## Search found 19 matches

Tue Mar 14, 2017 8:42 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: #8.101.c
Replies: 2
Views: 479

### #8.101.c

The reaction 2 SO2(g) + O2(g) --> 2 SO3(g) occurs at 25 degrees Celsius and 1 atm in a constant pressure cylinder. Initially, 0.030 mol SO2 and 0.030 mol O2 are present in the cylinder. Part C asks "Assuming that the reaction goes to completion and that the temperature and pressure of the react...
Thu Mar 09, 2017 2:30 pm
Forum: *Cycloalkanes
Topic: Multiple possible names
Replies: 2
Views: 323

### Re: Multiple possible names

I think it depends on the number of substituents. When there are just two substituents, it would make sense to assign the smaller number to the substituent that would be named first alphabetically, and then the second substituent would get the next number. However, when you have three or more substi...
Sun Mar 05, 2017 10:09 pm
Topic: Help on HW 4.30 and the Arrhenius Equation
Replies: 1
Views: 532

### Help on HW 4.30 and the Arrhenius Equation

The question asks: "The activation energy in organic reaction is known to be 125 kJ/mol. Will this reaction occur at room temperature?" How do I calculate this? I assumed we would use the Arrhenius equation and solve for k, and if k is less than 1, then the reaction wouldn't occur under ro...
Thu Feb 23, 2017 11:50 pm
Forum: General Rate Laws
Topic: When B and C is significantly larger than A
Replies: 3
Views: 430

### Re: When B and C is significantly larger than A

I believe it is just "significantly large" enough so that the concentrations of B and C remain constant when A is being used up. This way, as stated in the Course Reader, the reaction rate depends on just concentration of A.
Tue Feb 14, 2017 7:09 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: midterm 2015 #4&5 B
Replies: 3
Views: 515

### Re: midterm 2015 #4&5 B

I understand it is Cv because it is under constant volume due to the fact that the expansion occurs isothermally. However, in Ron's case, the temperature of the balloon actually changes. I'm confused because wouldn't this mean the expansion doesn't occur isothermally?
Thu Feb 09, 2017 2:02 pm
Forum: Balancing Redox Reactions
Topic: Reduction and Oxidation [ENDORSED]
Replies: 6
Views: 593

### Re: Reduction and Oxidation[ENDORSED]

Cu is being oxidized because it is losing two electrons, while Fe^3 is being reduced because it is gaining an electron.
Fri Feb 03, 2017 4:26 pm
Forum: Student Social/Study Group
Topic: Post All Chemistry Jokes Here
Replies: 7951
Views: 1160857

### Re: Post All Chemistry Jokes Here

Why are Helium, Curium, and Barium considered medical elements?
Because if you can't HEALium or CUREium, you got to BURYem.
Wed Jan 25, 2017 3:37 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: Delta S and what it favors?
Replies: 2
Views: 1057

### Delta S and what it favors?

Why does positive Delta S favor forward processes and why does negative Delta S not? Does "forward" refer to a reaction where a substance goes from a lower energy state to a higher one? Clarification please, thanks.
Fri Jan 20, 2017 3:40 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: What is Kb in Entropy? Entropy Clarification? [ENDORSED]
Replies: 2
Views: 607

### What is Kb in Entropy? Entropy Clarification?[ENDORSED]

In Chem14A, Ka and Kb dealt with acid and base equilibrium; however, I don't understand how this relates to entropy and how we're supposed to derive this value for calculations? Also, I don't fully understand the concept of entropy. I understand that it is randomness within a system, but in lecture ...
Wed Jan 11, 2017 11:03 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Help on HW 8.57
Replies: 4
Views: 734

### Help on HW 8.57

In this question, we must find the reaction enthalpy by subtracting the standard enthalpy of formation of all products with the reactants'. However, every time I do this, I get 312 kJ per mole, while the solutions manual says the correct answer is -312 kJ per mole. My math was -1560 - (-1300 + 2 * -...
Thu Dec 01, 2016 11:53 pm
Forum: *Titrations & Titration Calculations
Topic: Finding Stoichiometric Point for Weak Acids/Bases? [ENDORSED]
Replies: 1
Views: 448

### Finding Stoichiometric Point for Weak Acids/Bases?[ENDORSED]

Alright, so for a weak acid, the pH starts low so the stoichiometric point must be above pH 7, and for a weak base, the pH starts high so the stoichiometric point must be below pH 7. However, how would we calculate the EXACT stoichiometric point? For strong acids/bases it's easier because we can jus...
Tue Nov 22, 2016 9:01 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Difference between aq and l?
Replies: 1
Views: 7338

### Difference between aq and l?

When calculating equilibrium constants, we are supposed to disregard what is in the solid or liquid state. However, why don't we disregard the aqueous solution? I thought that an aqueous solution and a liquid were the same thing. Could someone clarify? Thanks.
Tue Nov 15, 2016 6:19 pm
Forum: Naming
Topic: Is (OH)2 aqua? [ENDORSED]
Replies: 1
Views: 273

### Is (OH)2 aqua?[ENDORSED]

In problem 17.29 in the textbook, the compound [Co(CN)5(OH)2]2- is named aquapentacyanocobaltate(III). However, the Course Reader says H2O is named aqua, and (OH)2 isn't the equivalent of H2O. Could someone clarify this for me? Thanks!

(I thought it would be named pentacyanodihydroxocobaltate(III)).
Sat Nov 12, 2016 5:35 pm
Forum: *Molecular Orbital Theory (Bond Order, Diamagnetism, Paramagnetism)
Topic: How to determine Nuclear Charge? [ENDORSED]
Replies: 1
Views: 365

### How to determine Nuclear Charge?[ENDORSED]

For MO energy diagrams, knowing the atoms' nuclear charge is important. However, I don't really know how to find it. Is nuclear charge the same as the number of valence electrons an atom has? If not, what is it? Thank you! Clarification much needed!
Tue Nov 01, 2016 2:33 pm
Forum: Electron Configurations for Multi-Electron Atoms
Topic: Size of Cations/Anions compared to Parent Atoms
Replies: 1
Views: 5313

### Size of Cations/Anions compared to Parent Atoms

The Course Reader states, "But cations are smaller than their parent atoms and anions are larger." However, shouldn't cations be larger than their parent atoms because losing an electron would mean decreasing nuclear charge and thus electrons would be further from the nucleus? Also, should...
Wed Oct 26, 2016 2:25 pm
Forum: Ionic & Covalent Bonds
Topic: Bond Angles?
Replies: 2
Views: 547

### Bond Angles?

How exactly do you calculate the angles of each bond? Also, how do these angles affect the molecule? Are we supposed to memorize the angles that correspond to a certain shape, or is there some way to calculate it? Thank you!
Wed Oct 12, 2016 2:30 pm
Forum: Properties of Electrons
Topic: Removing 2nd Electron
Replies: 2
Views: 887

### Removing 2nd Electron

Why does it become harder to remove an electron when an atom has a net positive charge? I understand the ionization energy becomes higher after the first electron is removed, but why?
Thu Oct 06, 2016 1:34 pm
Forum: Properties of Electrons
Topic: Wavelike Properties? [ENDORSED]
Replies: 2
Views: 563

### Wavelike Properties?[ENDORSED]

I need some clarification. Throughout the Course Reader, electrons are described as having "wavelike properties." Why so? There is also an example described where "If you are driving a 1.5E3 kg car at 27.0 m.s-1, what is the De Brogile wavelength of your car? Does your car have any me...
Fri Sep 30, 2016 3:04 pm
Forum: Properties of Electrons
Topic: Energy Level Model [ENDORSED]
Replies: 2
Views: 574

### Energy Level Model[ENDORSED]

I am having trouble understanding the model depicted in the course reader. I understand that it has to do with electrons, but what exactly is happening? Why are the arrows pointing downwards and why are they of different lengths and at different levels? What is "hR"? Help would be apprecia...