## Search found 50 matches

Fri Mar 16, 2018 11:46 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Test #2 Question 5
Replies: 5
Views: 230

### Re: Test #2 Question 5

If the reaction shows a reduction, then yes the strongest reducing agent would have the most negative E
Fri Mar 16, 2018 11:18 pm
Forum: Administrative Questions and Class Announcements
Topic: Final Topics
Replies: 3
Views: 220

### Re: Final Topics

The final will be cumulative. I think it's fair to say that the final will be mostly equal distributed around all the topic. My TA said there is a high chance of a reaction mechanism problem on the final since it was not covered in the last test.
Wed Mar 14, 2018 1:14 am
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Test 2 Question 5
Replies: 2
Views: 147

### Test 2 Question 5

They asked to rank Zn, Mn, Cr in order of reducing power. Zn +2 + 2e- = -0.76 V Mn +2 + 2e- = -1.18 V Cr +3 + 3e- = -0.74 V So I ranked them as Mn>Zn>Cr but the answer was the reverse of that. Can someone explain why am wrong? From my understanding, for a species to have a lot of reducing power, it ...
Wed Mar 14, 2018 12:53 am
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: 8.75
Replies: 2
Views: 183

### Re: 8.75

I would recommend drawing out the actual lewis structures. It helps out a lot. Then I would make a table showing which bonds are broken/formed.
Fri Mar 09, 2018 10:30 am
Forum: General Rate Laws
Topic: Problem 15.99
Replies: 1
Views: 118

### Re: Problem 15.99

F and and G are linear because if you have a first order reaction, the rate law is r=k{A} which is like y=mx. The initial rate (y) depends on the concentration (x) with a constant slope (k or m). G is linear because if you look at the equation of the half life of a zero order, you get t 1/2 = \frac{...
Fri Mar 09, 2018 3:02 am
Forum: Second Order Reactions
Topic: Half life of second order reactions
Replies: 8
Views: 628

### Half life of second order reactions

In the book, it says that we don't use the equation for a half-life for a second order reaction, but we still used it in one the exercises. Can someone explain why, it says "not used"
Wed Mar 07, 2018 12:01 am
Forum: Second Order Reactions
Topic: 15.35a
Replies: 3
Views: 282

### 15.35a

So I found the k value (0.02357), and used the integrated rate law for second order reactions, but my answer was 757.6 second but the answer was 7.4 x 10^2. Would this just be a rounding error on my part, or is the book wrong?
Mon Mar 05, 2018 1:23 pm
Forum: Method of Initial Rates (To Determine n and k)
Topic: determining order
Replies: 3
Views: 136

### Re: determining order

The units for the rate is always M/s, but the k value changes depending on the order.
Mon Mar 05, 2018 1:17 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Which Step is Slower?
Replies: 8
Views: 254

### Re: Which Step is Slower?

The slower step is which ever reaction shows the rate law.
Mon Mar 05, 2018 1:16 pm
Forum: General Rate Laws
Topic: When to Use Avg. vs Instantaneous
Replies: 5
Views: 163

### Re: When to Use Avg. vs Instantaneous

My TA told me that most of the time we would be using the instantaneous rate rather than the unique reaction rate because the instantaneous rate is more useful when determining the rate law.
Wed Feb 28, 2018 11:25 pm
Forum: Method of Initial Rates (To Determine n and k)
Replies: 1
Views: 126

When determining the k value, it says in the back of the book that it's 2.85 x 10-12 L4 /mmol4 s. But the only way to get that number would be to convert it to moles first. Is the answer key wrong, meaning that part d of the same problem is wrong too?
Fri Feb 23, 2018 1:36 am
Forum: Balancing Redox Reactions
Topic: 14.5 part d
Replies: 7
Views: 301

### Re: 14.5 part d

In this case you would H+ ions, and then later on the OH- ions would combine with the H+ ions to make water.
Thu Feb 22, 2018 10:14 pm
Forum: Balancing Redox Reactions
Topic: H+ or H3O+ [ENDORSED]
Replies: 3
Views: 201

### H+ or H3O+[ENDORSED]

So, my TA said to use the hydronium ion (H3O+) when balancing the hydrogen atoms, but the book says to use just a plain hydrogen ion. Does it matter which one we use?
Tue Feb 13, 2018 8:51 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: 9.57
Replies: 1
Views: 94

### 9.57

So, I got the answer for entropy and enthalpy, but when I use the Gibbs Free Energy equation, I get -753.01 X 103 kJ/mol using 298 K when the answer is -713.02 kJ/mol. Is the solution wrong, or am I doing something dumb and can't realize it?
Mon Feb 12, 2018 6:02 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: ∆Gº temperature
Replies: 1
Views: 112

### Re: ∆Gº temperature

It just means you're using the standard states of the element at a certain temperature, not specifically 298 K.
Mon Feb 12, 2018 5:44 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: Example 9.6
Replies: 1
Views: 138

### Example 9.6

In example 9.6, it talks about the entropy of vaporization of acetone at 296 K, but I'm kind of confused on why you we would use the molar heat capacity for the first step, and then 4R for the heat capacity in the third step. Can someone explain to me?
Sun Feb 11, 2018 5:46 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: Review Session Concept Clarification
Replies: 1
Views: 100

### Re: Review Session Concept Clarification

Just because you remove heat from the system it doesn't necessarily mean that the temperature will change. If you look at the phase change diagram, if you remove a certain amount of energy from the flat part of the graph, the temperature will remain constant. Like how if constantly added energy to a...
Sun Feb 11, 2018 5:43 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: 9.15
Replies: 1
Views: 93

### Re: 9.15

The question states to find the entropy change meaning you would use the delta H of the specific phase change to find the entropy.
Sun Feb 11, 2018 5:34 pm
Forum: Third Law of Thermodynamics (For a Unique Ground State (W=1): S -> 0 as T -> 0) and Calculations Using Boltzmann Equation for Entropy
Topic: 9.25
Replies: 2
Views: 169

### Re: 9.25

I think the best way is to draw out the lewis structure.
Mon Jan 29, 2018 7:33 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: 9.13
Replies: 3
Views: 150

### 9.13

For this problem how would you find the moles of nitrogen gas? I tried doing the 22.4L/mole conversion but when I did, my answer was way off. The specific heat I calculated was 29.101 since its a linear molecule at a constant pressure which is (7/2)R.
Mon Jan 29, 2018 7:04 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: 2. At the temperature of a phase transition, the transfer of heat is reversible."
Replies: 2
Views: 124

### Re: 2. At the temperature of a phase transition, the transfer of heat is reversible."

Say we have water which has a freezing point of 0 degrees Celsius. At that specific temperature, the addition of heat will cause it to melt, while the removal of heat will cause it freeze, so it reversible.
Mon Jan 29, 2018 6:58 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: Equations
Replies: 2
Views: 119

### Re: Equations

The equations are on the constants and equation sheets I think.
Mon Jan 29, 2018 6:56 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: estimating an entropy change
Replies: 2
Views: 98

### Re: estimating an entropy change

Just think about the position of solid vs gas molecules. The atoms in a solid are rigid and have little room to move so the entropy is low, while gases have a lot of space to move thus a higher entropy, which explains why delta S is positive.
Tue Jan 23, 2018 5:05 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: negative vs. positive
Replies: 1
Views: 90

### Re: negative vs. positive

The answer would be negative. Qsystem + Qsurrounding = 0, therefore Qsystem=-Qsurrounding
Mon Jan 22, 2018 11:07 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: Work, reversible and irreversible
Replies: 2
Views: 95

### Work, reversible and irreversible

So I was looking at Example 8.5 and it said that we should expect the work from a irreversible reaction to be less than that of a reversible reaction. Can someone explain to me why that is?
Sun Jan 21, 2018 8:56 pm
Forum: Phase Changes & Related Calculations
Topic: Irreversible vs reversible
Replies: 3
Views: 183

### Re: Irreversible vs reversible

I like to think of it like an equilibrium problem. A reversible reaction is kinda like a reaction that is at equilibrium. By adding/removing a reactant it will shift the reaction. By adding/removing pressure, the piston will shift. An irreversible reaction is one where the K value is really high so ...
Fri Jan 19, 2018 1:01 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: q and delta H interchangeable in calculations?
Replies: 4
Views: 217

### Re: q and delta H interchangeable in calculations?

Delta H is only equivalent to the heat absorbed/released (aka q) when the system has a constant pressure and no nonexpansion work.
Fri Jan 19, 2018 10:00 am
Forum: Thermodynamic Systems (Open, Closed, Isolated)
Topic: Internal Energy/Open System
Replies: 4
Views: 222

### Re: Internal Energy/Open System

For an open system you can increase the temperature of the system thus adding more energy to the overall system.
Sun Jan 14, 2018 8:12 pm
Forum: Phase Changes & Related Calculations
Topic: Another 8.41 Question
Replies: 3
Views: 231

### Re: Another 8.41 Question

Essentially yes. The negative sign is due to the loss of heat in the water, and then that heat enters the ice. Think of it as two systems. The heat leaves one system (negative sign) to enter another (positive sign)
Sun Jan 14, 2018 8:09 pm
Forum: Phase Changes & Related Calculations
Topic: Heating Curve Question
Replies: 2
Views: 181

### Re: Heating Curve Question

I think the heat capacity has nothing really to do with the slopes. The heat capacity has to do more with the x component.
Thu Jan 11, 2018 9:11 am
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Chapter 8
Replies: 6
Views: 232

### Re: Chapter 8

All homework problems that you can do are on the syllabus.
Thu Dec 07, 2017 2:08 pm
Forum: Bronsted Acids & Bases
Topic: Electronegativity vs Bond length
Replies: 1
Views: 144

### Electronegativity vs Bond length

So in lecture, he said that the shorter and stronger the bond, the weaker the acid since the H+ ion cannot break free of the molecule which makes sense, but in 12.9 of the book it says that the greater electronegativity, the stronger the acid since it makes the H-A molecule more polar and ionic mean...
Tue Dec 05, 2017 12:50 pm
Forum: Conjugate Acids & Bases
Topic: strong and weak acids and bases
Replies: 2
Views: 166

### Re: strong and weak acids and bases

Both strong acid/bases and weak acids/bases have conjugates. If the acid/base is strong that means its conjugate is weak, and if the acid/base is weak, it means the conjugate is strong. So the conjugate of HCl is Cl- which is a weak conjugate base, and CH3COOH has a strong conjugate base, CH3COO-
Wed Nov 29, 2017 2:29 am
Forum: Naming
Topic: 17.31d [ENDORSED]
Replies: 1
Views: 112

### 17.31d[ENDORSED]

So it says to give the chemical formula of sodium bisoxalato(diaqua)ferrate (III) but my question is why oxalato is named before aqua? It says when naming the ligands, it should be named in alphabetical order, but it clearly isn't so why is it written like that.
Wed Nov 29, 2017 2:08 am
Forum: Naming
Topic: 17.31b [ENDORSED]
Replies: 1
Views: 151

### 17.31b[ENDORSED]

So the answer has it so that there is no bracket between the SO4 and the Cl, but in the toolbox 17.1 adds the bracket in between the last ligand and the anion so which one is correct?
Wed Nov 22, 2017 1:20 am
Forum: Polarisability of Anions, The Polarizing Power of Cations
Topic: #4.25 Predicting Polarity of a molecule?
Replies: 1
Views: 352

### Re: #4.25 Predicting Polarity of a molecule?

This is where you would use VSPER. CH2Cl2 is a tetrahedral structure which is shown here https://www.restauro-online.com/WebRoot/Store6/Shops/63807438/54A9/4B53/2D0F/91BF/2F82/C0A8/2AB9/502E/diclorometano_struttura.jpg Since Cl2 is more electronegative, it will be partially negative on one side of t...
Wed Nov 22, 2017 1:15 am
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Ch.11 #1(c)
Replies: 1
Views: 108

### Re: Ch.11 #1(c)

Just because the pressure is higher it doesn't mean the temperature increased. The volume of the container could have decreased thus increasing the pressure while temperature remains the same. The pressure will simply affect the rate of the reaction, not how much product or reactants there are.
Tue Nov 14, 2017 10:24 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Ch 4 #11 Part b and more
Replies: 2
Views: 221

### Re: Ch 4 #11 Part b and more

It's because the electron geometry of the iodine trichloride is trigonal bipyramidal and the electron geometry of NH3 is tetrahedral. Electron geometry simply refers to the number of electron dense areas around the central atom, while the molecular geometry takes into account whether or not it has l...
Tue Nov 14, 2017 9:44 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: How to Find Bond Angle
Replies: 2
Views: 143

### Re: How to Find Bond Angle

Figure 4.1 in the textbook can help you determine the bond angles. And when they are lone pairs, the bond angle will be typically less than the standard do to the electron repulsion. So say I have a bent structure, with 3 regions of electron density. The bond angle would be less than 120 because the...
Mon Nov 06, 2017 11:15 am
Forum: Ionic & Covalent Bonds
Topic: 3.25 d
Replies: 3
Views: 242

### Re: 3.25 d

Typically we write the cation first, then the anion which means it would be H2Te
Mon Oct 30, 2017 10:23 pm
Forum: Heisenberg Indeterminacy (Uncertainty) Equation
Topic: H-Bar vs h
Replies: 2
Views: 330

### Re: H-Bar vs h

h bar is simply h/2pi. So in the book it says you can use (1/2) X h bar which simplifies to h/4pi therefore we cannot use h bar and planck's constant interchangeably
Mon Oct 30, 2017 10:19 pm
Forum: Lewis Structures
Topic: Formal Charge and Lewis Structures
Replies: 2
Views: 162

### Re: Formal Charge and Lewis Structures

There part where you mentioned the double bond and the Br with a +1 charge is actually incorrect. If you form a double bond by taking a pair of electrons from Br, that would mean O would have 10 electrons which can't happen since it has no d-orbital. In this case I think we consider Br the central a...
Mon Oct 23, 2017 8:58 pm
Forum: Wave Functions and s-, p-, d-, f- Orbitals
Topic: Question 2.27
Replies: 1
Views: 118

### Re: Question 2.27

You can tell how many orbitals there are based on the state. Like atoms in the p-orbital will have 3 orbitals which makes sense since the p orbital can hold 6 electrons, 2 per orbital. So since the d-orbital can hold 10 electrons, that must meant there are 5 orbitals and then so on for the rest of t...
Mon Oct 23, 2017 8:48 pm
Forum: Wave Functions and s-, p-, d-, f- Orbitals
Topic: Magnetic Numbers
Replies: 2
Views: 157

### Re: Magnetic Numbers

Magnetic quantum numbers can be found using 3 formulas (you have to use all of them to find all the magnetic numbers). They are: l, l-1, -1
Wed Oct 18, 2017 12:32 am
Forum: DeBroglie Equation
Topic: CHAPTER 1 QUESTION 33!!!
Replies: 8
Views: 462

### Re: CHAPTER 1 QUESTION 33!!!

The masses of electrons, protons, neutrons and all the other constants you need are in the very in the back of the book.
Wed Oct 18, 2017 12:23 am
Forum: Bohr Frequency Condition, H-Atom , Atomic Spectroscopy
Topic: Question 1.15
Replies: 6
Views: 300

### Re: Question 1.15

Okay based on my discussion section my TA said that n1 is considered the intial and n2 is the final. You would make the lowest n value (in this case 1) your initial that way the frequency always remains positive, which may explain why your initial n is 1 and your final n is 3. This might be confusin...
Wed Oct 11, 2017 4:59 pm
Forum: Properties of Light
Topic: 1.11
Replies: 1
Views: 162

### Re: 1.11

We know that the Lyman series begins with n=1 simply because a physicist, Theodore Lyman, studied the ultraviolet spectrum of hydrogen gas. I think it would be too complicated for the book to explain how he came up with n=1 so it is simply told to us. We can differentiate between different series by...
Wed Oct 11, 2017 4:48 pm
Forum: Properties of Light
Topic: Work Functions
Replies: 4
Views: 297

### Re: Work Functions

The work function refers to the amount of energy needed to eject the electron from the metal which is also known as the threshold energy.
So the energy of the incoming photon (E=hv) - work function = kinetic energy of the electron
Mon Oct 02, 2017 6:04 pm
Forum: Balancing Chemical Reactions
Topic: Fundamental Exercise H.11
Replies: 2
Views: 265

### Re: Fundamental Exercise H.11

No you would start "fresh." So in the answer Fe3O4 had a stoichiometric coefficient of 2, but in part 2 you wouldn't start with 2 Fe3O4. You would simply start with Fe3O4 + CO etc.
Mon Oct 02, 2017 5:55 pm
Forum: Limiting Reactant Calculations
Topic: M7 Part A
Replies: 1
Views: 293

### Re: M7 Part A

You can tell the formula for boron oxide is B2O3 based on what group each element is in. Since boron is in group 13 it'll have a charge of +3 and since oxygen is in group 16 it'll have a charge of -2. Then you simply make sure the charges match each other by changing the number of elements. B2 would...