CHEMISTRY COMMUNITY

Presley Gao 2C

You would need at least 200 points to pass (out of a total of 400 points) since a 50% or higher is a passing grade for this course. Otherwise, standard grading metrics apply.

Presley Gao 2C

Yes, there is a Sapling assignment for both weeks 9 and 10, but to compensate for the final exam being on Sunday, the Sapling assignment is due Friday night instead of the usual Sunday night.

Presley Gao 2C

The final exam will be on Sunday from 9:30 A.M. PST to 11:00 A.M. PST, and a thermodynamics review session will be on Saturday from 8:00 A.M. PST to 10:00 A.M. PST.

Presley Gao 2C

Personally, to deal with burnout, I generally try to plan out my week so that I can distribute my workload more efficiently. In addition, setting time to exercise and relax certainly does wonders as this allows for better and mental health as well as a break of school.

Presley Gao 2C

Personally, in my own opinion, the most effective way to take notes in this class is to handwrite them, since for me handwriting my notes help me retain the information better than other methods such as typing them

Presley Gao 2C

The slowest step is considered the rate determining state because it takes the most time and the overall reaction will not finish until the slowest step is complete.

Presley Gao 2C

Yes, the rate constant (k) of reaction can change by a change in temperature only.

Presley Gao 2C

Intermediates cannot be in the rate law because they cancel out on both sides of the chemical equation.

Presley Gao 2C

As the reaction proceeds, the instantaneous rate decreases over time.

Presley Gao 2C

Chemical equilibrium and acids and bases.

Presley Gao 2C

No, you do not need to memorize the oxidation numbers - just a remember a few of the more general ones (like H and O are usually +1 and -2 respectively) and you should be fine - often times you can find the rest of the oxidation numbers that you do not already know from this information.

Presley Gao 2C

Just use the phase states from the original equation, since they should not really change, and when you add water and ions they are in liquid and aqueous states respectively.

Presley Gao 2C

Order doesn't really matter - as long as your reactants and products are correct and in their respective places before or after the chemical equation sign then you should be fine.

Presley Gao 2C

Yes, states of matter can cause an equation on Sapling to be wrong, so make sure to include the correct phase states.

Presley Gao 2C

Try refreshing the page or maybe clearing your cookies - hope this helps!

Presley Gao 2C

Yes, when we are adding equations, the same rules that apply to delta H also apply to delta S. This is because enthalpy and entropy are both state functions, so only the initial and final values matter, but not the path taken to get there.

Presley Gao 2C

It depends on the context of the question, so use whichever unit / conversion that more relevant and applicable to the problem. Generally, entropy is solved in J/K though.

Presley Gao 2C

Entropy is the measure of the disorder or randomness of a system. It is usually denoted with S.

Presley Gao 2C

It depends on the context of the problem. Use whatever temperature scale that is relevant to the question. In general, when doing calculations for thermodynamics, Kelvin is usually used at a greater frequency than Celsius, but whichever one is applicable to the problem is the one you should use.

Presley Gao 2C

Yes, a gas become more orderly when it liquefies. Yes, its entropy changes. Since the transition from gas state to liquid state is more "orderly," entropy decreases as its disorder decreases.

Presley Gao 2C

An example where work is done on the system, resulting in a positive value for work, would be compressing the system.

Presley Gao 2C

The R value you use is the one that cancels out the rest of your units - they are all equivalent, just in different units.

Presley Gao 2C

The key difference between a closed and an isolated system is that a closed system can exchange energy with its surroundings, while an isolated system cannot exchange anything with its surroundings. An example of a closed system would be a piston system and an example of an isolated system would be ...

Presley Gao 2C

Entropy is a measure of the chaos in a system. In terms of how important it is to know for the next midterm, knowing how it works and understanding its equations might help.

Presley Gao 2C

A state function is a function that does not depend on the path that is taken to get the final value. Free energy is a state function because only the initial and final values matter - the path taken does not, however.

Presley Gao 2C

The side of the equation the negative sign goes for is the side that is exothermic (q is negative).

Presley Gao 2C

Extensive properties depend on the amount of a particular substance that we are dealing with.

Presley Gao 2C

We know when q = delta U (internal energy) when w is 0 and thus delta V is 0.

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No, I don't think heat capacities be negative - they can only be positive because it's how much energy is heat is gained, so it is endothermic.

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We use the initial volume, so we use V1 for PV = nRT.

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It is fine or restricted to assume x is so insignificant we can keep it out when it is less than 5% of the initial concentration.

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No, there is not a difference between vapor and gas - they are the same thing and are considered interchangeable with each other and vice versa.

Presley Gao 2C

Heat is denoted with q and enthalpy is denoted with H, specifically.

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A phase change specifically means when a substance transitions from one phase to another. These phases include solid, liquid, gas, plasma, etc. These phase transitions are completely reversible and do not change the component of the substance - just its state.

Presley Gao 2C

Yes, endothermic reactions will always have a positive delta H, and yes, exothermic reactions will always have a negative delta H. There are no exceptions to this rule.

Presley Gao 2C

When finding out which side has the least amount of moles, you only include gases, but not aqueous solutions.

Presley Gao 2C

The concentration of the reactants and products remain the same when inert gas is added because inert gases are not chemically reactive, so they will not react with the reactants or products and thus their concentrations will remain the same.

Presley Gao 2C

The relationship between the Ka and how strong an acid is the larger the Ka the stronger the acid.

Presley Gao 2C

You find the H+ concentration from the pH from just taking 10 to the power of the negative pH.

Presley Gao 2C

We have to use the inverse of Kc or any K when we are considering the reverse reaction.

Presley Gao 2C

For this problem, you would have to set up an ICE table just like any other equilibrium - related question. Once you have solved for x and consequently the equilibrium pressures, you would have to add all of them to get the total pressure at equilibrium.

Presley Gao 2C

The changes in x should be +x for both N2(g) and O2(g) and -2x for 2NO(g). This is because since you are adding products, the equilibrium reaction will shift to the left to create more reactants to compensate for the change, and thus reactants will increase and products will decrease.

Presley Gao 2C

For this question, you would have to set up an ICE table. One tip is that you can just take the square root the Kc formula and the value for Kc to solve for x. Although this is a shortcut, I would not recommend using this and instead solve the entire quadratic formula since taking the square root of...

Presley Gao 2C

I would double - check with your TA, but I would recommend doing 5 Chemistry Community posts per week for the duration of the 10 weeks. Not only does this minimize risk in terms of getting the 50 points for your 50 posts total, but it will also help keep you on track with the material.

Presley Gao 2C

Yes, exams are being held during lecture this quarter - this includes both midterm and final exams. This information comes from both the Syllabus and the Exam Schedule. The midterms are 50 minutes and the final is 1 hour and 30 minutes.

Presley Gao 2C

Molarity (or concentration) is represented in moles / volume, which is the respective unit of measure for molarity (or concentration).

Presley Gao 2C

You can find your posts my clicking on "Quick Links" and then "Your Posts." Sometimes, there is some discrepancy with the number of times you've actually posted and the displayed number, so be sure to double - check and refresh the page often.

Presley Gao 2C

Yes, it is 5 posts per week for a total of 50 posts (50 points). I personally have my display name as my full name and discussion section, but your account is linked to your UID so that grading our posts would be easier.

Presley Gao 2C

Yes, what is due each week are 5 posts on Chemistry Community and the Sapling assignments. Both are 5 points each for the 10 weeks, for a total of 100 points for both combined.

Presley Gao 2C

Try to go to as many TA review sessions as possible, and practice as many problems as you possibly can.

Presley Gao 2C

CaO is a strong base because it fully dissociates to give ions in solution.

Presley Gao 2C

Lewis acids are electron - pair acceptors and Lewis bases are electron - pair donors.

Presley Gao 2C

The definitions of a Lewis acid and base that Dr. Lavelle wants are electron - pair acceptor and electron - pair donor, respectively.

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Oxoacids are acids that contain oxygen. To be more specific, oxoacids are acids that contain oxygen, contain at least one other element, have at least one hydrogen atom bonded to oxygen, and form an ion by the loss of one or more protons in solution.

Presley Gao 2C

The difference between the terms cis and trans is that cis means polar and trans means nonpolar.

Presley Gao 2C

What the brackets signify when they are around the compound is a coordination compound.

Presley Gao 2C

The final exam is cumulative, so we can just base off what we need to know by using the outlines.

Presley Gao 2C

The roman numerals represent the oxidation number of the metal ion.

Presley Gao 2C

An oxidation number is a number associated with the charge that an atom would have if the compound was composed of ions.

Presley Gao 2C

I personally don't think we will ever have to draw molecules in such a way that was similar to what was on the test - it is most likely for a future chemistry class (nonetheless, you will be better off safe than sorry if you prepared so).

Presley Gao 2C

Lone pairs around a central atom affect the bond angles in a molecule by decreasing them due to the repulsion between electrons.

Presley Gao 2C

Whenever there's only one X or one E, we do not have to write a subscript of "1" - we just write "X" and "E," respectively.

Presley Gao 2C

Yes, the final is cumulative.

Presley Gao 2C

If one bond were to be broken, what happens to the melting point is that it decreases.

Presley Gao 2C

It is generally not recommended to look at a molecule's geometry / shape when determining if it's polar or non polar. It is best to use the VSEPR model and calculate the actual dipole moments to see if they add up to a net value of 0. If they do, the molecule is non polar, and if they do not, the mo...

Presley Gao 2C

We should know all of the ones on the chart instead of only the ones Dr. Lavelle went over in class for Test 2. It's better to be safe than sorry.

Presley Gao 2C

When determining if a molecule is polar or non polar on the test, it is not expected of us to know the electronegativity values of the elements in the given molecules. Just know the periodic trends for electronegativity and you should be fine.

Presley Gao 2C

In terms of studying for VSEPR for Test 2, just do as much practice problems as you can - the more the better. In terms of "good" practice problem suggestions, start by completing all the practice problems in the Molecular Shape and Structure unit outline (although only 5 are required for ...

Presley Gao 2C

We do not have to know hybridization for Test 2 (as stated by Dr. Lavelle in class). However, pi and sigma bonds will be on Test 2, for which Dr. Lavelle will cover those topics in class on Monday. Essentially, Test 2 will cover all the material covered in class up until Monday after the midterm exam.

Presley Gao 2C

Resonance structures are two or more forms of a molecule where the chemical connectivity is the same but the electrons are distributed differently around the structure.

Presley Gao 2C

Electronegativities generally increase from left to right across a period. This is due to an increase in nuclear charge. Electronegativities generally decrease from top to bottom within a group due to the larger atomic size.

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Yes, both depend on how you count the shared bond. The first equation treats the number of bonds as how many "lines" you draw as bonds, while the second equation treats the number of bonds as the amount of valence electrons that are shared in total between an atom and another respective at...

Presley Gao 2C

Yes, we want to make it so that the central atom has a formal charge of zero, or as close to zero as it can get - that would be the ideal situation.

Presley Gao 2C

We should write out the entire equation for formal charge on the midterm instead of just calculating it in our head and writing the formal charge by the element because not only will writing out the entire equation for formal charge make it easier to organize both your thoughts and work, but it will...

Presley Gao 2C

The trends for valence electrons are as follows: in a period, the number of valence electrons increases as we move from left to right side and in a group, the number of valence electrons remains the same.

Presley Gao 2C

Since this topic has not been covered in - depth yet in the lectures, you shouldn't worry too much about it. But, in general, it is better to be safe than sorry, so when drawing Lewis structures on tests, you should angle the bonds in the correct ways.

Presley Gao 2C

The concept of the octet rule is that elements tend to bond in such a way that each atom has eight electrons in its valence shell, giving it the same electronic configuration as a noble gas.

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When we draw the Lewis structure, we know which atom is in the middle in that usually the central atom will be the one that has the most unpaired valence electrons - usually it is also the least electronegative.

Presley Gao 2C

For homework this week, we can do either quantum to review or chemical bonding. I personally did chemical bonding for homework, but it doesn't really matter to your designated TA as long as the material has been recently covered in lectures.

Presley Gao 2C

For both the midterm and future tests, we should write the whole electron configuration instead of the shorthand notation because not only will you be more safe than sorry, you will gain better understanding of how to write electron configurations accurately.

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The difference between electron affinity and ionization energy is that electron affinity gives the amount of energy released when an atom gains an electron, and ionization energy is the amount of energy required to remove an electron from an atom.

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The magnetic quantum number m l determines the number of orbitals and their orientation within a subshell. Consequently, its value depends on the orbital angular momentum quantum number l. Given a certain l, m l is an interval ranging from –l to +l, so it can be zero, a negative integer, or a positi...

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Electron spin, s, has only two possible values: $+\frac{1}{2}$ and $-\frac{1}{2}$ , representing whether the electron is "spin - up" or "spin - down," respectively. Electron spin determines if an atom will or will not generate a magnetic field.

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The s subshell has 1 orbital that can hold up to 2 electrons, the p subshell has 3 orbitals that can hold up to 6 electrons, the d subshell has 5 orbitals that hold up to 10 electrons, and the f subshell has 7 orbitals with 14 electrons.

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In the photoelectric effect, if the energy of the photon is equal to that of the work function (i.e. no kinetic energy), what would happen is that the energy threshold will be met and the electron will be ejected.

Presley Gao 2C

In general, no memorization is required to solve a problem - everything you need will be given on the formula sheet. However, in this case, knowing the region of the frequency / wavelength of the electromagnetic spectrum will certainly be beneficial for you, both in terms of your chemistry knowledge...

Presley Gao 2C

In general, no memorization is required. All the information you will need to solve a problem will be given on the formula sheet.

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keV is the abbreviation for kiloelectron volts, a unit of energy equivalent to the kinetic energy gained by an electron falling through a potential of 1 volt.

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The unit for E is always implied as being J / photons, but if you want to convert to J / atoms, you must use Avogadro's number.

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Our final grade is calculated on a point system (specifically 500 points). Take a peak at the syllabus posted for more information.

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The effect shielding has on the atomic radius is that it prevents outer electrons from being attracted to the nucleus. Thus, since they are loosely held, the resulting atomic radius is large.

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In general, no memorization is required for tests, but you should be familiar with the majority of the elements listed on the periodic table.

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Electronegativity is a chemical property that describes the tendency of an atom to attract a shared pair of electrons toward itself. Electronegativities generally increase from left to right across a period and generally decrease from top to bottom within a group.

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In this case, the equation says that the energy of a particle of light is proportional to its frequency by a constant factor. Therefore, this equation can be used to calculate the energy required to remove an electron.

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Formula units are empirical formulas of any ionic or covalent network solid compound used as an independent entity for stoichiometric calculations. It is the lowest whole number ratio of ions represented in an ionic compound. There are 6.022 * 10 ^ {23} (Avogadro's number) formula units in 1 mole of...

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Molarity represents the concentration of a solution (specifically the number of moles of solute per liter of solution). You would need to calculate molarity in a wide variety of various situations, including calculating the moles of a solution, calculating the volume of a solution, calculating the m...

Presley Gao 2C

No, we cannot use fractions to balance chemical equations. We can use fractions in the process of balancing chemical equations, but in the end we should obtain whole number coefficients by multiplying each and every coefficient by the denominators of each and every fraction coefficient.

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In chemical reactions atoms are not created or destroyed. Total mass before = total mass after. The law of conservation of mass states that the total atoms of reactants = the total atoms of products, so you cannot add reactants or products to a chemical equation.

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The empirical formula of a compound gives the simplest whole - number ratio between the numbers of atoms of all the elements present in the compound.

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