CHEMISTRY COMMUNITY

lukezhang2C

The only non-integer order which is mentioned in the book which occurs commonly would be the 1/2 order, but the rest should be ranging from 0-3 at most.

lukezhang2C

Half life equations are given in the equation sheet, but they will not tell you which half-life equation corresponds to which order of reaction. You can also derive them using the standard half life equation, solving for t when the concentrations are half of the initial.

lukezhang2C

when given a table, you can use any reaction and the values to kind K, right? Yes, you should be able to use any of the values given to find k as long as they correspond to one another. For example, using random concentrations for an initial rate which was found using other concentrations would not...

lukezhang2C

What is a reaction rate and how does it relate to the rate law? The reaction rate is the rate of which the reaction proceeds (in M/s) and is related to the rate law as the rate law is used to calculate the initial rates of the reaction. In a problem typically we would use the reaction rate to find ...

lukezhang2C

Yes, the K value should be the same for all since you need to use the different concentrations and initial rates in order to find K in the first place.

lukezhang2C

A zero order reaction is one where changing the concentration of your reactants does not change the initial rate of the reaction, meaning that your reaction rate is independant of that reactant. Zero order reaction K values will have M/s units.

lukezhang2C

You can determine experimentally, when observing that the initial rates don't change when changing the concentration of the reactants, or by looking at your K units as your K would have to be in the units of M/s to offset the unitless reactant.

lukezhang2C

Catalysts lower the activation energy needed for a reaction to proceed, but should not innately change anything about the equilibrium. It would only serve to shift the reaction to the right as more products would be made.

lukezhang2C

K and Kc can mean similar things depending on the context of the problem, but Kp would mean partial pressures while Kc would mean concentration.

lukezhang2C

Kw is typically used to find Ka or Kb when given the other. The relation can be used in any number of ways depending on the problem and what you need to find.

lukezhang2C

Ka is the ionisation constant, used when dealing with acids and excess protons in a solution. Kb is typically used with bases, and finding the pOH of a solution. Kc is just the relation of Ka and Kb which is Ka X Kb = 10^-14

lukezhang2C

1 ATM = 760 torr and it is always on the equation sheet! Just remember to use the correct constants after converting from atm to torr!

lukezhang2C

For any derivations which I've had to do I always start by finding common factors/variables and playing around with them with substitution until I get the equation whic I need. Always look at which variables need to cancel and which ones you would need to keep, it is a crucial factor in derivations.

lukezhang2C

So delta U = delta H is only considered a very specific case of the original equation, which is delta U = q + w = q - P delta V. You can only use delta U = delta H when q = delta H and you are under constant pressure, otherwise you cannot use the other equation.

lukezhang2C

Enthalpy is a property which varies with the moles of reactants/products present, and oftentimes the units would be KJ/mole or would ask you to find it permole, so it makes sense to make stoichiometrically correct calculations when finding the enthalpy of the reaction.

lukezhang2C

Cp represents constant pressure while Cv represents constant volume, our problems will tell us whether or not we would be dealing with constant pressure or volume as one with two changing conditions would be extremely difficult, and would have to use another approach entirely.

lukezhang2C

I think for this question on the midterm it was far easier to approach it by finding the net moles of gas produced than it was to calculate each bond enthalpy as you have delta U = delta H (which is found by multiplying the delta H given by 4 moles) - nRT where your n is just the net change in moles...

lukezhang2C

So Delta U = q + w = q - PdeltaV, meaning that under constant pressure U = q = delta H. This is where most of the interchangeability comes from as systems with constant pressure appear often in our problems.

lukezhang2C

Looking at the equation Delta U = q + w, delta U is only 0 when q = -w which means heat put into the system is equal to the heat out of the system, in other words the system is isolated with no net change in internal energy.

lukezhang2C

A general cell diagram would be something like this for a Galvanic cell:

Conducting Solid | Anode || Cathode | Conducting Solid

Different states of matter are separated by | while different species of the same state are separated by commas

lukezhang2C

The balanced overall cell reaction that I got was 2N02 + 2H20 + Zn2+ --> Zn (S) + NO3- + 4H+, and I also got the cell diagram wrong. However from what I can ascertain you needed to flip No3 and Zn, and include a solid for the NO3 side.

lukezhang2C

It's not usually negative in the way that time can't be negative in a physics problem, but for the sake of some calculations we can set it to be negative. When flipping the equation for a half reaction your E can be negative at times, which may contribute to this as well.

lukezhang2C

For a Galvanic Cell it should be Anode || Cathode, where there are single lines (|) separating different states of matter, and commas separating different agents with the same state of matter. i.e (aq), (aq), || (aq)| (s)

lukezhang2C

It is due to the fact that a stronger reduction power indicates higher electronegativity, which makes for a stronger oxidising agent. Stronger reduction power also corresponds with a higher E value, which also increases oxidising power.

lukezhang2C

Which equations would be good to memorise for the midterm?

lukezhang2C

I don't see any other worksheets posted :(

lukezhang2C

Are there answers to these problems?

lukezhang2C

Ka and Kb are just used for acid/base dissociation, and Kc is just the equilibrium concentration.

lukezhang2C

Should we finish our three posts before our discussion date or before/on Friday?

lukezhang2C

Homework will now be due in discussion!

lukezhang2C

Anyone have any past final exam questions from Lavelle from the test bank?

lukezhang2C

Electronegativity is also a factor to consider!

lukezhang2C

I'm guessing it's because this would make the molecule larger while also making it more electronegative, which makes it a stronger acid, but I'm not 100% sure.

lukezhang2C

The more electronegative the atom is the stronger the acid due to the strong ionic nature of their electron-sharing nature!

lukezhang2C

I believer you can have email notifications, but I'm not sure how practical that would be.

lukezhang2C

Will we have to memorise the exact chemical reaction equation for acid rain?

lukezhang2C

The water molecules in rain react with pollutants in the air and becomes acidic in nature

lukezhang2C

They might give us a new equation sheet but I'm pretty sure you're just supposed to memorise it.

lukezhang2C

I would not think so, though it's a relatively simple formula so they might expect you to memorise it.

lukezhang2C

Most likely nothing computational as we don't know enough to do that, I would assume just labeling would work

lukezhang2C

Do we need to know how to calculate the Ka equilibrium of acid/base reactions?

lukezhang2C

Sigma bonds result from overlapping end-end atomic orbitals while pi bonds are overlapping side to side in a perpendicular plane.

lukezhang2C

Take a look at this site! https://sites.google.com/site/ed350201003/Task

lukezhang2C

His outline would give all necessary information, and he would probably email us as well soon!

lukezhang2C

For Atomic Radius it increases as it goes down due to the added number of shells to house the electrons

lukezhang2C

Will we be given the electronegativity difference numbers for non-obvious cases of covalent or ionic bonding?

lukezhang2C

The Bruin Online Testbank has previous chem 14A exams too but not from Lavelle

lukezhang2C

Will the work function of the metal be given when doing problems?

lukezhang2C

Which equations do we have to memorise vs which ones are on the equation sheet?

lukezhang2C

It should follow e=mc^2 for photons, which is kgm^2/s^2

lukezhang2C

Constructive interference simply means that an addition of the two waves results in a larger amplitude, while destructive interference is the opposite. The two are not mutually exclusive and can be in conjunction with one another.

lukezhang2C

Electrons have different properties than photons, and while it is near massless, it is often not considered as such when solving for kinetic energy which is why the same kinetic energy equations which work for photons do not work for electrons.

lukezhang2C

The two have an inversely proportional relationship, this property is just derived from the formula!

lukezhang2C

Does anyone know if there will be a periodic table provided for us?

lukezhang2C

Simran Athwal-Dis 3A wrote:Hi, I had a quick question. How do we check how many times we posted on Chemistry Community? Do we go on our profile?

I think theres an option in profile which shows your posts!

lukezhang2C

Diana Chavez 1K wrote:If we do not understand what a question on the test asks is it allowed to ask for clarity from our TA's?

I think in general during testing they're not really allowed to answer these types of questions unless it's a glaring wording error.

lukezhang2C

Significant figures allows us to measure the precision of our measurement instruments!

lukezhang2C

Yep! You do any seven problems from the assigned problems and turn it in.

lukezhang2C

So for the homework we turn in, do we pick seven problems from the list on the syllabus or should we turn in our answers to all of the problems but the TAs would only grade seven of them?

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