CHEMISTRY COMMUNITY

Ricky Ma DIS 4E

What are the different kinds of answers that the half life equation can give us?

Ricky Ma DIS 4E

delta U equals 0 when the system doesn't change. Either when q and w=0 or q=-w

Ricky Ma DIS 4E

When would one use the pre-equilibtium approach. What would the question be asking? I can't seem to find a problem where it explicitly asks for one to use the approach to solve for something?

Ricky Ma DIS 4E

How do we know which one to use? Does it matter?

Ricky Ma DIS 4E

All the intermediate steps between the beginning and final equation that is given to you. All the steps that happen that results in the equation that is given to you.

Ricky Ma DIS 4E

Ice melts by itself which requires no direct input of energy. A piece of ice outside would melt by itself thus spontaneous.

Ricky Ma DIS 4E

Don't you just write the coefficient under 1? For example 1/a(d(x)/d(t)?

Ricky Ma DIS 4E

If all your other values have kelvin within them, use kelvin. Check whether or not the units cancel. From my knowledge, Im pretty sure Kelvin is always used.

Ricky Ma DIS 4E

If you don't quite grasp the concept, I would suggest reading the book. Other than that I think you should be fine.

Ricky Ma DIS 4E

Ecell is not under standard conditions whether Ecell^o is under standard conditions. It will usually tell you it is under 1 atm of pressure or 25 degrees celsius etc.

Ricky Ma DIS 4E

I think pressure is correlated to volume which a change in volume affects the concentrations. I dont think we went over it yet but it is going to be related to the Nerdst equation.

Ricky Ma DIS 4E

"Know how to write and interpret cell diagrams." is on his course outline. In my opinion, wouldn't hurt to know.

Ricky Ma DIS 4E

Residual entropy is the entropy that remains after molecules stop moving at 0 degrees kelvin. The entropy lies within the orientation of the atoms of the molecule.

Ricky Ma DIS 4E

Yes i think so.

Ricky Ma DIS 4E

a negative gibbs free energy means that it is spontaneous. A postive gibbs free energy means that it is not spontaneous.

Ricky Ma DIS 4E

Delta n is used when you are given a reaction and you see that there is a change of moles within the equation. When there is a change in moles of a gas, there is work of expansion.

Ricky Ma DIS 4E

I think it is because ice is a solid and the molecules within are very tightly compacted meaning there is very minimal movement within the ice. Entropy would be very close to 0.

Ricky Ma DIS 4E

Yes, if you do not have enough reactants to form the products loss, the reaction will stop.

Ricky Ma DIS 4E

Doesnt negative work mean that the system is losing energy from work? if p=1 atm but there is an increase in volume, the equation would be negative meaning system did work of expansion.

Ricky Ma DIS 4E

When the work of a system on the atmosphere is positive, does that mean that work is being done on it instead? What does positive work mean conceptually.

Ricky Ma DIS 4E

it heat capacity and enthalpy of vaporization/sublimation the same thing?? Are they closely related conceptually?

Ricky Ma DIS 4E

q is heat whereas delta H is the total energy in the system at a constant pressure.

Ricky Ma DIS 4E

when i drew the molecular formula for benzene, there are 3 double and single bonds, therefore, I used those mean bond enthalpies. Within the solution manual, it used the other dotted doubly bond enthalpy. Why is this? Is this because benzene has resonance structures?

Ricky Ma DIS 4E

I think method 3 just gives you the deltaH of formation for the reactions and the deltaH of formation for the products in which you just do deltaH of the products minus the delta H of the reactants. That will give you the overall enthalpy change. It is probably the most straight forward one out of t...

Ricky Ma DIS 4E

It is pretty all over the place right now. I skipped around the sections to find some problems that pertained to what we learned in class. There are not a lot.

Ricky Ma DIS 4E

Percent ionization is ionized concentration/original concentration. That is a step further than just finding equilibrium composition.

Ricky Ma DIS 4E

Technically it will but in reality, it is the volume that is increasing/decreasing that makes the reaction shift.

Ricky Ma DIS 4E

You use the pH to find the pOH in which you can then use to find the concentration of OH-. From that you just set the quadratic equation and solve Kb from there.

Ricky Ma DIS 4E

(i), when i divide 1.0x10^-14/1.50 to get concentration of OH-, i get 6.667x10^-15 but the solution manual says the answer is 1.5x10^14. I tried to work backwards from the other values given in the table and it seems that the issue is the 1.50 molar concentration given in the table. Am I not seeing ...

Ricky Ma DIS 4E

When calculating the molarity for barium hydroxide, i got 2.5x10^-3 but the back of the book states that it is 2.5x10^-2, is this an error of the book?

Ricky Ma DIS 4E

Yes, I believe so

Ricky Ma DIS 4E

Some compounds can either act as a base or an acid, those compounds are labeled as amphoteric. The best way would be to draw the lewis structure and see if it can actually give off a proton or if the Nitrogen has a lone pair. In some cases, although it is amphoteric, acting as a base/acid is more fa...

Ricky Ma DIS 4E

Can someone show me what the set up for the quadratic equation for A is? I keep on getting 2X^2+1.2x10^-7X-1.2x10^-10 as my equation which when i plug it in into the quadratic formula, it gives me 8,69x10^-5 which gives me the wrong answer. Thanks!

Ricky Ma DIS 4E

N2+3H2---->2NH3 at 400k K=41

1/2N2+3/2H2---->NH3 at 400k K=41

Can someone explain to me how one would figure out K of the second equation by using the information in the first line? Thanks!

Ricky Ma DIS 4E

Can someone explain to me how P=(Conc)RT becomes Conc=P/RT? And for clarification P stand for partial pressure right?

Ricky Ma DIS 4E

Does it matter if we put Kp=[C2H4Cl2]^2 ect. instead of K=[PC2H4Cl2]^2? Thanks!

Ricky Ma DIS 4E

Cis- means on the cisplatinum means that Chlorine atoms on the platinum are on the same side. This allows the cisplatinum to bind to the guanines at two parts on the DNA structure. The Nitrogens on the guanene bases replaces the Cl- on the cis platinum. This process results in the inhibition of the ...

Ricky Ma DIS 4E

Grp 1 and grp 2 oxides are the strong bases.

Ricky Ma DIS 4E

Do I have to draw the lewis structures? How do I know if it is tri-bi-or mono dentate?

Ricky Ma DIS 4E

What does polydentate mean and how do I know which ligands can be polydentate?

Ricky Ma DIS 4E

How do I find the oxidation number of a complex?

Ricky Ma DIS 4E

Coordination sphere is just the name given to all of the compounds and molecules within the brackets.

Ricky Ma DIS 4E

it is just saying how strong the london forces are. Larger polarazability means stronger london forces.

Ricky Ma DIS 4E

Just think about the net dipoles and whether they cancel. You have to take in account the shape of the molecule.

Ricky Ma DIS 4E

The unhybridized p orbital is the pi bond of the double bond.

Ricky Ma DIS 4E

For these problems, should we be able to derive the answer by just looking at it or do we have to draw out all the different lewis structures?

?

Ricky Ma DIS 4E

ok thanks!

Ricky Ma DIS 4E

A trigonal planer has bond angles of 120 degrees though. 109.5 degrees is for tetrahedral species. so wouldnt the bond angles be slightly less than 120 degrees instead of 109.5?

Ricky Ma DIS 4E

And in that case wouldn't it be slightly less than 120 degrees since trigonal planar is 120 degrees? SO3^2- is just 3 bonding regions with one lone pair.

Ricky Ma DIS 4E

Wouldnt this make it not even close to a tetrahedral? why does it say in my notes that it has tetrahedral arrangement?

Ricky Ma DIS 4E

Within my notes from lecture, it says it has 4 areas of electron density but i only see 3 for S03^2-. Is the double bond counting as two regions of electron density? Is that also why the arrangement is considered tetrahedral since of the double bond despite only having 3 oxygen molecules surrounding...

Ricky Ma DIS 4E

Within the homework there are questions that go over Vespr formula but we didnt go over that. Would we need to know those for tests/quizzes?

Ricky Ma DIS 4E

Bond energy usually has to be searched up. I think doctor lavelle searched up the bond lengths in class.

Ricky Ma DIS 4E

It is just that electrons are moving around an atom at all times. Luckily and by chance, they would be at one side of the atom which can cause induced dipole movements.

Ricky Ma DIS 4E

The covalent characteristics are the Cl- having higher electronegativity so it pulls the electrons from the Na closer to itself. Although NaCl is an ionic bond, no bond is 100% ionic or covalent. The electronegativity of atoms gives atoms it's covalent characteristics.

Ricky Ma DIS 4E

Wasn't it a carbon monoxide molecude? not an oxygen?

Ricky Ma DIS 4E

The radical goes on the element where it will make the formal charge be 0 or closest to what your ion's charge is.

Ricky Ma DIS 4E

Sometimes not every formal charge all add up to 0. In cases where it is an ion, the formal charges have to add up to the charge of the given ion.

ex. Sc2+
the overall formal charge will always be 2+, never 0.

Ricky Ma DIS 4E

ms is the spin of the electron. There is no way to knowing, you can characterize it with either a +1/2 spin or -1/2 spin. It will always be those two. It doesn't matter just make sure that in an orbital, there is a maximum of two electrons, each with opposide spin.

Ricky Ma DIS 4E

The standards units for lambda is meters per second or m/s

Ricky Ma DIS 4E

Is this another exception???? Also, further in Tungsten is in the f orbital but I thought we aren't going to write electron configurations for those? We also didn't learn that as well right? I just googled it and apparently after Xenon, that is the F block?? Im just confused as to what I need to kno...

Ricky Ma DIS 4E

Write the ground-state electron configuration for each of the following atoms: (a): silver,
At the back of the book it said the answer is [Kr]4D10 5s1, why is this? why isnt it 4D9 5s2, how do we know when to subtract an electron from the 5s and give it to the D orbital? thanks.

Ricky Ma DIS 4E

b) Electrons in an s orbital are more effective than those in other orbitals at shielding other electrons from the nuclear charge because an electron in an s-orbial can penetrate to the nucleus of the atom. (true or false) The answer to this is True which confused me because I thought the reason why...

Ricky Ma DIS 4E

When an electron goes from 1s to a 2p, this is a result of them being excited right? by like light or something. Does this mean that the electron changes shapes as they are being excited by a light or something?

Ricky Ma DIS 4E

Yes, I think that the last thing we need to know for the test is orbitals and quantum numbers.

Ricky Ma DIS 4E

The velocity of an electron that is emitted from a metallic surface by a photon is 3.6 x10^3km/s (a) What is the wavelength of the ejected electron? I understand now that you use the Debroglie equation. My problem is that I tried using the Ek=0.5mv^2 first then using lambda=hc/E to find the waveleng...

Ricky Ma DIS 4E

Can someone explain to me why there are moles associated with Joules or the photoelectric effect in general? How are moles related to frequency etc? The mole questions really throw me off.

Ricky Ma DIS 4E

0.5 is just a parameter that is used in the equation. The M stands for mass of an electron which is a constant:9.10938356 × 10-31 kg. The V is this equation does not stand for wavelength but instead velocity. V^2 means velocity squared. Within the question, they should give you the velocity of the e...

Ricky Ma DIS 4E

Light hits a sodium metal surface and the velocity of the ejected electron is 6.61 x 105 m.s-1. The work function for sodium is 150.6 kJ.mol-1.
Ek=0.5m.v^2
How do I find the mass of an ejected electron? Is it just the molar mass of sodium?

Ricky Ma DIS 4E

(b) What mass of oxygen is needed to oxidize this amount of tristearin?

I understand part A but the different wording in part B throws me off. What does it mean what mass of O2 is needed to oxidize this amount? Are my steps still the same as normal stoichiometry? THANKS!

Ricky Ma DIS 4E

Aspartame (C14H18N2O5) is a solid used as an artificial sweetener. Its combustion produces carbon dioxide gas, liquid water, and nitrogen gas. I thought that combustion only releases Co2 and H20, why is there another product N? Isn't the standard rule for combustion you add oxygen and the products a...

Ricky Ma DIS 4E

To prepare a fertilizer solution, a florist dilutes 1.0 L of 0.20M NH4NO3 by adding 3.0L of water. The florist then adds 100.ml of the diluted solution to an intravenous bag. How many moles of nitrogen atom will each plant receive? Solve this exercise without using a calculator. I am just overall co...

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