CHEMISTRY COMMUNITY

EllaBerry

The three types are unimolecular, bimolecular, and termolecular. It depends on how many reactants there are in the rate law.

EllaBerry

You can essentially use the vant Hoff equation but this time plug in Ea instead of delta H. Solving that out should allow you to solve for any variable involved.

EllaBerry

You can tell if the concentration doesn’t affect the rate at all. Also the k will be a negative slope.

EllaBerry

You can tell if it is a zero order reaction by seeing whether the reaction rate is dependent on the concentration. If it is independent, the reaction is zero order.

EllaBerry

Why would a reaction involving [A][B] creating some product [P] not necessarily be a second order reaction even though two different molecules must collide for the reaction to occur? Is a reaction only second order if the concentration of the reactants are raised to the power of 2?

EllaBerry

When reaction orders are not whole numbers, its most likely due to experimental errors and therefore we just round them.

EllaBerry

The Ecell must be positive, and so you use the Ecathode -Eanode equation to determine which reaction is the cathode and anode by looking at the values you get when you put the E of one reaction in the cathode place and the other in the anode place. If the value is positive, the place you have the E ...

EllaBerry

Once you balance the reduction and oxidation reactions to add them together, you will get the same number of electrons being transferred on either side. The number in front of the e- (or the coefficient) is the n value.

EllaBerry

What makes an element be able to have a stranger reducing ability? A stronger oxidizing ability?

EllaBerry

n is just the amount of moles present, so the problem will give you that information or a way to calculate it.

EllaBerry

Platinum doesn't affect the reaction at all, so it should not need to be included.

EllaBerry

The reaction that is being oxidized will always be the reaction that needs to have its equation, and therefore the E cell potential value, flipped.

EllaBerry

An isolated system will never exchange energy regardless of how much time passes.

EllaBerry

S is equal to zero in a perfect crystal when the temperature is 0K.

EllaBerry

You would use the equation with the K when the reaction is at equilibrium. Meanwhile, use the equation with the Q at any time.

EllaBerry

We use Gibbs Free energy to determine spontaneity. Gibbs free energy is determined using entropy and enthalpy, and if the value of Gibbs free energy is negative, than the reaction is spontaneous. Therefore, entropy and enthalpy help to determine whether a reaction is spontaneous.

EllaBerry

The first equation is used in the case of a reversible expansion, meanwhile the second equation is used in the case of an irreversible expansion.

EllaBerry

Yes, negative work is done when a system does work on its surroundings.

EllaBerry

Latent heat is used in the case where a phase change is occurring while specific heat is defined as the amount of heat required to raise either a mol or a gram of something by 1 degree C.

EllaBerry

Why is it that when a bond is formed it uses energy and when it is broken it releases energy?

EllaBerry

The naught symbolizes that all the standard conditions are being met.

EllaBerry

If the Ka value is greater than 10^3 you know it is a strong acid and if it is less than 10^-3 than you know it is a weak acid. However, it is just good to know the list of strong acids so I recommend learning them at some point.

EllaBerry

Q and K are both calculated in the same way. However, they are different in that Q can be calculated at any time during the reaction, while K is the value only at equilibrium. Therefore you can use Q in comparison to K to determine which way a reaction is "shifted" towards. If Q is less th...

EllaBerry

The heat being added during a phase change solely contributes to breaking apart molecules instead of to increasing the temperature of the system.

EllaBerry

X is the variable you use to represent the unknown concentration of something. -X and +X therefore then represent the change in concentration of a reactant.

EllaBerry

What Lavelle was talking about is that if you have a very small amount of a weak acid the pH of the mixture remains at 7. This is because adding something like 10^-9 to 10^-7, which you have to do because the H30+ mixture starts off at 10^-7, would give you a number that would remain at 10^-7. There...

EllaBerry

Yes because % ionization relates to the amount of acid that reacts with water to form H30+.

EllaBerry

Kp and Kc are essentially the same. Kp is just used to specify that only gases are involved, and the p stands for partial pressure. Meanwhile Kc is in relation to equilibrium concentrations.

EllaBerry

I had Lavelle last quarter and what helped me more than anything was the step up lectures and other discussions set up by TAs and UAs. You can go to them and get all your questions answered, or just go more in depth on a topic you are confused about.

EllaBerry

The problem should specify whether or not you have to use Kp or Kc by either telling you, or having units that demonstrate that you should use one or the other. You shouldn't have to guess.

EllaBerry

I'm confused about 17.33 (6th edition) on the homework which asks which ligands can be polydentate. Part B gives the molecule CO 3 2- . Why is the answer that it can bind through either one or two oxygen atoms? Why isn't the answer definite? Why can't it bind to all three oxygens? It can bind throu...

EllaBerry

Can an acid be both a Bronsted and a Lewis acid at the same time? If so, when are they not?

EllaBerry

Do we have to memorize polyatomic ions and their charges in order to name a coordination compound that contains one?

EllaBerry

Yes, they relate to whether a molecule is polar. If the dipole moments are equal or point opposite directions, the molecule will be non polar. If they point towards similar directions (aren't opposite and canceling) then the molecule is polar.

EllaBerry

Polarizability relates to atomic radius because the larger the radius, the easier it is to distort electrons because they are farther away from the nucleus. Therefore the larger the atom, the higher the polarizability.

EllaBerry

There is a trend that when ionization energy and electron affinity of an element are high, it will also have a high electronegativity. Because Fluorine has both a high e affinity and a high ionization energy, it has a high electronegativity.

EllaBerry

VSEPR doesn't take into account the number of bonds between atoms because it doesn't affect the shape of the structure.

EllaBerry

The don't contribute because the non-central atoms aren't bonded to multiple atoms. Therefore there isn't an 'angle' created by the repulsion like there is with the central atom.

EllaBerry

I'm still confused on the topic of hybridization, can someone explain why when there is a single bond it is just a sigma bond but when there is a double bond it is a sigma and pi bond?

EllaBerry

To find the length of a resonance bond length you find the average of the length between the two bond lengths given. This is because in a resonance structure, no bonds are actually longer than others, it just appears that way when we draw them as a lewis structure.

EllaBerry

If there was a question on the test concerning bond lengths Lavelle would give us the length of them and then probably ask a question concerning the strength of them in comparison to each other.

EllaBerry

You draw an arrow pointing towards the most electronegative atom in the molecule.

EllaBerry

It is more stable when the 3d orbital is full, which it is when it is at 3d10.

EllaBerry

Yes helium would have the highest ionization energy.

EllaBerry

A radical is when there is an electron that is unpaired (meaning it would be one dot by itself on the lewis structure instead of 2 next to each other).

EllaBerry

Elements in period three can, but don't always have to, have an expanded octet. Usually just P, Cl, and S will in that period.

EllaBerry

We will not have to find these bond lengths. In lecture, he used the lengths to show that the more bonds, the shorter the length of the bonds. Therefore a single bond will have a shorter length than a double bond. Also, he used it to show how in resonance structures the true length of the bonds are ...

EllaBerry

Yes, when adding the individual charges of elements together they should equal the overall formal charge. This is a good way to check and make sure the work you have done in calculating the individual charges was correct.

EllaBerry

It is essentially saying that the number of valence electrons determine the number of covalent bonds an element can make. If an element has two valence electrons they can form two bonds.

EllaBerry

Yes, all objects have wavelike properties. However, the bigger the object, the harder it is to be able to detect the wavelength.

EllaBerry

It is between 400nm-700nm.

EllaBerry

I would suggest learning all of them that you can (they will also be useful on further tests). But also make sure you know not only nm but pm as well because that often comes up in the practice problems.

EllaBerry

They will be given to us on the formula sheet so don't worry.

EllaBerry

N is the shell. Based on n, l can be any number up to n-1. If 1=0 it is an s-orbital, if l=1 it is a p orbital, if l=2 it is a d-orbital, and if l=3 it is an f-orbital. Then, the MI can be l...l-1...to negative l. The last number, or the spin, is just either -1/2 of +1/2.

EllaBerry

Yes you would need to list them all, and don't forget 0.

EllaBerry

It is useful to conceptually understand the shapes of the orbitals however for the test itself you will not need to draw them.

EllaBerry

Yes, the answer would be 4f. You know this because n is always the first number, and in this case n=4. Then, looking at l=3 we know it has an f-orbital. Therefore it would be 4f.

EllaBerry

I am still slightly confused what the Heisenberg equation is used for. In class we used it to show that an atomic model was incorrect because the atom's diameter was too small. What other applications can this equation have?

EllaBerry

They should be given to us on the sheet with all of the constants but it is always good to ask your TA just to double check.

EllaBerry

So I know that we aren't taught the Rydberg Equation in class but should we still learn it ourselves? Are we allowed to use it on tests?

EllaBerry

Always multiply by the smallest number possible to get a whole number. In this case it sounds like you would multiply by 2 so that the 3.5 would turn into 7, a whole number.

EllaBerry

From what I've heard, we will be taught how to do that later on and so we shouldn't have to on the first test. However, I cannot promise anything.

EllaBerry

Like everyone else said, it isn't necessarily required. However, if you ever want to use that volume to find molarity or moles, you would need to convert it into L, so I would say that it is usually best to do so at the beginning of a problem regardless.

EllaBerry

I would always show my work on a test just to be safe. It also helps show whoever is grading it your thought process, and some teachers even give out partial credit if your work shows you just made a minor error instead of a conceptual one.

EllaBerry

Almost always, the actual yield will be given to you. You then will usually have to calculate the theoretical yield and divide the actual yield by the theoretical yield to get the percent yield.

EllaBerry

Formula mass is when you add together the molar mass of every element in the formula.

EllaBerry

We can choose any 7 questions we want. However, I recommend choosing ones on subjects that you feel you need the most practice on.

EllaBerry

How do you know which element to start balancing first?

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