## Search found 62 matches

Sat Mar 16, 2019 10:06 am
Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
Topic: Ecell Values
Replies: 3
Views: 307

### Re: Ecell Values

The E cell is never multiplied, only made negative/positive when the direction of the reaction is reversed to display that it is an oxidizing reaction.
Sat Mar 16, 2019 10:03 am
Forum: Arrhenius Equation, Activation Energies, Catalysts
Topic: Activation Energy
Replies: 2
Views: 82

### Re: Activation Energy

When comparing the two the endothermic reaction Ae will be higher, than that of an exothermic reaction. If you look up graphs of the progress reaction and reference the different lengths of the activation energy I think it will be more clear to you as of why.
Sat Mar 16, 2019 10:00 am
Forum: Phase Changes & Related Calculations
Topic: moles / mass in phase change problems
Replies: 3
Views: 320

### Re: moles / mass in phase change problems

You'll have to convert to moles I think.
Sat Mar 16, 2019 9:53 am
Forum: Arrhenius Equation, Activation Energies, Catalysts
Topic: Collisions/Temperature dependence
Replies: 2
Views: 113

### Re: Collisions/Temperature dependence

Collison model refers to how an increase in temperature allows more collisions to occur at the correct kinetic rate in order for the reactants to interact. The activated complex model account refers to the activated energy required for a reaction to take place to allow the transition state to form w...
Sat Mar 16, 2019 9:47 am
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: Temperature and Le Chatlier's Principle
Replies: 6
Views: 410

### Re: Temperature and Le Chatlier's Principle

In the case of an endothermic reaction where reactants + heat react to form the product, increasing the heat will encourage more product to form and increase the K value. In exothermic reaction where reactants interact to form the products and heat, increasing the temperature encourages more reactan...
Sat Mar 16, 2019 9:43 am
Forum: Phase Changes & Related Calculations
Topic: Bond Enthalpies
Replies: 3
Views: 273

### Re: Bond Enthalpies

In the case of bond enthalpy, stoichiometric coefficients play a role in informing you of how many of that molecule is present. With this information, you can then count how many of each type of bond there are. In the end, the delta H of the reaction will be given by delta H (bond breakage) - delta ...
Mon Mar 04, 2019 5:14 pm
Forum: Zero Order Reactions
Topic: Different Orders
Replies: 5
Views: 175

### Re: Different Orders

We likely will not go above second order because these reactions are less common and too complex.
Mon Mar 04, 2019 5:13 pm
Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
Topic: Delta G rules
Replies: 8
Views: 211

### Re: Delta G rules

When delta G is less than zero it is spontaneous, more than zero it is not spontaneous, and equal to zero it is at equilibrium.
Mon Mar 04, 2019 5:10 pm
Forum: Kinetics vs. Thermodynamics Controlling a Reaction
Topic: Kinetics
Replies: 7
Views: 241

### Re: Kinetics

A reaction is controlled by kinetics when it has a very high activation energy and therefore, despite being thermodynamically favorable, it does not occur.
Wed Feb 20, 2019 11:27 am
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Units of Gibbs Free Energy
Replies: 5
Views: 209

### Re: Units of Gibbs Free Energy

Gibbs free energy is extensive because it relies on the amount associated with it. This is why questions may ask for the change in Gibbs free energy under standard conditions.
Wed Feb 20, 2019 11:25 am
Forum: Non-Equilibrium Conditions & The Reaction Quotient
Topic: ignoring x validity
Replies: 6
Views: 459

### Re: ignoring x validity

You can also check to see if it was okay to make this approximation by calculating the value for x by the original concentration and multiplying by 100 to see if it was truly less than 5%.
Wed Feb 20, 2019 11:23 am
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Reverse Reaction
Replies: 8
Views: 257

### Re: Reverse Reaction

A reverse reaction would be the inverse of the equilibrium constant for the forward reaction.
Sun Feb 17, 2019 10:05 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: vibrational entropy
Replies: 2
Views: 95

### Re: vibrational entropy

There likely is a way to measure vibrational entropy but for the sake of this class, I think that we just need to understand this in a conceptual sense.
Sun Feb 17, 2019 9:55 pm
Forum: Calculating Standard Reaction Entropies (e.g. , Using Standard Molar Entropies)
Replies: 35
Views: 1163

Last quarter they were handed back after lecture by our TA's.
Sun Feb 17, 2019 9:53 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Spontaneity
Replies: 4
Views: 214

### Re: Spontaneity

When delta G is negative, the reaction is spontaneous because this means that it does not need energy to proceed and will naturally follow the second law of thermodynamics by increasing in entropy.
Sun Feb 10, 2019 9:51 pm
Forum: Phase Changes & Related Calculations
Topic: Celsius and Kelvin
Replies: 6
Views: 218

### Re: Celsius and Kelvin

Use Celcius in the case of heat capacity problems.
Sun Feb 10, 2019 9:50 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Open vs Closed System
Replies: 13
Views: 1043

### Re: Open vs Closed System

Nicole Lee, an example of an isolated system that was given in the textbook was a high-quality thermos bottle since it is insulated and therefore does not exchange matter or energy.
Sun Feb 10, 2019 9:48 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: DeltaU=q+w
Replies: 5
Views: 146

### Re: DeltaU=q+w

The change in q and w can be assumed whereas internal energy is a state function.
Sat Feb 02, 2019 11:19 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Compression of Gas
Replies: 4
Views: 167

### Re: Compression of Gas

Consider work being done as a chemical reaction. It will either be endothermic and require energy or exothermic and release energy. In both of these instances, the change in energy will be correlated with a change in temperature as energy is transformed into thermal energy.
Sat Feb 02, 2019 11:15 pm
Forum: Phase Changes & Related Calculations
Topic: Steam vs Boiling Water
Replies: 10
Views: 1594

### Re: Steam vs Boiling Water

There is a difference in energy that causes steam to produce more. Refer to the concept of how temperature does not change when more heat is added during a change of physical state.
Sat Feb 02, 2019 10:50 pm
Forum: Thermodynamic Systems (Open, Closed, Isolated)
Topic: isolated system
Replies: 5
Views: 200

### Re: isolated system

In this class we would probably not need to do any calculations for this type of system seeing as no change can happen but you should be able to identify the characteristics of what an isolated system is.
Sat Jan 26, 2019 9:17 am
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: State Properties
Replies: 6
Views: 147

### Re: State Properties

State functions simply observe your conditions at that current moment, but in the case of work and heat, the efficiency of each reaction or how it is carried out can determine its value, meaning that you must take into account the entire pathway.
Sat Jan 26, 2019 9:12 am
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Method 2
Replies: 3
Views: 124

### Re: Method 2

Furthermore, since the bond enthalpy is different for each molecule, it is the least accurate of the three methods.
Sat Jan 26, 2019 9:09 am
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Delta H
Replies: 4
Views: 140

### Re: Delta H

When delta H is positive the reaction is endothermic. To understand this you should think of this as determining the amount of heat that is still in the reaction. Since an endothermic reaction absorbs heat, it would make sense that its change in heat would increase. On the other hand, when the react...
Wed Jan 16, 2019 11:09 am
Forum: Ideal Gases
Topic: Using Kc or Kp
Replies: 13
Views: 418

### Re: Using Kc or Kp

Problems might also require you to convert between concentration and partial pressure so it is important to remember how to manipulate the ideal gas law to suit this purpose.
Wed Jan 16, 2019 11:06 am
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: Negative pH
Replies: 12
Views: 690

### Re: Negative pH

This would be known as a superacid, which will not be commonly presented or mentioned in this chemistry course due to its lack of presence in biology.
Wed Jan 16, 2019 11:03 am
Forum: Equilibrium Constants & Calculating Concentrations
Topic: ICE table
Replies: 2
Views: 94

### Re: ICE table

ICE tables will be used when you know the initial concentrations of all the reactants (initial concentration of products will be zero) and the equilibrium concentration of one of the molecules involved in the chemical reaction. Using the table, you will enter the given information and use molar rati...
Tue Jan 08, 2019 6:53 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: hw questions - points
Replies: 9
Views: 306

### Re: hw questions - points

There are 7 points each week denoted to completing 7 homework questions from the textbook. In addition to that, 3 points are rewarded each week in reflection to 3 posts being made on Chemistry Community. The 7 problems will be due in your discussion section while the posts must be made before midnig...
Tue Jan 08, 2019 6:49 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: liquid vs aqueous
Replies: 2
Views: 1508

### Re: liquid vs aqueous

A liquid is a state of matter while an aqueous solution is a substance that is dissolved in the solvent water.
Tue Jan 08, 2019 6:47 pm
Forum: Ideal Gases
Topic: Equilibrium Constants
Replies: 4
Views: 198

### Re: Equilibrium Constants

These will impact the equilibrium constant because K is the ration of products divided by reactants. The concentration of each component is then multiplied by its stoichiometric coefficient, causing a change to the ratio itself from what would be expected if the coefficients were one.
Fri Dec 07, 2018 1:19 pm
Forum: Conjugate Acids & Bases
Topic: Water as an Acid/Base
Replies: 20
Views: 644

### Re: Water as an Acid/Base

Yes, essentially water can be either an acid or a base depending on whether it is reacting with an acid or base.
Fri Dec 07, 2018 1:18 pm
Forum: Acidity & Basicity Constants and The Conjugate Seesaw
Topic: Final Exam
Replies: 3
Views: 192

### Re: Final Exam

If you look at Outline 6, the professor has outlined topics that are relevant and must be understood about this course.
Sun Dec 02, 2018 7:59 pm
Forum: Shape, Structure, Coordination Number, Ligands
Topic: Coordination Sphere
Replies: 4
Views: 160

### Re: Coordination Sphere

Atoms that are outside of the coordination sphere are not directly attached to the central atom.
Sun Dec 02, 2018 7:58 pm
Forum: Hybridization
Topic: pi vs sigma
Replies: 12
Views: 528

### Re: pi vs sigma

This is because pi bonds, unlike sigma bonds, are unable to rotate, meaning that they will break more easily in a chemical reaction.
Sun Dec 02, 2018 7:56 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Bond Angles
Replies: 12
Views: 483

### Re: Bond Angles

Using the VSEPR model, you will be expected to list the bond angle of a molecule in relation to its central atom.
Tue Nov 27, 2018 10:45 am
Forum: *Molecular Orbital Theory (Bond Order, Diamagnetism, Paramagnetism)
Topic: test #3
Replies: 14
Views: 716

### Re: test #3

He has posted the sections from the textbook that we should read. I would use this as a guideline for what you should know for the test.
Tue Nov 27, 2018 10:43 am
Forum: Determining Molecular Shape (VSEPR)
Topic: Seesaw or Square Planar
Replies: 3
Views: 410

### Re: Seesaw or Square Planar

Seesaw is when there are 5 regions of electron density with one lone pair whereas square planar has 6 regions of electron density and two lone pairs. It may be easier for you if find the electron region density and then consider where the electrons would exist in order to find the correct molecular ...
Tue Nov 27, 2018 10:41 am
Forum: Hybridization
Topic: Just Kind of Confused
Replies: 13
Views: 378

### Re: Just Kind of Confused

They are both the same and simply depend on your own preference.
Tue Nov 27, 2018 10:40 am
Forum: Determining Molecular Shape (VSEPR)
Topic: Double Bonds as Regions of Electron Density
Replies: 5
Views: 152

### Re: Double Bonds as Regions of Electron Density

All bonds count as one region of electron density. Instead of considering the number of bonds it will be easier for you if you consider the number of atoms bonded to the central atom.
Tue Nov 27, 2018 10:39 am
Forum: Hybridization
Topic: Number
Replies: 2
Views: 121

### Re: Number

Hybridization is based on regions of electron density meaning that you should count the number of bonded atoms and the number of lone pairs together.
Tue Nov 27, 2018 10:37 am
Forum: Determining Molecular Shape (VSEPR)
Topic: Bond angle
Replies: 5
Views: 454

### Re: Bond angle

No. Even though the two have the same molecular shape, the bond angle is also influenced by the lone pairs on the central atom since all regions of electron density play a role on the bond angles.
Tue Nov 27, 2018 10:35 am
Forum: Hybridization
Topic: Pi bonds
Replies: 3
Views: 153

### Re: Pi bonds

Pi bond overlap above and below the nuclear axis.
Fri Nov 16, 2018 2:39 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Lone Pairs in Molecular Shape
Replies: 4
Views: 203

### Re: Lone Pairs in Molecular Shape

Actually, lone pairs have a higher repulsion strength than an atom and work to repulse the bonded atoms, which is why it is important to consider them when finding the electron dispersion arrangement. After that, you will not draw them in the molecular shape, which accounts for why in these cases th...
Fri Nov 16, 2018 2:35 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Octahedral Shape
Replies: 4
Views: 253

### Re: Octahedral Shape

XeF4 has an electron dispersion arrangement of octahedral due to its six regions of electron but since lone pairs are not shown in the molecular shape despite their influence, this molecule's molecular shape would be square planar, leaving the two lone pairs of electrons not drawn.
Fri Nov 16, 2018 2:32 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Tetrahedral shape
Replies: 5
Views: 201

### Re: Tetrahedral shape

Any molecular shape can be slightly distorted when different atoms are bonded to the central atom due to their different numbers of valence shell electrons and the role they play in repulsing the other atoms of the molecule.
Sat Nov 10, 2018 9:34 am
Forum: Dipole Moments
Topic: Boiling Points
Replies: 3
Views: 138

### Re: Boiling Points

Hydrogen bonding is a form of bonding between atoms that can only occur when hydrogen bonds with lone pair electrons in nitrogen, oxygen, or fluorine. This form of electrostatic attraction creates a bond that is so strong, it is almost similar to that of a covalent bond. In this example, H2O can for...
Sat Nov 10, 2018 9:25 am
Forum: Determining Molecular Shape (VSEPR)
Topic: Naming the molecular shape
Replies: 4
Views: 227

### Re: Naming the molecular shape

The steric number has not yet been discussed in lectures but it is the number of atoms bonded to the central atom and the number of lone pairs. This number is used in the VESPR model and determined from the Lewis structure. This number determines shape by maximizing the distance between the valence ...
Sat Nov 10, 2018 9:17 am
Forum: Electronegativity
Topic: Electronegativity
Replies: 8
Views: 369

### Re: Electronegativity

Electronegativity is the measure of the tendency of an element to attract or steal another element's electrons. The tendency increases as you go to the right of a periodic table because the nuclear charge of the element increasing, attracting more elements to its center. Similarly, the tendency incr...
Sun Nov 04, 2018 10:23 pm
Forum: Properties of Light
Topic: Photoelectric Effect
Replies: 7
Views: 384

### Re: Photoelectric Effect

Yes, the intensity of the light will influence the number of electrons released, but first, the light must reach the needed frequency to eject any electrons.
Sun Nov 04, 2018 10:21 pm
Forum: Formal Charge and Oxidation Numbers
Topic: Formal Charge and Lewis Structures
Replies: 5
Views: 254

### Re: Formal Charge and Lewis Structures

No, but it is recommended that you still identify the formal charge of each atom to ensure that you have drawn the best possible structure.
Sun Nov 04, 2018 10:19 pm
Forum: Formal Charge and Oxidation Numbers
Topic: Formal Charge on Central Atom
Replies: 9
Views: 405

### Re: Formal Charge on Central Atom

Any sort of charge on the central atom will cause the molecule to be less stable, meaning that it is not the best possible structure. For this reason, it is better to find another better structure that has the charge on one of the other atoms.
Fri Oct 26, 2018 4:10 pm
Forum: Ionic & Covalent Bonds
Topic: Calculating number of valence electrons in bonds
Replies: 5
Views: 671

### Re: Calculating number of valence electrons in bonds

First, you should reference the periodic table to identify how many valence electrons this element has. Valence electrons are the element in the highest energy orbital of that atom and are the electrons that are used in chemical bonding. After counting the number of valence electrons for each atom, ...
Fri Oct 26, 2018 4:02 pm
Forum: Ionic & Covalent Bonds
Topic: Chemical Bonding
Replies: 8
Views: 299

### Re: Chemical Bonding

Today we began going over chemical bonding by going into the basics of the Lewis dot structure and the difference between ionic and covalent bonds.
Fri Oct 26, 2018 4:00 pm
Forum: Ionic & Covalent Bonds
Topic: Ground State Electron Configurations
Replies: 7
Views: 176

### Re: Ground State Electron Configurations

In an effort to save time when writing the elecron configuration of an element, it is recommended to write the name of the noble gas on that occurs just before the element for which you are writiuabout. From there you continue with the electron configuration as you would normally.
Mon Oct 15, 2018 3:55 pm
Forum: Bohr Frequency Condition, H-Atom , Atomic Spectroscopy
Topic: Planck's constant
Replies: 7
Views: 221

### Re: Planck's constant

Planck's constant is a number used in quantum mechanics that displays the proportionality found between the energy and frequency of a photon.
Mon Oct 15, 2018 3:52 pm
Forum: Student Social/Study Group
Topic: Note Taking
Replies: 32
Views: 2501

### Re: Note Taking

For myself, handwritten notes have been the most useful method that I have tried for note taking in class. By writing out my notes, it is easier to copy down any diagrams that I find important and note down equations. In addition, I tend to write down the things that are said that resonate with me o...
Mon Oct 15, 2018 3:48 pm
Forum: Properties of Light
Topic: Test 2
Replies: 17
Views: 453

### Re: Test 2

The second test will include topics from chapter 1 and chapter 2. If you review the Outline 2, it will tell you to read both chapter and will assign you problems related to key concepts that will most likely also be found on the test.
Fri Oct 12, 2018 10:12 am
Forum: Properties of Light
Topic: Threshold Energy
Replies: 11
Views: 301

### Re: Threshold Energy

Threshold energy is the energy required in an experiment to remove an electron from a metal surface. Different metals will require different threshold energies. This energy will either be provided in the problem or be something that you must solve for.
Fri Oct 12, 2018 10:10 am
Forum: Photoelectric Effect
Topic: electron with no KE in reality
Replies: 2
Views: 141

### Re: electron with no KE in reality

If an electron has no kinetic energy, then there was still enough energy in the incoming light to remove the electron from the metal. Because the threshold used up all of the energy, there is no excess or kinetic energy that would allow the electron to move from its current position to another.
Fri Oct 12, 2018 10:07 am
Forum: General Science Questions
Topic: Exams.
Replies: 2
Views: 173

### Re: Exams.

Similarly to the large equations sheet that was included in test 1, for each test, the midterm and final included, we will be provided with an equations sheet and a periodic table. It will be your task to understand the problem and know how to utilize the various equations and constants give to find...
Tue Oct 02, 2018 10:03 pm
Forum: Significant Figures
Topic: Significant Figures
Replies: 6
Views: 363

### Re: Significant Figures

Does anybody know if you must maintain a correct number of significant figures while working out, for example, a molarity problem, or if you would simply apply the correct number of significant figures once you have found your solution?
Tue Oct 02, 2018 9:49 pm
Forum: Molarity, Solutions, Dilutions