CHEMISTRY COMMUNITY

LaurenJuul_1B

calculate the equilibrium constants for the following reactions: a. Mn(s) + Ti^2+(aq) <--> Mn^2+(aq) + Ti(s) b. In^3+(aq) + U^3+(aq) <--> In^2+(aq) + U^4+(aq) for part a, I split the equation into two reactions, Mn(s) --> Mn^2+(aq) +2e- Ti^2+(aq) + 2e- --> Ti(s) then I found the E for each one, -1.1...

LaurenJuul_1B

the second part of this question gives [A]0 = 0.15 mol/L and [B] = 0.19 mol/L for the equation A --> 2B + C

how do I turn the 0.19 mol/L of B into the [A]t I need to be able to calculate the time it takes for the reaction to take place?

LaurenJuul_1B

The reaction won't shift because the partial pressures of the reactants and the products are not altered when the gas is added. an inert gas is basically a noble gas, so it does not undergo chemical reactions because it is so stable. it is unreactive so it does not impact the chemical equation/react...

LaurenJuul_1B

if there is no solid/conductor on either your cathode or anode side of the cell diagram, you need to add platinum

LaurenJuul_1B

basically if you notice in your cell diagram that there is no solid/conducting component, you add platinum to either the cathode, anode, to both depending on which is missing a conductor.

in general, if there is no solid in the cell diagram you need to add platinum

LaurenJuul_1B

they are both the same and will give the same value. it is up to you which is easier to visualize and use in the equation

LaurenJuul_1B

you also need to know how to derive the rate laws for zero, first, and second order reactions

LaurenJuul_1B

an intermediate appears in multi-step reactions and is basically something that is formed during the first step of the reaction and is then subsequently used in the following step of the reaction. So, it goes from being a product to being a reactant and will be canceled out from your final equation.

LaurenJuul_1B

reaction orders can only be determined experimentally, so it could be a first order but is not necessarily

LaurenJuul_1B

an intermediate is formed and then used up in the reaction

a catalyst is there the whole time and is not used up in the reaction

LaurenJuul_1B

What should you do if no one laughs at your chemistry jokes?
Keep telling them until you get a reaction.

LaurenJuul_1B

Two chemists walk into a bar.
One says, “I’ll have an ‎H2O.” The other says, “I’ll have an ‎H2O, too.”
The second chemist dies.

LaurenJuul_1B

When you are given a chemical reaction and the final concentration of one of the products, how do you translate that to the final concentration of the reactant over your given time interval? For example, if A --> 3B and we know reactant A began with .012 moles and then over the time period the conce...

LaurenJuul_1B

never mind--I just made a mistake.

the Mn actually starts as 7+ so it makes sense now

LaurenJuul_1B

(a) write the balanced half-reactions for the redox reaction of an acidified solution of potassium permanganate and iron (II) chloride. (b) write the balanced equation for the cell reaction and devise a galvanic cell to study the reaction (write its cell diagram). so the reaction itself would be MnO...

LaurenJuul_1B

this question asks you to depict the process of the reaction in question 5G.13 graphically. In the back of the book, it indicates a decrease in the partial pressure of I (reactant) and an increase in the partial pressure of I2 (product) over time until they reach equilibrium. In question 13, however...

LaurenJuul_1B

you use the different equations depending on which initial conditions you are given and what variables are changing/remain constant in the system

LaurenJuul_1B

n is the number of molecules, not individual atoms

LaurenJuul_1B

W=(# of micro states)^(# of molecules)

or using s=kb(ln(W))

LaurenJuul_1B

delta S is zero when there is no change in the disorder of the system between the initial and final values

S itself I think can be zero if you have a perfect system, but I'm not 100%

LaurenJuul_1B

Did you know that you can cool yourself to -273.15 degrees Celsius and still be 0K?

LaurenJuul_1B

it means that you can use the equation w=-PdeltaV

LaurenJuul_1B

^ yes I think that is correct. the system will spontaneously approach equilibrium, but will not be spontaneous when at equilibrium exactly because it does not want to leave equilibrium

LaurenJuul_1B

5/2 is for when pressure is constant and 3/2 is for when volume is constant

LaurenJuul_1B

only is the H2O is a gas it will be used. if it is a liquid then it will not be in the keq or in the ICE table

LaurenJuul_1B

enthalpy is the heat released from the system and entropy is the amount of disorder of the system

LaurenJuul_1B

it is a specific arrangement of the molecules. different micro states have different energy levels and having multiple micro states increases the entropy of a system

LaurenJuul_1B

Cl2 is the more stable one.
The ratio for Cl2:Cl is greater than F2:F. This shows that Cl2 is more stable because at equilibrium, chlorine favors the reactants more. So basically, whichever K is smaller is the reaction that is more stable.

LaurenJuul_1B

Use the information in table 5G.2 to determine the value of K at 300 K for the reaction 2BrCl(g) + H2(g) --> <-- Br2(g) + 2HCl(g) How do you use the table to determine this? I'm a bit stuck because I'm not sure which reaction to use in the table since none match the one given. Would I use the first ...

LaurenJuul_1B

In regards to the question above, when is Kp used? Kp is the same as Kc, but it just represents the equilibrium constant as a value of partial pressures rather than molar concentrations. You can use the equation mentioned in the responses above to convert between the two. You just must make sure th...

LaurenJuul_1B

Think about when you reverse a reaction. The reactants and products will get flipped, so similarly, you just have to flip your value of Kc (take the inverse) and you will get the Kc of the reverse reaction since Kc is just a ratio.

LaurenJuul_1B

the change in concentration is too small and can be omitted--only worry about non-pure substances that are aqueous or gaseous

LaurenJuul_1B

yes. shape depends entirely on what is connected to the central atom. AlCl3, for example, is trigonal planar even though each of the chlorines has 3 pairs of lone electrons

LaurenJuul_1B

a neutral ligand has no affect on the charge of the compound. like H2O for example

LaurenJuul_1B

just add up all of the charges of the transition metal and ligands

LaurenJuul_1B

I'd say memorize. better safe than sorry-plus some of the practice problems use those

LaurenJuul_1B

if the two atoms attached are the same, then yes. But if they are different, then the dipoles may not cancel and you could have a polar molecule.

LaurenJuul_1B

one sigma and two pi bonds

a single has just one sigma

a double has one sigma and one pi

LaurenJuul_1B

Question 3F.1 in 7th Edition asks to identify the types of attractive intermolecular interactions that might arise between molecules of each of the following substances: a) NH2OH b) CBr4 c) H2SeO4 d) SO2 I am a bit confused on how to do this. For part a, for example, I can tell that there are hydrog...

LaurenJuul_1B

fluorine is the most electronegative atom since it is in the top right corner of the periodic table. just remember that electronegativity is how badly an atom wants another electron, so those closest to a full octet will be more electronegative. In addition, the smaller the atom is (the higher up in...

LaurenJuul_1B

The idea about the "unique" atom being the central atom does typically hold true and is a good starting point. Another way to help distinguish which atom goes where is that the central atom will typically have a positive formal charge while the surrounding atoms will take a negative formal...

LaurenJuul_1B

VSEPR just helps us visualize the 3-D structure of a molecule while a lewis structure is a 2-D drawing. While lewis structures are useful in showing where bonds and lone pairs are, the VSEPR model helps us understand more about how a molecule will act in an environment and what 3-D structure it will...

LaurenJuul_1B

axial bond angles are angles between atoms that reside on the axis of a molecule

LaurenJuul_1B

and to answer the second part of your question, yes hydrogen has relatively high electronegativity due to only having one electron in its 1s shell. Atoms are more stable with a full shell, so hydrogen has a high electronegativity, (or in other words a high want to attract an electron) since it only ...

LaurenJuul_1B

The positive charge on fluorine is +9, but on hydrogen it is +1, so the magnitude positive charge (which is responsible for high electronegativity because it contributes to the pull on the electrons by the nucleus) is very high on fluorine.

LaurenJuul_1B

Yep. Our test number 3 is the week of November 19th and our final is December 9th

LaurenJuul_1B

I do not believe that we have to memorize bond lengths--just know how to use them and know what they tell us about a molecule.

LaurenJuul_1B

electronegativity is more of a concept than anything. It simply helps us understand the pull between atoms due to periodic trends and so it doesn't really require a unit

LaurenJuul_1B

the 1/2 shared portion of formal charge has to do with the shared bonds between electrons. Each bond represents 2 electrons, but since they are being shared, we only calculate with half of this number. (I.e. if two atoms share 2 bonds you take 4(electrons)/2(bonds) to get two. An easier way to think...

LaurenJuul_1B

Dipole has to do with polar covalent bonds! This means that one of the atoms will always be more electronegative, and in turn you will be able to draw the arrow without worrying about the atoms being too close in electronegativity.

LaurenJuul_1B

Lavelle's rule of thumb is that anything smaller than 10^-18 will be too small to measure. Conceptually, though, if you are working on the atomic scale wavelength will normally be detected and if you are working with objects that can be seen by the human eye, wavelength will not be able to be detect...

LaurenJuul_1B

The number comes from the octet rule. The octet rule is a chemical rule of thumb that states that atoms of main-group elements tend to combine in a way that each atom has eight electrons in its valence shell, giving it the same electron configuration as a noble gas.

LaurenJuul_1B

No, there is not a particular order that you need to follow. As long as there are no more than two dots on each side you should be fine.

LaurenJuul_1B

Problem 1E.1 goes as follows: Which of the following increase when an electron in a lithium atom undergoes a transition from the 1s-orbital to a 2p-orbital? (a) energy of the electron. (b) value of n. (c) value of l. (d) radius of the atom. Which answers would be different for a hydrogen atom and in...

LaurenJuul_1B

Professor Lavelle stated that only the material covered in lecture up until last Friday (10/19/18) will be on the test. Since we did not cover periodic trends in lecture, it will not be on the test. If you know everything up until multi-electron atoms, which I believe is section 1E in the seventh ed...

LaurenJuul_1B

I understand the basis of the shrodinger equation, but Lavelle mentioned that we won't be using it. So what about shrodinger do we need to know, if anything, for our test/for the class in general? Is it just background knowledge, or will it be something we are tested on?

LaurenJuul_1B

Personally, I prefer hand written. It helps me retain the information better. Also, I find it best not to just copy exactly what your professor has on their slides--making yourself write it in your own words/summarize it deepens your understanding and makes you think about the material.

LaurenJuul_1B

light cannot physically exist in a stationary state, so there cannot be a mass for it stationary

LaurenJuul_1B

Amplitude and frequency are related in that they are inversely proportional to one another. So, if the amplitude increases, the frequency decreases, or if the amplitude decreases, the frequency increases. This relationship is derived from the equation v = c/(lamda). Actually, amplitude and frequenc...

LaurenJuul_1B

Units in an equation must ALWAYS be the same! You can't multiply nanometers by meters, because then what would be the units of your answer? Once you get your answer, however, it can sometimes be easier to convert to nanometers or maybe kilometers if you are giving a really large or really small numb...

LaurenJuul_1B

Typically you don't want to round by more than 0.05, so I recommend rounding something like 7.30 to 7.33 and then multiply by 3 to get 22. When working with the empirical formula in particular, if you get numbers that are 0.1 or less off from a whole number then usually you are in the clear, but it ...

LaurenJuul_1B

Hi! So on the outline for our first test next week, one of the topics to know is to write the symbols of the elements given their name and vice versa. I haven't taken chem in a while, so I am still reviewing nomenclature, and I know Dr. Lavelle mentioned that we will learn names as we go, but I was ...

LaurenJuul_1B

Hi! so in step 5, it asks to compare the calculated moles (step 4) to the required moles (step 2) to determine in there is a limiting reactant. This basically means that you take the moles you calculated in step 4 of each of the reactants and look back to the balanced chemical equation in step 2 to ...

LaurenJuul_1B

Both notations are the same! It is more of a personal preference on which to use. I, for example, prefer g/mol because I am used to writing units that way. In g.mol^-1, the -1 just means that the mole is raised to the negative first power, meaning it is in the denominator of the fraction just like y...

LaurenJuul_1B

Here are a couple mnemonic devices that list the order from largest to smallest: King Henry Doesn't Usually Drink Chocolate Milk (kilo, hecto, deka, unit, deci, centi, milli) Kittens Hate Dogs But Do Chase Mice (kilo, hecto, deca, base, deci, centi, milli) Good Models Know How Dunkin Donuts Can Make...

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