## Search found 32 matches

Sat Mar 12, 2016 11:51 pm
Forum: Phase Changes & Related Calculations
Topic: 2011 Final Question 1A
Replies: 1
Views: 387

### 2011 Final Question 1A

"Suppose you want to use methane gas (deltaH = -890 kJ/mol) to boil 50.0 mL of water at 25.0 degrees C. How many grams of methane gas would need to be combusted to generate the required heat?" The answer for this question only calculates the amount of heat to raise the water to 100 degrees...
Sat Mar 05, 2016 1:26 pm
Forum: *Alkanes
Topic: "Tert-" Prefix
Replies: 5
Views: 594

### Re: "Tert-" Prefix

No, tert is not taken into consideration for alphabetical ordering. I use INST to remember that iso and neo count for alphabetizing, while sec and tert do not.
Sat Mar 05, 2016 1:22 pm
Forum: *Alkynes
Topic: Tripple bond line structure
Replies: 2
Views: 1138

### Re: Tripple bond line structure

A Triple bond forces the two carbons it is attached to to have an sp structure, which is 180 degrees and makes the bonds of that carbon be in a straight line. Therefore, triple bonds must always be drawn as straight lines. Single bonds are usually 109.5 degrees and one double bond would make 120 deg...
Sun Feb 28, 2016 6:51 pm
Forum: *Alkanes
Topic: Structural Isomers
Replies: 1
Views: 307

### Re: Structural Isomers

The chain of 4 is the same as the T-shaped chain. Carbon has an sp3 structure in alkanes, so it can rotate, and this is just a rotation of the same molecule. If you draw it with line structure instead of lewis structure you can see it a lot more easily - I would recommend using line structure to loo...
Sun Feb 28, 2016 6:44 pm
Forum: *Alkanes
Topic: IUPAC vs Common Name
Replies: 1
Views: 279

### Re: IUPAC vs Common Name

If they don't specify, you can use either one you want. If the questions says IUPAC then you have to use IUPAC. Just depends on what the question says.
Sun Feb 28, 2016 6:42 pm
Forum: *Alkanes
Topic: Naming Cycloalkanes
Replies: 1
Views: 317

### Re: Naming Cycloalkanes

You count in the direction that gives you lower numbers for the substituents.
Sun Feb 28, 2016 6:38 pm
Forum: *Alkanes
Topic: "Tert-" Prefix
Replies: 5
Views: 594

### Re: "Tert-" Prefix

Just so you know, the central carbon in a tert- substituent will actually be quaternary because it will also need to attach to the parent chain, so it is bonded to 4 other carbons. But the fact that it's bonded to 3 other carbons that are part of the substituent is probably where the tert- name come...
Sun Feb 28, 2016 6:32 pm
Forum: *Alkanes
Topic: Common Names
Replies: 4
Views: 701

### Re: Common Names

Yes, common names can also be used with unsaturated parent chains.
Sun Feb 28, 2016 6:30 pm
Forum: *Nucleophiles
Topic: Ambident Nucleophile
Replies: 2
Views: 474

### Re: Ambident Nucleophile

I think it is usually either resonance or if two atoms have a similar electronegativity, like with CN- or SCN-
Mon Feb 22, 2016 9:33 pm
Forum: *Alkanes
Topic: Condensed structural formula
Replies: 1
Views: 285

### Re: Condensed structural formula

The ones that are part of the main chain will be the ones in the chain that has the largest amount of carbon atoms. The other carbons will be substituents coming off the main chain. If there are two equally long longest chains, you can use either one for naming and it will not matter which you choose.
Wed Feb 17, 2016 1:59 am
Forum: Kinetics vs. Thermodynamics Controlling a Reaction
Topic: Energetically Favorable vs. Spontaneous
Replies: 2
Views: 2245

### Re: Energetically Favorable vs. Spontaneous

Yes, there is a difference. If the products have lower energy, delta H is negative and the reaction is energetically favorable but not necessarily spontaneous. Remember delta G = delta H - T(delta S). A negative delta H makes it likely that the reaction is spontaneous, but if delta S is negative and...
Wed Feb 17, 2016 1:56 am
Forum: Kinetics vs. Thermodynamics Controlling a Reaction
Topic: K
Replies: 3
Views: 2738

### Re: K

Uppercase K is not a constant but is the ratio of products to reactants of a reaction at equilibrium. I think you mean lowercase k which is the rate constant for a reaction. This is just a number that you multiply the concentrations of the reactants by to get the rate of the reaction. Just don't get...
Sun Feb 07, 2016 11:48 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: K from delta G at different temperatures
Replies: 1
Views: 532

### K from delta G at different temperatures

Why do you need to calculate delta G from H and S when you're finding K at different temperatures? Why is the value you get from that equation different from using delta G of formation values? This is how the answer key solved 11.83.
Sat Jan 30, 2016 11:51 am
Forum: Balancing Redox Reactions
Topic: Redox Reactions
Replies: 3
Views: 584

### Re: Redox Reactions

Mon Jan 25, 2016 10:54 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Enthalpy
Replies: 3
Views: 2909

### Re: Enthalpy

Cl2 is more stable than 2Cl, since Cl appears as Cl2 in nature. In order to go from a more stable state to a less stable state, you have to put energy into the reaction, like how with radicals you have to put in energy to form them since they are unstable. Because the Cl2 needs to absorb energy from...
Mon Jan 25, 2016 10:45 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Bonds Formed v Bonds Broken
Replies: 1
Views: 292

### Re: Bonds Formed v Bonds Broken

You have to draw the Lewis structures for the molecules in the equation, and from that you can see what bonds would have to be broken on the left and formed on the right to turn the reactants into products. So basically just look for the differences between the structures of the reactants and produc...
Mon Jan 11, 2016 12:13 am
Forum: Phase Changes & Related Calculations
Topic: Phase changes
Replies: 2
Views: 469

### Re: Phase changes

Not all phase changes are endothermic - just the ones you mentioned (vaporization, melting, and sublimation) are endothermic. The other three phase changes that go in the opposite direction (condensation, freezing, and deposition) are exothermic but not mentioned in the course reader because in calc...
Sun Jan 10, 2016 11:59 pm
Forum: Phase Changes & Related Calculations
Topic: Required and Released Energy
Replies: 3
Views: 421

### Re: Required and Released Energy

When a bond is broken, the parts of the former molecule are now less stable than they were, especially if radicals are formed. They "do not want" to be less stable, so you need to use energy to force it into that state. On the other hand, atoms are more stable when bonded together, so they...
Sat Dec 05, 2015 11:53 pm
Forum: Hybridization
Topic: Clarification of lone pairs
Replies: 3
Views: 713

### Re: Clarification of lone pairs

lone pairs are a region of electron density :)
Sat Dec 05, 2015 11:51 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Question on molecules with linear shape
Replies: 2
Views: 665

### Re: Question on molecules with linear shape

Bond angles are only less than the values we memorize only when there are electron pairs that make the molecule not symmetric. Although XeF2 has three electron pairs, they are in a symmetrical arrangement around Xe so the bond angle is still exactly 180 degrees. The values we memorize are for when t...
Sun Nov 29, 2015 9:43 pm
Forum: *Making Buffers & Calculating Buffer pH (Henderson-Hasselbalch Equation)
Topic: Question about Buffers and Use of a Salt
Replies: 4
Views: 654

### Re: Question about Buffers and Use of a Salt

The salt is there so that you can have a reaction that is trying to reach equilibrium. If you just add, say, HCl to water, you will have an acidic pH but this pH can be easily changed by adding more OH- or H+ ions because HCl is a strong acid and the H+ ions won't react with the Cl- ions when in wat...
Sun Nov 29, 2015 9:34 pm
Forum: *Making Buffers & Calculating Buffer pH (Henderson-Hasselbalch Equation)
Topic: Polyprotic acids and bases
Replies: 1
Views: 364

### Re: Polyprotic acids and bases

I think you just look at how many hydrogens are attached to the molecule that would be reasonable to remove... For example H2SO4 is polyprotic because it has 2 hydrogens that can be removed (which is more than one, making it polyprotic). But HCl is not polyprotic because only one hydrogen is availab...
Tue Nov 24, 2015 12:47 am
Forum: Equilibrium Constants & Calculating Concentrations
Topic: When K=1
Replies: 3
Views: 4123

### Re: When K=1

The previous answer is wrong. K=1 does not give any information about whether the reaction is at equilibrium. Q=K will tell you that the reaction is at equilibrium (rates of forward and reverse reactions are equal). K=1 just means that the concentration of reactants and of products are equal at equi...
Tue Nov 24, 2015 12:30 am
Forum: Administrative Questions and Class Announcements
Topic: Videos Submissions
Replies: 8
Views: 11693

### Re: Videos Submissions

edit: He commented on the post "Videos on Chemistry Community": "For each student to receive credit, each student must upload the video in a different video file format (MP4, WMV, MOV). This ensures Chemistry Community 'counts' the video uploaded for each student. All videos must be u...
Sun Nov 15, 2015 11:03 pm
Forum: Naming
Topic: Which naming convention?
Replies: 1
Views: 324

### Which naming convention?

We can memorize either naming convention for coordination compounds as long as we use the same one the whole time on a test right? I wouldn't get docked if I used the new convention right?
Wed Nov 04, 2015 9:57 pm
Forum: Naming
Topic: Ligand names
Replies: 2
Views: 334

### Ligand names

Do we need to memorize all the names for ligands in coordination compounds that are on page 105 of the course reader? I know someone else asked this but this part didn't get answered.
Thu Oct 29, 2015 10:11 am
Forum: Hybridization
Topic: Sigma and Pi Bonds
Replies: 4
Views: 1080

### Re: Sigma and Pi Bonds

Yes, I agree that you should draw the lewis structure first in order to find the number of sigma and pi bonds. Also, it's correct that only period 2 and higher elements can form pi bonds because hydrogen and helium will not form double bonds since their "octet" (2 electrons) is satisfied w...
Thu Oct 29, 2015 10:05 am
Forum: Determining Molecular Shape (VSEPR)
Topic: Ch.3 #95
Replies: 1
Views: 317

### Re: Ch.3 #95

I think the solutions didn't draw the bonds between the carbon and hydrogen just because they were kind of being lazy/simplifying the lewis structure. Usually in organic chem you will draw CH2s like that because you know that the carbon will just have one bond with each hydrogen so it isn't really n...
Thu Oct 15, 2015 11:39 pm
Forum: Electron Configurations for Multi-Electron Atoms
Topic: Electron Configuration
Replies: 1
Views: 252

### Re: Electron Configuration

I'm fairly sure you can just use the shorthand electron configuration unless you're asked for the full version.
Thu Oct 15, 2015 11:37 pm
Forum: Electron Configurations for Multi-Electron Atoms
Topic: Valence Electrons
Replies: 2
Views: 3591

### Re: Valence Electrons

The first reply is not entirely correct. Yes, the number of valence electrons is the number of electrons in the outermost shell and the electron configuration of Ni is [Ar] 3d^8.4s^2. However, this makes the number of valence electrons of Nickel 2, not 10, because the d electrons are in the 3 shell ...
Thu Oct 15, 2015 11:01 pm
Forum: Properties of Light
Topic: wavelength verbiage
Replies: 2
Views: 526

### Re: wavelength verbiage

Wavelength is the distance before the wave begins to repeat itself. For example, wavelength is usually measured from peak to peak of a wave (the highest point of a wave) or from trough to trough (the lowest point of a wave). On the other hand, the frequency of a wave is the number of wavelengths tha...
Thu Oct 15, 2015 10:48 pm
Forum: Administrative Questions and Class Announcements
Topic: Green Workbook Quizzes
Replies: 2
Views: 527

### Re: Green Workbook Quizzes

Yeah, I think the other two are just for practice.