## Search found 49 matches

Sat Mar 17, 2018 10:32 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Catalyst and Intermediate
Replies: 7
Views: 566

### Re: Catalyst and Intermediate

A catalyst is added to the reaction first appears as a reactant, and then as a product. An intermediate is created from a reaction, so it first appears as a product, and then as a reactant.
Sat Mar 17, 2018 12:41 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Enthalpy of RXN using standard enthalpy of formation
Replies: 2
Views: 276

### Re: Enthalpy of RXN using standard enthalpy of formation

You do not change the sign. The equation is the [sum of standard enthalpy of formation(products)] - [sum of standard enthalpy of formation(reactants)] = enthalpy of RXN. It seems you are confusing this with calculating enthalpy using bond enthalpies, which would be [bonds broken - bonds formed], but...
Sat Mar 17, 2018 12:37 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: Delta S
Replies: 2
Views: 574

### Re: Delta S

The second law can be written many ways, I know it as the entropy is always increasing in the universe. delta S only = 0 if the system is at equilibrium. deltaS universe=deltaSsys + deltaSsurr, meaning if deltaSuniv > 0, the process is spontaneous because both the entropy of the system, and the surr...
Sat Mar 17, 2018 12:31 pm
Forum: *Alkanes
Topic: Tips and Tricks for remembering Functional Groups?
Replies: 2
Views: 485

### Re: Tips and Tricks for remembering Functional Groups?

I remember them by where they can occur in a molecule. ketones and ethers can go anywhere, aldehydes alcohols and carboxyl's must be at the end, and amines (if CNH2) must be at the end, otherwise can go anywhere.
Sat Mar 17, 2018 12:24 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: phase diagram
Replies: 1
Views: 220

### phase diagram

Why does a lower heat capacity equate to a higher slope? Shouldn't it be the opposite?
Sun Mar 11, 2018 11:22 pm
Forum: *Free Energy of Activation vs Activation Energy
Topic: Relation between k and activation energy
Replies: 6
Views: 2033

### Re: Relation between k and activation energy

You can observe the relationship through the Arrhenius Equation - basically, the formula implies that the rate constant increases exponentially as the activation energy decreases.
Sun Mar 11, 2018 11:16 pm
Forum: General Rate Laws
Topic: Determining Orders
Replies: 2
Views: 191

### Re: Determining Orders

You can also plug your values into the differential rate law for the order you are assuming, and if you are correct, the slope of the line you create will be a straight line
Sun Mar 11, 2018 11:12 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Rate constant
Replies: 6
Views: 348

### Re: Rate constant

The reaction rate how fast a chemical reaction occurs when going from R-->P. A reaction rate constant gives the comparative amount of the reaction rates of reactants and products. Meaning that the rate of reaction is influenced the types of reaction, the concentration, pressure, and the temperature ...
Sat Feb 24, 2018 11:35 am
Forum: General Rate Laws
Topic: Reaction Rate and Spontaneity
Replies: 5
Views: 682

### Re: Reaction Rate and Spontaneity

Chemical reactions do have both thermodynamic and kinetic aspects, but I don't think you can determine spontaneity by the reaction rates. Thermodynamics has to do with the stability of a reaction and its characteristics at equilibrium while kinetics has to do with the reactivity and the rates that g...
Sat Feb 24, 2018 11:29 am
Forum: Kinetics vs. Thermodynamics Controlling a Reaction
Topic: units of the rate of reaction
Replies: 7
Views: 541

### Re: units of the rate of reaction

The units of k vary depending on the order of the reaction.
Sat Feb 24, 2018 11:26 am
Forum: Method of Initial Rates (To Determine n and k)
Topic: Differential Rate Law
Replies: 3
Views: 228

### Re: Differential Rate Law

Yes this is possible and it means that the order would be 0! I am not sure if Dr. Lavelle will cover this but it is in the book so I assume so.
Sun Feb 18, 2018 10:23 am
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: salt bridge
Replies: 3
Views: 251

### Re: salt bridge

Basically, the salt bridge is used to maintain the charge balance of the cell. During oxidation, the anode makes electrons and positively charged ions.The electrons move, so there is an unbalanced positive charge. To counteract this and keep neutral, the negatively charged ions from the salt bridge ...
Sun Feb 18, 2018 10:14 am
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Inert Conductor
Replies: 3
Views: 152

### Inert Conductor

Can someone please explain what the purpose of an inert conductor is?
Sun Feb 18, 2018 10:12 am
Forum: Balancing Redox Reactions
Topic: Test 2
Replies: 5
Views: 256

### Re: Test 2

I believe we will be given the half reactions and cell potential, but will have to manipulate them in order to fit the problem. I think it's more important that we know how to
Thu Feb 08, 2018 2:36 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: Boltzmann's Equation
Replies: 1
Views: 146

### Boltzmann's Equation

When exactly do we use Boltzmann's equation? I know it's to calculate entropy but when is it best to use this approach? Additionally, should weediest know if the system is a 1, 2, etc. state system, or will we be told?
Thu Feb 08, 2018 1:11 pm
Forum: Phase Changes & Related Calculations
Topic: Phase changes with entropy?
Replies: 6
Views: 341

### Re: Phase changes with entropy?

Yes, both enthalpy and entropy change during a phase change, but keep in mind when simply asked is the reaction spontaneous at a given temp, you do not account for entropy or enthalpy change to get to that temp, but are only looking at the spontaneity of the phase change itself.
Thu Feb 08, 2018 1:08 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: "Molar Convention"
Replies: 2
Views: 143

### Re: "Molar Convention"

I believe the two are interchangeable since deltaG sub r is just the deltaG of the reaction. There is, however, a difference between delta G and delta G with the degree sign meaning *standard gibbs free energy,* which would be at standard temp and pressure (cannot measured directly, you must use sta...
Thu Feb 08, 2018 12:59 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Exothermic/Endothermic
Replies: 2
Views: 159

### Re: Exothermic/Endothermic

This has to do with the general formula deltaG = deltaH - TdeltaS. A negative deltaH (exothermic) and a negative deltaS is favorable at a low temp because the negative from the S and from the equation cancel so it's a negative plus a positive, and the result should be a negative deltaG meaning produ...
Tue Jan 30, 2018 2:57 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: isothermal
Replies: 5
Views: 289

### Re: isothermal

delta U would equal 0 because deltaU = (3/2)nR(deltaT), and since deltaT=0, deltaU is therefore also equal to zero.
Tue Jan 30, 2018 2:54 pm
Forum: Phase Changes & Related Calculations
Topic: Hw #8.49 standard state
Replies: 4
Views: 324

### Re: Hw #8.49 standard state

We know it is in standard state because all od the reactants and products are given in their standard states, in this case - gases.
Tue Jan 30, 2018 2:47 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: Question from 1/24/18 Lecture
Replies: 2
Views: 148

### Re: Question from 1/24/18 Lecture

I believe it's because deltaQ=nCdeltaT so you can make the substitution
Wed Jan 24, 2018 10:47 am
Forum: Phase Changes & Related Calculations
Topic: Phase Changes Equations
Replies: 4
Views: 294

### Re: Phase Changes Equations

Typically deltaH(fusion) and deltaH(vap) will be given to us since what we are usually solving for is initial/final temp or the enthalpy of the reaction. I believe it is more important that you know how to distinguish and apply all of the different values given to you than it is to calculate these s...
Wed Jan 24, 2018 10:43 am
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: 8.63
Replies: 4
Views: 274

### Re: 8.63

The enthalpy of formation for H2O(l) is -285.83, but you would have to multiply that number by 2 because there are 2 moles in the reaction.
Wed Jan 24, 2018 10:40 am
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Bond Enthalpies
Replies: 4
Views: 228

### Re: Bond Enthalpies

An easy way to think of it is the [sum of the reactants (aka the bonds broken)] - [the sum of the products (aka the bonds formed)] but I'm not sure if it's technically correct to say that which is why it's not on the formula sheet (or maybe we should just know breaking is endo and forming is exo)
Sat Jan 20, 2018 9:43 am
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: 8.37
Replies: 3
Views: 195

### Re: 8.37

Unless the question specifies desired units, my TA said that either answer would be acceptable.
Sat Jan 20, 2018 9:40 am
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Standard enthalpies on test 1 [ENDORSED]
Replies: 7
Views: 389

### Re: Standard enthalpies on test 1[ENDORSED]

Yes, I would assume the halogens and the transition metals. Dr. Lavelle said if it is some element we wouldn't know, he would give us the standard state.
Sat Jan 20, 2018 9:38 am
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Enthalpy
Replies: 4
Views: 171

### Re: Enthalpy

Formation enthalpy refers to the formation of a compound while bond enthalpy is used when forming a molecule from isolated atoms. I believe the difference is just the creation of a compound vs a molecule.
Sat Jan 13, 2018 9:24 am
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: q=mCdeltaT
Replies: 2
Views: 1688

### Re: q=mCdeltaT

You could have q=mCdeltaT where "m" refers to the mass in grams and the "C" refers to the specific heat capacity, or you could have q=nCdeltaT where "n" refers to the number of moles and "C" refers to the molar heat capacity. Just make sure that all of your un...
Sat Jan 13, 2018 9:18 am
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Periodic Trend for Heat Capacity
Replies: 2
Views: 424

### Re: Periodic Trend for Heat Capacity

Could it be the same as the trend for atomic radius? since specific heat capacity is related to the size of the atom.
Sat Jan 13, 2018 9:12 am
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Closed System
Replies: 7
Views: 412

### Re: Closed System

A calorimeter is a closed system because it has a fixed amount of matter but can exchange energy with its surroundings. A calorimeter is not an isolated system.
Fri Dec 08, 2017 7:48 am
Forum: Bronsted Acids & Bases
Topic: Bronsted and Lewis Acids
Replies: 3
Views: 305

### Re: Bronsted and Lewis Acids

I would double check with Dr. Lavelle, but I do not believe this is possible. Every bronsted acid is a lewis acid, but not every lewis acid is a bronsted acid. This occurs because a proton donation is really an election donation, but not vis versa. The same applies for bronsted and lewis bases.
Fri Dec 08, 2017 7:42 am
Forum: Naming
Topic: What is delocalized bonding? [ENDORSED]
Replies: 5
Views: 645

### Re: What is delocalized bonding?[ENDORSED]

Delocalized bonding comes into play when we talk about resonance. Since the correct lewis structure of a molecule that has resonance (a drawback of lewis structures) is a hybrid of all of the structures, we would say that the double bonds in each resonance structure are delocalized, meaning they are...
Sat Dec 02, 2017 9:17 am
Forum: Properties & Structures of Inorganic & Organic Acids
Topic: Strong acid vs weak acid [ENDORSED]
Replies: 7
Views: 505

### Re: Strong acid vs weak acid[ENDORSED]

A strong acid is one that is completely ionized in solution, whereas a weak acid can have a reverse reaction. Some common strong acids are HCl, HNO3, H2SO4, HBr, HI, HClO4, and HClO3. These were just strong acids I was taught to remember in high school, but I'm not sure there is any other way to qui...
Sat Dec 02, 2017 9:12 am
Forum: Bronsted Acids & Bases
Topic: Bronsted Acid vs Lewis Acid [ENDORSED]
Replies: 3
Views: 343

### Re: Bronsted Acid vs Lewis Acid[ENDORSED]

I believe that is the only difference. The bronsted acid is a proton (or H+ ion) donor, and base is the acceptor. The lewis acid is an electron acceptor, and base is the donor. Different definitions arose because of the context of different reactions. As our knowledge of different fields of chemistr...
Sun Nov 26, 2017 6:38 am
Forum: Determining Molecular Shape (VSEPR)
Topic: Lone Pairs vs. Bonding Pairs
Replies: 6
Views: 477

### Re: Lone Pairs vs. Bonding Pairs

In addition to the lone pair occupying a greater volume, a bonding pair is part of a sigma bond, placing it further away from the central atom whereas the negatively charged lone pair is pulled in close by the positively charged central atom, creating more repulsion power.
Sun Nov 26, 2017 6:33 am
Forum: Sigma & Pi Bonds
Topic: Sigma and Pi Bonds
Replies: 5
Views: 585

### Re: Sigma and Pi Bonds

You can have one sigma bonds and two pi bond because the sigma bond is the first bond formed. The following bonds that are created are pi bonds which bond at two or more locations, prohibiting rotation. You will not encounter any molecule with two sigma bonds connecting only two atoms.
Sun Nov 26, 2017 6:24 am
Forum: Naming
Topic: Ligand Attachments
Replies: 1
Views: 169

### Re: Ligand Attachments

You can think about it by how many points at which the ligand attaches to the central metal atom. One time - mono dentate, two times - bidentate etc. If it's too difficult to think about, you can also draw them out to get a visual representation.
Mon Nov 06, 2017 9:00 pm
Forum: Lewis Structures
Topic: Lone Pairs and H2O
Replies: 2
Views: 279

### Re: Lone Pairs and H2O

The unshared electron pair on the oxygen occupies a larger volume than the shared pairs, pushing down on the entire atom - because of the electrons pushing down, the hydrogen atoms are in a different plane than the oxygen atom.
Mon Nov 06, 2017 8:55 pm
Forum: Octet Exceptions
Topic: Octet Exceptions
Replies: 8
Views: 607

### Re: Octet Exceptions

I believe anything on the periodic table past phosphorus can be an exception. Also important to note that Boron often has less than octet- for example: BF3.
Mon Oct 30, 2017 8:16 pm
Forum: Octet Exceptions
Topic: Sulfur as an Octet Exception
Replies: 1
Views: 209

### Re: Sulfur as an Octet Exception

P, S, and Cl can have more than 8 electrons, therefore breaking octet. This occurs because atoms in a period of three or higher have d-orbitals in the valence shell which can accommodate additional electrons. It helps to remember that octet, 8 electrons, would be s^2,p^6 without a d-orbital --> n=1 ...
Mon Oct 30, 2017 8:11 pm
Forum: Formal Charge and Oxidation Numbers
Topic: Finding the Formal Charge
Replies: 3
Views: 334

### Re: Finding the Formal Charge

In the case of SO4^2-, the total charge should add up to 2-. Since "S" has the lowest ionization energy, it is the central atom and should therefore have a formal charge of zero, which would leave two of the oxygens with a formal charge of 1-. Oxygen is much more likely to have a negative ...
Wed Oct 25, 2017 4:52 pm
Forum: Wave Functions and s-, p-, d-, f- Orbitals
Topic: Difference between subshell and orbital [ENDORSED]
Replies: 9
Views: 1594

### Re: Difference between subshell and orbital[ENDORSED]

Electrons with the same "n," or principal quantum number, belong to an orbital. So, for example, if a configuration had 2s^2, 2p^5, both the "p" and the "s" would be considered part of the same orbital. Within the orbital, the subshell refers to electrons with the same ...
Mon Oct 23, 2017 3:28 pm
Forum: Wave Functions and s-, p-, d-, f- Orbitals
Topic: 3d, 4s orbital
Replies: 3
Views: 258

### Re: 3d, 4s orbital

The 3d orbital comes before the 4s orbital because the 3d state has lower energy - making it more difficult to remove. When looking at which electrons an atom will give away, it is most likely to give away the "s" electrons because they have higher energy and therefore, are easier to remov...
Sat Oct 21, 2017 11:07 pm
Forum: Quantum Numbers and The H-Atom
Topic: "No two electrons are the same..." [ENDORSED]
Replies: 5
Views: 529

### Re: "No two electrons are the same..."[ENDORSED]

When referring to the Pauli Exclusion Principle, it is true that no 2 elections in the *same* atom can have the same 4 quantum numbers. However, I believe that electrons in different atoms can have the same 4 quantum numbers, but for out purposes we look at each atom independently.
Sat Oct 21, 2017 11:00 pm
Forum: Wave Functions and s-, p-, d-, f- Orbitals
Topic: Px, Py, Pz
Replies: 10
Views: 773

### Re: Px, Py, Pz

Yes, this is the same as 2p^3 and we are allowed to write it that way; however, Dr. Lavelle said that this notation could be confusing when contemplating paired or parallel electrons so he thinks that the px, y, and z format is much more clear/avoids all confusion and recommends this version. Additi...
Sun Oct 15, 2017 12:02 pm
Forum: Photoelectric Effect
Topic: Photon vs. Energy [ENDORSED]
Replies: 6
Views: 426

### Re: Photon vs. Energy[ENDORSED]

They are not the same thing, yet they relate to each other. When asked to find energy, it is related to the photon's frequency and EM wavelength - the higher the Energy, the higher the frequency and vis versa. Same with the wavelength - the lower the E, the longer the EM wavelength is and vis versa....
Sun Oct 15, 2017 11:54 am
Forum: Einstein Equation
Topic: Stefan-Boltzmann Law
Replies: 2
Views: 254

### Re: Stefan-Boltzmann Law

The law states that the total heat energy/radiant energy from an object is in proportion with its absolute temperature, and it only applies to blackbodies [the ideal blackbody does not reflect any incoming light, but rather absorbs it]. With this equation, you can solve for total radiant heat energy...
Sun Oct 15, 2017 11:42 am
Forum: DeBroglie Equation
Topic: Ch.1 #41 [ENDORSED]
Replies: 7
Views: 823

### Re: Ch.1 #41[ENDORSED]

Yes, Gwen is correct. The mass of a neutron, like that of a proton, or planks constant, or Avogadro's number are all constant and therefore, will not change. The mass of a neutron is typically given in grams, so you have to convert by dividing by 1000 in order to get kg.
Sun Oct 15, 2017 11:28 am
Forum: Properties of Light
Topic: 1.9
Replies: 2
Views: 176

### 1.9

Hi there,
So I didn't have any trouble with the calculations for 1.9, however, how do I match the event to the frequency, wavelength, and energy?

Go to advanced search