CHEMISTRY COMMUNITY

Maayan Epstein 14B

Thank you for these!

Maayan Epstein 14B

Thank you for all your help this quarter, Lyndon!

Maayan Epstein 14B

Thank you for all your help this quarter, Joyce!

Maayan Epstein 14B

Can anyone explain 1D?
Thanks!

Maayan Epstein 14B

It is similar to how we do pseudo rate constants. We make one reactant so large that it basically doesn't affect the reaction rate, enabling us to just study the other reactant as if it is the only thing that affects the rate. Same thing with liquids and solids. They are in such high excess that the...

Maayan Epstein 14B

The equilibrium constant will tell you this. If K is greater than 10^3 then it favors the products, meaning that the products are much mnore stable than the reactants. If K is smaller than 10^-3 then it favors the reverse reaction and the reactants are much more stable than the products. If K is bet...

Maayan Epstein 14B

When you report the moleculairty of a step, and that step includes a catalyst, do you include the catalyst in the molecularity or not? Thanks!

Maayan Epstein 14B

The reaction that is least likely to occur has higher molecularity (i.e. third order reactions are less likely to occur than second order which are less likely to occur than first order). This is because two things need to happen for a reaction to occur: the molecules need to collide in the proper o...

Maayan Epstein 14B

The second method is correct. I am not sure how you solved the first method, but you use the equation ln(k2/K1)= RT(1/T2 -1/T1) to solve for K2. Then you use K2 to find the concentration of H+. The equilibrium concentration of H+ at 10 degrees C for a neutral solution (we know it is neutral because ...

Maayan Epstein 14B

Do you mean Ecell or E (standard) cell? Because E (with the circle on the top symbolizing standard conditions) is different from Ecell.
The Nernst equation shows the relationship between these: Ecell = E(standard) - (R*T)/(n*F) * lnQ

I hope that helps!

Maayan Epstein 14B

I am not totally sure what you mean by net rate of reaction, but for each elementary step the rate should look the same. For example: Step 1: A + B ----> C Step 2: C -----> D Both should have rate = k[reactants] so for step 1 use rate constant k1: rate = k1[A][B] and for step 2 use rate constant k2:...

Maayan Epstein 14B

I think that it is better to just know the rule that a catalyst is something that appears in the beginning and end of the reaction (is not consumed, and is not an intermediate).

Maayan Epstein 14B

How does changing the concentration of different species affect the rate of the reaction? If a reactant has a coefficient of 1 and you double its concentration and the rate of reaction doubles then this is a first order reaction. If a reactant has a coefficient of 1 and you double its concentration ...

Maayan Epstein 14B

I still a bit confused on what exactly order of reaction means and how this interacts with different species. For example, in the reaction: H2 + I2 ----> 2HI. Why is this a second order reaction? Is it because each reactant has a coefficient of 1 and 1+1 equals 2, or because the product has a coeffi...

Maayan Epstein 14B

You can calculate the unique rate by dividing the rate of reaction of a specific species by its coefficient. This is the unique rate of reaction, and will be the same rate if you use any of the species in the reaction.

Maayan Epstein 14B

If this is 15.7 in the 6th edition, I noticed that on the syllabus Dr. Lavelle did not include this in the practice problems to do.

Maayan Epstein 14B

How do you balance the H+ in a cell when it is basic?
I don't understand how to convert H+ into OH- and balance from there (what order of steps should I take?)

Thank you!

Maayan Epstein 14B

Hi, in homework question 14.1 in the 6th edition, I am supposed to name the elements that undergo either oxidation or reduction. The answer solution does not include oxygen in it, even though it is oxidized. Can someone explain? H+ (aq) +cr2o7^2- (aq) +c2H5OH (aq) --> Cr^3+ (aq) + C2H4OH (aq) + H2O ...

Maayan Epstein 14B

When something is a "reducing agent", does this mean it gets oxidized or reduced? Furthermore, does this mean it is the cathode or the anode?

Maayan Epstein 14B

Why is delta S of reaction different than delta S molar/delta S of formation of a substance? For example, in problem 9.55 (6th edition), we use an appendix to look up the delta S of formation (listed as delta S molar) of a substance, i.e. NH3, and subtract from it the delta S molar of its reactants ...

Maayan Epstein 14B

How do buffers work in acid base reactions? Can someone explain, thank you!

Maayan Epstein 14B

Thank you!

Maayan Epstein 14B

Is there a difference between calculating percent ionization and percent deprotonation? Are they the same thing?

Thanks!

Maayan Epstein 14B

Thermodynamics is work, heat, and energy (this includes enthalpy and entropy), whereas thermochemistry is about the bonds and the molecular structure. I think of thermochemistry as the microscopic level, whereas thermodynamics is bigger picture.

Maayan Epstein 14B

Thank you for the responses!

Maayan Epstein 14B

When do I plug in the ideal gas constant, R, as 0.0825, and when do I plug it in as 8.314?
Not sure when to use which!

Maayan Epstein 14B

Homework problem 8.23 in the 6th edition textbook states: "A calorimeter was calibrated with an electric heater, which supplied 22.5 kJ of energy as heat to the calorimeter and increased the temperature of the calorimeter and its water bath from 22.45 C to 23.97 C. What is the heat capacity o...

Maayan Epstein 14B

Enthalpy refers to the change in the internal heat of the system at constant pressure (qp).

Maayan Epstein 14B

Something else to note is that this equation is only used when temperature is constant, because all the other q equations involve a delta T, whereas this one is just T by itself.

Maayan Epstein 14B

Cp and Cv are constants. Cp=20.8 and Cv=12.5.
They are used in the q (or delta H) equations, where qp (q at constant pressure) = nCp(delta T), and qv (q at constant volume) = nCv(delta T).
Hope that helps!

Maayan Epstein 14B

Also something to be aware of is that if there is an increase in pressure but the same number of moles of gas on each side of the equation, then nothing happens to the system. If the question states that the PARTIAL pressure of one of the chemicals in the reaction increases, and not the total pressu...

Maayan Epstein 14B

Do we need to know second deprotonation for tomorrow's test?
Some of the homework problems for chapter 12 mention it (i.e. 6th edition 12.81)
Thanks!

Maayan Epstein 14B

Thank you Kim for your response! Super helpful.
Do you know why heat and temperature are not treated in the same way in terms of how they affect equilibrium? It seems like both heat and temperature would affect the rate that the molecules hit each other.

Maayan Epstein 14B

If Kc of the forward reaction is the inverse of the Kc of the reverse reaction, then does this mean that in an acid-base chemical equilibrium reaction, the conjugate acid would dissociate at the inverse rate that the conjugate base would accept a proton (in the opposite direction)? If my logic is fl...

Maayan Epstein 14B

Why does changing temperature change the equilibrium constant K, but changing pressure, heat, and concentration does not?

Maayan Epstein 14B

The reason that you can do an approximation where you "ignore" the x in the denominator, is because if the K value is smaller than 10^-3, then the x when multiplied out by this k value will be very negligible. So, instead of going through the whole process and doing the quadratic formula i...

Maayan Epstein 14B

How do I know what to plug into ice tables? For example, I know that I can plug in molarity to find initial, change, and equilibrium. Will this work for pressure too?
Thanks!

Maayan Epstein 14B

Thank you so much for your response! It makes much more sense now. I guess another way to think about it is that the reactants are the diatomic (stuck together) gas molecules and the products are the single, free floating molecules.

Maayan Epstein 14B

For this week's homework, one of the problems (11.7 in the 6th edition) shows a picture of four flasks with gas molecules in them. The gas is an unknown diatomic molecule, X2. Part a of the questions asks: "Which flask represents the point in time at which the reaction has reached equilibrium?&...

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