## Search found 87 matches

Sun Mar 18, 2018 4:03 pm
Forum: Student Social/Study Group
Topic: Final
Replies: 11
Views: 1235

### Re: Final

I believe the overall idea is that you'd want to use the Nernst equation to write a general eq. that sets [Zn2+] equal to some function of Ecell, with all other values plugged in and solved for.
Sat Mar 17, 2018 4:00 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Replies: 1
Views: 232

### Re: Linking Degeneracy and Entropy

Ah, I got it! The first line should read Nkln(V2/V1), where N is the number of molecules.
Sat Mar 17, 2018 3:40 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Replies: 1
Views: 232

In the notes, we determine that deltaS = Kb * ln(V2/V1).

The next line states that deltaS = nR ln(V2/V1). How do we transition from Kb to nR ?
Sun Mar 11, 2018 5:08 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Rate Constants, Special EQ Situation?
Replies: 1
Views: 140

### Rate Constants, Special EQ Situation?

Let's say we have the reaction A + B --> C + D; we know that the rates of the forward and reverse reactions are equal at equilibrium (EQ). In the case where [C][D] = [A][B] at EQ, would this mean that the rate constants of the forward and reverse reactions are also equal? If so, is this the only typ...
Sun Mar 11, 2018 5:05 pm
Forum: Arrhenius Equation, Activation Energies, Catalysts
Topic: Reasoning Behind Arrhenius Equation
Replies: 1
Views: 117

### Reasoning Behind Arrhenius Equation

How did Arrhenius determine why plotting lnk vs. 1/T yields a straight line (i.e. what was his reasoning)?
Sun Mar 11, 2018 5:03 pm
Forum: Arrhenius Equation, Activation Energies, Catalysts
Topic: A and Ea: Slight Temperature Dependence
Replies: 1
Views: 98

### A and Ea: Slight Temperature Dependence

In Chapter 15, Section 11 of the text, it states "A and Ea are nearly independent of temperature." Even though this difference is negligible, I'm curious:

In what ways can temperature slightly affect Ea and A?
Sun Mar 04, 2018 4:17 pm
Forum: Second Order Reactions
Topic: Linearization of a Second Order Reaction
Replies: 3
Views: 663

### Re: Linearization of a Second Order Reaction

Thank you, this makes sense! However, if we were to graph [A]t = kt + [A]0, we would not have a straight line.

Perhaps a better way to phrase my question is: why do we take the inverse of [A] for a 2nd order reactant in order to linearize the graph?
Sun Mar 04, 2018 4:13 pm
Forum: First Order Reactions
Topic: Clarification on Integrated Rate Law
Replies: 1
Views: 165

### Clarification on Integrated Rate Law

The integrated rate law for a first order reactant is written as ln[A] = -kt + ln[A] 0 . However, some reactions will eventually begin to run in the reverse direction, and the delta[A] will depend on the difference in the rates between the forward and reverse reactions. So when the rate law is given...
Sun Mar 04, 2018 4:08 pm
Forum: Method of Initial Rates (To Determine n and k)
Topic: Rate Constant in Terms of B, C, D, etc.
Replies: 1
Views: 155

### Rate Constant in Terms of B, C, D, etc.

Given the reaction aA + bB --> cC + dD:

The rate constant k is often given in terms of "loss of A." How would k be different if it were given in terms of the loss of B, the gain of C, or the gain of D? How would the integrated rate laws and their graphs be different?
Sun Mar 04, 2018 4:05 pm
Forum: Second Order Reactions
Topic: Second Order/Zero Order Half-Life
Replies: 2
Views: 211

### Second Order/Zero Order Half-Life

Why is it that the half-lives for zero order and second order reactants depend on initial concentration (but not of first order)?

I understand the mathematical derivation, so a theoretical/conceptual answer would be appreciated !
Sun Mar 04, 2018 4:02 pm
Forum: First Order Reactions
Topic: Molecular Basis for First and Second Order? [ENDORSED]
Replies: 1
Views: 331

### Molecular Basis for First and Second Order?[ENDORSED]

In terms of molecular interactions, how can we explain the behavior of reactants that are first and second order?
Sun Mar 04, 2018 3:58 pm
Forum: Second Order Reactions
Topic: Linearization of a Second Order Reaction
Replies: 3
Views: 663

### Linearization of a Second Order Reaction

For a reactant A that is 2nd order, when we graph 1/[A] vs. time, which mathematical property justifies the fact that taking the inverse of the concentration yields a straight line?
Sun Feb 25, 2018 10:24 pm
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: 14.43
Replies: 1
Views: 187

### Re: 14.43

When you subtract 0.14V from 0.061V, you would indeed get a negative number.

However, keep in mind that the -RT/nF * lnQ term of the Nernst equation has a -1 as the coefficient, so the overall values you work with will be positive.
Sun Feb 25, 2018 10:19 pm
Forum: Balancing Redox Reactions
Topic: Recognizing a redox reaction in acidic or basic solution
Replies: 5
Views: 301

### Re: Recognizing a redox reaction in acidic or basic solution

If given a redox reaction to balance, the question will explicitly state whether it's in acidic or basic solution. Some textbooks may not (I'm not sure if ours is one of them), but in these cases, it's generally assumed that the reaction takes place in an acidic solution. If you're unsure, feel free...
Sun Feb 25, 2018 10:16 pm
Forum: Calculating Work of Expansion
Topic: Midterm Q4A
Replies: 3
Views: 213

### Re: Midterm Q4A

That would be because the -nRTlnV2/V1 equation is used for reversible, isothermal expansion; because the problem describes expansion against a constant, external pressure of 0.5 atm, we'd use w = -PexdeltaV

Hope this helps!
Sun Feb 18, 2018 9:45 pm
Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
Topic: n
Replies: 3
Views: 231

### Re: n

n refers to the number of electrons transferred in a chemical equation For example, in the equation 10I - + 16H + + 2MnO 4 - --> 5I 2 + 2Mn 2+ + 8H 2 O, one way we can determine n is: 1) the oxidation number of Mn in the reactants is +7, and Mn is reduced to +2 2) the difference in charge is 5, so f...
Sun Feb 18, 2018 9:38 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Eº in 14.11, 13, 15
Replies: 2
Views: 214

### Re: Eº in 14.11, 13, 15

When adding the half-reactions, we want to form a chemical equation such that Eº is positive and maximized. By writing out the Eº of each half-reaction, we can determine which is oxidized and which is reduced.
Sun Feb 18, 2018 9:33 pm
Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
Topic: Nernst Equation
Replies: 6
Views: 487

### Re: Nernst Equation

nr is essentially the molar coefficient (in this case, the number of moles of e- transferred); nr is unitless

Reference: P. 429
Sun Feb 11, 2018 3:08 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Gibbs free energy and spontaneity
Replies: 3
Views: 207

### Re: Gibbs free energy and spontaneity

A spontaneous process is one that increases the entropy of the universe, which we can calculate by taking the sum deltaS sys + deltaS surr . So deltaG is not the ONLY way to determine thermodynamic favorability, but as it is often difficult to measure the change in entropies of system and surroundin...
Sun Feb 11, 2018 3:04 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: 8.49
Replies: 3
Views: 229

### Re: 8.49

Under conditions of constant pressure, deltaH = q because the work of expansion terms cancel out:

H = U + PV
deltaH = deltaU + PdeltaV
deltaH = q + w +PdeltaV
w = -PexdeltaV
deltaH = q - PdeltaV + PdeltaV

deltaH = q
Sun Feb 11, 2018 2:48 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: 9.13
Replies: 3
Views: 209

### Re: 9.13

N2 is a diatomic gas and has more degrees of freedom due to greater rotational energy. Cv is 5/2R
Sun Feb 11, 2018 2:07 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: Equation for Entropy
Replies: 1
Views: 135

### Re: Equation for Entropy

The internal energy U is a state property, so deltaU is also a state function. In both a reversible and irreversible process, the initial and final states are the same, but the magnitude of reversible work is greater than that of the magnitude of irreversible work. deltaU = q + w since wrev is more ...
Sat Feb 10, 2018 8:13 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: deltaG=0, Phases Coexist ?
Replies: 2
Views: 239

### deltaG=0, Phases Coexist ?

When, for example, Br2(l) --> Br2(g), it is said that at the boiling point, the liquid and gaseous phases are in equilibrium and coexist. How would we visualize the "coexistence" of two different phases? ^I understand this concept in terms of spontaneity but am unsure of what it means in t...
Thu Feb 01, 2018 12:37 am
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: The value of Cp
Replies: 8
Views: 592

### Re: The value of Cp

Yup--for a monatomic ideal gas, Cv = 3/2R and Cp = Cv + R = 5/2R

Note that for diatomic gases, it gets a little tricker (e.g. for N2, Cv = 5/2R) due to more rotational degrees of freedom
Thu Feb 01, 2018 12:32 am
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: Entropy: Units and Justification
Replies: 1
Views: 115

### Entropy: Units and Justification

Conceptually, how can we justify the units (J/K) of entropy ?
Thu Feb 01, 2018 12:29 am
Forum: Thermodynamic Systems (Open, Closed, Isolated)
Topic: Can a system exchange matter but not energy?
Replies: 4
Views: 223

### Re: Can a system exchange matter but not energy?

A fourth way to think about this is that, in some way, matter IS energy... think of the eq. E = mc^2
Thu Feb 01, 2018 12:23 am
Forum: Gibbs Free Energy Concepts and Calculations
Topic: phase change change in entropy
Replies: 2
Views: 145

### Re: phase change change in entropy

During the phase change, the transfer of heat is reversible, and since we assume the phase change to take place at 1 atm, q = deltaH
Thu Feb 01, 2018 12:21 am
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: Entropy as a Probability
Replies: 1
Views: 108

### Entropy as a Probability

I recall reading somewhere that we can treat every possible microstate of a system as having a certain probability of occurring--and that the microstate exhibiting the most "freedom" has the highest probability of occurring and is the one the system will naturally tend toward. My question ...
Thu Feb 01, 2018 12:10 am
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: q(rev)
Replies: 1
Views: 156

### Re: q(rev)

The equation deltaS = q/T determines the change in entropy at constant temperature. Only when the heat transfer is reversible is the T relatively constant (theoretically, it changes a very minute amount, so we approximate it as constant temperature)
Thu Feb 01, 2018 12:07 am
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: Question 9.1 part a
Replies: 1
Views: 78

### Re: Question 9.1 part a

Sure! The units of watts are J/s (another way we can look at this is by saying "every second, x J of heat are given off"), and we can calculate the change in entropy using the equation deltaS = q/T. This would be the entropy change per second. Overall, I'd say try to focus on the thermodyn...
Thu Jan 18, 2018 2:25 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: 8.47
Replies: 1
Views: 141

### Re: 8.47

When work is done on the system, energy is being input, so we can think about it as a positive change in the system's energy
Thu Jan 18, 2018 2:22 pm
Forum: Phase Changes & Related Calculations
Topic: 8.39
Replies: 2
Views: 140

### Re: 8.39

There's a section in the book on calorimetry; probably around 8.4 or 8.5
Sun Jan 14, 2018 3:40 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: 8.43 Heat Capacity (Units)
Replies: 1
Views: 115

### 8.43 Heat Capacity (Units)

For Exercise 8.43, is there a reason why heat capacity is given in J/mol ?

Heat capacity is the amount of energy required to raise the temperature of a substance by 1 degree C (or 1 K ), so shouldn't the units be J/degree C ?
Sun Jan 14, 2018 3:36 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Different Molar Heat Capacities For Gases
Replies: 5
Views: 374

### Re: Different Molar Heat Capacities For Gases

The molar heat capacity at constant volume would be lower than that at constant pressure because all the heat goes into increasing the internal energy.
Thu Jan 11, 2018 5:29 pm
Forum: Phase Changes & Related Calculations
Topic: Phase Change Calculations
Replies: 2
Views: 194

### Re: Phase Change Calculations

It would be useful to know the standard enthalpies of fusion and vaporization for water since we do so many exercises on them.

On a test, the standard enthalpies of other substances (e.g. copper) will almost definitely be provided.
Thu Jan 11, 2018 5:27 pm
Forum: Phase Changes & Related Calculations
Topic: Enthalpy is a state property
Replies: 13
Views: 734

### Re: Enthalpy is a state property

Yep!
Thu Jan 11, 2018 2:20 am
Forum: Phase Changes & Related Calculations
Topic: Enthalpy of Freezing
Replies: 4
Views: 469

### Re: Enthalpy of Freezing

Yep, that's right! I think Kaelie made a small error in her 1st statement, but everything else is correct.
Thu Jan 11, 2018 2:16 am
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Equation for a non-state property?
Replies: 4
Views: 212

### Re: Equation for a non-state property?

For expansion work under constant external pressure, you can use the eq. w = -P external * deltaV to calculate the work done by the system. There's also a table somewhere in the beginning of Chapter 8, which if I remember correctly, lists various types of work. As for heat, when pressure is constant...
Thu Jan 11, 2018 2:06 am
Forum: Phase Changes & Related Calculations
Topic: Energy
Replies: 2
Views: 232

### Re: Energy

An interesting question! The best way I can put it is that energy isn't something that physically "exists" in nature and can't be visualized--I remember reading somewhere that energy is a convenient concept we created as a means of documenting changes in a substance's state. In terms of co...
Thu Jan 11, 2018 1:59 am
Forum: Phase Changes & Related Calculations
Topic: Why steam burns are worse explained
Replies: 5
Views: 282

### Re: Why steam burns are worse explained

In essence, yes. When the steam hits your skin, there is a temperature difference, and heat passes from the steam to your skin as the water vapor condenses. Because there is so much more energy in steam than 100 degree water b/c of the energy "invested" during the phase change, the burn is...
Thu Jan 11, 2018 1:54 am
Forum: Phase Changes & Related Calculations
Topic: Enthalpy is a state property
Replies: 13
Views: 734

### Re: Enthalpy is a state property

Heat would not be considered a state property. Heat represents the transfer of energy to or from a system as a result of temp. change. Even though temperature is a state function, there are many possible paths, for example, that a sample of water can take to go from 10 to 20 degrees C. In one scenar...
Thu Jan 11, 2018 1:49 am
Forum: Calculating Work of Expansion
Topic: Reversible vs. Irreversible Reaction
Replies: 2
Views: 214

### Re: Reversible vs. Irreversible Reaction

In a reversible reaction, an infinitesimally small change in the independent variable reverses the direction of the reaction. In an irreversible reaction, the same change would have no effect on the direction of the reaction. During a reversible reaction, the changes are extremely small, and when ap...
Thu Jan 11, 2018 1:40 am
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: Equipartition Theorem
Replies: 1
Views: 134

### Re: Equipartition Theorem

The equipartition theorem is essentially a means of calculating/estimating the translational and rotational kinetic energies (which are components of internal energy) of molecules in the gaseous state; internal energy itself is comprised of kinetic energy (translational, rotational, or vibrational) ...
Thu Jan 11, 2018 1:30 am
Forum: Phase Changes & Related Calculations
Topic: Phase Changes: Molecular Level [ENDORSED]
Replies: 2
Views: 174

### Phase Changes: Molecular Level[ENDORSED]

During a phase change, why is it that the temperature of the substance does not rise or fall until all of the substance has changes phases?

For example, in the fusion of water from s-->l, why does the temperature of the liquid H2O remain 0 degrees C even though heat is being supplied?
Mon Jul 31, 2017 11:45 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Difference Between Kp and Kc
Replies: 4
Views: 674

### Re: Difference Between Kp and Kc

Kp is an equilibrium involving the partial pressures of the gases involved, whereas Kc (for the same gaseous reaction) is an equilibrium involving the concentrations of the gases. In the former, we would use partial pressure=(nRT)/V, while in the latter, we would have M=n/V=P/(RT). When solving for ...
Mon Jul 31, 2017 11:37 pm
Forum: Lewis Acids & Bases
Topic: Electronegativity and Acid Strength
Replies: 1
Views: 339

### Re: Electronegativity and Acid Strength

Check p. 154 in the course reader. When an ion has a high electronegativity, the bond is more polar, so there is a greater partial positive charge on the H--this the H less tightly held. This trend holds especially true for elements of the same period. As we go down a group, bond length is the deter...
Mon Jul 31, 2017 11:33 pm
Forum: Properties & Structures of Inorganic & Organic Acids
Topic: Identifying Oxoacids
Replies: 1
Views: 387

### Identifying Oxoacids

Rules of thumb for identifying oxoacids based off the chemical formula? I am afraid of overgeneralizing and stating that all acids containing O are oxoacids...
Mon Jul 31, 2017 11:29 pm
Forum: *Titrations & Titration Calculations
Topic: Stoichiometric Point Ca(OH)2 and HCOOH
Replies: 2
Views: 720

### Re: Stoichiometric Point Ca(OH)2 and HCOOH

Thanks! A small question though: isn't calcium hydroxide a strong base? From what I remember, it's not very soluble, but it does ionize ~100%….please let me know!
Mon Jul 31, 2017 8:32 pm
Forum: *Titrations & Titration Calculations
Topic: Stoichiometric Point Ca(OH)2 and HCOOH
Replies: 2
Views: 720

### Stoichiometric Point Ca(OH)2 and HCOOH

During the review session today, we did an example where we added a certain volume of NaOH to a aqueous HCOOH such that moles NaOH=moles HCOOH. If we were to use Ca(OH)2, would we simply add half the volume to reach the stoichiometric point? If so, then how would that fit our definition of the stoic...
Mon Jul 31, 2017 8:23 pm
Forum: Calculating pH or pOH for Strong & Weak Acids & Bases
Topic: CH 12 HW problem 12.27 [ENDORSED]
Replies: 1
Views: 1094

### Re: CH 12 HW problem 12.27[ENDORSED]

We multiply the volume by the molarity to determine the moles of HCl added.

We divide the moles HCl by the new volume (250 L) to determine the new molarity.
Tue Jul 25, 2017 8:11 am
Forum: Shape, Structure, Coordination Number, Ligands
Topic: [Fe(NCS)(OH2)5]2+ Naming
Replies: 2
Views: 1690

### Re: [Fe(NCS)(OH2)5]2+ Naming

Thanks, much clearer now! :-)
Mon Jul 24, 2017 9:45 pm
Forum: Shape, Structure, Coordination Number, Ligands
Topic: Polydentates
Replies: 3
Views: 412

### Re: Polydentates

H2O has a bent molecular geometry, so when one lone pair is bonded to the central atom, the other lone pair points about 109 degrees away and is unable to form a bond.
Mon Jul 24, 2017 4:35 pm
Forum: Acidity & Basicity Constants and The Conjugate Seesaw
Topic: pKa+pKb=pKw Conceptually?
Replies: 1
Views: 874

### pKa+pKb=pKw Conceptually?

[H30+][OH-]=10^-14 Mathematically and in terms of equilibrium, I understand this, but how could we explain this on the molecular level? For example, if we had distilled water and added a strong base to it, how would the newly introduced OH- molecules react with water, and how would this reduce the [...
Mon Jul 24, 2017 4:30 pm
Forum: Calculating pH or pOH for Strong & Weak Acids & Bases
Topic: Sig Figs in pH and pOH
Replies: 1
Views: 305

### Sig Figs in pH and pOH

When calculating pH and pOH, do we count sig figs only after the decimal point? I was looking at some in-class examples, where for the same situation (think it was 0.0030 M Ca(OH)2 or something similar), one answer for was stated as 12 while another was stated as 11.78. Both ways make sense, since &...
Mon Jul 24, 2017 4:23 pm
Forum: Trends in The Periodic Table
Topic: Inert Pair Effect
Replies: 1
Views: 323

### Inert Pair Effect

I was reading in Ch. 4 and ended up going back to Ch. 2, but the book's description of the inert pair effect puzzles me: "In the later periods of the periodic table, valence s=electrons are very low in energy because of their good penetration and the low shielding ability of the d-electrons.&qu...
Mon Jul 24, 2017 4:18 pm
Forum: Shape, Structure, Coordination Number, Ligands
Topic: [Fe(NCS)(OH2)5]2+ Naming
Replies: 2
Views: 1690

### [Fe(NCS)(OH2)5]2+ Naming

[Fe( N CS)(OH2)5]2+ is named in the text (p. 741) as thiocyanato(kN)pentaaqua(III)iron In this case why is it that the guidelines for placing ligand names in alphabetical order is ignored? Also, why is the roman numeral placed before the metal name, and why is there no indication in the name that th...
Mon Jul 24, 2017 4:08 pm
Forum: Ionic & Covalent Bonds
Topic: Bond Strongth & Internuclear Distance
Replies: 2
Views: 531

### Bond Strongth & Internuclear Distance

In the picture below (fig. 3.15, p. 93) why is it that, for diatomic molecules, a strong bond has maximum potential energy at a closer internuclear distance than a weak bond?
Mon Jul 24, 2017 4:02 pm
Forum: Ionic & Covalent Bonds
Replies: 1
Views: 210

In a molecule, why isn't an atom's covalent bond radius (in single bonds) dependent on the atom it's bonded to? Would the electron density distribution not be overly affected by the covalently bonded atom's size?
Reference: p. 97 in the text
Sun Jul 23, 2017 12:36 am
Forum: Determining Molecular Shape (VSEPR)
Topic: Chelate
Replies: 1
Views: 302

### Re: Chelate

A bidentate will often follow the pattern: lone pair-spacer-spacer-lone pair (where "spacer" refers to an atom)
A tridentate will often follow the pattern: lone pair-spacer-spacer-lone pair-spacer-spacer-lone pair

Examples of this are ethylenediamine and diethylenediamine, respectively.
Sun Jul 23, 2017 12:31 am
Forum: Determining Molecular Shape (VSEPR)
Topic: Chatper 17 HW: 17.29 (c)
Replies: 1
Views: 305

### Re: Chatper 17 HW: 17.29 (c)

When the compound has an overall negative charge, we add -ate to the end of the metal.
Sun Jul 23, 2017 12:29 am
Forum: Shape, Structure, Coordination Number, Ligands
Topic: Chapter 4 Hw , 4.13A
Replies: 1
Views: 297

### Re: Chapter 4 Hw , 4.13A

When we look at the electron domain (ED) geometry it's trigonal bipyramidal. There are 3 ED's on the equatorial plane (120 degrees apart) and 2 ED's on the axial plane (180 degrees apart). The bond angles between atoms in the equatorial plane and atoms in the axial plane are 90 degrees. Because we w...
Sun Jul 23, 2017 12:20 am
Forum: Dipole Moments
Topic: Question 4.29
Replies: 1
Views: 1378

### Re: Question 4.29

A) 1 and 2 are polar. A polar covalent bond is formed when one atom attracts electrons better than the other (directly related to electronegativity). The Cl is bonded with a C, and of the two, Cl is much more electronegative and holds a partial negative charge, while carbon has a partial positive ch...
Sat Jul 22, 2017 11:59 pm
Forum: Naming
Topic: Naming Ligands
Replies: 4
Views: 444

### Re: Naming Ligands

Personally I used p. 118 in the course reader with Toolbox 17.1 on p. 741 in the text as a supplement; and practiced with some of the in-class examples for fluency. Hope it works just as well for you!
Sat Jul 22, 2017 11:53 pm
Forum: Formal Charge and Oxidation Numbers
Topic: hw ch3. 57
Replies: 1
Views: 284

### Re: hw ch3. 57

Even though both structures have the same overall charge, we should take a deeper look at the formal charges. For the Lewis structure that follows the octet rule, the FC of S is +1, while the FC of each O is -1. For the 3 Lewis structures which do not conform to the octet rule, the FC of S is 0, the...
Sat Jul 22, 2017 11:47 pm
Forum: Ionic & Covalent Bonds
Topic: Homework 3.33
Replies: 2
Views: 278

### Re: Homework 3.33

We would want to form a C=O double bond because that would result in a more stable Lewis structure. When we check the formal charges for the structure with the C=O, all FC's are 0. If we were to form a double bond between C and Cl and a single bond between C and O, the O would have a FC of +1 and th...
Sat Jul 22, 2017 11:44 pm
Forum: Lewis Structures
Topic: 10, 12, or more electrons in extended octet?
Replies: 1
Views: 323

### Re: 10, 12, or more electrons in extended octet?

You would have to take into account the total number of electrons available as well as how many bonds the central atoms makes.

As a general guideline I've found that compounds comprised of halogens and noble gases (e.g. ClF3, XeF2, SF6, SeF4) tend to have expanded octets.
Sat Jul 22, 2017 11:37 pm
Forum: Lewis Structures
Topic: Problem 3.45
Replies: 2
Views: 343

### Re: Problem 3.45

Yep, and adding on to that a bit, if you think of the molecular geometry, the placement of the atoms in space is the same regardless of how the Lewis structure is drawn.
Sat Jul 22, 2017 8:57 pm
Forum: Lewis Structures
Topic: Chapter 3, Question 61
Replies: 1
Views: 206

### Re: Chapter 3, Question 61

Write the formal charge next to the element. If the compound has an overall charge, then write that around the brackets.
Sat Jul 22, 2017 8:53 pm
Forum: Lewis Structures
Topic: Tips for completing Lewis Structures
Replies: 4
Views: 430

### Re: Tips for completing Lewis Structures

Amino acids follow the structure of a central C bonded to an amine (NH2), a carboxyl group (COOH), a H, and an R group. Without getting too deep into the biochemistry, we can essentially think of an R group as any group of C or H attached to the rest of the molecule. In the case of glycine, the simp...
Sat Jul 22, 2017 8:38 pm
Forum: Lewis Structures
Topic: Formal Charge Relationship
Replies: 1
Views: 250

### Re: Formal Charge Relationship

You, good sir, are correct! The sum of formal charges will equal the overall charge (if any) of the compound.
Sun Jul 16, 2017 1:09 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Bond Angle question when Lone pair exists
Replies: 1
Views: 257

### Re: Bond Angle question when Lone pair exists

That is correct! The presence of a lone pair pushes other bonding regions farther away, so the angle between the atoms of the other bonding regions will decrease. Similarly, the bond angles that include the atom with a lone pair will increase, so it could be said that it's a matter of perspective!
Sun Jul 16, 2017 1:04 pm
Forum: Trends in The Periodic Table
Topic: 1st and 2nd ionization energy? [ENDORSED]
Replies: 7
Views: 2226

### Re: 1st and 2nd ionization energy?[ENDORSED]

The removal of the first electron reduces the effect of electron-electron repulsion, thus increasing the effective nuclear charge.

Because e- are now more tightly held by the nucleus, a greater amount of energy is required to remove yet another e-.
Sun Jul 16, 2017 12:57 pm
Forum: Lewis Structures
Topic: Formal Charge
Replies: 5
Views: 646

### Re: Formal Charge

Correct, the set of formal charges closest to zero (think of it as smallest absolute value) give the most stable Lewis structure.

However, all possible structures contribute to the actual resonance structure, and some (e.g. the more stable structures) more so than others.
Mon Jul 10, 2017 8:13 pm
Forum: Wave Functions and s-, p-, d-, f- Orbitals
Topic: For Exam 1
Replies: 4
Views: 655

### Re: For Exam 1

The exam covers Chapters 1 and 2, so p. 19 to p. 74 in the course reader.
Mon Jul 10, 2017 12:04 am
Forum: Properties of Light
Topic: Problem 1.57
Replies: 1
Views: 222

### Re: Problem 1.57

This question requires that you have some knowledge of spectral lines. The Balmer series, in the visible region, has lines where n 1 =2 (for the record, the Lyman series (UV region) has lines where n 1 =1 and the Paschen series (infrared region) has lines where n 1 =3). The problem gives us 4 lines,...
Sun Jul 09, 2017 11:47 pm
Forum: Wave Functions and s-, p-, d-, f- Orbitals
Topic: Question 2.49
Replies: 2
Views: 338

### Re: Question 2.49

Row 6 of the periodic table includes elements from the f block, so electrons for tungsten come from the f orbital as well.
When we consider both the d-electrons and f-electrons, we have:
2 e- from the s orbital (6s^2)
14 e- from the f orbital (4f^14)
4 e- from the d orbital (5f^4)
for a total of 20.
Sun Jul 09, 2017 11:29 pm
Forum: Lewis Structures
Topic: Formal Charge
Replies: 5
Views: 646

### Re: Formal Charge

Correct, it is a method we use to help identify the most stable structure.
Sun Jul 09, 2017 11:26 pm
Forum: Properties of Electrons
Topic: Energy of an Electron
Replies: 2
Views: 423

### Re: Energy of an Electron

As the e- is totally gone (i.e. when n approaches infinity), the e- has 0 energy. As the e- falls in energy levels, it gives off/loses energy through photons; so from our perspective, the energy becomes negative. An analog to this would be the equation for gravitational potential energy, where 0 pot...
Tue Jul 04, 2017 10:10 pm
Forum: *Shrodinger Equation
Topic: Obtaining the Wave Function
Replies: 3
Views: 460

### Re: Obtaining the Wave Function

Hello! I'm going to preface this response by saying that my answer is in no way completely correct, but I hope a fresh perspective will be useful in your quest for insight. The E k in the Schrodinger Equation equals -h 2 /(2m) * (2nd derivative of the wave function w/ respect to x) Classical mechani...
Tue Jul 04, 2017 9:33 pm
Forum: Wave Functions and s-, p-, d-, f- Orbitals
Topic: Wavefunction and Nodes
Replies: 1
Views: 217

### Wavefunction and Nodes

Hi folks! Can anyone explain why the wavefunction must pass through zero and not simply approach zero in order for there to be a node? With the Born interpretation of a wavefunction, my understanding is that there is a zero probability density whenever the wavefunction is at zero, regardless of whet...
Tue Jul 04, 2017 9:08 pm
Forum: Photoelectric Effect
Topic: Example 1.5
Replies: 3
Views: 486

### Re: Example 1.5

Yes, you are correct, 3.49*10-7 m!

The textbook's conversion to 349 nm also corresponds.
Tue Jul 04, 2017 8:58 pm
Forum: Balancing Chemical Reactions
Topic: Fundamental H11
Replies: 2
Views: 573

### Re: Fundamental H11

Since we have CO on one side of the equation and Co 2 on the other side, we can't simply balance the oxygens by having 9/2C0 2 on the products side, since the carbons would then be unbalanced. So what I did was set up a small equation representing the number of oxygen atoms on each side (where x is ...
Tue Jul 04, 2017 8:48 pm
Forum: General Science Questions
Topic: Chemical Reactions vs Physical Changes
Replies: 1
Views: 523

### Re: Chemical Reactions vs Physical Changes

Baking soda is a weak base and chemically reacts as follows: NaHCO 3 + H 2 O ---> H 2 CO 3 + NaOH B.S. is a weak base and has a low percent ionization, which is why if you add a large amount to water you will see excess sodium bicarbonate at the bottom. I believe this will be covered in more detail ...
Thu Jun 29, 2017 6:27 pm
Forum: Accuracy, Precision, Mole, Other Definitions
Topic: Fundamental E3
Replies: 1
Views: 715

### Re: Fundamental E3

Hmm, in the picture below the question, there are 9 Ga atoms displayed on the left hand side and another huge mass of At atoms on the right side, but I can totally understand how this was confusing because I was at first confused by it as well! I believe the 9 Ga atoms are given, while the chunk of ...
Thu Jun 29, 2017 5:35 pm
Forum: Molarity, Solutions, Dilutions
Topic: G.25 -- Homeopathy Question
Replies: 2
Views: 286

### Re: G.25 -- Homeopathy Question

Your understanding of the problem seems correct, and the way the solution manual approaches it errs of the side of dubiousness (more on this later). Here's what I did: 1) 0.1M and a 0.01L sample 2) gives us 0.001 moles of X. 3) We take our 10 mL and... double it 1x: V=10*2=20mL double it 2x: V=20*2=...
Thu Jun 29, 2017 5:04 pm
Forum: SI Units, Unit Conversions
Topic: Conversion Shortcuts!
Replies: 1
Views: 277

### Re: Conversion Shortcuts!

Yes, you can convert directly from cm to mm by multiplying by 10^-1 ! However, conversions for measurements in 2 dimensions and 3 dimensions are not so straightforward. Take the following examples: To convert 1 m^2 to cm^2: 1m 2 *(100 2 cm 2 /1 m 2 )=10000 cm 2 That is to say, 1m 2 = 100 2 cm 2 ! Si...
Thu Jun 29, 2017 4:50 pm
Forum: Limiting Reactant Calculations
Topic: Audio visual topic limiting reactant assessment
Replies: 3
Views: 526

### Re: Audio visual topic limiting reactant assessment

This is a question which tests your knowledge of limiting reactants and dimensional analysis (aka unit conversion). The given chemical reaction is balanced and has a 1:1 ratio for all reactants:products, meaning that for ever 1 mole of each reactant that's consumed, 1 mole of each product will be fo...