## Search found 64 matches

Sun Mar 17, 2019 2:21 am
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: galvanic cells
Replies: 6
Views: 464

### Re: galvanic cells

A porous disk is a single line | as opposed to a salt bridge which is two lines ||. In a cell diagram, porous disks look the same as a phase change which is also indicated by a single line |.
Sun Mar 17, 2019 2:13 am
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Cell Diagram
Replies: 2
Views: 266

### Re: Cell Diagram

H+ would be on whichever side of the redox reaction it is on. The redox reaction is the overall reaction found when you combine both half reactions.
Sat Mar 16, 2019 2:01 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: C(gr) vs Pt(s)
Replies: 1
Views: 80

### Re: C(gr) vs Pt(s)

Pt(s) is an inert conductor used as an electrode to transfer e- when a half reaction has no conducting solids.
Tue Mar 12, 2019 12:53 am
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Molecularity
Replies: 2
Views: 111

### Re: Molecularity

I believe Dr. Lavelle expects us to determine the molecularity of an elementary step in order to determine the rate law.
Thu Mar 07, 2019 10:27 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Reaction Rate Orders
Replies: 4
Views: 177

### Re: Reaction Rate Orders

The overall order of a reaction is determined by the sum of the exponents (the order of each reactant).
Thu Mar 07, 2019 9:44 pm
Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
Topic: Test 2
Replies: 4
Views: 230

### Re: Test 2

Can you be more specific? What was the question?
Wed Mar 06, 2019 1:40 am
Forum: First Order Reactions
Topic: Units
Replies: 1
Views: 83

### Re: Units

It is the reaction rate given the amount of moles provided. Question 15.11 is asking for the initial rate of decomposition of N2O5 given 3.45 g of N2O5.
Sun Mar 03, 2019 4:41 pm
Forum: General Rate Laws
Topic: Kinetics
Replies: 3
Views: 142

### Re: Kinetics

The average rate is the average instantaneous reaction rate over a period of time during the reaction. The average rate of reaction can be calculated for any time interval. The instantaneous rate is the rate at a particular instant of time during the reaction represented by the instantaneous slope o...
Sun Mar 03, 2019 12:53 am
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: E vs E naught
Replies: 5
Views: 196

### Re: E vs E naught

Eº is the standard state cell potential. This means that it is under standard conditions (1 atm and 25°C).
Thu Feb 28, 2019 12:22 am
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Half rxn
Replies: 1
Views: 49

### Re: Half rxn

Conceptually, a half reaction is either a reduction half reaction or a oxidation half reaction. A half reaction makes up one part of a redox reaction. The redox reaction is separated into two half reactions by identifying identify what is getting reduced and what is getting oxidized. Mathematically,...
Sun Feb 24, 2019 11:54 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Salt Bridges
Replies: 3
Views: 127

### Re: Salt Bridges

Usually potassium chloride or sodium chloride are used because they are chemically inert.
Sun Feb 24, 2019 11:42 pm
Forum: Balancing Redox Reactions
Topic: Redox Rxns in Acidic and Basic Solutions
Replies: 6
Views: 182

### Re: Redox Rxns in Acidic and Basic Solutions

The problem will usually specify if it is in an acidic or basic solution. From there you can decide whether to use H20 or OH-.
Sun Feb 24, 2019 11:36 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Gibbs Free Energy
Replies: 2
Views: 144

### Re: Gibbs Free Energy

Gibbs free energy of reaction is the standard free energy of formation of products minus the standard free energy of formation of the reactants. It is modeled by the equation: ΔG(rxn)=∑ΔG(products)−∑ΔG(reactants). The standard free energies of formation can be used to calculate the free energy chang...
Sun Feb 17, 2019 5:13 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: Calculating Standard Entropy of Fusion
Replies: 2
Views: 119

### Re: Calculating Standard Entropy of Fusion

Enthalpy of fusion is the amount of heat energy required to change the state of a substance from a solid to a liquid, at its melting point. When a solid becomes a liquid, it's called melting or fusion.
Sun Feb 17, 2019 5:00 pm
Forum: Van't Hoff Equation
Topic: Different Constants of Eqn
Replies: 2
Views: 138

### Re: Different Constants of Eqn

The Van't Hoff Equation can be used to calculate K at a different temperature if the standard enthalpy is known.
Tue Feb 12, 2019 10:06 pm
Forum: Calculating the pH of Salt Solutions
Topic: Test 1 Question 5
Replies: 1
Views: 324

### Test 1 Question 5

Question 5: Sodium propionate (NaC3H5O2) is used as a food preservative. What is the pH of a 0.020 M solution of sodium propionate? The pKa of propionic acid (C3H6O2) is 4.88. C3H5O2-(aq) + H20(l) ⇌ C3H6O2(aq) + OH-(aq) I don't understand the steps that need to be done to answer this question. Can s...
Sun Feb 10, 2019 11:33 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: How to Calculate Degeneracy
Replies: 5
Views: 163

### Re: How to Calculate Degeneracy

Degeneracy(w) is the number of ways to achieve a given energy state. w = (#of microstates available)^n , n=# of particles present. This is the used in the equation deltaS = Kb ln w
Sun Feb 10, 2019 11:22 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Using R
Replies: 10
Views: 358

### Re: Using R

All the different values for R should be on the constants and equations sheet provided.
Sun Feb 10, 2019 11:19 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Work
Replies: 2
Views: 93

### Re: Work

Work is being done on the system by its surroundings when the system absorbs heat. This would be positive. When work is being done by the system on its surroundings then they system releases heat. This would be negative.
Sun Feb 10, 2019 11:13 pm
Forum: Phase Changes & Related Calculations
Topic: Heat vs Q
Replies: 5
Views: 191

### Re: Heat vs Q

The reaction quotient, Q, is calculated when you need to determine which direction a non-equilibrium reaction will proceed.
Sun Feb 10, 2019 11:02 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: conversions
Replies: 3
Views: 110

### Re: conversions

They should be on the constants and equations sheet provided.
Sun Feb 03, 2019 1:14 am
Forum: Concepts & Calculations Using First Law of Thermodynamics
Replies: 4
Views: 175

Adiabatic means that it is not permitting or accompanied by the passage of energy as heat.
Sun Feb 03, 2019 12:54 am
Forum: Phase Changes & Related Calculations
Topic: Heat
Replies: 6
Views: 210

### Re: Heat

If the reaction releases heat and the surroundings warm, then the reaction is exothermic and negative.
If the reaction requires heat and the surroundings cool, then the reaction is endothermic and positive.
Sun Feb 03, 2019 12:49 am
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: Entropy in Reversible Process
Replies: 2
Views: 100

### Re: Entropy in Reversible Process

Reversible processes are when you are able to convert all of the energy you put into a system into work. The second law of thermodynamics states that in a reversible process, the entropy of the universe is constant.
Sun Jan 27, 2019 11:14 pm
Forum: Phase Changes & Related Calculations
Topic: Steam
Replies: 11
Views: 390

### Re: Steam

Yes, steam causes more severe burns because it has more energy, with a temperature of 40.7 kJ/mol, as opposed to liquid which has a temperature of 7.5 kJ/mol. This is demonstrated using the heating curve for water.
Sun Jan 27, 2019 11:06 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Heat and Enthalpy
Replies: 2
Views: 90

### Re: Heat and Enthalpy

Enthalpy is the amount of heat released or absorbed at a constant pressure. Heat is the energy that causes those changes.
Sun Jan 27, 2019 11:00 pm
Forum: Phase Changes & Related Calculations
Topic: reversible/irreversible
Replies: 8
Views: 225

### Re: reversible/irreversible

Combustion cannot be reversible. The products (carbon dioxide and water) cannot react to form the reactants (fuel and oxygen).
Sun Jan 20, 2019 10:40 pm
Forum: Non-Equilibrium Conditions & The Reaction Quotient
Topic: Salt formation
Replies: 3
Views: 133

### Re: Salt formation

Salts are ionic compounds formed by a neutralization reaction between an acid an a base. They can either raise or lower the pH of a solution.
Sun Jan 20, 2019 10:30 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Water in ICE tables
Replies: 10
Views: 631

### Re: Water in ICE tables

The concentration of a pure substance does not change in a reaction! Therefore solids and liquids are not included in K expression.
Sun Jan 20, 2019 10:14 pm
Forum: Calculating pH or pOH for Strong & Weak Acids & Bases
Topic: Question 12.45 (Sixth Edition)
Replies: 1
Views: 61

### Re: Question 12.45 (Sixth Edition)

pKa is the negative base-10 log of Ka. Ka is the acid dissociation constant.The smaller the pKa, the stronger the acid. pKb is the negative base-10 log of Kb. Kb is the base dissociation constant. The smaller the pKb, the stronger the base. For this question we would just order then from increasing ...
Sun Jan 13, 2019 6:25 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Partial Pressure and Concentration [ENDORSED]
Replies: 3
Views: 109

### Re: Partial Pressure and Concentration[ENDORSED]

To convert between partial pressure and concentration you would use the ideal gas law, PV=nRT.
To convert partial pressure to concentration, you would use the equation (n/V)=P/RT or conc.=P/RT
To convert concentration to partial pressure, you would use the equation P=(n/V)RT or P=(conc.)RT
Sun Jan 13, 2019 6:15 pm
Forum: Non-Equilibrium Conditions & The Reaction Quotient
Topic: Converting Qc to Qp [ENDORSED]
Replies: 3
Views: 139

### Re: Converting Qc to Qp[ENDORSED]

Would it be the same as K=[products]/[reactants]?
Sun Jan 13, 2019 6:03 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: constants
Replies: 4
Views: 185

### Re: constants

Also, the reaction quotient, Q, is compared to the equilibrium constant, K, to determine which direction a reaction will proceed. Q, Qc, or Qp are calculated the same way as K.
Wed Jun 13, 2018 8:08 am
Forum: Molarity, Solutions, Dilutions
Topic: test 1 Q.1 Help?
Replies: 1
Views: 177

### Re: test 1 Q.1 Help?

For this question you are looking for molarity. You would start this problem by converting your grams of Li2CO3 to moles, then multiply that by 2mol Li2/1mol Li2CO3 to find the amount of Li2 in 1 mol of Li2CO3. After this, divide your amount of moles by 1.00L of water since molarity is mol/L.
Sun Jun 10, 2018 11:57 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Pi/Sigma bonds clarification
Replies: 4
Views: 193

### Re: Pi/Sigma bonds clarification

There is always one sigma bond in any kind of bond, and additional bonds are pi bonds. A single bond is 1 sigma bond. A double bond is 1 sigma bond and 1 pi bond. A triple bond is 1 sigma bond and 2 pi bonds.
Sun Jun 10, 2018 1:44 am
Forum: Determining Molecular Shape (VSEPR)
Topic: Drawing Tetrahedral Structures
Replies: 4
Views: 234

### Re: Drawing Tetrahedral Structures

No we do not need to draw the VSEPR models, they are just used to visualize the 3D structure.
Sun Jun 03, 2018 3:22 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Textbook 4.21 part d
Replies: 3
Views: 204

### Re: Textbook 4.21 part d

Dr. Lavelle replied to another student saying to write slightly less than 109.5 since students are not expected to know the exact (experimentally measured) bond angles for individual molecules.
Sun Jun 03, 2018 3:17 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Naming shape
Replies: 7
Views: 390

### Re: Naming shape

Since you are taking into consideration the lone pairs, the molecule would not be trigonal bipyramidal.
Fri Jun 01, 2018 11:06 pm
Forum: Shape, Structure, Coordination Number, Ligands
Topic: Bond types
Replies: 6
Views: 271

### Re: Bond types

The dashed and solid lines are used to show the 3D shape of the molecule. The solid lines are used as the backbone for the structure, here bonds exist on the plane of the paper. The solid wedges represent groups that are pointing out of the page, towards you, and dashed lines represent groups pointi...
Mon May 28, 2018 2:59 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: I3- Molecular Shape
Replies: 2
Views: 792

### Re: I3- Molecular Shape

The lewis structure for I3- has two iodines attached to the central iodine and three lone pairs on the central iodine. This gives you 5 regions of electron density around the central atom. This is a trigonal bipyramidal shape. The electron pairs repel each other to maximize their distance from one a...
Wed May 23, 2018 11:17 am
Forum: Determining Molecular Shape (VSEPR)
Topic: VSEPR on test 3?
Replies: 3
Views: 234

### Re: VSEPR on test 3?

Test 3 is on chapter 3 so just lewis structures. VSEPR is chapter 4.
Wed May 23, 2018 11:14 am
Forum: Electronegativity
Topic: Question for Exams [ENDORSED]
Replies: 5
Views: 495

### Re: Question for Exams[ENDORSED]

We just need to know the general trends on the periodic table.
Fri May 18, 2018 12:01 pm
Forum: Ionic & Covalent Bonds
Topic: Help on 3.21
Replies: 2
Views: 127

### Re: Help on 3.21

The ground state configuration for Te2- is [Xe] because it has gained 2 electrons. Xe has filled its orbitals meaning it has no unpaired electrons. The ground state configuration for Ag+ is [Kr]4d10 because it has lost one electron from the 4s orbital. Remember that the electron configuration for Ag...
Fri May 18, 2018 11:49 am
Forum: Lewis Structures
Replies: 4
Views: 537

Also, after drawing the Lewis structure and finding the total amount of valence electrons, if there is a radical you will notice that the central atom does not complete its octet. For 3.55 part B, CH3 has 7 valence electrons. Carbon will form 3 bonds with the hydrogens and will have one lone pair el...
Sat May 12, 2018 1:36 pm
Forum: Lewis Structures
Topic: NO
Replies: 3
Views: 83

### Re: NO

At the end of lecture, the TA explaining this section started drawing the Lewis structure of NO with a double bond. I didn't hear what she said, but I believe a double bond would work. Also, this would not be resonance.
Sat May 12, 2018 1:28 pm
Forum: Ionic & Covalent Bonds
Topic: Metals
Replies: 4
Views: 198

### Re: Metals

These elements are trying to lose electrons to obtain a noble gas configuration.
Tue May 08, 2018 2:28 pm
Forum: Wave Functions and s-, p-, d-, f- Orbitals
Topic: Paramagnetic vs Diamagnetic
Replies: 2
Views: 229

### Re: Paramagnetic vs Diamagnetic

Paramagnetic means it has unpaired electrons. Diamagnetic means it has paired electrons.
Sun May 06, 2018 11:37 pm
Forum: Electron Configurations for Multi-Electron Atoms
Topic: 3d before 4s
Replies: 9
Views: 503

### Re: 3d before 4s

The 4s orbital has higher energy then the 3d orbital. After the 4s is completely filled, 3d is lower in energy than 4s.
Wed May 02, 2018 12:13 am
Forum: Electron Configurations for Multi-Electron Atoms
Topic: Ground state for Sc
Replies: 2
Views: 187

### Re: Ground state for Sc

For your first question, electron configuration should be ordered primarily by increasing order of shells, the principle quantum number n. The ground state of scandium is [Ar] 3d¹ 4s² because 3 comes before 4. For your second question, [Ar] is present in the ground state because it is the last noble...
Tue May 01, 2018 3:15 pm
Forum: Wave Functions and s-, p-, d-, f- Orbitals
Topic: 2.17
Replies: 4
Views: 223

### Re: 2.17

Yes, the pattern for mI will always be -I to +I. Count the values to get the number of orbitals.
Tue May 01, 2018 3:08 pm
Forum: Wave Functions and s-, p-, d-, f- Orbitals
Topic: Question 2.13
Replies: 1
Views: 113

### Re: Question 2.13

The question is just asking for the orientation of the lobes, meaning what axis they are on. The Px orbital will have its lobes oriented along the x-axis, the Py orbitals will have its lobes oriented along the y-axis, and the Pz orbital will have its lobes oriented along the z-axis.
Mon Apr 30, 2018 11:51 pm
Forum: Quantum Numbers and The H-Atom
Topic: Electron Configuration form
Replies: 4
Views: 180

### Re: Electron Configuration form

It would not be incorrect to use shorthand, but it is better to show the electron configurations because they provide more detail. For example, the shorthand for K+ is [Ar] but it is better to write it out as [Ne] 3s^2 3p^6.
Sun Apr 29, 2018 10:10 pm
Forum: Bohr Frequency Condition, H-Atom , Atomic Spectroscopy
Topic: Lyman Series
Replies: 4
Views: 195

### Re: Lyman Series

The Lyman Series uses UV light which is stronger than visible light. It releases electrons to n=1, the lowest energy level.
Sun Apr 29, 2018 9:55 pm
Forum: Heisenberg Indeterminacy (Uncertainty) Equation
Topic: In class problem [ENDORSED]
Replies: 6
Views: 472

### Re: In class problem[ENDORSED]

The uncertainty (3.4x10^10 m/s) is greater than the speed of light (3.0x10^8 m/s). This makes it an unrealistic number.
Sun Apr 29, 2018 9:39 pm
Forum: Quantum Numbers and The H-Atom
Topic: Four Different Quantum Numbers
Replies: 7
Views: 327

### Re: Four Different Quantum Numbers

There can be a maximum of two electrons in the same orbital. Their Spin Magnetic Quantum Number cannot be the same, since they have opposite spins. This is supported by the Pauli Exclusion Rule.
Sun Apr 22, 2018 5:43 pm
Forum: DeBroglie Equation
Topic: Wavelength and De Broglie Equation [ENDORSED]
Replies: 9
Views: 463

### Re: Wavelength and De Broglie Equation[ENDORSED]

De Broglie's equation only applies to objects with mass. So, it does not apply to light because photons don't have a mass.
Sun Apr 22, 2018 5:37 pm
Forum: Bohr Frequency Condition, H-Atom , Atomic Spectroscopy
Topic: Which Equation Do We Never Use for Light? [ENDORSED]
Replies: 3
Views: 279

### Re: Which Equation Do We Never Use for Light?[ENDORSED]

Dr. Lavelle said that de Broglie's Equation ( lambda=h/p) doesn't apply to light because it measures objects with mass and photons do not have mass.
Sun Apr 22, 2018 5:34 pm
Forum: Photoelectric Effect
Topic: Example 1.5 [ENDORSED]
Replies: 8
Views: 428

### Re: Example 1.5[ENDORSED]

I was also confused about 9.109x10^-31 being the mass of an electron. Did he briefly go over this during lecture because I don't remember this being mentioned.
Sun Apr 15, 2018 10:37 pm
Forum: Photoelectric Effect
Topic: Threshold Energy [ENDORSED]
Replies: 12
Views: 664

### Re: Threshold Energy[ENDORSED]

In Friday's lecture, Dr. Lavelle mentioned that the energy of of the photon is equal to the sum of the threshold energy and the kinetic energy.
Sun Apr 15, 2018 10:21 pm
Forum: Properties of Light
Topic: Equations [ENDORSED]
Replies: 8
Views: 307

### Re: Equations[ENDORSED]

It depends on the information given in the problem. Equations can be rearranged or combined to form an equation that will fit the problem. For example, E=hv can be combined with c=lambda x v, to form the equation E=hc/lambda, when you are looking for the wavelength but are not given the frequency.
Fri Apr 13, 2018 11:31 am
Forum: Properties of Light
Topic: Speed in vacuum
Replies: 3
Views: 243

### Re: Speed in vacuum

He did say 3.00x10^8 m/s is the speed in vacuum during Monday's lecture. By this I believe he means the speed of light in a vacuum, which is the constant 3.00x10^8 m/s., meaning the light is traveling through empty space where nothing else can travel through. If light is not traveling at c (constant...
Sun Apr 08, 2018 12:58 am
Forum: Balancing Chemical Reactions
Topic: Balancing equations with fractions [ENDORSED]
Replies: 13
Views: 737

### Re: Balancing equations with fractions[ENDORSED]

Yes, you have to multiply by 2 to cancel out the fraction. The stoichiometric coefficients should be whole numbers, not fractions.
Sun Apr 08, 2018 12:24 am
Forum: Empirical & Molecular Formulas
Topic: Homework Problem F9
Replies: 2
Views: 219

### Re: Homework Problem F9

Yes, the ratio between atoms in a molecule is the empirical formula.
Fri Apr 06, 2018 12:55 pm
Forum: Limiting Reactant Calculations
Topic: M.5
Replies: 4
Views: 235

### Re: M.5

In this problem, we know that 12 moles of the product ClO2F is produced and 2 moles of the product Br2. Only 4 BrF3 were needed for the reaction, but it is carried out with 5 moles of BrF3. That is the excess reactant, so there is 1 mole of excess BrF3.