CHEMISTRY COMMUNITY

Mike Matthews 1D

Hey everyone, many of you may not know this but Emily Warda's birthday is the same day as our final so if you see Emily tomorrow make sure you wish her happy birthday!

Mike Matthews 1D

When writing a cell diagram when is it necessary to include an inert electrode such as Pt(s)?
Thank you!

Mike Matthews 1D

If delta S total is positive can you say that a reaction is spontaneous or is the only way to determine the spontaneity of a reaction through calculating Gibbs free energy?

Mike Matthews 1D

Hi, I still do not understand the following question from test 1: "Answer yes or no if heat is being transferred in the following processes, and justify your reasoning. a. A tank of liquefied propane is punctured, emitting gaseous propane vapors. b. A balloon filled with gas is expanded to a la...

Mike Matthews 1D

A catalyst will appear in both the reactants and products since it is not consumed during a reaction. On the other hand, an intermediate does not appear in the reactants or products because the intermediate is produced and consumed during the course of a reaction.

Mike Matthews 1D

Could someone please explain to me how to do homework problem 15.69: "A reaction rate increases by a factor of 1000 in the presence of a catalyst at 25 degrees Celsius. The activation energy of the original pathway is 98 kJ per mol. What is the activation energy of the new pathway, all other fa...

Mike Matthews 1D

Could someone please explain to me how to do homework problem 15.67: "The presence of a catalyst provides a reaction pathway in which the activation energy of a certain reaction is reduced from 125 kJ per mol to 75 kJ per mol. By what factor does the rate of reaction increase at 298K, all other...

Mike Matthews 1D

Can someone please explain to me what raising the temperature does to the equilibrium constant of a reaction.

Mike Matthews 1D

Could someone please explain to me the effect that raising the temperature has on the rate constants of a reaction?

Mike Matthews 1D

When deriving an overall rate law using pre-equilibrium approximation and a proposed mechanism, do we have to consider the rate determining step?

Mike Matthews 1D

Homework question 15.3: "In 20 s the concentration of nitrogen dioxide, NO2, decreases from 450 mmol.L-1 to 320 mmol.L-1 in the reaction 2NO2(g)--->2NO(g) + O2(g). Determine the rate of reaction of NO2" Why is it that in the answer key the rate of reaction of NO2 is not divided by its stoi...

Mike Matthews 1D

Could someone please explain what a pre-equilibrium condition is and the purpose that it serves.
Thank you.

Mike Matthews 1D

I'm very confused by the book's explanation of steady state approximation to determine an overall rate law. Could someone please explain to me how to do steady state approximation to determine an overall rate law from a reaction mechanism? Why do we need to assume that any intermediate formed remain...

Mike Matthews 1D

Homework question 14.51 asks you to find that maximum work (per mol of Ag) that the following cell can do: Ag(s)/Ag+(aq, 5.0 mmol/L)//Ag+(aq, 0.15 mol/L)/Ag(s). Since I need to find Q to answer this question and since the oxidation and reduction half reactions cancel each other out for this problem,...

Mike Matthews 1D

How does one determine which elements and or compounds are reactants and which are products from looking at a cell diagram? In other words, if you looked at the left (anode) side of a cell diagram, how do you know which are reactants and which are products in the oxidation half reaction?

Mike Matthews 1D

Could someone please explain to me how to do homework problem 14.11d, "Write the half reactions and the balanced equation for the cell reaction for each of the following galvanic cells:......d. Pt(s)/O2(g)/H+(aq)//OH-(aq)/O2(g)/Pt(s).
Thank you

Mike Matthews 1D

Could someone please explain in detail the difference between delta S and delta S naught. Why is it that delta S total can be used to indicate the spontaneity of a reaction while delta S naught cannot be used to indicate spontaneity?

Mike Matthews 1D

Could someone please explain, in detail, the difference between Gibbs Free Energy and standard Gibbs free energy to me. Thank you.

Mike Matthews 1D

In the two equations delta S = n Cv ln(T2/T1) and delta S = nRln(v2/v1), what does n represent? Please be specific in terms of whether n represents products or reactants.

Mike Matthews 1D

For homework problem 14.1, it asks you to write the oxidation and reduction half reactions for the reaction: H+(aq) + Cr2O7^2- (aq) + C2H5OH (aq)---->Cr^3+(aq) C2H4OH (aq) + H2O (l). According to the solutions manual, the balanced reduction half reaction is Cr2O7^2- (aq) + 14H+(aq) + 6e- ----> 2Cr^3...

Mike Matthews 1D

Could someone please explain to me how to do homework problem 11.77b, "Predict whether each of the following equilibria will shift toward products or reactants with a temperature increase: X2(g)---->2X(g), where X is a halogen."
Thank you.

Mike Matthews 1D

What are the standard units for pressure that we should use in Gibbs Free Energy calculations so that the result has the correct units?

Mike Matthews 1D

Provided that when using the van't Hoff equation for reactions involving gases, the equilibrium constants must be K not Kc, when using the equation delta G= standard delta G - RTlnQ, can one use Qc for gases or does this equation also require you to use partial pressures?

Mike Matthews 1D

Homework 9.27a: Which substance has the higher molar entropy at 298K, HBr (g) or HF (g). Provided that both of these molecules have the same number of microstates, how does one determine the molar entropy difference between these two molecules?

Mike Matthews 1D

Page 348 equations (15) and (16). I understood the derivation of the equation for change in Gibbs Free Energy we did in lecture but was somewhat confused reading this page.

Mike Matthews 1D

Could someone please explain to me what the book means when it says that the standard Gibbs free energy of reaction is a fixed quantity for a given reaction and does not vary as the reaction proceeds.

Mike Matthews 1D

Provided that the change in Gibbs free energy for a process occurring at constant temperature is equal to the change in enthalpy minus the temperature times the change in entropy of the system, why is it that when a process occurs at constant temperature and pressure the change in Gibbs free energy ...

Mike Matthews 1D

Could someone please explain, in detail, the difference between U (internal energy) and H (enthalpy). Why does the equation for Cv use U while the equation for Cp use H?

Mike Matthews 1D

I'm confused about the sign of entropy change since q is negative when it is released by a system and positive when it is gained by the system's surroundings. That being said, when calculating the change in entropy how do you know what sign to use? Also how does positive entropy differ from negative...

Mike Matthews 1D

Provided that in order to calculate the change in entropy of a system, the energy must be transferred reversibly and that for a reversible transfer of energy as heat to occur, the temperature of the surroundings and the system must be infinitesimally different and both must be constant.... how would...

Mike Matthews 1D

Could someone please explain to me how to do homework problem 8.41: "A 50 gram ice cube at 0.0 degrees Celsius is added to a glass containing 400.0 grams of water at 45.0 degrees Celsius. What is the final temperature of the system? Assume that no heat is lost to the surroundings." Thank y...

Mike Matthews 1D

The equation relating the heat capacity of an ideal gas at constant pressure and the heat capacity of an ideal gas at constant volume is:
Cpm=Cvm + R
That being said, what is R? Is it the gas constant? If so how does one go about deciding which value to use for R?

Mike Matthews 1D

Could someone please explain to me how to do homework problem 8.31, "Calculate the heat released by 5.025 g of Kr(g) at 0.400 atm as it cools from 97.6 degrees Celsius to 25.0 degrees Celsius at a. a constant pressure and b. constant volume. Assume that krypton behaves like an ideal gas." ...

Mike Matthews 1D

Could someone please explain to me how to do homework problem 8.21, "A piece of copper of mass 20.0 g at 100.0 degrees Celsius is placed in a vessel of negligible heat capacity but containing 50.7 g of water at 22.0 degrees Celsius. Calculate the final temperature of the water. Assume that no e...

Mike Matthews 1D

Homework problem 8.19 reads, "Calculate the heat that must be supplied to a 500.0 g copper kettle containing 400.0 g of water to raise its temperature from 22.0 degrees Celsius to the boiling point of water, 100 degrees Celsius. What percentage of the heat is used to raise the temperature of th...

Mike Matthews 1D

Hi,
Could someone please clarify the difference between a reversible and an irreversible reaction. Also why is the work done during a reversible expansion of a gas the maximum expansion work possible?
Thanks.

Mike Matthews 1D

Hi,
Is there any way you could post the answers to the practice test for those people that are unable to come to the review session?
Thank you!

Mike Matthews 1D

12.13 Asks you to draw the Lewis structure for several different species and to identify each as a Lewis acid or Lewis base. I'm confused because part c asks for the Lewis structure of Ag+. How does one go about doing this since the electron configuration of Ag+ is [Kr]4d95s1?

Mike Matthews 1D

Question 12.7 asks you to name two different oxoacids. Does anyone know if there is a section in the book that explains how to name acids and bases/if we need to know it for the final? Thanks.

Mike Matthews 1D

Question 12.3 in the text says, "Write the proton transfer equilibria for the following acids in aqueous solution and identify the conjugate acid-base pairs in each one." Part a asks you to do this for H2SO4. I'm confused because I identified the conjugate base to H2SO4 as SO4 (-2) and acc...

Mike Matthews 1D

So in the book on page 482, it says that "the greater the electronegativity of A, the stronger the acid HA." However, it then goes on to say that in group 17, the acid strengths are HF<HCl<HBr<HI. I'm confused by this because isn't Fluorine more electronegative than Iodine? Therefore shoul...

Mike Matthews 1D

"A change in temperature will always favor the exothermic reaction whether it is an increase or decrease." ---Pretty sure if temperature is raised, a reaction mixture at equilibrium will actually shift the reaction in the endothermic direction in order to counter the effect of heat being a...

Mike Matthews 1D

I'm confused by the book's statement, "Compression of a reaction mixture at equilibrium tends to drive the reaction in the direction that reduces the number of gas phase molecules; increasing the pressure by introducing an inert gas has no effect on equilibrium." Doesn't compression increa...

Mike Matthews 1D

I'm a little bit confused because the book says that water as a ligand is denoted OH2 but in the solution for 17.31c the formula for tetraamminediaquacobalt(III) bromide is written as [Co(NH3)4(H20)2]Br3. Does anyone know why water is written as H2O here? I'm also confused because the book tells us ...

Mike Matthews 1D

Midterm question 8b: "Draw the Lewis structure for the compound (HOCO)" When I drew the Lewis structure for this compound I gave one of the oxygens the extra, unpaired electron and it was wrong even though the formal charge of all of the atoms was zero. Could someone please explain to me w...

Mike Matthews 1D

For problem 4.19c, it asks you to predict the shape and estimate the bond angle of BH2-. Could someone please explain to me how to do both of these things. I'm somewhat confused because the Lewis Structure makes it seem like the shape will be linear and the angle will be 180 degrees but according to...

Mike Matthews 1D

In question 4.13c it asks you to determine the bond angle for IO3-. After determining the Lewis structure, I found the VSEPR formula for this molecule to be AX3E. That being said, the shape of the molecule is trigonal pyramidal. However, I'm confused about how to determine the bond angle. The soluti...

Mike Matthews 1D

If in the Lewis structure of BF3, the boron atom has an incomplete octet due to the fact that fluorine has such a high ionization energy and is unlikely to exist with a positive formal charge, then how can a tetrafluoroborate anion form when boron trifluoride is passed over metal fluoride? Wouldn't ...

Mike Matthews 1D

Homework question 4.11b asks you to find the VSEPR formula and predict the shape of iodine trichloride. The VSEPR formula for this molecule is AX3E2. With that in mind I expected the arrangement of electrons to be trigonal bipyramidal around the atom with the two lone pairs in equatorial positions. ...

Mike Matthews 1D

4.11a asks you to give the VSEPR formula and predict the shape for sulfur tetrachloride. After figuring out the Lewis structure one finds the VSEPR formula to be AX4E. With this in mind, I predicted the arrangement of electron pairs to be triangular bipyramidal and the shape of the molecule to be py...

Mike Matthews 1D

Hi. I was hoping someone could explain to me how to do homework problem 3.37. The problem says, "The following Lewis structure was drawn for a Period 3 element. Identify the element." The Lewis Structure shows a central atom "E" surrounded by 3 Cl atoms and 1 O atom. There is a d...

Mike Matthews 1D

Hi, I'm wondering how one would go about writing the electron configuration for Bi+3. Since Xenon is the previous noble gas, I started by writing [Xe]. Then since Bi is in the 6th period I continued adding electrons with n=6 until I reached 80 electrons. I got the configuration [Bi]6s2 6p6 6d10 6f8....

Mike Matthews 1D

Could someone please explain to me when 3d is filled before 4s and when it is not. I'm very confused about this. What are the exceptions to the rules regarding 3d and 4s? Also could someone explain to me why the electron configuration of Titanium is [Ar]3d24s2 instead of [Ar]3d4. Thank you.

Mike Matthews 1D

I understand that the probability of finding the particle in a region is proportional to the value of the wave function squared in that region. However, I'm confused as to how one determines what region of an atom is being described by the wave function. I'm having a hard time understanding how a tw...

Mike Matthews 1D

I was hoping that someone would be able to clarify what l and ml actually represent. I understand that l distinguishes the shape of the orbital and ml indicates the orientation of the orbital. However, I'm confused because on page 35 of the textbook it says, "As its name suggests, l tells us th...

Mike Matthews 1D

Does the Balmer and Lyman Series only apply to the element hydrogen? I was hoping that someone could clarify this for me.
Thanks

Mike Matthews 1D

When an electron drops down energy levels, it releases its energy as a photon and light is emitted. The Lyman Series consists of the wavelengths of light that are emitted when an electron drops down from any of the outer orbitals (n=2,3,4,5....) to the first orbital (n=1). Similarly, the Balmer Seri...

Mike Matthews 1D

I'm comfortable finding the concentration of certain molecules in solution. However I'm confused because some of the problems on the homework ask for the concentration of specific ions in a solution. For example problem G21: "A solution is prepared by dissolving 0.500 g of KCl, 0.500 g of K2S, ...

Mike Matthews 1D

Hi could someone please explain to me how to do homework problem E3....I was able to find the weight of 9 Ga atoms but am confused about how to proceed from there.
Thanks

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