CHEMISTRY COMMUNITY

Christina Cen 2J

we use the hess's law approach to add up enthalpies, which is only possible because it is a state function

Christina Cen 2J

what makes steady state more flexible in contrast to pre equilibrium?

Christina Cen 2J

the graph of 1/[reactant] over time has a positive slope which is equal to k for 2nd order reactions

Christina Cen 2J

One reactant is in large excess so we can ignore its concentration and find the psuedo rate law of the other reactant.

Christina Cen 2J

For this problem it tells us that there is CrCl3 (aq), CuSO4 (aq), copper wire, and chrome plated metal. How do we know that the copper wire is the cathode and that the chrome plated metal is the anode?

Christina Cen 2J

Why does NO have more residual entropy than BF3?

Christina Cen 2J

Why is it that when K<1, G is + and when K>1, G is -? I know that this is because of the equation G = -RTlnK, but what does it mean conceptually?

Christina Cen 2J

If breaking bonds is an endothermic process and requires energy, then why does breaking down ATP into ADP also release energy?

Christina Cen 2J

Reactions generally speed up when temperature increases and slow down when temperature decreases. This means that k increases with increasing temperature, which in turn increases the overall rate of the reaction.

Christina Cen 2J

I asked my TA and he says it doesn't matter what order they are in if they are the same phase.

Christina Cen 2J

Yes, the reaction for the final rate law should not contain intermediates. Solve for the intermediates in terms of the reactants that should be in the final reaction and substitute it instead of the concentration of the intermediate if you have to.

Christina Cen 2J

It is important in organic chemistry and relates to gibbs free energy

Christina Cen 2J

rate = k[reactant concentrations] so if k increases by a factor of 1000, the rate would also increase by a factor of 1000

Christina Cen 2J

0 and first order: -k
second order: k

Christina Cen 2J

For 29, how do we know which elements are aqueous, solid, etc. when we write the cell diagram?

Christina Cen 2J

When there are 2 elements in the same phase in a cell diagram separated by a comma like in 14.17 with
Pt(s)|Fe3+(aq), Fe2+(aq)||H+(aq), MnO4-(aq), Mn2+(aq)|Pt(s), how do you know which element comes first within the series of commas?

Christina Cen 2J

But it uses w = -nRTln(P1/P2), not -nRTln(V1/V2). Shouldn't we use both equations since there is both a change in pressure and volume?

Christina Cen 2J

In the Winter 2014 midterm 5C, it asks which are state functions for w, G, q, H, E, and S.
G,H,S are state functions and w,q, E are not. I'm not sure what E is in this problem.

Christina Cen 2J

I'm a bit confused about the distinction between these two. In the winter 2013 midterm 5B, it tells us that CH3F<CH2F2<CHF3<CF4 in terms of increasing standard molar entropy. I think this is because F is more massive, so that it has more elementary particles. But then, doesn't CH3F have more possibl...

Christina Cen 2J

Going for point B to point C has a change in both pressure and volume, but the answer seems to only account for the work done based on the change in pressure. Yet it states both equations. Why do we not calculate the work done by change in volume?

Christina Cen 2J

But why is it C = nq/T and not just C= q/tusing the q = CT formula?

Christina Cen 2J

For this problem why do we not use the equation q=mC(deltaT) to find C?

Christina Cen 2J

In this problem, why are the moles of HBr formed 2(5.35x10^-3) and not just 5.35x10^-3?

Christina Cen 2J

Can someone explain why the answers for each part of this problem has the number of sig figs it has? I don't see where it is coming from.

Christina Cen 2J

nothing can be exchanged outside the universe because nothing outside the universe exists

Christina Cen 2J

Also, a more massive element would have a higher molar entropy because there are fundamental particles (electrons, protons, neutrons), and so would a molecule made up of multiple atoms vs. one atom.

Christina Cen 2J

So in this question, is the system considered the contents of the cooler as well as the cooler itself, rather than just the contents being the system?

Christina Cen 2J

For 37 part d) 4KClO3(s) => 3KClO4(s) + KCl(s) why are the products more ordered than the reactants, resulting in a negative entropy?

Christina Cen 2J

There isn't any exchange in heat or matter with the surroundings of an isolated system, but heat can still be generated inside the system itself. This change is isolated because it is contained within the system, and the heat is not released into the surroundings.

Christina Cen 2J

Can someone please explain to me how delta U is a state function and = w + q, but w and q are not state functions?

Christina Cen 2J

Can someone explain to me again why carbon is more stable as graphite and why in 67 b, it isn't a gas like hydrogen and oxygen?

Christina Cen 2J

pkb = 14 - pka
The lower the pkb is, the stronger the base, so the higher the pka = smaller pkb = stronger base

Christina Cen 2J

From the homework problems that we've done, it seems that they usually tell us if the change in pressure is caused by adding gas (which would not shift the reaction) or by changing volume, so I would assume the test would do the same.

Christina Cen 2J

Use the formula Ephoton = work function + Kinetic energy of electron. The KE of an electron is (1/2)mv^2 so Ephoton = work function + (1/2)mv^2. Convert the 2 given energies to joules and plug them in for Ephoton and work function. The mass of an electron is a constant so you have all the needed qua...

Christina Cen 2J

Does it matter if we use double arrows or a single arrow when writing the reactions for strong acids and bases? For example, the dissociation of H2SO4 on 12.3a on the homework is a strong acid reaction, so I was under the impression that it would be a single arrow but the solutions manual shows a do...

Christina Cen 2J

On Q4B on the 2010 final, why is the shape of [Co(en)2(Br)2] octahedral if the coordination number is 4?

Christina Cen 2J

For the reaction in 5b with (CH3)3N and HNO3, why does it not produce water and a salt? Is it not a neutralization reaction?

Christina Cen 2J

You compare heat in endothermic reactions to a reactant (since it is required to start the reaction) and heat in exothermic reactions to a product (it is produced by the reaction). If you increase a reactant, more product will form, as in adding heat to an endothermic reaction. If you increase produ...

Christina Cen 2J

The transition metal, which is the central metal atom, is the Lewis acid and it accepts electron pairs. This element comes last in the naming process. The surrounding ligands are Lewis bases and they are the electron donors.

Christina Cen 2J

Does the strength of acids and bases relate in anyway to electronegativity differences or ionization energy?

Christina Cen 2J

Could someone explain to me how to find the balanced chemical equation for this problem? I understand how to do part b based on the graph and the answer for part a, but I am unsure of how to find the coefficients for the equation.

Christina Cen 2J

For elements with extended octets, how do we determine to what extent they can be expanded to?

Christina Cen 2J

The bond angles are determined theoretically by the different geometric shapes of the compounds with consideration of any lone pairs that may change the arrangement.

Christina Cen 2J

ICl3 has 5 regions of electron density with the 3 Cl atoms and 2 lone pairs, where as NH3 has 4 regions with 3 H atoms and 1 lone pair. The 5 regions of ICl3 makes the electron arrangement trigonal bipyramidal, and the 2 lone pairs make it T shaped unlike NH3 which has a tetrahedral arrangement and ...

Christina Cen 2J

I think it would be best to memorize all the shapes and angles in the diagrams of the textbook, including t shaped.

Christina Cen 2J

A dipole moment is where one atom is more electronegative than the other, which results in separation of positive and negative charges.

Christina Cen 2J

Hybridization results in orbitals with lower energy compared to separate s and p orbitals.

Christina Cen 2J

the equation is wavelength = planck's constant / mass x velocity. If there is 0 mass and/or velocity, the denominator would be zero and we cannot use the equation.

Christina Cen 2J

Why is it that 4s is filled before 3d but when cations are formed, electrons are taken from 4s before 3d and not 3d first?

Christina Cen 2J

I believe by "group 5 transition metals" it means the fifth column of the transition metals starting with Mn, and not group 5 of the periodic table. If you use the fifth column then it gives you (n-1)d^5ns^2 like in the solutions manual.

Christina Cen 2J

The lower the formal charge is, the more stable the molecule is and the less likely it will form reactions. Since the model with double bonds has a lower formal charge, it has a higher stability and is a better representation.

Christina Cen 2J

I think the goal is the have the formal charge of all atoms to be as low as possible but having 4 double bonds for S is not possible.

Christina Cen 2J

The two numbers seem to be different because 3.29 x 10^15 has the units of s^-1 and the number you found online is in m^-1. For 13, we would use 3.29 x 10^15 s^-1 to cancel with the s^-1 unit in the speed of light constant.

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