CHEMISTRY COMMUNITY

Sam McNeill 1E

I also would look at khan academy, that always helps me, or do the practice tests in the textbook!

Sam McNeill 1E

Additionally, kr/k prime=K, the equilibrium constant.

Sam McNeill 1E

Also, depending on the order, the slope of the linear line is equal to either -k(in 0 and 1st order) or k (in 2nd order).

Sam McNeill 1E

Lavelle also specified that we will only be using the pre-equilibrium approximation and not the steady state.

Sam McNeill 1E

If the reactants are being consumed, then the rater is negative. Simultaneously, while products are being formed, they are increasing in amount and the rate is positive.

Sam McNeill 1E

I don't think so, because you would write that the other substances are aqueous, which implies the presence of water.

Sam McNeill 1E

When setting up or drawing a diagram of a cell, typically there is a salt bridge to keep charges balanced, and that is when NO3 and other ions are used. OH- is used when balancing things in acidic condition. Khan Academy has a very helpful video on it if you search balancing redox reactions in basic...

Sam McNeill 1E

E must be found by comparing an anode and a cathode, so you would use the SHE as the comparative E when finding other reactions E since E=0 for SHE.

Sam McNeill 1E

I have seen problems where both occur, so I would just double check your work and not assume where anything goes, just to be safe. Also, you should be able to tell if the total unbalanced reaction is given.

Sam McNeill 1E

N is not moles how we have been using it previously, but the number of electrons transferred. To find this n, balance the half reactions so that the number of electrons is the same, and that is n.

Sam McNeill 1E

In a redox reaction, there must be both reduction and oxidation, so I would use process of elimination. Also, once you balance out the equation using H+ and H2O, it should be clear which side needs electrons to balance out the charges, and from there you can also decide if it is reduction or oxidati...

Sam McNeill 1E

I think the question will specify what the conditions are, and for basic conditions you use the exact same steps as acidic condition, but at the end balance out H+ with OH-.

Sam McNeill 1E

Just as with Ho,Go, and So, the o means not, which is under standard conditions. If it is not present, you know the conditions are not standard.

Sam McNeill 1E

A little bit less fun, but you can also remember that Anode and Oxidation both start with vowels, so they are paired and Reduction and Cathode with start with consonants so they are paired.

Sam McNeill 1E

Also, keep in mind that the half reactions must be able to cancel out each others number of electrons to form the overall equation.

Sam McNeill 1E

For balancing half reactions in acidic conditions, use 1) Balance everything other than H and O 2)Balance O using H2O 3)Balance H using H+ 4)Balance charges by adding electrons 5)Add the half reactions together. For basic conditions, follow the same steps but at the end cancel out H+ by adding OH- t...

Sam McNeill 1E

When there is a temperature change, make sure to use this equation in kelvin. Also, moles are always taken into account I believe, but not written down when there is only 1 mol of substance. If moles are not given, I would use the PV=nRT equation to find the amount of moles.

Sam McNeill 1E

The elements that have 0 enthalpy of formation are when there is no energy needed to keep them in that state or to get them into that state.

Sam McNeill 1E

You can also think about how larger elements have more electrons, and the possible states that those electrons could occupy contribute to the positional entropy, causing it to have a larger entropy than smaller elements with the less electrons.

Sam McNeill 1E

You can also use the standard entropies to find the change in entropies.

Sam McNeill 1E

It is also helpful to look at units and use stoichiometry to find the enthalpy. For example, Hc is typically in units that have per mol of something (an element or substance)

Sam McNeill 1E

The monoatomic values are also on the constants and equations sheet, and just remember that for diatomic, you add 1/2 to the value :) Lavelle also said we only really need to know monoatomic because that is all he covered in class.

Sam McNeill 1E

Delta H can be used in the equation U=q+w for q when there is constant pressure, but you still will need to account for w, which is PdeltaV for irreversible expansion.

Sam McNeill 1E

The only thing that isothermal affects is delta T and delta U are equal to 0.

Sam McNeill 1E

Isothermal means that the temperature is constant, which translates to delta T is 0, but isothermal is a specific pathway where the temperature is constant.

Sam McNeill 1E

The problem state "You have a system consisting of 0.40 moles of an ideal gas contained in a 100.0L container at 1.0 atm. You just love chemistry to a fault, so you perform a series of steps to the system. First, you perform an isobaric compression of the container to 10.0L. Then, you pressuriz...

Sam McNeill 1E

The first law mostly concerns that how in an isolated system, and how its internal energy is always constant

Sam McNeill 1E

If something is heating something, the q will be negative since it is releasing heat into its surroundings.

Sam McNeill 1E

Standard enthalpies of formation is the energy required to make a compound from the most basic forms of elements, and the standard reaction enthalpy is the energy of a reaction as a whole.

Sam McNeill 1E

I remember it as intensive being internal, and can't be changed, and extensive as external, meaning external forces can alter it.

Sam McNeill 1E

The temperature remains the same because all of the energy from the heat is being used to transition the substance into the next phase.

Sam McNeill 1E

Whenever the standard enthalpy of formation is 0, you know that that is the most stable form of the element.

Sam McNeill 1E

The standard enthalpy of formation is equal to zero when the compound is already in its most stable form.

Sam McNeill 1E

I assume so, or use the combination of them, such as fusion and vaporization to get sublimation, if its not directly given.

Sam McNeill 1E

I think that we need to know all three, however just remember that using bond enthalpies is the least accurate of the three.

Sam McNeill 1E

I believe that it depends on what the most stable for of that element is, for example N2 is more stable than N by itself.

Sam McNeill 1E

For approximating the value of x, does K have to be smaller than 10^-3 or can it also be equal to 10^-3

Sam McNeill 1E

In addition, you can use the pH and pOH to find each other using the equation pH+pOH=14

Sam McNeill 1E

I was confused on this as well, the textbook made it seem like there were different values for K and Kc?

Sam McNeill 1E

If Ka1 is larger than Ka2, then ignore Ka2 since it will be insignificant. Also, I believe that H2SO4 is the only time in the textbook that Ka2 is used and makes a difference in pH.

Sam McNeill 1E

Look at which side is affected more in terms of the exponents when you solve for a new Q. When volume is halved, concentration doubles and then apply the exponents to that double to find if Q is greater then or less than K, then decide which direction the reaction will proceed in.

Sam McNeill 1E

Pure liquids are never used, since there cannot be a concentration of a pure liquid.

Sam McNeill 1E

Is there a difference between Kc and Kp in terms of calculating them? Also, is there a difference between K, Kc, and Kp? On the graph in the textbook it seems that there is.

Sam McNeill 1E

In addition, K is a constant that will remain the same as long as no conditions such as temperature change, and Q varies in value depending on when you calculate it during the reaction.

Sam McNeill 1E

I think we need to think about it in terms of reactants as a whole and products as a whole and not each individual reactant and product in the reaction, if that clarifies things.

Sam McNeill 1E

Lavelle clarified in class that the "quick way" would not actually give the correct reasoning to answer the question, so I would just know the long way since the quick way does not correctly give reasoning.

Sam McNeill 1E

When do we use the equation PV=nRT? And how would we use it?

Sam McNeill 1E

Q is calculated the exact same way as K, it is simply just used to determine if more products or more reactants need to be made in order to reach equilibrium.

Sam McNeill 1E

It would be true, since K is a constant and the forward and reverse reactions will occur until that constant is reached.

Sam McNeill 1E

You can also see that when Q<K, the equation shifts right, towards the product, which shows it favors making more product in a forward reaction. When Q>K, it is shifted left, which means more reactants are favored. I hope this helps :)

Sam McNeill 1E

A homogenous equation includes substances where all of the phases are the same, for example all gases, and a heterogenous equation has a mixture of different phases.

Sam McNeill 1E

For this problem, also remember that the activity of solids and liquids is 1, so you would not consider them when calculating.

Sam McNeill 1E

I believe that the 10^3 is referencing acids and bases, as Dr. Lavelle mentions in the video module.

Sam McNeill 1E

I just practiced by doing a lot of homework problems and having the written out way to name in front of me while doing it until I didn't need to look at it anymore.

Sam McNeill 1E

The chart that is posted on the class website lists the compounds and their charges that we need to know.

Sam McNeill 1E

A molecule is accepting when it takes something from another molecule, either a proton or an electron.

Sam McNeill 1E

How do you know K+ is a weak acid?

Sam McNeill 1E

There also is no overall charge in HF and Hal reactions, so electronegativity wouldn't affect the stability.

Sam McNeill 1E

Wait I thought that hybridization occurred on all atoms, so it is only those that make more bonds than the number of electrons in their highest energy level?

Sam McNeill 1E

S-character I believe is the ratio of s to p, so as the ratio grows for s, the angles grow. Just think less p, less regions of density to repel the other regions.

Sam McNeill 1E

Which names should we focus on memorizing? Is it just the ones that Lavelle posted on his site in the chart?

Sam McNeill 1E

The coordination number is the number of points the ligand can attach to a central atom.

Sam McNeill 1E

I think that you have to draw out the lewis structure and see where the ligand can attach and if those spots are next to each other.

Sam McNeill 1E

I would also look at the difference in electronegativity, which I believe would also help determine the strength.

Sam McNeill 1E

For a tetrahedral shape, the only time it is non polar is when all 4 of the bonded atoms are the same.

Sam McNeill 1E

Just remember that anything with a lone pair has less than angles of the original parent electron configuration.

Sam McNeill 1E

It also means that when pi bonds are present, atoms cannot rearrange themselves to become less or more polar.

Sam McNeill 1E

You also know that since there are formal charges on the structure when N is the central atom and therefore is less stable, the C being the central atom is more stable and thus correct.

Sam McNeill 1E

Besides knowing that pi bonds are any bonds past a single bond, also know that pi bonds do not allow the molecule to rotate.

Sam McNeill 1E

I would email your TA to ask specifically, but I think Lavelle would let us know either tomorrow or Friday in lecture.

Sam McNeill 1E

I would ask your TA specifically, but we are still on Chemical Bonding and haven't had many lectures since the midterm.

Sam McNeill 1E

Think about how the electrons are constantly moving, so when they are clumped together on one side with a high density, that creates a temporary dipole.

Sam McNeill 1E

The strongest interactions have the highest boiling point, which is the ion ion interaction.

Sam McNeill 1E

Just like triple bonds are the strongest and hardest to pull apart, think about the ion-ion bond being the strongest, and therefore the hardest to pull apart, or boil.

Sam McNeill 1E

With double and triple bonds, I believe because there are more electrons involved, the atoms are pulled closer together which shortens the bond length.

Sam McNeill 1E

I know that atomic radius affects the anions polarizability and a more highly charged cation has a higher polarizing power, but does the charge of an anion affect the polarizability? If so, how?

Sam McNeill 1E

Just follow the atomic radius trend, with smaller being more polarizing and larger being more polarizable. Also, a high positive charge means that it is more polarizing.

Sam McNeill 1E

I asked this question at a review and the UA said to think if phone call, F O N Cl, where F is the most electronegative in that group and Cl is the least.

Sam McNeill 1E

Check the formal charges to determine which atom gets the radical, I believe that it is typically the more electronegative atom.

Sam McNeill 1E

Anything past group 3 can have an expanded octet, making it so that Xe can bond with F while exceeding an octet.

Sam McNeill 1E

Write out below the arrow structures that the actual structure is a hybrid of the above individual structures.

Sam McNeill 1E

Once you draw all of the resonance structures with the arrows between them, write that the actual structure is a hybrid of each individual structure.

Sam McNeill 1E

You know you are dealing with the most stable version when the Formal Charges are closest to zero. Try to find the different structure for the naturally occurring molecule, and whichever is closest to zero is the most stable.

Sam McNeill 1E

When drawing Lewis Structures that have multiple elements, how do you know which go where? For example, problem 2B, where the structure is ONF?

Sam McNeill 1E

One exception is if the element is in the p-block in Period 3 or below, since those have the option to move electrons into the d-block.

Sam McNeill 1E

All p-block elements Period 3 and down can be expanded because they have the option to move electrons to the d-block.

Sam McNeill 1E

Think of it as the electron not having an exact location, or bond, but instead is involved in multiple bonds.

Sam McNeill 1E

I believe that Z is equal to the number of electrons in an atom, at least this is how it was used in the lecture Dr. Lavelle gave examples in.

Sam McNeill 1E

The ground state refers to the electrons filling up the lowest possible energy levels, so if asked for the ground state I believe that means the electron configuration where the electrons fill the lowest orbitals.

Sam McNeill 1E

There are orbitals that go beyond f, but I believe we only have to be familiar with s, p, d, and know that f exists.

Sam McNeill 1E

Think about how for each p, there are 3 possible options, x, y, and z. There is 1 for s, and 5 for d. The amount always increases by two, if that makes sense.

Sam McNeill 1E

l is n-1, and goes all the way to 0 with each s, p, and d corresponding to 0,1, and 2.

Sam McNeill 1E

Try to think of it as whatever the difference between the energy of the photon absorbed and the energy actually needed to remove an electron results in the kinetic, left over energy of the photon pushing out the electron at different velocities.

Sam McNeill 1E

The energy of the photon has to exactly match the energy difference otherwise it will not be absorbed, which is why changing the intensity of the wave does not matter when considering what is absorbed.

Sam McNeill 1E

If the electron is moving up levels, then energy is absorbed, and if the electron is moving down in levels, then energy is released from the atom.

Sam McNeill 1E

I believe that light is neither a wave nor a particle specifically but possesses properties of and behaves in ways similar to both.

Sam McNeill 1E

How would we use Schrodingers Equation? Im confused about what there is to know about that equation in general and what would be plugged in to it.

Sam McNeill 1E

A photon is the quanta, or smallest measurement, of light.

Sam McNeill 1E

Your TA should give it back at the next discussion or you could go to their office hours and ask.

Sam McNeill 1E

Yes, and to do this you would use molar ratios to find how much reactant is used up based on the limiting reactant, then subtracting that number from the given amount of that reactant.

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