## Search found 51 matches

Sun Mar 18, 2018 9:43 am
Forum: General Rate Laws
Topic: Rate constant units
Replies: 6
Views: 507

### Re: Rate constant units

for first order, M/s
for second order, 1/s
for third order, 1/Ms
in general: $M^{1-n}$$time^{-1}$
Sat Mar 17, 2018 9:19 pm
Forum: Arrhenius Equation, Activation Energies, Catalysts
Topic: when exactly do you use the Arrhenius equation?
Replies: 3
Views: 364

### Re: when exactly do you use the Arrhenius equation?

The Arrhenius equation can be used to find pre-exponential factor, the rate constant, activation energy, or temperature based on what information given in the question.
Sat Mar 17, 2018 9:18 pm
Forum: Calculating Work of Expansion
Topic: Work with changeP and constant V
Replies: 4
Views: 338

### Re: Work with changeP and constant V

A gas enclosed by a piston in a cylinder can do work on the piston, the work being the pressure multiplied by the change in volume. If the volume doesn't change, no work is done. If there is no change in volume ($\Delta$V=0), work will equal 0.
Sun Mar 11, 2018 3:44 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Energy barrier
Replies: 3
Views: 120

### Re: Energy barrier

An activation energy is a potential energy barrier that reactants have to get over in order to react. The higher this potential, the slower the reaction (the exact relationship is shown by the Arrhenius equation). It follows naturally that the step with the highest activation energy will be the slow...
Sun Mar 11, 2018 3:39 pm
Forum: *Enzyme Kinetics
Topic: Catalysts and activation energy?
Replies: 2
Views: 219

### Re: Catalysts and activation energy?

Catalysts increase the reaction rate without being consumed. A catalyst provides an alternative route for the reaction. That alternative route has a lower activation energy.
Sun Mar 11, 2018 3:23 pm
Forum: Arrhenius Equation, Activation Energies, Catalysts
Topic: Elementary Step
Replies: 4
Views: 190

### Re: Elementary Step

An elementary reaction is a chemical reaction in which one or more chemical species react directly to form products in a single reaction step and with a single transition state. There are no intermediates and only one transition state. It can be unimolecular, bimolecular, or termolecular. With regar...
Sun Mar 04, 2018 6:27 pm
Forum: General Rate Laws
Topic: Half-Life
Replies: 2
Views: 177

### Re: Half-Life

Half-Life is the time it takes for one-half of the atoms of a radioactive material to disintegrate. The "half" is an arbitrary amount that represents the amount disintegrated; it can be a "quarter-life" or a "fifth-life". It is useful in dating artifacts, treating patie...
Sun Mar 04, 2018 6:21 pm
Forum: Arrhenius Equation, Activation Energies, Catalysts
Topic: Catalysts
Replies: 3
Views: 225

### Re: Catalysts

Catalysts are not reactants; they just lower the activation energy. They are substances added to a chemical reaction to speed up the reaction rate without being consumed. Catalysts are not in the overall chemical reaction. For example, enzymes are catalyst in biochemical reactions.
Sun Mar 04, 2018 3:10 pm
Forum: First Order Reactions
Topic: orders of a reaction
Replies: 3
Views: 172

### Re: orders of a reaction

For zero-order reactions, the concentration of one of the reactants is independent to the reaction rate. For first-order reactions, the concentration of one of the reactants and reaction rate is directly proportional. So if the concentration of one of the reactants is doubled, the reaction rate is d...
Sun Feb 25, 2018 7:14 pm
Forum: *Free Energy of Activation vs Activation Energy
Topic: What is Free Energy of Activation
Replies: 5
Views: 1199

### Re: What is Free Energy of Activation

Moreover, free energy of activation includes both the standard enthalpy of activation and the standard entropy of activation; thus, it is more accurate than the activation energy, which only accounts for the standard enthalpy of activation. Although both free energy of activation and activation ener...
Sun Feb 25, 2018 7:07 pm
Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
Topic: Electrochemical Series
Replies: 3
Views: 223

### Re: Electrochemical Series

Electrochemical series is a series of chemical elements arranged in order of their standard electrode potentials.
Sun Feb 25, 2018 6:56 pm
Forum: Kinetics vs. Thermodynamics Controlling a Reaction
Topic: Kinetic vs. Thermodynamics
Replies: 3
Views: 225

### Re: Kinetic vs. Thermodynamics

A kinetic product is one that forms the fastest as the product is associated with the lowest energy barrier to its formation. At low temperatures, the reaction is under kinetic control (rate, irreversible conditions) and the major product is that from fastest reaction. A thermodynamic product is one...
Sun Feb 25, 2018 6:43 pm
Forum: Kinetics vs. Thermodynamics Controlling a Reaction
Topic: Positive Slope???
Replies: 4
Views: 263

### Re: Positive Slope???

If the slope of the tangent line is positive, the forward reaction is favored. Because products are favored, the amount of products should be increasing. Thus, they have a positive rate of change. If the slope of the tangent line is negative, the reverse reaction is favored. More reactants will be p...
Sun Feb 18, 2018 5:23 pm
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: electrolytic cells
Replies: 3
Views: 251

### Re: electrolytic cells

An electrolytic cell is an electrochemical cell in which electrolysis takes place. Just like a galvanic cell, electrolytic cells have reduction occurring at the cathode and oxidation occurring at the anode. Unlike in a galvanic cell, however, in which the current is generated spontaneously, in an el...
Sun Feb 18, 2018 5:18 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Cell reactions
Replies: 3
Views: 186

### Re: Cell reactions

For Example 14.4, we know Hg2Cl2 is the element that gets reduced because the right side of the cell diagram corresponds to reduction.
H2 is getting oxidized because the left side of the cell diagram corresponds to oxidation.
Sun Feb 18, 2018 5:04 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Cell Potential
Replies: 1
Views: 108

### Re: Cell Potential

Potential difference is also known as voltage. It is the electron moving force in electricity and is responsible for the electric current through a circuit. This current is the pushing and pulling of electrons.
Sat Feb 10, 2018 5:48 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: 9.27a
Replies: 3
Views: 193

### Re: 9.27a

For 9.27a, where the book is asking which substance has the higher molar entropy at 298K between HBr (g) and HF (g), HBr (g) has the higher molar entropy because it has a greater molar mass.
Sat Feb 10, 2018 5:45 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Delta G
Replies: 4
Views: 209

### Re: Delta G

\Delta G measures how much potential a reaction has left to do a net amount of something. If \Delta G is negative, the forward reaction is favored. If \Delta G is positive, the reaction is reactant favored. If the free energy is zero, the reaction is at equilibrium because there is no more net work...
Sat Feb 10, 2018 5:40 pm
Forum: Balancing Redox Reactions
Topic: Oxidation vs. reduction
Replies: 8
Views: 286

### Re: Oxidation vs. reduction

An easy way to remember this is LEO says GER. It stands for "lose electrons oxidation; gain electrons reduction"
Sun Feb 04, 2018 3:52 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: Using dS vs change in S
Replies: 3
Views: 183

### Re: Using dS vs change in S

dS is the instantaneous rate of change at a specific point.
$\Delta s$ is the change in entropy.
So far, we just had to find $\Delta s$.
Sun Feb 04, 2018 3:43 pm
Forum: Thermodynamic Definitions (isochoric/isometric, isothermal, isobaric)
Topic: Question 9.10
Replies: 2
Views: 226

### Re: Question 9.10

Use the equation nRln(V2/V1)=$\Delta s$
n= 4.80 moles
V2= 4.80 moles
V1= 12.86
Expect a decrease in entropy because the volume decreased.
Sun Feb 04, 2018 2:27 pm
Forum: Calculating Standard Reaction Entropies (e.g. , Using Standard Molar Entropies)
Topic: standard states
Replies: 3
Views: 191

### Re: standard states

Standard pressure is 1 atm. 1 atm is equivalent to 1.01325 bar. Although they are close, 1 bar is not standard pressure.
Sun Jan 28, 2018 3:27 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Different Changes in Enthalpy symbols -ΔH
Replies: 3
Views: 320

### Re: Different Changes in Enthalpy symbols -ΔH

ΔHc is the enthalpy of combustion.
ΔHL is the lattice enthalpy (ions).
ΔHb is bond enthalpy.
Sun Jan 28, 2018 2:22 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: Thermal Disorder vs. Positional Disorder
Replies: 2
Views: 100

### Re: Thermal Disorder vs. Positional Disorder

Thermal disorder is the disorder arising from the thermal motion of the molecules. Thermal disorder will increase if a system is heated up because the supply of energy increases the motion of the molecules. Positional disorder is the disorder arising from the location of the molecules. Entropy incre...
Sun Jan 28, 2018 2:18 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Replies: 3
Views: 90

The first law of thermodynamics is basically the conservation of energy. Energy can't be created or destroyed; however, it can change from more useful forms to less useful forms. Every energy transfer has some amount of less useful energy generated (usually in the form of heat). Heat that doesn't do...
Sun Jan 21, 2018 5:58 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Cv vs. Cp [ENDORSED]
Replies: 13
Views: 2015

### Re: Cv vs. Cp[ENDORSED]

Use Cv when there's constant volume. This is the specific heat when there's constant volume.
Use Cp when there's constant pressure. This is the specific heat when there's constant pressure.
Sun Jan 21, 2018 5:51 pm
Forum: Phase Changes & Related Calculations
Topic: Work Equation
Replies: 3
Views: 126

### Re: Work Equation

At constant pressure, when the system expands, it loses energy. Thus, the internal energy of the system decreases. The negative sign means energy is losing the system when it expands.
Sun Jan 21, 2018 5:16 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: Heat versus work
Replies: 6
Views: 274

### Re: Heat versus work

Heat and work are similar in that they both describe energy transfer.
I think of work as referring to something more mechanical, like pushing a piston.
I think of heat as referring to the thermal process thats responsible for temperature differences.
Sun Jan 21, 2018 4:54 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: Homework Problem 8.41
Replies: 2
Views: 141

### Re: Homework Problem 8.41

The heat gained by the water in the ice cube will be equal to the heat lost by the initial sample of hot water. The change in enthalpy for the water surrounding the ice cube will have two parts: 1. the heat to melt the ice at 0 degrees 2. the heat required to raise the ice from 0 degrees to the fina...
Sun Jan 14, 2018 11:12 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Standard States
Replies: 3
Views: 4261

### Re: Standard States

The standard state of an element is stated on the periodic table.
Liquid is the standard state for bromine and mercury. Gas is the standard state for the noble gases, hydrogen, helium, nitrogen, oxygen, fluorine, and chlorine. Solid is the standard state for all other elements.
Sun Jan 14, 2018 11:01 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: U vs H
Replies: 2
Views: 121

### Re: U vs H

Enthalpy includes internal energy. Enthalpy is the sum of the internal energy and the product of the pressure and volume of the system.
Internal energy is the sum of the potential energy and the kinetic energy of the system.
The unit for both is joules.
Sun Jan 14, 2018 10:55 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: 8.5
Replies: 2
Views: 162

### Re: 8.5

Yes, the for the change of internal energy is:
$\Delta U$=q (heat) + w (work)
Fri Dec 08, 2017 7:19 pm
Forum: Acidity & Basicity Constants and The Conjugate Seesaw
Topic: PKa and Pkb vs Ka and Kb
Replies: 4
Views: 837

### Re: PKa and Pkb vs Ka and Kb

Ka is the acid dissociation constant. pKa is the negative base-10 log of Ka. They both represent the strength of the acid in a solution; they are just expressed in different ways. The smaller the pKa, the stronger the acid. The larger the Ka, the stronger the acid. Likewise, Kb is the base dissociat...
Sun Dec 03, 2017 9:40 pm
Forum: Sigma & Pi Bonds
Topic: What is a localized and delocalized Bond?
Replies: 5
Views: 15349

### Re: What is a localized and delocalized Bond?

A localized bond pair travels between two atoms. A bond pair that moves between two different pairs of atoms is considered delocalized. You can identify delocalized bonds by checking the electron locations in two different resonance forms; if the pair changes location and form, it is delocalized.
Sun Dec 03, 2017 9:30 pm
Forum: Sigma & Pi Bonds
Topic: Delocalized Pi-Bonding
Replies: 5
Views: 490

### Re: Delocalized Pi-Bonding

A pi bond happens when two sets of electron orbitals involved in the bond overlap. A common example occurs in benzene. They are seen in resonance structures with different locations of double and triple bonds.
Sun Nov 26, 2017 9:16 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: #7
Replies: 1
Views: 112

### Re: #7

The diagrams depict the disassociation of the diatomic molecule, X2, over time. If by which state of the equation you mean equilibrium, the number of non-disassociated X2 molecules is the same for flask 3 and flask 4. Because the number did not change, equilibrium was reached in flask 3.
Sat Nov 25, 2017 7:21 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Homework Question 11.7 [ENDORSED]
Replies: 4
Views: 318

### Re: Homework Question 11.7[ENDORSED]

You can determine that equilibrium was reached in flask 3 because there is no further disassociation from flask 3 to flask 4.
Sun Nov 19, 2017 8:40 pm
Forum: Hybridization
Topic: Hybridization character (Problem 4.43)
Replies: 1
Views: 142

### Re: Hybridization character (Problem 4.43)

S-character is the percentage of sigma bonds in the hybridization. For example, sp hybridization has 50% s-character, 50% p-character; sp2 has 33% s-character, 66% p-character; ect. The s-character coincides with the bond angle. sp is linear and has 180 degree bond angle. sp2 is 120 degrees. sp3 has...
Sun Nov 19, 2017 8:25 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: 180degrees and lone pairs?
Replies: 4
Views: 240

### 180degrees and lone pairs?

In problem 4.1, the ball-and-shape model b is 180 degrees. The answer says "may contain lone pairs". If lone pairs affect the shape of the molecule, how can a molecule with lone pairs be 180 degrees (linear)?
Sun Nov 12, 2017 9:40 pm
Forum: Octet Exceptions
Topic: Expanded Octet
Replies: 6
Views: 952

### Re: Expanded Octet

All elements can hold an octet except for hydrogen. All of the d-block and above can have an expanded octet. For the Lewis dot diagram, all the orbitals do not need to be filled because atoms can have a formal charge.
Sun Nov 12, 2017 9:20 pm
Forum: Lewis Structures
Topic: Bonding
Replies: 3
Views: 287

### Re: Bonding

There are cases of quadruple bonds in the transition metals. Transition metals have d-orbital which is required to form a quadruple bond.
Sun Nov 05, 2017 6:19 pm
Forum: Trends in The Periodic Table
Topic: electron affinities
Replies: 2
Views: 220

### Re: electron affinities

Electron Affinities of:
Group IIA- around zero because filled s subshell discourages addition of an electron
Noble Gases- completely filled shell discourages addition of an electron; electron affinity values are positive, meaning it requires input of energy to add an electron
Sun Nov 05, 2017 5:49 pm
Forum: Resonance Structures
Topic: Homework Problem 3.41Part C
Replies: 1
Views: 219

### Re: Homework Problem 3.41Part C

Glycine is an amino acid so it has an amino group on one end (the NH2) and a carboxyl group (the COOH) on the other. For COOH, one O shares a double bond with C and the other O shares a bond with C and H. For NH2, the two Hs are bonded to N. The N should be bonded to the C in CH2. The C of COOH shou...
Sun Oct 29, 2017 10:23 pm
Forum: Ionic & Covalent Bonds
Topic: Homework 3.5 part c [ENDORSED]
Replies: 3
Views: 312

### Re: Homework 3.5 part c[ENDORSED]

Ga^3+: [Ar]3d10
1. Take Gallium's electron configuration [Ar]3d10 4s2 4p1
2. Remove 3 electrons (remove 4s2 4p1)
Sun Oct 29, 2017 9:24 pm
Forum: Electron Configurations for Multi-Electron Atoms
Topic: Electron Spins [ENDORSED]
Replies: 2
Views: 237

### Re: Electron Spins[ENDORSED]

Why do electrons with parallel spins tend to avoid each other and occupy different orbitals? Why would the direction of spin influence this repulsion? According to Hund's Rule, electrons always occupy an empty orbital before pairing up. Because electrons are negatively charge, paired electrons repel...
Sun Oct 22, 2017 5:26 pm
Forum: Electron Configurations for Multi-Electron Atoms
Topic: Chromium and Copper Electron Configuration Exceptions [ENDORSED]
Replies: 5
Views: 608

### Chromium and Copper Electron Configuration Exceptions[ENDORSED]

Is there an explanation for the chromium and copper electron configuration exception? Do we have to memorize the electron configurations or is there a way to figure it out?
Sun Oct 22, 2017 5:23 pm
Forum: Electron Configurations for Multi-Electron Atoms
Topic: unpaired electrons [ENDORSED]
Replies: 4
Views: 558

### Re: unpaired electrons[ENDORSED]

How do you determine how many unpaired electrons an atom has? 1. Write the electron configuration 2. Find any incomplete orbitals, if any (s-orbitals with less than 2 electrons; p-orbitals with less than 6 electrons; d-orbitals with less than 10 electrons) 3. For the incomplete orbital, fill in the...
Sun Oct 15, 2017 9:46 pm
Forum: Photoelectric Effect
Topic: Wavelike properties [ENDORSED]
Replies: 4
Views: 284

### Re: Wavelike properties[ENDORSED]

According to De Broglie's equation, anything with mass and velocity has wavelike properties, including a baseball or a car. However, these larger items have too small of a wavelength to be considered "measurable".
Sun Oct 15, 2017 9:27 pm
Forum: Properties of Light
Topic: Homework 1.3
Replies: 1
Views: 179

### Re: Homework 1.3

In this case, change in the electrical field means light emitted since its an electromagnetic wave. According to the equation E=hv, frequency is directly proportional to energy. So, when frequency decreases, the energy decreases (answer: C).
Fri Oct 06, 2017 9:44 am
Forum: Accuracy, Precision, Mole, Other Definitions
Topic: E1
Replies: 6
Views: 867

### Re: E1

The solutions manual wasn't very clear about this question... Question: The field of nanotechnology offers some intriguing possibilities, such as the creation of fibers one atom wide. Suppose you were able to string together 1.00 mol Ag atoms, each of radius 144 pm, into one of these fibers by enca...
Fri Oct 06, 2017 9:38 am
Forum: Molarity, Solutions, Dilutions
Topic: Molarity and Dilution [ENDORSED]
Replies: 7
Views: 1273

### Re: Molarity and Dilution[ENDORSED]

A solution is prepared by dissolving 55.1g of KCl in approximately 75mL of water and then adding water to a final volume of 125mL. What is the molarity of KCl(aq) in this solution? I know that Molarity equals: Molarity=moles of solute/ volume of the solution but in this case would we not use this f...