of light. Because an electron’s mass can be determined, as it exists when it is at rest, it is said to have rest mass. Light, on the other hand, ceases to exist when it is not moving and can therefore not be weighed, therefore having n...

Elisa Bass 4L

It’s probably helpful to know some of the electromagnetic spectrum, specifically around the visible light and UV range. The order of the spectrum is expressed in terms of the wavelengths of each type of light. So from the longer wavelength (and lower energy) to shorter (and higher energy) would be: ...

Elisa Bass 4L

S-orbitals fully encompass the area around the nucleus. There is no area surrounding the nucleus in an s-orbital where the probability of finding an electron is 0, which is what a nodal plane defines, so there is no nodal plane for the s-orbital.

Elisa Bass 4L

Additionally, light does not exist when it is not moving. Unlike an object like an electron, which is said to have a “rest mass”, light has no mass when it is not moving because it doesn’t exist when it is resting. Something must be in existence when it is not moving for its mass to be measured. Obj...

Elisa Bass 4L

Delta p is the uncertainty in the momentum of the electron or whatever is being studied, with units kg*m*s^-1. Delta v is the uncertainty of the velocity of the object being studied, with units m*s^-1. Delta v is related to delta p by the equation delta p=mass times delta v. Also the values of delta...

Elisa Bass 4L

Additionally, in the case of the energy levels of electrons being quantized, it means that they have to have the energy at a distinct level, ie. n=1 or n=2, and cannot have levels of energy between those distinct levels.

Elisa Bass 4L

I believe Lavelle said that Planck’s constant is the proportionality constant derived from experimental data on the relationship between energy and frequency, since energy and frequency are proportional. If you were to graph them both on a regular coordinate plane, the data points would be in a stra...

Elisa Bass 4L

V1 should not be 0.150L because the problem says that only 20.00mL of the 0.211M solution is used in the dilution. Therefore, V1 should be 0.020L.

Elisa Bass 4L

It looks like the problem gave the electron volts for the (b) section of the Example 1B.3. They went from Joules from electron volts using a conversion factor. The Ek function is used specifically to find the kinetic energy of an ejected electron, otherwise known as the excess energy the photon tran...

Elisa Bass 4L

Start by calculating the molar mass of the compound. The molar mass will be in grams/mol.

Elisa Bass 4L

Find the moles of Cl- in each compound by using stochiometry and then add the two and divide by the total volume.

Elisa Bass 4L

What about when you are calculating molar mass and the problem gives you a rounded mass for an element, such as 16 g for oxygen or 1 g for hydrogen? Are those also considered conversion factors or do you use them when determining sig figs?

Elisa Bass 4L

If a conversion factor is necessary in solving a problem, do the significant figures in that conversion factor matter?

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