CHEMISTRY COMMUNITY

Jasmine Wu 1L

Technically, you can use both to get the same answer. Dr. Lavelle taught us the pre-equilibrium approach, which the the "preferred" method for less complex mechanisms. Pre-equilibrium is less flexible than steady-state and more difficult to extend to more complex mechanisms (i.e. with lots...

Jasmine Wu 1L

UA Lyndon has a practice final up on Chemistry Community already.

viewtopic.php?f=160&t=29688&p=92277&hilit=red+panda&sid=8519397833e3adfee6753eddb79ace3b#p92277

Good luck studying!

Jasmine Wu 1L

A is the pre-exponential factor and it represents the frequency of collisions between the molecules in correct orientation. It is the constant obtained from the y-intercept in an Arrhenius plot. The Arrhenius plot is a graph of ln k against 1/T.

Jasmine Wu 1L

Enzymes are "living" catalysts, and catalysts can increase the rate of a reaction.

Jasmine Wu 1L

A represents the frequency of collisions between the molecules in correct orientation and is the y-intercept in an Arrhenius plot. The Arrhenius plot is a graph of ln k against 1/T.

Jasmine Wu 1L

Yes, it does. For reactions to occur, the particles must collide and also have sufficient energy to cause that reaction. By increasing the concentration, you are also increasing the chances and frequency of collision between those particles.

Jasmine Wu 1L

On the kinetics lecture outline on Dr. Lavelle's website, it says that you should "know how to derive the differential and integrated rate laws for zero, 1st and 2nd order reactions and know how to derive their respective half-life equations". The constants and equations give the integrate...

Jasmine Wu 1L

For a chemical reaction a A + b B \rightarrow c C + d D the formula for rate is k [A] a [B] b , where k is the rate constant, [A] is the concentration of reactant A, and [B] is the concentration of reactant B. Each reaction has its own unique rate law and rate constant, so Table 15.1 is just general...

Jasmine Wu 1L

"n" is the amount of electrons (in moles) of electrons transferred in the reaction. You'd find it by first writing out the balanced half-reactions for the redox reaction given. Then, from the balanced redox reaction, find the number of electron needed to balance the charges. For this probl...

Jasmine Wu 1L

According to the announcements on Dr. Lavelle's website, Sections 15.1 to the end of 15.6 of the textbook will be covered on Test 3 (Kinetics).

Jasmine Wu 1L

Xihui Yin 1I wrote:
Adrian Lim 1G wrote:Isn't I2 a solid though?

You need a conducting solid.

And how do you tell if something is or can act as a "conducting solid"?

Jasmine Wu 1L

In the cell diagrams, the convention is: anodes on the left, and cathodes on the right.

Jasmine Wu 1L

The double-line ( || )part represents the salt bridge. To the left of the || is the anode, where oxidation half-reaction is taking place. To the right of the || is the cathode, where the reduction half-reaction happens. Platinum basically functions as an inert electrode that do not participate in th...

Jasmine Wu 1L

Veritas Kim 2L wrote:What is the difference between Gibbs free energy of reaction and Standard Gibbs free energy of reaction?

Standard Gibbs free energy of reaction is the Gibbs free energy collected under standard state conditions.

Jasmine Wu 1L

An oxidizing agent removes electrons from something that's being oxidized and is thus reducing itself, while a reducing agent gives electrons to the thing being reduced and oxidizes itself. The book gives examples for the oxidizing agent (O 2 , O 3 , MnO 4 - , and Fe 3+ ) and the reducing agent (H 2...

Jasmine Wu 1L

Yes, enthalpy is a state function. The formula for enthalpy (H=U+PV) consists of terms also defined as state functions. Enthalpy change relies solely on the initial and final states of the system and it does not matter how you get from the initial and final state, which is essentially the definition...

Jasmine Wu 1L

Gibbs free energy is the system's energy that is available or free to do work at constant pressure and temperature. Formula: G=H-TS

Enthalpy(H) change ( $\Delta$ H) is the heat absorbed or released at a constant pressure, given by the equations: H=U+PV and $\Delta$ H=q

Jasmine Wu 1L

The standard temperature is 0*C (273K) and pressure is 1 bar, for STP.

However, STP is rare in lab settings, so SATP (Standard Ambient Temperature and Pressure) is used. In SATP, the temperature is 25*C and pressure is 1 bar.

Hope this helped you!

Jasmine Wu 1L

Hello! Hopefully I'm not alone with this, but I feel that there are so many equations in Chapter 8, 9, and 11! A lot of them look quite similar, too. How would you know when to use what the book describes as "molar" convention (i.e. which formula to use). Sometimes I see that the units of ...

Jasmine Wu 1L

Toolbox K.1 does a good job explaining how to assign oxidation numbers. Use it as a reference to help you! In summary, the oxidation number for groups 1 and 2 is equal to their group number. The halogens have an oxidation number of -1. For oxygen it is -2. Hydrogen combined with nonmetals is +1, whi...

Jasmine Wu 1L

For transition metals: uncombined elements have an oxidation state of zero. The oxidation state for ions equals the charge of the ion, and for neutral compounds it equals zero.

Jasmine Wu 1L

You can use this to calculate the change in the entropy of a system, provided that the temperature is constant. The "rev" subscript of q signifies that the energy must have been transferred reversibly. Recall that, for a reversible energy transfer, the surrounding's and the system's temper...

Jasmine Wu 1L

For 9.69: yes, I believe that you would use Hess's Law approach. The chemical equation for the oxidation of 1 mole NADH can be obtained by adding equations (2) and (3) given. Then just multiply what you got after you added by 3 (because you want to find for delta G for 3 moles NADH). Remember to add...

Jasmine Wu 1L

For question 9.85 part c, the entropy change in the system is due to change in positional disorder, because it is doing from a solid to aqueous state. In the aqueous state, molecules/ions can move more freely as opposed to when they are rigidly packed together in a solid. Thus, entropy is higher in ...

Jasmine Wu 1L

To answer this question: a) Find the correlation between the enthalpy change and the number of moles of NO from thermochemical equation. The heat absorbed to form 2 mol NO is the given 180.6 kJ. Then, just multiply the 1.55 mol NO by the ratio described above: (180.6kJ / 2 mol). b) Use the ideal gas...

Jasmine Wu 1L

I find that, when doing bond enthalpy problems, it really helps to draw the Lewis structures because they really help you "visualize" what bonds are there and what is to be broken and formed. Once you have determined what bonds there are to be broken/formed, then using Table 8.6 or 8.7 wou...

Jasmine Wu 1L

Combustion of a hydrocarbon produces carbon dioxide in the gaseous phase, water in the liquid phase, and heat.

Jasmine Wu 1L

8.59 asks us to use Appendix 2A calculate the standard reaction enthalpy for the reaction of pure nitric acid with hydrazine, which is: 4HNO 3 (l) + 5N 2 H 4 (l) \rightarrow 7N 2 (g) + 12H 2 O(l) According to Appendix 2A: \Delta H f for HNO 3 (l) is -174.10 kJ/mol \Delta H f for N 2 H 4 (l) is +50.6...

Jasmine Wu 1L

An adiabatic process is a process in which energy is transferred by just work, not heat. Think of it as something that is thermally insulating.

Jasmine Wu 1L

In a reversible process, the system and surroundings can be "reversed" to its initial state by an infinitely small change, thus not changing the thermodynamic properties of the universe. In an irreversible process, which is most natural, the infinitely small change does not reverse to the ...

Jasmine Wu 1L

The units for heat capacity/specific heat capacity are in Joules. For example, the specific heat capacity for water is 4.18 J.K -1 .g -1 I guess it would be fine to use kJ or J, as long as you do your conversions in the end to match the units for heat capacity/specific heat capacity. Remember: (1 kJ...

Jasmine Wu 1L

The term "energy" is the ability and capacity to transfer heat or do work. But, "heat" is the flow of energy transferred because of a temperature difference .

Jasmine Wu 1L

Given in this example: A piston confines 0.100 mol Ar(g) in 1.00L at 25 degrees Celsius. a) The gas is allowed to expand through an additional 1.00L against a constant pressure of 1.00 atm. The book says to use Equation 3 (w= -P ex \Delta V ) to part a because it is an "irreversible path"....

Jasmine Wu 1L

Just out of curiosity, does work (as defined in Chapter 8.2 in the book) have anything to do with the work function we learned about in CHEM 14A?

Jasmine Wu 1L

Strong acids/bases are completely ionized in solution, but weak acids/bases are not. So you would need to calculate the concentrations, which is what the ICE box is for.

Jasmine Wu 1L

I think you would multiply by 2 because, in the formula Ba(OH)₂, there are 2 moles of OH- (look at the subscript) for 1 mole of Ba(OH)₂. So, there's a 2:1 ratio.

Jasmine Wu 1L

According to the Solutions Manual, Formic Acid, HCOOH, withdraws more electrons than Acetic Acid, CH₃COOH, does because of the H attached to the carboxyl group. The CH₃ in Acetic Acid has "electron-donating properties".

Formic Acid is the stronger acid in this case.

Jasmine Wu 1L

In the solutions manual, it says that the compound As₂O₃ (from part c) and that Bi₂O₃ are amphoteric. How do you tell that those compounds are amphoteric?

Thank you!

Jasmine Wu 1L

What is a delocalized pi-bond, and how do you find them?

Thanks! :)

Jasmine Wu 1L

Appendix 2D of the textbook has a whole list of the elements and their name origins. Some have Latin names. I really don't believe that you would have to know all of the Latin names, just some of the most common ones. Use the Latin stem is the symbol for the metal comes from the Latin name. Like, fo...

Jasmine Wu 1L

When you solve for x after completing the ICE box and setting up the quadratic equation, I noticed that sometimes you could get two positive answers. How would you choose which solution for x is relevant to the question and answer? I know for the solutions with one positive and one negative answer, ...

Jasmine Wu 1L

Hi :) Both versions would be acceptable- my TA said so. Also, on Dr. Lavelle's class site, there's a file on there called "Naming Coordination Compounds" and it's got those anionic compounds you were talking about on there. On the top of the 2nd page of that document, it says that for the ...

Jasmine Wu 1L

My TA said both versions would be acceptable for the class (like on Test 4)

Jasmine Wu 1L

In Toolbox 17.1> B. Naming the complex> (1), it says that the Roman numerals represent the oxidation state of the central metal atom. So, in your example, the Roman numerals are describing iron. But, sorry, I am actually not sure of the rules about where to put the Roman numerals in parentheses. Tha...

Jasmine Wu 1L

It is my understanding that lone pairs repel other atoms and alter the shape of the VSEPR model. For example, we would have to predict that, for an AX3E species, the angle will be less than 109.5 degrees, but the actual angle can't be predicted. By experiment, we would find that the actual value wou...

Jasmine Wu 1L

What does it mean when a question asks for a VSEPR formula and the hybridization of the central atom? Would it be the same thing as the VSEPR models Dr. Lavelle drew in class?

Thanks :)

Jasmine Wu 1L

What about the clockwise/counter-clockwise direction? Which direction do -1/2 and 1/2 belong to?

Jasmine Wu 1L

It is my understanding that the spin magnetic quantum number, m_s, has a value of either 1/2 or -1/2. Which way does the electron spin if it has a m_s value of 1/2 and if it has a m_s value of -1/2?

Thanks!

Jasmine Wu 1L

Section 2.13 of the textbook briefly explains the concept of diagonal relationships, but I don't quite understand it.

Do you know if we need to know this for Test 3, or if it would be a good idea to commit this concept to memory for future reference?

Thanks!

Jasmine Wu 1L

Hi! I had a similar question to this.

You would multiply the kinetic energy that you found by Avogadro's constant to get J/mol.

Jasmine Wu 1L

Hello! I'm having some trouble doing #20 from the Heisenberg Indeterminacy Equation post-module. Use the above uncertainty in velocity (which I calculated to be delta v = 3.4*10^10 m/s) to calculate the electron's uncertainty in kinetic energy. Then calculate the uncertainty in kinetic energy per mo...

Jasmine Wu 1L

Hello! Does anyone know whether or not we will be given an electromagnetic spectrum for the test? I've only memorized that the Balmer series is in the visible region and that the Lyman series is in the UV region, but it would be really helpful if we get the wavelengths that correspond to each region...

Jasmine Wu 1L

Hello!

What is the difference between the work function and the threshold energy?

Jasmine Wu 1L

Hello!

The little capital m is the molarity.

So, for G.9, the molarity of AgNO3 is 0.179 mol/L

Hope that helps :)

Jasmine Wu 1L

Hello! I'm having some trouble with fundamentals M.19... The question is: A stimulant in coffee and tea is caffeine, a substance of molar mass 194 g/mol. When 0.376 g of caffeine was burned, 0.682 g of carbon dioxide, 0.174 g of water, and 0.110 g of nitrogen were formed. Determine the empirical and...

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