CHEMISTRY COMMUNITY

Louise Lin 2B

termolecular would cause third order reactions, which is when three molecules collide a the exact same time in the exact very specific orientation to generate a reaction. the possibility of this is very low, so it is a rare occurrence

Louise Lin 2B

yes rate constants are always positive because even when reactions slow down or reverse, the rate from product to reactant is still moving forward, making the rate constant positive.

Louise Lin 2B

Although Dr. Lavelle does a lot of derivations in class, I believe he does them so we can see the correlations. I doubt we would be asked to derive the integrated rate law since practical application seems to be more the theme of his exams

Louise Lin 2B

The third order is when three molecules collide at the same time and in a certain correct orientation that causes a reaction to take place.

Louise Lin 2B

the half-life of a zero-order reaction actually depends on the initial concentration and the rate constant

Louise Lin 2B

reaction rates are always positive because despite the possibility of reactions slowing down, it is nevertheless moving forward still.

Louise Lin 2B

Adriana_4F wrote:Does anyone know if this will be on Test 2?

I believe that test 2 only goes up till electrochemistry, and rate laws are part of kinetics, so I don't think rate laws will be on test 2.

Louise Lin 2B

the order of the reaction means that the rate is proportional to the concentration of types of molecules involved in the reaction. the reactants must collide simultaneously, with enough energy and the correct orientation to make a reaction happen.

Louise Lin 2B

reactions that quickly react usually mean that it is controlled more via kinetics, while reactions that are carried out more slowly suggest that they are being controlled more via thermodynamics. this is also the reason why the terms spontaneous and nonspontaneous might be misleading,

Louise Lin 2B

Intermediates ultimately get canceled out when you write out chemical equations in the full, so they will not show up in the rate law because only the initial reactants and final products have an influence on the rate law.

Louise Lin 2B

Faraday's constant is the charge in coulombs of 1 mole of electrons

Louise Lin 2B

the n in the NERNST equation is the number of electrons from the half reactions

Louise Lin 2B

to add on to the above responses, aside from platinum, another suitable solid inert substance is graphite.

Louise Lin 2B

Yes; anodes are oxidized and cathodes are reduced. Thus the flow of electrons is from oxidized substances to reduced substances.

Louise Lin 2B

the reaction depends on the molecules involved; if acidic, use H+ and if acidic, use OH-

Louise Lin 2B

A negative deltaG means that the reaction is spontaneous, and usually exothermic. A positive delta G means that the reaction is nonspontaneous, and usually endothermic.

Louise Lin 2B

ions have less or more electrons than the pure substance; thus their charge is never zero

Louise Lin 2B

you can also find oxidation numbers in the context of the reactions, like when you write out the oxidation and reduction half-reactions

Louise Lin 2B

Splitting the reactions allows you to see the intermediate molecules that would not be seen in the net reaction. Also, it allows you to identify the electron transfer more easily.

Louise Lin 2B

also, delta G naught usually refers to the reaction in a laboratory setting, while delta G refers to reactions in a biological setting, like within the body.

Louise Lin 2B

also, to add on to the answers above, the degree symbol next to the delta variables indicate that they occur under lab conditions. without the degree symbol, the delta variables are typically in regards to biological conditions.

Louise Lin 2B

Adding on to the previous answer, volume and pressure changes are temporary, so it will affect Q, but the reaction will always adjust to return to equilibrium K.

Louise Lin 2B

There are still some cases that might differ! For example, imagine that the enthalpy value and the entropy value were both positive. If the value this would mean the (-TdeltaS) would be negative. However, if the value of enthalpy is higher than the value of -TdeltaS, overall Gibbs free energy would ...

Louise Lin 2B

Not necessarily, spontaneous and nonspontaneous would have to depend on how large the values of entropy and enthalpy are compared to each other. For example, if both entropy and enthalpy were negative, it is still possible for the overall reaction to be nonspontaneous if the value of entropy multipl...

Louise Lin 2B

I really like going to Lyndon's workshops on Mondays, but to study I also rewrite my notes the day of the lecture (mainly because I have bad handwriting haha but it really helps), and doing the problems from the textbook! Also! study buddies are super helpful, even if it's just to help you stay focu...

Louise Lin 2B

For entropy changes due to temperature, does it vary depending on whether or not the reaction is exothermic or endothermic? I was thinking that increasing temperature for an endothermic reaction would actually decrease the entropy of the system...

Louise Lin 2B

entropy is the measure of disorder in a system. the more disorderly, the more (positive) the entropy and vice versa. disorder in a system also modifies energy, so it is important to include entropy when describing a system.

Louise Lin 2B

in a perfect system, q(system)=-q(surroundings). if we apply this to the universe as a whole (surroundings), this would be true. besides that, there are no true perfect systems.

Louise Lin 2B

standard states also mean that since the molecule/element is in its most stable form, it will not undergo a change that changes enthalpy. Therefore, enthalpy of standard state molecules/elements are zero.

Louise Lin 2B

The more kJ/mol that the phase change takes, the more energy is released. A liquid burn does not have a phase change; it is merely the water that gets heated, but has not reached the point where enough energy changes the liquid into a gas. By contrast, a steam burn, upon contact with your skin, turn...

Louise Lin 2B

Some examples of state properties are temperature, pressure, and volume.

Louise Lin 2B

the unit for delta H_f is kJ/mol, but for delta H_c I believe that the units are kJ/C, in which C represents a unit uniform throughout the problem

Louise Lin 2B

unless specified otherwise, the conditions in which the substances are in should usually use the standard enthalpies of formation

Louise Lin 2B

from what I understand, the standard enthalpy of an element is dependent on the standard state that the element is typically found in. For example, oxygen is not typically found as just O, but it is found as O 2 . Thus, like a previous comment said above, the standard enthalpy of the element in its ...

Louise Lin 2B

A state function describes the type of system the observed materials are in, and quantitatively describe the equilibrium state of said system.

Louise Lin 2B

Depending on if the reaction is exothermic or endothermic, temperature will change the equilibrium constant (K) of the reaction. Usually, unless a problem says otherwise, we can treat the reaction like it is at room temperature.

Louise Lin 2B

K is appropriate to use when the reaction is already at equilibrium. There is only one K value for each reaction and its circumstances (temperature, pressure, etc.) Q is appropriate to use at any point in time of the reaction, and is used to compare to K.

Louise Lin 2B

the -x was ignored because the value is so small that it makes no difference to include it or not. This is called a small approximation.

Louise Lin 2B

H₂O isn't usually included because it is provided in excess in experiments, and is usually in liquid form. Liquid and solids are not supposed to be included in ICE tables.

Louise Lin 2B

A high pH and a low pOH means that the resulting solution is basic. A low pH and a high pOH means that the resulting solution is acidic. pH and pOH values should add up to be 14.

Louise Lin 2B

An example of Le Chatelier's would be to decrease the volume, and if there are more moles of gas on the left, then the reaction would shift to the right to accommodate for the change and vice versa.

Louise Lin 2B

Q is only the constant calculated from the ratio between the products and reactants at some point in time during the reaction before it reaches equilibrium. It does not actually tell us the speed at which the reaction takes place.

Louise Lin 2B

All of the above are correct, but also, as discussed in class, it's important to add that catalysts only speed up the reaction, but the ultimate yield of the concentration will be the same as letting the reaction proceed by itself. This means that catalysts only help the reaction reach its equilibri...

Louise Lin 2B

Le Chatelier's Principle basically means that a reaction will adapt to any changes as a response to minimize the effect of the change. This means that if pressure is increased or decreased, Le Chatelier's principle tells us that the reaction will adjust to keep K, the equilibrium constant, stable.

Louise Lin 2B

Can someone re-explain the real reason behind why reactions, upon changing the pressure, respond to minimize the effect of increasing pressure? Dr. Lavelle said in class that many of us learned the shortcut version, wherein upon increasing pressure, the reaction would go opposite the direction of th...

Louise Lin 2B

adding on to the above replies, an example of a common amphoteric molecule is water. Water can act as either an acid or base depending on the reactions.

Louise Lin 2B

Yes, double arrows typically indicate that the reaction does not completely dissociate and is reversible. Single arrows indicate that the reaction dissociates completely.

Louise Lin 2B

I’d like to add that strong bases include group 1 hydroxides, alkaline earth metal hydroxides, and group 1 and 2 oxides.

Louise Lin 2B

Lewis acids are electron acceptors, meaning they usually receive lone pairs. The molecule that is more electron deficient is typically the Lewis acid. On the other hand, Lewis bases are electron donors, so they give away lone pairs.

Louise Lin 2B

One example of an amphoteric compound is water, H₂O.
Water as a base:
HCl_(aq) + H₂O_(l) —> H₃O⁺_(aq) + Cl^-_(aq)

Water as an acid:
H₂O_(l) + NH₂^-_(aq) —> OH^-_(aq) + NH_3(aq)

Louise Lin 2B

An amphoteric compound can donate and/or accept protons. Amphoteric compounds have both acid and base-like properties. Some examples of amphoteric compounds are water and amino acids (which make up proteins).

Louise Lin 2B

It's possible to calculate a negative pH, but in practice in a lab, negative pH can't really be tested for.

Louise Lin 2B

to convert between [H₃O⁺] and [OH^-], use [H₃O⁺]=10^-pHmol . L^-1. pH+pOH = 14 maximum, so we can use this equation to find and convert between [H₃O⁺] and [OH^-].

Louise Lin 2B

Elements that are in and close to the diagonal line of metalloids usually make amphoteric oxides. If you look at figure 6A.7 on page 450, Bi₂O₃ is classified as an amphoteric oxide.

Louise Lin 2B

Strong acids have a higher concentration of hydrogen ions than weak acids. This means that for strong acids, all of the hydrogen ions dissociate immediately, while weak acids dissociate more slowly.

Louise Lin 2B

I believe we'll be expected to know how to draw some of the coordination compounds for the test, but they might give us the chemical formula, since that seems to be the pattern from previous tests.

Louise Lin 2B

Chromium as an element in general is a beneficial to one's health, but doing some research after Dr. Lavelle's lecture, the best chromium supplementation is said to be chromium picolinate, which is a coordination compound.

Louise Lin 2B

The pros of cisplatin are that they kill cancer cells very effectively. A minor con is that cisplatin also works on healthy cells, but Dr. Lavelle mentioned that the degree at which they kill healthy cells is relatively less than the amount of cancer cells killed.

Louise Lin 2B

It is possible for cations to be outside the coordinate sphere if the net charge of the coordinate sphere is negative. This would allow for positive cations to be attracted to the outside of the coordinate sphere as a whole.

Louise Lin 2B

Transition metals having multiple oxidation states allows them to lose electrons fairly easily when compared to the metals in group 1 and group 2. This allows them to transfer electrons more easily as well, like the previous commentator stated.

Louise Lin 2B

Only the lone and bonded pairs pertaining to the central atom are important to determining the regions of electron density in molecule shape and structure.

Louise Lin 2B

Bent shapes occur when the molecule has lone pairs due to electron repulsion. For ths example, then, the model with lone pairs would be the one with a bent shape.

Louise Lin 2B

If the central atom has two bonded pairs and either one or two lone pairs, this would result in the bent shape. The bond angle would be smaller if the central atom has two lone pairs because of electron repulsion.

Louise Lin 2B

The shape will not vary, since, even though resonance structures exist, we count single, double, and triple bonds as one grouping.

Louise Lin 2B

The formula is derived from A being the central atom, X being the atoms bonded to the central atom (with the subscript being the number of atoms bonded to the central atom), and E being the number of lone pairs the central atom has.

Louise Lin 2B

If compounds have a higher electronegativity, they are more polar. Since water itself is a polar molecule, it would dissolve polar compounds well, especially compounds with higher electronegativity.

Louise Lin 2B

I believe this will depend on if the molecule has any lone pairs left and the structure of the molecule. It would be better if you had a specific example in mind, too!

Louise Lin 2B

Yes, polar molecules can be more polar than another. You can tell when you look at the difference in electronegativity of the atoms in the molecules.

Louise Lin 2B

Yes, lone pairs affect how polar a molecule is. Take H₂O for example: oxygen has two lone pairs, which makes water a polar molecule. There is a higher negative partial charge on the oxygen end, and a higher positive partial charge on the hydrogen end.

Louise Lin 2B

Polarizability increases as the volume of the atoms increase. This means that polarizability typically increases down a group and decreases left to right in a period. High polarizability makes molecules have larger dispersion forces that allow them to form temporary dipoles more easily. Bonds betwee...

Louise Lin 2B

Polarizablility increases generally when volume occupied increases. This means, as a periodic trend, it increases down a group, but decreases across a period. Polarizability determines what kinds of bonds the atom will form, which then determines the state of the molecule.

Louise Lin 2B

A bigger difference in electronegativity does not mean a higher charge, but any difference larger than 1.7 or 1.8 mean that ionic bonds will form. Electronegativity increases as you move left to right on a period.

Louise Lin 2B

Arianna Perea 3H wrote:Does FC determine where we make double bonds?

Yes, it does! The FC equation needs to know the number of paired and unpaired electrons, and the most stable structures are those with a net charge of zero. FC can determine where double bonds will be when calculated.

Louise Lin 2B

Exactly! As you move down a group, covalent characteristics of a bond increases, which causes a decrease in electronegativities of the bonded atoms and a decrease in polarity. Since water is a polar molecule, it becomes harder for it to dissolve silver halides as the covalent character increases.

Louise Lin 2B

Water is typically more effective when breaking ionic compounds because the ions are attracted to the polar water molecules, which break the ionic compounds apart. Water is not as effective when breaking covalent bonds because many covalent compounds are nonpolar. Since water is polar, and many cova...

Louise Lin 2B

Ionic bonds have covalent properties that depend on the polarizability of the anion and the cation's polarizing power. Ionic bonds have more covalent character when the anion is more polarizable or when the cation has high polarizing power.

Louise Lin 2B

Adding on to the replies above, make sure to always calculate the formal charge of each atom to make sure that you have arranged the best possible structure. Not all molecules with double or triple bonds will have resonant structures, so it is important to make sure.

Louise Lin 2B

a) Mg₃As₂
b) In₂S₃
c) AlH₃
d) H₂Te
e) BiF₃

Louise Lin 2B

The octet rule does not apply to boron because it only has 6 electrons. It also does not apply strictly when elements are in the third period or higher. This is because of the presence of d-orbital electrons allowing for exceptions when chemically bonded.

Louise Lin 2B

Adding on to the poster above, the location of double and triple bonds will depend on where the octet rule can be accommodated. They cannot be replaced wherever “because of resonance,” because we must also determine if the atom has resonance structures in the first place. If there is resonance, then...

Louise Lin 2B

In line with all above answers, yes, atomic radii increases the more electrons there are. However it is important to also note that atomic radii increases not per electron, but per subshell. Each subshell will hold a certain amount of electrons, and atomic radii increases with each new subshell.

Louise Lin 2B

The principle quantum number is "calculated" depending on the energy level that the electron is on. We can find it by looking at the period the element is on. As for atom excitation, I'm not too sure about that either...

Louise Lin 2B

a) when n=7, there are 7 quantum numbers: 0,1,2,3,4,5,6
b) when an electron is in a 6d-subshell there are five values of m_l: -2,-1,0,1,2
c) when an electron is in a 3p-subshell, there are three values for m_l: -1,0,1
d) when n=4, there are four subshells: 4s, 4p,4d, 4f

Louise Lin 2B

Adding on to the above comment, two electrons with the "same spin" means that they are both either spinning upward or spinning downward. Take the element carbon: the atomic number is 6, so the electron configuration would be 1s 2 2s 2 2p 2 . The 1s and 2s shells are both at the maximum occ...

Louise Lin 2B

r as distance between two charges is more accurate. r can describe the distance between two electrons, or the distance between and electron and a proton. At your high school, your class may have calculated using r as the distance between an electron and proton (which are in the nucleus) and just cal...

Louise Lin 2B

The 4s orbital actually has higher energy than the 3d orbital if the 4s orbital is occupied by electrons. So, when we write out the electron configurations, the 3d orbital goes before 4s!

Louise Lin 2B

Electrons travel the different energy levels that an atom has. They don't necessarily follow a wavelength; rather, an electron acts as both a wave and a particle.

Louise Lin 2B

The number of energy levels that an electron can jump to depends on the number of energy levels an atom of the element has. The number of energy levels an atom has depends on its placement on the periodic table.

Louise Lin 2B

In the two images he showed during the lecture, the model with the connected oscillating wave meant that the electron circulating the nucleus was at an energy level like n=3, where the level is an integer, or whole number. The model that had the disconnected wave means that it does not "work;&q...

Louise Lin 2B

Microwave ovens are dangerous because they fit about 1 kilowatt of power inside a small box. Regular microwave radiation may have less energy than 1 photon of light, but imagine concentrating a kilowatt's worth of microwave radiation into a small box. This amount of power is how food gets reheated i...

Louise Lin 2B

A "black body" is a concept that is created to imagine the complete absence of color or light or anything. Professor Lavelle said that a true black does not actually exist, so black bodies are the hypotheticals we would imagine.

Louise Lin 2B

Start by visualizing the molecules side by side, strung together! The 144 pm they give you for radius should be calculated into the diameter of the atom (so 288 pm). First, like you said, convert 1 mole of Ag into number of atoms with Avogadro's number. Next, multiply your answer by 288 pm to find o...

Louise Lin 2B

Typically, it's best to save rounding for the end, just so your answer is as precise as possible! ;)))) If we round in the middle steps, the answer may turn out different than intended.

Louise Lin 2B

For discussion credit, we'll be turning in 5 homework problems and do 5 posts; questions and replies both count! :))

Louise Lin 2B

It sounds like a plain old scientific or four-function should serve you well. Personally, I use the Casio - fx115ES Plus Scientific calculator. I remember that AP Chem in high school didn't really need a graphing calculator, so I suppose that's why Chem 14A doesn't necessarily require one, either.

Louise Lin 2B

Hey there!

You did receive a reply already, but here's a similar mnemonic that I used in high school that might be of help to you:
Kings Have Died Under Dreadful Circumstances: Meteors
They don't always make sense, but if you create your own mnemonic, that might help you more! :))

Louise Lin 2B

Your journey sounds like it has been amazing! As someone that also wants to go into the medical field, this is very inspiring. And you certainly made me more excited for Dr. Lavelle's class. Do you currently have other interests outside the medical field, and do you still have time to engage in them...

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