Search found 67 matches

by Evelyn L 1H
Sat Mar 17, 2018 5:56 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Pressure and Volume in a Bomb Calorimeter
Replies: 1
Views: 160

Re: Pressure and Volume in a Bomb Calorimeter

External pressure is only zero in a vacuum. In a calorimeter, it doesn't matter what Pext is because it's being multiplied by delta V which is zero.
by Evelyn L 1H
Sat Mar 17, 2018 2:14 pm
Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
Topic: Test 2 Q7
Replies: 3
Views: 205

Re: Test 2 Q7

You have to use deltaG=-nFE because the number of moles of electrons are different in each equation. After splitting up the given equation into the half reactions and finding Enaught, to find the standard potential of the reaction you would use deltaG = -nFE -nFE = -nFE + -nFE -3FE= -1FE - 2FE -- ca...
by Evelyn L 1H
Sat Mar 17, 2018 2:00 pm
Forum: *Enzyme Kinetics
Topic: Two Paths
Replies: 5
Views: 403

Re: Two Paths

The slow step is the rate-determining law, not the fast step. If it is the slowest step, the entire reaction must wait for it, then it is the rate-determining step. Dr. Lavelle used the example of the bottleneck/funnel neck effect to describe this. Here is a helpful analogy I found: The rate determi...
by Evelyn L 1H
Sat Mar 17, 2018 1:56 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Rule when writing cell diagrams?
Replies: 5
Views: 144

Re: Rule when writing cell diagrams?

The most negative cell potential is the anode in a galvanic cell in order to make E positive.
by Evelyn L 1H
Wed Mar 14, 2018 6:36 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: pH
Replies: 1
Views: 89

pH

Why and how exactly does pH give you H+ concentration?
by Evelyn L 1H
Tue Mar 13, 2018 1:33 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: 9.23
Replies: 4
Views: 197

Re: 9.23

Is the lewis structure arrangements more important than the molar mass?
by Evelyn L 1H
Tue Mar 13, 2018 12:36 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: 9.23
Replies: 4
Views: 197

9.23

I don't really understand the solutions manual's explanation about why COF2 has a higher molar entropy than BF3, could someone please explain it? I thought the molecule with the higher molar entropy is the one with the highest molar mass but the molar mass of BF3 is higher than COF2. What are the ge...
by Evelyn L 1H
Wed Mar 07, 2018 3:13 pm
Forum: General Rate Laws
Topic: Table 15.2 in Textbook
Replies: 1
Views: 88

Re: Table 15.2 in Textbook

I had this same question, I think it means the initial concentration is used. As in [A]0 aka A not (but i'm not sure that's how you spell "not") because for the first order reaction, half-lives do not depend on concentration while zero and second order half life equations do.
by Evelyn L 1H
Wed Mar 07, 2018 3:11 pm
Forum: Administrative Questions and Class Announcements
Topic: Formulas on test?
Replies: 3
Views: 127

Re: Formulas on test?

Those formulas are on the formula sheet! You can see that sheet on Lavelle's website under "Constants and Equations"
by Evelyn L 1H
Wed Mar 07, 2018 2:35 pm
Forum: Zero Order Reactions
Topic: Half-life problem
Replies: 2
Views: 201

Re: Half-life problem

Thank you that was so helpful!!
by Evelyn L 1H
Wed Mar 07, 2018 2:20 pm
Forum: Zero Order Reactions
Topic: Half-life problem
Replies: 2
Views: 201

Half-life problem

This is a question from a practice quiz: A given compound decomposes with a half-life of 8.0 s and the half-life is independent of the concentration. How long does it take for the concentration to decrease to 1/9th of its initial value? How would I solve this? I think it's zero order but there's no ...
by Evelyn L 1H
Thu Mar 01, 2018 12:24 pm
Forum: Student Social/Study Group
Topic: Post All Chemistry Jokes Here
Replies: 7337
Views: 788856

Re: Post All Chemistry Jokes Here

how did avogadro write to his friends?
by e-mole
by Evelyn L 1H
Thu Mar 01, 2018 12:23 pm
Forum: Student Social/Study Group
Topic: Post All Chemistry Jokes Here
Replies: 7337
Views: 788856

Re: Post All Chemistry Jokes Here

chemistry jokes are sodium funny
by Evelyn L 1H
Thu Mar 01, 2018 12:23 pm
Forum: Student Social/Study Group
Topic: Post All Chemistry Jokes Here
Replies: 7337
Views: 788856

Re: Post All Chemistry Jokes Here

Chemistry puts the cation in education
by Evelyn L 1H
Wed Feb 21, 2018 5:27 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: 14.13 c
Replies: 1
Views: 57

14.13 c

The solutions manual says the half reactions of Cl2 + H2 --> HCL are Cl2+2e --> 2Cl and 2H+ + 2e --> H2
How can you just split up HCL into H and Cl and then add them together to get HCL?
by Evelyn L 1H
Wed Feb 21, 2018 4:18 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Reduction Half Potential [ENDORSED]
Replies: 1
Views: 62

Reduction Half Potential [ENDORSED]

When we flip a reaction, for example flipping Ni2+ +2e- --> Ni to Ni --> Ni2+ +2e- to show oxidation, why don't we flip the sign of the reduction half potential?
by Evelyn L 1H
Wed Feb 21, 2018 2:28 pm
Forum: Balancing Redox Reactions
Topic: 14.3 (a)
Replies: 3
Views: 142

Re: 14.3 (a)

Update I figured it out:

it asks for the oxidization/reduction agent not what is being oxidized/reduced.
by Evelyn L 1H
Wed Feb 21, 2018 2:17 pm
Forum: Balancing Redox Reactions
Topic: 14.3 (a)
Replies: 3
Views: 142

Re: 14.3 (a)

The solutions manual says Cl2 is the oxidizing agent and S2O3 is the reducing agent. But I thought since Cl goes from +0 to -2 it is reduced and S2O3 2- is oxidized because it goes from +4 to +12. Is that a solutions manual error or did I do something wrong?
by Evelyn L 1H
Tue Feb 20, 2018 8:05 pm
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: Equilibrium constant
Replies: 3
Views: 125

Re: Equilibrium constant

no, K is the equilibrium constant while Q is when the rxn is not at equilibrium
by Evelyn L 1H
Tue Feb 13, 2018 11:11 pm
Forum: Calculating Work of Expansion
Topic: Free Expansion
Replies: 1
Views: 106

Re: Free Expansion

Yes, there is no work being performed because there is no opposing pressure in a vacuum. Therefore it is freely expanding without any work being done.
by Evelyn L 1H
Tue Feb 13, 2018 11:10 pm
Forum: Calculating Work of Expansion
Topic: Formulas for monatomic vs diatomic gases
Replies: 2
Views: 140

Re: Formulas for monatomic vs diatomic gases

Monoatomic: 3/2R
Diatomic: 5/2R
by Evelyn L 1H
Tue Feb 13, 2018 11:09 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Delta H=Delta U
Replies: 1
Views: 783

Re: Delta H=Delta U

Delta H would be equal to Delta U when there is no work being done.
No work is being done when volume is constant or if there is no external pressure (vacuum)
by Evelyn L 1H
Tue Feb 13, 2018 11:07 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Practice Midterm W18 by Lyndon and Michael (Q 1B)
Replies: 2
Views: 176

Re: Practice Midterm W18 by Lyndon and Michael (Q 1B)

q=m1CdeltaT + m2* delta Hfusion

q=234kj
temp: -2.8 --> 0 delta T = 2.8
m1 = 125g
m2= .5*125 = 62.5g (bc half the ice cream melted)

234000 J = 125 * 10 (found in previous problem) * 2.8 + delta H fusion * 62.5
delta H fusion = 3688 J/g --> 3.7 kj/g
by Evelyn L 1H
Tue Feb 13, 2018 11:00 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Delta G
Replies: 3
Views: 104

Re: Delta G

Since G is a state function, only the final and initial states matter, not the path to get there. Since the final and initial states are the same, then delta G is 0.
by Evelyn L 1H
Tue Feb 13, 2018 10:58 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Practice Problem
Replies: 1
Views: 103

Re: Practice Problem

1). Delta U is zero because the final reaction was the same as the first reaction, and because internal energy is a state function, only the initial and final state matter. 2). Delta S is also zero because of the same reason and there was no temperature change. 3). q=-w because delta U=0 solve for w...
by Evelyn L 1H
Tue Feb 13, 2018 10:47 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: Delta U Formulas
Replies: 3
Views: 135

Re: Delta U Formulas

To clarify, Isochoric means Isovolumetric which I think you meant but I don't know what isometric is.
by Evelyn L 1H
Tue Feb 13, 2018 10:46 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: Delta U Formulas
Replies: 3
Views: 135

Re: Delta U Formulas

Isobaric means pressure is constant but that doesn't affect the delta U formula.
Isochoric means volume is constant which means work = 0 so delta U = q.
by Evelyn L 1H
Tue Feb 13, 2018 10:43 pm
Forum: Thermodynamic Definitions (isochoric/isometric, isothermal, isobaric)
Topic: reversible and isothermal
Replies: 1
Views: 100

Re: reversible and isothermal

Reversible reactions take more work than irreversible reactions (remember the graphs in Lavelle's lecture).
Isothermal means temperature is constant.
Isothermal reversible reactions happen very slowly.
by Evelyn L 1H
Tue Feb 13, 2018 10:41 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: Examples of Change Values = 0
Replies: 1
Views: 71

Re: Examples of Change Values = 0

a). when change in entropy is zero, it is a reversible reaction or reaction at equilibrium b). when change in gibbs free energy is zero, the reaction is at equilibrium and doesn't favor the products or reactants c). when change in internal energy is zero, the reaction is isothermal (I think there ma...
by Evelyn L 1H
Wed Feb 07, 2018 1:00 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: 9.47 [ENDORSED]
Replies: 1
Views: 102

9.47 [ENDORSED]

This question: Initially, a sample of ideal gas at 323 K occupies 1.67 L at 4.95 atm. The gas is allowed to expand to 7.33 L by two pathways: (a) isothermal, reversible expansion; (b) isothermal, irreversible free expansion. Calculate delta Stot, delta S, and delta Ssurr for each pathway. Why for th...
by Evelyn L 1H
Sun Feb 04, 2018 4:02 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: 9.35
Replies: 4
Views: 97

9.35

Can someone explain and why vibrationally active diatomic molecules have a higher change in entropy than non-vibrationally active diatomic molecules.
by Evelyn L 1H
Sun Feb 04, 2018 3:57 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: Problem 9.19 about Standard Entropy
Replies: 6
Views: 141

Re: Problem 9.19 about Standard Entropy

How are we supposed to know to calculate the change in entropy back down to 85 degrees from the way the problem is worded?
by Evelyn L 1H
Fri Feb 02, 2018 7:20 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Van Hoff Equation
Replies: 3
Views: 102

Re: Van Hoff Equation

Lavelle also clarified that the Van Hoff Equation in the chemistry text book is actually two Van Hoff equations subtracted.
by Evelyn L 1H
Fri Jan 26, 2018 8:07 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Homework question 8.41
Replies: 4
Views: 144

Re: Homework question 8.41

Sorry, I just realized that which side the negative sign is on doesn't matter too much because it will end up canceling out and giving you the same answer, but it helps to think of it conceptually and visualize what is actually physically happening.
by Evelyn L 1H
Fri Jan 26, 2018 8:05 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Homework question 8.41
Replies: 4
Views: 144

Re: Homework question 8.41

It would actually be q_ice= -q_water because the heat used to melt the ice comes from the water so water is losing the energy that the ice gains.
by Evelyn L 1H
Fri Jan 26, 2018 8:02 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: exothermic vs endothermic [ENDORSED]
Replies: 7
Views: 263

Re: exothermic vs endothermic [ENDORSED]

That's why in problems with isolated systems we can use qice=-qwater
by Evelyn L 1H
Wed Jan 24, 2018 12:12 am
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: kj/mol vs kj
Replies: 2
Views: 86

Re: kj/mol vs kj

The kJ/mol describes the enthalpy of formation of a mole of a molecule (like H2O) but when you get the enthalpy of formation for the entire reaction, it's not per mole because it's for the whole reaction. (I think)
by Evelyn L 1H
Wed Jan 24, 2018 12:08 am
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Hess's Law
Replies: 5
Views: 158

Re: Hess's Law

To make things cancel out more easily, you can switch the products and reactants. All you would have to do is switch the sign of delta H.
by Evelyn L 1H
Wed Jan 24, 2018 12:07 am
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: 8.65
Replies: 6
Views: 171

Re: 8.65

I don't understand where they got the target reaction from the two given reactions. Why can't we use Hess's law to find delta H?
by Evelyn L 1H
Sat Jan 20, 2018 5:03 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: J vs. kJ [ENDORSED]
Replies: 4
Views: 97

Re: J vs. kJ [ENDORSED]

Make sure to have constant units so you could cancel them out if necessary.
by Evelyn L 1H
Sat Jan 20, 2018 4:57 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Standard reaction enthalpies
Replies: 1
Views: 54

Standard reaction enthalpies

I am confused about how to calculate the standard reaction enthalpies. For example, in 8.63, part a asks to calculate the standard reaction enthalpy for the final stage in the production of nitric acid. 3NO2(g)+H2O(l) --> 2HNO3(aq) + NO(g).
What are the steps to finding the answer?
by Evelyn L 1H
Sat Jan 13, 2018 12:40 pm
Forum: Student Social/Study Group
Topic: Post All Chemistry Jokes Here
Replies: 7337
Views: 788856

Re: Post All Chemistry Jokes Here

Image
by Evelyn L 1H
Sat Jan 13, 2018 12:39 pm
Forum: Student Social/Study Group
Topic: Post All Chemistry Jokes Here
Replies: 7337
Views: 788856

Re: Post All Chemistry Jokes Here

Image
by Evelyn L 1H
Thu Dec 07, 2017 10:34 pm
Forum: Properties & Structures of Inorganic & Organic Acids
Topic: Arrhenius, Lewis, and Bronsted Definitions
Replies: 1
Views: 167

Re: Arrhenius, Lewis, and Bronsted Definitions

Lewis acid: Electron pair accepter
Lewis base: Electron pair donor

Bronsted acid: Proton (H+) donor
Bronsted base: Proton (H+) accepter

Arrhenius acid: Proton donor (same as bronsted acid)
Arrhenius base: produces hydroxide ions (OH-) (ie NaOH)
by Evelyn L 1H
Wed Dec 06, 2017 2:22 pm
Forum: Acidity & Basicity Constants and The Conjugate Seesaw
Topic: 12.47 [ENDORSED]
Replies: 2
Views: 131

Re: 12.47 [ENDORSED]

Oxidation means losing electrons which increases lewis acidity. This is because the more positive charge, the more likely to accept electrons.
by Evelyn L 1H
Wed Dec 06, 2017 1:43 pm
Forum: Shape, Structure, Coordination Number, Ligands
Topic: Charge of ligands
Replies: 3
Views: 157

Re: Charge of ligands

No they are either neutral or negative. They cannot be positive if they are interacting with positive transition metals.
by Evelyn L 1H
Tue Dec 05, 2017 11:49 am
Forum: Lewis Acids & Bases
Topic: Classifying Oxides as Amphoteric
Replies: 3
Views: 152

Re: Classifying Oxides as Amphoteric

Be, Al, Ga, Ge, As, In, Sn, Sb, Pb, Bi are elements that will form amphoteric compounds. This closely follows the metalloid band but not completely. Figure 12.7 on page 469 in the textbook shows this.
by Evelyn L 1H
Tue Dec 05, 2017 11:46 am
Forum: Conjugate Acids & Bases
Topic: Acids and Bases [ENDORSED]
Replies: 8
Views: 454

Re: Acids and Bases [ENDORSED]

Everything that isn't a strong base or strong acid (which were listed above) is considered weak.
by Evelyn L 1H
Tue Dec 05, 2017 11:40 am
Forum: Equilibrium Constants & Calculating Concentrations
Topic: partial pressure in ice boxes? [ENDORSED]
Replies: 2
Views: 218

Re: partial pressure in ice boxes? [ENDORSED]

Just make sure the units are correct when using concentration or pressure. Concentration would be measured in moles.L^-1 and Pressure can be in bars or atm.
by Evelyn L 1H
Mon Nov 27, 2017 9:36 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Equilibrium constants
Replies: 1
Views: 81

Equilibrium constants

What is the difference between K and K with a subscript of c?
by Evelyn L 1H
Wed Nov 22, 2017 12:33 pm
Forum: Hybridization
Topic: Why is (CH3)2Be is sp? [ENDORSED]
Replies: 7
Views: 3090

Re: Why is (CH3)2Be is sp? [ENDORSED]

On number 4.19, it says that (CH3)2BE is tetrahedral - how is that right if it's VSEPR is sp?
by Evelyn L 1H
Sun Nov 19, 2017 11:49 am
Forum: Student Social/Study Group
Topic: Post All Chemistry Jokes Here
Replies: 7337
Views: 788856

Re: Post All Chemistry Jokes Here

6986e94d6b8b81af3b049a51ced46e66.jpg
by Evelyn L 1H
Sun Nov 19, 2017 11:47 am
Forum: Student Social/Study Group
Topic: Post All Chemistry Jokes Here
Replies: 7337
Views: 788856

Re: Post All Chemistry Jokes Here

@all these jokes

f0cb1d66732f2d9699542547f6a585d2.jpg
by Evelyn L 1H
Mon Nov 13, 2017 8:01 pm
Forum: Student Social/Study Group
Topic: Post All Chemistry Jokes Here
Replies: 7337
Views: 788856

Re: Post All Chemistry Jokes Here

What do you call a salty fish?
2NA
by Evelyn L 1H
Mon Nov 13, 2017 7:32 pm
Forum: Lewis Structures
Topic: Bond Lengths [ENDORSED]
Replies: 3
Views: 172

Re: Bond Lengths [ENDORSED]

single bonds are the weakest and longest, double bonds are stronger and shorter than single bonds, and triple bonds are the strongest and the shortest
by Evelyn L 1H
Sun Nov 05, 2017 10:30 pm
Forum: Formal Charge and Oxidation Numbers
Topic: Formal Charge
Replies: 8
Views: 356

Re: Formal Charge

Also, if there must be a formal charge, elements like Oxygen which have a higher ionization energy are more likely than elements that have lower ionization energies (left, down) to have a charge.
by Evelyn L 1H
Sun Nov 05, 2017 7:19 pm
Forum: Lewis Structures
Topic: 3.51
Replies: 3
Views: 162

Re: 3.51

I've heard electronegativity and ionization energy being used interchangeably by multiple different UA's. But either way, isn't it the least highest ionization energy that is the central atom, which in this case is Chlorine. And Chlorine can have an expanded octet.
by Evelyn L 1H
Sun Nov 05, 2017 12:38 pm
Forum: Lewis Structures
Topic: 3.51
Replies: 3
Views: 162

3.51

In 51, it asks for two Lewis structures with different atom arrangements for HClO and to select the most likely structure by identifying the structure with the formal charges closest to zero. Since Cl has the lowest electronegativity, I thought it was supposed to be in the middle and made a structur...
by Evelyn L 1H
Sun Oct 29, 2017 3:41 pm
Forum: Trends in The Periodic Table
Topic: Diagonal Relationships of the Periodic Table [ENDORSED]
Replies: 4
Views: 547

Re: Diagonal Relationships of the Periodic Table [ENDORSED]

This would definitely be something to study because the test covers everything from section 1.5 and all of chapter 2.
by Evelyn L 1H
Sun Oct 29, 2017 3:27 pm
Forum: Lewis Structures
Topic: Valence electrons [ENDORSED]
Replies: 1
Views: 154

Valence electrons [ENDORSED]

How do you calculate the total number of valence electrons when making a lewis structure.
by Evelyn L 1H
Sat Oct 21, 2017 5:33 pm
Forum: SI Units, Unit Conversions
Topic: Prefixes [ENDORSED]
Replies: 6
Views: 356

Re: Prefixes [ENDORSED]

Also if you keep your answers in meters it's ok. However you should know the prefixes so you can convert values given in the problem to meters.
by Evelyn L 1H
Wed Oct 18, 2017 11:37 pm
Forum: Bohr Frequency Condition, H-Atom , Atomic Spectroscopy
Topic: Atomic Spectra Module Question 44
Replies: 2
Views: 170

Atomic Spectra Module Question 44

In the hydrogen atomic spectrum, what is the wavelength of light associated with the n = 4 to n = 1 electron transition? What part of the electromagnetic spectrum is this wavelength? A. 1.03 x 107 m; radio waves region B. 9.73 x 10-8 m; UV region C. -9.73 x 10-8 m; visible light region D. -2.044 x 1...
by Evelyn L 1H
Fri Oct 06, 2017 9:28 pm
Forum: Significant Figures
Topic: Integers and Exact Numbers- Sig Figs [ENDORSED]
Replies: 4
Views: 311

Re: Intergers and Exact Numbers- Sig Figs [ENDORSED]

Also, to add on, it would be best to save your rounding of sig figs until the last step for the most accurate answer.
by Evelyn L 1H
Thu Oct 05, 2017 8:13 pm
Forum: SI Units, Unit Conversions
Topic: Sig Figs [ENDORSED]
Replies: 16
Views: 1740

Re: Sig Figs [ENDORSED]

There are 3 sig figs in 0.0450. This is more clearly shown if you write it in scientific notation as 4.50 x 10^-2
The 0s before 450 do not count as sig figs.

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