## Search found 60 matches

Sat Mar 17, 2018 12:04 am
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Cell Diagram: Porous Disk and Salt Bridge
Replies: 5
Views: 462

### Re: Cell Diagram: Porous Disk and Salt Bridge

i believe that when using a porous disk we use a single line, and when using a salt bridge we use a double line.
Fri Mar 16, 2018 11:53 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: Test 2 Question 8 wording
Replies: 3
Views: 342

### Re: Test 2 Question 8 wording

Hi, I believe that Test 2 question 8 is different for different discussion sections. Would you be able to send the problem?
Fri Mar 16, 2018 11:42 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Porous disk
Replies: 1
Views: 170

### Re: Porous disk

The problem should tell us whether or not we should use a porous disk or a salt bridge.
Fri Mar 16, 2018 8:24 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: 9.1
Replies: 5
Views: 540

### Re: 9.1

Hi! Because it asks for the rate your body generates heat "in your surroundings" the formula has a -q. This because the system is releasing heat into the surroundings, or heat is flowing out of the system (with the system being the body).
Fri Mar 16, 2018 6:26 pm
Forum: General Rate Laws
Topic: Substitution Reactions
Replies: 2
Views: 228

### Re: Substitution Reactions

The way I understand it, Intermediates come into the reaction as a product, and are later consumed so they do not show up in the overall reaction equation. Catalysts are reactants that speeds up the reaction and go away but show up again in the product, so they also cancel out, and do not show up in...
Fri Mar 16, 2018 6:20 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: State functions?
Replies: 9
Views: 772

### Re: State functions?

Yes entropy, enthalpy and Gibb's free energy are all examples of state functions in that they do not depend on the pathway, and instead only rely on the initial and final values. It is important to note that Cell potential (E) is NOT a state function, so if we need to add the values together, we nee...
Fri Mar 16, 2018 6:16 pm
Forum: Kinetics vs. Thermodynamics Controlling a Reaction
Topic: Kinetics Formulas for the Final
Replies: 2
Views: 407

### Re: Kinetics Formulas for the Final

I don't think Dr. Lavelle went over that collision theory formula in lecture, so we shouldn't need to know that, but knowing the concepts would be beneficial for the final.
Fri Mar 16, 2018 6:14 pm
Forum: Arrhenius Equation, Activation Energies, Catalysts
Topic: 15.65 Part b
Replies: 2
Views: 257

### Re: 15.65 Part b

You can determine whether or not the reaction is endothermic or exothermic by looking at the Activation energies. Because the activation of the forward reaction is greater than that of the reverse reaction, it can be determined that the reaction is endothermic. If you think of this graphically, the ...
Fri Mar 16, 2018 6:08 pm
Forum: Arrhenius Equation, Activation Energies, Catalysts
Topic: Activation Energy
Replies: 5
Views: 521

### Re: Activation Energy

Every step of the overall reaction has its own unique activation energy so on the graph you will observe different Ea for each step.
Fri Mar 16, 2018 2:39 am
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Question 15.87
Replies: 1
Views: 236

### Question 15.87

this question asks- "Under what conditions can these two mechanisms be distinguished by using kinetic data?" Could someone please explain what this means and what the answer might be? Thanks!
Fri Mar 16, 2018 2:30 am
Forum: Arrhenius Equation, Activation Energies, Catalysts
Topic: Question 15.95
Replies: 1
Views: 184

### Question 15.95

For this problem, we are given a reaction profile. From this we can tell that there are three steps to the reaction. In part c we are told that a catalyst is added that accelerates the third step only. the question in part c asks, "What affect if any will the catalyst have on the rate of the ov...
Thu Mar 15, 2018 2:55 pm
Forum: *Amines
Topic: Memorization
Replies: 2
Views: 671

### Re: Memorization

A good way to memorize some of them is by thinking of how some molecules are like others with a little change. For example you could think of a ketone as an aldehyde that has a double-bonded O in the middle rather than at the end, and a carboxylic acid is pretty much a ketone that has an OH (alcohol...
Thu Mar 15, 2018 2:51 pm
Forum: Calculating Work of Expansion
Topic: Irreversible and Reversible Expansion
Replies: 1
Views: 171

### Re: Irreversible and Reversible Expansion

Reversible expansion occurs when the pressure outside the system matches that inside the system, so that if there was a slight change in pressure cause the reaction to move a specific way. Irreversible expansion occurs when you are told that the system is working with a constant pressure or against ...
Thu Mar 15, 2018 2:41 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Test 2 #6
Replies: 3
Views: 281

### Re: Test 2 #6

The Cell Diagram should be Pt(s)|O3(g),O2(g)|OH-(aq)||O2(g),O3(g)|H+(aq)|Pt(s)
Thu Mar 15, 2018 2:39 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Test 2 #6
Replies: 3
Views: 281

### Re: Test 2 #6

We were supposed to use the half reactions on the back sheet provided to us. By comparing the two reactions, we can find which reaction will take place in the anode by looking at the one with the lower reduction potential. This means that this should be an oxidation reaction, so we can flip the equa...
Thu Mar 15, 2018 2:28 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: 14.13 b
Replies: 4
Views: 369

### Re: 14.13 b

an inert metal conductor like Pt(s) needs to be added to the left side because I2(s) is a nonconductive nonmetal solid.
Thu Mar 15, 2018 2:25 pm
Forum: *Enzyme Kinetics
Topic: Catalysts in a reaction
Replies: 12
Views: 1040

### Re: Catalysts in a reaction

If the catalyst shows up in the reactant side, then it must show up again in the products side of the equation at some step (not necessarily only the second) because catalysts cannot be totally consumed by the reaction.
Thu Mar 15, 2018 2:17 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Test #2 #7
Replies: 5
Views: 860

### Re: Test #2 #7

Hi! To answer solve this problem you had to first identify the two half reactions involved. They were (Cr2O7)^2- (aq) +14H+(aq) +6e- ==> 2(Cr)^3+ (aq) + 7(H2O)(l) with a standard cell potential of 1.33V and Cr^3+ +3e- ==> Cr(s) with a standard cell potential of -0.74V. THEN because cell potential is...
Thu Mar 15, 2018 2:08 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: 8.57
Replies: 1
Views: 173

### Re: 8.57

Hi, this is just an example of Hess' Law where we add the reactions together to get the final overall balanced overall reaction and the overall reaction enthalpy. I do not think we will be expected to know the balanced equations of formations of compounds without any information given to us on the f...
Thu Mar 15, 2018 1:59 pm
Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
Topic: Test #2 Question 5B
Replies: 2
Views: 341

### Re: Test #2 Question 5B

Hi, I2 and Br2 are actually in the reactants side. They accept 2e- and thus become 2I- ad 2Br-. We don't reverse these equations because this is naturally what happens. I think what you were talking about was whether or not we had to flip the equation for Al because that is in the product side. We d...
Thu Mar 15, 2018 1:43 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Collision theory for Reaction Mechanisms
Replies: 2
Views: 240

### Collision theory for Reaction Mechanisms

Hi! Sorry if this is phrased in a confusing way- I was wondering why collision theory allows us to use the number of molecules colliding (the coefficient) to find the order of the reaction when we are finding reaction mechanisms, when typically for chemical reactions the order must be determined exp...
Thu Mar 15, 2018 1:38 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Questions in the second test
Replies: 2
Views: 305

### Re: Questions in the second test

for an element to have high oxidizing power, it would have to have a more positive value for reduction potential. This is because the higher the reduction potential, the better the element is at being reduced. An element that is being reduced is called the oxidizing agent because it is accepting ele...
Tue Feb 27, 2018 5:30 pm
Forum: Calculating Standard Reaction Entropies (e.g. , Using Standard Molar Entropies)
Topic: Midterm question 6a
Replies: 5
Views: 578

### Re: Midterm question 6a

Hi, The question was "Which of the following statements is correct?" and both A and B (shown below) were accepted as correct answers on the past midterm. My question is, in the future, which answer is correct? Should we think that any gas always has more entropy than any liquid? If not, ho...
Mon Feb 26, 2018 2:11 pm
Forum: Student Social/Study Group
Topic: Post All Chemistry Jokes Here
Replies: 8894
Views: 1574238

### Re: Post All Chemistry Jokes Here

Hey are you made of Curium and Tellurium??
'Cause dang you're CuTe!
Mon Feb 26, 2018 2:01 pm
Forum: Calculating Standard Reaction Entropies (e.g. , Using Standard Molar Entropies)
Topic: Midterm question 6a
Replies: 5
Views: 578

### Midterm question 6a

On this problem on the midterm, both A and B were considered correct answers. For future reference, what answer is correct? Should we think that any gas always has more entropy than any liquid? If not, how do we know if a molecule is complex enough to have more entropy as a liquid than a simple mole...
Mon Feb 26, 2018 1:55 pm
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: 14.37 part a
Replies: 2
Views: 177

### Re: 14.37 part a

This is possible because HCl is aqueous, and thus dissolves into H+ and Cl- ions. Since the other reactant/product is H2, the half reaction only involves the H+ ion from HCl.
Mon Feb 26, 2018 1:47 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: changing sign of of standard cell potentials
Replies: 4
Views: 447

### changing sign of of standard cell potentials

Are we allowed to change the sign (as in multiply by -1) of the standard cell potentials of the half reactions if we are looking for the standard cell potential of the reverse half reaction? I had thought that this was not possible because reversing a reduction half reaction makes it an oxidation re...
Mon Feb 26, 2018 1:36 pm
Forum: General Rate Laws
Topic: Half Rxns [ENDORSED]
Replies: 2
Views: 194

### Re: Half Rxns[ENDORSED]

Substances that more readily decompose are less stable, and thus decompose fast causing it to have a shorter half life.
Substances that do not readily decompose are more stable, and thus decompose relatively slowly, causing it to have a longer half life.
Mon Feb 26, 2018 1:33 pm
Forum: Thermodynamic Systems (Open, Closed, Isolated)
Topic: Isolated [ENDORSED]
Replies: 3
Views: 530

### Re: Isolated[ENDORSED]

the universe can be considered isolated because energy nor matter can leave or enter the universe.
Mon Feb 26, 2018 1:31 pm
Forum: Calculating Work of Expansion
Topic: Midterm Q4A [ENDORSED]
Replies: 4
Views: 402

### Re: Midterm Q4A[ENDORSED]

Hi! I also made this same mistake and treated it as though pressure was not constant. The thing is that it is never explicitly states that the system is reversible, or that the external pressure matches the internal pressure. Therefore you can assume that pressure remains constant throughout the pro...
Tue Feb 13, 2018 6:02 pm
Forum: Thermodynamic Systems (Open, Closed, Isolated)
Topic: "Ideal"
Replies: 6
Views: 498

### Re: "Ideal"

The point of telling us that a gas is ideal and monoatomic is so that we know we can use the constants Cv= 3/2R and Cp= 5/2R.This allows us to calculate work and entropy when only either volume or pressure remains constant, or the reaction is reversible.
Tue Feb 13, 2018 5:58 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: 11.83
Replies: 1
Views: 143

### Re: 11.83

Hi, In this problem we actually use both of those methods to ultimately solve for k at each temperature. We cannot directly use the equation delta G(standard) = -RTlnK because we do not know G(standard) in 11.83. Thus we need to solve for it using the formula delta G(standard)= delta H(standard)- T*...
Sun Jan 14, 2018 7:01 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Which q is negative?
Replies: 2
Views: 152

### Which q is negative?

Hi! When solving a problem where heat transfers from one object to another, like from copper to water for instance, how do we know which heat is negative and which is positive? I thought that in a situation where heat is being transferred from a piece of copper to the water, the copper would have ne...
Fri Jan 12, 2018 4:18 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Are there any periodic trends for enthalpy?
Replies: 4
Views: 215

### Are there any periodic trends for enthalpy?

I was just wondering if there was any trend for bond enthalpy? Does it correspond to bond strength or ionization energy or anything like that?
Fri Jan 12, 2018 4:10 pm
Forum: Phase Changes & Related Calculations
Topic: Irreversible process vs reversible process
Replies: 4
Views: 206

### Re: Irreversible process vs reversible process

To my understanding, an irreversible reaction can only go in one direction, such that when the reactants react to become the product, the product cannot convert back into reactants. These reactions are represented with a unidirectional arrow, and can never be at equilibrium. On the contrary, reversi...
Thu Dec 07, 2017 6:30 pm
Forum: Calculating pH or pOH for Strong & Weak Acids & Bases
Topic: 12.19
Replies: 1
Views: 229

### Re: 12.19

[HCl]0 does represent the initial value. for 12.19, we do not need to know the actual value for [HCl]0 as this value cancels out because it is in both the numerator and denominator. Hope this helps!
Thu Dec 07, 2017 6:25 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Pi bond
Replies: 3
Views: 369

### Re: Pi bond

it depends on whether the molecule has resonance structures or not. If the pi bond is in a molecule that has resonance, then it is delocalized. If it is in a molecule that does NOT have resonance such that the pi bond is between only two atoms, then it is localized. Hope this Helps!
Thu Dec 07, 2017 6:23 pm
Forum: Acidity & Basicity Constants and The Conjugate Seesaw
Topic: Relationship between Kpa and Ph
Replies: 3
Views: 612

### Re: Relationship between Kpa and Ph

Ka describes the rate at which the acid deprotonizes and gives an H+ atom to H20. The concentration of H30+ is described by pH. Kb is the same except for bases, where Kb describes the rate at which the base gains protons from H20, and pOH represents the concentration of OH- molecules.
Wed Dec 06, 2017 3:32 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Calculations using ice box
Replies: 4
Views: 406

### Re: Calculations using ice box

You can also use the 5% rule, which states that if the value of x is less than or equal to 5% of the initial, then you can assume the equilibrium amount to be approximately the same value.
Wed Dec 06, 2017 3:28 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: 4.13 (b)
Replies: 1
Views: 214

### Re: 4.13 (b)

I also share the same question. I believe that the solution manual may be wrong because this molecule does not have resonance and thus the pi bond is localized, which means the presence of a double bond should decrease the Cl-P-Cl bond angles to make them less than 109.5 degrees. If this is wrong, I...
Wed Dec 06, 2017 3:25 pm
Forum: Shape, Structure, Coordination Number, Ligands
Topic: Polarity/Dipole Moment
Replies: 2
Views: 222

### Re: Polarity/Dipole Moment

A bond can be polar if there is a large difference in electronegativity between two atoms. This difference in electronegativity also expresses how big the dipole moment is. A molecule can have polar bonds and dipole moments between two atoms, but if the bonds in this molecule are symmetrical such th...
Wed Dec 06, 2017 2:53 pm
Forum: Hybridization
Topic: Delocalized pi bonds [ENDORSED]
Replies: 2
Views: 308

### Re: Delocalized pi bonds[ENDORSED]

A localized pi bond occurs when there is only 1 pi bond between two atoms and the molecule has no resonance structures.
Wed Dec 06, 2017 2:50 pm
Forum: Limiting Reactant Calculations
Topic: Limiting reagent [ENDORSED]
Replies: 3
Views: 311

### Re: Limiting reagent[ENDORSED]

Another way you can find the limiting reactant is by converting the masses of each reactant to moles and than comparing that molar ratio to that which is described by the balanced equation. For example if the left side of an equation was 2Cl + 4H and once converting the mass of each reactant to mole...
Mon Dec 04, 2017 8:51 pm
Forum: Bronsted Acids & Bases
Topic: Bronsted Acid and Base vs Lewis Acid and Base
Replies: 3
Views: 433

### Re: Bronsted Acid and Base vs Lewis Acid and Base

To add on to the previous response, a Lewis acid is an electron PAIR acceptor, and a lewis base is a electron PAIR donor.
Mon Dec 04, 2017 8:33 pm
Forum: Properties & Structures of Inorganic & Organic Acids
Topic: F and Cl in acids
Replies: 2
Views: 344

### Re: F and Cl in acids

To add on to the previous response, C2O2HF3 is a stronger than C2O2HCl3, because the F atom is more electronegative than the Cl atom, which means that it will pull pull more electrons from the Oxygen, which thereby makes it easier for the oxygen to loose the H+ ion.
Mon Dec 04, 2017 3:17 pm
Forum: Calculating pH or pOH for Strong & Weak Acids & Bases
Topic: Sig Figs for Calculating pH and pOH
Replies: 4
Views: 466

### Re: Sig Figs for Calculating pH and pOH

1.60 actually has 3 sig figs, because all 0's after nonzero values after the decimal count as sig figs. I believe the correct answer would be 1.6, with 2 sig figs as was used in the original question.
Mon Dec 04, 2017 3:09 pm
Forum: Dipole Moments
Topic: Dipole moments on test 4
Replies: 2
Views: 323

### Re: Dipole moments on test 4

None of these molecules have dipole moments because the more electronegative atoms in each compound are surrounded symmetrically around the central atom. For example in PCl5, the Chlorine atoms surround the central atom equally in a trigonal bi-pyramidal fashion. Dipole movements would only occur if...
Fri Nov 17, 2017 10:19 am
Forum: Determining Molecular Shape (VSEPR)
Topic: Hybridization of VSEPR Models
Replies: 2
Views: 201

### Re: Hybridization of VSEPR Models

If I understand what you are asking correctly, You look at the number of bonding regions (bonds and lone pairs) that a central atom in a molecule has. For Example, CH4 has 4 bonding regions, and will thus be sp3 hybridization. Hope this helped!
Fri Nov 17, 2017 10:16 am
Forum: Hybridization
Topic: axial vs equatorial lone pair
Replies: 2
Views: 979

### Re: axial vs equatorial lone pair

If I understood it correctly, I believe that the lone pairs will always be equatorial first, before going to the axial positions (so seeing lone pairs in the axial position is quite uncommon). This is because lone pairs have more repulsion (they don't want to have a smaller bond angle in relation to...
Thu Nov 09, 2017 3:26 pm
Forum: Limiting Reactant Calculations
Topic: Extra Practice Problem #2
Replies: 2
Views: 263

### Re: Extra Practice Problem #2

Also to find the total hydrogen produced, you need to add the hydrogen produced in the first reaction to the hydrogen produced in the second reaction.
Thu Nov 09, 2017 2:58 pm
Forum: Electronegativity
Topic: problem 3.75
Replies: 1
Views: 259

### Re: problem 3.75

HI! Perhaps you read the solution manual wrong? you are right in that Beryllium should have a greater value for electropositivity than Lithium. Checking my solutions manual for the same problem you are referring to, the answer agrees with that answer and is correct.
Thu Nov 09, 2017 2:53 pm
Forum: Properties of Light
Topic: Atomic Spectra
Replies: 2
Views: 225

### Re: Atomic Spectra

Higher Frequency means higher energy, as can be told from the formula E=hv, where v is frequency. Because v and wavelength (λ) are inversely related in c=λ v, the larger the wavelength, the lower the frequency, and so the lower the energy.
Thu Nov 09, 2017 2:48 pm
Forum: Heisenberg Indeterminacy (Uncertainty) Equation
Topic: Test 3, Question #1
Replies: 3
Views: 355

### Re: Test 3, Question #1

Hi! So because the uncertainty in velocity is 1.5 +/- 4m/s, the delta v is 0.8 m/s. To find delta p, you multiply delta v by the mass of an electron (9.11 x10^-31 kg). Then to find delta x, you do h/(4pi)/delta p which numerically is (6.626 x 10 ^-34)/(4 x pi)/(0.8 x (9.11 x 10-31)) and you get the ...
Thu Nov 09, 2017 2:41 pm
Forum: Limiting Reactant Calculations
Topic: Extra Practice Problem #2
Replies: 2
Views: 263

### Re: Extra Practice Problem #2

Hi! I'm guessing that the second reaction uses H2O in excess? If so, then first you find the limiting reagent in the first reaction, and calculate the maximum amount of CO that can be produced while keeping the limiting reactant in mind. The product, CO, from the first reaction is used as a reactant...
Thu Nov 09, 2017 2:35 pm
Forum: Lewis Structures
Topic: Lewis Structure of SO2
Replies: 1
Views: 998

### Lewis Structure of SO2

Hi! I was just wondering if the Lewis structure of SO2, sulfur dioxide, has two double bonds between S-O with a lone pair on Sulfur (making expanded octet), OR if it has one single bond and one double bond, with one lone pair on Sulfur (allowing it to stay within the octet rule). The first option al...
Mon Nov 06, 2017 11:12 am
Forum: Wave Functions and s-, p-, d-, f- Orbitals
Topic: Energy of subshells
Replies: 2
Views: 199

### Re: Energy of subshells

4d has a greater energy than 5s when the 4d orbitals are empty. However when the 4d orbital starts to fill up with electrons, it has a lower energy than 5s because the electrons in the 4d orbital shield the electrons in the 5s orbital. Therefore when an element in the d-block is ionized, or loses el...
Fri Oct 27, 2017 10:47 am
Forum: Electron Configurations for Multi-Electron Atoms
Topic: Zn1+
Replies: 2
Views: 519

### Re: Zn1+

Yes, the electron configuration for Zn1+ is [Ar]3d^10 4s^1, the same as that of Cu. This is because electrons are removed from the higher energy level, which in this case would be the 4s level. Further more, due to electron shielding that results from all the electrons in the 3d orbital, the 4s ener...
Mon Oct 23, 2017 11:41 am
Forum: Electron Configurations for Multi-Electron Atoms
Topic: electron configuration for cation of Cr? [ENDORSED]
Replies: 1
Views: 138

### electron configuration for cation of Cr?[ENDORSED]

Hi! I was just wondering what the electron configuration would be of a cation of Cr, as Cr is an exception to the usual notation? So if one electron was lost from Cr, which has the neutral notation of [Ar](3d^5)(4s^1), what would the notation become?
Fri Oct 20, 2017 10:23 am
Forum: Photoelectric Effect
Topic: Energy emitted from an Electron [ENDORSED]
Replies: 4
Views: 528

### Energy emitted from an Electron[ENDORSED]

Hi! I just wanted to clarify if when we are calculating for the energy emitted by an electron that is relaxing from n=5 to n=1, would the initial energy level be n=5 and the final level be n=1? Or would the initial be n=1 and the final be n=5?
Fri Oct 20, 2017 10:06 am
Forum: DeBroglie Equation
Topic: When to use De Broglie Equation [ENDORSED]
Replies: 11
Views: 3104

### Re: When to use De Broglie Equation[ENDORSED]

In addition to what everyone else has already said, it is important to note that DeBroglie's Eq is reserved for objects that have momentum. An objects momentum (p) is equal to its mass (m) times its velocity (v). This is why DeBroglie's equation has the notation λ=h/p, where λ is wavelength, h is Pl...