Search found 29 matches

by Tara_Shooshani_3N
Wed Mar 15, 2017 5:34 pm
Forum: Thermodynamic Systems (Open, Closed, Isolated)
Topic: dU, q, w
Replies: 3
Views: 466

Re: dU, q, w

Since U=0, w=-q
by Tara_Shooshani_3N
Wed Mar 15, 2017 5:31 pm
Forum: *Cyclohexanes (Chair, Boat, Geometric Isomers)
Topic: Q5B on 2008 Final
Replies: 1
Views: 261

Re: Q5B on 2008 Final

There is a cis to indicate the placement of the substituents on the chair structure. The cis means that the methyl is axial and the isopropyl is equatorial (or vice-versa).
by Tara_Shooshani_3N
Wed Mar 08, 2017 9:17 pm
Forum: Student Social/Study Group
Topic: Post All Chemistry Jokes Here
Replies: 7774
Views: 1073928

Re: Post All Chemistry Jokes Here

Why do aromatics belong in the nuthouse?

Because they’re all CYCLO.
by Tara_Shooshani_3N
Sat Mar 04, 2017 1:35 pm
Forum: *Alkanes
Topic: Order in naming [ENDORSED]
Replies: 2
Views: 373

Order in naming [ENDORSED]

For chapter 1 Qs 16 and 17, why are the molecules named:
2-isopropyl-1,1-dimethylcyclopentane in instead of 1,1-dimethyl-2-isopropylcyclopentane
and
4-tertbutyl-1,2-dimethylcyclohexane instead of 1,2-dimethyl-4-tertbutylcyclohexane ?

Thanks!
by Tara_Shooshani_3N
Sat Mar 04, 2017 12:17 pm
Forum: *Alkanes
Topic: 1.24
Replies: 1
Views: 214

Re: 1.24

Yes, it appears as if they are ¯\_(ツ)_/¯ Both 2-pentene molecules.
by Tara_Shooshani_3N
Wed Mar 01, 2017 2:50 pm
Forum: *Organic Reaction Mechanisms in General
Topic: Drawing Reaction Profiles
Replies: 1
Views: 270

Re: Drawing Reaction Profiles

Based on what I've seen in examples, as long as you label each step and section of the graph, you can make the graph as high/low/wide as you want. Obviously, you need to have every segment of the graph line up with the right step of the reaction and have them proportional to each other. Hope that he...
by Tara_Shooshani_3N
Wed Feb 22, 2017 5:15 pm
Forum: *Electrophilic Addition
Topic: intermediate
Replies: 2
Views: 387

Re: intermediate

An intermediate is a molecule that is produced from the reactants in the early steps of a mechanism, but is not present in the final molecular formula of the chemical reaction. When you add the mechanism formulas together to get the simplified chemical formula, the intermediates will always cancel.
by Tara_Shooshani_3N
Thu Feb 16, 2017 8:31 pm
Forum: First Order Reactions
Topic: homework 15.21 and 15.23
Replies: 1
Views: 334

Re: homework 15.21 and 15.23

It's negative when you're finding the concentration of a reactant, which is decreasing. It's positive when finding the concentration of the products, which is increasing.
by Tara_Shooshani_3N
Sun Feb 12, 2017 3:54 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Methods of finding K
Replies: 1
Views: 221

Methods of finding K

Can the following equations be used interchangeably to find K?:

deltaG = -RTlnK
deltaEcell = ((RT)/(nF))lnk = (.0257/n)lnK

Thank you!
by Tara_Shooshani_3N
Mon Feb 06, 2017 9:40 pm
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: Plugging in #s for Q [ENDORSED]
Replies: 2
Views: 338

Plugging in #s for Q [ENDORSED]

In the equation E=E - (RT)/(nF) * ln(Q), how do we know which molecules are the products and which are the reactants to plug in for Q? Is it always the cathode, or always the anode, or based off something else entirely?

Thanks
by Tara_Shooshani_3N
Mon Jan 30, 2017 4:30 pm
Forum: Phase Changes & Related Calculations
Topic: Entropy vs Enthalpy
Replies: 2
Views: 409

Re: Entropy vs Enthalpy

Entropy (S) is a measurement of disorder and randomness, while enthalpy (H) is the amount of heat a reaction releases or absorbs. Each question will probably specify whether to use entropy or enthalpy, or you can tell from the information the question provides.
by Tara_Shooshani_3N
Sun Jan 29, 2017 11:43 pm
Forum: Administrative Questions and Class Announcements
Topic: Quiz 1 Preparation Answers
Replies: 130
Views: 14149

Re: Quiz 1 Preparation Answers

For #8, I don't understand why the reaction will not be spontaneous at any temperature.

Please help! Thanks!
by Tara_Shooshani_3N
Wed Jan 25, 2017 11:06 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: Entropy and Stability
Replies: 1
Views: 240

Entropy and Stability

Is high entropy more stable than low entropy?

For example, which is more stable: a system with entropy 10 or entropy 20?
by Tara_Shooshani_3N
Sun Jan 22, 2017 6:16 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: Degeneracy and Entropy
Replies: 1
Views: 254

Degeneracy and Entropy

In the equation relating degeneracy and entropy, S = kB * ln(W), where do we get the value for kB (k-sub-B)?
by Tara_Shooshani_3N
Mon Jan 16, 2017 10:57 am
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Enthalpy [ENDORSED]
Replies: 3
Views: 404

Re: Enthalpy [ENDORSED]

It depends on the elements being used, but in general, you subtract the mean bond enthalpy of the double bond you are forming from the single bond you are breaking. For example, if we take a single bonded C-C and convert it to a C=C bond, we first have to add energy to break the single bond, and the...
by Tara_Shooshani_3N
Wed Jan 11, 2017 8:07 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Standard Enthalpy of Formation
Replies: 1
Views: 265

Re: Standard Enthalpy of Formation

Heat is an extensive property because it changes when the size of the sample changes. Somethkng that has mass 10 grams will not have the same temperature as something with mass 100 grams.
by Tara_Shooshani_3N
Tue Nov 29, 2016 12:40 pm
Forum: Calculating pH or pOH for Strong & Weak Acids & Bases
Topic: Identifying a strong acid
Replies: 6
Views: 1147

Re: Identifying a strong acid

I don't think that strong and weak acids and bases are determined based on a set number on the pH scale because temperature and solvent change pH. Instead, a strong acid/base is one that completely ionizes in a reaction. A weak acid/base does not completely ionize. You can tell in a question whether...
by Tara_Shooshani_3N
Tue Nov 29, 2016 12:32 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Both Roots are positive
Replies: 2
Views: 255

Re: Both Roots are positive

One of the roots will be larger than one or both of your concentrations, so when you try subtracting it from your concentration you will get a negative new concentration, which does not make sense. So use the other value that results in two positive concentrations.
by Tara_Shooshani_3N
Fri Nov 25, 2016 6:25 pm
Forum: Identifying Acidic & Basic Salts
Topic: #12.75
Replies: 3
Views: 786

#12.75

During the analysis of an unknown acid HA, a 0.010 m solution of the sodium salt of the acid was found to have a pH of 10.35. Use Table 12.1 to write the formula of the acid.

I don't clearly understand the answer key, please help.

Thanks!!
by Tara_Shooshani_3N
Mon Nov 21, 2016 12:35 am
Forum: Conjugate Acids & Bases
Topic: Fundamental J.5
Replies: 1
Views: 292

Fundamental J.5

The question reads: Complete the overall equation, and write the complete ionic equation and the net ionic equation for each of the following acid-base reactions. HF (plus) NaOH = LiOH (plus) HI = I understand how to write the overall equations, but I am confused on how to write the complete ionic a...
by Tara_Shooshani_3N
Tue Nov 15, 2016 3:00 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Reaction at equilibrium
Replies: 1
Views: 264

Reaction at equilibrium

This is a question from the first equilibrium module: For a chemical reaction that has reached equilibrium which statement is false ? a) the forward reaction rate is the same as the reverse reaction rate b) no matter what combination of concentrations of reactants and products we start with the reac...
by Tara_Shooshani_3N
Sat Nov 12, 2016 2:21 pm
Forum: Shape, Structure, Coordination Number, Ligands
Topic: What is a Ligand?
Replies: 3
Views: 847

Re: What is a Ligand?

A ligand is a molecule or ion that bonds with a metal atom. What we're focusing on is ligands bonding to central transition metals to form coordination compounds. The transition metal itself is typically not the ligand.
by Tara_Shooshani_3N
Sat Nov 12, 2016 2:16 pm
Forum: Naming
Topic: Subscripts of atoms outside the brackets
Replies: 1
Views: 333

Subscripts of atoms outside the brackets

When writing the formula for potassium tetracyanonickelate (II), why is the answer K2[Ni(CN)4] and not just K[Ni(CN)4]?

Thanks.
by Tara_Shooshani_3N
Tue Nov 01, 2016 4:12 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Trigonal pyramidal vs. pyramidal
Replies: 2
Views: 1169

Trigonal pyramidal vs. pyramidal

Are trigonal pyramidal and pyramidal the same thing? What are the bond angles?

Thanks.
by Tara_Shooshani_3N
Tue Oct 25, 2016 3:54 pm
Forum: Lewis Structures
Topic: Lewis Structure Octet Rule Exceptions
Replies: 4
Views: 563

Re: Lewis Structure Octet Rule Exceptions

H, He, Li, and Be are exceptions since they cannot hold 8 electrons. As for elements that have expanded octets, most of the elements after Si have expanded octets since they're in the third energy level (third row of the periodic table) and have empty d orbitals. I've specifically seen a lot of P an...
by Tara_Shooshani_3N
Mon Oct 17, 2016 10:38 pm
Forum: Electron Configurations for Multi-Electron Atoms
Topic: Chapter 2 Question 29 [ENDORSED]
Replies: 3
Views: 378

Re: Chapter 2 Question 29 [ENDORSED]

I'll go part by part to explain where the numbers come from: a) when l=1, we know it is a p-orbital, and 6 electrons can fit in a p-orbital, so the answer is 6. b) and d) in any m group there are always only 2 electrons maximum. One has upward spin, one has downward. c) when n=2, l can be either 0 o...
by Tara_Shooshani_3N
Tue Oct 11, 2016 10:26 pm
Forum: SI Units, Unit Conversions
Topic: Quiz 1 number 3
Replies: 2
Views: 477

Re: Quiz 1 number 3

You do not need to convert the units. Another way to write Hz is s^-1, so the seconds cancel and you're left with J. The book tends to use s^-1 instead of Hz when giving the units of frequency.
by Tara_Shooshani_3N
Tue Oct 04, 2016 5:26 pm
Forum: Properties of Electrons
Topic: C-C bond breakage by visible light? [ENDORSED]
Replies: 1
Views: 508

Re: C-C bond breakage by visible light? [ENDORSED]

To answer this you first need to convert the given energy from 348 kJ/mol to J/c-c bond. Basically, multiply by 1000J and divide by 6.022 * 10^23 c-c bonds to get 5.78 * 10^-19 J. Then substitute this energy value into the equation wavelength=hc/E. Your answer ends up being 344 nm, which is in the u...
by Tara_Shooshani_3N
Tue Sep 27, 2016 9:22 pm
Forum: Limiting Reactant Calculations
Topic: Combustion Analysis
Replies: 1
Views: 465

Combustion Analysis

Can someone explain the series of conversions needed to use combustion analysis to find the empirical formula of a molecule given the mass of an unknown compound and the masses of carbon dioxide and water (and any other product) produced? I understand the concept of combustion analysis, but I always...

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