CHEMISTRY COMMUNITY

Sara Varadharajulu

yes it is. I think it is because you are only using one type of ion/metal and the current is caused by a difference in concentration.

Sara Varadharajulu

at equilibrium the total change in entropy is 0, so delta g would be zero.
using the formula delta g= deltaH - Temp(deltaS), at Tb or Tf, deltaH=deltaS*T, meaning that delta g would be zero.

Sara Varadharajulu

electrolytic cell converts electric energy into chemical energy (need external power source to drive current). a galvanic cell converts chemical energy into electrical energy.

Sara Varadharajulu

if e cell is very positive, it means the element has high oxidizing power because it is able to be reduced very easily.

if e cell is very negative, it means the element has high reducing power because it is able to be oxidized very easily (the reverse reaction, in this case oxidation, is favored).

Sara Varadharajulu

I think we only need to distinguish between a galvanic/voltaic and a concentration cell.

Sara Varadharajulu

the only thing you would have to take into account the coefficient of the product is the unique rate

Sara Varadharajulu

Will a catalyst appear in the overall reaction or the rate law?

Sara Varadharajulu

there are certain equations that we are expected to know not on the constants sheet I think----I believe these are more intuitive or can be easily derived.

Sara Varadharajulu

k itself cannot be negative but the slope involving k as with 1rst order or 0 order reactions can be negative.

Sara Varadharajulu

aside from set elements like 0, H, etc, the oxidation number can very depending on the compound. most of the time by knowing that 0 is 2- and H is +1 you can figure out the rest of the oxidation states.

Sara Varadharajulu

yes, I think we do.

Sara Varadharajulu

I think for this test we don't have to worry about this topic

Sara Varadharajulu

coefficients don't directly relate to the order of the reaction. however, for the unique rate, coefficients do matter.

Sara Varadharajulu

when we are doing calculations it is good to note that we are always calculating the max

Sara Varadharajulu

it is important to note that k is for a given reaction at a fixed temperature. so when T increases, k also increases and vice versa.

Sara Varadharajulu

theoretically, I think that hydroxide ion can be reduced or oxidized, but I think it usually gains a proton to become h20.

Sara Varadharajulu

internal energy cannot change without a temperature change; this means for isothermal reactions delta U is zero. this is because of the equation delta U=(3/2)nR(delta T)---it should be on the equation sheet as internal energy for an ideal gas.

Sara Varadharajulu

at room temperature, water does have a entropy of vaporization---its like how a puddle evaporates---no one is boiling the puddle but eventually it becomes vapor. to solve these problems you usually 1) calculate entropy change for raising the temp to boiling point 2) calculate entropy of vaporization...

Sara Varadharajulu

I am actually not sure if there is a standard molar entropy of formation?---I thought it was just standard molar entropy for a substance...
for residual entropy, it is the entropy remaining when the temperature is 0K. unless the substance is a perfect crystal at 0k, it will have a residual entropy.

Sara Varadharajulu

I also had the same question!

Sara Varadharajulu

I think the sig figs would just come from the amount of sig figs the book used for the standard Gibbs free energy of formations. in general though, for this unit, I don't think sig figs matter.

Sara Varadharajulu

what is the difference between cis and trans isomers?

Sara Varadharajulu

yes, you do. the entropy increases when going from solid to liquid to gas and decreases in the opposite direction. you can use delta s= q(rev)/T. the q for a reversible reaction is equal to the enthalpy of fusion, vaporization etc. this will help you account for the entropy change during phase chang...

Sara Varadharajulu

delta s total will only be zero when the system is at equilibrium---for reversible isothermal expansion, it is like the system is at equilibrium, so you can assume delta s total is 0. since part b talks about irreversible expansion, the system is not at equilibrium. this means that delta s total is ...

Sara Varadharajulu

When reading the book on pg 347 there is self test 9.18A: Confirm that liquid water and water vapor are in equilibrium when the temperature is a 100 degree C and the pressure is 1 atm. Data are available in Table 8.3 and 9.2. Does anyone know how to solve this? I understand the concept but I don't g...

Sara Varadharajulu

In the corrected solutions manual, for calculating the change in entropy due to temperature, the manual states that Cv,m is equal to (5/2)R. Isn't heat capacity at a constant volume for an ideal gas 3/2R? Did they mean to say to use heat capacity at constant pressure? Could someone share their work ...

Sara Varadharajulu

for these types of problems, I would highly encourage drawing a diagram---this helps you keep track of the state of the substance at hand so you now the correspond specific heat capacity. since ice melts into water before the water raises temperature, you need to use the specific heat capacity of wa...

Sara Varadharajulu

Usually if he wants us to know a specific table, he makes sure to point it out on the chapter review sheet---since this box wasn't specifically mentioned, I'm sure you don't have to memorize it.

Sara Varadharajulu

when its a combustion reaction, I generally assume the water is in a liquid state.

Sara Varadharajulu

ZnCl2 is aq, which means you can think of it as zn 2+ ions and 2 cl- ions (in the solution they appear as ions anyway). look up the enthalpies of formation for these two ions (these are in the book).

Sara Varadharajulu

I agree---if gas in a piston is doing work, it means its pushing the piston, therefore increasing the volume and decreasing the overall pressure. I don't know exactly why T is constant (besides looking at PV=nRT), but maybe it has to do with system vs surroundings? I also don't know for sure if addi...

Sara Varadharajulu

as a note, for this particular test, I think it was mentioned that we don't need to know calculations for problems concerning reversible, isothermal expansion

Sara Varadharajulu

The enthalpy of formation will be different as we are using bond enthalpies to estimate. While the bond enthalpies for diatomic molecules are accurate (since they are measured for these molecules), the other bond enthalpies are simply estimates---they are found by averaging the data gathered from ma...

Sara Varadharajulu

I think the only thing we will need to know are the standard states for common reactants like hydrogen, oxygen, etc. all other values should be provided.

Sara Varadharajulu

I think what she means (as this was the same for me too), if you do you homework in pencil for example, get something wrong and correct it in pen, and turn in that marked up homework, you still get full credit.

Sara Varadharajulu

I think when the volume is not constant (like with a piston), you need to take into account work (to move the piston?). im not quite sure though.

Sara Varadharajulu

general info: a high value of ka or kb correlates with a strong acid or base since the products are heavily favored. a low value of ka or kb correlates with a weak acid or base since the reactants are favored. ka*kb=Kw=10^-14 If its a weak acid, then its ka will be quite small; because Ka*Kb equals ...

Sara Varadharajulu

I part A, but can someone please explain parts B and C to me? In particular, I don't understand the solution manuals work for part b (why do you multiply by 500ml/5ml?).

Sara Varadharajulu

Why does the answer state that 2A forms B + C. Where did they get 2A from the graph?

Sara Varadharajulu

if im correct a bronsted base is a proton acceptor and a bronstead acid is a proton donor.
a lewis acid is an electron donor and a lewis base is an electron acceptor.

Sara Varadharajulu

when you decrease the volume and that results in an increase in pressure, the reaction will go toward the side with less mols (bc that has lower pressure in terms of concentration).
when you increase the pressure in terms of inert gas, nothing happens.

Sara Varadharajulu

i think the order only matters when you are naming; when you are writing the equation the order of the ligands doesnt matter. when writing the name of the compound you must list the ligands in alphabetical order.

Sara Varadharajulu

it depends on what the question is asking. if the states are all aqueous, you will need to write concentrations, so use brackets. if it is a gas you can write it as a partial pressure using P or as a concentration using brackets---this will depend on what the question is asking and the information i...

Sara Varadharajulu

the change for the reactant should be negative if the reactant is turning into product.

Sara Varadharajulu

me too for sure----there's just so much content and all of it is new for me since i never took Ap chem.

Sara Varadharajulu

Why would the bond angle increase when the s-character of a hybrid orbital increases? What does it mean to say "the s-character of a hybrid orbital increases"? How does s-character increase?

Sara Varadharajulu

the only thing that affects the bond angle in the VSEPR are lone pairs---the more lone pairs on the central atoms, the lesser the angle because the lone pairs push the bonding pairs closer together. bond multiplicity does not matter.

Sara Varadharajulu

Since the electron arrangement is linear and on either side of the Si are 0 atoms, the dipole moments cancel (dipole moments are formed when there is a difference in electronegativity between the two atoms). this means the molecule is non polar.

Sara Varadharajulu

i don't quite understand the formatting of your question so i will answer in terms of general concepts in general...anions are larger than the normal atoms bc you add an extra electron which creates more electron to electron repulsion and makes the atom larger. cations are smaller than normal atoms ...

Sara Varadharajulu

i think the formula is written as HOCO to emphasize the order in which the atoms are bonded (which is why its not CH02 or something).

Sara Varadharajulu

Why are multiple bonds shorter than a single bond between the same two elements?

Sara Varadharajulu

Keep in mind the number of valence electrons. If your atoms needs a lot more valence electrons to complete its octet, most likely you will be using double or even triple bonds. Atoms like Cl with almost an octet will only need single bonds. It is fine to use just single bonds. Some lewis structure c...

Sara Varadharajulu

I think its fine to take 14B and 14BL in the same quarter; from what I know, its just not recommended to take 14BL and 14C together.

Sara Varadharajulu

Essentially they are the same thing. Things with high, positive electron affinity have high electronegativity. Electron affinity is the energy released when an electron is added to a gas phase atom; when the energy is positive is means that the atom "wants" the electron and when its negati...

Sara Varadharajulu

On pg 44 of the book, it states that an atom has an inner core consisting of electrons in filled orbitals that around surrounded by valence electrons, which are the electrons in the outermost shell. Is the "core" the last noble gas or does it also consist of e- in the last filled orbital? ...

Sara Varadharajulu

I understand that when n, the principal quantum number, increases, the size of the shell of the atom also increases. But, why do increasing values of n also corresponding to increasing energy of the orbital?

Sara Varadharajulu

Hi Rachel, We use a negative sign in this equation because the energy of an electron completely removed from an atom is 0; therefore, as it falls and emits a photon, its energy becomes more and more negative. so the energy of an electron you calculate at each energy level will be negative. when you ...

Sara Varadharajulu

Hi Rachel, You are right---if light mirrored a wave, changing the intensity, or the amplitude of the wave, should have increased the energy of the wave and booted off an electron. However, in this instance, light is behaving light a particle. This means that changing the intensity, or the number of ...

Sara Varadharajulu

You are correct to say there are 2 atoms of Na in NA2(C03). However, I would think about that a bit differently. What this really means is that for every mole of sodium carbonate, you have 2 mols of Na; the ratio of Na to sodium carbonate is 2:1. So, to get a certain number of moles of Na, you need ...

Sara Varadharajulu

This problem is asking you for the length of the fiber---I imagine the fiber to be all the Ag atoms lined up in a row. The length each atom contributes to the total fiber length is its diameter. (eg: if you had 2 atoms each with a diameter of 2cm and you wanted to make a fiber, the fiber would be 4c...

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