## Search found 61 matches

Sun Mar 10, 2019 4:47 pm
Forum: General Rate Laws
Topic: writing rate laws
Replies: 4
Views: 145

### Re: writing rate laws

I believe that both phrases refer to the same equation. The second phrase is just specifying which reactants the rate law applies to.
Sun Mar 10, 2019 4:45 pm
Forum: First Order Reactions
Topic: graph
Replies: 3
Views: 130

### Re: graph

For first order reactions, the graph of the concentration of reactant vs time is exponentially decaying. However, a linear plot is obtained when graphing the natural log of the reactant concentration vs time.
Sun Mar 10, 2019 4:42 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Rate Determining Step
Replies: 2
Views: 121

### Re: Rate Determining Step

No, only the slowest elementary step determines the overall reaction rate. The other faster steps before it do not have to be considered when determining the reaction rate.
Wed Mar 06, 2019 10:07 pm
Forum: General Rate Laws
Topic: Deriving Rate Laws
Replies: 3
Views: 155

### Re: Deriving Rate Laws

My TA said that we should know how to derive the rate laws, and that it was fair game for Professor Lavelle to test us on.
Wed Mar 06, 2019 10:05 pm
Forum: General Rate Laws
Topic: Slope
Replies: 2
Views: 123

### Re: Slope

With [A] denoting the concentration of a reactant, for first order reactions, the graph of the ln[A] versus time will yield a straight line. For second order reactions, the slope will be linear but for a graph of 1/[A] versus time. For zero order reactions, a linear graph is produced only when graph...
Wed Mar 06, 2019 9:07 pm
Forum: General Rate Laws
Topic: Negative sign for reactant rate
Replies: 2
Views: 103

### Re: Negative sign for reactant rate

Yes, the negative sign is just to make the reaction rate positive. With respect to reactant concentration, the initial reaction rate will always be negative as reactant is being used up to form product as the reaction progresses.
Sun Mar 03, 2019 10:01 pm
Forum: Kinetics vs. Thermodynamics Controlling a Reaction
Topic: difference between chemical reaction and reaction mechanism?
Replies: 2
Views: 107

### Re: difference between chemical reaction and reaction mechanism?

A chemical reaction gives the overall net change from the reactants to the products. A reaction mechanism gives information about how the products form through certain steps and different collisions.
Sun Mar 03, 2019 9:57 pm
Forum: Zero Order Reactions
Topic: how do we tell if a reaction is zero order?
Replies: 5
Views: 204

### Re: how do we tell if a reaction is zero order?

Zero order reactions have rates that do not vary with changes in reactant concentrations. If the reactant concentration changes but the rate remains the same, then the reaction is zero order.
Sun Mar 03, 2019 9:52 pm
Forum: General Rate Laws
Topic: Instantaneous vs unique
Replies: 1
Views: 78

### Re: Instantaneous vs unique

Instantaneous reaction rate does not take in to account the coefficients of the balanced chemical reaction while the unique rate does. The unique reaction rate is a single value for all the reactants and products while the instantaneous reaction rate can be different depending on which reactant or p...
Sun Feb 24, 2019 11:17 am
Forum: Balancing Redox Reactions
Topic: How do you balance a redox reaction
Replies: 4
Views: 142

### Re: How do you balance a redox reaction

If you treat the redox reaction like any regular chemical equation and balance it like how you normally would, everything should work out. Do you have a specific example?
Fri Feb 22, 2019 10:14 am
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Electron Transfer and Galvanic Cells
Replies: 2
Views: 82

### Re: Electron Transfer and Galvanic Cells

If a species is reduced, this means it is gaining electrons. If a species is oxidized, the opposite is true and it loses electrons. A cathode is where reduction occurs and an anode is where oxidation occurs. In a galvanic cell, this transfer of electrons is responsible for creating electrical energy.
Fri Feb 22, 2019 10:08 am
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: delta S= q(rev)/ T
Replies: 5
Views: 323

### Re: delta S= q(rev)/ T

This entropy equation can be used to calculate the change in entropy when temperature is constant. For example, you can use this equation to calculate the entropy associated with phase changes because they occur at a constant temperature.
Fri Feb 15, 2019 2:21 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Gibbs free energy idea
Replies: 2
Views: 94

### Re: Gibbs free energy idea

I believe that in class Dr. Lavelle mentioned the change in Gibbs free energy is the energy free to do useful work.
Fri Feb 15, 2019 2:18 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: At Equilibrium G
Replies: 6
Views: 235

### Re: At Equilibrium G

Yes, for K < 1, lnK will be negative, cancelling out the negative in -RTlnK. This means that G is positive. For K > 1, lnK will be positive and G will be negative. When G is negative, the reaction is spontaneous.
Fri Feb 15, 2019 2:14 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Equation based on equilibrium
Replies: 5
Views: 181

### Re: Equation based on equilibrium

The G= G + RTlnQ equation holds true for all reactions, even reactions not at equilibrium. However, for reactions at equilibrium, G=0 and Q=K so G=-RTlnK.
Sun Feb 10, 2019 11:11 pm
Forum: Calculating Work of Expansion
Topic: Reversible vs Irreversible
Replies: 10
Views: 372

### Re: Reversible vs Irreversible

The equation for isothermal, reversible reactions is derived from taking the integral of the change in volume.
Sun Feb 10, 2019 11:08 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Constant Vol.
Replies: 8
Views: 493

### Re: Constant Vol.

Constant volume means that the change in volume is zero. Thus in the work equation, the overall work done would be zero as you would multiply pressure by zero. If volume does not change, then the system does no work,
Tue Feb 05, 2019 10:43 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: Specific Heat Capacity vs Heat Capacity
Replies: 1
Views: 94

### Re: Specific Heat Capacity vs Heat Capacity

Heat capacity is defined as the heat required to raise the temperature of an object by 1 degree Celsius while specific heat capacity is the heat required to raise the temperature of one gram of a substance by one degree Celsius. Use specific heat capacity when given the amount of the substance in gr...
Sun Feb 03, 2019 11:15 pm
Forum: Thermodynamic Systems (Open, Closed, Isolated)
Topic: Closed Systems
Replies: 6
Views: 178

### Re: Closed Systems

A closed system can exchange energy with its surroundings while an isolated system cannot.
Sun Feb 03, 2019 11:10 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Hess's Law depends on enthalpy as a state function
Replies: 3
Views: 212

### Re: Hess's Law depends on enthalpy as a state function

Hess's law allows you to add two reaction enthalpies together to determine the reaction enthalpy of a third reaction. If enthalpy were not a state function, its value would be dependent on the pathway it took to form the products. This would then invalidate the method of adding two other reaction en...
Mon Jan 28, 2019 10:31 am
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Bond Enthalpies
Replies: 2
Views: 105

### Re: Bond Enthalpies

Bond enthalpies of diatomic molecules are averages because the bond is identical in all cases, with only two atoms of the same element. For example, with H2 or Cl2. However, for other bond enthalpies, the other chemical species bonded to the atoms affect its energy. For example, for a C-H bond, the ...
Fri Jan 25, 2019 2:11 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: bond enthalpies
Replies: 5
Views: 208

### Re: bond enthalpies

The values for bond enthalpy will always be given as a positive value. However, if bonds are being formed instead of broken, then this value will take on a negative sign to indicate this.
Tue Jan 22, 2019 10:18 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Weak vs Strong Acid and Bases
Replies: 2
Views: 103

### Re: Weak vs Strong Acid and Bases

The equation to calculate the pH of strong vs weak acids and bases is the same. In both cases pH is equal to the negative log of the H3O+ concentration. However when finding the concentration of hydronium ions, for strong acids, it is assumed that at equilibrium the acid dissociates completely. For ...
Tue Jan 22, 2019 10:13 pm
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: Changes in Pressure, Volume, and Concentration
Replies: 2
Views: 104

### Re: Changes in Pressure, Volume, and Concentration

The general principle of Le Chatelier is to minimize the effects of the changes done to the system. For increases in pressure, the equilibrium can be thought of as shifting towards the side of the reaction with less moles of gas. An increase in volume would mean a decrease in pressure and concentrat...
Tue Jan 22, 2019 10:06 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Hmwrk 12.57 part b
Replies: 1
Views: 89

### Re: Hmwrk 12.57 part b

The pH of the solution is given as 11.86, so the pOH can be calculated by subtracting from 14 to give pOH=2.14. With this pOH, you can calculate the concentration of OH- ions at equilibrium by taking 10^-2.14, which is approximately 0.00724. The equation for CH3H7NH2's reaction with water is CH3H7NH...
Fri Jan 18, 2019 10:24 am
Forum: Equilibrium Constants & Calculating Concentrations
Topic: 11.39 6th edition
Replies: 4
Views: 187

### Re: 11.39 6th edition

If a reaction is composed of two different reactions, multiply the K constants to determine the K constant of the third reaction.
Fri Jan 18, 2019 10:17 am
Forum: Equilibrium Constants & Calculating Concentrations
Topic: 11.39 6th Ed Multiplying K constants
Replies: 3
Views: 100

### Re: 11.39 6th Ed Multiplying K constants

For example, given three reactions: (1) A + B -> C (2) C -> A + D (3) B -> D The K constants for the reactions would be: (1) K= [C]/[B]*[A] (2) K= [A]*[D]/[C] (3) K = [D]/[B] If you multiply the two K constants together for reaction one and reaction two, you'll find that the [A] and [C] cancel out l...
Fri Jan 18, 2019 10:07 am
Forum: Equilibrium Constants & Calculating Concentrations
Replies: 3
Views: 75

If the K constant for the weak acid is less than 10^-3, the quadratic equation can be bypassed because the change in concentration is so small compared to the actual initial concentration that it is negligible. After you solve for the equilibrium concentration, if the answer is less than 5% of the i...
Sat Jan 12, 2019 4:52 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: 11.39 6th Ed Multiplying K constants
Replies: 3
Views: 100

### Re: 11.39 6th Ed Multiplying K constants

If two reactions are added together to form another reaction, then their K constants are multiplied to give the new reaction's K constant.
Sat Jan 12, 2019 4:48 pm
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: Effect of Partial Pressure on Concentration
Replies: 2
Views: 84

### Re: Effect of Partial Pressure on Concentration

Decreasing the partial pressure of CO2 would mean that the concentration of CO2 is also decreased. Because the equilibrium is experiencing a removal of reactant, it will shift to form more reactants, thus decreasing the O2 concentration. In a reaction mixture at equilibrium, I am not sure it is poss...
Sat Jan 12, 2019 4:29 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Why no units for K?
Replies: 3
Views: 165

### Re: Why no units for K?

K has no units. In class it was mentioned that concentration estimates chemical activities (a topic more advanced than this course requires), which has no units, and so K also has no units.
Mon Dec 03, 2018 10:33 pm
Forum: Bronsted Acids & Bases
Topic: Bronsted Acids and Bases?
Replies: 2
Views: 130

### Re: Bronsted Acids and Bases?

There are two types of acids and bases, bronsted and lewis. Bronsted acids are defined as proton donators and bronsted bases as proton acceptors. However, lewis acids are defined as electron acceptors and lewis bases as electron donators.
Mon Dec 03, 2018 5:03 pm
Forum: Conjugate Acids & Bases
Topic: Charges of conjugate acids and bases
Replies: 1
Views: 74

### Re: Charges of conjugate acids and bases

Without memorizing the charges, one way to tell the charge of the conjugate acid/base is to look at the original compound. For example, for the acid CH6H5OH, the charge is neutral. Thus when this acid gives up its proton (one positive charge), its conjugate base takes on a negative charge. In your o...
Mon Dec 03, 2018 11:09 am
Forum: Lewis Acids & Bases
Topic: Acid/Super Acid & Base/Super Base
Replies: 2
Views: 109

### Re: Acid/Super Acid & Base/Super Base

An acid and a super acid follow the same chemical principles, but a super acid can dissolve more hydrogen ions in solution such that its pH is outside of the "normal" pH range (0-14) and is negative. Likewise, super bases have pHs larger than 14.
Thu Nov 29, 2018 9:39 am
Forum: Determining Molecular Shape (VSEPR)
Topic: 4.95
Replies: 1
Views: 66

### Re: 4.95

The example is saying that the composition of the C-H sigma bond is one sp2 hybridized orbital from carbon and one s orbital from hydrogen. These two orbitals make up that specific sigma bond.
Thu Nov 29, 2018 9:34 am
Forum: Determining Molecular Shape (VSEPR)
Topic: Polar vs Nonpolar for CH2Cl2
Replies: 2
Views: 108

### Re: Polar vs Nonpolar for CH2Cl2

CH2Cl2 may appear nonpolar from the Lewis structure, but since its VSEPR structure is tetrahedral, the Cl dipole moments do not cancel each other.
Tue Nov 27, 2018 1:37 pm
Forum: Sigma & Pi Bonds
Topic: Pi bonds and hybridization
Replies: 2
Views: 130

### Re: Pi bonds and hybridization

All sigma bonds are hybridized as sigma bonds are defined as single bonds between two atoms created by the hybridization of their orbitals. In order for a sigma bond to be formed, hybrid orbitals must be created. Pi bonds are not hybridized as they are composed of the overlap between two atoms' p or...
Sun Nov 25, 2018 5:40 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: 4.19 6th edition
Replies: 4
Views: 207

### Re: 4.19 6th edition

After drawing the Lewis structure and determining the VSEPR shape, the bond angle can be determined from the shape. Each VSEPR shape has certain bond angles associated with the shape. Part (b) is linear because the Lewis structure consists of Be bonded to two CH3 groups. The central atom Be only has...
Sun Nov 25, 2018 5:31 pm
Forum: Hybridization
Topic: Hybridization
Replies: 4
Views: 238

### Re: Hybridization

sp2 orbitals should be used when there are three regions of electron density in a molecule. sp3 orbitals should be used when there are four regions of electron density in a molecule. sp orbitals are used when there are only two regions of electron density. sp4 does not exist, to create five bonding ...
Sun Nov 25, 2018 5:24 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: 4.21 6th edition
Replies: 2
Views: 71

### Re: 4.21 6th edition

For C2H4, the most stable Lewis structure consists of two carbon atoms double bonded to each other and two hydrogens bonded to each of the carbons. For each carbon, there are three atoms bonded to it, which gives it the shape of trigonal planar. The trigonal planar shape has bond angles of 120 degre...
Sun Nov 18, 2018 10:05 am
Forum: Sigma & Pi Bonds
Topic: usage of sigma/pi
Replies: 6
Views: 266

### Re: usage of sigma/pi

One usage of the number of sigma and pi bonds is that it can determine the rotation of the molecule/ its rigidity. The more pi bonds a molecule has, the less rotation it will be able to perform.
Sun Nov 18, 2018 10:02 am
Forum: Determining Molecular Shape (VSEPR)
Topic: Dipole-Dipole forces
Replies: 4
Views: 197

### Re: Dipole-Dipole forces

No, it depends on the electronegativity differences between the atoms involved in the bond. If the electronegativity difference between the two atoms involved in the bond is small, then the bond is non-polar and its arrangement around the central atom does not matter.
Fri Nov 16, 2018 2:52 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: tetrahedral vs trigonal planar
Replies: 9
Views: 487

### Re: tetrahedral vs trigonal planar

Tetrahedral geometry requires four atoms bonded to a central atom. Trigonal planar only has three atoms bonded to the central atom.
Fri Nov 09, 2018 5:19 pm
Forum: Limiting Reactant Calculations
Topic: Actual Yield
Replies: 7
Views: 696

### Re: Actual Yield

Actual yield can be experimentally determined, but I think in most, if not all cases, actual yield will just be given.
Fri Nov 09, 2018 5:18 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Symbol meanings between chemical bonds
Replies: 2
Views: 115

### Re: Symbol meanings between chemical bonds

The dashes and wedges are used to represent atoms in 3-D space. If you can imagine your paper as a plane, the dash lines show atoms going backwards behind the plane and the wedges show atoms sticking out towards you.
Fri Nov 09, 2018 5:15 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Bond Strength of H2S
Replies: 1
Views: 66

### Re: Bond Strength of H2S

H2S is polar. While the lewis structure is symmetrical, in 3-D space, the two lone pairs on the Sulfur atom repel the bonding electrons, which results in a bent shape (we haven't went over this in class yet). This bent shape has a dipole moment with a partial positive charge on the Hydrogens and a p...
Sun Nov 04, 2018 1:33 pm
Forum: Ionic & Covalent Bonds
Topic: 3.19 (6th edition)
Replies: 4
Views: 149

### Re: 3.19 (6th edition)

I believe that should be the right answer as the two electrons that would be removed due to the 2+ positive charge on Ni would be the two electrons in the 4s orbital.
Fri Nov 02, 2018 3:10 pm
Forum: Ionic & Covalent Bonds
Topic: Highly Distorted Electrons?
Replies: 3
Views: 101

### Re: Highly Distorted Electrons?

I think the term"highly distorted" electrons is referring to the electron cloud surrounding the anion participating in an ionic bond. If the bonded cation's charge attracts the electrons from the anion, the electron cloud becomes "distorted," and the anion is described as being h...
Thu Nov 01, 2018 5:54 pm
Forum: Lewis Structures
Topic: 6th Edition, Problem 3.33
Replies: 1
Views: 58

### Re: 6th Edition, Problem 3.33

The placement of the other atoms around the central atom shouldn't matter because Lewis structures are only 2-D models of bonding. In 3-D space, the molecule will take on a specific structure that will dictate the placement of the atoms.
Fri Oct 26, 2018 4:36 pm
Forum: Heisenberg Indeterminacy (Uncertainty) Equation
Topic: Heisenberg Uncertainity Principle
Replies: 2
Views: 187

### Re: Heisenberg Uncertainity Principle

Linear momentum p can also be defined as mass times velocity. In the uncertainty principle equation, the uncertainty in linear momentum can be substituted with the expression m times the uncertainty in velocity. In this context, the linear momentum is important because as an object's velocity is mea...
Fri Oct 26, 2018 3:17 pm
Forum: Ionic & Covalent Bonds
Topic: Bonding Between Cations and Anions
Replies: 3
Views: 67

### Re: Bonding Between Cations and Anions

In the case of (NH4)+ and (SO4)2-, (NH4)+ only has a full valence shell because it gave up one of its electrons, generating a positive charge and (SO4)2- only has a full valence shell because it stole two electrons, generating the negative 2 charge. Cations and anions form ionic bonds through this t...
Fri Oct 26, 2018 3:09 pm
Forum: Electron Configurations for Multi-Electron Atoms
Topic: zeff
Replies: 1
Views: 83

### Re: zeff

"Zeff" refers to effective nuclear charge. Zeff is not independent of the number of electrons in an atom because as the number of electrons increase, the inner electrons "shield" the outer electrons from experiencing the full effects of the nucleus' positive charge. Thus, as the ...
Fri Oct 19, 2018 4:43 pm
Forum: Wave Functions and s-, p-, d-, f- Orbitals
Topic: orbitals
Replies: 6
Views: 168

### Re: orbitals

"px, py, and pz" describe the orientation of the lobes of the p orbitals. For the px orbital, the two lobes lie along the x axis. For the py orbital, the lobes lie along the y axis. For the pz orbital, the lobes lie along the z axis.
Fri Oct 19, 2018 4:40 pm
Forum: Photoelectric Effect
Topic: help on 1.15 6th edition
Replies: 2
Views: 148

### Re: help on 1.15 6th edition

The ultraviolet spectrum, or the Lyman series, involves electron transitions from a higher energy level to n=1. The wavelength of the emitted light can be converted into frequency. This frequency can then be used in conjunction with Rydberg's equation to determine the value of the second principal q...
Fri Oct 19, 2018 4:16 pm
Forum: Electron Configurations for Multi-Electron Atoms
Topic: Electrostatic Potential Energy Example
Replies: 2
Views: 126

### Re: Electrostatic Potential Energy Example

I believe that the main idea he was trying to convey is that the higher the nuclear charge is (for Carbon it would be 6+ because it has 6 protons in the nucleus), the greater the attraction between the electrons and the nucleus. The overall idea presented is that electrostatic attraction grows with ...
Sat Oct 13, 2018 9:02 pm
Forum: Bohr Frequency Condition, H-Atom , Atomic Spectroscopy
Topic: Balmer Series
Replies: 2
Views: 95

### Re: Balmer Series

I believe that the Balmer series only refers to transitions that end in n=2, but n=2 is not considered the ground state of the electron. If an electron is at n=2, it is still considered excited.
Sat Oct 13, 2018 7:47 pm
Forum: Properties of Light
Topic: Photoelectric Effect Module #34b
Replies: 1
Views: 31

### Re: Photoelectric Effect Module #34b

The minimum frequency needed to be absorbed by molybdenum metal can be converted into energy using E=hv. This energy is the same as the metal's threshold energy. Similarly, the 194 nm of light can be converted into energy using the E=hv equation, this is the energy of the light photon. The maximum k...
Sat Oct 13, 2018 6:40 pm
Forum: Properties of Light
Topic: De Brogile Equation
Replies: 6
Views: 113

### Re: De Brogile Equation

The DeBroglie equation is used to calculate the wavelength of any moving particle. However, as mentioned in class, all matter has wavelike properties, but this can only be measured for objects with small masses, such as electrons.
Thu Oct 04, 2018 10:43 pm
Forum: Limiting Reactant Calculations
Topic: Calculating Maximum Mass
Replies: 5
Views: 677

### Re: Calculating Maximum Mass

I'm not sure if this is the cause of your problems with part b, but copper (II) hydroxide should have the chemical formula of Cu(OH)2.
Thu Oct 04, 2018 10:35 pm
Forum: Accuracy, Precision, Mole, Other Definitions
Topic: Percision and Accuracy
Replies: 5
Views: 308

### Re: Percision and Accuracy

This is similar to what was said in class. Imagine you are running three trials of an experiment that require you to measure out a certain number of grams of an element. The balance that you use could give measurements numerically close to each other all three times. If this is the case, then the ba...
Thu Oct 04, 2018 10:21 pm
Forum: Significant Figures
Topic: Sig figs for Avogadro's number
Replies: 3
Views: 107

### Re: Sig figs for Avogadro's number

I believe that Avogadro's number is typically rounded off to 6.022 x 10^23.