## Search found 51 matches

Fri Mar 15, 2019 1:55 am
Forum: First Order Reactions
Topic: Half life
Replies: 4
Views: 200

### Half life

Where does the 0.693 come from in the half life equation for first order reactions. Will that value ever change? I just want to know where it comes from and why we use it.
Fri Mar 15, 2019 1:52 am
Forum: Second Order Reactions
Topic: 3rd order and fractional orders
Replies: 1
Views: 314

### 3rd order and fractional orders

In self test 15.4B, it tells you that the order is not an integer. If this is the case how do you determine this and what rate order expression do you use?
Fri Mar 15, 2019 1:48 am
Forum: Arrhenius Equation, Activation Energies, Catalysts
Topic: Catalysts
Replies: 3
Views: 129

### Catalysts

Do Catalysts change the reaction mechanism? Since something new is being added into the chemical equation does that mean there will be entirely new intermediates?
Fri Mar 08, 2019 12:29 am
Forum: Kinetics vs. Thermodynamics Controlling a Reaction
Topic: Reaction mechanisms
Replies: 3
Views: 183

### Reaction mechanisms

Why is the rate determining step always the slowest reaction
Fri Mar 08, 2019 12:25 am
Forum: Kinetics vs. Thermodynamics Controlling a Reaction
Topic: The slope of the tangent line with respect to the rate
Replies: 3
Views: 176

### The slope of the tangent line with respect to the rate

I don't understand how the slope of the tangent line is significant to finding a true rate if the rate is exponentially reaching a plateau.
Thu Mar 07, 2019 11:45 pm
Forum: General Rate Laws
Topic: Graph of ln[A] against time
Replies: 4
Views: 199

### Graph of ln[A] against time

In lecture Lavelle had a graph that had ln[A] on the Y axis and time on the X axis. I was confused to see that the plot for the graph was linear. Why is it linear if the graph of ln is exponential?
Fri Mar 01, 2019 2:43 am
Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
Topic: 4J.7
Replies: 2
Views: 112

### 4J.7

When calculating the delta H why do we do the delta H products minus reactants oppose to just using the sum of the enthalpies like the questions previously. Like in questions 4J.5 we just use the products delta H when finding Gibbs.
Thu Feb 28, 2019 10:41 pm
Forum: Balancing Redox Reactions
Topic: Short hand notation
Replies: 8
Views: 333

### Short hand notation

In the shorthand notation for the redox reactions, the textbook says that the double verticle line represents the salt bridge. What is a salt bridge and what is its importance to a Galvanic cell
Thu Feb 28, 2019 7:34 pm
Forum: Balancing Redox Reactions
Topic: Question 6K.3 part (d)
Replies: 1
Views: 87

### Question 6K.3 part (d)

I understand that there was an error in the textbook, however, the answer in the solutions manual doesn't make sense, why for one of the answers does it include the electrons and in the other answer, the coefficients are missing?
Fri Feb 22, 2019 12:17 am
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Proportionality and current?
Replies: 2
Views: 132

### Proportionality and current?

Is the amount of chemical change proportional to the amount of current passed?
Thu Feb 21, 2019 5:00 pm
Forum: Balancing Redox Reactions
Topic: problem 14.1 6th edition
Replies: 1
Views: 91

### problem 14.1 6th edition

The problem asks for both the reduction and oxidation half reaction. For the oxidation reaction I got 6e+14H+Cr2O7^2- -----> 2Cr^3+ +7H2O.
But for some reason, I am confused about how to write the reduction half-reaction because of the H+ and the C2H5OH
Thu Feb 21, 2019 4:55 pm
Forum: Balancing Redox Reactions
Topic: Oxidation States
Replies: 2
Views: 116

### Oxidation States

Will we be expected to know all of the oxidation numbers for all the elements or will we be given a table? If we are expected to know is there some kind of shorthand or way of figuring them out?
Thu Feb 14, 2019 10:08 pm
Forum: Thermodynamic Systems (Open, Closed, Isolated)
Topic: intensive and extensive
Replies: 2
Views: 362

### intensive and extensive

What is the difference between an intensive property and extensive property and why are specific heat capacity and specific heat capacity them respectively?
Thu Feb 14, 2019 10:00 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Finding the change in H from a reaction/molecules
Replies: 2
Views: 94

### Finding the change in H from a reaction/molecules

In problem 4B in Lydon's midterm review packet when we added up both sides of the reaction we subtracted the reactant side from the product side when we generally do the opposite. Why was this problem an exception?
Thu Feb 14, 2019 9:56 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Replies: 8
Views: 357

Why do we calculate separate reaction entropies and why is that final accurate? For example in question 5 of Lydon's review packet we did 3 separate change in entropy equations then added them to get the final answer. I guess what I'm not understanding is how is the sum of those entropies an accurat...
Thu Feb 14, 2019 9:52 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: Degeneracy
Replies: 4
Views: 382

### Degeneracy

When solving for degeneracy when is W equal to 0. There was a problem on the Midterm that I had seemed to misinterpret.
Fri Feb 08, 2019 1:00 am
Forum: Calculating Work of Expansion
Topic: Hess's Law
Replies: 2
Views: 92

### Hess's Law

When calculating the overall enthalpy, particularly with the bond enthalpy problems will the bond energies always be given to us and if not how do we calculate them?
Fri Feb 08, 2019 12:58 am
Forum: Calculating Work of Expansion
Topic: 4F.1 7th Edition
Replies: 4
Views: 215

### 4F.1 7th Edition

For part A, when solving for change in enthalpy why do we place a negative in front of energy transferred as heat (q)?
Fri Feb 08, 2019 12:32 am
Forum: Thermodynamic Systems (Open, Closed, Isolated)
Topic: Isolated System
Replies: 5
Views: 464

### Isolated System

What is the point of an Isolated system? If no matter or heat can leave or enter the system and the heat and mass stay constant what would be the interest in using an Isolated system?
Thu Jan 31, 2019 10:04 pm
Forum: Phase Changes & Related Calculations
Topic: Chemical potential energy
Replies: 4
Views: 136

### Chemical potential energy

Lavelle did a chemical potential energy problem, where he took the delta H of all the bonds on both sides of the reaction. He mentioned how there was a short cut to the method where you didn't have to calculate the energy of each bond what was that short cut?
Thu Jan 31, 2019 10:01 pm
Forum: Phase Changes & Related Calculations
Topic: Entropy vs Enthalpy concept
Replies: 3
Views: 133

### Entropy vs Enthalpy concept

What's the difference between enthalpy and entropy? Entropy is the measure of gain or loss of heat. Entropy is the measure of chaos, but what does that mean and does it have units?
Thu Jan 31, 2019 9:59 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Gibbs
Replies: 5
Views: 258

### Gibbs

What does exergonic mean in terms of Gibbs free energy. How does it determine spontaneity?
Fri Jan 25, 2019 12:12 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: ICE BOX and coefficients
Replies: 4
Views: 238

### ICE BOX and coefficients

When doing ice box problems what are you supposed to do with the coefficient in front of a molecule? do you add it to the change or do you multiply? Also when you are adding Mols to the equation do you change it for the base equation?
Thu Jan 24, 2019 10:16 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: 5%
Replies: 10
Views: 419

### 5%

What is the 5% rule and how does it relate to the ICE box?
Thu Jan 24, 2019 10:13 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Pressure and gas equilibria
Replies: 2
Views: 117

### Re: Pressure and gas equilibria

Pressure and Volume have a inverse relationship. Thus if you pump an inert gas into a system at equilibrium you are increasing the pressure you are lessening volume which leads to the reaction favoring the side of the reaction with a lower concentration.
Thu Jan 17, 2019 9:30 pm
Forum: Non-Equilibrium Conditions & The Reaction Quotient
Topic: Acid and Base
Replies: 3
Views: 230

### Acid and Base

Why does the KA and KB value have to add up to 10x^14?
Thu Jan 17, 2019 9:28 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Quadratic equation and ICE box
Replies: 3
Views: 88

### Quadratic equation and ICE box

When is it appropriate to use the quadratic equation when solving for the ICE box. In lecture lavelle was completing a problem and let us know that the quadratic equation wasnt needed why is this and when is it needed.
Thu Jan 17, 2019 9:20 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Kw and water
Replies: 2
Views: 89

### Kw and water

In lecture we did the calculations for Kw, I am unsure what the significance of this constant is. I thought that water was not an important part of equilibrium, why do we calculate a constant for it and what is it used for?
Thu Jan 10, 2019 10:20 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Q and K
Replies: 13
Views: 362

### Re: Q and K

In regards to calculating K, the values that are inputted into the equation are concentrations or partial pressures whereas when Calculating Q the values inputted are initial values not equilibrium values.
Thu Jan 10, 2019 9:44 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Q and K
Replies: 4
Views: 168

### Q and K

If K is the equilibrium constant, or the rate at which both the forward and reverse reaction are happening simultaneously. What is the Q value and what is its significance in determining whether the products or the reactants are going to be favoured?
Fri Dec 07, 2018 3:54 am
Forum: Amphoteric Compounds
Topic: Oxalate bidentate
Replies: 4
Views: 164

### Oxalate bidentate

Why is Oxalate bidentate? It seems that all four of the oxygens are able to donate an electron pair I am confused by why it is considered bidentate.
Fri Dec 07, 2018 3:41 am
Forum: Amphoteric Compounds
Topic: Polydentate
Replies: 2
Views: 128

### Polydentate

What is a polydentate would it be just an anion that has more than 4 bonding sites? Can someone give an explanation and example?
Fri Dec 07, 2018 3:28 am
Forum: Amphoteric Compounds
Topic: Coordination compounds
Replies: 1
Views: 100

### Coordination compounds

On problem 9C3 part d), My final answer was [Fe(C2O4)2(H2O)2]Na while the book answer was Na[Fe(OH2)2(C2O4)2] will it matter on the exam if the aqua is written as H2O or OH2? Is one answer more right than the other? If so can someone please explain!
Thu Nov 29, 2018 8:46 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: polarity
Replies: 11
Views: 343

### polarity

Is it safe to assume that any covalently bonded molecule with a lone pair on the central atom will be polar? How can polarity be determined with larger molecules in class Lavelle usually draws arrows to demonstrate what direction the positive and negative poles are at how is this determined.
Thu Nov 29, 2018 8:42 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: repulsion
Replies: 3
Views: 210

### repulsion

Why do the lone pairs on the central atom have more repulsion than all of the valence electrons on the other atoms of the molecule? Why do the lone pairs on the central atom dictate shape.
Thu Nov 29, 2018 8:39 pm
Forum: Hybridization
Topic: Pi bonds in triple bond
Replies: 17
Views: 912

### Re: Pi bonds in triple bond

usually you can figure out the amount of pi and sigma bonds assuming every first bond is a sigma bond and every bond after that is a pi bond. So in a triple bond the first of three would be a sigma and the other two would have to be pi
Thu Nov 29, 2018 8:35 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: One lone electron
Replies: 3
Views: 188

### One lone electron

what is the significance of molecules that have just one electron on the central atom not a lone pair. How does that affect the shape?
Thu Nov 29, 2018 8:24 pm
Forum: Hybridization
Topic: Ground state hybridization
Replies: 1
Views: 105

### Ground state hybridization

Do we need to know how to write the ground state configuration for the hybridized molecules? If what is the logic behind writing them. Like the ground state sp^4d. Im just lost
Thu Nov 29, 2018 12:52 am
Forum: Determining Molecular Shape (VSEPR)
Topic: 7th edition 2E.1 mistake ?
Replies: 6
Views: 364

### Re: 7th edition 2E.1 mistake ?

The question doesn't specify how many lone pairs there can be on the central atom, it only says "one or more lone pairs". After doing some research online, apparently a AX2E3 molecule will give a bond angle of 180 degrees.
Fri Nov 16, 2018 12:02 am
Forum: Hybridization
Topic: Pi bonds in triple bond
Replies: 17
Views: 912

### Re: Pi bonds in triple bond

The reading says that you can identify the pi bonds by the number of nodal planes, how are you supposed to know how many nodal planes there are in a molecule is there a better way to figure it out?
Thu Nov 15, 2018 11:57 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Lone Pairs
Replies: 3
Views: 158

### Re: Lone Pairs

Is it fair to say that if there is a lone pair on the central atom that the molecule is going to be polar? Most of the examples I'm seeing demonstrate this point? Will there be more electron density there, therefore, repelling the other atoms creating a dipole.
Thu Nov 15, 2018 11:53 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Vsepr Formula
Replies: 7
Views: 134

### Re: Vsepr Formula

For the E in the vesper formula does that take in account only the lone pairs of electrons on the central atom or in the whole structure.
Thu Nov 08, 2018 7:11 pm
Forum: Lewis Structures
Topic: Determining bond length from lewis structure [ENDORSED]
Replies: 1
Views: 152

### Determining bond length from lewis structure[ENDORSED]

When estimating bond length from Lewis structure would a very electronegative and low electronegative atom have a shorter bond than two very electronegative atoms? Is there a trend in missing.
Thu Nov 08, 2018 7:04 pm
Forum: Hybridization
Topic: the ground state and ion exceptions
Replies: 2
Views: 133

### the ground state and ion exceptions

For Cr and Cu what is the exception and what does it mean? from what I understand you take from the S orbital and give to the D?
Thu Nov 08, 2018 7:01 pm
Forum: Resonance Structures
Topic: Dominant resonance structure
Replies: 4
Views: 404

### Dominant resonance structure

I don't understand what it means by dominant. How are you supposed to tell what structure is dominant over the other one?
Thu Oct 25, 2018 11:58 pm
Forum: Wave Functions and s-, p-, d-, f- Orbitals
Topic: pauli exclusion
Replies: 3
Views: 199

### pauli exclusion

What is the explanation behind the Pauli exclusion principle?
Thu Oct 25, 2018 11:54 pm
Forum: Heisenberg Indeterminacy (Uncertainty) Equation
Topic: Conceptual question
Replies: 3
Views: 226

### Conceptual question

Why is it that we can only know the measurement of either the position or momentum at a given time? I don't understand the idea behind this equation.
Thu Oct 25, 2018 11:30 pm
Forum: Quantum Numbers and The H-Atom
Topic: The values of L and ML
Replies: 3
Views: 185

### The values of L and ML

In the lecture, we went over that l=n-1 but it also says that it can be anything lower than n. Why is this, and when do we stick to n-1?
Wed Oct 17, 2018 3:29 pm
Forum: Properties of Light
Topic: Atomic Spectrum and Series
Replies: 4
Views: 87

### Re: Atomic Spectrum and Series

Thank You!
Wed Oct 17, 2018 1:27 pm
Forum: Properties of Light
Topic: Atomic Spectrum and Series
Replies: 4
Views: 87

### Atomic Spectrum and Series

In the spectrum of atomic hydrogen, several lines are generally classified together as belonging to a series (for example, Balmer series, Lyman series, Paschen series), as shown in Figs. 1.10 and 2.1. What is common to the lines within a series that makes grouping them together logical? Having troub...
Wed Oct 17, 2018 1:03 pm
Forum: Photoelectric Effect
Topic: Photoelectric Effect Post-Module Assessment
Replies: 2
Views: 134

### Re: Photoelectric Effect Post-Module Assessment

Once you've found the energy you can use the formula λ=(hc)/E to find wavelength.