Search found 73 matches

by Clement Ng
Sun Mar 18, 2018 2:41 am
Forum: Calculating Standard Reaction Entropies (e.g. , Using Standard Molar Entropies)
Topic: cis and trans molecules
Replies: 3
Views: 380

Re: cis and trans molecules

In chapter 9 #75, the molecule cis-MX2Y4 has a higher molar entropy than trans-MX2Y4.
by Clement Ng
Sat Mar 17, 2018 5:26 pm
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: nernst eqn
Replies: 1
Views: 184

nernst eqn

E = Eo - RT/nF * ln Q
E = Eo -0.05916 V/n * log Q

In the 2016 final exam #4A, I used the latter equation but the answer key used the first equation. I got roughly the same answer (944V). The answer key said 942V. Would I get marked down for an answer a few volts off?
by Clement Ng
Sat Mar 17, 2018 5:00 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: equations
Replies: 1
Views: 179

equations

What are the equations of the definitions for the 3 laws of thermodynamics?

For the 2nd law, is it right to say that 2nd law is deltaS(univ) > 0?

For the 1st law, is it delta U univ =0?
by Clement Ng
Sat Mar 17, 2018 4:58 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: salt bridge and porous disks
Replies: 1
Views: 88

salt bridge and porous disks

Do salt bridge/porous disk: does it allow cations to move or do they only allow counter ions such as Cl- to be transferred?
by Clement Ng
Sat Mar 17, 2018 4:57 pm
Forum: Calculating Standard Reaction Entropies (e.g. , Using Standard Molar Entropies)
Topic: cis and trans molecules
Replies: 3
Views: 380

cis and trans molecules

Why do cis molecules have a higher molar entropy than trans molecules?
by Clement Ng
Sat Mar 17, 2018 1:28 am
Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
Topic: units
Replies: 2
Views: 158

units

w(max) = deltaG of a voltaic cell, but then the units of w are J and deltaG's units are J/mol. Why is this?
by Clement Ng
Sat Mar 17, 2018 1:12 am
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: acidic/basic
Replies: 2
Views: 101

acidic/basic

Whenever a redox equation is acidic or basic, is the H+/OH- ion on the left side of the equation or the right?
by Clement Ng
Wed Mar 14, 2018 2:04 pm
Forum: Student Social/Study Group
Topic: Post All Chemistry Jokes Here
Replies: 7348
Views: 891037

Re: Post All Chemistry Jokes Here

Practice Exam Problem:

How many views does Chemistry Community have? (10 pts)

a) 100,000

b) 1,000,000

c) 5,000,000

d) none of the above
by Clement Ng
Mon Mar 12, 2018 3:00 pm
Forum: Student Social/Study Group
Topic: Post All Chemistry Jokes Here
Replies: 7348
Views: 891037

Re: Post All Chemistry Jokes Here

Is it me or did I stumble into 14C today?
by Clement Ng
Mon Mar 12, 2018 2:59 pm
Forum: *Alcohols
Topic: study tips
Replies: 3
Views: 582

study tips

Is there any good mnemonic device for memorizing all the functional groups?
by Clement Ng
Thu Mar 08, 2018 12:08 am
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Slow step
Replies: 3
Views: 90

Re: Slow step

The step with the smaller k value.
by Clement Ng
Thu Mar 08, 2018 12:07 am
Forum: First Order Reactions
Topic: Simpler way to calculate change in concentrations
Replies: 2
Views: 86

Re: Simpler way to calculate change in concentrations

No, I wouldn't see a reason why you would be penalized for using that equation. As long as it helps you get the right answer, you're good.
by Clement Ng
Thu Mar 08, 2018 12:05 am
Forum: Student Social/Study Group
Topic: Post All Chemistry Jokes Here
Replies: 7348
Views: 891037

Re: Post All Chemistry Jokes Here

me: that midterm was so easy

me: *gets back grade
by Clement Ng
Sun Mar 04, 2018 10:14 pm
Forum: Kinetics vs. Thermodynamics Controlling a Reaction
Topic: rates of reaction vs rates of consumption and formation (15.3)
Replies: 3
Views: 337

Re: rates of reaction vs rates of consumption and formation (15.3)

I think it's because the rate for consumption is negative[change in concentration]/change in time, and the change in concentration was negative. Thus, the answer was positive.
by Clement Ng
Sun Mar 04, 2018 9:53 pm
Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
Topic: test 2 last Q
Replies: 3
Views: 152

test 2 last Q

For those who took the test for 2I, is Q=1?
by Clement Ng
Sun Mar 04, 2018 9:53 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: oxidizing power
Replies: 2
Views: 114

oxidizing power

How would you rank different reactions' oxidizing power based on their reduction potentials?
by Clement Ng
Wed Feb 21, 2018 11:16 pm
Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
Topic: mistake in Ch 14. #35.b?
Replies: 1
Views: 74

mistake in Ch 14. #35.b?

In the solutions manual for #35.b in chapter 14, it uses the half reaction In3+ + 2e- --> In2+, but in the appendix, the half reaction is In3+ + 1e- --> ln 2+. Is this a mistake?
by Clement Ng
Wed Feb 21, 2018 10:29 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: E and Eo
Replies: 2
Views: 123

E and Eo

What's the difference between E and Eo?
by Clement Ng
Wed Feb 21, 2018 8:06 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Cell potential
Replies: 1
Views: 73

Cell potential

When cell potential is negative since anode potential is larger than cathode, the reaction does not favor products. Can we assume that the reaction favors reactants then? (chapter 14, #31.b)
by Clement Ng
Wed Feb 21, 2018 3:40 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: #29.c
Replies: 1
Views: 46

#29.c

In the cell diagram for chapter 14 #29.c, the cell diagram goes Pt(s) l H2(g) l H+ (aq) ll Fe2+, Fe3+ l Pt(s). Does the order of the iron ions within the brackets matter?
by Clement Ng
Wed Feb 21, 2018 12:33 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: appendix 2
Replies: 2
Views: 83

appendix 2

In the back of the textbook, appendix 2, page A18, it says that Fe2+ + e- --> Fe2+. Eo= +0.77V. Isn't the charge of the ion supposed to change?
by Clement Ng
Wed Feb 14, 2018 3:23 am
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: sign of delta S
Replies: 1
Views: 95

sign of delta S

When determining the sign of delta S, do you look at only moles of gas on both sides of reaction or can you also look at moles of liquid and solid?
by Clement Ng
Wed Feb 14, 2018 2:47 am
Forum: Gibbs Free Energy Concepts and Calculations
Topic: delta S total and delta G
Replies: 2
Views: 247

delta S total and delta G

How are delta S total and delta G related?
by Clement Ng
Wed Feb 14, 2018 12:39 am
Forum: Gibbs Free Energy Concepts and Calculations
Topic: stability and +/- delta G
Replies: 1
Views: 701

stability and +/- delta G

On 9.63, it says that whenever deltaG (formation) is negative, it is thermodynamicaly stable. Why is this?
by Clement Ng
Tue Feb 13, 2018 12:14 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: deltaG and deltaS(sys) at zero
Replies: 1
Views: 68

deltaG and deltaS(sys) at zero

A sample of 1 mole of gas initially at 1 atm and 298 K is heated at constant pressure to 350 K, then the gas is compressed isothermally to its initial volume and is then cooled to 298 K at constant volume. Why are deltaS(sys) and deltaG zero in this case? Which equations would you use to figure what...
by Clement Ng
Mon Feb 12, 2018 3:07 am
Forum: Balancing Redox Reactions
Topic: midterm W18
Replies: 1
Views: 86

midterm W18

Will electrochemistry be on the midterm? If so, up to what part?
by Clement Ng
Mon Feb 12, 2018 3:05 am
Forum: Calculating Standard Reaction Entropies (e.g. , Using Standard Molar Entropies)
Topic: Delta S total
Replies: 1
Views: 289

Delta S total

Could someone explain to me how do equilibrium and reversible reactions relevant when answering the question: "Is delta Surrounding = - delta System" ?
This was on Lyndon's practice midterm #3f.
by Clement Ng
Mon Feb 12, 2018 3:03 am
Forum: Phase Changes & Related Calculations
Topic: phase change
Replies: 1
Views: 102

phase change

How is it possible for H20 gas to stay in that form at 25 Celsius?
by Clement Ng
Fri Feb 02, 2018 1:28 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: enthalpy
Replies: 1
Views: 69

enthalpy

What is deltaH when chem community is on fire?
by Clement Ng
Fri Feb 02, 2018 1:22 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: reversible and irreversible with entropy
Replies: 2
Views: 103

reversible and irreversible with entropy

deltaS= q(rev)/T. Will we ever use q(irrev)to calculate deltaS and if so when?
by Clement Ng
Fri Feb 02, 2018 1:19 pm
Forum: Phase Changes & Related Calculations
Topic: Phase change
Replies: 4
Views: 149

Re: Phase change

Usually when temperature is constant and no chemical reaction is occurring.
by Clement Ng
Thu Jan 25, 2018 3:11 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: constant pressure
Replies: 5
Views: 187

constant pressure

I understand that at constant pressure, q= delta H, but do you use enthalpy of the reaction or enthalpy of formation?
by Clement Ng
Wed Jan 24, 2018 8:23 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: isothermal system
Replies: 3
Views: 173

isothermal system

In an isothermal system, if the change in moles is not zero, would delta U still be zero?
by Clement Ng
Wed Jan 24, 2018 1:38 am
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: C at constant V and P [ENDORSED]
Replies: 1
Views: 85

C at constant V and P [ENDORSED]

Why is it that at constant pressure C= delta H/ delta T but at constant volume C = delta U/ delta T?
by Clement Ng
Tue Jan 23, 2018 10:24 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: 8.25
Replies: 1
Views: 100

8.25

Could someone explain this problem to me? A constant-volume calorimeter was calibrated by carrying out a reaction known to release 3.50 kJ of heat in 0.200 L of solution in the calorimeter (q 3.50 kJ), resulting in a temperature rise of 7.32 C. In a subsequent experiment, 100.0 mL of 0.200 m HBr(a...
by Clement Ng
Tue Jan 23, 2018 9:08 pm
Forum: Calculating Work of Expansion
Topic: reversible and irreversible
Replies: 2
Views: 100

reversible and irreversible

Conceptually what's the difference between reversible and irreversible processes?
by Clement Ng
Tue Jan 23, 2018 3:44 pm
Forum: Calculating Work of Expansion
Topic: reversible and irreversible [ENDORSED]
Replies: 1
Views: 78

reversible and irreversible [ENDORSED]

Conceptually what's the difference between reversible and irreversible processes?
by Clement Ng
Sun Jan 21, 2018 8:00 pm
Forum: Phase Changes & Related Calculations
Topic: Irreversible and Reversible
Replies: 7
Views: 236

Re: Irreversible and Reversible

Questions about both reversible and irreversible have been on the homework, so it's safe to assume that they may be on the test.
by Clement Ng
Sun Jan 21, 2018 8:00 pm
Forum: Calculating Work of Expansion
Topic: What do these variables mean?
Replies: 4
Views: 161

Re: What do these variables mean?

Yep! P is pressure too.
by Clement Ng
Fri Jan 19, 2018 3:39 pm
Forum: Thermodynamic Systems (Open, Closed, Isolated)
Topic: atm*L to J
Replies: 1
Views: 132

atm*L to J

When calculating work, when do you multiple -PdeltaV by 101.325 J/(atm*L) versus multiplying by (8.314 J*K*mol-1)/(0.08206L*atm*K-1*mol-1)?
by Clement Ng
Fri Jan 12, 2018 1:04 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Enthalpy Change Signs
Replies: 5
Views: 194

Re: Enthalpy Change Signs

Yes there's a sign change, because the reaction would change from endo to exothermic or vice versa.
by Clement Ng
Fri Jan 12, 2018 1:03 pm
Forum: Phase Changes & Related Calculations
Topic: ∆Hsub= ∆Hfus+ ∆Hvap
Replies: 4
Views: 354

Re: ∆Hsub= ∆Hfus+ ∆Hvap

Sublimation is the phase change from solid to gas, and vaporization is the phase change from liquid to gas and fusion is the phase change from slid to liquid.
by Clement Ng
Fri Jan 12, 2018 1:02 pm
Forum: Administrative Questions and Class Announcements
Topic: Times to post per week
Replies: 5
Views: 262

Re: Times to post per week

Yeah it's 3 times.
by Clement Ng
Sun Dec 10, 2017 4:08 pm
Forum: Einstein Equation
Topic: Einstein Constant [ENDORSED]
Replies: 1
Views: 207

Re: Einstein Constant [ENDORSED]

Einstein constant is a cosmological constant that Einstein used to describe general relativity. It is not the inverse of the planck's constant.
by Clement Ng
Sun Dec 10, 2017 4:04 pm
Forum: Properties & Structures of Inorganic & Organic Bases
Topic: HClO [ENDORSED]
Replies: 1
Views: 298

Re: HClO [ENDORSED]

No, it is not. HClO4 and HCl are strong acids.
by Clement Ng
Sun Dec 10, 2017 4:02 pm
Forum: Biological Examples
Topic: Hemoglobin
Replies: 5
Views: 505

Re: Hemoglobin

myoglobin and Fe. It is used to transport O2 molecules
by Clement Ng
Sun Dec 10, 2017 4:00 pm
Forum: Student Social/Study Group
Topic: Post All Chemistry Jokes Here
Replies: 7348
Views: 891037

Re: Post All Chemistry Jokes Here

my gpa
by Clement Ng
Sun Dec 10, 2017 12:15 am
Forum: Electron Configurations for Multi-Electron Atoms
Topic: Cl -2
Replies: 2
Views: 145

Cl -2

Why is the electron configuration for Cl -2 [Ne] 3s^2 3p^6 4s^1 and not [Ar]4s^1?
by Clement Ng
Sat Dec 09, 2017 9:44 pm
Forum: Calculating pH or pOH for Strong & Weak Acids & Bases
Topic: titration
Replies: 3
Views: 168

titration

Is any knowledge of titration required on the final?
by Clement Ng
Fri Dec 08, 2017 9:47 pm
Forum: Conjugate Acids & Bases
Topic: naming [ENDORSED]
Replies: 1
Views: 133

naming [ENDORSED]

Do we have to know how to name acids and bases?
by Clement Ng
Fri Dec 08, 2017 7:36 pm
Forum: Calculating pH or pOH for Strong & Weak Acids & Bases
Topic: 12.33 part c
Replies: 1
Views: 104

Re: 12.33 part c

It's probably a typo. I think it meant concentration.
by Clement Ng
Fri Dec 08, 2017 7:32 pm
Forum: Calculating pH or pOH for Strong & Weak Acids & Bases
Topic: pH vs pOH
Replies: 2
Views: 189

Re: pH vs pOH

pH is equal to 14-pOH. pH can be calculated from concentration of H3O+ and pOH is calculated from concentration of OH-.
by Clement Ng
Fri Dec 08, 2017 7:31 pm
Forum: Student Social/Study Group
Topic: Post All Chemistry Jokes Here
Replies: 7348
Views: 891037

Re: Post All Chemistry Jokes Here

What was the combustion reaction for the skirball fire?
by Clement Ng
Tue Nov 28, 2017 8:21 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: K constant
Replies: 2
Views: 149

K constant

Let's say there is a chemical equation that involves a gas and an aqueous solution. If the questions asks for K, do you include only gas, only concentration, or both?
by Clement Ng
Tue Nov 28, 2017 8:16 pm
Forum: Shape, Structure, Coordination Number, Ligands
Topic: coordination compounds
Replies: 1
Views: 113

coordination compounds

How do you know the number of bonds a central metal atom has in a coordination compound?
by Clement Ng
Wed Nov 22, 2017 4:31 pm
Forum: Hybridization
Topic: Hypervalent Hybridization
Replies: 2
Views: 177

Re: Hypervalent Hybridization

The hybridization of a sulfate ion would be sp3. You can picture it like it's Ch4 as if it's a tetrahedral. Hope this answered your question.
by Clement Ng
Wed Nov 22, 2017 4:27 pm
Forum: Shape, Structure, Coordination Number, Ligands
Topic: Determine the Charge on Ligands
Replies: 4
Views: 343

Re: Determine the Charge on Ligands

You would determine the charge on coordination compounds by comparing the charges of the ligands, which are given in a table on professor Lavelle's website. The charge of the metal/central atom can be given by the name of the compound. (ex: (IV)) By combining all the charges of the central atom and ...
by Clement Ng
Sun Nov 19, 2017 9:33 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: 180degrees and lone pairs?
Replies: 4
Views: 167

Re: 180degrees and lone pairs?

The molecule may have an electron configuration of a square planar.
by Clement Ng
Sun Nov 19, 2017 9:30 pm
Forum: Biological Examples
Topic: Cobalt
Replies: 4
Views: 281

Re: Cobalt

It is also important for the production of red blood cells and myelin sheath.
by Clement Ng
Sun Nov 19, 2017 9:21 pm
Forum: Biological Examples
Topic: hemoglobins
Replies: 1
Views: 162

hemoglobins

Can someone explain the structure of hemoglobins and how they bind and disconnect oxygenatoms?
by Clement Ng
Sun Nov 19, 2017 9:19 pm
Forum: *Molecular Orbital Theory (Bond Order, Diamagnetism, Paramagnetism)
Topic: Difference Between Sigma and Pi Bonds [ENDORSED]
Replies: 4
Views: 374

Re: Difference Between Sigma and Pi Bonds [ENDORSED]

You can think of sigma bonds connecting atoms directly along the x-axis while pi bonds connect the two atoms between the top and bottom of the y-axis of atoms.
by Clement Ng
Sun Nov 05, 2017 10:16 pm
Forum: Dipole Moments
Topic: S+ and S- Dipole Moment
Replies: 4
Views: 1224

Re: S+ and S- Dipole Moment

S+ usually refers to the atom which lost an electron while S- refers to the atom that gained an electron.
by Clement Ng
Sun Nov 05, 2017 10:14 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: electron density
Replies: 3
Views: 147

electron density

What is the definition of electron density?
by Clement Ng
Sun Oct 29, 2017 10:59 pm
Forum: Resonance Structures
Topic: Resonance Structures [ENDORSED]
Replies: 3
Views: 239

Re: Resonance Structures [ENDORSED]

You draw a resonance structure by drawing all the possible structures and arrows that show that the molecule oscillate between the different lewis diagrams.
by Clement Ng
Sun Oct 29, 2017 10:58 pm
Forum: Wave Functions and s-, p-, d-, f- Orbitals
Topic: d and s blocks
Replies: 16
Views: 684

Re: d and s blocks

S blocks are written before d blocks always, unless the n value of s is equal or higher than the n value of d.
by Clement Ng
Tue Oct 17, 2017 6:20 pm
Forum: Bohr Frequency Condition, H-Atom , Atomic Spectroscopy
Topic: Rydberg Formula
Replies: 2
Views: 166

Rydberg Formula

The equation in the book uses the formula: frequency = R(1/n^2 - 1/N^2)

However, when I google the formula, it is 1/wavelength = R(1/n^2 - 1/N^2).

Why is that?
by Clement Ng
Tue Oct 17, 2017 6:16 pm
Forum: Bohr Frequency Condition, H-Atom , Atomic Spectroscopy
Topic: Question 1.15
Replies: 6
Views: 266

Re: Question 1.15

This is because in the formula v= R(1/n^2 - 1/N^2), if n was 3 and N was 1, the frequency would be a negative number.

1/9 - 1/1 = negative number.
by Clement Ng
Fri Oct 13, 2017 2:44 pm
Forum: Photoelectric Effect
Topic: What is the extent of elements for the photoelectric effect?
Replies: 2
Views: 153

Re: What is the extent of elements for the photoelectric effect?

Non metals are not likely to exhibit any photoelectric effect, because only metals have 'spare' electrons available in their outer shells.
by Clement Ng
Fri Oct 13, 2017 2:42 pm
Forum: Photoelectric Effect
Topic: Post-Assessment #16
Replies: 1
Views: 101

Re: Post-Assessment #16

The answer is threshold energy.
by Clement Ng
Fri Oct 06, 2017 2:16 am
Forum: SI Units, Unit Conversions
Topic: Significant Figures [ENDORSED]
Replies: 9
Views: 661

Re: Significant Figures [ENDORSED]

For multiplication and division, the least number of significant figures in any number of the problem determines the number of significant figures in the answer. For example 4.00 x 3.0 = 12 Since the number with the least sig figs in the problem is "3.0", which has 2 sig figs, the answer h...
by Clement Ng
Fri Oct 06, 2017 2:08 am
Forum: Limiting Reactant Calculations
Topic: Exercise M.11 [ENDORSED]
Replies: 3
Views: 285

Re: Exercise M.11 [ENDORSED]

Yes, that is correct. To answer this question in simpler terms, you take the excess moles of oxygen left over from the first reaction, and use that value to calculate the number of moles of P4O10 formed. Then, you use the moles of P4O6 formed from the first reaction to find the moles of P4O10 formed...

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