## Search found 51 matches

Thu Mar 15, 2018 11:12 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: HW 15.63
Replies: 2
Views: 151

### HW 15.63

Why is there '-0.59' at the end? is this the ln A value? If so, where in the question is the A value given?
Wed Mar 14, 2018 1:22 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: HW 15.49
Replies: 2
Views: 178

### HW 15.49

For 15.49b, why is [HOBr] included in the rate law? Shouldn't it be expressed in a different way (like we did in class today) because it is an intermediate?
Sun Mar 11, 2018 10:17 pm
Forum: Calculating Work of Expansion
Topic: Midterm 4a
Replies: 4
Views: 362

### Midterm 4a

For 4A, how do I know that I'm using irreversible eq. instead of reversible eq?
Thu Mar 08, 2018 10:48 am
Forum: First Order Reactions
Topic: One of the equations for 1st order rxn
Replies: 3
Views: 260

### One of the equations for 1st order rxn

What is the equation d[A]/[A] for? Is this just change in [A] over time? What is the difference between d[A]=-kdt and d[A]/[A]?
Thu Mar 08, 2018 10:44 am
Forum: Method of Initial Rates (To Determine n and k)
Topic: Units for rate
Replies: 4
Views: 404

### Units for rate

For rate, is it okay to leave the answer as mmol or do I have to convert to mol? Does rate unit always have to be M*L-1*s-1?
Mon Mar 05, 2018 9:21 pm
Forum: Kinetics vs. Thermodynamics Controlling a Reaction
Topic: HW 15.23
Replies: 2
Views: 238

### HW 15.23

For 15.23c, why is 'ln' not included in the equation? Since the equation that we start with is ln([A]t-[A]0)=-kt, I thought the equation we end up with should be ln[A]t=whatever?
Thu Mar 01, 2018 11:31 am
Forum: General Rate Laws
Topic: K value related to half life
Replies: 2
Views: 135

### K value related to half life

Why is large k = fast reaction?

Also, just in general, why do we want to know half-life?
Thu Mar 01, 2018 11:28 am
Forum: First Order Reactions
Topic: Overall reaction order
Replies: 2
Views: 1488

### Overall reaction order

Can someone explain what n and m is for the equation

overall reaction order = n + m?

Also, I thought I could determine reaction order by looking at k; is this just another method?
Wed Feb 28, 2018 2:08 pm
Forum: Student Social/Study Group
Topic: Post All Chemistry Jokes Here
Replies: 8219
Views: 1434462

### Re: Post All Chemistry Jokes Here

I have a pick up line instead.
"You must be made of Florine, Iodine, and Neon, because you are FINe :))"

Actually don't use it I don't think it'll work
Wed Feb 21, 2018 2:24 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Cell diagram for Fe and Cu [ENDORSED]
Replies: 1
Views: 101

### Cell diagram for Fe and Cu[ENDORSED]

For the diagram Cu(s)|Cu2+(aq)||Fe3+(aq),Fe2+(aq)|Pt(s), why is Fe3+ before Fe2+? Does the order matter?
Wed Feb 21, 2018 2:17 pm
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: Nernst equation usage
Replies: 3
Views: 289

### Nernst equation usage

Is Nernst equation simply used to find cell potential under non-standard conditions (not 1M)? I'm confused b/c there are different Nernst equations and I think one of them's supposed to be use to calculate k for redox reactions at equilibrium.
Wed Feb 21, 2018 2:14 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Gold ring example
Replies: 1
Views: 83

### Gold ring example

Au(s) + NO3-(aq) + 4H+(aq) -> Au3+(aq) + NO(g) + H2O(l)

^ I don't understand how to get NO3- and NO from HNO3.
Tue Feb 13, 2018 9:55 am
Forum: Phase Changes & Related Calculations
Topic: HW 9.37 calculating Hvap
Replies: 1
Views: 143

### HW 9.37 calculating Hvap

Can I calculate Hvap without using/given Hvap=Hvapor-Hliquid? Similarly, can I get Hsub or Hfus?
Tue Feb 13, 2018 9:00 am
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: 9.25 Question
Replies: 1
Views: 172

### Re: 9.25 Question

I think it just means that SO2F2 can exist in six different arrangements knowing that S has to be the middle.
Tue Feb 13, 2018 8:57 am
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: Change in temp vs Change in volume equations
Replies: 2
Views: 177

### Re: Change in temp vs Change in volume equations

I think C is for constant volume, which is 3/2R, and R is just gas constant? Cv, constant volume, cannot be used for the second equation b/c volume is changing (V1 -> V2).
Mon Feb 12, 2018 1:53 am
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Gibbs = 0
Replies: 2
Views: 196

### Gibbs = 0

When is Gibbs free energy equal to zero?

For this question:

The entropy of vap of water is 109.0J/mol*K. What is the enthalpy of vap of water at its normal boiling point of 100 degree C?

Why do we set G equal to zero?
Thu Feb 08, 2018 11:43 am
Forum: Phase Changes & Related Calculations
Topic: Phase changes with entropy?
Replies: 6
Views: 373

### Re: Phase changes with entropy?

So both enthalpy and entropy change during phase changes?
Tue Feb 06, 2018 9:59 am
Forum: Gibbs Free Energy Concepts and Calculations
Topic: G for non-equilibrium
Replies: 2
Views: 198

### G for non-equilibrium

For the equation deltaG=G+R*T*lnQ, what is Q?
Tue Feb 06, 2018 8:56 am
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: Boltzmann Equation
Replies: 2
Views: 119

### Boltzmann Equation

Is Kb simply equal to R, or is it only when we are calculating W for 1 mole? If it is only for 1 mole, what is Kb?
Thu Feb 01, 2018 10:30 am
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Energy calculation precision
Replies: 2
Views: 148

### Energy calculation precision

Out of three methods for calculating free energy, which one is the most accurate/least accurate and why?
Thu Feb 01, 2018 10:28 am
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: Reversible vs. Irreversible work amount
Replies: 1
Views: 157

### Reversible vs. Irreversible work amount

Can someone explain why reversible system does more work than irreversible using the 2atm pushing against 1atm vs. 2atm pushing against 2atm diagram? I get the general concept but I don't understand the diagram.
Wed Jan 31, 2018 12:52 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Dependence of free energy on pressure
Replies: 2
Views: 153

### Dependence of free energy on pressure

I don't really understand the equation for G. Is it G = free energy of the gas at 1 atm + free energy difference due to different pressure? Also, is the G just simple G or deltaG?
Tue Jan 23, 2018 10:42 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: Potential energy comparison
Replies: 1
Views: 135

### Potential energy comparison

When is potential energy highest? For example, for combustion, is it highest before or after combustion? Why? Does the book cover this?
Tue Jan 23, 2018 5:13 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: R -> P vs. P -> R
Replies: 3
Views: 205

### R -> P vs. P -> R

So I understand that the equation for finding change in enthalpy of reaction is sum of products' change in Hf - sum of reactants' change in Hf. However, when using bond enthalpies to find change in enthalpy, why are we simply adding enthalpies on the product side and subtracting that from reactant s...
Sat Jan 20, 2018 7:49 am
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Standard enthalpies on test 1 [ENDORSED]
Replies: 7
Views: 392

### Standard enthalpies on test 1[ENDORSED]

For the test, what are the standard states we have to remember? (For example, O2?)
Wed Jan 17, 2018 12:54 am
Forum: Calculating Work of Expansion
Topic: 8.27
Replies: 1
Views: 99

### 8.27

For 8.27, I thought the equation for an reversible isothermal expansion is: w = -nRT*ln(V2/V1). However, on the answer sheet, "ln" is not part of the equation. Which then is the correct equation? Also, is V2 = final volume and V1 = initial volume?
Mon Jan 15, 2018 11:58 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: HW 8.21
Replies: 2
Views: 147

### HW 8.21

For 8.21, why is heat lost by metal = - heat gained by water? Feels like it should be: since metal (Cu) is the system, so - heat lost by the system (metal) = heat gained by water. Why are the signs flipped?
Sun Jan 14, 2018 6:03 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: U=q or U=q+w?
Replies: 3
Views: 221

### U=q or U=q+w?

When is the change in internal energy (U) equal to heat (q) and when is it equal to heat+work (q+w)? What is the difference between U=q and U=q+w?
Wed Jan 10, 2018 8:42 am
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: R in the equation
Replies: 2
Views: 175

### R in the equation

In the equation w = -nRT * ln(Vfinal/Vinitial), what does R represent?
Wed Jan 10, 2018 8:05 am
Forum: Administrative Questions and Class Announcements
Replies: 5
Views: 389

Maybe start from the back? Questions are divided into big sections so I'm starting with the ones covered in class!
Tue Jan 09, 2018 9:03 am
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Book 8.11 [ENDORSED]
Replies: 5
Views: 307

### Book 8.11[ENDORSED]

On page 283, for equation 14, what exactly is Hm (vapor) and Hm (liquid)? Is it related to moles like molar heat capacity (Cm)?
Fri Dec 08, 2017 8:26 am
Forum: Shape, Structure, Coordination Number, Ligands
Topic: dipole moment of PO4 3-
Replies: 1
Views: 770

### dipole moment of PO4 3-

My understanding is that there is no dipole moment for PO4 3- because of resonance and hybrid bond lengths are equal. Does this mean that there is no dipole moment for O3 as well?

If attached molecules are all same and there is resonance, can I say that there is always no dipole moment?
Thu Dec 07, 2017 3:44 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: ICE table
Replies: 7
Views: 618

### Re: ICE table

Does x=0 mean that the amounts of both reactants and products stay the same?
Fri Dec 01, 2017 10:23 am
Forum: Lewis Acids & Bases
Topic: Strong acid+weak base
Replies: 2
Views: 249

### Strong acid+weak base

Is the conjugate base for strong acid weak base or strong base? Does it differ between Lewis acid/base & Bronsted acid/base?
Mon Nov 27, 2017 4:16 pm
Forum: Non-Equilibrium Conditions & The Reaction Quotient
Topic: Chemical Equilibrium Part 2 Post-Module #19 & 27
Replies: 2
Views: 217

### Chemical Equilibrium Part 2 Post-Module #19 & 27

19. Calculate the reaction quotient, QC, from the following equilibrium data collected in a 3.00 L sealed reaction vessel for the reaction: AsH3 (g) ⇌ As (s) + H2 (g) AsH3 = 5.55 x 10-4 mol, As = 3.31 x 10-3 mol, H2 = 1.23 x 10-3 mol. First I divided given mols with 3.00L to find mol*L-1 and did wha...
Sun Nov 26, 2017 5:25 pm
Forum: Shape, Structure, Coordination Number, Ligands
Topic: Polydentate and chelate
Replies: 1
Views: 153

### Polydentate and chelate

What is the difference between polydentate and chelate? By looking at [Co(en)3]3+, can I determine what ligands are attached to Co?
Fri Nov 24, 2017 11:58 am
Forum: Determining Molecular Shape (VSEPR)
Topic: IF7
Replies: 2
Views: 401

### IF7

What is IF7's geometrical shape and why?
Fri Nov 17, 2017 1:32 pm
Forum: Ionic & Covalent Bonds
Topic: Determining oxidation state
Replies: 3
Views: 487

### Determining oxidation state

How can I figure out the oxidation state by looking at LS? Are there any other ways to figure out oxidation states?
Mon Nov 13, 2017 1:04 pm
Forum: Dipole Moments
Topic: Dipole for cis-dichloroethene
Replies: 2
Views: 281

### Dipole for cis-dichloroethene

For cis-dichloreothene, I understand that there is a dipole arrow (force? what's the exact term for this) between C-Cl, but should we be thinking about C-H as well or is it just ignored completely?
Mon Nov 06, 2017 8:11 am
Forum: Lewis Structures
Topic: Exceptions to octet rule?
Replies: 6
Views: 644

### Exceptions to octet rule?

Can someone list the exceptions to octet rule? I know that
1. Any element from 3rd row or below can have more than 8 e-,
2. Be & B usually don't get all 8 e-, but I don't know if there are any other group of elements like them/the reason why.
Mon Nov 06, 2017 8:03 am
Forum: Lewis Structures
Topic: Lewis Structures
Replies: 10
Views: 630

### Re: Lewis Structures

I think the center atom's supposed to be the one with lowest ionization E.
Mon Oct 30, 2017 5:43 pm
Forum: Trends in The Periodic Table
Topic: 2-43e tungsten e- config
Replies: 1
Views: 191

### 2-43e tungsten e- config

On 2-43, shouldn't ground state e- config of tungsten be [Xe]4f^14 5d^5 6s^2 because tungsten originally has ... 5d^4 and it takes e- to make 5d^5? (Answer on the solution is [Xe]4f^14 5d^4 6s^2.)
Fri Oct 27, 2017 10:18 am
Forum: Electron Configurations for Multi-Electron Atoms
Topic: Ti e- Configuration
Replies: 1
Views: 212

### Ti e- Configuration

Should Ti's electron configuration be [Ar]3d^2 4s^2 or [Ar]4s^2 3d^2? Why?
Thu Oct 26, 2017 1:07 pm
Forum: Heisenberg Indeterminacy (Uncertainty) Equation
Topic: Test 3 [ENDORSED]
Replies: 7
Views: 2509

### Re: Test 3[ENDORSED]

Wed Oct 25, 2017 3:21 pm
Forum: Lewis Structures
Topic: ClO Chemical Formula&LS [ENDORSED]
Replies: 1
Views: 486

### ClO Chemical Formula&LS[ENDORSED]

For chlorine monoxide, why is its chemical formula ClO instead of Cl2O (considering ionic charge)?

Also, when I drew its LS, Cl&O had single bond, and Cl had five e- (six including e- from the bond). Does this mean I have to write 1- next to Cl?
Tue Oct 17, 2017 11:33 am
Forum: Photoelectric Effect
Topic: Post Module #29 (KJ*mol^-1 problem)
Replies: 4
Views: 318

### Post Module #29 (KJ*mol^-1 problem)

Light hits a sodium metal surface and the velocity of the ejected electron is 6.61 x 105 m.s-1. The work function for sodium is 150.6 kJ.mol-1. (From previous Q, Ek = 1.99*10^-19J) #29. How much energy is required to remove an electron from one sodium atom? I know this question is just asking for wo...
Tue Oct 17, 2017 11:21 am
Forum: Photoelectric Effect
Topic: Post Module #23 [ENDORSED]
Replies: 2
Views: 219

### Post Module #23[ENDORSED]

To interpret the results of photoelectric experiments the model of light needs to change from a ___ model to ___ model. What are the two missing words?

I thought the blanks should be waves & photon, but it's wrong. Anyone understand this question? What is the answer and why?
Wed Oct 11, 2017 2:48 pm
Forum: Einstein Equation
Replies: 3
Views: 330

For the equation Ek = (1/2)m*v^2, does ^2 apply to the whole equation ((1/2)m*v)^2 or just v (v^2)?
Wed Oct 11, 2017 2:27 pm
Forum: Einstein Equation
Topic: E=hv and ΔE=hv
Replies: 3
Views: 589

### E=hv and ΔE=hv

Under Atomic Spectra, I wrote down "E = hv, ΔE = hv". What is the difference between the two equations? Is E equal to ΔE? When are these equations used?
Fri Oct 06, 2017 8:51 am
Forum: Limiting Reactant Calculations
Topic: M18 hELP!
Replies: 3
Views: 356

### M18 hELP!

The acid H2A (where A stands for an unknown group of atoms) has molar mass 168 g mol 1. H2A reacts with the base XOH (molar mass 125 g mol -1) to produce H2O and the salt X2A. In one experiment, 1.20 g of H2A reacts with 1.00 g of XOH to form 0.985 g of X2A. What is the percentage yield of the react...
Wed Oct 04, 2017 12:18 am
Forum: Limiting Reactant Calculations
Topic: Homework problem L.7b
Replies: 1
Views: 1920

### Homework problem L.7b

The camel stores the fat tristearin, C57H110O6, in its hump. As well as being a source of energy, the fat is also a source of water because, when it is used, the reaction 2 C57H110O6(s) + 163 O2(g) -> 114 CO2(g) + 110H2O(l) takes place. What mass of oxygen is needed to oxidize this amount of trister...