CHEMISTRY COMMUNITY

taline_n

on the unit outlines, some bullet points do state that we should know how to derive certain equations (like integrated rate laws). I would know it just in case; Dr. Lavelle went over the process several times in lecture so it could definitely be something we're tested on.

taline_n

no, although K=k1/k1' that doesn't mean that k1=k1'

taline_n

The "A" is known as the frequency factor, or the pre-exponential factor. This represents the amount of times a collision between molecules happens at the correct orientation.

taline_n

Usually, if you're given components of the integrated rate law (such as initial concentration, final concentration, k or time) and told to solve for one variable, you can plug it into the equation and solve. As far as key words go, the question will have to tell you that the reaction is first order....

taline_n

When NO is doubled and the rate increases by 4, you have the equation 2^n=4. the 2^n represents the concentration of NO to the power of the order (n), and the 4 represents the rate. Therefore, n=2 and the NO is second order. When both NO and O2 are doubled and the rate of the reaction increases by 8...

taline_n

The rate of the reaction will always be in terms of mol/L•s, but the units for k changes based on the overall order of the reaction. If order=1, the unit for k is s^-1. If order=2, the unit for k is L/mol•s. If order=3, the unit for k is L^2/mol^2•s.

taline_n

To calculate the order for C, I used experiments 1 and 4. I divided experiment 1 ([A]=10^x, [B]=100^y, [C]=700^z) by experiment 4 ([A]=10^x, [B]=100^y, [C]=400^z). The rates for exp 1/exp 4 are 2/2=1 (so your order for C will have to result in a rate of 1). [A] and [B] cancel out, so you're left wit...

taline_n

When the graphs of reactants and products have leveled off and remain at a constant concentration, the system has reached equilibrium.

taline_n

The solid should always come first, then aqueous and gas substances. The solid stands for the anode/cathode, so it should always go on the ends. As for the order of aqueous/gas solutions, I'm not too sure if there's any particular way to write them; Dr. Lavelle hasn't specified so I would think it d...

taline_n

no, but it is safe to assume that the reverse reaction is very unlikely to occur.

taline_n

When the half-reaction for either reduction or oxidation doesn't contain a solid (reactants and products are both in aqueous form), you would have to use either Pt (s) or C (graphite) as the electrode. Usually, we use Pt (s).

taline_n

the anode is where oxidation takes place (the reaction that loses electrons; or electrons show up on the products side). the cathode is where reduction takes place (the reaction that gains electrons; or electrons show up on the reactants side). a good way to remember this is that anode and oxidation...

taline_n

electromotive force is the difference in cell potential (Ecell) that gives rise to an electric current.

taline_n

we won't be expected to have standard enthalpies/entropies of formation memorized for any compound, unless enough information is given for use to solve otherwise. most likely it'll be given to us in the question if we're asked to solve for free energy.

taline_n

this value can either be Cv or Cp (equations for heat capacity of monoatomic ideal gases are on our equations sheet) depending on which one is constant in the reaction, volume or pressure.

taline_n

1. calculate the entropy from the ΔV, by using the equation ΔS=nRlnV2/V1
2. calculate the entropy from the ΔT, by using the equation ΔS=nCvlnT2/T1
3. since entropy is a state function, you can add these values together to get your total entropy of the change in volume and temperature.

taline_n

There are certain elements of a system that are true when the observed substance is an ideal gas. Cv and Cp do have specific equations, depending on whether that gas is monoatomic, linear, or nonlinear (equations are on equation sheet). There are other factors that are true, such as ΔU=0 for isother...

taline_n

The values of enthalpy you should be using to calculate the total enthalpy of the reaction (ΔHrxn) are the bond enthalpies (ΔHb) and they will be given to you in a table. As for determining which bonds are broken/formed, I personally benefit from drawing out the Lewis Structures and from there, visu...

taline_n

the enthalpy for a reaction is the heat released/abosrbed per mole in the reaction; therefore use kJ/mol

taline_n

since the reaction is happening out in the open (open system), we can assume that the only pressure acting upon it is atmospheric pressure, which is constant (1 atm).

taline_n

A reversible process is one that is infinitely slow because it is at equilibrium (any slight change to the reaction can cause a shift, which is why it's called reversible). If the system is doing work on the surroundings, more work is done if the process goes by slowly (because then, less heat is lo...

taline_n

The X axis represents temperature, while the Y axis represents heat. The slated lines represent the water at a set phase, increasing in temperature. As heat is supplied, the slope increases and the temperature of water rises, but the phase does not change. The straight lines represent water going th...

taline_n

usually, the final and initial volumes will be included in the question.

taline_n

(a) for this part of the problem, we use w=-(Pex)*(deltaV). from the question, we know that the change in volume is 1.20 L. w=-(1.00 atm)*(1.20 L) = -1.20 L atm. Then, convert to Joules. -1.20 L atm x (101.325 J/L atm) = -121.59 J. (b) since the expansion is reversible and isothermic, we use the equ...

taline_n

will we be expected to derive 14 = pOH + pH from 10^-14=[H3O+][OH-] on the test?

taline_n

If Ka1>>Ka2 (which means if the number is at least 10^3 times bigger), only use the first deprotonation.

taline_n

Molarity is the measure of the amount of moles / liters of a substance in a reaction. Questions asking about the effect of adding or removing certain substances are usually looking for us to answer which reaction proceeds (the forward reaction which yields products, or the reverse reaction which yie...

taline_n

An easier way to remember this is that if the reaction is endothermic and the temperature is increased, products are formed. If the reaction is exothermic and the temperature is increased, reactants are formed.

taline_n

All chemical reactions require energy to break bonds OR release energy when new bonds are form. It's highly unlikely that these energies will equal one another within the same reaction and "cancel out", therefore each reaction is classified as either endothermic or exothermic. I don't thin...

taline_n

If you're having trouble solving part c, the way I did it was by multiplying the initial pressure of X2 (.1 bar)*(1-.545), to find the pressure of X2 molecules at equilibrium (.1 bar)*(100% X2 molecules - 54.5% decomposed X2 molecules). You'll get 0.0455 bar, which is the pressure of X2. To find the...

taline_n

When asked to write out the equilibrium constant for an equation, is Kp or Kc preferred?

taline_n

Q is the reactant quotient, which is a number that changes throughout the course of the reaction, depending on how much product vs. reactant is formed. K is the equilibrium constant, which is an unchanging number that is specific to each equilibrium reaction. Q and K are calculated in the same way (...

taline_n

On the test, I would write aqua as (OH2), as how it's listed on the table in the textbook.

taline_n

I'm not too sure about bases, but acid strength is determined by bond length and stability of the anion in the compound. The longer/weaker the bond between the atoms, and the more stable the anion, the stronger the acid. For example, HI is a stronger acid than HF because I is a larger atom than F, m...

taline_n

The definitions of Bronsted and Lewis acids/bases are different, therefore some compounds like AlCl3 can be one and not the other. Bronsted acid: proton donor Bronsted base: proton acceptor Lewis acid: electron acceptor Lewis base: electron donor Al cannot donate protons, but accepts electrons from ...

taline_n

Do we need to memorize the ligand names listed in ONLY table 9C.1 for the final?

taline_n

On the syllabus it says we should " be familiar with the rules for naming coordination compounds". What exactly does this entail? Should we know how to name complicated compounds, or will we just be asked to state the general rules for naming?

taline_n

the definition of a Bronsted Acid is "a solution that has an excess of H+ ions", which means that Bronsted Acids are basically proton donors. The strength of the acid is determined by it's dissociation, but just the sole fact that it dissociates to some extent isn't enough to label the com...

taline_n

Unfortunately there's no chart, you have to have all the bond angles memorized.

taline_n

Lone pairs do affect the shape of the VSEPR model. Since lone pairs count as a region of electron density, they contribute to the formation of the structure, therefore to the overall molecular shape as well (lone pair electrons repel the atoms further away and change the shape and bond angles). Howe...

taline_n

How can we tell when we're supposed to draw regular Lewis structures vs. the separated Lewis structures with charges? For questions 2B.9 and 2B.11 in the textbook (7th edition), the question is the same ("Draw the complete Lewis structure for each of the following compounds") yet the answe...

taline_n

For test 3 will we need to know the VSPER formulas / molecular shapes for compounds with more than 2 electron pairs on the central atom?

taline_n

When drawing lewis structures, the first rule to fulfill is the octet rule. Formal charges come after, as a way to guide you to the correct structure by adding and rearranging double/triple bonds to lower the formal charges of each atom. However, the octet rule comes first. Each atom must have an oc...

taline_n

Ideally, a nonzero formal charge should be located on the outer atoms rather than the central atom. If there's no way of avoiding a formal charge on the central atom, it should be the smallest nonzero formal charge out of all the atoms in the compound.

taline_n

A dipole - induced dipole is when 2 compounds, one of each kind (such as HCl which has a dipole moment and N2 which does not), are attracted to one another. N2 has a lone pair of electrons on each N atom, which is slightly negative, but not strong enough to have a dipole moment. When the slightly ne...

taline_n

Elements in the 3rd period and below can have more than an octet because they can access their d orbital electrons, while other elements without d orbital electrons (in period 2, such as C,N,O) cannot, therefore restricting them to only having 8 electrons.

taline_n

In induced dipole-induced dipole bonds, molecules from 2 compounds that do not have a dipole moment (like N-N) are attracted to each other due to slight charges acquired through the electron clouds of each molecule. The electrons surrounding an atom "fluctuate", and create a (+) or (-) cha...

taline_n

Bond lengths are averaged in resonance hybrids; whether it's a single bond or double bond, the average between them is the number used for bond length in the molecule as a whole.

taline_n

I use the equation deltaE = -hR((1/nfinal^2) - (1/ninitial^2)) In this situation, since light is emitted, deltaE is negative as well, and deltaE can be rewritten as hv (h x nu). -hv = hR((1/nfinal^2) - (1/ninitial^2) The two negatives cancel out, and the two Planck's constants cancel out, so you're ...

taline_n

The formal charge only pertains to each individual atom in a molecule. The molecule as a whole will always remain one indicated charge. For example, SO4^(-2) will always have the charge of -2, although depending on the structure of the molecule, the formal charges for the individual S and O atoms ma...

taline_n

We also find the formal charge of each atom to determine the most stable Lewis Structure of the ion. The closer an atom's formal charge is to equaling 0, the more stable the structure is.

taline_n

Will our midterm only be covering the Review of Chemical and Physical Properties, The Quantum World, and Chemical Bonds?

taline_n

no, she didn't specify!

taline_n

I asked a UA and she said that no more online modules will be posted for the rest of the quarter.

taline_n

(a) false; the effective nuclear charge (Zeffe) IS dependent on the number of electrons in an atom. The effective nuclear charge is the charge experienced by the electrons themselves, so the physical number of electrons affects the value of Zeffe. (b) true; s-orbital electrons are closer to the nucl...

taline_n

We'll also have a reference sheet of all the equations / constant values needed for each test stapled to the front (like we just had on test #1), so no need to stress over memorizing!

taline_n

This doesn't have to do with the physical textbook, but does anyone know if we'll be needing the access code for chem 14A at all?

taline_n

Thank you! These are an immense help (especially for studying for the tests)

taline_n

What kind of device would be used to detect the electrons removed from photons bouncing off the metal? (from the experiment we went over in lecture)

taline_n

I think viewing the video modules is the best way to review topics you didn't understand in lecture; as far as the textbook goes, it's a great resource for more examples and longer descriptions/definitions of terms and concepts!

taline_n

The test will only be covering what we learned in high school chemistry, which is the "Review of Chemical and Physical Principles" unit we just learned.

taline_n

Do our 3 posts a week need to fall within the Monday-Friday of said week, or do weekends count as well?

taline_n

Today in lecture we learned the SI units for: mass (kg), length (m), time (s), volume (m³), density (kg/m³), and the prefixes specific to those units. Since our first test is a only a review of high school chemistry, these should be all we need to know! I hope this helps :)

taline_n

On the syllabus it says one of the homework problems from each unit will be on the test, so I think it's best to try to do all of them, then choose whichever 7 you're most confident on to turn in for homework credit!

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