## Search found 22 matches

Sat Feb 07, 2015 10:09 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Cell Diagram Liquids_Midterm 2014,Q7B
Replies: 1
Views: 278

### Re: Cell Diagram Liquids_Midterm 2014,Q7B

Hey,
H2O is the only species that we exclude from the cell diagram.
Sat Feb 07, 2015 10:04 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: Change in Entropy Equations
Replies: 2
Views: 394

### Re: Change in Entropy Equations

If the volume of the system changes, then we use deltaS=nRlnv2/V1. If heat is supplied reversibly to the system, then we used deltas=qrev/T. Isothermal reversible expansion signifies that the volume of the system is changing because the gas is expanding and thus occupies more volume. Therefore, we u...
Sat Feb 07, 2015 9:58 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Midterm 2007 Q3B- Explanation of (delta)S total
Replies: 3
Views: 545

### Re: Midterm 2007 Q3B

According to the second law of thermodynamics, "A spontaneous change is accompanied by an increase in the total entropy of the system and its surroundings." Therefore, we can only determine if a reaction is spontaneous based off the total change in entropy.
Fri Feb 06, 2015 7:08 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Balancing chemical reactions to find Gibbs or enthalpy!
Replies: 2
Views: 442

### Re: Balancing chemical reactions to find Gibbs or enthalpy!

I am assuming that we use whole number coefficients whenever we are calculating standard values of the reaction. Essentially every problem involving the calculation of standard reaction values involves the use of whole number coefficients.
Fri Feb 06, 2015 7:03 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: Determining greater change in entropy!
Replies: 2
Views: 547

### Re: Determining greater change in entropy!

The question states that "the heat pump heats a house in winter by extracting heat from the cold outdoors and releasing it into the warm interior. Therefore, based off the statement, we can deduce that the temperature of the interior is greater than the temperature of the exterior.
Fri Feb 06, 2015 4:52 pm
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: Effect of adding mass to an electrode (problem 13.99)
Replies: 1
Views: 424

### Re: Effect of adding mass to an electrode (problem 13.99)

A way to look at this situation is through a mathematical perspective (the formula for cell potential). \Delta G=nFEcell . Even if the mass of the anode is increased, the change in Gibbs Free energy and the moles of electrons transferred still remain the same. Therefore, the cell potential is also n...
Fri Feb 06, 2015 4:45 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: n when calculating Ecell (h2,h+)
Replies: 1
Views: 388

### Re: n when calculating Ecell (h2,h+)

For 39a, the reaction can essentially be written as H+(aq,1E-3M) +e - -->H+(aq,1E-4M)+ e - . As you can see, only one electron is transferred and therefore, n=1. For 41a, although the value of n=2, the products and reactants are squared in the reaction quotient. However, notice that the equation in ...
Fri Feb 06, 2015 3:51 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Units & sig figs for calculating gibbs free energy
Replies: 1
Views: 1144

### Re: Units & sig figs for calculating gibbs free energy

During the final step, when you multiply -53.45kJ by 2, you will obtain -106.9 kJ/mol which only consists of one decimal place. When subtracting or adding values, the final answer should contain the same number of decimal places as the smallest number of decimal places in the data which in this case...
Fri Feb 06, 2015 3:38 pm
Forum: Balancing Redox Reactions
Topic: 13.3 b Reducing/Oxidizing Agent
Replies: 2
Views: 589

### Re: 13.3 b Reducing/Oxidizing Agent

I recommend looking at the individual oxidation numbers for the element. (Attached is a list of common oxidation numbers): For MnO4-, we know that the oxidation number of O is -2 and the total sum of the oxidation numbers of each element has to equal the charge of polyatomic ion (-1). Therfore, x+4(...
Thu Feb 05, 2015 6:29 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: 13.13 b Anode in cell diagram question
Replies: 1
Views: 382

### Re: 13.13 b Anode in cell diagram question

1. I 2 (s) is not a metal and therefore, a metal conductor is required for the anode half cell. 2. "An inert electrode such as Pt is necessary when both oxidized and reduced species are in the same solution". This simply means that when both both species are aqueous in a half cell, an iner...
Thu Feb 05, 2015 6:18 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Creating Diagrams and Reactions Question 13.15
Replies: 3
Views: 1239

### Re: Creating Diagrams and Reactions Question 13.15

The way this question is worked out is through simply determining two different half reactions that can be combined to create the overall reaction. (You can locate the half reactions in the Appendix). Therefore, Step 1. Determine the two half reactions that can be combined to create AgBr(s)-->Ag+(aq...
Wed Dec 10, 2014 10:17 pm
Forum: *Titrations & Titration Calculations
Topic: Final pH of Titration
Replies: 1
Views: 478

### Re: Final pH of Titration

After calculating the excess amount of hydronium/hydroxide, you divide the excess number of moles over the total volume. For instance, if we we were given 25 mL of 0.1 M HCL and 30 mL of 0.1 M NaOH, you would divide the excess number of moles over 0.055 L.
Wed Dec 10, 2014 10:48 am
Forum: *Titrations & Titration Calculations
Topic: Question: pH at Stoichiometric Point (Fall2010 Q8)
Replies: 1
Views: 300

### Re: Question: pH at Stoichiometric Point (Fall2010 Q8)

The solution skipped a step. You have to calculate the molarity of CH3CO2-. I attached the full solution. Let me know if something doesn't make sense.
Wed Dec 10, 2014 10:14 am
Forum: *Molecular Orbital Theory (Bond Order, Diamagnetism, Paramagnetism)
Topic: 2 different elements for MO
Replies: 1
Views: 340

### Re: 2 different elements for MO

Hey,
This was a post from last year.

Chem_Mod wrote:
"It has been determined by calculations that heteronuclear diatomics follow the Z < 8 MO diagram, regardless of the elements involved (even if both atoms have Z greater than 8)."
Tue Dec 09, 2014 12:05 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: When can Cl be an acceptable central atom?
Replies: 2
Views: 1544

### Re: When can Cl be an acceptable central atom?

Hey
Cl is less electronegative than O and as a result, it will be drawn in the middle.
Tue Dec 09, 2014 11:56 am
Forum: *Titrations & Titration Calculations
Topic: pKa/b and pH
Replies: 1
Views: 336

### Re: pKa/b and pH

Hey,
If the analyte is a weak acid and the titrant is a strong base, then the ph=pka at the halfway mark to the equivalence point. If the analyte is a weak base and the titrant is a strong acid then the poH=pkb at the halfway mark to the equivalence point.
Thu Nov 27, 2014 12:46 am
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Conversions regarding pressures
Replies: 2
Views: 395

### Re: Conversions regarding pressures

Hey, The units actually do matter for partial pressures in which you use bars. The toolbox on page 401 states, " As always, use molar concentrations (in moles per liter) and parial pressures (in bars) but strike out the units." Also, regarding your second question, you can directly convert...
Thu Nov 27, 2014 12:25 am
Forum: Naming
Topic: Are we expected to name cis and trans molecules?
Replies: 3
Views: 569

### Re: Are we expected to name cis and trans molecules?

I'm not entirely sure if we are expected to draw the structures but as the previous poster stated, simply know that cis means that the two atoms are next to each other while trans means that the two atoms are opposite from each other.
Thu Nov 27, 2014 12:21 am
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: Problem 10.77 in textbook
Replies: 2
Views: 409

### Re: Problem 10.77 in textbook

Hey,
The coefficient for NH3 should be 4 but regardless, the answers are still the same.
Thu Nov 27, 2014 12:04 am
Forum: Bronsted Acids & Bases
Topic: Lewis structure of SO2?
Replies: 1
Views: 593

### Re: Lewis structure of SO2?

Hey,
Sulfur can have an expanded octet and as a result, it can act as a Lewis Acid and accept another pair of electrons.
Fri Nov 14, 2014 7:05 pm
Forum: *Molecular Orbital Theory (Bond Order, Diamagnetism, Paramagnetism)
Topic: L.U.M.O. & H.O.M.O.
Replies: 5
Views: 836

### Re: L.U.M.O. & H.O.M.O.

L.U.M.O and H.O.M.O apply to the whole energy level. For instance, in a Z<8 diagram σ*s can be the H.O.M.O while πpx can be the L.U.M.O .
Fri Nov 14, 2014 6:48 pm
Forum: *Molecular Orbital Theory (Bond Order, Diamagnetism, Paramagnetism)
Topic: Molecular Orbital Diagram
Replies: 4
Views: 683

### Re: Molecular Orbital Diagram

This was a comment from last year. " Chem_Mod wrote: It has been determined by calculations that heteronuclear diatomics follow the Z < 8 MO diagram, regardless of the elements involved (even if both atoms have Z greater than 8)." Therefore, we don't essentially have to take the lower nucl...