CHEMISTRY COMMUNITY

Tim Foster 2A

Why do we use E(naught)=lnK for this problem, instead of E=E(naught)-lnQ in which Enaught would be zero (PH7)
I paraphrased the equations because I'm lazy

Tim Foster 2A

Why dont you need to balance the equation before you begin solving it?

Tim Foster 2A

The question states that CH4 + H20 -> CO2 + 3H2, and I need to find the work done by this reaction. After balancing the equation, I found the change in N to be 1/2 with respect to 1 mol of H2 (1/4+4/4 - 2/4 -1/4), and I know that work= -nRT. What do I use for T? When I use 298K I get an incorrect an...

Tim Foster 2A

What do you call the guest registry at the Annual Bovine Convention of Cows in Chemistry?

A Cattle-List!
moooo

Tim Foster 2A

Let's say we had a second order rate law that was equal to k[A][B]. To render this a pseudo-first order reaction, one could ensure that the concentration of A was so high relative to the concentration of B (lets say .85M and .003M, respectively) that the concentration of A effectively stayed constan...

Tim Foster 2A

when finding Q from the half reactions
Ag(s) + I-(aq) -> AgI(s) + e- E(anode)=-0.15V
AgCl(s) + e- -> Ag(s) + Cl- (aq) E(cathode) = 0.22V

How do you identify Cl- and I- as products or reactants?

Tim Foster 2A

How do you identify the oxidizing and reducing agents for the redox couple
O3/O2 and OH- and O3, H+/02 ?

Tim Foster 2A

Does Br2 have a weaker reducing power compared to I2? Does this also correlate to a stronger oxidizing power for Br2 in comparison to I2?

Tim Foster 2A

Hey! To find the standard cell potential, we extrapolate oxidation and reduction half reactions from the cell diagram, from the left and right sides, respectively. Once we have these half rxns, we can use our handy dandy chart in Appendix 2B to search for standard reduction potentials (subtracting t...

Tim Foster 2A

When dealing with two compounds that are in different phases, how do you know which to list first in the cell diagram? For instance, if the two compounds on the reduction side of my diagram are Cl2(g) and Cl-, which do I put first?

Tim Foster 2A

When writing a cell diagram, why are I- ions and I2(s) separated on the oxidation side?

Tim Foster 2A

Should we use H+ or H3O+ to balance half-rxns in acidic conditions?

Tim Foster 2A

In 14.1 part c, why does the answer in the textbook include 14 H- in the reduction half reaction instead of 14H+?

Tim Foster 2A

Hey Lily Fe3O4(s) + O2(g) = Fe2O3(s) This is the unbalanced equation for the oxidation of Magnetite to Hematite. If we balance the equation, we get 4Fe3O4(s) + O2(g) = 6Fe2O3(s). For your method to work, you would need to compare the deltaG of formation of six moles of Hematite to 4 moles of Magneti...

Tim Foster 2A

Does Boron Triflouride have a degeneracy of one? Further implying that at T=0, it has no entropy?

Tim Foster 2A

zanekoch1A wrote:I'm not sure what I am doing wrong but I keep getting an answer around 1.5kj. I am using in the Gnot part of the equation a T of 273 and a k of 6.8 and and in the G side a T of 1200 and ln(.13/.98). What am I doing wrong?

Hey Zane, I think your natural log should be of (.98)^2/(.13)

Tim Foster 2A

The equation q=mCdeltaT is somewhat useless for isothermal processes because it has to do specifically with heat capacities. It's not that a substance that doesn't change in temperature has no heat capacity at all, its just that its impossible to tell what that heat capacity is when the temperature ...

Tim Foster 2A

1) I'm not sure about this either, I know that combustion can produce water vapor when it is carried out at temperatures above 100 C, but this reaction appears to be at 25 C. 2) However, I do know that if you consider water vapor as a product instead of liquid water, you will find that the system lo...

Tim Foster 2A

This problem wants us to find the range over which each reaction will be spontaneous and lists a few reactions. My calculations are all slightly off for some reason; am I correct in that to solve this problem you need to use the difference in enthalpy and entropy of the products and reactants to fin...

Tim Foster 2A

I believe constant pressure only dictates that the pressure is kept constant, not that volume and/or work are kept constant.

Tim Foster 2A

If you write your equation with water as a gas instead of a liquid, you will find the change in moles to be +3 and you will get -3.71 KJ as the change in energy of the system due to work. If a system is losing energy due to work, that means it is performing work. Thus the work done against the atmos...

Tim Foster 2A

When finding entropy of vaporization from a temperature that is not the boiling point, we include the change in entropy that arises when you cool the vapor back down to original temperature. Why is this last value calculated using the heat capacity for the gaseous state? Why does cooling down a vapo...

Tim Foster 2A

When finding the standard entropy of vaporization of water at 85 C, why do we cool the vapor back down from 100 C? I get that entropy is a state function, but enthalpy is also a state function and when finding the enthalpy of vaporization of water at 85 C, we would simply add the Hvap of water to 4....

Tim Foster 2A

How does one solve this problem? Is there a way to figure out the melting point of iodine or is that not needed at all?

Tim Foster 2A

If a 50.0 g ice cube is added to 250 ml of tea at 20.0 degrees celsius, what is the final temperature at thermal equilibrium?

Tim Foster 2A

Hey Emma, Delta G is not always negative, it is a measure of the energy available to do work in a system. For example, because the hydrolysis of ATP allows your cells to harness the energy from that spontaneous reaction and do work with it, it has a negative Delta G. A reaction that requires an net ...

Tim Foster 2A

What is degeneracy and how can we use it?

Tim Foster 2A

Page 281 in the textbook tells us that
C=3/2RT for monatomic gases at constant volume, while C=5/2RT for monatomic gases at constant pressure.

Tim Foster 2A

Hey Michelle, You need to use the specific heat capacity of liquid water because once the ice melts, all heat being transferred will be subject to the properties and heat capacity of liquid water. This problem can be essentially be split into two parts; the first of which you use the heat capacity o...

Tim Foster 2A

U=3/2RT for monatomic gases at constant volume, while U=5/2RT for monatomic gases at constant pressure. Rotational and translational contributions come into play when dealing with diatomic or polyatomic gases, for which we observe LINEAR MOLECULES- U= 5/2R, 7/2R (Constant volume, constant pressure) ...

Tim Foster 2A

8.67) Use the information in Tables 8.3, 8.6, 8.7 to estimate the enthalpy of formation of each of the following compounds in the liquid state. The standard enthalpy of sublimation of carbon is +717 kj/mol. b)CH3OH c)C6H6 (without resonance) d)C6H6 (with resonance) For b), I created the formation re...

Tim Foster 2A

Thanks Remi, one more question: Do two gases always form another gas when they react? More specifically, how did you know that H2 gas and O2 gas reacted to form H20 in its gaseous form?

Tim Foster 2A

8.67) Use the information in Tables 8.3, 8.6, 8.7 to estimate the enthalpy of formation of each of the following compounds in the liquid state. The standard enthalpy of sublimation of carbon is +717 kj/mol. a)H20 b)CH3OH c)C6H6 (without resonance) d)C6H6 (with resonance) How do you find the enthalpi...

Tim Foster 2A

Why is the answer to this problem written as "23.9 KJ/L x 10^3" and not "2.39 KJ/L x 10^4"?

Tim Foster 2A

When calculating the change in enthalpy of a rxn by subtracting the standard enthalpy of formation of the reactants from the standard enthalpy of the products, how do you find the enthalpies of formation for individual products/reactants? Is there a way to calculate this or is there a chart somewher...

Tim Foster 2A

An isolated system has no interaction with its surroundings whatsoever, while a closed system has a fixed amount of matter, but can exchange energy with its surroundings. A good example of a closed system is something like an ice pack, and a good example of an isolated system is something sealed off...

Tim Foster 2A

The main difference between a true bomb calorimeter and the coffee cup calorimeter is that the bomb is much more sophisticated and thus gives more accurate calculations. Other than that, the function of each is the same. As far as how it works, I think all we should know for this course is that a bo...

Tim Foster 2A

Hey! I know this much, rxn enthalpy is heat given off or taken up for the rxn, or just the enthalpy difference between the reactants and products. The enthalpy of formation of a compound is the enthalpy change between the reactants in their standard state and the product.
Hope that helps

Tim Foster 2A

Can enthalpy and temperature be related?

Tim Foster 2A

Which Nicki Minaj song is the best to listen to while studying Chapter 12?
Superbass!

Tim Foster 2A

Why does increasing the temperature of the rxn X2(g)<--->2X(g), where X is a halogen, favor the products? How should we know that is endothermic in the forward direction?

Tim Foster 2A

What is this, and why does it lead to hydronium/hydroxide ions moving through water much faster than other kinds of ions?

Tim Foster 2A

When writing net ionic equations, do solid (s) or liquid (l) compounds get split into ions?
If not, why is the Bronsted Acid in the equation NH4I (s) + H20 (l) ---> NH3 (aq) + H3O+ (aq) + I- (aq)
considered to be NH4+, instead of NH4I

Tim Foster 2A

Okay, thanks!

Tim Foster 2A

The syllabus says that final grades will not be assigned until the class average score out of 500 is known, which makes me think (hope) that perhaps our grade will be out of slightly less than 500, but I am not sure

Tim Foster 2A

How do you know that there are two hydroxide ions in Zinc Hydroxide?

Tim Foster 2A

When writing the chemical equation for the proton transfer reaction of NaC6H5O, I realized that my answer (NaC6H5O + H2O --> NaOH + C6H5OH)
differed from the textbook solution in that the solution did not include sodium at all (C6H5O- + H20 --> C6H5OH + OH-). Why is sodium left out?

Tim Foster 2A

How does one draw the lewis structure of this compound?

Tim Foster 2A

What would a neutralization reaction that resulted in the formation of zinc nitrite look like?

Tim Foster 2A

If H20 has two atoms with lone pairs on them, why is it monodentate and not bidentate?

Tim Foster 2A

"If one starts with a higher pressure of reactant, the equilibrium constant will be larger."
Why is this false? I thought K=[Products]/[Reactants]

Tim Foster 2A

Why is this molecule polar? What's stopping the chlorines from being on opposite sides of the carbon, and their dipoles canceling? Why are they adjacent to each other instead?

Tim Foster 2A

What are the different bond angles in a seesaw arrangement of atoms in a molecule?

Tim Foster 2A

What's an example of a t-shaped molecules and how does this shape come to be? What stops the atoms attached to the central atom from getting as far away from each other as possible and forming a trigonal planar shape?

Tim Foster 2A

Hey! Not sure about calculating the exact measure of bond angles being influenced by a lone pair, I believe that's a little above this course's pay grade, but I do know that bond angles in a molecule adjacent to the bond angle containing the lone pair will be slightly smaller than they would have be...

Tim Foster 2A

How does one name this molecule?

Tim Foster 2A

The necessity of the hybridization of orbitals can be traced back to Valence Bond theory, the theory that calculates covalent bonds angles and lengths. When we try to apply this theory to a compound like methane (CH4), it begins to fall apart. This is due to something called Electron Promotion, in w...

Tim Foster 2A

How does one depict the progress of a reaction graphically?

Tim Foster 2A

What do all of the different variables in the ideal gas law above represent?

Tim Foster 2A

What does the correct lewis structure for this molecule look like?

Tim Foster 2A

The question asks how many atoms of oxygen are in 5.15 grams of epsom salt, or magnesium sulfate heptahydrate. Firstly, are we going to need to know nomenclature like this for the midterm? Secondly, I googled the formula and got MgSO4(7H20). I am unsure of whether or not this problem would like me t...

Tim Foster 2A

What is an oxidation state, and how can chlorine have both positive and negative oxidation states?

Tim Foster 2A

How are we supposed to know how electron affinity changes as you go down a group on the periodic table? I know that (generally) electron affinity increases from left to right across the table, but how should I know that Na has a lower EA than Li, for example?

Tim Foster 2A

How do we know what the most stable amount of double bonds is for a sulfur atom in a Sulfide molecule?

Tim Foster 2A

How do we draw a representation of a resonance structure? Is it just a combination of all possible configurations?

Tim Foster 2A

What is the minimum uncertainty in the speed of an electron confined to within a lead atom of diameter 350. pm?

Tim Foster 2A

how do I convert cm-1 into meters? Thanks!

Tim Foster 2A

Hey! I'm having trouble with part c of this problem. When I use the equation wavelength=c/frequency I get around 12 nm, but the back of the book says 8.8

Tim Foster 2A

Hey Irma! A key step of this problem is to find the energy created by one photon from this source of radiation, which we can do by using the formula E=hv, h being planck's constant (6.626x10^-34) and v being the frequency. In order to plug the frequency into the above equation we must use the formul...

Tim Foster 2A

Using the formula
V=R(1/nsquared - 1/nsquared)
in atomic spectra problems, what does it mean when the initial n is greater than the final n (ex// n=1 transitioning to n=5) and you get a negative value for the frequency of the energy emitted?

Tim Foster 2A

The problem asks which statement is true A) x-rays travel faster than infrared radiation B) the wavelength of visible radiation decreases as its color changes from blue to green C) the frequency of infrared radiation is half that of radio waves D) the frequency of infrared radiation is twice that of...

Tim Foster 2A

What are coefficients in chemical equations called?

Tim Foster 2A

Hey, what is the difference between percent yield and theoretical yield?

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