CHEMISTRY COMMUNITY

Nikki Razal 1L

Does anyone know if Matthew's and Lyndon's final review got posted for us to work on? or was that canceled because of the current situation?

Nikki Razal 1L

no, Lavelle said we would focus on using pre-equilibrium only

Nikki Razal 1L

Intermediates are produced and then consumed, and catalysts are consumed and then (re)produced

Nikki Razal 1L

I assume the final would be similar to the previous exams we have taken, where not every question is from the homework, but the concepts from the hw would be tested and a couple problems would mirror hw problems

Nikki Razal 1L

the oxidizing agent is the reactant that gets reduced, whereas the reducing agent is the one that gets oxidized

Nikki Razal 1L

I feel like the rates would both be positive because I think they are technically the same, just working in the opposite direction. either way, the book says that positive reaction rate is the normal convention in chemical kinetics

Nikki Razal 1L

^ one thing to note though is that you should only add an inert solid if there is not a solid METAL at the cathode or anode side

Nikki Razal 1L

^^ for each half reaction, instead of adding H+ to an equation, add water, then add that same amount of OH- to the other side of the reaction

Nikki Razal 1L

just to add on, one way you can decipher between a 0, 1st, and 2nd order reaction is by looking at what the units of the rate constant, "k", is:
0 order= conc/s
1st= 1/s
2nd= 1/(conc*s)

Nikki Razal 1L

the elementary step with the rate matching the overall reaction should be the slow step considering 1) the sum of elementary steps=overall rate and 2) the mechanism agrees w the experimentally determined rate law

Nikki Razal 1L

How would you go about solving the question: A 1.0 m NiSO4(aq) solution was electrolyzed by using inert electrodes. Write (a) the cathode reaction; (b) the anode reaction. (c) With no overpotential at the electrodes, what is the minimum potential that must be supplied to the cell for the onset of el...

Nikki Razal 1L

n refers to the number of moles of electrons transferred, basically it is the total number of electrons you end up cancelling out in your half reaction equations

Nikki Razal 1L

how do you balance the reaction:
Cd(s) + 2 Ni(OH)3 (s) --> Cd(OH)2 (s) + 2 Ni(OH)2 (s)?

Nikki Razal 1L

when writing the cell diagram for AgBr(s) <--> Ag+(aq) + Br-(aq), where does the AgBr(s) in Ag(s)|AgBr(s)|Br-(aq)||Ag+(aq)|Ag(s) come from?

Nikki Razal 1L

you flip the sign when you are given the reduction potential of a reaction but you have an oxidation reaction you are trying to find the Ecell for

Nikki Razal 1L

How would you balance the redox reaction: H+(aq) + OH-(aq) --> H2O(l), the Brønsted neutralization reaction?
In the answer key, they use o2(g) to balance out the oxygens, but how would you know to do that?

Nikki Razal 1L

I think they basically are the same. The textbook states that a battery is a collection of galvanic cells connected in a series

Nikki Razal 1L

when balancing reactions in a basic solution, you end up having OH- as a product, whereas in acidic solution, you have H+

Nikki Razal 1L

standard conditions refers to a 1M solution at 1 atm and 273.15 K

Nikki Razal 1L

You use platinum whenever you need to carry electrons into or out of the electrode compartment. Platinum is an inert conductor

Nikki Razal 1L

as far as i know, it would tell you because whether it is in an acidic or basic solution determines the products

Nikki Razal 1L

the way i think abt is where heat is placed when it's written in a chemical rxn, when the rxn is endothermic, heat is on the left, and when it's exothermic it's on the left (you can think of this happening bc when heat is released, it is written as -)

Nikki Razal 1L

when a system does work, it is by a negative sign

Nikki Razal 1L

or you could be talking about the boltzmann formula for entropy , "S=klnW" where, S=entropy, k=1.381*10^-23 j/k (the boltzmann constant), and W is the number of ways that the atoms or molecules in the sample can be arranged with the same total energy

Nikki Razal 1L

a closed system has a fixed amt of matter but can exchange energy w the surroundings, while an isolated system cannot exchange matter or energy with the surroundings

Nikki Razal 1L

I think the person above is right, in chem 14a, test 2 wasn't cumulative

Nikki Razal 1L

for an intensive property, the value of something will be the same no matter how much of a substance you have (ie, specific heat). for an extensive property, the value of something depends on how much substance you have (ie heat capacity)

Nikki Razal 1L

for parts a and b, you would use similar processes. for part a, you would use the equation q=nCpdeltaT, and for part b, the equation q=nCvdeltaT. These are pretty much the same equations, just one is for constant pressure, whereas the other one is for constant volume. Plug in the values in each equa...

Nikki Razal 1L

If I'm reading this correctly, I think you are correct because when energy is released, deltaH is negative, and when delta H is negative, delta G is also negative in most cases

Nikki Razal 1L

Enthalpy is a state function, so enthalpy is additive

Nikki Razal 1L

substances with a lower heat capacity are easier to heat up, so the change in temperature is more extreme after the same period of time taken to heat up a substance with a higher heat capacity. as a result, the heating curve is steeper for a substance with a low heat capacity

Nikki Razal 1L

i believe so because one of the causes of entropy is change in position (of the molecules in a substance)

Nikki Razal 1L

a calorimeter is "a device in which energy transferred as heat is monitored by recording the change in temperature produced by a process taking place within it" a bomb calorimeter is a more sophisticated version of the calorimeter. it is a sturdy sealed metal vessel of constant volume (the...

Nikki Razal 1L

1) Hess's Law: use when you know delta H, use addition/subtraction to add up total enthalpy changes 2) using bonding enthalpies to calculate deltaH: add together energy required for the bonds in the reactants to break (positive values) and the energy released when bonds break (the energy of the prod...

Nikki Razal 1L

to add, i think dr. lavelle stated that if a system is at equilibrium, it is a reversible process

Nikki Razal 1L

^^ the longer line going from liquid to vapor indicates that more heat was released, making the steam burn more than liquid water

Nikki Razal 1L

I dont think Lavelle ever offers extra credit, but I would just talk to your ta about it, or just do five chemistry community submissions late

Nikki Razal 1L

a reaction is reversible when the products of a chemical reaction can convert back to reactants. this is commonly shown in equilibrium reactions in which reactants and products form simultaneously. reversible reactions are written with a double arrow denoting the forward and reverse reactions

Nikki Razal 1L

left because in an exothermic reaction, heat will start on the right side because deltaH is negative, and heating favors reactant formation

Nikki Razal 1L

pure substances (solids and liquids) won't be included in the equilibrium constant

Nikki Razal 1L

to add, enthalpy is a state property, means that its value is determined only by its current state, and it is not dependent on the path taken to obtain that state

Nikki Razal 1L

Hess's Law states that enthalpy changes are additive because enthalpy changes are a state function, which must be additive.

Nikki Razal 1L

^^ a lot of homework problems should help because Dr. Lavelle often gets problems from homework and put them on the test

Nikki Razal 1L

I feel like you would start by changing grams of PCl5 to moles then finding the molarity of the initial PCl5 by dividing this number by the liters, then continue solving the problem as an ICE box

Nikki Razal 1L

neither affects equilibrium because they are both pure substances

Nikki Razal 1L

no, solids or liquids (pure substances) would not affect le chatelier because they are not technically included in the equilibrium expression

Nikki Razal 1L

you can only avoid using the quadratic formula when you are given a small k value (<10^-3), otherwise you would have to solve for x normally, which may require you to use the quadratic formula

Nikki Razal 1L

K is calculated at equilibrium , while Q is calculated anytime during the reaction

Nikki Razal 1L

yes, you use partial pressure when all products and reactants are in the gas phase, and you use the equilibrium constant Kp

Nikki Razal 1L

^^^ the molar concentrations of a pure substance (solid or liquid) does not affect K

Nikki Razal 1L

Yes! Q or Qc or Qp is calculated the same way as K :)

Nikki Razal 1L

K is the equilibrium constant (this tells us where the equilbrium sits), while Q is the reaction quotient (this determines which direction a rxn will proceed)

Nikki Razal 1L

for this question, the statement, "If one starts with a higher pressure of reactant, the equilibrium constant will be larger" is false because your initial concentration increases, causing the equilibrium constant to be smaller. For example,if you had the equation N2+3H2 <-->2NH3 and an in...

Nikki Razal 1L

for question 40c, how do you know whether o2 or o3 has the stronger bond and why?

Nikki Razal 1L

^^ to add on to that, dipole moments are created by lone pairs if the lone pairs don't cancel each other out, and one factor that can influence whether or not they cancel out is by looking at the bond angles

Nikki Razal 1L

between the metal oxides (bases) and nonmetal oxides (acids), there is a diagonal band of amphoteric oxides closely matching the diagonal band of metalloids

Nikki Razal 1L

amphiprotic= means that a molecule has the ability to either donate and accept H+
amphoteric= means that a molecule can either act as an acid or a base

Nikki Razal 1L

AngieGarcia_4F wrote:(N2p, N2p) because pi bonds happen when p orbitals overlap.

does this mean that pi bonds can only be formed in p orbitals only?

Nikki Razal 1L

^^ tungsten and molybdenum can get up to +6 I believe, and arsenic can be +5

Nikki Razal 1L

Once you find out what "l" is, you can figure out how many orbitals there are because to find the number of orbitals you can plug "l" into the equation 2*l+1, and that will give you the number of orbitals. Or you can think that ml=-l,...0...,+l, and the number of values you get a...

Nikki Razal 1L

carbon is from the energy level, n=2

Nikki Razal 1L

I usually just look at the products of the equation, and the product with an additional H+ is the conjugate acid because bases accept protons based on the Bronsted- Lowry definition. Similarly, since acids donate protons, the product with an H+ taken away from it will be the conjugate base

Nikki Razal 1L

On the syllabus, Dr. Lavelle said to know 3: hemoglobin, myoglobin, and vitamin B12

Nikki Razal 1L

I don't think it will be heavily tested either, but just so you know "diamagnetic" means that all electrons are paired, whereas "paramagnetic"means that not all electrons are paired

Nikki Razal 1L

What is the biological function of the naturally occurring coordination compound, vitamin B12?

Nikki Razal 1L

How would you know that Bi2O3 is amphoteric?

Nikki Razal 1L

An arrhenius:
- acid: gives off H+
- base: gives off OH-

Bronsted-Lowry
- acid: is a proton donor
- base: is a proton acceptor

Lewis
- acid: is an electron acceptor
-base: is an electron donor

Nikki Razal 1L

I agree with Kayley and Megan, I took AP chem in high school, and I think it definitely helped, but I also am not having an easy time in the class either. There's a lot of concepts like they were saying that go more in depth here in college

Nikki Razal 1L

In reference to HW 9C.7 (Which of the following isomers of diaminobenzene can form chelating complexes? Explain your reasoning.) and/or 9C.8 (Which of the following ligands do you expect to form chelating complexes? Explain your reasoning.) How do you know what isomers or ligands can form chelating ...

Nikki Razal 1L

^^ in Lavelle's lectures I feel like he uses the English name, plus the book uses the English name from what I've seen

Nikki Razal 1L

In the book, a ligand refers to "A group attached to the central metal ion in a complex"

Nikki Razal 1L

^^ just to add on, Lavelle was saying how transplatin is only able to form one bond in DNA (which is weak, so it can't stop cell division), whereas cis platin is able to form 2 bonds in the DNA, causing for the DNA to be interfered with enough to the point of stopping cell division & ultimately,...

Nikki Razal 1L

805097738 wrote:
Zoya Mulji 1F wrote:Intermolecular forces:
ionic bonding --> H-bonding --> dipole-dipole bonding --> induced dipole/London dispersion

is this ascending or descending in strength?

this is in decreasing strength. hydrogen bonds are the strongest and LDF /induced dipole forces are the weakest

Nikki Razal 1L

^^ i think we would also need to know the bond angles and were not necessarily graded on the lewis structure, but in order to determine the shape, we'd have to know how to draw the lewis structure

Nikki Razal 1L

sigma bonds are just single bonds, pi bonds occur when you have a double bond or triple bond. if you have a double bond, you would have one sigma and one pi bond, and if you had a triple bond, youd have one sigma and two pi bonds

Nikki Razal 1L

no, some of the lone pairs will create dipole moments that cancel each other out, resulting in a molecule not necessarily becoming polar

Nikki Razal 1L

They'll always be smaller because the lone pairs repel shared electrons, reducing bond angles. In general, atoms/electrons want to be as far away as possible due to electron repulsion. Molecules w/ lone pairs lower bond angles because lone pairs repel shared electrons, leading shared electrons to be...

Nikki Razal 1L

^^^ the geometric angles correspond with the VSEPR chart which depends on how many bonding pairs and lone pairs you have. for example a structure with 2 bonding pairs and 2 lone pairs would be bent and would have bond angles of less than 109.5 because of the lone pairs “pushing” on the angles in the...

Nikki Razal 1L

just to add on, cis structures will have the same elements on one side of a structure, making it polar, whereas trans structures will have the same elements on opposite sides of the structure, making it nonpolar

Nikki Razal 1L

Can someone explain to me why BaBr2 has bonds primarily ionic?
(in reference to HW question 2D.3:
"Which of these compounds has bonds that are primarily ionic? (a) BBr3; (b) BaBr2; (c) BeBr2."

Nikki Razal 1L

How would you solve the problem Focus 1.3 in the textbook: "In each second, a certain lamp produces 2.4 x 10^21 photons with a wavelength of 633 nm. How much power (in watts) is produced as radiation at this wavelength (1W = 1 J x s^-1)?" I tried using E=hv and c=wavelength(frequency) and ...

Nikki Razal 1L

The question: "Your bowling ball of mass 4.02kg rolls down a lane with a speed of 2.35+/-0.1m/s. What is the minimum indeterminancy of its position? Can you blame the Heisenberg Uncertainty Principle when your ball misses the pins" appeared in Karen's Quantum World WS. How do you know when...

Nikki Razal 1L

There's a few conversions on the sheet, such as 1nm=10^-9m, but I would look at the conversion sheet to see what conversions you should become more familiar with

Nikki Razal 1L

the lowest energy lewis structure has an overall formal charge of 0/close to 0

Nikki Razal 1L

Why can only some elements in the 3rd period have an expanded valence shell?

Nikki Razal 1L

You can draw a molecule in different ways/ a molecule has resonance when you can draw a structure with multiple bonds in different positions (ie move one bond to another to create a double bond)

Nikki Razal 1L

a resonance structure is a blending of lewis structures with the same arrangements of atoms but different arrangement of electrons. it spreads multiple bond character over a molecule and also can lower its energy

Nikki Razal 1L

^^ the central atom/all atoms would have a formal charge of 0; basically the lowest energy lewis structure will be the lewis structure with the overall formal charge closest to zero

Nikki Razal 1L

Find the formal charge of each bound atom then add up all the individual formal charges to find the overall formal charge. The most stable atoms have a formal charge of 0.

Nikki Razal 1L

The most stable compounds typically have an overall total charge of zero (the exception would be if the compound or element is an anion or cation, that is, if they have an overall charge other than zero). And just a quick note, formal charge = # of valence electrons an atom has - (# bonds + lone pai...

Nikki Razal 1L

The central atom is the element with the lowest ionization energy. Usually, it is the first element in a compound, and when it is placed in the middle, you are able to draw atoms symmetrically around it.

Nikki Razal 1L

^^ atoms in period 3 or higher have d-orbitals in valence shell that can accommodate additional electrons.

Nikki Razal 1L

For me, the easiest way to determine how many atoms are unpaired or paired is just to draw out an energy diagram and fill up the orbitals until all electrons are accounted for. Just a note, when all electrons are paired, the compound is known to be diamagnetic, and when they're not al paired, it is ...

Nikki Razal 1L

Electron affinity is the energy released when an electron is added to a neutral atom to become an anion.

Nikki Razal 1L

Ionic bonds form when a metal transfers its electrons with a nonmetal (this involves cation and anion interactions), and covalent bonds form when nonmetals share electrons. Nonmetals do not form cations because their ionization energies are too high.

Nikki Razal 1L

If electronegativity increases from left to right and bottom to top of the periodic table, why is fluorine the most electronegative element?

Nikki Razal 1L

yup just to add on, you could either write nitrogen is 1s^2, 2s^2, 2px^1, 2py^1, 2pz^1, or nitrogen is 1s^2, 2s^2, 2p^3 and both would be correct

Nikki Razal 1L

He said the two exceptions were for the elements copper (Cu) and chromium (Cr)

Nikki Razal 1L

In reference to question 1.E.1, "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 ato...

Nikki Razal 1L

For HW problem 1.D.23: "How many orbitals can have the following quantum numbers in an atom:(a)n=2,l=1;(b)n=4,l=2,m1=-2; (c)n=2;(d)n=3,l=2,m1 =+1?" Would it be better to state the max number of orbitals, or all the different possibilities? For example, for part c, you can assume l = -1,0,1...

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