CHEMISTRY COMMUNITY

Aleeque Marselian 1A

If the value of K is less than 10^-3 then the assumption can be made that x is very small and would be negligible.

Aleeque Marselian 1A

The equilibrium value, K, is a ration of products to reactants, so mathematically the units should cancel out and the calculation would not have units.

Aleeque Marselian 1A

With most examples, the slow step should be identified. However, if we're given the rate law, we should be able to pinpoint the step out of a list based on this information.

Aleeque Marselian 1A

n is the number of electrons transferred after you've balance the oxidation and half reactions.

Aleeque Marselian 1A

Dr. Lavelle usually sends an email or announces the date of the review sessions in class. Usually it starts during week 10!

Aleeque Marselian 1A

It depends on what your TA prefers, but usually you would do problems based on the information we're covering in lecture. However, I'm pretty sure you could include a few problems from previous topics.

Aleeque Marselian 1A

The test covers everything we learned after the midterm until the end of week 7. Dr. Lavelle's website gives more information regarding the test. "Test 2 covers all topics on Gibbs free energy and electrochemistry up to but not including the Nernst equation (which is all the new material covere...

Aleeque Marselian 1A

I believe Gibbs Free Energy should almost always be measured in kj overall, however if the question asks for the Standard Gibbs Free Energy of formation of the reaction then the units should be kj/moles. Hope this helps!

Aleeque Marselian 1A

The salt bridge keeps solutions from mixing. It consists of a gel containing a concentrated aqueous salt solution in an inverted U-tube and allows the flow of ions, which done affect the cell reaction. The salt bridge completes the circuit.

Aleeque Marselian 1A

The final exam is scheduled for Sunday, March 17th from 11:30-2:30.

Aleeque Marselian 1A

I was planning on taking math, chem 14c, cheer 14bl, and a lab! I heard a lot of people combine 14c and 14bl and because 14bl is a lab, worth 3 units, it's not as much work as adding an entirely new class. A lot of people told me it's more busy work. Hope this helps.

Aleeque Marselian 1A

Electrochemistry and Gibbs Free Energy!

Aleeque Marselian 1A

Try your best to use atm, since the gas constant (R) is in terms of atm.

Aleeque Marselian 1A

Dr. Lavelle said in lecture on Friday that Gibbs Free Energy won't be on the midterm, which is section 4J. Therefore, I'm assuming everything from 4F-4I can be on the midterm.

Aleeque Marselian 1A

This is the equation and constant sheet on Dr. Lavelle's website. https://lavelle.chem.ucla.edu/wp-content/supporting-files/Chem14B/Constants_Equations.pdf
Hope this helps!

Aleeque Marselian 1A

I know that they do not need to be taken together, but I remember Dr. Lavelle saying in the beginning of the quarter that knowledge from 14B is needed for 14 BL, so it should be taken after. You can take 14 C and 14 BL together (I know multiple people who have done this), but it isn't required.

Aleeque Marselian 1A

qv is heat at constant volume, while qp is heat at constant pressure, as denoted by the subscripts. The question would typically ask you which one to solve for or would typically state which one is constant. Hope this helps!

Aleeque Marselian 1A

J.C^-1.mol^-1 = J/C.mol

Aleeque Marselian 1A

The ideal gas law (PV=nRT) can be used to solve for any of the variable in it and can also be used to convert between partial pressure and molar concentration.

Aleeque Marselian 1A

Heat and work aren't state properties because you would need to evaluate the path taken in order to determine its value, whereas with state functions only the final and initial values are needed.

Aleeque Marselian 1A

Yes the state of matter will definitely affect enthalpy because different amounts of heat are required to change a substance through each phase.

Aleeque Marselian 1A

You can approximate the x in the denominator when the value of K is less than 10^-3. However, it is not mandatory and you would still get the same value of x if you choose not do use the shortcut.

Aleeque Marselian 1A

Most of the time the quadratic formula needs to be used unless K<10^-3 in which case you can approximate the equation and get rid of the need to use the quadratic formula.

Aleeque Marselian 1A

We use the ideal gas law to convert between partial pressure and molar concentration. R is a constant, therefore it will always be give and T will most probably be given in order to find either P or n/v.

Aleeque Marselian 1A

Kelvin is the most commonly and used unit for temperature when solving problems regarding equilibria. When using the formula PV=nRT, for example, the unit for temperature must be in Kelvin.

Aleeque Marselian 1A

Only temperature effects and changes the equilibrium constant K. Pressure, volume, and concentration adjust to match the same result as the equilibrium constant.

Aleeque Marselian 1A

An aqueous solution is a mixture of something with water, therefore water can be referred to as a solid, liquid, or gas, but cannot be considered aqueous.

Aleeque Marselian 1A

Yes, based on Dr. Lavelle's slides in lecture, the temperature in the ideal gas law is measured in Kelvin.

Aleeque Marselian 1A

The formula to find K and Q are the same. However, K is the ratio of at equilibrium and therefore includes the values of the reaction at equilibrium. Meanwhile, Q is the reaction quotient and is the ratio at any given time in the reaction.

Aleeque Marselian 1A

Since the products are not gases, you put a 1 in the numerator. Then place the reactants that are gases in the denominator. Hope this helps!

Aleeque Marselian 1A

The final will be cumulative and will cover everything on the syllabus.

Aleeque Marselian 1A

Dissociation energy is always positive because it is the energy required to break a bond, therefore it would require an input of energy, which is always positive. However, to form a bond, energy would have to be released, resulting in a negative charge.

Aleeque Marselian 1A

There are two pi bonds and one sigma bond in a triple bond.

Aleeque Marselian 1A

The trend for polarizability is the same as the trend for atomic radii. Therefore it generally decreases when moving left to right on a period and increases when going down a group.

Aleeque Marselian 1A

The octahedral shape is almost always non polar because it is symmetric, causing the dipole moments to cancel one another. Hope this helps!

Aleeque Marselian 1A

It doesn't matter. Professor Lavelle showed the class both because the book shows it differently, so it's just based on preference.

Aleeque Marselian 1A

Test 3 covers: End of Bonding from 3.12 (6 Ed.) and from 2D (7 Ed.); and all of Molecular Shape and Structure (see Syllabus and Outlines for details).

This is from Dr. Lavelle's class website. Hope this helps!!

Aleeque Marselian 1A

A is the central atom, X is the number of bonded pairs, ad E is the number of lone pairs. Therefore, you can figure out a molecules AXE by looking at the molecule.

Aleeque Marselian 1A

Bond angles of a seesaw are <90 and 120 degrees.

Aleeque Marselian 1A

In my opinion, it is always better to show work just in case. Especially if the grader prefers to see the steps.

Aleeque Marselian 1A

Yes, Hydrogen Bonds are a type of dipole-dipole force that only occurs with Nitrogen, Oxygen, and Fluorine.

Aleeque Marselian 1A

On Professor Lavelle's website, it says the next test will be administered starting November 27th in discussion classes. So, after Thanksgiving break.

Aleeque Marselian 1A

Elements on and after period 3 can have an expanded octet because they have a d orbital, where they can accommodate more electrons in. Common ones include, Sulfur, Phosphorous, and Chlorine.

Aleeque Marselian 1A

Phosphorous, Chlorine, and Sulfur can accommodate more than eight electrons and therefore break the octet rule because they contain a 3d orbital.

Aleeque Marselian 1A

Yes, we still have homework due in our discussion class.

Aleeque Marselian 1A

Yes!! Ionic bonds are always between metals and nonmetals, while covalent bonds are between two nonmetals.

Aleeque Marselian 1A

Although most of the time it doesn't have a drastic difference, it's better to apply significant figures for the final answer only. This way, your final answer can be more accurate, since no numbers were rounded in the process. Hope this helps!

Aleeque Marselian 1A

The sum of the formal charges of individual elements in an ion should add up to the overall charge of the ion. Hope this helps!

Aleeque Marselian 1A

Although they look similar, the symbols used for velocity and frequency are not the same. The symbol for frequency is the Greek letter nu, while velocity is denoted the the lowercase letter v.

Aleeque Marselian 1A

A nodal plane is a plane, where the probability of finding an electron is zero. For example, the p orbitals have one nodal plane and d orbitals have two.

Aleeque Marselian 1A

On the class website, Professor Lavelle stated that Test 2 will cover the information relating to the quantum world up to quantum numbers. So no, we don't need to know electron configurations for this upcoming test. "Test 2 covers all quantum material up to and including quantum numbers (all qu...

Aleeque Marselian 1A

I'm pretty sure that for this class, we treat the speed of light as a constant all the time.

Aleeque Marselian 1A

The Heisenberg Uncertainty Principle states that there is a limit to the accuracy of determining both the position and momentum of an electron because photons change the path of the electron. Therefore, if the path is uncertain, so is the velocity and momentum. The Heisenberg Uncertainty Principle p...

Aleeque Marselian 1A

The precise value of the distance (x) and momentum (p) of an electron cannot be precisely known because the photons it is exposed to will affect the electron's path. Therefore, the distance of the electron is unknown, creating uncertainty in its velocity and momentum. The value of the position and m...

Aleeque Marselian 1A

The terms reactant and reagent are usually used interchangeably and therefore it does not make much of a difference which one you use. However, for a detailed explanation, a reactant is a substance consumed during a chemical reaction, while a reagent refers more to the substance used in chemical ana...

Aleeque Marselian 1A

All mass percent composition questions should provide you with information adding up to 100 or should give you a solution that is equal to 100. If not there is either in error in the question or the method used to solve.

Aleeque Marselian 1A

It depends on the units being asked for in the original question. However, if the answer itself is correct the units should not matter, unless the question has asked for the answer to be in mL or L.

Aleeque Marselian 1A

Both notations are virtually the same because g.mol^-1 is rewritten as g/mol when the negative exponent is moved to the denominator in order to make it positive. Therefore, the use of one of the notations is based on personal preference. Hope this helps!!

Aleeque Marselian 1A

It is best to not round the atomic weight in order to produce a more accurate result, especially when having to conform to the appropriate number of significant figures. However, if the number is very long, I usually round to the nearest thousands place.

Aleeque Marselian 1A

Significant figures only come into play when the final answer is being evaluated. Therefore, a more accurate answer would be calculated if you used the exact molar mass and then rounded your final answer to the appropriate number of significant figures, in this case two.

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