CHEMISTRY COMMUNITY

Kobe_Wright

Meachelle_Lum_1I wrote:Hi, does anyone know why delta H was 300 and not -300 when calculating the reverse activation energy? Didn't they give it as -300, and it's an exothermic reaction so deltaH should be negative?

Going in reverse, you'd switch the sign around. You're doing the reaction backwards.

Kobe_Wright

Thank You!

Kobe_Wright

Yes. When you look at the Arrhenius equation we can see that increasing temperature makes the rate larger, as does lowering the activation energy, which is what a catalyst does, so doing these together should theoretically increase the enhancement of the rate. But isn't the statement saying that th...

Kobe_Wright

In isothermal dU=0, and we know that work is done so U=w, so what this means is that 0=q+w, q=-w/w=-q, while there's no temp change heat is released but counteracted by work. heat being measured in joules. If there was no heat across the system then it would be adiabatic system not isothermal.

Kobe_Wright

You can't assume that the pressure is constant, but you can assume that volume is constant. So youre able to calculate one change for that temp change and one change for the volume change. Since entropy is a state function, its independent of the path taken so you're able to calculate them separate...

Kobe_Wright

You can't assume that the pressure is constant, but you can assume that volume is constant. So youre able to calculate one change for that temp change and one change for the volume change.

Kobe_Wright

Yes. When you look at the Arrhenius equation we can see that increasing temperature makes the rate larger, as does lowering the activation energy, which is what a catalyst does, so doing these together should theoretically increase the enhancement of the rate.

Kobe_Wright

It'll be negative because in order to form products you have to lost matter from the reactants

Kobe_Wright

jane_ni_2d wrote:so its correct that the anode is always on the left of the concentration cell right?

Yes.

Kobe_Wright

BenJohnson1C wrote:T can be completely canceled out. Think of it as the -q=w. Because the function for work involves the multiplication of T but deltaS is q/T, the q is simply taken out and the negative sign is omitted.

Thanks Ben that helps!!!

Kobe_Wright

Summer de Vera 2C wrote:
Lauren Huang 1H wrote:The second law of thermodynamics states that delta S=q/T=nRln(V2/V1). So q=nRTln(V2/V1) if you multiply both sides by temperature. I believe the unit for q is Joules.

Wouldn't you have to divide rather than multiply both sides by T?

I believe its divide;.

Kobe_Wright

If youre given the a small rate in a multi compound reaction then the one with the smallest rate has stoichiometric coefficient of 1 while the other rates will be relative to this value (x) divided by their own stoichiometric coefficients, which means all of these values will be equal to each other ...

Kobe_Wright

There's good examples of this in this weeks worksheets posted by a UA

Kobe_Wright

Thank you! Very helpful

Kobe_Wright

The problem tells you that N2O5 decomposes by a first order reaction, so the rate law will have the form rate = k[A] where A is the reactant, N2O5, and the it is raised to the first power since it is a first order reaction. You are also given k = 5.2 x 10^-3. As mentioned before, you don't need to ...

Kobe_Wright

I cannot figure out how to solve this problem or how heat is even factored into it?

Kobe_Wright

In this problem, the solutions manual says that heat lost by metal = - heat gained by water. Why would the heat gained by water be negative? Well thinking about it, if the metal loses heat its value will be negative and since that is negative, H(metal)=-H(water), H(metal)=-x, H(water)=-(-H(metal)= ...

Kobe_Wright

When two aqueous solutions are in the same cell they're split with a comma while if they're other phases they're separated with a line. Right, but Ni(OH)3(s) and Ni(OH)2(s) are in the same phase still and is still separated by a line? Yeah, if theyre any other phase except aqueous they are split wi...

Kobe_Wright

As said above you get the cell potentials of the cathode and anode then do E(standard)=E(cathode)-E(anode).

Kobe_Wright

You'd use dG=-nFE. Where you need to find the electrons that flow between the two cells and that is your n while E is given and F is a constant, this gives you your gibbs free energy of the cell.

Kobe_Wright

When two aqueous solutions are in the same cell they're split with a comma while if they're other phases they're separated with a line.

Kobe_Wright

In order to balance the waters, and hydrogens, and electrons of both half reactions you'll need to multiply by those coefficients.

Kobe_Wright

Yup everything up to the nernst equation

Kobe_Wright

I just try to remeber that when it says reducing it means reducing the oxidation number by making it more negative by gaining electrons which reduce the oxidation number while oxidating increases oxidation number.

Kobe_Wright

Youd use that when they are asking about equilibrium onstants, G=gstandard+RTln(q) when not at equilibrium, G=Gstan+RTln(p) when talking about pressure, and G=-RTln(k) when talking about equilibrium constant.

Kobe_Wright

Professor lavelle said the anode is always on the left and cathode on the right to represent electron flow.

Kobe_Wright

Thanks for the worksheet it helped a lot!

Kobe_Wright

Matthew Mar 1J wrote:I don't know if this is directly related, but 3/2R (without the T) is the specific heat capacity of a monatomic ideal gas at constant volume (Cv) which is used in entropy problems (/\S = n Cv ln(T1/T2)) which is a more practical application.

Then what about when it is constant pressure?

Kobe_Wright

The outline says through entropy but gibbs free energy is last and theres a few other things so what is it?

Kobe_Wright

As in how would it be presented in a problem and in what units?

Kobe_Wright

Is this because the heat exploited is being contained by the same amount of work hence the dU=0 because they counteract each other?

Kobe_Wright

Title

Kobe_Wright

What would cp be in this equation?

Kobe_Wright

What would cp be in this equation?

Kobe_Wright

Im extremely lost in this chapter as im using the sixth edition do you think finding a 7th edition would help?

Kobe_Wright

Steam is hotter water, so hot it turned into a different phase state.

Kobe_Wright

when a problem says there is 3 moles or 6 moles of a certain molecule do we just use that value to find the concentration or do we put the moles given in the exponent of our equilibrium constant equation?

Kobe_Wright

The solution is neutral when K is between 10^-3 and 10^3 as the reaction does not significantly favor either sides reaction.

Kobe_Wright

Do you ignore the change in acid when its 1 x 10^-3 or less?

Kobe_Wright

This is problem 12.25 and when I added up the atomic number of BrOH2 and then divided the given grams by that I got 2.5x10^-2.

Kobe_Wright

Remember that on the pH scale Acid is a lower number so when you have a low Pka that means its a strong acid.

Kobe_Wright

If we are given pKa=2.12 would we find Ka by simply taking 10^2.12 = 131.825 or ? How do you find Ka from pKa?

Kobe_Wright

If we are given pKa=2.12 would we find Ka by simply taking 10^2.12 = 131.825 or ? How do you find Ka from pKa?

Kobe_Wright

If you add a solid you decrease the amount of volume which would increase pressure it seems to me?

Kobe_Wright

Kp simply related to the equilibrium constant when everything reacting is a gas but the process of finding it is the same as the Kc equation.

Kobe_Wright

If there is a reaction in which there is only gas in the reactants and they form solids do you then just put a one in the denominator of the kc equation.

Kobe_Wright

I'd say at least learn the whole chemical formula, and why it acts that way behind the formation of acid rain.

Kobe_Wright

Yup if the mol/l is greater than one then the pH is negative.

Kobe_Wright

Well you can determine the charge of the ligand by drawing the lewis strucuture and finding formal charge and by doing this you will find NH3 is neutral so the metal ion must have a 3+ charge

Kobe_Wright

Following this same exact reason.

Kobe_Wright

Usually if it is binding with a metal it is basic, and if its binding with a non metal its acidic but you usually need to find out experimentally but generally the first two groups are basic.

Kobe_Wright

If the acid has a higher a equilibrium constant that means it is a stronger acid which means its bond is stronger which makes sense that it would have a higher equilibrium constant because it would have the hardest bond to break.

Kobe_Wright

The more Electronegative the atom the stronger it's force is so a Fluoride is very strong(because of how many valence electrons it has, and how small its atomic radius is) and extremely electronegative when compared to say a regular carbon bond, it's charge isn't entirely negated by bonding so its s...

Kobe_Wright

Hybridization allows for certain Transition metal Cations to form a complex with an electron rich molecule, this can form coordination compounds which have many important biological significances such as how Iron forms a Heme complex by bonding with a Porphyrin Ligand, then when you bind a heme comp...

Kobe_Wright

Because if you're forming sigma bonds, youre doing so through a new hybridized spx orbital, but Pi bonds are formed by electrons that do not leave the p block so they are just simple p block electrons that make non rotating bonds with other P orbitals.

Kobe_Wright

There will always be a slight difference between different molecules, and their intramolecular processes which we probably won't cover, but lmk if anyone gives you a table with Lavelles exact wants because right now it seems like as long as you're close it's okay.

Kobe_Wright

However the structure is tetrahedral, the way that the atoms align in real life will have the hydrogens on the dorsal side and the chlorines on the ventral(or vice versa), and because the the very different electronegativities of H and CL they will create an effective polar molecule.

Kobe_Wright

Awesome, thank you.

Kobe_Wright

When we say that at atom has entered 2sp^3 (say carbon) what exactly has happened to the electrons that broke in the S orbital and joined the P orbital and what does a sp3 orbital now look like?

Kobe_Wright

You get points for all interactions, and also I have heard that the limit is not simply 3 a week but if you continue to interact you will be given more points.

Kobe_Wright

It is an experimentally observed way that bonds are formed, for instance in carbon there is 4 bonds made however carbon has 2s^2 and 2p^2 so technically it only has 2 valence electrons in an incomplete shell, so what happens when carbon is entering it's bonding state the 2s electrons diffract and jo...

Kobe_Wright

I put to conserve the law of conservation of mass and I got it right.

Kobe_Wright

The number of bonding atoms (bond type is irrelevant), and the number of lone electrons on the central atom. We can see this in the VSEPR formulas AXE. A= central atom, X= bonding pairs to central atom, E= number of lone electron pairs, each of these is denoted with subscripts telling the quantity o...

Kobe_Wright

Cation refers to elements that want to give electrons while anions refer to elements that want to receive electrons. Anions are highly polarizable because they are highly electronegative which means they want to receive an electron, and a cation is highly polarizing because it has a highly positive ...

Kobe_Wright

Because Ionic bonds are complete giving of one electron to another due to a high electonegative difference, while hydrogen bonding is the slight positive and negative sides of a molecule allowing two molecules to interact. The former is a stronger interaction.

Kobe_Wright

They are basically the same oxidation is the number of electrons needed to fill, or number needed to take away to fill an octet, and formal charge shows the overall charge of an atom and what it needs to balance that charge which is usually done by the formation of an octet.

Kobe_Wright

Any atom with an unpaired valence electrong for instance sc2+.

Kobe_Wright

Because potassium in this instance does not ever fill it's d shell because it doesnt have the atomic configuration to be in that orbital while for scandium it has the atomic configuration(protons+neutrons+electrons) that has it fill the 3d orbital which is of higher energy than the 4s in the ion, an...

Kobe_Wright

Nope! Shorter bond length= stronger attractions, longer bond length=weaker attraction.

Kobe_Wright

The above comment is wrong, Ca is actually more electronegative. Electronegativity increases as you go up a group and across a row because the farther up a group the less protons which means less pull to the nucleus and across the row means more valence electrons which increases the negative charge,...

Kobe_Wright

I asked about this in class, you do not need to write the formal charge of each atom in its lewis structure, but if you're checking for resonance you'll need to calculate it and see if there are any alternate structures.

Kobe_Wright

Check the formal charge of the lewis strucutre you drew, and then see if you can optimize it at all and come up with the same formal charge. If you can do this then there is resonance.

Kobe_Wright

Because when molecules have access to the d orbital they are able to store more electrons.

Kobe_Wright

Just try to limit the amount of charges, and the quantity of that charge as much as possible as that shows the most stable structure but yes the charges should add up from each atom to the overall formal charge. Also make sure that if you have to make a decision about where to put - or + charges the...

Kobe_Wright

Observe the atom numbers of the elements in the f block,notice where they fit in with the rest of the table, everything with atomic numbers above 58 will have electrons in the f block.

Kobe_Wright

If you can figure out how to write the electron structure youll see Mn=[Ar]3d^54s^2. You see that there are 5 electrons in the last empty shell so it has 5.

Kobe_Wright

Pretty sure its completely arbitrary as long as the other electron in pair has the other sign.

Kobe_Wright

Each shell consists of orbitals in which you can calculate the probability of finding electrons within certain parts of through mathematical processes like Schrodingers equation. You cannot determine the exact position or velocity of these electrons as they are so small and moving so fast we may onl...

Kobe_Wright

Shouldn't it be three significant figures considering in the problem he has 1.11 which has 3 sig figs compared to 1.1 which only has two, despite the scientific notation of the 10^x?

Kobe_Wright

Each s,p,d,f all have their own specific numbers of orbitals they go like this s:1 p:3 d:5 and f:7 so the shells start at 1 and increase b two in every subsequent shell.

Kobe_Wright

So the question is asking how long would 1.00 mol of Ag (6.022 x 10^23 atoms) strung together end to end would be. So, you know that the radius of each atom is 144pm, then the length of each atom would be double that, so now you have diameter 288, you then take 288pm(length of one atom in its entire...

Kobe_Wright

I am unsure as to what book and problem you are referring to, I think the rules are that we need to post the full problem in context.

Kobe_Wright

Well you would have to get the info that the composition of caffeeing is c(8)H(10)N(4)O(2), then you could construct a chemical equation and balance it, then using the known molecular mass, and the weight of the products we could use dimensional analysis and come up with the empirical, then molecula...

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