## Search found 66 matches

Fri Mar 16, 2018 9:52 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: Textbook Example 9.5
Replies: 1
Views: 205

### Textbook Example 9.5

The book uses 1.5R for the Cv of O2 in step 2, but since O2 is a linear molcule shouldn't the Cv be 2.5R?
Fri Mar 16, 2018 2:00 am
Forum: Calculating Work of Expansion
Topic: 8.117
Replies: 2
Views: 197

### Re: 8.117

If we ignore the unbalanced oxygen atoms, conservation of mass is not upheld which seems illogical.
Fri Mar 16, 2018 12:56 am
Forum: Calculating Work of Expansion
Topic: 8.117
Replies: 2
Views: 197

### 8.117

I am in doubt that the back of the book as well as lavelle's solution manual answer are correct for this problem. Immediately upon seeing the equation provided for the reaction: CH4(g) + H2O(g)\rightarrow CO2(g) + 3H2(g) I realized that the equation is NOT balanced as...
Thu Mar 15, 2018 11:33 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: H+
Replies: 3
Views: 276

### H+

Why does H+ in an aqeouous solution have an enthalpy of formation of zero? Isn't H2 (gas) the most stable form of hydrogen thus it is 0 enthalpy of formation for hydrogen?
Thu Mar 15, 2018 7:35 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Standard Enthalpy of combustion
Replies: 2
Views: 246

### Standard Enthalpy of combustion

I understand that all the reactants and products need to be in their standard states and that only 1 mole of substance needs to be burned. Since the table for these data values is given at 25C, would H2O be in liquid state for products? Thank you.
Thu Mar 15, 2018 7:33 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Standard Enthalpy of combustion
Replies: 1
Views: 199

### Standard Enthalpy of combustion

I understand that all the reactants and products need to be in their standard states and that only 1 mole of substance needs to be burned. Since the table for these data values is given at 25C, would H2O be in liquid state for products? Thank you.
Thu Mar 15, 2018 7:07 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Heat curve
Replies: 1
Views: 205

### Heat curve

The steeper the slope of a heat curve, the smaller the heat capacity is? can someone provide also provide a mathematical example to prove/disprove my statement as well.
Thu Mar 15, 2018 7:06 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Heat curve
Replies: 2
Views: 256

### Heat curve

The steeper the slope of a heat curve, the smaller the heat capacity is? can someone provide also provide a mathematical example to prove/disprove my statement as well.
Thu Mar 15, 2018 6:57 pm
Forum: Phase Changes & Related Calculations
Topic: Helium
Replies: 1
Views: 218

### Helium

Why is helium melting not an endothermic process? Isn't the liquid molecules of any element more energetic than that of its solid state.
Thu Mar 15, 2018 2:56 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: Internal energy change = 0
Replies: 2
Views: 159

### Re: Internal energy change = 0

The change in internal energy for an irreversible expansion is not always zero. See part b of example 8.1 in the book if you need an example. Delta U will be zero if an expansion is isothermal
Thu Mar 15, 2018 2:53 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Bomb calorimeter
Replies: 2
Views: 236

### Bomb calorimeter

How is it possible for a bomb calorimeter to be constant volume if the water's density is not constant at all temperatures? Unless I am misunderstanding and the constant volume is for the total volume of the calorimeter assuming that it isn't filled to the brim with water. Any clarification would be...
Sun Mar 11, 2018 10:59 pm
Forum: *Enzyme Kinetics
Topic: Enzyme
Replies: 5
Views: 534

### Enzyme

Do enzymes always speed up the reaction by lowering the activation energy or can they also act as inhibitors and slow down the reaction?
Sun Mar 11, 2018 10:51 pm
Forum: Calculating Work of Expansion
Topic: Midterm 4a
Replies: 5
Views: 374

### Midterm 4a

How are we supposed to identify that this expansion is irreversible or reversible? Are there any hints or clues in the problem that imply one type of expansion over the other? Thank you in advance.
Sun Mar 11, 2018 10:47 pm
Forum: Calculating Work of Expansion
Topic: Midterm Q3B
Replies: 7
Views: 414

### Re: Midterm Q3B

Because copper has the lowest specific heat capacity, it is the most efficient metal listed for boiling water. Conceptually speaking, copper requires the least amount of joules to raise its temperature per gram. It is important to look at specific heat capacity and not molar heat capacity because al...
Sun Mar 04, 2018 1:18 pm
Forum: Arrhenius Equation, Activation Energies, Catalysts
Topic: Activation Energy???
Replies: 7
Views: 323

### Re: Activation Energy???

Quick note, enzymes are not always catalysts and can be inhibitors. Inhibitors work the opposite to catalysts as they increase the activation energy for the reaction.
Sun Mar 04, 2018 1:12 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: K
Replies: 7
Views: 297

### K

I was wondering what factors would change the value of k for a reaction?
Sun Mar 04, 2018 1:05 pm
Forum: First Order Reactions
Topic: k
Replies: 16
Views: 690

### Re: k

In general, it is useful to keep k units for time in terms of seconds. You can always convert to other units of time if the problem specifically asks for it, aka minutes or hours.
Sat Feb 24, 2018 5:32 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: What other elements could be used besides Pt?
Replies: 5
Views: 262

### Re: What other elements could be used besides Pt?

Pt is so commonly used because it is an inert metal and does not participate in redox reactions under normal conditions.
Sat Feb 24, 2018 5:22 pm
Forum: Zero Order Reactions
Topic: Concept of Zero Order
Replies: 5
Views: 413

### Re: Concept of Zero Order

A real world example of a zero order reaction is N2O decomposing into nitrogen and oxygen with hot platinum wire as a catalyst. Once all the platinum is covered by N2O, the concentration no longer matters until new space is available.
Sat Feb 24, 2018 4:38 pm
Forum: Kinetics vs. Thermodynamics Controlling a Reaction
Topic: units of the rate of reaction
Replies: 7
Views: 456

### Re: units of the rate of reaction

The units of the rate of reaction,K, is solely dependent on the order of the reaction. A zero order reaction will have the units M/s, a first order reaction will have the units of 1/s, a second order reaction will have the units of 1/Ms.
Sun Feb 18, 2018 11:18 pm
Forum: Balancing Redox Reactions
Topic: 14.15
Replies: 2
Views: 120

### 14.15

The solutions manual has a 2 subscript for the nickel hydroxide in the final step but shouldn't it be a 3 subscript so that hydroxides cancel out?
Sun Feb 18, 2018 11:03 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Salt Bridge
Replies: 4
Views: 154

### Salt Bridge

I do not understand the structure or importance of a salt bridge. Could someone explain to me physcially what it is, which type(s) of cells require it, and why it is important? Thank you in advance.
Wed Feb 14, 2018 3:19 am
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: Example 9.6
Replies: 1
Views: 128

### Example 9.6

I am confused how the textbook knew how to use the constant for constant pressure not constant pressure for example 9.6, step 3, pg329.
Mon Feb 12, 2018 12:00 am
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: heat capacity sign
Replies: 2
Views: 183

### Re: heat capacity sign

To my understanding, the heat capacity of a system or molecule cannot be negative, as it represents the amount of energy required to increase or decrease the temperature by one degree. Energy is inherently a positive value unless with regards to a system.
Sun Feb 11, 2018 11:54 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Exercise 14.87
Replies: 1
Views: 86

### Re: Exercise 14.87

The E of the cathode is -.76V and the E of the anode is unknown. The E of the cell overall is .16V. Set E of cell to E cathode minus E anode. Solving for E of cathode results in -.92V for M(s) to M4+
Sun Feb 11, 2018 11:48 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Homework Problem 9.69
Replies: 2
Views: 135

### Re: Homework Problem 9.69

Use the second and third reaction to get the total amount of energy released in the regeneration of ATP. Make sure to multiply he second equation by 3 to get the correct factor. Then divide the free energy by 30.5 (energy required in the first reaction) to get the number of moles of ATP that would b...
Sun Feb 04, 2018 9:52 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: 9.13 Equation Confusion
Replies: 3
Views: 176

### Re: 9.13 Equation Confusion

This is rare instance where the solutions manual is incorrect. Please refer to the link on his website Solution Manual Errors for this problem.
Sun Feb 04, 2018 9:48 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Homework Problem 9.69
Replies: 1
Views: 88

### Re: Homework Problem 9.69

The pH isn't relevant to this problem. Multiply both the second and third equation by 3 to represent 3 moles of NADH being used. Add the free energy sums of the two equations and divide by 30.5kJ which is the energy reuquired for the formation of ATP to calculate the moles of ATP produced.
Sun Feb 04, 2018 9:38 pm
Forum: Administrative Questions and Class Announcements
Topic: Midterm Question
Replies: 3
Views: 224

### Re: Midterm Question

He sent out an email earlier today saying that he will tell us more information about the midterm in this upcoming week.
Sun Feb 04, 2018 9:37 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: positional residual entropy
Replies: 4
Views: 177

### Re: positional residual entropy

Positional residual entropy is basically the absolute entropy and the equation was derived statically. The formula is S=Kb*lnW. Regular entropy to my understanding is usually delta S of the system.
Sun Jan 28, 2018 8:25 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: 8.49
Replies: 2
Views: 136

### Re: 8.49

I think you are the using the wrong gas constant. Try using 8.314 J/molK for the gas constant.
Sun Jan 28, 2018 8:16 pm
Forum: Calculating Work of Expansion
Topic: In which situation does delta U=0 and that q=-w
Replies: 4
Views: 225

### Re: In which situation does delta U=0 and that q=-w

The situation occurs when the system experiences isothermal change, thus delta U is zero. Subsequently, q=-w means that heat loss is equal work done on the system and visa versa is also true.
Sun Jan 28, 2018 8:09 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: 9.13
Replies: 7
Views: 258

### Re: 9.13

9.13 is one of the problems listed in the errors in solution manual. Definitely check out the link here: https://lavelle.chem.ucla.edu/wp-content/supporting-files/Chem14B/Solution_Manual_Errors_6Ed.pdf
Sun Jan 28, 2018 8:03 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: Question 9.13
Replies: 1
Views: 76

### Re: Question 9.13

9.13 is one of the problems, listed in errors in solution manual. Definitely, check that link out here: https://lavelle.chem.ucla.edu/wp-conten ... rs_6Ed.pdf[/url]
Sun Jan 21, 2018 10:18 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Bomb Calorimeters
Replies: 2
Views: 126

### Re: Bomb Calorimeters

All combustion reactions can be treated as if they are in a bomb calorimeter as long as all the heat and matter are accounted for.
Sun Jan 21, 2018 10:03 pm
Forum: Phase Changes & Related Calculations
Topic: heat vs ΔH vs work
Replies: 2
Views: 135

### Re: heat vs ΔH vs work

Conceptually, the difference is that heat is transferred between surroundings and system while delta heat is used to describe the change of heat in the system.
Sun Jan 21, 2018 9:48 pm
Forum: Thermodynamic Systems (Open, Closed, Isolated)
Topic: Bomb calorimeter
Replies: 7
Views: 315

### Re: Bomb calorimeter

Because no heat or matter is allowed to go between the system and surrounding for an isolated system and such occurs in a calorimeter and its surroundings.
Sun Jan 14, 2018 10:32 pm
Forum: Phase Changes & Related Calculations
Topic: Problem 8.29
Replies: 4
Views: 214

### Re: Problem 8.29

NO2 has greater enthalpy than NO because there are more bonds that require more energy thus greater enthalpy.
Sun Jan 14, 2018 10:31 pm
Forum: Calculating Work of Expansion
Topic: 8.3 Solution Question
Replies: 1
Views: 126

### Re: 8.3 Solution Question

If I am not mistaken d is the distance that the surface moved and gives us the correct units for volume
Sun Jan 14, 2018 10:29 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Extensive vs Intensive Properties
Replies: 3
Views: 159

### Re: Extensive vs Intensive Properties

The differences between the two properties is that extensive properties are dependent on mass while intensive properties are not. An example for each respectively would be mass for extensive and density for intensive
Sun Jan 14, 2018 10:26 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: U vs H
Replies: 2
Views: 113

### Re: U vs H

Delta H is change in enthalpy while delta U is change in internal energy. The units for each is joules.
Sat Dec 09, 2017 10:33 pm
Forum: Calculating pH or pOH for Strong & Weak Acids & Bases
Topic: Last Minute question
Replies: 2
Views: 207

### Re: Last Minute question

Buffers are chapter 13 material which is not included in the acid base.
Sat Dec 09, 2017 10:14 pm
Forum: *Particle in a Box
Topic: Purpose
Replies: 1
Views: 435

### Re: Purpose

The particle in a box is a simplification of finding an electron within a certain region. Both require use of Schrodinger's equation. It is useful primarily in quantum theory.
Sun Dec 03, 2017 11:18 pm
Forum: Calculating pH or pOH for Strong & Weak Acids & Bases
Topic: 12.29
Replies: 1
Views: 138

### Re: 12.29

To find pOH, the formula is -log(OH molarity).
I would write the chemical equation just to be safe.
Bases do react with water:
NH3 + H2O <--> NH4+ + OH-
Sun Dec 03, 2017 10:58 pm
Forum: Amphoteric Compounds
Topic: Amphiprotic [ENDORSED]
Replies: 5
Views: 511

### Re: Amphiprotic[ENDORSED]

An additional amphiprotic substance is hydrogen carbonate ion HCO3-
It can either donate its hydrogen to become CO3 (2-) or accept another hydrogen to become H2CO3
Sun Dec 03, 2017 10:52 pm
Forum: Properties & Structures of Inorganic & Organic Acids
Topic: Weak Acids / Strong Acids
Replies: 5
Views: 299

### Re: Weak Acids / Strong Acids

The following are strong acids:
HCl
HNO3
HBr
HI
H2SO4
HClO4
All other acids are considered weak.

The following are strong bases:
All group 1 metal hydroxides
LiOH
NaOH
KOH
RboH
CsOH
Some of the heavier group 2 metal hydroxides
Ca(OH)2
Sr(OH)2
Ba(OH)2
All other bases are considered weak.
Sun Dec 03, 2017 10:43 pm
Forum: Shape, Structure, Coordination Number, Ligands
Topic: Oxidation States
Replies: 4
Views: 243

### Re: Oxidation States

Look at the charge of the ligands and then the overall charge of the coordination complex. The sum of the ligand charges plus that of the transition metal equals the overall charge. From this equation solve for the transition metal charge which is the oxidation state.
Sun Dec 03, 2017 10:37 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Reverse Reactions [ENDORSED]
Replies: 3
Views: 242

### Re: Reverse Reactions[ENDORSED]

The k value of the reverse reaction is inverse of k.
If k is the equilibrium value for A+B<-->C K=C/(A*B)
then C<-->A+B 1/K=(A*B)/C
Sun Nov 26, 2017 11:41 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Kc or Kp for a heterogenenous equilibrium?
Replies: 2
Views: 173

### Re: Kc or Kp for a heterogenenous equilibrium?

For this example, as long as all the units are the same the equilibrium constant will be the same.
Sun Nov 26, 2017 11:27 pm
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: Pressure and Volume
Replies: 4
Views: 361

### Re: Pressure and Volume

According to the chemistry email, the test will go up to HW 11.63
Sun Nov 26, 2017 11:18 pm
Forum: Non-Equilibrium Conditions & The Reaction Quotient
Topic: Temperature
Replies: 4
Views: 472

### Re: Temperature

Think of the reaction based energy change, endothermic or exothermic. If the reaction is endothermic then energy can be treated as a species on the right side of the chemical equation. If the reaction is exothermic then energy can be treated as a species on the left side of the chemical equation. If...
Sun Nov 26, 2017 11:06 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: delta G
Replies: 2
Views: 147

### Re: delta G

When delta G is negative, the reaction is spontaneous in the forward direction. Subsequently when it is positive, the reaction is non-spontaneous in the forward direction and requires additional energy to progress. When delta H is positive and delta S is negative, the reaction is always non-spontane...
Sun Nov 26, 2017 10:57 pm
Forum: Ideal Gases
Topic: Inert gases
Replies: 2
Views: 373

### Re: Inert gases

Also when an inert gas is added to a system in equilibrium in a rigid container aka constant volume, the concentration of the respective products and reactants does not change. However, the total pressure of the system will increase by adding the inert gas.
Sun Nov 26, 2017 10:49 pm
Forum: Ideal Gases
Topic: Conversions- Gases
Replies: 3
Views: 247

### Re: Conversions- Gases

Even if we do need to convert between different units of pressure, it would ultimately just be dimensional analysis.
Sun Nov 12, 2017 11:41 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Drawing VSEPR Models
Replies: 2
Views: 164

### Re: Drawing VSEPR Models

The dashed line and the wedge/solid triangle are merely drawn to the portray that the molecule is three dimensional. The dashed line usually shows that the bonded pair is going into the plane of the page and the wedge is going out of the plane of the page. Use them when the molecule cannot be drawn ...
Sun Nov 12, 2017 10:54 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: 4.5
Replies: 2
Views: 198

### Re: 4.5

The shape of a molecule is independent of the dipole moments and based off the numbers of bonded atoms and lone pairs of electrons. ClO2+ has one central atom, two bonded pairs, and one lone pair of electrons (AX2E1). The lone pair-bonding pair has greater repulsion than the bonding pair-bonding pai...
Sun Nov 05, 2017 11:55 pm
Forum: Lewis Structures
Topic: 11/5 Review Sess. [S3N3]^-1
Replies: 2
Views: 295

### Re: 11/5 Review Sess. [S3N3]^-1

The structure is circular with the sulfur and nitrogen atoms alternating. One of the sulfur atoms will have a double bond for each of the adjacent nitrogen atoms and a lone pair. Another sulfur will have a single bond, a double bond, and two lone pairs. The final sulfur has two single bonds and two ...
Sun Nov 05, 2017 11:36 pm
Forum: Trends in The Periodic Table
Topic: Electron Affinity [ENDORSED]
Replies: 6
Views: 541

### Re: Electron Affinity[ENDORSED]

The general trend for electron affinity is that it increases across periods and decreases down groups with a few exceptions in the upper corner of the p-block. Group 15 elements generally have lower electron affinities than that of group 14 because the electron is entering an already half full p orb...
Sat Oct 28, 2017 11:02 pm
Forum: Ionic & Covalent Bonds
Topic: Test 3 preparation and date [ENDORSED]
Replies: 5
Views: 362

### Re: Test 3 preparation and date[ENDORSED]

For a comprehensive review you can do all the assigned problems for chapter 2 and review chapter 1 problems from section 1.6 onwards. According to the website we will only be tested on information from October 27th and before. The test will be whenever you have your scheduled discussion in the upcom...
Sat Oct 28, 2017 10:45 pm
Forum: Ionic & Covalent Bonds
Topic: Bond Strongth & Internuclear Distance
Replies: 2
Views: 475

### Re: Bond Strongth & Internuclear Distance

Just a follow up, you can use the coulomb potential energy equation to justify the fact that strong bonds have a shorter internuclear distance than weak bonds. The equation states that electrostatic energy is proportional to charge times charge divided by distance. If the charges are similar for the...
Sun Oct 22, 2017 11:54 pm
Forum: Electron Configurations for Multi-Electron Atoms
Topic: Electron Configuration of Th [ENDORSED]
Replies: 3
Views: 471

### Re: Electron Configuration of Th[ENDORSED]

The energy level 6d is actually lower than that the 5f orbital for thorium, so the d orbital would get filled first because that is more energetically favorable. Also, I think I remember Dr. Lavelle mentioning in class that f block elements are rare and radioactive and that we'll probably not focus ...
Sun Oct 22, 2017 11:33 pm
Forum: Electron Configurations for Multi-Electron Atoms
Topic: Silver electron configuration [ENDORSED]
Replies: 1
Views: 240

### Re: Silver electron configuration[ENDORSED]

From my understanding the electron configuration of silver would be 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s1 4d10. This occurs because the d (n-1) orbital is in a lower energy level than the s (n) orbital, so the d orbital is filled instead of the s orbital. I am pretty sure this exception will be expla...
Sun Oct 15, 2017 2:40 pm
Forum: DeBroglie Equation
Topic: Exercise 1.39 [ENDORSED]
Replies: 4
Views: 603

### Re: Exercise 1.39[ENDORSED]

Quick reminder that once you convert ounces to grams, then grams must then be converted to kg, as SI units must be used to solve debroglie equation problems. The other SI unit in the problem is meters per second for velocity.
Sun Oct 15, 2017 2:32 pm
Forum: Einstein Equation
Topic: Lyman and Blamer series [ENDORSED]
Replies: 7
Views: 731

### Re: Lyman and Blamer series[ENDORSED]

Another main difference between the Balmer and Lyman Series is their respective regions of the electromagnetic spectrum. The Balmer series generally occurs in the visible light region whereas the Lyman series occurs in the ultraviolet spectrum.
Wed Oct 04, 2017 12:04 pm
Forum: Empirical & Molecular Formulas
Topic: Empirical and Molecular Formulas
Replies: 3
Views: 329

### Re: Empirical and Molecular Formulas

To go from the empirical formula to the molecular formula, the molar mass of the molecular formula must be known. Divide the molecular formula molar mass by the empirical formula molar mass to get a natural number. Then multiply all the coefficients in the empirical formula by that number to get the...
Wed Oct 04, 2017 11:40 am
Forum: Significant Figures
Topic: Basic Sig Figs
Replies: 13
Views: 1068

### Re: Basic Sig Figs

If you are still confused, the link "Everything you want to know about Sig Fig" on Dr. Lavelle's website is extremely helpful. Another resource would be the appendix section 1C for the 6th edition of the textbook which covers sig figs in depth.

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