CHEMISTRY COMMUNITY

hazelyang2E

For the graphs of the different order reactions, do we need to know anything about the graph besides the axises, y-intercept, and the slope?

hazelyang2E

I believe that is just one of the conditions that must be met for collisions, but the definition of the frequency factor is already defined for molecules under the same orientation, so you don't need to change or solve for anything.

hazelyang2E

I believe that if you are flipping one of the half reactions you also need to reverse the sign of the reduction potentials, and then you would add the potentials together instead of subtracting them. If you are using the equation E(cathode)-E(anode) to find the cell potential, you do not reverse the...

hazelyang2E

The purpose of the unique rate is to be able to compare the rates of all the reactants to one another. It also shows the unique average rate of the overall reaction.

hazelyang2E

I believe that you consider the reactants for the molecularity which includes any catalysts but not intermediates.

hazelyang2E

I believe Professor Lavelle said in lecture that we will only be using the pre-equilibrium approach to solve problems. He mentioned the steady state approximation to make us familiar with it because it is a method that is more commonly used in the textbook.

hazelyang2E

pH is not neutral at 7 if the conditions are not standard. A pH of 7 may be acidic or basic depending upon the pH at nonstandard conditions.

hazelyang2E

For the final, do we need to know how to derive the first order reaction rate law or just how to identify and use it?

hazelyang2E

For the final, do we need to know how to derive the first order reaction rate law or just how to identify and use it?

hazelyang2E

When using the Nernst Equation, how do you know when to use the variation that takes lnQ versus the one that take logQ? Will they produce the same result or is there a difference between them?

hazelyang2E

Another reason you can identify AB as an intermediate is because it is present in both of the reactions: As a product in the first reaction, and as a reactant in the second reaction.

hazelyang2E

I believe that when Professor Lavelle was talking about units for K in lecture he emphasized the fact that the units change depending on which order the reaction is. For example, the units of K for a first order reaction sec^-1 whereas the units of K for a second order reaction (M^-1)(s^-1). I belie...

hazelyang2E

The reason why iron lost 5 electrons is because the entire oxidation reaction of Fe2+ --> Fe3+ + 1e- was multiplied by 5 so that the 5e- in the reduction reaction (8H+ + MnO4- + 5e- --> Mn2+ + 4H2O) would cancel out in the overall oxidation reduction reaction.

hazelyang2E

If a reaction has negative delta H and negative delta S, it will be spontaneous when the absolute values of Temperature x Delta S is greater than the absolute value of delta H because delta G will also be negative.

hazelyang2E

You separate the equations into two half reactions because it is easier to see which compounds are being reduced and which ones are being oxidized. When you separate the reaction into two reactions it is also easier to balance out the equations and clearly see where electrons are being lost or gaine...

hazelyang2E

I believe Professor Lavelle also mentioned in lecture today that when you balance out the reaction using stoichiometric methods, the oxidation numbers will usually balance out as well. In addition to balance out the charges you can add electrons to either the reactants or products side of the reacti...

hazelyang2E

Also remember that because a salt bridge prevents charges from building up on either side by allowing from ion transfer, it also ensures that the two solutions both remain neutral.

hazelyang2E

Can someone please explain how to differentiate when we should use Hess's Law to calculate the overall reactions enthalpy versus using the sum of the enthalpies of formation of the products minus the sum of the enthalpies of the reactants? Will they yield the same result if you use them on the same ...

hazelyang2E

I believe that it is acceptable to express entropy as disorder as you have described in your post. However, Professor Lavelle also said mentioned that as entropy increases, the amount of possible positions a molecule can occupy also increases, which is why we say that the overall disorder of the sys...

hazelyang2E

I believe that the reason why all of those values include the /mol is because they are the standard values which means they are specifically expressing the heat, disorder, energy, etc. for 1 mol of the substance or compound.

hazelyang2E

Both matter and energy can be exchanged in an open system because matter is allowed to move in and out of the system, as in an open beaker. However, in a closed system, the amount of matter must stay constant so only the energy is exchanged.

hazelyang2E

I believe all you need to know about a bomb calorimeter is that it is used to measure the temperature of a combustion reaction and that it would be considered a closed system.

hazelyang2E

Forming a bond is exothermic because it releases energy whereas breaking a bond would require energy so it would be endothermic.

hazelyang2E

Standard reaction enthalpy is ΔH when all of the reactants and products are in their standard states at 1 atm. Standard Enthalpy of Formation is ΔH for the formation of 1 mole of a substance from its elements in their most stable form. I believe standard reaction enthalpy relates more to the transfo...

hazelyang2E

Tables 12.1 and 12.2 in the textbook (6th edition) list the pKa and Ka for common acids and the pKb and Kb of common bases. In addition, many problems will give you either the pKa, Ka, pKb, and Kb which you can then use to figure out the other three values, using 1.00 x 10^-14 = Kw = Ka x Kb, pKa = ...

hazelyang2E

For a majority of the ICE tables, "-x" will be located in the "C" or change row for the reactants, and "+x" will be located in the "C" row for the products. It is also important to remember to multiply "x" by the molar ration of that compound. For ex...

hazelyang2E

In addition to what was already said in the previous answer, it is important to understand that when we approximate we are saying that x is an extremely small number, but it is not zero.

hazelyang2E

Could someone please explain to me the difference between K and Q, the reaction quotient? I'm just a little confused on the differences between the two as they are essentially calculated in the same way. Thank you!

hazelyang2E

Yes, you will need to use the quadratic equation to solve for x, unless K<10-3, in which case you can use approximation and say that x is a very small number and simplify the equation down to make it easier to solve.

hazelyang2E

As the previous answers stated, the equilibrium constant is not affected by the addition of more products or reactants because the reaction will re-adjust to this change to minimize the effect of changes (according to Le Chatelier's Principle). It is important to remember that this is due to the fac...

hazelyang2E

I believe that both Keq and Kc are used to represent the equilibrium constant. I don't think you would be marked down for using one over the other because Professor Lavelle mentioned in lecture that K, Kc, and Kp are often used interchangeably to represent the same thing, the equilibrium constant.

hazelyang2E

I believe one of the most commonly used values for the R constant is 8.206 x 10-2 L·atm/K·mol, but it is important to keep in mind that this value can change depending on which units are being used as shown in the previous answers. Also, my TA mentioned that this constant will be provided for us on ...

hazelyang2E

Yes, because nonmetals have a higher electronegativity they are more likely to attract and gain electrons in order to achieve a full octet. For example, the halogens are more likely to gain 1 electron than to lose the 7 electrons that they already have. By gaining that 1 electron, they achieve the e...

hazelyang2E

It may also help for you to think of electronegativity as how badly an atom wants to form a bond or how strongly an atom attracts an electron pair. Because of this, an acid with a high electronegativity will dissociate completely in water, making it a strong acid.

hazelyang2E

I'm also not completely sure, but I think it would be a good idea to memorize the names and chemical formulas for the weak and strong acids and bases that Professor Lavelle specifically discussed and listed out during lecture

hazelyang2E

Additionally, sigma bonds have cyclical symmetry around the internuclear axis which allows the bound atoms to rotate. However, pi bongs have electron density on either side of the internuclear axis which prevents the bound atoms from rotating.

hazelyang2E

Sigma bonds are are formed from end to end orbital overlap while pi bonds are formed from side by side orbital overlap. A single bond between atoms is a sigma bond, a double bond between atoms is a sigma bond plus 1 pi bond, and a triple bond between atoms is a sigma bond plus 2 pi bonds.

hazelyang2E

You can determine whether a compound/molecule is polar or nonpolar based on the polarity of the bonds between the atoms within the compound/molecule. A polar compound/molecule has polar bonds with dipoles that do NOT cancel. A nonpolar compound/molecule has nonpolar bonds or polar bonds with dipoles...

hazelyang2E

In addition to what has already been said in previous answers, the symmetry of a molecule's shape can indicate whether a molecule is polar or nonpolar. If atoms are arranged symmetrically around the central atom so that their dipole moments cancel each other out, then the molecule will be nonpolar. ...

hazelyang2E

Yes, symmetric atoms and molecules will generally be nonpolar because the symmetric dipole moments will cancel each other out because they are moving in opposite directions. So, even if the bonds are polar within a molecule, they will cancel each other out and make the molecule nonpolar overall.

hazelyang2E

In addition, you can find the bond length of a molecule using its other properties such as ionization energy difference. So, if the ionization energy is greater, then the bond length will be shorter.

hazelyang2E

Yes, combustion reactions will always yield carbon dioxide and water. If there are other elements involved in the reaction then there will be other products.

hazelyang2E

When looking at the trend of ionization energy it can be helpful to look at the trend of atomic radii alongside it. Because the ionization energy is the energy required to remove an electron from an atom, the atomic radius, half the distance between the centers of neighboring atoms, can help to dete...

hazelyang2E

Yes! I believe that your assumptions would be correct based on what Professor Lavelle taught in lecture. He introduced the concepts of correcting BOTH the covalent and iconic models. For covalent models, he discussed the fact that electron pairs in covalent bonds may not be equally shared all the ti...

hazelyang2E

Most of the time you will not be asked to calculate the electronegativity of a specific element, but to find the difference between the electronegativity of two elements in order to determine what type of bond they will create. Generally, the electronegativity will be high if the ionization energy a...

hazelyang2E

You can also clearly see the trends in the periodic table as you write out the electron configuration for any given element. Because you write an element's configuration based on their physical position on the periodic table, the organization of the periodic table according to their chemical charact...

hazelyang2E

m labels the different orbitals of a subshell (l) and also determines the orientation. I think it would be a good idea to familiarize yourself wth this concept and to also know that m = l, l-1, ..., -l

hazelyang2E

I believe the terms shell and orbital refer to two separate phenomenons. "Shell" defines the energy level and size of the a wave function and is determined by the principle quantum number, or n. "Orbital" refers to the orientation of a specified subshell and is determined by the ...

hazelyang2E

This can also be explained through the concept of the effective nuclear charge which essentially says that because the inner electrons shield the outer electrons from electrostatic attraction of the positive nucleus, the outer electrons feel reduced electrostatic attraction. Because the s-electron i...

hazelyang2E

I believe Professor Lavelle said that this exam is only on the quantum world sections, so everything from after the last exam to today's lecture. You can also look at the exam outlines on Professor Lavelle's website for a comprehensive list of all of the topics and concepts we need to know for the e...

hazelyang2E

Professor Lavelle mentioned in lecture that while we should understand the basic concept of the Shrodinger Equation, he would not be expecting us to solve problems using the actual equation. In the exam outline posted on his website, it states that we should know the relationship between Shrodinger ...

hazelyang2E

Hi! I understand the general concept of photoelectric effect, but started to get confused once more specific concepts and examples were discussed during lecture. I was most confused by the diagram of the metal and the uv radiation that was pictured in the lecture slides and how the different formula...

hazelyang2E

Just like everyone else has already said, it's usually not recommended to round up or down by more than 0.1. So in your case, you would not want to round down 7.30 to 7. Everyone uses their own method to determine what factor to multiply their moles by, but personally I like to use a simple method o...

hazelyang2E

I believe that the Audio-Visual assignments are not a part of our grade because they are not listed in the grade breakdown in the syllabus and it also states on the actual assignment that the results are anonymous. However, both in class and in the syllabus, Professor Lavelle has states that these a...

hazelyang2E

1.001 would have 4 sig figs because the two zeroes are in between two ones which are significant figures. Zeroes are not considered significant figures when they are the leading or ending digits in a number. For example, both of the numbers 0.001 or 100 only have one significant figure because the z...

hazelyang2E

Yes, I believe the standard for most chemistry problems is to round of your final answer using the lowest number of sig figs presented through the original problem. For example, if you original problem gave you measurements such as 1.35, 1.445, and 0.0001, you would round off your final answer to on...

hazelyang2E

Yes, your inference is correct because when you are calculating the amount (in moles) of an element within a compound, you need to know the ratio of that specific element within your compound. So the calculation they used was: 71.587 mol UF6 x (6 mol F)/(1 mol UF6) = 429.48 mol F = 430. mol F So, if...

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