## Search found 61 matches

Sat Mar 09, 2019 10:35 pm
Forum: First Order Reactions
Topic: 15.27 6th edition
Replies: 1
Views: 101

### Re: 15.27 6th edition

To find the equation for a 1st order reaction half-life you use t1/2=(1/k)(ln([A]initial/.5[A]initial)). In order to find a _%-life equation for any 1st order reaction just substitute _% for the .5 in the half-life equation. The solutions manual used this idea to answer the question and in A and B, ...
Sat Mar 09, 2019 10:21 pm
Forum: First Order Reactions
Topic: self test 15.8A (6th edition)
Replies: 1
Views: 75

### Re: self test 15.8A (6th edition)

The half-life for a 1st order reaction is t1/2= ln2/k. The 10%-life for a 1st order reaction is t1/10= ln10/k. To find the answer, solve for k for both the half-life and 10%-life equations and equal both the equations together since k should be the same. Then plug in 70 days for t1/2 and solve for t...
Sat Mar 09, 2019 10:06 pm
Forum: First Order Reactions
Topic: 15.19c (6th ed)
Replies: 2
Views: 126

### Re: 15.19c (6th ed)

I had that problem too. You have to convert all of the concentrations to mol/L and the rates to mol/(L*s). Also, the answers in the back of the book should be in mol not mmol.
Tue Mar 05, 2019 6:05 pm
Forum: Zero Order Reactions
Topic: Zero Order reactions
Replies: 2
Views: 112

### Re: Zero Order reactions

Zero order reaction: Rate of the reaction is independent of the concentration of the reactants. rate=k First order reaction: Rate of the chemical reaction is directly proportional to the concentration of the reactants. rate=k[A] The order is just the exponent of the concentration of one of the subst...
Tue Mar 05, 2019 5:55 pm
Forum: Zero Order Reactions
Topic: Half life
Replies: 5
Views: 196

### Re: Half life

The equation t1/2=0.693/k is only used for 1st order reactions.
Tue Mar 05, 2019 5:49 pm
Forum: First Order Reactions
Topic: Exponential Curve
Replies: 6
Views: 229

### Re: Exponential Curve

The plot is an exponential curve because as the reaction progresses, there are fewer and fewer reactants and the reaction rate decreases. The reaction rate decreases because there are fewer successful collisions between the reactants to form products since there are fewer reactants as time goes on.
Tue Feb 26, 2019 2:42 am
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Anode reaction
Replies: 3
Views: 141

### Re: Anode reaction

Both ways are correct, but it would be better if you left the electrons on the reactant side of the reaction so that you don't mix up the signs of the standard reduction potential.
Tue Feb 26, 2019 2:38 am
Forum: Balancing Redox Reactions
Topic: Carbon charges
Replies: 1
Views: 103

### Re: Carbon charges

The carbons have different charges because a carbon's oxidation number can change in a reaction while the oxidation number of oxygen is almost always -2 and the oxidation of hydrogen is almost always +1.
Tue Feb 26, 2019 2:33 am
Forum: Balancing Redox Reactions
Topic: Homework Question: 6th edition, 14.1
Replies: 1
Views: 94

### Re: Homework Question: 6th edition, 14.1

First you separate and balance the two half reactions. The oxidation half reaction is C2H5OH -> C2H4O. You know this because the oxidation number of carbon in the first molecule is -2 and in the product molecule, it's -1. You then balance the half reaction by adding H+ and e- and you should get C2H5...
Sun Feb 17, 2019 10:29 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Gases
Replies: 3
Views: 128

### Re: Gases

If you look at the list of thermodynamic data in appendix 2a you'll find that most compounds have a negative delta G (formation), not only gases.
Sun Feb 17, 2019 10:21 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: Remembering Equations
Replies: 5
Views: 194

### Re: Remembering Equations

You can also come up with equations based off of the information given by the question. From this you can check if the given information matches up with any equation on the equation sheet and if the information matches with multiple equations, you can combine equations to generate a new one.
Sun Feb 17, 2019 10:10 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Problem 115 ch 11 6th edition
Replies: 2
Views: 94

### Re: Problem 115 ch 11 6th edition

The reaction shifts to the reactants side because more O2 is added and according to Le Chatelier's, adding a product should cause more reactants should be formed.
Sat Feb 09, 2019 1:19 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: Gas constant, R
Replies: 3
Views: 159

### Re: Gas constant, R

In most situations both would work, but if you use the wrong one you would just have to convert the R you used to the other R through 101.325.
Sat Feb 09, 2019 1:17 pm
Forum: Calculating Work of Expansion
Topic: Reversible and constant pressure
Replies: 2
Views: 116

### Re: Reversible and constant pressure

The problem may have said constant pressure in reference to the irreversible path of expansion.
Sat Feb 09, 2019 1:11 pm
Forum: Calculating Standard Reaction Entropies (e.g. , Using Standard Molar Entropies)
Topic: 9.37 6th Edition
Replies: 1
Views: 101

### Re: 9.37 6th Edition

The units of the coefficients for the reaction are not mols. "4 KClO3" may be 4 moles of KClO3 but the 4 by itself is not in mols"
Mon Feb 04, 2019 11:46 pm
Forum: Phase Changes & Related Calculations
Topic: HW 8.41 6th edition
Replies: 2
Views: 169

### Re: HW 8.41 6th edition

The ice cube is already at 0 degrees celsius so it goes through a phase change to liquid before its temperature (as a liquid) raises to the final temperature of the system.
Mon Feb 04, 2019 11:35 pm
Forum: Calculating Work of Expansion
Topic: ideal gas
Replies: 2
Views: 151

### Re: ideal gas

Usually the question will not specifically say whether or not the gas is an ideal gas, but for most cases we just assume the gas is ideal and continue using the equation. This is better explained on page 266 of the 6th edition book.
Mon Feb 04, 2019 11:11 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: Ideal Gas Internal Energy
Replies: 2
Views: 89

### Re: Ideal Gas Internal Energy

The 3/2 coefficient comes from the equipartition theorem which states, "The average value of each quadratic contribution to the energy of a molecule in a sample at a temperature T is equal to (1/2)kT" and since there are three translational modes of motion, each giving a quadratic contribu...
Tue Jan 29, 2019 9:52 pm
Forum: Student Social/Study Group
Topic: Post All Chemistry Jokes Here
Replies: 8252
Views: 1444711

### Re: Post All Chemistry Jokes Here

Q: When one physicist asks another, "What's new?" what's the typical response?
A: C over lambda.
Tue Jan 29, 2019 9:49 pm
Forum: Student Social/Study Group
Topic: Post All Chemistry Jokes Here
Replies: 8252
Views: 1444711

### Re: Post All Chemistry Jokes Here

Did you know that you can cool yourself to -273.15˚C and still be 0k?
Tue Jan 29, 2019 9:43 pm
Forum: Calculating Work of Expansion
Topic: Irreversible and reversible expansion, 6th edition 8.11
Replies: 2
Views: 118

### Re: Irreversible and reversible expansion, 6th edition 8.11

We know that part a in 8.11 is referring to irreversible expansion because the gas is expanding against a constant pressure of 1 atm. In a reversible expansion, the external pressure is always equal to the pressure of the gas.
Tue Jan 22, 2019 9:05 pm
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: Salts
Replies: 4
Views: 223

### Re: Salts

The pH of a solution with salt depends on the relative acidity and basicity of the salt's ions.
Tue Jan 22, 2019 8:58 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Making more product
Replies: 3
Views: 125

### Re: Making more product

More product will be made if there are more moles on the reactant side than the product side and pressure is increased/volume is decreased. More product will also be formed if the reaction is endothermic and heat is added to the system. Also if more of one reactant is added, then usually more produc...
Tue Jan 22, 2019 8:52 pm
Forum: Calculating pH or pOH for Strong & Weak Acids & Bases
Topic: determining x for weak acids and bases
Replies: 6
Views: 416

### Re: determining x for weak acids and bases

Yes, if you need more clarification it is explained on page 441 of the 6th edition textbook in toolbox 11.1.
Tue Jan 15, 2019 6:35 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: HW Question 11.89
Replies: 1
Views: 71

### Re: HW Question 11.89

You find the coefficients by setting up an ice table since they give you the initial and final partial pressures. So the initial for A is 28, B is 0, and C is 0. The final for A is 18, B is 5, and C is 10. From this you know that the change for A is -2X, for B is +X, and C is +2X because it would on...
Tue Jan 15, 2019 6:31 pm
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: Exothermic vs. Endothermic Reaction
Replies: 9
Views: 1047

### Re: Exothermic vs. Endothermic Reaction

You can predict if a reaction is endothermic or exothermic by looking at the energies of the reactants and products (but this way is really hard with more complicated reactions). For example if you're given H2 = 2H, it would probably be endothermic since H2 is lower in energy than 2 H.
Tue Jan 15, 2019 6:25 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: If you calcuate Kp and Kc for the same reaction, will they be the same?
Replies: 2
Views: 140

### Re: If you calcuate Kp and Kc for the same reaction, will they be the same?

They are the same in some cases and different in others. If you look at table 11.2 on page 428 in the sixth edition of the book, some values of Kc and Kp are the same and some are different even thought its the same chemical reaction.
Thu Jan 10, 2019 2:28 am
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Equilibrium in a System
Replies: 2
Views: 101

### Re: Equilibrium in a System

Yes, chemical reactions always head towards equilibrium even though it may take a long time to reach it. When reactions go to completion, they still reach equilibrium. It's just that the constant rate of the forward reaction is extremely greater than the constant rate of the reverse reaction, so muc...
Thu Jan 10, 2019 2:21 am
Forum: Ideal Gases
Topic: Post Assessment
Replies: 3
Views: 156

### Re: Post Assessment

Equilibrium constants give us an indication of where the equilibrium lays. So if K>1, the reaction has a greater concentration of products compared to reactants and if K<1, the reaction has a greater concentration of reactants.
Thu Jan 10, 2019 2:17 am
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Calculating K
Replies: 3
Views: 60

### Re: Calculating K

It doesn't matter if you use partial pressure or concentration unless the question specifically says Kc or Kp. Yes, the coefficient in the formula is always in the exponent regardless of which K you're solving for.
Tue Dec 04, 2018 2:32 pm
Forum: Electron Configurations for Multi-Electron Atoms
Topic: Electron Configurations for ions
Replies: 2
Views: 200

### Re: Electron Configurations for ions

It is also helpful to look at the element's group in the periodic table when determining their ionic form.
Tue Dec 04, 2018 2:29 pm
Forum: Bronsted Acids & Bases
Topic: Determining Acidity
Replies: 3
Views: 215

### Re: Determining Acidity

For your example problem, anything that weakens the O-H bond would cause the molecule to be a stronger acid. So the answer would be HClO<HClO2<HClO3<HClO4 due to the impact the added oxygen atoms have on the O-H bond. This is generally the same idea with bases as molecules that dissociate more easil...
Tue Dec 04, 2018 2:23 pm
Forum: Sigma & Pi Bonds
Topic: Pi bonds
Replies: 4
Views: 445

### Re: Pi bonds

Sigma bonds acts like joints which allows for rotation in a molecule, but pi bonds are like two parallel joints and if you try to turn only one joint, you wouldn't be able to because of the other "joint" in the pi bond.
Mon Nov 26, 2018 9:22 pm
Forum: Lewis Structures
Topic: HW #3.67b (6th Ed)
Replies: 2
Views: 124

### Re: HW #3.67b (6th Ed)

You're right, the ClO2 lewis structure with two double bonds is the most stable.
Mon Nov 26, 2018 9:10 pm
Forum: Hybridization
Topic: hybridization
Replies: 3
Views: 161

### Re: hybridization

Hybridization occurs because hybridized orbitals are lower in energy than unhybridized ones so they are favored when forming molecules.
Mon Nov 26, 2018 9:06 pm
Forum: Administrative Questions and Class Announcements
Topic: Textbook
Replies: 3
Views: 184

### Re: Textbook

Yes, the textbook is the same.
Tue Nov 20, 2018 9:17 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Molecular Size
Replies: 3
Views: 173

### Re: Molecular Size

It tends to make it stronger since larger molecules tend to have larger london forces due to the greater amount of electrons, but the strength of a molecule is dependent on many other things besides size.
Tue Nov 20, 2018 8:49 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: HW help 6th edition 4.23
Replies: 1
Views: 84

### Re: HW help 6th edition 4.23

The solution manual considers the more stable structure with the double bond with Oxygen but since the lesson primarily focuses on shape, they accepted both structures.
Tue Nov 20, 2018 8:45 pm
Forum: Dipole Moments
Topic: Dipole Moment
Replies: 1
Views: 91

### Re: Dipole Moment

The tetrahedral molecule has a dipole moment if one of the outer atoms is heavier than the others. For example, CH3Cl is polar because of the greater amount of electrons on the Cl than the three H atoms. If the non-central atoms are all the same like in CH4 or CCl4 the molecule will be nonpolar beca...
Tue Nov 13, 2018 11:24 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: Lewis Structures before Forces
Replies: 3
Views: 182

### Re: Lewis Structures before Forces

Drawing out the lewis structure definitely helps in determining the shape of the molecule and I think it's best if you go that route until you're confident enough to determine the shape without drawing the lewis structure.
Tue Nov 13, 2018 11:18 pm
Forum: Dipole Moments
Topic: Determining Intermolecular Forces
Replies: 5
Views: 337

### Re: Determining Intermolecular Forces

You can determine the intermolecular forces on most molecules just by its chemical equation. For example, if the molecule has hydrogen and N,O, or F it has hydrogen bonding. If the molecule is polar like CHCL3 then it will have dipole dipole interaction and all molecules are able to have London inte...
Tue Nov 13, 2018 11:01 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Remembering
Replies: 8
Views: 388

### Re: Remembering

I don't think you can get away without remembering the names of the different shapes but it is helpful to know the lewis structures and bonds and lone pairs when determining the shape.
Tue Nov 06, 2018 5:04 pm
Forum: Ionic & Covalent Bonds
Topic: O vs N [ENDORSED]
Replies: 4
Views: 204

### Re: O vs N[ENDORSED]

The fourth valence electron in oxygen's p orbitals has a lower ionization energy because of the electron electron repulsion formed by the lower three valence electrons. This ionization energy is lower than nitrogen because of the three parallel electrons in nitrogen's p orbitals.
Tue Nov 06, 2018 1:06 am
Forum: Electron Configurations for Multi-Electron Atoms
Topic: More Lewis Structure Help
Replies: 1
Views: 117

### Re: More Lewis Structure Help

Tue Nov 06, 2018 1:03 am
Forum: Lewis Structures
Topic: Sodium Hypochlorite
Replies: 2
Views: 203

### Re: Sodium Hypochlorite

No, hypo- is a common prefix used to name the lowest number of atoms for a certain polyatomic ion group. For example, perchlorate = ClO4-, chlorate=ClO3-, chlorite=ClO2-, hypochlorite=ClO-. I think Dr. Lavelle will go more in depth on this later.
Tue Nov 06, 2018 12:55 am
Forum: Bond Lengths & Energies
Topic: Bond Lengths
Replies: 6
Views: 235

### Re: Bond Lengths

Bond lengths are usually given on questions and if they are asking to find the bond length of lewis structures, you have to take into consideration resonance structures.
Wed Oct 31, 2018 1:35 pm
Forum: Electron Configurations for Multi-Electron Atoms
Topic: Group 11 configurations
Replies: 1
Views: 109

### Re: Group 11 configurations

Yes, this is one of the electron configuration exceptions. A half full d and full d subshell have lower energy than the s subshell in periods 4 and up (5+) so the electrons will tend to occupy 4d before 5s.
Wed Oct 31, 2018 1:26 pm
Forum: Resonance Structures
Topic: resonance hybrids
Replies: 4
Views: 184

### Re: resonance hybrids

The resonance hybrid shows the delocalized electrons in a molecule and it is a representation of the sum of all the resonance structures.
Wed Oct 31, 2018 1:20 pm
Forum: Formal Charge and Oxidation Numbers
Topic: Formal Charge and correct numbers
Replies: 2
Views: 165

### Re: Formal Charge and correct numbers

The positive or negative formal charge of an element is based on the surrounding electrons (bonded or lone pairs), but the formal charges of electrons in a molecule can "cancel" each other out resulting in a net charge of 0 for the molecule.
Wed Oct 24, 2018 1:27 pm
Forum: Trends in The Periodic Table
Topic: Isoelectronic Clarification
Replies: 2
Views: 119

### Re: Isoelectronic Clarification

Since isoelectronic atoms and ions have the same number of valence electrons they should display similar chemical properties. For example, hydrogen and hydrogen-like atoms such as Li2+ display similar properties since they both have only one electron.
Wed Oct 24, 2018 1:22 pm
Forum: Quantum Numbers and The H-Atom
Topic: Which electrons have most energy?
Replies: 3
Views: 301

### Re: Which electrons have most energy?

Yeah you're right. The electrons closest to the nucleus do have lower energy, which is why the electrons in the 2s orbital are lower in energy than the electrons in the 2p orbital. The electrons in the 2p orbital are shielded by the electrons in the 2s orbital, which cause the 2p orbital electrons t...
Wed Oct 24, 2018 11:30 am
Forum: Bohr Frequency Condition, H-Atom , Atomic Spectroscopy
Topic: Spectral Lines and Series
Replies: 3
Views: 203

### Re: Spectral Lines and Series

A question might ask you to name the spectroscopic series to which the transition of radiation from n=4 to n=2 belongs and I guess you would just have to know that this transition belongs to the Balmer Series.
Wed Oct 17, 2018 10:21 pm
Forum: Wave Functions and s-, p-, d-, f- Orbitals
Topic: Nodal Plane
Replies: 2
Views: 47

### Re: Nodal Plane

The nodal plane is an area that goes through the nucleus where no electrons will be found. It separates lobes of orbitals and on the nodal plane "psi" is equal to 0.
Wed Oct 17, 2018 10:15 pm
Forum: Properties of Light
Topic: Sig Figs in Problem 1.13 (6th Edition)
Replies: 5
Views: 202

### Re: Sig Figs in Problem 1.13 (6th Edition)

The question asks to calculate the wavelength and since the majority of the wavelengths on the electromagnetic radiation spectrum range from ~300nm to ~1000nm it would only make sense for the answer to be in between those two numbers and have three significant figures, but in this case, I don't thin...
Wed Oct 17, 2018 9:21 pm
Forum: Heisenberg Indeterminacy (Uncertainty) Equation
Topic: Heisenberg > and equal to or =
Replies: 1
Views: 57

### Re: Heisenberg > and equal to or =

Conceptually we should think of the equation as having the greater than or equal sign but when we do problems involving the Heisenberg Uncertainty Principle we generally only use the equal sign.">" only tells us that the product of the uncertainty in position and the uncertainty in linear ...
Wed Oct 10, 2018 11:50 pm
Forum: Significant Figures
Topic: Module: Molarity #15
Replies: 6
Views: 693

### Re: Module: Molarity #15

I don't think multiple choice questions are as stringent on significant figures.
Wed Oct 10, 2018 11:47 pm
Forum: Properties of Light
Topic: Why Short Wavelengths Can Eject e-
Replies: 6
Views: 235

### Re: Why Short Wavelengths Can Eject e-

All metals have a specific work function or threshold, which is the minimum energy required to eject an electron. Shorter wavelengths usually have an energy greater than the threshold whereas longer wavelengths do not, which is why light with shorter wavelengths are more commonly able to eject elect...
Mon Oct 08, 2018 10:42 pm
Forum: Bohr Frequency Condition, H-Atom , Atomic Spectroscopy
Topic: Question 1.27
Replies: 2
Views: 73

### Question 1.27

How do you solve question 1.27? Here's the question: "A lamp rated at 32 W (1 W = 1 J*S^-1) emits violet light of wavelength 420 nm. How many photons of violet light can the lamp generate in 2.0 s? How many moles of photon are emitted in that time interval?"
Wed Oct 03, 2018 9:48 pm
Forum: Molarity, Solutions, Dilutions
Topic: V=n/c
Replies: 7
Views: 288

### Re: V=n/c

n is the moles of solute
Mon Oct 01, 2018 9:31 pm
Forum: Accuracy, Precision, Mole, Other Definitions
Topic: E 23 Part C sixth edition
Replies: 2
Views: 89

### Re: E 23 Part C sixth edition

Yeah, since the question asks for the amount of F^- ions and there are 6 moles of F^- ions for every one mole of UF6 we would have to multiply the amount (in moles) of UF6 by 6. Also, yes for your second question.
Mon Oct 01, 2018 9:22 pm
Forum: SI Units, Unit Conversions
Topic: Audio-Visual Focus-Topics, Assessments & Surveys
Replies: 10
Views: 552

### Re: Audio-Visual Focus-Topics, Assessments & Surveys

I'm pretty sure the Audio-Visual Focus-Topics, Assessments & Surveys do not affect our grades. They're just supplemental questions and videos to assist with the coursework.