## Search found 58 matches

Tue Mar 13, 2018 4:49 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: 15.89
Replies: 2
Views: 200

### 15.89

I understand Step #2 is the slow step, but how do we know if Step #1 is faster than Step #3 (or vice versa)?
Tue Mar 13, 2018 1:34 am
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Cell Diagrams- Line Notation
Replies: 4
Views: 402

### Re: Cell Diagrams- Line Notation

By using this notation, we assume that E°cell > 0 and that the Gibbs free energy is negative.
Mon Mar 12, 2018 11:22 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Reaction Mechanisms
Replies: 1
Views: 139

### Reaction Mechanisms

Will we always be given the proposed reaction mechanisms?
Mon Mar 12, 2018 11:21 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Reaction Mechanism Steps
Replies: 4
Views: 295

### Reaction Mechanism Steps

If there is only one step in the reaction, do we assume it is the slow step?
Wed Mar 07, 2018 12:39 am
Forum: Zero Order Reactions
Topic: zeroth order rate
Replies: 4
Views: 427

### Re: zeroth order rate

The differential rate law for the a zero-order reaction is k[A]^0 and the integrated rate law is [A] = -kt + [A]^0
Wed Mar 07, 2018 12:10 am
Forum: Second Order Reactions
Topic: Page 10 of Kinetics Integrated Law Examples [ENDORSED]
Replies: 1
Views: 295

### Page 10 of Kinetics Integrated Law Examples[ENDORSED]

2C4H6(g) → C8H12(g) The dimerization reaction of butadiene is second order and has a rate constant of 0.0140M-1·s-1 at 500˚C. Determine the C4H6 concentration after 115.0 seconds if the initial concentration of C4H6 is 0.0500 M. I tried solving this part of the problem, but my solution doesn't quite...
Tue Mar 06, 2018 12:39 am
Forum: First Order Reactions
Topic: Zero-order vs. First-order reaction graphs
Replies: 5
Views: 2725

### Zero-order vs. First-order reaction graphs

What is the difference between the zero-order reaction graph and the first-order reaction graph?
Tue Feb 27, 2018 9:37 am
Forum: Calculating Work of Expansion
Topic: Midterm Q4A [ENDORSED]
Replies: 4
Views: 344

### Re: Midterm Q4A[ENDORSED]

As mentioned, the key words, external pressure, helped me identify that pressure is constant.
Tue Feb 27, 2018 9:31 am
Forum: Balancing Redox Reactions
Topic: Recognizing a redox reaction in acidic or basic solution
Replies: 5
Views: 350

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

The question should specify if the reaction is in acidic or basic conditions, but a reaction in acidic conditions usually contains H+ while a reaction in basic conditions usually contains OH-
Tue Feb 27, 2018 9:30 am
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: Standard Potential
Replies: 4
Views: 350

### Re: Standard Potential

I believe standard potentials occur when the substances are in their stable states at 25 degrees Celsius.
Wed Feb 21, 2018 10:18 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: H+ in cell diagram
Replies: 1
Views: 142

### Re: H+ in cell diagram

I think it's because those reactions take place in acidic solution since H+ is part of the reaction.
Tue Feb 20, 2018 8:05 am
Forum: Balancing Redox Reactions
Topic: oxidation states
Replies: 4
Views: 278

### Re: oxidation states

An example of finding the oxidation state could be MnO4-. We know the overall charge of MnO4- is -1 and oxygen as O4 has a charge of -8, so we only need to find the charge of Mn.

x + 4(-2) = -1

x-8 = -1

x = +7

The charge of Mn is +7.
Tue Feb 20, 2018 7:55 am
Forum: Balancing Redox Reactions
Topic: Oxidation Numbers
Replies: 6
Views: 483

### Re: Oxidation Numbers

As mentioned, the oxidation state of oxygen as a diatomic molecule (O2) is zero. However, when oxygen is in a compound, the charge varies between -1 and -2.
Sun Feb 18, 2018 8:24 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Anodes vs. Cathodes
Replies: 3
Views: 223

### Anodes vs. Cathodes

When referring to the voltage of redox potential, how do we know which reaction is the anode and which reaction is the cathode?
Sat Feb 17, 2018 10:54 pm
Forum: Balancing Redox Reactions
Topic: 14.1 Part D
Replies: 4
Views: 288

### 14.1 Part D

I am confused as to how the chemical equation on 14.1, Part D was balanced.
Mon Feb 12, 2018 2:28 am
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Van't Hoff Equation
Replies: 3
Views: 233

### Re: Van't Hoff Equation

Based on the learning objectives listed for Chapter 9, it would be helpful to know how to derive the equation.
Mon Feb 12, 2018 1:45 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: Gibbs Free Energy
Replies: 1
Views: 197

### Gibbs Free Energy

Do all diatomic molecules have 0 standard Gibbs free energy?
Sun Feb 11, 2018 10:47 pm
Forum: Calculating Standard Reaction Entropies (e.g. , Using Standard Molar Entropies)
Topic: 9.5
Replies: 4
Views: 398

### 9.5

What is the total entropy change of a process in which 40.0 kJ of energy is transferred as heat from a large reservoir at 800. K to one at 200. K?

For 9.5, the student solutions manual uses a negative sign for (delta)S = -40000 J/800 K, and I do not know why.
Tue Feb 06, 2018 9:38 am
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: 9.25
Replies: 5
Views: 335

### Re: 9.25

In order to find W, I think it would help drawing out different Lewis structures to identify the various ways the molecule can exist.
Tue Feb 06, 2018 9:37 am
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Gibbs Free Energy
Replies: 7
Views: 394

### Re: Gibbs Free Energy

Gibbs free energy is amount of energy available to do work, and it can be used to predict whether a reaction will be spontaneous or not. If delta G is negative, then the reaction will be spontaneous in the forward reaction (meaning that the reactants have enough energy to move the reaction forward)....
Tue Feb 06, 2018 9:33 am
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: temperature
Replies: 5
Views: 339

### Re: temperature

I would also suggest you using 273.15 to avoid any discrepancies in your answer.
Thu Feb 01, 2018 12:21 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: what exactly is free energy?
Replies: 5
Views: 371

### Re: what exactly is free energy?

In addition, if ΔG is negative, then it means that the reactants have more energy than the products which will allow the reaction to move forward (occurs spontaneously). If ΔG is positive, then it means that the reactants have less energy than the products, which will require an input of energy (doe...
Thu Feb 01, 2018 12:12 pm
Forum: Calculating Work of Expansion
Topic: Work Equations [ENDORSED]
Replies: 9
Views: 714

### Re: Work Equations[ENDORSED]

As mentioned, if the work done is reversible, then you would use w = -nRTln(V2/V1). If the work done is irreversible, then you would use w = -P(ext)ΔV.
Thu Feb 01, 2018 12:04 pm
Forum: Biological Examples (*DNA Structural Transitions, etc.)
Topic: Heat Capacity [ENDORSED]
Replies: 4
Views: 1129

### Re: Heat Capacity[ENDORSED]

The heat capacity increases with molecular complexity. As more atoms are present in the molecule, there are more possible bond vibrations that can absorb added energy.
Mon Jan 22, 2018 10:49 pm
Forum: Phase Changes & Related Calculations
Topic: Heat capacities
Replies: 5
Views: 354

### Re: Heat capacities

Celsius and Kelvin can be used interchangeably in this case because the degree change in Celsius is equivalent to the degree change in Kelvin.
Mon Jan 22, 2018 10:31 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Open System [ENDORSED]
Replies: 4
Views: 269

### Re: Open System[ENDORSED]

Examples of open systems include a living plant, gasoline burning in an automobile engine, and boiling water without a lid. These systems are open systems because they freely allow energy and matter to be transferred in an out of the system.
Mon Jan 22, 2018 10:22 pm
Forum: Phase Changes & Related Calculations
Topic: Question on Cv(vap)
Replies: 2
Views: 153

### Question on Cv(vap)

A pressure cooker containing 100.0 g of liquid water at 25 C is placed on the stove until all water becomes superheated steam at 121 C. Assume no steam escapes the pressure cooker. a) Find q from 25C to 100C b) Find q during boiling c) Find any other heat gained or lot by the water as it goes from 2...
Tue Jan 16, 2018 5:16 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: U = q + w assumptions
Replies: 5
Views: 414

### Re: U = q + w assumptions

According to page 273, the first law of thermodynamics (delta)U = q + w mentions that the internal energy of an isolated system is constant; however, I am unsure if we can assume pressure is constant.
Tue Jan 16, 2018 5:01 pm
Forum: Phase Changes & Related Calculations
Topic: Problem 8.29
Replies: 4
Views: 266

### Re: Problem 8.29

NO2 would have higher molar heat capacity because heat capacity increases with molecular complexity. This means that as more atoms are present in the molecule, there are more possible bond vibrations that can absorb added energy.
Tue Jan 16, 2018 4:58 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: What does R stand for?
Replies: 13
Views: 1402

### Re: What does R stand for?

As mentioned, R is the gas constant which is equal to . . .
8.314 J.K^-1.mol^-1 = 8.206 x 10^-2 L.atm.K^-1.mol^-1 = 8.314 x 10^-2 L.bar.K^-1.mol^-1 = 62.364 L.Torr.K^-1.mol^-
Thu Jan 11, 2018 9:53 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: Celsius the same as Kelvin? [ENDORSED]
Replies: 9
Views: 3035

### Re: Celsius the same as Kelvin?[ENDORSED]

As mentioned, using one unit over the other does not matter because the change in temperature would be the same, but I would just stick to the units that are initially given.
Thu Jan 11, 2018 8:47 pm
Forum: Thermodynamic Systems (Open, Closed, Isolated)
Topic: 8.1 part c [ENDORSED]
Replies: 8
Views: 754

### 8.1 part c[ENDORSED]

Identify the following systems as open, closed, or isolated: (a) coffee in a very-high-quality thermos bottle; (b) coolant in a refrigerator coil; (c) a bomb calorimeter in which benzene is burned; (d) gasoline burning in an automobile engine; (e) mercury in a thermometer; (f) a living plant. I'm a ...
Thu Jan 11, 2018 8:04 pm
Forum: Phase Changes & Related Calculations
Topic: Open, Closed, or Isolated Systems
Replies: 6
Views: 6645

### Re: Open, Closed, or Isolated Systems

To add on, an isolated system has no contact with surroundings. However, in the case of the thermometer, the heat of the mercury can be transferred to or from the thermometer.
Fri Dec 08, 2017 1:28 pm
Forum: Administrative Questions and Class Announcements
Topic: Final exam [ENDORSED]
Replies: 7
Views: 687

### Re: Final exam[ENDORSED]

Right. Based on Dr. Lavelle's email, I don't think titrations will be covered on the final.
Fri Dec 08, 2017 1:23 pm
Forum: Calculating pH or pOH for Strong & Weak Acids & Bases
Topic: 12.21
Replies: 2
Views: 166

### Re: 12.21

In addition, when the pH is 7 (neutral), it implies that [H3O+] is 1.0 x 10^-7 and [OH-] is 1.0 x 10^-7--all which equals 1.0 x 10^-14 when they are multiplied together.
Fri Dec 08, 2017 1:16 pm
Forum: Administrative Questions and Class Announcements
Topic: Final exam [ENDORSED]
Replies: 7
Views: 687

### Re: Final exam[ENDORSED]

Fundamentals J was covered, and it is useful to get practice and some background on Chapter 12 concepts.
Fri Dec 08, 2017 1:14 pm
Forum: Limiting Reactant Calculations
Topic: Limiting Reactant Calculations [ENDORSED]
Replies: 3
Views: 396

### Re: Limiting Reactant Calculations[ENDORSED]

I think we would need to assume CaCO3 is the limiting reactant based on what the problem tells us. If we had to find the limiting reactant, I believe they would give us the mass for both reactants.
Thu Dec 07, 2017 10:12 pm
Forum: Properties & Structures of Inorganic & Organic Acids
Topic: Arrhenius acids and bases
Replies: 2
Views: 272

### Re: Arrhenius acids and bases

According to the Acids and Bases outline, we have to know how to identify Bronsted acids and bases + Lewis acids and bases, so I don't think we need to worry about Arrhenius acids and bases.
Mon Dec 04, 2017 11:14 pm
Forum: Identifying Acidic & Basic Salts
Topic: 12.67
Replies: 1
Views: 255

### 12.67

I'm a little confused on how you would determine the pH given this information.

Rank the following solutions in order of increasing pH:
(a) 1.0 10^-5 M HCl(aq);
(b) 0.20 M CH3NH3Cl(aq);
(c) 0.20 M CH3COOH(aq);
(d) 0.20 M C6H5NH2(aq). Justify your ranking.
Mon Dec 04, 2017 3:22 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Table 11.2
Replies: 4
Views: 308

### Re: Table 11.2

To add on, K = Kp is for gases and it is denoted by the units atm (bar, torr, Pa etc.). Kc is for concentration which is denoted by molarity units.
Wed Nov 29, 2017 8:20 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Chemical Equilibrium Part 2 Question #12
Replies: 1
Views: 265

### Chemical Equilibrium Part 2 Question #12

I'm a little confused on how to solve this problem that's in the Chemical Equilibrium Part 2 Module. Consider the following reaction at 1200 K, for which you know Kc = 1.7 x 10-3. Br2 (g) ⇌ 2 Br (g) Your experimental setup is able to measure the equilibrium concentration of Br2 based on its color, b...
Wed Nov 29, 2017 8:16 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Kc vs. Kp
Replies: 3
Views: 346

### Re: Kc vs. Kp

In general, you would use P when referring to gases. However, this does not mean you will use P whenever you have gases. If it's atm (bar, torr, Pa, etc.), then you would use Kp. If you have M or any other concentration units, then you would use Kc.
Thu Nov 23, 2017 12:37 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: 4.19 b)
Replies: 2
Views: 168

### Re: 4.19 b)

Sn-Cl2 only has 6 valence electrons because the formal charge of the structure would be 0, and that is the ultimate goal when drawing Lewis dot structures.
Thu Nov 23, 2017 12:34 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Bent vs. Angular
Replies: 5
Views: 574

### Re: Bent vs. Angular

I don't think there is a difference between bent and angular.
Wed Nov 15, 2017 11:26 pm
Forum: Hybridization
Topic: Notation
Replies: 6
Views: 461

### Re: Notation

I don't think we need to write out the electron configuration in this notation unless it is asked. However, I think this notation is good just to see how orbitals are filled up.
Wed Nov 15, 2017 11:19 pm
Forum: Hybridization
Topic: Does hybridization only occur when bonding?
Replies: 3
Views: 204

### Re: Does hybridization only occur when bonding?

Are there any exceptions to the Hybridization guidelines given in lecture?
Tue Nov 07, 2017 11:07 pm
Forum: Balancing Chemical Reactions
Topic: Balancing Chemical Reactions post-module assessment
Replies: 2
Views: 229

### Re: Balancing Chemical Reactions post-module assessment

The correct answer is stoichiometric coefficients.
Mon Nov 06, 2017 12:20 am
Forum: Lewis Structures
Topic: Formal charge [ENDORSED]
Replies: 3
Views: 317

### Re: Formal charge[ENDORSED]

The formal charge could be indicated by a number, depending on the answer you get from using the formal charge equation, which is V - (L + B/2).

V: # of valence electrons in free atom
L: # of electrons present on bonded atom as lone pairs
B: # of bonding electrons on atoms

Hope this helps!
Tue Oct 31, 2017 11:40 pm
Forum: Trends in The Periodic Table
Replies: 4
Views: 388

To add on, the atomic radius increases down a group because electrons occupy sub-shells with increasing quantum number, which suggests that the atomic radius increases as the quantum number increases.
Tue Oct 31, 2017 11:30 pm
Forum: Trends in The Periodic Table
Topic: Writing Electron Config for Chromium after being ionized once?
Replies: 2
Views: 312

### Re: Writing Electron Config for Chromium after being ionized once?

I would say that option 1 is correct because the correct electron configuration of Chromium is [Ar](3d^5)(4s^1). When the electron is ionized, the electron taken out is from the s-orbital. I believe the reasoning will be provided for all elements in the d-block. However, we need to be most concerned...
Thu Oct 26, 2017 12:04 am
Forum: Wave Functions and s-, p-, d-, f- Orbitals
Topic: 2.1 part d
Replies: 4
Views: 236

### Re: 2.1 part d

Does this mean that there is a direct relationship between the number of electrons and the size of the radius?
Wed Oct 25, 2017 11:59 pm
Forum: Electron Configurations for Multi-Electron Atoms
Topic: Electron Configuration writing
Replies: 8
Views: 508

### Re: Electron Configuration writing

Like others have said, putting 3d before 4s in electron configuration will help us understand how orbitals fill up. However, is it wrong if we put 4s before 3d?
Thu Oct 19, 2017 6:26 pm
Forum: Bohr Frequency Condition, H-Atom , Atomic Spectroscopy
Topic: Wavelength Units
Replies: 5
Views: 418

### Re: Wavelength Units

If the problem asks for the wavelength in nanometers, I would provide it in nanometers. However, when you are solving the problem, I would use meters since the SI unit is meters and the values of the other constants are given in meters. Hope this helps!
Thu Oct 19, 2017 6:14 pm
Forum: Bohr Frequency Condition, H-Atom , Atomic Spectroscopy
Topic: Homework
Replies: 3
Views: 230

### Re: Homework

For this week, you can still turn in homework from Chapter 1 as long as the problems are not the same ones you turned in last week. Next week, we can turn in homework from Chapter 2.
Thu Oct 12, 2017 9:56 am
Forum: Properties of Light
Topic: Planck Constant [ENDORSED]
Replies: 8
Views: 743

### Re: Planck Constant[ENDORSED]

Sig figs are mainly important in the final answer, so do not worry about rounding in the middle of a problem. For the final answer, I would determine the number of sig figs based on the number that has the least number sig figs in the original problem.
Wed Oct 11, 2017 2:27 pm
Forum: Properties of Light
Topic: Chapter 1 #3
Replies: 9
Views: 596

### Re: Chapter 1 #3

With respect to Part C, is there a relationship between the extent of change in an electrical field and the frequency of electromagnetic radiation?
Wed Oct 04, 2017 1:31 am
Forum: Significant Figures
Topic: Use of Significant Figures in Self Test E.2A
Replies: 3
Views: 390

### Re: Use of Significant Figures in Self Test E.2A

Right. Since 3.20 has the least number of sig figs based on the original problem, your final answer should have three sig figs as well. Hope this helps!
Tue Oct 03, 2017 11:25 pm
Forum: Balancing Chemical Reactions
Topic: Nitrogen
Replies: 5
Views: 459

### Re: Nitrogen

Yes. If a problem states that nitrogen is produced in their elemental form, then we can assume the product is gaseous nitrogen and that it is a diatomic molecule (N2).