Search found 48 matches

by Chris Freking 2G
Fri Feb 15, 2019 11:28 am
Forum: Student Social/Study Group
Topic: last problem on midterm
Replies: 4
Views: 124

Re: last problem on midterm

Athena L 1B wrote:What was the problem for this one?


This was question 8A for the Fall 2018 Chem 14A Midterm
by Chris Freking 2G
Fri Feb 15, 2019 11:26 am
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: HOTDOG problem
Replies: 2
Views: 13

Re: HOTDOG problem

You do flip the enthalpies when the equation is flipped. The final equation should be (2*-345kJ) + (2*21kJ) + (150kJ), where the first equation is multiplied by 2, the second equation is flipped and multiplied by 2, and the final equation is flipped as to give the final reaction 2GingerAle + 5RootBe...
by Chris Freking 2G
Tue Feb 12, 2019 3:13 pm
Forum: Administrative Questions and Class Announcements
Topic: DOWNLOAD SESSION WORKSHEETS HERE - Sun 7-9PM (Karen)
Replies: 108
Views: 2385

Re: DOWNLOAD SESSION WORKSHEETS HERE - Sun 7-9PM (Karen)

Madeline Ho 1C wrote:Can someone explain how to do #3?
I got deltaHrxn= 1mol(1560 kJ/mol) - [1mol(-1300 kJ/mol)+2mol(-286 kJ/mol)] = 3432 kJ


Using Hess' Law will give the reaction
deltaHrxn = (1mol)(-1300kJ/mol) + (2mol)(-286kJ) + (1mol)(1560kJ) = -312kJ
by Chris Freking 2G
Sun Feb 10, 2019 5:33 pm
Forum: Ideal Gases
Topic: Calculating Pressure of a Gas Mixture Using PV=nRT
Replies: 1
Views: 7

Calculating Pressure of a Gas Mixture Using PV=nRT

It is given that the gas mixture has 2.250 mol of helium gas and 1.492 mol of krypton gas. The temperature of the system is 348.15K and the volume of the system is 11.0L. To calculate the total pressure of the system, do we first calculate the pressure using mol of helium gas, then calculate the pre...
by Chris Freking 2G
Fri Feb 08, 2019 4:36 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: If not Gibbs Free Energy then what is the last topic for midterm?
Replies: 4
Views: 24

Re: If not Gibbs Free Energy then what is the last topic for midterm?

According to Lavelle's important midterm information document on his website, the midterm will cover "Chemical Equilibrium, Acid and Base Equilibria, Thermochemistry, Thermodynamics to the end of entropy."
by Chris Freking 2G
Fri Feb 01, 2019 2:28 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Open, closed, or isolated systems
Replies: 10
Views: 44

Re: Open, closed, or isolated systems

Some examples:
Open - An unsealed flask of liquid; an open soda can
Closed - A sealed flask of liquid, an unopened soda can
Isolated - The universe; A high-quality sealed thermos*; a bomb calorimeter*

* (these are not 100% isolated, but for our reference the heat transfer is approximated to 0)
by Chris Freking 2G
Fri Feb 01, 2019 2:24 pm
Forum: Thermodynamic Systems (Open, Closed, Isolated)
Topic: Midterm
Replies: 4
Views: 41

Re: Midterm

Chem14BTestSchedule.pdf
(132.76 KiB) Downloaded 6 times
by Chris Freking 2G
Fri Feb 01, 2019 2:18 pm
Forum: Thermodynamic Systems (Open, Closed, Isolated)
Topic: Isolated Systems
Replies: 6
Views: 21

Re: Isolated Systems

The bomb calorimeter is also an example of an "isolated system." There is no truly 100% isolated system other than the universe (arguably). But we refer to a high-quality sealed thermos or a bomb calorimeter as an isolated system because the heat transfer is so slow that it can be approxim...
by Chris Freking 2G
Fri Jan 25, 2019 10:00 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: adding two reactions together
Replies: 2
Views: 18

Re: adding two reactions together

From the lecture on 1/25/19:

N2(g) + O2(g) --> 2NO(g) (ΔHrxn = 180kJ)
2NO(g) + O2(g) --> 2NO2(g) (ΔHrxn = -112 kJ)

Adding the above reactions gives the net reaction:
N2(g) + 2O2(g) --> 2NO2(g) (Hnet = 68kJ)
by Chris Freking 2G
Fri Jan 25, 2019 9:54 pm
Forum: Administrative Questions and Class Announcements
Topic: Homework
Replies: 5
Views: 245

Re: Homework

@504909207

Probably Outline 3 (Thermochemistry and The First Law of Thermodynamics) since we have already started covering that material and the 1st and 2nd outlines have already been tested on
by Chris Freking 2G
Fri Jan 25, 2019 9:52 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Stable carbon
Replies: 3
Views: 19

Re: Stable carbon

1920px-Carbon-phase-diagramp.svg.png


It can also be seen in this carbon phase diagram that carbon is in the form of granite at standard conditions
by Chris Freking 2G
Sat Jan 19, 2019 6:49 pm
Forum: Administrative Questions and Class Announcements
Topic: Studying for First Discussion Test
Replies: 10
Views: 57

Re: Studying for First Discussion Test

Lavelle emphasizes to do the homework as a way to prepare for the tests.
by Chris Freking 2G
Sat Jan 19, 2019 6:41 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Post Assessment Part 2
Replies: 1
Views: 13

Re: Post Assessment Part 2

If 18.3% of the BrCl gas remains at equilibrium and we have the initial concentration of BrCl, it is possible to calculate the amount of BrCl left at equilibrium. 0.183 * (1.84 * 10^-4) = 3.36 * 10^-5 M of BrCl at equilibrium. Then use the ICE box and plug in this value: 2BrCl(g) ⇌ Br2 (g) + Cl2(g) ...
by Chris Freking 2G
Tue Jan 15, 2019 9:28 pm
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: Negative pH
Replies: 11
Views: 71

Re: Negative pH

pH can be negative if the concentration of H+ ions have a molarity over 1.

See viewtopic.php?t=24564
by Chris Freking 2G
Fri Jan 11, 2019 9:29 am
Forum: Ideal Gases
Topic: What does K represent?
Replies: 9
Views: 33

Re: What does K represent?

K is the equilibrium constant, which is derived from dividing the concentration of product by the concentration of reactant. (K=[P]/[R]). When a reaction is at equilibrium, products and reactants are being formed at equal rates, so the concentration of either remains constant.
by Chris Freking 2G
Fri Jan 11, 2019 9:26 am
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Help with Q 11.7.c (6e)
Replies: 1
Views: 14

Re: Help with Q 11.7.c (6e)

In part C, K = (Partial pressure of X)^2 / (Partial Pressure of X2)

Plug in the mole fractions of each molecule (X = 12 molecules/17 molecules) and (X2 = 5 molecules/17 molecules)
Plugging those fractions to K and multiplying by the initial pressure of X2 (0.10 bar) will give the answer 0.17 .
by Chris Freking 2G
Wed Jan 09, 2019 2:20 pm
Forum: Non-Equilibrium Conditions & The Reaction Quotient
Topic: Reaction Quotient
Replies: 5
Views: 42

Re: Reaction Quotient

K refers to the [P]/[R] ratio at equilibrium. Although Q also refers to the [P]/[R] ratio, it can be measured at any point in time in a reaction--including equilibrium. If Q<K, then the forward reaction (products forming) is favored. If Q>K, then the reverse reaction (reactants forming) is favored. ...
by Chris Freking 2G
Sat Dec 08, 2018 2:06 pm
Forum: Administrative Questions and Class Announcements
Topic: FINAL PRACTICE - Lyndon's Churro Review Session [ENDORSED]
Replies: 118
Views: 3543

Re: FINAL PRACTICE - Lyndon's Churro Review Session [ENDORSED]

Reese - Dis 1G wrote:Can someone explain 27? I thought you only added -ate when the compound was negative.


If K2 has a +2 charge, then [Ni(CN)4] must have a -2 charge since the overall compound is neutral. It's called "nickelate" because the compound in the brackets has the -2 charge.
by Chris Freking 2G
Sat Dec 08, 2018 1:51 pm
Forum: Bohr Frequency Condition, H-Atom , Atomic Spectroscopy
Topic: Energy Levels
Replies: 2
Views: 24

Re: Energy Levels

The electron gains energy when it jumps from a lower energy level to a higher energy level.
by Chris Freking 2G
Fri Dec 07, 2018 9:00 pm
Forum: Interionic and Intermolecular Forces (Ion-Ion, Ion-Dipole, Dipole-Dipole, Dipole-Induced Dipole, Dispersion/Induced Dipole-Induced Dipole/London Forces, Hydrogen Bonding)
Topic: Review questions
Replies: 3
Views: 27

Re: Review questions

You are also already told initially that H2Se has a higher boiling point than H2S, so you don't have to worry about determining which one has the higher boiling point. All you have to do is explain why H2Se is the one with the higher boiling point, and in this case the only possible way for H2Se to ...
by Chris Freking 2G
Fri Dec 07, 2018 2:13 am
Forum: Amphoteric Compounds
Topic: Amphiprotic vs. amphoteric
Replies: 3
Views: 33

Re: Amphiprotic vs. amphoteric

I understand that all amphiprotic compounds can be amphoteric compounds. But what is an example of an amphoteric compound that is not amphiprotic?
by Chris Freking 2G
Fri Nov 30, 2018 6:09 pm
Forum: Properties & Structures of Inorganic & Organic Acids
Topic: Acid vs base [ENDORSED]
Replies: 15
Views: 130

Re: Acid vs base [ENDORSED]

Lewis Acids accept electrons while Lewis Bases donate electrons.

This is not to be confused with Bronsted:
Bronsted acids donate protons while Bronsted Bases accept protons.
by Chris Freking 2G
Fri Nov 30, 2018 5:59 pm
Forum: Properties & Structures of Inorganic & Organic Acids
Topic: Physical properties of acids and bases
Replies: 1
Views: 23

Re: Physical properties of acids and bases

Hydronium ions trigger taste buds that send a signal of "sourness" to the brain.

Hydroxide ions break down fatty acids and oils on the skin which reduces friction on your skin, which is why they feel soapy.
by Chris Freking 2G
Fri Nov 30, 2018 5:55 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Pentagonal bipyramidal
Replies: 4
Views: 38

Re: Pentagonal bipyramidal

ZrF73- and HfF73 also have pentagonal bipyramidal shape.
by Chris Freking 2G
Sat Nov 24, 2018 3:41 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: 4.25 6th edition: Polarity of SF4
Replies: 4
Views: 38

Re: 4.25 6th edition: Polarity of SF4

SF4 has the AXE notation AX4E. Therefore it has the see-saw molecular shape which is asymmetric and the dipole moments do not cancel out.

Screen Shot 2018-11-24 at 3.35.29 PM.png
Screen Shot 2018-11-24 at 3.35.29 PM.png (9.24 KiB) Viewed 32 times
by Chris Freking 2G
Sat Nov 24, 2018 3:31 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Incomplete octet
Replies: 2
Views: 24

Re: Incomplete octet

Aluminum can also sometimes have an incomplete octet for molecules like AlCl3. However, AlCl3 only exists at high temperatures--in normal temperatures, two molecules of AlCl3 combine to form Al2Cl6 where both Al atoms obey the octet rule.
by Chris Freking 2G
Sat Nov 24, 2018 3:26 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: CH 4 HW 4.41 6TH EDITION
Replies: 3
Views: 44

Re: CH 4 HW 4.41 6TH EDITION

In acrylonitrile, yes, the C-N bond is a triple bond. However not every C-N bond has to be a triple bond (eg. Methylamine)
by Chris Freking 2G
Fri Nov 16, 2018 12:36 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Linear for AX2E3
Replies: 2
Views: 30

Re: Linear for AX2E3

AX2E3-3D-balls.png


The 3 lone electrons form a trigonal shape in the equatorial plane as it is the most favorable in terms of electron repulsion, so the two other bonded atoms will take on a linear shape.
by Chris Freking 2G
Sun Nov 11, 2018 11:47 am
Forum: Interionic and Intermolecular Forces (Ion-Ion, Ion-Dipole, Dipole-Dipole, Dipole-Induced Dipole, Dispersion/Induced Dipole-Induced Dipole/London Forces, Hydrogen Bonding)
Topic: Dipole vs Induced Dipole
Replies: 3
Views: 43

Re: Dipole vs Induced Dipole

A dipole is a molecule with opposite charges on both ends (positive on one side, negative on the other side). For example, H2O is a dipole as the hydrogens have a partial positive charge and the oxygen has a partial negative charge. An induced dipole is the result of two molecules interacting and ca...
by Chris Freking 2G
Wed Nov 07, 2018 11:13 pm
Forum: Ionic & Covalent Bonds
Topic: Covalent or ionic?
Replies: 4
Views: 64

Re: Covalent or ionic?

Be and Br have similar electronegativities. Since the electronegativity values of Be and Br are so close, they both pull the electron with nearly the same strength, meaning the electron is closer to the middle and is shared between both Be and Br
by Chris Freking 2G
Thu Nov 01, 2018 5:23 pm
Forum: Electron Configurations for Multi-Electron Atoms
Topic: Electron Configuration of Ruthenium
Replies: 1
Views: 28

Electron Configuration of Ruthenium

The electron configuration of Ru is [Kr] 4d^7 5s^1.

Why is the electron configuration not [Kr] 4d^6 5s^2? Wouldn't it make more sense to have a filled 5s and a partially filled 4d rather than a half-filled 5s and partially filled 4d?
by Chris Freking 2G
Thu Nov 01, 2018 4:56 pm
Forum: Ionic & Covalent Bonds
Topic: Electron Configuration of a Cation (hw problem 3.21 part d)
Replies: 4
Views: 40

Re: Electron Configuration of a Cation (hw problem 3.21 part d)

Ag has an electron configuration of [Kr] 4d^10 5s^1 because the element is much more stable when the electrons are configured in the element to have a full d shell and a half-full s shell. When Ag is ionized (Ag+), the electron is removed from the outermost shell 5s. Therefore, the electron configur...
by Chris Freking 2G
Thu Nov 01, 2018 3:26 pm
Forum: Lewis Structures
Topic: Determining Lewis Structure
Replies: 3
Views: 54

Re: Determining Lewis Structure

The correct Lewis structure is the one with as many atoms having a formal charge of 0. Sometimes for compounds like SO3 2- there are variations of the Lewis structure that all have the same overall formal charge which is where resonance comes into play (multiple possible lewis structures)
by Chris Freking 2G
Thu Oct 25, 2018 10:40 pm
Forum: Quantum Numbers and The H-Atom
Topic: The values of L and ML
Replies: 3
Views: 82

Re: The values of L and ML

l refers to the subshells of n. The allowed values of l depend on the value of n and range from 0 to n-1. For example, if n=3, then l can = 0, 1, or 2.
by Chris Freking 2G
Thu Oct 25, 2018 10:31 pm
Forum: Trends in The Periodic Table
Topic: CH 2 6TH EDITION 2.85
Replies: 2
Views: 62

Re: CH 2 6TH EDITION 2.85

In the heavier transition-metal elements, the energy levels of the subshells get so close that their energy levels actually depend on how many electrons are occupying them. For example, 4s is filled before 3d because 4s has a lower energy level (rather than 3d filling before 4s like we might normall...
by Chris Freking 2G
Thu Oct 25, 2018 10:13 pm
Forum: Bohr Frequency Condition, H-Atom , Atomic Spectroscopy
Topic: H spectrum
Replies: 3
Views: 67

Re: H spectrum

The Rydberg equation does not take into account electron-electron repulsion, which is why it's okay to use for Hydrogen and H-spectrum (only one electron to worry about). It will not work for atoms with multiple electrons because of electron-electron repulsion.
by Chris Freking 2G
Fri Oct 19, 2018 8:45 pm
Forum: Electron Configurations for Multi-Electron Atoms
Topic: Electrostatic Attraction
Replies: 5
Views: 38

Re: Electrostatic Attraction

Electrostatic attraction refers to the attraction between a positively charged nucleus and a negatively charged electron.
by Chris Freking 2G
Mon Oct 15, 2018 10:11 pm
Forum: Wave Functions and s-, p-, d-, f- Orbitals
Topic: Negative v. Positive when calculating energy
Replies: 8
Views: 61

Re: Negative v. Positive when calculating energy

When delta E is negative, it means that energy has been released. Positive delta E refers to the absorption of energy.
by Chris Freking 2G
Mon Oct 15, 2018 10:03 pm
Forum: Student Social/Study Group
Topic: Note Taking
Replies: 25
Views: 773

Re: Note Taking

Handwriting notes is very helpful because I feel that I comprehend the material more, but it's all a matter of personal preference.
by Chris Freking 2G
Thu Oct 11, 2018 11:10 pm
Forum: Einstein Equation
Topic: Symbol for frequency
Replies: 12
Views: 117

Re: Symbol for frequency

Both are commonly used as symbols for frequency. Perhaps you could use whichever one is given to you in the problem but ultimately it should not matter.
by Chris Freking 2G
Wed Oct 10, 2018 10:42 pm
Forum: Molarity, Solutions, Dilutions
Topic: Question G.11 (Sixth Edition)
Replies: 2
Views: 98

Re: Question G.11 (Sixth Edition)

Use the formula M = n/V. In the context of this problem, solve for V.

V = n/M = (4.50 * 10^-3 mol)/(0.278 mol*L^-1) = 1.62 * 10^-2 L, or 16.2 mL
by Chris Freking 2G
Wed Oct 10, 2018 4:07 pm
Forum: Empirical & Molecular Formulas
Topic: Problem L39
Replies: 1
Views: 72

Re: Problem L39

The crucible and product together weigh 28.35g. Subtract the mass of the crucible (26.45g) from the mass of the crucible and the product (28.35g) to get the mass of the product (1.900g). Since we know we started with 1.500g of Sn, you can subtract that mass from the mass of the product (1.900g) to f...
by Chris Freking 2G
Fri Oct 05, 2018 10:52 am
Forum: Molarity, Solutions, Dilutions
Topic: Fraction of total mass due to oxygen?
Replies: 1
Views: 39

Re: Fraction of total mass due to oxygen?

To clear up any confusion, it's referring to the oxygen itself, not oxygen gas molecules. To find the fraction of the total mass of the sample due to oxygen, divide the molar mass of the oxygen by the molar mass of the entire compound. (4 * 15.999 g mol^-1) / (206.53 g mol^-1) (The 4 comes from the ...
by Chris Freking 2G
Fri Oct 05, 2018 10:37 am
Forum: Molarity, Solutions, Dilutions
Topic: Water Added to Solution Placed in a New Flask
Replies: 3
Views: 36

Re: Water Added to Solution Placed in a New Flask

Since only 20 mL of the first solution is diluted, you should first find the molarity of the first solution and using that molarity and 20 mL volume as your M1V1 later on. Start by finding the molarity of the original solution. Convert the 5.00g of KMnO 4 into moles by dividing it by the molar mass....
by Chris Freking 2G
Fri Oct 05, 2018 10:21 am
Forum: General Science Questions
Topic: Periodic Table
Replies: 16
Views: 319

Re: Periodic Table

I will typically use the exact atomic weight listed on the periodic table and round my final answer if needed. Future problems should supposedly have given atomic weights

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