## Search found 62 matches

Tue Mar 12, 2019 6:17 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: 6A.19 7th edition
Replies: 1
Views: 94

### Re: 6A.19 7th edition

I don't have 7th edition but check to see if there's any mL because that would account for the discrepancy.
Tue Mar 12, 2019 12:14 am
Forum: Equilibrium Constants & Calculating Concentrations
Topic: 5I.13
Replies: 1
Views: 88

### Re: 5I.13

A smaller equilibrium constant means at equilibrium the reactants are more favored, or it is less likely to decompose. This means that the lower the equilibrium constant, the more stable.
Tue Mar 12, 2019 12:08 am
Forum: General Rate Laws
Topic: slow step
Replies: 11
Views: 573

### Re: slow step

It is either stated explicitly or has the smaller k value
Tue Mar 12, 2019 12:04 am
Forum: Second Order Reactions
Topic: Homework, 6th edition, 15.35
Replies: 3
Views: 164

### Re: Homework, 6th edition, 15.35

Use the formula t1/2= [A]/2k to solve for k, then modify the formula for the other proportions.
eg.
t1/16= 15[A]/16k
t1/4= 3[A]/4k
etc
Mon Mar 11, 2019 11:52 pm
Forum: Zero Order Reactions
Topic: zero order in rate law
Replies: 7
Views: 405

### Re: zero order in rate law

It is included in the unique rate law but in the overall rate law it is only included if it is greater than zero. If the reactant is zero order then it will be to the power of zero and equal to 1.
Mon Mar 11, 2019 11:48 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: K
Replies: 1
Views: 79

### Re: K

If it doesn't specify then it doesn't matter. It's usually Kc.
Sun Feb 17, 2019 7:24 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: Calculating entropy
Replies: 4
Views: 132

### Re: Calculating entropy

If there's a change in pressure/volume, the entropy is dependent on Temperature. If there's a change in Temperature, the entropy is dependent on volume. You've gotta do one before the other or else there's just no calculation (that a 14B student knows how to do, idk about actual chemists).
Wed Feb 13, 2019 10:25 am
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: Midterm Prep Question
Replies: 3
Views: 157

### Re: Midterm Prep Question

Thank you! That clears up a lot :)
Wed Feb 13, 2019 8:17 am
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: Midterm Prep Question
Replies: 3
Views: 157

### Midterm Prep Question

Q: A balloon expands from 3.3L at 298K to 9.2 x 105 L at 333K. What is ΔS ?
can someone post steps on how to solve?
Wed Feb 13, 2019 8:11 am
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: units
Replies: 7
Views: 460

### Re: units

P: atm
V: L
n: mol
R: J/k.mol
T: K
Tue Feb 12, 2019 11:10 pm
Forum: Calculating Standard Reaction Entropies (e.g. , Using Standard Molar Entropies)
Topic: R constants
Replies: 21
Views: 718

### Re: R constants

It depends on the constants and what needs to cancel. Both values should be provided so you just have to look at the question. It should usually be 8.314 J/k.mol
Tue Feb 12, 2019 11:04 pm
Forum: Calculating pH or pOH for Strong & Weak Acids & Bases
Topic: Quiz 1 #5
Replies: 7
Views: 458

### Re: Quiz 1 #5

What day is your discussion, the answers are different depending on the day.
Tue Feb 12, 2019 11:02 pm
Forum: Calculating Work of Expansion
Topic: Substituting -nrT for -PΔV
Replies: 4
Views: 177

### Re: Substituting -nrT for -PΔV

It will say in the question. Isothermal, same T, moles have to change. Increased Temperature, T changes.
Tue Feb 12, 2019 11:00 pm
Forum: Third Law of Thermodynamics (For a Unique Ground State (W=1): S -> 0 as T -> 0) and Calculations Using Boltzmann Equation for Entropy
Topic: Boltzmann Equation
Replies: 3
Views: 421

### Re: Boltzmann Equation

Use the Boltzman constant when finding statistical Entropy
∆S=K•lnW
Tue Feb 12, 2019 10:58 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: C
Replies: 3
Views: 81

### Re: C

Heat capacity
Tue Feb 12, 2019 7:34 pm
Forum: Administrative Questions and Class Announcements
Topic: Midterm Review Question
Replies: 10
Views: 475

### Re: Midterm Review Question

Jim Brown 14B Lec1 wrote:
Jim Brown 14B Lec1 wrote:I think you need the bond enthalpy for ethane, then use it to heat water to 100º C and to reach its ∆Hvap

Enthalpy of combustion*

nvm this [censored] is rough idk how to do it :'(
Tue Feb 12, 2019 7:18 pm
Forum: Administrative Questions and Class Announcements
Topic: Midterm Review Question
Replies: 10
Views: 475

### Re: Midterm Review Question

Jim Brown 14B Lec1 wrote:I think you need the bond enthalpy for ethane, then use it to heat water to 100º C and to reach its ∆Hvap

Enthalpy of combustion*
Tue Feb 12, 2019 7:16 pm
Forum: Administrative Questions and Class Announcements
Topic: Midterm Review Question
Replies: 10
Views: 475

### Re: Midterm Review Question

I think you need the bond enthalpy for ethane, then use it to heat water to 100º C and to reach its ∆Hvap
Tue Feb 12, 2019 5:44 pm
Forum: Administrative Questions and Class Announcements
Replies: 179
Views: 12565

can someone explain 6(d)? I tried using the additive equation for standard enthalpy of a reaction but I don't think I'm inputting the correct value for it or if that's even a possible way to get the answer We know the total enthalpy needs to equal 42, so add the enthalpies of formation for all the ...
Tue Feb 12, 2019 5:34 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: 4F.11) 7th edition
Replies: 1
Views: 89

### Re: 4F.11) 7th edition

Yes you can use this for a change in T
Tue Feb 12, 2019 5:33 pm
Forum: Student Social/Study Group
Topic: Equations Sheet
Replies: 4
Views: 444

### Equations Sheet

Anyone got the supplied equations? :)
Tue Feb 12, 2019 5:23 pm
Forum: Phase Changes & Related Calculations
Topic: Negative and Positive values of delta H and w
Replies: 6
Views: 1115

### Re: Negative and Positive values of delta H and w

A negative Delt. H means a -q (heat loss)
Tue Feb 12, 2019 5:12 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: Cp vs Cv
Replies: 1
Views: 102

### Re: Cp vs Cv

The problem will tell you whether it is constant temperature or pressure, either explicitly or through the other information it gives (i.e. ethalphy indicates constant pressure)
Tue Feb 05, 2019 8:18 am
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: HW Problem 8.9 6th edition
Replies: 2
Views: 133

### HW Problem 8.9 6th edition

8.9 An ideal gas in a cylinder was placed in a heater and gained 5.50 kJ of energy as heat. If the cylinder increased in volume from 345 mL to 1846 mL against an atmospheric pressure of 750. Torr during this process, what is the change in internal energy of the gas in the cylinder?
Tue Feb 05, 2019 7:37 am
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: 7th edition 4F.7
Replies: 3
Views: 158

### Re: 7th edition 4F.7

Those are used for Entropy calculation at constant Volume or Pressure. Lavelle didn't explain why other than for 3/2 is a result of there being 3 dimensions and velocity being "1/2"
Tue Feb 05, 2019 7:30 am
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: temperature of a reversible reaction
Replies: 3
Views: 146

### Re: temperature of a reversible reaction

The reaction is not isolated and takes place in a heat reservoir. This way, even if the reaction is exothermic, the overall temperature will remain the same at the beginning and the end of the reaction.
Thu Jan 31, 2019 10:51 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: Entropy Calculations (9.1)
Replies: 5
Views: 2245

### Re: Entropy Calculations (9.1)

2015 Chem class coming in CLUTCH
Thu Jan 31, 2019 10:51 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: Entropy Calculations (9.1)
Replies: 5
Views: 2245

### Re: Entropy Calculations (9.1)

2015 Chem class coming in CLUTCH
Thu Jan 31, 2019 10:13 pm
Forum: Student Social/Study Group
Topic: Lecture Notes (1/30)
Replies: 4
Views: 218

### Re: Lecture Notes (1/30)

My handwriting is terrible but
Thu Jan 31, 2019 10:05 pm
Forum: Phase Changes & Related Calculations
Topic: Chemical potential energy
Replies: 4
Views: 113

### Re: Chemical potential energy

You only have to take the bond enthalpy of the bonds broken and the new bonds formed
Thu Jan 31, 2019 10:04 pm
Forum: Phase Changes & Related Calculations
Topic: Entropy vs Enthalpy concept
Replies: 3
Views: 127

### Re: Entropy vs Enthalpy concept

Both use J/kg
Thu Jan 31, 2019 10:02 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Gibbs
Replies: 5
Views: 231

### Re: Gibbs

If Gibbs Free Energy is negative, the reaction is spontaneous (exergonic). If Gibbs is positive, the reaction is nonspontaneous (endergonic).
The change in Gibbs is equal to the change in enthalpy minus the change in entropy times T.
Tue Dec 04, 2018 7:49 pm
Forum: Calculating pH or pOH for Strong & Weak Acids & Bases
Topic: strong or weak base
Replies: 3
Views: 273

### Re: strong or weak base

There are 8 common strong bases worth committing to memory. It consists of Alkali and Alkaline Earth metals paired with Hydroxide Ions. LiOH - lithium hydroxide NaOH - sodium hydroxide KOH - potassium hydroxide RbOH - rubidium hydroxide CsOH - cesium hydroxide Ca(OH)2 - calcium hydroxide Sr(OH)2 - s...
Tue Dec 04, 2018 7:45 pm
Forum: Amphoteric Compounds
Topic: amphoteric oxides
Replies: 3
Views: 172

### Re: amphoteric oxides

In Lecture Lavelle said we should just commit them to memory. The staircase that is similar to that of the metalloids can be a good guiding line for which oxides this includes.
Sun Dec 02, 2018 10:28 pm
Forum: Lewis Acids & Bases
Topic: Lewis acid/ bronsted acid
Replies: 1
Views: 88

### Re: Lewis acid/ bronsted acid

All Brönstead acids/bases are Lewis Acids/Bases, but something can be considered a lewis acid even if it might not qualify as a Brönstead acid. This is because a Brönstead acid needs to donate a proton (needs to contain hydrogen) while a Lewis Acid only needs to be able to accept the lone pair.
Sun Dec 02, 2018 10:25 pm
Forum: Naming
Topic: Ions with more than one possible charge
Replies: 1
Views: 62

### Re: Ions with more than one possible charge

This is only possible with transition metals. Transition metals lose electrons more easily, and they do not lose them based on completing an octet because they utilize the d-orbital.
Sun Dec 02, 2018 10:23 pm
Forum: Lewis Acids & Bases
Topic: Amphoteric Compounds
Replies: 1
Views: 97

### Re: Amphoteric Compounds

You've just gotta memorize which elements bond to make amphoteric compounds. The list is similar (but not identical) to the list of metalloids.
Sun Nov 25, 2018 10:33 pm
Forum: Hybridization
Topic: pi bonds and rotation
Replies: 3
Views: 171

### Re: pi bonds and rotation

Pi-bonds do not allow free rotation, if the molecule is rotated, the pi-bond will break. This results in rigidly structured molecules.
Sun Nov 25, 2018 10:28 pm
Forum: Hybridization
Topic: regions of electron density and double bonds
Replies: 2
Views: 113

### Re: regions of electron density and double bonds

A single bond and a double bond are both 1 region of electron density. Double bonds will determine the different hybridizations and the shape of the molecule, but even with these added it still follows the same rules as the single region of electron density in the VSEPR model.
Sun Nov 25, 2018 12:36 pm
Forum: Student Social/Study Group
Topic: Post All Chemistry Jokes Here
Replies: 8032
Views: 1407498

### Re: Post All Chemistry Jokes Here

sodium chloride
Thu Nov 15, 2018 9:05 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: 6th Edition Ch4 Q7
Replies: 2
Views: 122

### Re: 6th Edition Ch4 Q7

There aren't different bond angles, all the angles are the same. You just have to memorize the general rules for the specifics of each shape and apply it to the various molecules that follow that structure.
Thu Nov 15, 2018 9:03 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Vespr Formula
Replies: 6
Views: 223

### Re: Vespr Formula

Not sure but it's pretty easy. Its the character A followed by X with a subscript of the number of bonds with another atom, then E with a subscript of the number of lone pairs.
Thu Nov 15, 2018 9:01 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Linear Shape
Replies: 5
Views: 161

### Re: Linear Shape

Rosha Mamita 1E wrote:Yes, though the shape will be different and would not be called linear

This is true for most electron geometries and will result in a bent shape, but you can still get a linear shape when there are 5 areas of electron density and 3 of them are lone pairs
Thu Nov 15, 2018 9:00 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Linear Shape
Replies: 5
Views: 161

### Re: Linear Shape

Yes, a trigonal bipyramidal electron geometry with 3 lone pairs will give you a linear shape with 180º angles
Thu Nov 15, 2018 6:50 am
Forum: Lewis Structures
Topic: 7th Edition #2E.13
Replies: 3
Views: 181

### Re: 7th Edition #2E.13

You want to try and minimize the formal charge
Thu Nov 15, 2018 6:42 am
Forum: Determining Molecular Shape (VSEPR)
Topic: Molecular Geometry vs Electron-Pair Geometry
Replies: 4
Views: 1052

### Re: Molecular Geometry vs Electron-Pair Geometry

Molecular geometry takes into account only the atoms surrounding the central atom. This includes shapes like bent, trigonal pyramidal, square planar, etc. Electron-pair geometry is based on the number of electron density fields. This includes only the basic geometries (linear, trigonal planar, tetra...
Thu Nov 15, 2018 6:35 am
Forum: Determining Molecular Shape (VSEPR)
Topic: The difference between placing lone pairs in certain positions?
Replies: 3
Views: 168

### Re: The difference between placing lone pairs in certain positions?

It depends on the number of electron fields. See how the T-shaped has five and the square planar has 6? It's worth committing to memory.
Sun Nov 04, 2018 5:33 pm
Forum: Trends in The Periodic Table
Topic: Electron Affinity
Replies: 3
Views: 118

### Re: Electron Affinity

Electron affinity increases across a period and decreases down a group.
Sun Nov 04, 2018 5:32 pm
Forum: Trends in The Periodic Table
Topic: Electron Affinity
Replies: 2
Views: 112

### Re: Electron Affinity

The Noble gasses are nonreactive. Neon has a greater effective charge, but its octet is complete, so it won't pick up any electrons, where chlorine will in order to complete the octet.
Sun Oct 28, 2018 8:58 pm
Forum: Ionic & Covalent Bonds
Topic: Variable Valence
Replies: 2
Views: 50

### Re: Variable Valence

Variable valency just refers to chemicals (typically [if not always?] a metal) that form multiple ions with different charges. (Chemicals like iron (II) and iron (III), tin (III) and tin (IV), etc.)
Tue Oct 23, 2018 8:47 pm
Forum: Student Social/Study Group
Topic: Post All Chemistry Jokes Here
Replies: 8032
Views: 1407498

### Re: Post All Chemistry Jokes Here

salttime
Mon Oct 22, 2018 11:18 pm
Forum: Wave Functions and s-, p-, d-, f- Orbitals
Topic: Calculate orbitals and subshells
Replies: 3
Views: 144

### Re: Calculate orbitals and subshells

l corresponds to the orbital (s, p, d, f, etc.) Orbitals increase by two for each new shape (s has 1, p has 3, d has 5, etc) The l quantum number 2 represents a p orbital, so there are 3 subshells. The l quantum number 3 represents a d orbital, so there are 5 subshells. The l quantum number 1 repres...
Fri Oct 19, 2018 9:54 am
Forum: Properties of Electrons
Topic: Rydberg Formula 1.13
Replies: 3
Views: 165

### Re: Rydberg Formula 1.13

Ryberg's constant is 3.29e+15
Fri Oct 19, 2018 9:51 am
Forum: Properties of Electrons
Topic: HW help 1.15
Replies: 1
Views: 88

### Re: HW help 1.15

Use wavelength to calculate E then work backwards from total Energy. Set up the problem E=Rh(1/(n[final])^2 - 1/(n[initial])^2). Divide everything by hR. You end up with .888 = 1/(n[final])^2 - 1/(n[initial])^2. Test values of integers and you'll end up with a change from 1 to 3.
Mon Oct 15, 2018 11:08 am
Forum: Photoelectric Effect
Topic: 1B.7
Replies: 2
Views: 147

### Re: 1B.7

Convert wavelength to energy by using the energy formula E=hν. Because νλ is equal to the speed of light this can be rewritten as E=hC/λ. You now have a formula that you can plug in values for and get the energy for one the emission of one atom (3.37 e-17). Next, convert the mass of sodium into atom...
Sun Oct 14, 2018 10:19 pm
Forum: Administrative Questions and Class Announcements
Replies: 1
Views: 113

I asked Lavelle, he said a pdf is fine. The textbook is to help you learn so whatever works for you.
Sun Oct 14, 2018 12:41 pm
Forum: Student Social/Study Group
Topic: Water
Replies: 1
Views: 101

### Water

Is water wet? @Dr. Lavelle
Sun Oct 14, 2018 12:39 pm
Forum: Bohr Frequency Condition, H-Atom , Atomic Spectroscopy
Topic: Empirical Equation for H Atom
Replies: 1
Views: 97

### Re: Empirical Equation for H Atom

The "R" is a constant like "h", "C" or Avogadro's number. It was derived through experimentation.
Sat Oct 06, 2018 11:05 am
Forum: SI Units, Unit Conversions
Topic: Chemistry Community Points
Replies: 3
Views: 115

### Re: Chemistry Community Points

I meant like if I made a post during week zero (24th-30th) does that count as points for week one?
Sat Oct 06, 2018 10:18 am
Forum: SI Units, Unit Conversions
Topic: Chemistry Community Points
Replies: 3
Views: 115

### Chemistry Community Points

Do posts made during week zero count as posts for week one?
Sat Oct 06, 2018 10:02 am
Forum: General Science Questions
Topic: Orbitals
Replies: 2
Views: 217

### Re: Orbitals

The 4S orbital is located closer to the nucleus, so the energy level is higher and will fill out first. It's easy to tell which orbitals have higher energy levels by looking at the organisation of the elements filling those orbitals on the periodic table.
Sat Sep 29, 2018 7:06 pm
Forum: Limiting Reactant Calculations
Topic: Is there a specific way to solve limiting reactant problems?
Replies: 4
Views: 255

### Re: Is there a specific way to solve limiting reactant problems?

The method I use to solve limiting reactant problems is by converting the reactants' mass into moles. I don't think this is impossible because once you have converted the reactants into moles, you compare the two. The reactant with less moles is the limiting reactant. I believe you can solve these ...