## Search found 27 matches

Mon Feb 09, 2015 8:24 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: When to use Cv vs Cp
Replies: 6
Views: 1102

### Re: When to use Cv vs Cp

I asked the same thing in a different post but it wasn't really answered! I'm also wondering the same thing.
Sun Feb 08, 2015 1:08 am
Forum: Calculating Standard Reaction Entropies (e.g. , Using Standard Molar Entropies)
Topic: Molar Hear Capacity Vs. Constant Pressure or Volume
Replies: 1
Views: 453

### Re: Molar Hear Capacity Vs. Constant Pressure or Volume

I figured it out.
If anyone was wondering, it's because you're only able to use 5/2 R or 7/2 R... etc. when it's an ideal gas. In this case, h2o is not an ideal gas that is why they used molar heat capacity of water (75.3)
Sun Feb 08, 2015 12:24 am
Forum: Calculating Standard Reaction Entropies (e.g. , Using Standard Molar Entropies)
Topic: Molar Hear Capacity Vs. Constant Pressure or Volume
Replies: 1
Views: 453

### Molar Hear Capacity Vs. Constant Pressure or Volume

Midterm 2011 Q3, they used the molar heat capacity of water (76.3 J/k mol) but I thought we would use constant pressure 7/2 R because the problem specifically said it's at constant pressure?

So when would we use molar hear capacity and constant pressure then?
Wed Feb 04, 2015 2:25 pm
Forum: Calculating Work of Expansion
Topic: R (constant 8.314 or 8.206)
Replies: 3
Views: 2267

### R (constant 8.314 or 8.206)

How do we know when to use R= 8.314 or R = 8.206?
Wed Feb 04, 2015 2:00 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: Nernst equation: Difference between E and G
Replies: 1
Views: 390

### Nernst equation: Difference between E and G

What is the difference between the equation
$\Delta$G=-RT lnK and the Nernst equation ( E= Eo - RT/nF ln Q)?

In what instance would we use each of these equations?
Wed Feb 04, 2015 1:25 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: Question regarding 'C' value in Entropy calculations
Replies: 6
Views: 1456

### Re: Question regarding 'C' value in Entropy calculations

This is a question in one of our practice midterms (midterm 2010 Q4A.) During the test of an internal combustion engine, 3.00 L of nitrogen gas at 18.5 C was compressed suddenly ( and irreversibly) to .500 L by driving in a piston. In the process the temperature of the gas increased to 28.1 C. Assum...
Mon Jan 19, 2015 3:24 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Enthalpy of formation of Zinc
Replies: 3
Views: 1669

### Re: Enthalpy of formation of Zinc

Why don't we account for Cl2 in ZnCl2? Also, this question refers to the problem 7.53 in the textbook and it asks for the Delta Hrxn using standard enthalpy formation. 2HCl + Zn ---> H2 + ZnCl2 Delta Hrxn = Hf (ZnCl2) - Hf 2(HCl) Since we don't include Zn and H2. But why is that wrong according to t...
Sat Dec 13, 2014 9:18 pm
Forum: Calculating pH or pOH for Strong & Weak Acids & Bases
Topic: Fall 2010 Q5
Replies: 1
Views: 320

### Re: Fall 2010 Q5

It is the most acidic when you can easily lose H+. In this case, HClO4 is the most acidic because there are Cl and 4 O that are pulling H+ making it easy to be removed. And HClO is the least acidic out of the 4 because there is a less pull on H+ comparing to the rest.
Sat Dec 13, 2014 9:15 pm
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: Change in Volume
Replies: 3
Views: 491

### Re: Change in Volume

When the volume increases, pressure decreases. The equilibrium will shift to were there are more moles. As for when the volume decreases, the equilibrium will shift to were there are less moles.
Fri Dec 12, 2014 6:04 pm
Forum: *Titrations & Titration Calculations
Topic: Fall 2012 Final, 7B
Replies: 5
Views: 728

### Re: Fall 2012 Final, 7B

^ Yes, that is true as well.

Basically the equation should look like this
HCOOH + NaOH <==> H2O + HCOO- <==> HCOOH + -OH

Professor Lavelle also did his equations like this in class to show that HCOOH (acid) and NaOH (base) are reacting with each other.
Wed Dec 10, 2014 9:40 pm
Forum: *Titrations & Titration Calculations
Topic: Fall 2012 Final, 7B
Replies: 5
Views: 728

### Re: Fall 2012 Final, 7B

The chemical reaction is set up with HCOO- as a product because when you mix HCOOH with NaOH, you get HCOO- and water.
Wed Dec 10, 2014 8:00 pm
Forum: *Titrations & Titration Calculations
Topic: Fall 2012 Final, 7B
Replies: 5
Views: 728

### Re: Fall 2012 Final, 7B

To get the volume of NaOH, you use the info that is already given to you. Given: 15mL (.015L) of .100 M HCOOH .150 M NaOH First you find an equation for this reaction. HCOOH + NaOH <==> H2o + HCOO- Then you find the mole of HCOOH, using the formula, n= (V)(M) (.015L)(.100M)= 1.5x10^-3 mol of HCOOH F...
Sat Dec 06, 2014 11:00 pm
Forum: Calculating pH or pOH for Strong & Weak Acids & Bases
Topic: What is the difference between pKa and Ka?
Replies: 1
Views: 1516

### What is the difference between pKa and Ka?

I know that pKa= -log Ka and Ka= 10^(-pKa), but when do we use pKa and Ka?

For instance, table 11.1, 11.2, and 11.3 have both pKa and Ka, but I don't know which ones to use.
Fri Dec 05, 2014 4:35 pm
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: Pressure
Replies: 5
Views: 818

### Re: Pressure

Pressure does not change K, only temperature does. However, if pressure increases or decreases in the reaction, the equilibrium will shift/alter in order to minimize the effects of the stress. If pressure increases, the reaction will shift to where there are less moles (coefficients). If pressure de...
Wed Dec 03, 2014 2:06 am
Forum: Naming
Topic: Chemical Formula
Replies: 4
Views: 675

### Chemical Formula

What is the difference between [CoCl(NH3)5]Cl2 and [Co(NH3)5Cl]Cl2? Why is the first chem. formula right and the second one wrong?
Wed Nov 26, 2014 12:02 am
Forum: Equilibrium Constants & Calculating Concentrations
Topic: HW Ch.10 #33
Replies: 2
Views: 327

### Re: HW Ch.10 #33

During lecture, Dr. Lavelle stated that we use gas and aqueous phases to calculate both Kc and K(Kp), and we don’t use liquid or solid to calculate K/Kc. K is used to calculate partial pressures and Kc is always for concentration.
Mon Nov 24, 2014 12:23 am
Forum: Properties of Electrons
Topic: elctrons
Replies: 2
Views: 450

### Re: elctrons

Quantum number (n) is also known as energy or shell. Therefore, when n=4, l=3 because l is the angular momentum. To calculate the angular momentum (l), you use the the formula l=n-1. ml is the magnetic quantum, if l=3 then ml= -3,-2,-1,0,1,2, or 3. ms is the magnetic spin which is whether it spins u...
Sun Nov 16, 2014 6:00 pm
Forum: Trends in The Periodic Table
Topic: Which compound is more ionic?
Replies: 7
Views: 17663

### Re: Which compound is more ionic?

LiH is more ionic than HCl because H's electronegativity is 2.1, Cl has a electronegativity of 3.0, and Li's electronegativity is 1.0. There is a bigger difference from 2.1 to 1.0 than 3.0 to 2.1. The electronegativity trend on the period table doesn't work in this case because H has the same electr...
Fri Nov 14, 2014 5:20 pm
Forum: Limiting Reactant Calculations
Replies: 2
Views: 591

^ Yes, what the comment said above is correct.

But going off what she said, you always use the limiting reactant to find the mass of the product since that is the one you're gonna run out of first.
Fri Nov 14, 2014 5:13 pm
Forum: Ionic & Covalent Bonds
Topic: What to use to find the EN difference
Replies: 4
Views: 1817

### Re: What to use to find the EN difference

The trend is kind of weird, but you have to be familiar it. I found this periodic table really helpful. http://www.bargainorgonite.com/wp-content/uploads/2013/06/electronegativities.gif"onclick="window.open(this.href);return false; Notice that O has higher electronegativity than Cl. Also, something ...
Tue Nov 11, 2014 4:14 am
Forum: DeBroglie Equation
Topic: Fall 2010 Midterm Q5A
Replies: 1
Views: 440

### Fall 2010 Midterm Q5A

The average of a helium atom at 25C is 1.23x10^3 m.s^-1. What is the average wavelength of a helium atom at this temperature? My question is why do we have to divide the mass of He (4.003g/mol^-) by avogadro constant? I would've just changed 4.003 g --> 4.003 x 10^-3 kg and use that for the "m&...
Sun Nov 02, 2014 12:52 am
Forum: Lewis Structures
Topic: Correct Lewis Structure for SO2?
Replies: 1
Views: 717

### Re: Correct Lewis Structure for SO2?

SO2 molecule can be seen with single or a double bond due to the formal charge and S is one of the elements that can break the octet rule so SO2 should have a double bond, but many prefer not to violate the octet rule because S in the lewis structure, O=S=O , would be surrounded by 10 electrons.
Sat Oct 18, 2014 6:25 pm
Forum: Electron Configurations for Multi-Electron Atoms
Topic: s-orbitals and d-orbitals
Replies: 1
Views: 349

### s-orbitals and d-orbitals

Why aren't the s-orbitals for the elements Cr, Cu, Nb, Mo, Ru, Rh, Ag filled up?

for example, why is the electron configuration for Nb [Kr] 4d^4 5s^1 and not [Kr] 4d^3 5s^2 instead?
Sat Oct 18, 2014 6:24 pm
Forum: Electron Configurations for Multi-Electron Atoms
Topic: s-orbitals and d-orbitals
Replies: 1
Views: 313

### s-orbitals and d-orbitals

Why aren't the s-orbitals for the elements Cr, Cu, Nb, Mo, Ru, Rh, Ag filled up?

for example, why is the electron configuration for Nb [Kr] 4d^4 5s^1 and not [Kr] 4d^3 5s^2 instead?
Mon Oct 13, 2014 1:07 am
Forum: Photoelectric Effect
Topic: Sodium Vapor Lamps (1.19 hw) [ENDORSED]
Replies: 6
Views: 10217

### Re: Sodium Vapor Lamps (1.19 hw)[ENDORSED]

a)

wavelength = 589nm convert it to m, 5.89 x10^-7 m

you use the formula E= hc/wavelength

E = (6.626 x 10^-34)(2.99 x 10^8) / (5.89 x 10^-7)
= 3.37 x 10^-19 J
Mon Oct 13, 2014 1:03 am
Forum: Photoelectric Effect
Topic: Sodium Vapor Lamps (1.19 hw) [ENDORSED]
Replies: 6
Views: 10217

### Re: Sodium Vapor Lamps (1.19 hw)[ENDORSED]

b) First, you convert mg to g 5.00 mg * (1g/1000mg) = 5.00 x 10^-3 g of Na Since, it's asking for the how much energy is emitted by an excited SODIUM, you use the molar mass of Na 5.00x10^-3 g Na * (1 mol Na/ 23g Na) * (6.022 x10^23 atoms Na/ 1 g Na) = 1.31 x10^20 atoms of Na (1.31 x10^20 atoms Na) ...
Fri Oct 10, 2014 8:51 pm
Forum: Photoelectric Effect
Topic: If ∅ for Na is 150.6 kJ.mol-1, how do I get the mass of Na?
Replies: 1
Views: 583

### If ∅ for Na is 150.6 kJ.mol-1, how do I get the mass of Na?

On the photoelectric effect pre-assessment this was given Light hits a sodium metal surface and the velocity of the ejected electron is 6.61 x 105 m.s-1. The work function for sodium is 150.6 kJ.mol-1 and it asked for the kinetic energy of the ejected electron. I started off using this formula: λ=h/...