CHEMISTRY COMMUNITY

Maria1E

I know that if the number of moles on the product side of a given equation is larger, then entropy increases. My question is, when counting moles to determine this, are we supposed to count the moles of all molecules, including aqueous, liquids, and solids, or simply the ones in the gas phase?

Maria1E

On the final, will we be provided with a sheet of half-reaction and standard cell potentials for each reaction like we were on Test 2?

Maria1E

Do we need to know how to solve problems with pseudo first order reactions on the final? Are there any homework problems on it?

Maria1E

Will we need to know how to derive rate laws on the final?

Maria1E

Will Lyndon's review session have any kind of practice final? Or is he simply reviewing general material from electrochemistry and kinetics?

Maria1E

Will we be tested on the functional groups/intro to ochem that was discussed in today's lecture on our final?

Maria1E

I think the only thing we would need to know is to be able to identify whether it is a third or fourth order reaction based on initial rates.

Maria1E

Will today's lecture on collision theory be on Test 3?

Maria1E

I know that Test 3 will be on sections 15.1 to 15.6, but does anyone know exactly which homework problems we should study? Thank you!

Maria1E

I am confused on how to draw proposed structures overall.

Maria1E

To find the overall order, you simply add the orders of all the reactants. For example, the order of [A]^3[B]^1 is 4.

Maria1E

Can someone please explain the (k2k1)/k' formula, and give examples of when we would use it? Thank you!

Maria1E

Question: The following rate laws were each derived from an elementary reaction. In each case, write the chemical equation for the reaction, determine its molecularity, and draw a proposed structure for the activated complex. a) Rate = k[CH3CHO] (products are CH3 and CHO) b) Rate = k[I]^2[Ar] (produ...

Maria1E

Heat does not enter or leave the system, so q = 0. Therefore, delta U is equal to w (work).

Maria1E

Determine the unknown quantity in each of the following cells.
a) Pt(s) I H2 (g, 1 bar) I H+ (pH = ?) II Cl- (aq, 1 M) I Hg2Cl2 (s) I Hg (l)
E = .33 V

Can someone please write out and explain the calculations? I'm confused about how the pH value was obtained at the end.

Maria1E

How do we know if we need Pt(s) on both sides or only one one side of a cell diagram?

Maria1E

Volta discovered that when he used different metals in his "pile", some combinations had a stronger effect than others. From that information he constructed an electromotive series. How would Volta have ordered the following metals, if he put the most strongly reducing metal first: Fe, Ag,...

Maria1E

Calculate E for each of the following concentration cells: b) Pt(s) I H2 (g, 1 bar) I H+ (aq, pH = 4.0) II H+ (aq, pH = 3.0) I H2 (g, 1 bar) I Pt(s) The solution manual states that n = 1. Can someone please explain why this is? I thought that the 2 half-reactions were 2H+ + 2e --> H2 and H2 --> 2H+ ...

Maria1E

Will we be given half-reactions on Test 2 (i.e. how they are listed in Appendix 2B)?

Maria1E

Standard conditions would also mean that all solutions are at 1 M concentration.

Maria1E

My TA said that he wouldn't mark down for sig figs, so I don't think they matter very much for thermodynamics.

Maria1E

When given a cell diagram such as C(gr) I H2(g) II Cl-(aq) I Cl2(g) I Pt(s), how are we supposed to determine which is the cathode and which is the anode? I read that we need to look at which side is "positive" and which is "negative", but I'm not really sure what that means or h...

Maria1E

6Co2 (g) +6H2O (l) --> C6H12O6 (aq) + 6O2 (g) deltaH = +2802 kJ State the effect the following changes will have on the equilibrium composition. I am confused on part e: e) Some of the C6H12O6 is removed The solution manual states that this would result in the favoring of the formation of products. ...

Maria1E

Chapter 11 is on the second outline as well, so that may be on the midterm.

Maria1E

The units are Joules per Kelvin, or J/K.

Maria1E

My TA, Joe, said that the homework you turn in has to somewhat correspond to what we are learning in class, but it doesn't have to be from a specific chapter. For example, this week we were tested on Chapter 8 while learning Chapter 9 in lecture. Therefore, you can turn in homework problems from eit...

Maria1E

What is the total entropy change of a process in which 40 kJ of energy is transferred as heat from a large reservoir at 800 K to one at 200 K? In the solution manual, the calculation for the entropy change at 800 K is shown as deltaS = -40000 J/800 K. For the entropy change at 200 K, the calculation...

Maria1E

Are we supposed to know how to use the formula 3/2RT for Test 1?

Maria1E

For irreversible reactions, use w = -P(delta V). However, depending on the information you are given you may also need to use w = -(delta n)RT since PV = nRT.

Maria1E

Hydrochloric acid oxidizes zinc metal in a reaction that produces hydrogen gas and chloride ions. A piece of zinc metal of mass 8.5 g is dropped into an apparatus containing 800 mL of .500M HCl(aq). If the initial temperature of the hydrochloride acid solution is 25 degrees celsius, what is the fina...

Maria1E

Calculate the standard enthalpy of formation of dinitrogen pentoxide from the following data, 2NO(g) + O2(g) --> 2NO2(g) deltaH = -114.1 kJ 4NO2(g) + O2(g) --> 2N2O5(g) delta H = -110.2 kJ and from the standard enthalpy of formation of nitric oxide, NO (which is 90.25 kJ). I understand that the equa...

Maria1E

Why does the solution manual state the final units for this problem as kJ/mol, even though the units given for delta H in all other problems on reaction enthalpies (such as #61) are kJ? Are the final units for delta H in reaction enthalpy problems kJ/mol or kJ?

Maria1E

OF2 (g) + H2O (g) --> O2 (g) + 2HF (g) Delta H is -318 kJ. What is the change in internal energy for the reaction of 1.00 mol OF2? I understand that we need to use the equation P(delta)V = (delta)nRT. However, I am confused about how we are supposed to know that the temperature is 298 K as stated in...

Maria1E

On the tests, will we be given the values of the standard enthalpies of physical change, such as ΔH(fusion) and ΔH(vaporization) for the appropriate substance? Or do we need to memorize any of them?

Maria1E

Is Mg(OH)2 a strong or weak base?

Maria1E

No, this was a question on the midterm and I put that it was polar and got it right. But I'm not exactly sure what makes it polar.

Maria1E

Don't its dipole moments cancel out?

Maria1E

How do we go about determining if there is a dipole moment when the central atom has lone pairs on it?

For example, why would KrCl4 (which has 2 pairs of lone electrons on the K) have no dipole moment, while IF5 (which has one pair of lone electrons on the I) has a dipole moment?

Maria1E

Calculate the pH of the following solutions:

b) .055 M AlCl3 (aq)

Why does the solution manual replace AlCl3 with Al(H20)6 in the explanation? I noticed that it did the same thing in 12.65 (d).

Maria1E

A student added solid Na2O to a 200. mL volumetric flask, which was then filled with water, resulting in 200. mL of NaOH solution. 5.00 mL of the solution was then transferred to another volumetric flask and diluted to 500 mL. The pH of the diluted solution is 13.25. I figured out the answer to part...

Maria1E

SO3 (g) + NO (g) --> SO2 (g) + NO2 (g)

117 b) Given that at a certain temperature K = 6.0 x 10^3, calculate the amount (in moles) of NO that must be added to a 1.00 L vessel containing .245 mol SO3 (g) to form .240 mol SO2 (g) at equilibrium.

How do you go about solving this? Thank you!

Maria1E

A reactor for the production of ammonia by the Haber process is found to be at equilibrium with P(N2) = 3.11 bar, P(H2) = 1.64 bar, and P(NH3) = 23.72 bar. If the partial pressure of N2 is increased by 1.57 bar, what will the partial pressure of each gas be once the equilibrium is reestablished? I f...

Maria1E

Regions of electron density repel each other and want to be as far apart as they can, so if there are only two regions they would be farthest apart in the linear shape, at 180 degrees.

Maria1E

In 29a, why is the answer hexacyanoferrate (II) ion instead of hexacyanidoferrate (II) ion? I thought that since cyanide had an -ide ending it would be converted to -ido.

Thank you!

Maria1E

For that question, I stated that the compound was a radical, but my Lewis structure was slightly off (I placed the lone electron on the wrong element). I got 2 out of 10 points. I think it was two points for stating that the compound was a radical, and the Lewis structure was 8 or nothing. You shoul...

Maria1E

Write the Lewis structure and give the approximate bond angles of N2H4. I understand that the molecular shape is trigonal pyramidal, but I am confused as to how we are supposed to know that the precise bond angle is 107 degrees (rather than just 'slightly less than 109.5 degrees'), as stated in the ...

Maria1E

Additionally, the more electronegative an element is, the less electropositive it is and vice versa.

Maria1E

Do we need to know anything about nodes for the midterm (i.e. angular nodes, radial nodes)? This topic was briefly mentioned in my discussion section but I wasn't sure if we are going to be tested on it or if it's just for our own knowledge.

Maria1E

What are the exceptions to the periodic trends for ionization energy, electron affinity, and atomic radii? Thank you!

Maria1E

For number 1, how is the answer C24H42O21? Once I divided by the molar masses, I got 3.5967 moles of C, 6.2996 moles of H, and 3.15 moles of O. I divided all three by 3.15 to get the ratio 1.14 C, 2 H, and 1 O. Then I multiplied each number by 7 to get whole numbers and got C7H14O7 for the empirical...

Maria1E

I'm still a little confused as to why CH2 wouldn't form an octet. Carbon on its own only has four valence electrons but it usually forms an octet, so why wouldn't CH2?

Maria1E

Draw resonance structures for the trimethylenemethane anion C(CH2)3^2- in which a central carbon atom is attached to three CH2 groups.

Why does the solution manual show each CH2 group as only having 4 valence electrons? I'm confused as to how that was calculated. Thank you!

Maria1E

In 1999, Karle Christe synthesized and characterized a salt that contained the N5+ cation, in which the five N atoms are connected in a long chain. This cation is the first all-nitrogen species to be isolated in more than 100 years. Draw the most important Lewis structure for this ion, including all...

Maria1E

I'm confused about the solution manual's assignment of the elements to the figures A,B,C, and D in the diagram. First of all, why would B be chlorine and A be sodium if chlorine is farther across the period than sodium is? I thought that atomic radii decrease across a period, so why would chlorine b...

Maria1E

The principal quantum number is n, and in 6p n=6. The angular momentum is l. This is equal to one because each value of l corresponds to a particular subshell. It is true that when n = 6 you have 6 possibilities for n, which are 0, 1, 2, 3, 4, and 5. However, you are told the subshell in this proble...

Maria1E

You decide what equation to use based on the information you are given in the question. If the frequency is given in the equation and you want to find wavelength, use λ=c/v. In addition, if you are given energy in J and you need to find wavelength, you would use E = hv to find the frequency and then...

Maria1E

It will not; that is what the scientists performing this experiment found surprising. If light had only wave properties then increasing the intensity should have resulted in the ejection of electrons, but it didn't. The conclusion of the experiment was that light is made of photons, or individual pa...

Maria1E

My TA told us to use whatever number is given to us on the equation sheet on the front page of the test, just to be safe. But either way should work!

Maria1E

An undergraduate assistant told me that the chemistry department doesn't allow course readers anymore.

Maria1E

You use a key concept that Dr. Lavelle outlined in his lecture on 10/2: When diluting a solution, moles of solute remain the same. Therefore, you can use the formula (M initial)(V initial) = (M final)(V final), where M is molarity and V is volume. For this problem, we are told that a florist dilutes...

Maria1E

The ratio of CO3 to Na2CO3 is 1:1. The subscript 3 only applies to the oxygen, so there are 3 moles of oxygen for every 1 mole of NaCO3. However, the subscript does not apply to CO3 as a whole so there is only 1 mole of CO3 for every mole of Na2CO3.

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