CHEMISTRY COMMUNITY

Angela Wu-2H

For part e of 7.17, I understand that the catalyst will have no effect on the overall rate if the catalyst only affects the third step. However, if the problem changed and says it only affects the first step, which is the rate-determining step, would the catalyst thus have an effect on the overall r...

Angela Wu-2H

How do I tell which compound is the catalyst? For example, in the homework problem 7E.5, I thought the OH was an intermediate (in addition to the other listed intermediates), rather than the catalyst. How was I supposed to know that OH is a catalyst rather than an intermediate?

Angela Wu-2H

The question states: Step 1: NO + Br2 ---> NOBr2 (slow) Step 2: NOBr2 + NO ---> NOBr + NOBr (fast) Write the rate law for the formation of NOBr implied by this mechanism. I know how to write the rate law (rate=k[NO][Br2]), but I was just curious as to how to write the overall reaction, just to prepa...

Angela Wu-2H

When do we use the Arrhenius Equation? Is the activation energy (Ea) always given?

Angela Wu-2H

What is the difference between differential and integrated rate law? When do we use each one?

Angela Wu-2H

I think the larger the species, the electron cloud is bigger, thus having more area for the electrons to travel, thus having more randomness and a higher degree of disorder.

Angela Wu-2H

How do we know how to determine or know the electrochemical series? Or is it just something we need to memorize?

Angela Wu-2H

What are first, second, and zero order reactions? Like what does it mean to be a first order reaction, etc.? Why does it make a difference in kinetics?

Angela Wu-2H

So, from the cell diagram, the two elements don't have to be on opposite sides of the rxn? Like since O2 and H+ on the anode side of the cell diagram doesn't have to have a half rxn of O2--->H+? I have the same question. Shouldn't the half reaction go from O2 to H+ because the cell diagram says O2(...

Angela Wu-2H

Instead of writing Zn --> Zn2+ + 2e- for oxidation, can I write: Zn - 2e- --> Zn2+ ? This method seems to make more sense in my opinion because it allows me to think Zn is losing two electrons in order to form Zn2+, thus Zn minus 2 electrons. This makes the oxidation process more obvious in my opini...

Angela Wu-2H

Anode = Left = Oxidation (Losing electrons) meanwhile Cathode = Right = Reduction (Gaining electrons)

Angela Wu-2H

Nohemi Garcia 1L wrote:I believe you add platinum to a cell diagram when the anode and/or the cathode need a solid conductor.

How do we know/tell if the anode or cathode needs a solid conductor?

Angela Wu-2H

Is there an equation or chemical formula we have to write down for the salt bridge? Or do we just say we have a salt bridge or draw it into the cell diagram?

Angela Wu-2H

What is the purpose of delta phi in terms of electrochemistry? Why do we need it or when do we use it? What's the equation aside from delta phi = phi right - phi left ?

Angela Wu-2H

What is delta phi? My notes say, "delta phi is the electromotive force (emf), E, of the cell (E=cell potential)." But I don't understand this concept at all. Delta phi (as i approaches 0) = E, but what is "i"?

Angela Wu-2H

When do we use this equation? I don't recall learning this in lecture.

Angela Wu-2H

Will test 2's difficulty be more like test 1's difficulty or the midterm's difficulty?

Angela Wu-2H

What's the difference between calculating standard cell potentials and non-standard cell potentials?

Angela Wu-2H

Ronak Naik wrote:Higher cell potentials will indicate a greater level of spontaneity; however, spontaneity is a thermodynamic concept. It does not relate to kinetics, and thus, will not tell us anything about the speed of a reaction.

So then what tells us about the speed of a reaction? Is it just a catalyst?

Angela Wu-2H

What's the difference between oxidation numbers and oxidation states? Also, how do I calculate oxidation numbers and why are oxidation numbers important?

Angela Wu-2H

Why are cell diagrams important? Also, can someone explain cell diagrams to me? I'm super confused.

Angela Wu-2H

What is a cathode and what is an anode? Is cathode just always the one on the left side of the cell diagram?

Angela Wu-2H

Anisha Chandra 1K wrote:An example of some half reactions would be:

Zn(s) --> Zn2+(aq)
Cu2+(aq) --> Cu (s)

So in these examples, which one is oxidizing and which one is reducing?

Angela Wu-2H

Is reduction based on charges and electrons or is it based on moles?

Angela Wu-2H

Will there be any extra credit opportunities? Or any opportunities to get points to boost our grades?

Angela Wu-2H

Why does it matter if a system is reversible or irreversible? Does it change the formulas utilized?

Angela Wu-2H

What is the official definition of the First Law of Thermodynamics that we should know for this class? I know my notes simply say that "Internal energy of an isolated system is constant. Universe is an isolated system; therefore, energy of the universe is constant." Does the first law of t...

Angela Wu-2H

The formula is basically derived from each other, so I believe we could use both.

qp=delta H so
delta U = q+w ------> delta U = delta H + w
w = -p*delta V -------> delta U = delta H -p*delta V
solve for delta H so...
delta H = delta U + p*delta V

Angela Wu-2H

Under my class notes, it states "Because heat is required during melting or boiling (phase transitional), the temperature of the sample remains constant even though heat is being supplied." Is this basically saying temperature stays constant because the heat required cancels out with the h...

Angela Wu-2H

For 4D.21, I have the exact numbers and equation correct according to the book, but my final answer was different from the book answer manual. The book says the correct answer is "-138.18 kJ" but I got -709.84 kJ. Am I making a minor calculation mistake based on how I put it into the calcu...

Angela Wu-2H

Delta U is the change in internal energy; meanwhile, delta H is enthalpy, or the change in heat.

Angela Wu-2H

By standard form, is this referring to the STP vs. NTP thing?

Angela Wu-2H

Will we need to memorize all these formulas or will they be given on the formula sheet?

Angela Wu-2H

Why does it matter if something is a state function or not? How does it affect the problem/question? I'm very confused.

Angela Wu-2H

Is the constant pressure being referred to by everyone just 1 atm? Or will the actual pressure be given with the question?

Angela Wu-2H

Can you elaborate on what info should be given for each method?

Angela Wu-2H

Pressure does not affect the equilibrium constant. Only temperature changes the equilibrium constant.

Angela Wu-2H

What is the difference between delta H and delta U?

Angela Wu-2H

Are there different ways to calculate or determine the bond enthalpy versus the standard enthalphy?

Angela Wu-2H

I also believe that, through the diagram that he showed in lecture, steam is hotter than liquid because the temperature was much higher above 100 degrees, meanwhile the liquid for temperature went between 0 degrees and 100 degrees.

Angela Wu-2H

The test is in your chem discussion. The points are usually based on the amount of time given. I believe this test should be 50 points (so 50 mins to take it) and about 7-8 questions long.

Angela Wu-2H

To clarify, what is the pH scale for acidity? The most acidic is a lower pH, meanwhile the more basic is a higher pH right?

Angela Wu-2H

Adding a catalyst will not change the equilibrium concentrations. A catalyst simply speeds things up, so equilibrium will be reached quicker.

Angela Wu-2H

You can use the ideal gas law (PV=nRT) with concentration as well because Molarity is mol/liter, which is also what n/v is (if you divide V over to the right side).

PV=nRT --> P= (n/v)RT

Angela Wu-2H

For a small equilibrium constant (K<10^-3), it favors the reactants so more reactants are produced. Why?

Angela Wu-2H

K has no units because of "activity"; however, activity is really low (close to 1) for the most part, so the equation ratio is simplified to the form that we know. But also, in the ratio, the units in the numerator and denominator will cancel out.

Angela Wu-2H

To clarify, by "inert gas", you guys are referring to mostly helium and the noble gasses right? These are inert gasses because they will not react due to their full valence shells?

Angela Wu-2H

Can partial pressure be measured in bars and atm or just bars?

Angela Wu-2H

Q is focused on the reactants and products that are gasses or aqueous solutions, meanwhile K can be for all forms including solids I believe.

Angela Wu-2H

In class, Professor Lavelle mentioned Le Chatelier's Principle. What is Le Chatelier's Principle and how does it apply to chemical equilibrium and the ideal gas law?

Sorry, I don't have a strong background in chemistry because I didn't take AP Chem and don't remember sophomore year's chemistry.

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