## Search found 60 matches

Tue Mar 12, 2019 9:43 pm
Forum: Kinetics vs. Thermodynamics Controlling a Reaction
Topic: Rate constant
Replies: 4
Views: 405

### Re: Rate constant

Rate constant k should always be positive. From the Arrhenius Equation, we know k = A x exp(-Ea/RT). "A" (frequency factor) will always be positive because (according to Google) there are no experimental cases where A is negative, and mathematically exp(-Ea/RT) can never be negative. If rx...
Tue Mar 12, 2019 9:41 pm
Forum: Kinetics vs. Thermodynamics Controlling a Reaction
Topic: molecularity
Replies: 4
Views: 399

### Re: molecularity

The molecularity of a reaction is defined as the number of molecules or ions that participate in the rate determining step, the slowest step in a chemical reaction.
Tue Mar 12, 2019 9:37 pm
Forum: Kinetics vs. Thermodynamics Controlling a Reaction
Topic: 15.39
Replies: 2
Views: 258

### Re: 15.39

"(b) A -> 2B + C, when [A]0 = 0.15 mol*L-1, for the concentration of B to increase to 0.19 mol*L-1, given that k = 0.0035 L*mol-1*min-1 in the rate law for the loss of A."
Tue Mar 05, 2019 11:45 pm
Forum: General Rate Laws
Topic: Unit for reaction rates
Replies: 4
Views: 187

### Re: Unit for reaction rates

The unit will include time because the rate of a reaction is measured in M/s or mol*L-1*s-1
Tue Mar 05, 2019 11:41 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Concentration cells
Replies: 6
Views: 411

### Re: Concentration cells

A concentration cell is an electrolytic cell that is comprised of two half-cells with the same electrodes, but differing in concentrations. A concentration cell acts to dilute the more concentrated solution and concentrate the more dilute solution, creating a voltage as the cell reaches an equilibri...
Tue Mar 05, 2019 11:39 pm
Forum: Method of Initial Rates (To Determine n and k)
Topic: Units
Replies: 6
Views: 255

### Re: Units

The rate of a reaction is measured in terms of how fast the concentration of one of the reactants is falling. Its units are mol*L-1*s-1

The exponents m and n are called partial orders of the reaction which depend on the reaction mechanism and can be determined experimentally.
Tue Mar 05, 2019 11:25 pm
Forum: Kinetics vs. Thermodynamics Controlling a Reaction
Topic: kinetics and thermodynamics
Replies: 4
Views: 229

### Re: kinetics and thermodynamics

In principle, every reaction is on the continuum between pure kinetic control and pure thermodynamic control. These terms are with respect to a given temperature and time scale. A process approaches pure kinetic control at low temperature and short reaction time. At the other end of the continuum, t...
Tue Mar 05, 2019 11:17 pm
Forum: Kinetics vs. Thermodynamics Controlling a Reaction
Topic: kinetic control
Replies: 2
Views: 169

### Re: kinetic control

In principle, every reaction is on the continuum between pure kinetic control and pure thermodynamic control. These terms are with respect to a given temperature and time scale. A process approaches pure kinetic control at low temperature and short reaction time. At the other end of the continuum, t...
Tue Mar 05, 2019 11:08 pm
Forum: Kinetics vs. Thermodynamics Controlling a Reaction
Topic: Electrolysis
Replies: 4
Views: 219

### Re: Electrolysis

Electrolysis takes an electric current to drive an otherwise non-spontaneous chemical reaction.
Tue Mar 05, 2019 6:17 pm
Forum: Kinetics vs. Thermodynamics Controlling a Reaction
Topic: Purpose of Kinetics
Replies: 6
Views: 428

### Re: Purpose of Kinetics

Kinetics is the measurement of how quickly reactions occur. If changes in conditions affect the speed of reaction, we can learn something about how the reaction happens. Kinetic studies are important in understanding reactions, and they also have practical implications. By understanding how a reacti...
Tue Mar 05, 2019 4:52 pm
Forum: Kinetics vs. Thermodynamics Controlling a Reaction
Topic: speed of reaction based on activation energy
Replies: 6
Views: 239

### Re: speed of reaction based on activation energy

Typically yes because the reaction will require a greater buildup of energy to overcome the activation barrier. Take a look at the Arrhenius Equation:
k = Ae^-(EA/RT)
A higher activation energy would result in a slower reaction.
Tue Mar 05, 2019 4:40 pm
Forum: Kinetics vs. Thermodynamics Controlling a Reaction
Topic: Kinetically Stable
Replies: 3
Views: 240

### Re: Kinetically Stable

Kinetics deals with the rate of a reaction and thermodynamics deals with whether the reaction is favorable or not. Kinetic stability basically occurs when the reactants react at a slower rate. The slower the reaction occurs, the greater the kinetic stability. Thermodynamic stability depends on wheth...
Fri Feb 15, 2019 2:42 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Question 8.39 (Sixth Edition)
Replies: 4
Views: 196

### Re: Question 8.39 (Sixth Edition)

You have to break this problem up into two steps: 1. Find m * Heat of fusion 2. Find m * C * delta T When you find those two values, you add them up, and that is the total heat needed. Is it n*Heat of fusion or m* Heat of fusion? For the first part we use moles and the second part we use mass right...
Fri Feb 15, 2019 2:37 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Most stable form?
Replies: 4
Views: 231

### Re: Most stable form?

An element's most stable form is most likely its standard elemental form, usually either in a monatomic or diatomic form
Fri Feb 15, 2019 2:31 pm
Forum: Phase Changes & Related Calculations
Topic: 4.18J or 0.38J
Replies: 8
Views: 610

### Re: 4.18J or 0.38J

4.18 J refers to the specific heat capacity of water.
0.38 J refers to the specific heat capacity of copper.
Fri Feb 15, 2019 2:29 pm
Forum: Calculating Work of Expansion
Topic: 4F.1 7th Edition
Replies: 4
Views: 194

### Re: 4F.1 7th Edition

Because qsystem=-qsurroundings, the amount of heat given off by your body (the system) is the same amount of heat absorbed by the surroundings.
Fri Feb 15, 2019 2:21 pm
Forum: Thermodynamic Definitions (isochoric/isometric, isothermal, isobaric)
Topic: 6th edition 8.25
Replies: 4
Views: 2827

### Re: 6th edition 8.25

A calorimeter is an isolated system so no heat is lost to the surroundings. Any heat released from the reaction will be absorbed by the calorimeter. Therefore, qcalorimeter = -qreaction
Fri Feb 15, 2019 2:18 pm
Forum: Thermodynamic Systems (Open, Closed, Isolated)
Topic: Liquid and moles
Replies: 8
Views: 574

### Re: Liquid and moles

H2O is a liquid so it would not be included in calculating the equilibrium constant. This is because solids and liquids do not affect the reactant amount at equilibrium in the reaction, so they are disregarded and kept at 1.
Sun Feb 03, 2019 8:47 pm
Forum: Calculating Work of Expansion
Topic: value of R?
Replies: 4
Views: 199

### Re: value of R?

Depending on the question, the gas constant, R = 8.314 J*K-1*mol-1 = 8.206*10-2 L*atm*K-1*mol-1 = 8.314*10-2 L*bar*K-1*mol-1 = 62.364 L*Torr*K-1*mol-1
Sun Feb 03, 2019 8:39 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: 103 6th edition
Replies: 2
Views: 125

### Re: 103 6th edition

The average kinetic energy is obtained from the expression: average kinetic energy = $\frac{3}{2}$*R*T. Using this equation you should get the answers: a)4103.2 J*mol-1; b)4090.7 J*mol-1; c)12.5 J*mol-1
Sun Feb 03, 2019 8:31 pm
Forum: Phase Changes & Related Calculations
Topic: Type of systems
Replies: 12
Views: 599

### Re: Type of systems

An isolated system and a closed system are two different types of systems. An isolated system has no contact with its surroundings, neither energy nor matter can interact with the system. A closed system has a fixed amount of matter but it can exchange energy with its surroundings.
Thu Jan 24, 2019 12:09 am
Forum: Ideal Gases
Topic: Ideal Gas Law
Replies: 7
Views: 287

### Re: Ideal Gas Law

The ideal gas law (Pv = nRT) can be rearranged to create the equation P = (n/v)RT. P represents pressure and n/v represents concentration while R and T are constants/given so you can convert between partial pressure and molar concentration based on the information given in the problem.
Thu Jan 24, 2019 12:05 am
Forum: Equilibrium Constants & Calculating Concentrations
Topic: How to know when to use partial pressure or molar concentrations?
Replies: 4
Views: 222

### Re: How to know when to use partial pressure or molar concentrations?

When asked for Kp, use partial pressure and when asked for Kc, use molar concentrations. Partial pressure can be converted into molar concentrations and vice versa using the ideal gas law (Pv = nRT).
Thu Jan 24, 2019 12:01 am
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Sig Figs
Replies: 3
Views: 182

### Re: Sig Figs

When calculating pH and pOH, sig figs are calculated from the initial concentration and applied after the decimal of the pH/pOH
Sun Jan 20, 2019 10:35 am
Forum: Non-Equilibrium Conditions & The Reaction Quotient
Topic: Equilibrium Conditions
Replies: 2
Views: 143

### Equilibrium Conditions

What conditions outside of the chemical equilibrium reaction affect the equilibrium constant?
Sun Jan 20, 2019 10:33 am
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Equilibrium Constant
Replies: 2
Views: 2856

### Equilibrium Constant

How do we know whether products or reactants are favored based on the equilibrium constant?
Sun Jan 20, 2019 10:32 am
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Equilibrium Arrow
Replies: 7
Views: 395

### Re: Equilibrium Arrow

The two way arrow is used for chemical reactions that are in equilibrium. However, when an arrow is only pointing in one direction, that indicates that the equilibrium is favoring either product or reactant.
Mon Jan 14, 2019 12:11 am
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Question 11.7 [ENDORSED]
Replies: 3
Views: 151

### Re: Question 11.7[ENDORSED]

Flask 3 is at equilibrium because there is an equal ratio of X2 molecules and X atoms
Mon Jan 14, 2019 12:07 am
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Change in ICE tables
Replies: 1
Views: 101

### Re: Change in ICE tables

If you are given initial concentrations and all of them are nonzero, calculate the reaction quotient Q. If Q<K, the reaction moves toward the products, so the ICE table would have +x on the product's side and -x on the reactant's side. If Q>K, the reaction moves toward the reactants, so the ICE tabl...
Mon Jan 14, 2019 12:02 am
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Question 11.11
Replies: 2
Views: 56

### Re: Question 11.11

I believe this question is actually 11.7. To calculate the value of K you use the equation (Px)2/PX2. Multiply the mole fraction of the reactant and product respectively by the initial pressure of 0.1 bar to get the partial pressures. Solve and you should get 0.17
Sun Dec 09, 2018 9:58 am
Forum: Naming
Topic: -ate in naming
Replies: 7
Views: 582

### Re: -ate in naming

After naming the ligands, name the central metal. If the complex ion is an anion, the name of the transition metal ends with the suffix "-ate." If the complex ion is a cation, the metal is named same as the element.
Sat Dec 08, 2018 10:15 pm
Forum: Bronsted Acids & Bases
Topic: Lewis vs Bronsted
Replies: 10
Views: 847

### Re: Lewis vs Bronsted

A Bronsted acid donates protons and a Bronsted base accepts protons. A Lewis acid accepts an electron pair and a Lewis base donates electron pairs. Also, a conjugate acid accepts protons and conjugate base donates protons.
Sat Dec 08, 2018 10:08 pm
Forum: Lewis Acids & Bases
Topic: Lewis Acid
Replies: 6
Views: 251

### Re: Lewis Acid

HBr is a stronger acid than HF because Br is a larger atom than F meaning the bond length between H and F is closer than H and Br. That means HBr is more likely to dissociate and a strong acid more readily dissociates in water.
Wed Nov 28, 2018 1:47 am
Forum: Hybridization
Topic: s-character
Replies: 6
Views: 1044

### Re: s-character

s-character is the contribution of sigma type bonds in a hybridization. e.g sp = 50% s-character, 50% p-character; sp2 = 33% s-character, 66% p-character; sp3 = 25% s-character, 75% p-character. The more s-character a bond has, the shorter and stronger the bond is.
Wed Nov 28, 2018 1:43 am
Forum: Hybridization
Topic: 4.31
Replies: 2
Views: 90

### Re: 4.31

Relative orientations would refer to how the molecule is arranged. For instance, the sp3 orbitals are oriented toward the corners of a tetrahedron (109.5o apart)
Wed Nov 28, 2018 1:38 am
Forum: Hybridization
Topic: sigma and pi bonds
Replies: 5
Views: 214

### Re: sigma and pi bonds

Pi bonds are usually weaker than sigma bonds. Quantum mechanics says this is because the orbital paths are parallel so there is much less overlap between the p-orbitals.
Wed Nov 28, 2018 1:35 am
Forum: *Molecular Orbital Theory (Bond Order, Diamagnetism, Paramagnetism)
Topic: 4.46
Replies: 4
Views: 279

### Re: 4.46

Like the similar problem 4.45, the question asks you to find the sigma and pi bonds for the entire molecule.
Wed Nov 28, 2018 1:26 am
Forum: Determining Molecular Shape (VSEPR)
Topic: Bent and Angular
Replies: 5
Views: 202

### Re: Bent and Angular

There is a 2014 post where Chem_Mod states "No, there is no difference. You can use either "angular" or "bent" to refer to the molecular shape of AX2E or AX2E2 molecules."
Wed Nov 28, 2018 1:22 am
Forum: Determining Molecular Shape (VSEPR)
Topic: 3.39
Replies: 2
Views: 130

### Re: 3.39

When drawing Lewis structures for ionic compounds, you draw the separate ions in their own brackets to denote the "donating" and "receiving" of electrons between the two.
Wed Nov 14, 2018 1:09 am
Forum: Formal Charge and Oxidation Numbers
Topic: 3.53 6th edition
Replies: 4
Views: 578

### Re: 3.53 6th edition

Use the formula FC=V-(L+S) to determine the formal charge. The structure that has more atoms with a formal charge of 0 has lower energy. For part a) we can calculate the formal charge of the left molecule with the O to the left of Cl having a formal charge of 0 [6-(4+ \frac{1}{2} (2))], the Cl havi...
Wed Nov 14, 2018 12:59 am
Forum: Formal Charge and Oxidation Numbers
Topic: 3.37 6th edition
Replies: 3
Views: 321

### Re: 3.37 6th edition

The solution manual identifies the element as phosphorus (P).
Wed Nov 14, 2018 12:56 am
Forum: Lewis Structures
Topic: 7th edition 2E #5
Replies: 2
Views: 166

### Re: 7th edition 2E #5

If you draw out the Lewis structure for ClO2+, you will see that Cl is attached to one O by a double bond and the other by a single bond while Cl has a lone pair. The VSEPR formula for ClO2+ is AX2E1 which has bond angles slightly <120o
Wed Nov 14, 2018 12:46 am
Forum: Lewis Structures
Topic: Molecule Shape
Replies: 8
Views: 368

### Re: Molecule Shape

Using the Lewis structure, you can see how many electron pairs and lone electron pairs there are. From that you can write the VSEPR equation in the form AXnEn. From the VSEPR equation, you can refer to a chart for the molecular shape
Wed Nov 14, 2018 12:43 am
Forum: Octet Exceptions
Topic: What are the octet exceptions?
Replies: 9
Views: 435

### Re: What are the octet exceptions?

taywebb wrote:I understand why H is an exception to the octet rule, but can someone explain why Hi, Le, and Be are as well?

Lithium and beryllium need to lose either one or two electrons, respectively, to attain an electron configuration of 1s^2 which is most stable.
Wed Nov 14, 2018 12:39 am
Forum: Formal Charge and Oxidation Numbers
Topic: Stable Vs. Formal
Replies: 4
Views: 624

### Re: Stable Vs. Formal

Formal charge is the electric charge of an atom in a molecule assigned on the assumption that the bonding is nonpolar covalent. It is calculated by FC = number of valence electrons in the free atom - (number of lone-pair electrons + 1/2 * number of shared electrons). Stable charge refers to the form...
Thu Nov 01, 2018 11:14 pm
Forum: Quantum Numbers and The H-Atom
Topic: Degeneration
Replies: 3
Views: 226

### Re: Degeneration

Degenerate means having the same energy. In the context of orbitals, degeneracy refers to all atomic orbitals in the same subshell
Thu Nov 01, 2018 11:06 pm
Forum: Quantum Numbers and The H-Atom
Topic: Test #2 Question
Replies: 1
Views: 111

### Test #2 Question

What are the possible sets of quantum numbers for a 3p orbital?
Thu Nov 01, 2018 10:58 pm
Forum: Quantum Numbers and The H-Atom
Topic: Test #2
Replies: 3
Views: 212

### Re: Test #2

Degenerate means having the same energy. In the context of orbitals it is the number of atomic orbitals in the same subshell. Say the question is, how many degenerate 3p orbitals exist? (Remember: we need to see how many orbitals share the same n and l quantum numbers) If n = 3 and l = 1, ml could b...
Sat Oct 27, 2018 10:40 pm
Forum: Einstein Equation
Topic: 6th Edition, Question 1.55
Replies: 2
Views: 416

### Re: 6th Edition, Question 1.55

Using the method given above ^ you should get 4.3 x 10^4 J/mol or 43 kJ/mol
Sat Oct 27, 2018 10:36 pm
Forum: DeBroglie Equation
Topic: HW Problem 1.39 (6th Edition)
Replies: 4
Views: 242

### Re: HW Problem 1.39 (6th Edition)

I believe 28.9 is a typo, the correct number should be 28.3. In one ounce there are 28.3495 grams.
Sat Oct 27, 2018 10:33 pm
Forum: DeBroglie Equation
Topic: problem 43 6th edition
Replies: 4
Views: 189

### Re: problem 43 6th edition

Yes, the diameter of the lead atom is given in the problem as 350 pm or 350 x 10^-12 m
Tue Oct 23, 2018 2:22 am
Forum: Properties of Light
Topic: Photoelectric Effect
Replies: 8
Views: 455

### Re: Photoelectric Effect

The book defines photoelectric effect as "the emission of electrons from the surface of a metal when electromagnetic radiation strikes it."
Tue Oct 23, 2018 2:18 am
Forum: Properties of Light
Topic: 6th Edition: Problem 1.9
Replies: 3
Views: 179

### Re: 6th Edition: Problem 1.9

On page 6 there is a paragraph that begins with, "As far as we know, ..." Within the paragraph there are a few examples of events corresponding to ultraviolet radiation and infrared radiation. However, like the other answers have suggested, the most important thing to know probably is what...
Tue Oct 23, 2018 2:07 am
Forum: Properties of Light
Topic: Problem 1A.3
Replies: 3
Views: 189

### Re: Problem 1A.3

The electric field refers to the electromagnetic wave, more specifically its amplitude (height of wave). When frequency decreases, the wavelength (distance between peaks) broadens thus decreasing the change in the electrical field at any given point.
Fri Oct 12, 2018 11:26 am
Forum: Molarity, Solutions, Dilutions
Topic: E23 part b
Replies: 4
Views: 476

### Re: E23 part b

Unless it specifically asks you for the number of molecules, then you would need to take the moles and convert it to molecules by multiplying the number of moles with Avogadro's number. Otherwise, the problem just says find the number of moles so you're good where you're at
Fri Oct 12, 2018 11:20 am
Forum: Empirical & Molecular Formulas
Topic: F13
Replies: 3
Views: 348

### Re: F13

Once you've solved part a you'll end up with PCl5. To name the compound you start with the first element P (Phosphorus) and then you look at the second part of the compound Cl5 which translates to pentachoride (penta- denoting five and chloride is the naming structure for chlorine). Your answer woul...
Fri Oct 12, 2018 11:17 am
Forum: Balancing Chemical Reactions
Topic: Where to start [ENDORSED]
Replies: 10
Views: 844

### Re: Where to start[ENDORSED]

Something else I've noticed is that compounds with more elements tend to have smaller values (1-3) so you could look to them to give you an idea on how to balance the equation
Fri Oct 05, 2018 1:28 am
Forum: Empirical & Molecular Formulas
Topic: Empirical Formula (HW problem F.11, part a)
Replies: 2
Views: 122

### Re: Empirical Formula (HW problem F.11, part a)

Yes, it is safe to round these ratio values into whole numbers. I believe that values can be off .1 and rounding would still produce a valid answer.
Fri Oct 05, 2018 1:18 am
Forum: Balancing Chemical Reactions
Topic: 7th Edition L.35 question
Replies: 3
Views: 199

### Re: 7th Edition L.35 question

I believe you were looking at the second line when trying to copy the third line to balance. The textbook does say that the equation needed to be balanced is Fe3Br8 + Na2CO3 -> NaBr + CO2 + Fe3O4
Fri Oct 05, 2018 1:03 am
Forum: Limiting Reactant Calculations
Topic: Limiting Reactant
Replies: 8
Views: 734

### Re: Limiting Reactant

I don't believe you need to find theoretical yield for limiting reactant problems. To find the limiting reactant, just take the information you're given and convert to moles (however needed). Once you have all the reactants in moles, compare to see which uses more moles quickly based on the given am...