CHEMISTRY COMMUNITY

juleschang16

I understand how to find m and n using concentrations of different initial rates but then how do you find k? Do you just plug in a random rate with its corresponding concentrations?

juleschang16

What is the difference between homogeneous and heterogeneous reactions?

juleschang16

What is the difference between homogeneous and heterogeneous reactions?

juleschang16

I found this posted by chem mod in another post regarding the same question: "AVERAGE RATE = (CONC(t2) − CONC(t1))/(t2 −t1) = ∆CONC/∆t INSTANTANEOUS RATE = −(d[R])/dt OR INSTANTANEOUS RATE = (d[P])/dt AVERAGE & INSTANTANEOUS RATES CAN BE DIFFERERENT FOR THE INDIVIDUAL R & P. THINK OF TH...

juleschang16

In the textbook it says "Doubling the concentration of a reactant in a first-order reaction doubles the reaction rate." Does this mean that it will make a first-order reaction into a second-order reaction as well or is that not possible?

juleschang16

Why is it that for most reactions, the instantaneous rate decreases as the reaction proceeds? Does this mean the reaction is going towards consumption most of the time?

juleschang16

In which situation would you want to find the average rate and in which situation would you want to find the instantaneous rate?

juleschang16

When you are not given any values for change in enthalpy, temperature, and change in entropy, but are given a situation such as ice melting, how are you supposed to determine Gibbs Free Energy and its spontaneity?

juleschang16

What is the relationship between how negative/positive the cell potential is and how much more likely it is to be reduced/oxidized?

juleschang16

Does the side that the cathode and anode are on matter? In lecture, Lavelle said that the cathode is always on the right and the anode is always on the left, but my TA said it does not matter. However, in the textbook, it also says that switching the sides between anode and cathode will chance the s...

juleschang16

Since the Van't Hoff Equation is derived from the Gibbs Free Energy equation, how will we know which one to use? Like, in what scenario would the Van't Hoff Equation be used over the standard Gibbs Free Energy equation where deltaG = deltaH - T*deltaS ?

juleschang16

Why can you not measure the electron transfer of one cell? Since this is the case, why must you compare the electron transfer of the half reactions to the standard hydrogen electrode (what exactly is the standard hydrogen electrode)?

juleschang16

I don't think we need to memorize the exact diagram, but just the important components of the galvanic cell and how it works. For example, know the difference between a cathode and an anode and how the salt bridge connects the two to allow electron flow.

juleschang16

On the midterm Q3B was:
Phosphoric acid (additive E338) is used to acidify foods and beverages such as various colas and jams and provides a tangy or sour taste.
Write the reaction that represents Ka2 for phosphoric acid (H3PO4).

How would you go about solving this?

juleschang16

The purpose of a salt bridge is not to move electrons from the electrolyte, rather it's to maintain charge balance because the electrons are moving from one-half cell to the other. The electrons flow from the anode to the cathode.

juleschang16

The direction of electron flow in electrolytic cells, however, may be reversed from the direction of spontaneous electron flow in galvanic cells, but the definition of both cathode and anode remain the same, where reduction takes place at the cathode and oxidation occurs at the anode

juleschang16

In my discussion section, my TA said entropy is not disorder but the amount of microstates. This is much different from what I've learned in highschool, so on the midterm when asked to explain what entropy is, should I use the explanation of microstates?

juleschang16

Will the different types of systems affect the calculations in the change of energy on a system?

juleschang16

Why is temperature not in delta S when delta S = nRln(V2/V1)?

juleschang16

Some other types of calorimeters that we may need to know are reaction calorimeters and constant pressure calorimeters.

juleschang16

Delta H is the change in enthalpy and Delta U is the change in internal energy. Internal energy is the amount of energy a system has. However, we must realize that a system doesn't exist in a vacuum. Rather, there must be some sort of change in volume/pressure because of the presence of a system. If...

juleschang16

The Gibbs free energy graph shows whether or not a reaction is spontaneous-- whether it is exergonic or endergonic. ... Generally, all reactions want to go to a lower energy state, thus a negative change is favored. Negative ΔG indicates that the reaction is exergonic and spontaneous.

juleschang16

Heat capacity is an extensive property. As a reminder, an extensive property of a substance is one where QUANTITY does matter. Specific heat capacity is an intensive property. No matter how much aluminum you have, its ability to absorb heat energy at a particular temperature is the same.

juleschang16

In a irreversible reaction, the reactants react to form the products, which cannot revert back into reactants. In reversible reactions, as the reactants react with other reactants to form products, the products are reacting with other products to form reactants

juleschang16

Heat and enthalpy are two terms describing the energy flow and properties of a system. Heat is the form of energy transfer from a high temperature to a lower temperature. Enthalpy is the heat transfer at a constant pressure. Enthalpy cannot be measured directly. Rather, the heat added or lost from t...

juleschang16

What is the difference in calculating the pH of weak vs strong acid and bases?

juleschang16

What is protonation and what does the percent protonated mean?

juleschang16

What are the rules for Le Chatelier's Principle in response to changes in pressure, volume, and concentration?

juleschang16

When it is written as a subscript of P, that indicates the partial pressure of a substance. You will only use this when the molecule is given in a gaseous state which is indicated by (g) as a subscript in a reaction. For example, PCl5(g) <--> PCl3(g) + Cl2(g)

juleschang16

You can calculate Q and K the same way by following the formula [products]/[reactants] . The only difference is that the reaction quotient, Q is for ANY TIME during the reaction while the values for K are always the concentrations at equilibrium.

juleschang16

I don't think we have yet talked about how the equilibrium constant relates to free and relative energy quite yet. So far, we have learned that Kc shows how the reaction is balanced at equilibrium. For example, if Kc is small, then there are more reactants at equilibrium and if Kc is large, then the...

juleschang16

There were a couple problems on Test 3 where you had to use the AXE notation.

juleschang16

You always use the negative sign in the pH formula, regardless of the outcome.

juleschang16

They are amphoteric because they can act as both a base and an acid in redox reactions.

juleschang16

In the textbook, it says that lone pairs are not included when identifying molecular shapes. However, I thought we learned in class that the number of lone pairs and bonds determine the shape of molecules. Can someone clarify which one is correct?

juleschang16

For trigonal pyramidal geometry the bond angle is slightly less than 109.5 degrees, around 107 degrees. For bent molecular geometry when the electron-pair geometry is tetrahedral the bond angle is around 105 degrees.

juleschang16

What is the order of increasing bond lengths? Do triple bonds have the longest bond length or do single bonds have the longest bond length?

juleschang16

Do the number of sigma and pi bonds influence the shape/structure of a molecule? How so?

juleschang16

I understand that fluctuating dipoles are caused by fluctuating electron distribution but what exactly does it mean when dipoles fluctuate?

juleschang16

What are the expanded octet rules? Which elements can have expanded octets?

juleschang16

Could someone explain 13c to me? -13c is a Heisenberg Uncertainty Principle problem. The equation for this problem is ΔPΔX=>h/4pi. For this equation we need the mass, the velocity(these two values multipled together are ΔP), and we need ultimately to find ΔX. -We are given the mass which is 2.8 gra...

juleschang16

For question 4, the answer is given with only 2 sig figs (the answer is 9.9 mL of 9.9x10^-3 L, even though the question uses 3 sig figs. The question is: What volume of 0.0380 M KMnO4 is needed to prepare 250 mL of 1.50 x 10-3 M KMnO4? (Hint: In these types of problems, the volume containing solute ...

juleschang16

The question is: Which M^2+ ions (where M is a metal) are predicted to have the following ground-state electron configurations: (a) [Ar]3d^4; (b) [Kr]4d^9; (c) [Kr]4d^5; (d) [Kr]4d^3? I looked in the solutions manual for the answers but I was always one element off. The answers are (a) Co^3+; (b) Fe...

juleschang16

The question reads: Draw complete Lewis structure for each of the following compound: (c) glycine, H2C(NH2)COOH, the simplest of the amino acids, the building blocks of proteins. I looked in the solutions manual for the correct structure but I don't understand how they came up with that structure or...

juleschang16

What is the difference between ionization energy and electron affinity and what are their trends?

juleschang16

I believe that the line is only used to signify shared electrons and the point of writing the dots is to show that they are not bonded to anything. So, I would say follow what Lavelle taught and only use the lines for shared electron bonds.

juleschang16

What is the difference between atomic and molecular spectroscopy?

juleschang16

Which is the correct answer and why? 13. In the above experiment if only the absorbed wavelengths of light are detected what is the experiment called? What is the spectrum called? A. Atomic absorption spectroscopy; Emission line spectrum B. Atomic emission spectroscopy; Absorption line spectrum C. A...

juleschang16

Which is the correct answer and can you explain why?

In the photoelectric effect what condition must occur for an electron to be emitted from a metal surface?

A. E (photon) > 0

B. E (photon) < E (remove e-)

C. E (photon) = E (remove e-)

D. E (photon) > E (remove e-)

E. C and D

juleschang16

In the photoelectric experiment, an ultraviolet radiation source is shined on a metal and UV light is used over visible light because it has a higher intensity and therefore, more electrons can be emitted.

juleschang16

In Dr. Lavelle's lecture, he said that the smallest measurable length that has wavelike properties is 1x10^-18 m.

juleschang16

I'm pretty sure it's just the subjects in Chapter 2. I think if you complete the next five modules you'll be set for the test.

juleschang16

Can someone explain the key concept of "equations in quantum mechanics have variables that are quantized or discrete". What is the difference between quantized and discrete?

juleschang16

It is the easiest way to think about calculating the mass percentage of each element. So usually, when you find the mass composition, it is given in a percentage. You take this percentage out of 100 grams. For example if the mass composition of carbon was 20%, it would be 20 grams.

juleschang16

Yes, so scientific notation figures are normally written as for example 2.00 x 10^6 implying that there are three significant figures.

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