Search found 60 matches
- Mon Mar 11, 2019 2:48 pm
- Forum: First Order Reactions
- Topic: Half-life Clarification
- Replies: 5
- Views: 625
Re: Half-life Clarification
Yes, each order has its own half life equation, because each order has different rates. However, in all the types of orders for reactions, the higher the k, the faster the rate.
- Mon Mar 11, 2019 2:46 pm
- Forum: Reaction Mechanisms, Reaction Profiles
- Topic: Pre equilibrium approach
- Replies: 3
- Views: 451
Re: Pre equilibrium approach
The pre-equilibrium approach shows that the fast step before the slow step will be at equilibrium, while the slow step will be the rate determining step.
- Mon Mar 11, 2019 2:44 pm
- Forum: Reaction Mechanisms, Reaction Profiles
- Topic: "Bottle Neck"
- Replies: 2
- Views: 339
Re: "Bottle Neck"
What the bottleneck means is that the first step prior to the slow step is assumed to be in equilibrium. If the early step is fast and the later step is slow, then there is a bottleneck and a buildup of intermediate results in the 1st step at equilibrium. Because of the bottleneck, we can do the pre...
- Mon Mar 04, 2019 3:06 pm
- Forum: General Rate Laws
- Topic: 1st and 2nd order
- Replies: 6
- Views: 729
Re: 1st and 2nd order
A zeroth-order reaction is one whose rate is independent of concentration; its differential rate law is rate = k. In a first-order reaction, the reaction rate is directly proportional to the concentration of one of the reactants.The simplest kind of second-order reaction is one whose rate is proport...
- Mon Mar 04, 2019 3:02 pm
- Forum: Kinetics vs. Thermodynamics Controlling a Reaction
- Topic: how is kinetics different?
- Replies: 17
- Views: 1694
Re: how is kinetics different?
Thermodynamics tells us if a forward or reverse reaction is favored. Kinetics tells us how fast the reaction is and the likelihood of the reaction occurring. Just because a reaction is thermodynamically favored does not mean it is kinetically favored. For example, the reaction of diamond to graphite...
- Mon Mar 04, 2019 2:59 pm
- Forum: Kinetics vs. Thermodynamics Controlling a Reaction
- Topic: Activation energy
- Replies: 8
- Views: 867
Re: Activation energy
The activation energy of a reaction can tell how fast the reaction will occur. A reaction with a low activation energy will occur faster than a reaction with high activation energy.
- Mon Feb 25, 2019 2:49 pm
- Forum: Gibbs Free Energy Concepts and Calculations
- Topic: Gibbs Free Energy
- Replies: 7
- Views: 934
Re: Gibbs Free Energy
When Gibbs Free Energy changes, it means that the reaction is more or less favorable. If the change in Gibbs free energy is negative, then the forward reaction is favorable or spontaneous. If the change in Gibbs free energy is positive, then the forward reaction is not favorable. This means that the...
- Mon Feb 25, 2019 2:41 pm
- Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
- Topic: DeltaG at Equilibrium
- Replies: 2
- Views: 292
Re: DeltaG at Equilibrium
Delta G at equilibrium is equal to zero because at equilibrium, neither the forward nor the reverse reaction is favored. If the forward reaction was favored delta G would be negative and if the reverse reaction was favored delta G would be positive. Since the reaction is at equilibrium, delta G is 0.
- Mon Feb 25, 2019 2:38 pm
- Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
- Topic: Adding Pt(s) to cell diagram
- Replies: 3
- Views: 368
Re: Adding Pt(s) to cell diagram
You know to add Pt(s) when the half reaction for either the cathode or the anode does not contain a solid. For the battery to function, we need a solid like platinum, which is an inert conductor, in order to exchange the electrons between the two reactions.
- Mon Feb 18, 2019 3:09 pm
- Forum: Calculating Work of Expansion
- Topic: Units for R
- Replies: 10
- Views: 1402
Re: Units for R
The units for R vary depending on which of the Rs you want to use. Usually you will be using 8.314 J/molK or 0.08206 Latm/molK. Make sure to look at what the problem gives you and what the problem wants in regards to units.
- Mon Feb 18, 2019 3:06 pm
- Forum: Gibbs Free Energy Concepts and Calculations
- Topic: Change in free energy for a reaction at equilibrium
- Replies: 3
- Views: 311
Re: Change in free energy for a reaction at equilibrium
The change in Gibbs free energy for a reaction at equilibrium is 0 J because at equilibrium neither the forward reaction nor the reverse reaction is favored so the change in Gibbs free energy is 0. Both reactions are equally spontaneous.
- Mon Feb 18, 2019 3:03 pm
- Forum: Gibbs Free Energy Concepts and Calculations
- Topic: deltaG=0
- Replies: 2
- Views: 326
Re: deltaG=0
When delta G is equal to 0, the reaction is at equilibrium and it is neither spontaneous nor unspontaneous.
- Mon Feb 11, 2019 3:19 pm
- Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
- Topic: Constant Vol.
- Replies: 8
- Views: 1065
Re: Constant Vol.
When the volume is constant, this means that work equals zero because work=-PdeltaV and work=-nRTln(V2/V1). At constant volume, both of these equations lead to the work equaling zero.
- Mon Feb 11, 2019 3:16 pm
- Forum: Entropy Changes Due to Changes in Volume and Temperature
- Topic: Ideal Behavior
- Replies: 3
- Views: 422
Re: Ideal Behavior
When the problem says assume ideal gas behavior, this means that we can use the constants Cp=5/2R and Cv=3/2R. These constants help in solving a problem where you need to use the formula S=nCln(T2/T1).
- Mon Feb 11, 2019 3:12 pm
- Forum: Ideal Gases
- Topic: The Difference between Q and Kc [ENDORSED]
- Replies: 18
- Views: 8845
Re: The Difference between Q and Kc [ENDORSED]
Q and Kc are both constants used to look at a reaction. Q deals with the the reaction not at equilibrium and it can tell what direction the reaction will proceed as it moves toward equilibrium. When Q>K, reaction favors reverse. When Q<K, reactions favors forward. Kc is the equilibrium constant and ...
- Mon Feb 04, 2019 3:39 pm
- Forum: Concepts & Calculations Using First Law of Thermodynamics
- Topic: Delta U
- Replies: 7
- Views: 750
Re: Delta U
Delta U is the change in internal energy and it is a state property. A positive delta U value tells us that Ufinal is greater than Uinitial or the system gained energy. A negative delta U tells us that Ufinal is less than Uinitial or the system has lost energy.
- Mon Feb 04, 2019 3:34 pm
- Forum: Concepts & Calculations Using First Law of Thermodynamics
- Topic: qv vs qp
- Replies: 9
- Views: 2570
Re: qv vs qp
qv is heat at a constant volume while qp is heat at a constant pressure. qp is usually measured with a calorimeter while qv can be measured with a bomb calorimeter.qp also equals delta H or enthalpy where pressure is constant. At a constant volume, deltaU = qv, since no work of expansion is being do...
- Mon Feb 04, 2019 3:22 pm
- Forum: Thermodynamic Definitions (isochoric/isometric, isothermal, isobaric)
- Topic: Degeneracy
- Replies: 8
- Views: 753
Re: Degeneracy
Degeneracy (W) is the number of ways of achieving a given energy state. This value is important because when using the Blotzman equation S=kB lnW, degeneracy can help find the entropy of the system.
- Mon Jan 28, 2019 2:31 pm
- Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
- Topic: Heat Capacity
- Replies: 3
- Views: 209
Re: Heat Capacity
Heat capacity tells us how much heat is required to raise the temperature of an object by 1 degree Celsius. An object with high heat capacity can take a lot of heat before changing in temperature like water. An object with low heat capacity changes temperature at low heat like a metal.
- Mon Jan 28, 2019 2:28 pm
- Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
- Topic: Specific heat capacity
- Replies: 3
- Views: 508
Re: Specific heat capacity
Specific heat capacity is determined by taking the heat capacity of the substance and dividing that by the amount of substance present in grams. This is an intensive property and will have the units of J/(degreeC*g). You can also get the specific heat capacity by using the formula q = (g)(Csp)(delta...
- Mon Jan 28, 2019 2:25 pm
- Forum: Phase Changes & Related Calculations
- Topic: Heat Capacity
- Replies: 10
- Views: 967
Re: Heat Capacity
The difference between heat capacity and molar heat capacity is that heat capacity is the heat required to raise the temperature of any amount of an object by 1 degree Celsius whereas molar heat capacity is the amount of heat required to raise the temperature of a 1 mol of a certain substance by 1 d...
- Fri Jan 25, 2019 9:32 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: pH
- Replies: 9
- Views: 1101
Re: pH
pH is a measure of the acidity of a solution. It is the negative log of the proton concentration of a solution. It is used because it is a simpler way to look at acidity rather than look at the actual concentration of the protons.
- Fri Jan 25, 2019 9:30 pm
- Forum: Non-Equilibrium Conditions & The Reaction Quotient
- Topic: Calculating Q
- Replies: 11
- Views: 3938
Re: Calculating Q
You calculate Q when the reaction has been disrupted from equilibrium. Q is similar to K except Q is used to tell which direction the reaction will proceed in order to reach equilibrium.
- Fri Jan 25, 2019 9:28 pm
- Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
- Topic: Stable carbon
- Replies: 3
- Views: 304
Re: Stable carbon
Graphite is the most stable form of carbon because it is the most thermodynamically stable. Graphite does not require as much pressure to be formed than like diamond.
- Mon Jan 14, 2019 3:21 pm
- Forum: Non-Equilibrium Conditions & The Reaction Quotient
- Topic: "Shifting"
- Replies: 15
- Views: 1797
Re: "Shifting"
What Dr. Lavelle means when a reaction at equilibrium is sitting left, he means that there are more reactants at equilibrium than products so the K is very small. When a reaction is sitting right, there are more products at equilibrium than reactants so the K is very big. The direction the reaction ...
- Mon Jan 14, 2019 3:19 pm
- Forum: Ideal Gases
- Topic: R in PV=nRT
- Replies: 34
- Views: 7096
Re: R in PV=nRT
The ideal gas law is PV = nRT, where n is the number of moles, and R is universal gas constant. The value of R depends on the units involved, but is usually stated with S.I. units as: R = 8.314 J/mol. It is just a constant to use in the equation.
- Mon Jan 14, 2019 3:17 pm
- Forum: Ideal Gases
- Topic: Using Kc or Kp
- Replies: 13
- Views: 1044
Re: Using Kc or Kp
Kp should be used when the reactants and products deal with partial pressures and are gaseous while Kc should be used when the reactants and products are aqueous and deal with molarity.
- Tue Jan 08, 2019 1:34 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Kc vs Kp
- Replies: 4
- Views: 172
Re: Kc vs Kp
It just depends on what the problem gives you and what it is asking for. If we need to find partial pressures we are dealing with Kp but if we need to find concentrations we are dealing with Kc.
- Tue Jan 08, 2019 1:31 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Water in equilibrium constants
- Replies: 4
- Views: 1188
Re: Water in equilibrium constants
You don't count water in the equilibrium constant as it is a pure liquid, and there is so much of it as a solvent that it doesn't matter the small amount that is lost in a chemical reaction.
- Tue Jan 08, 2019 1:29 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Concentrations
- Replies: 5
- Views: 462
Re: Concentrations
According the Le Chatelier's Principle, when there is a high concentration of reactants, you favor the forward reaction. For the solution to reach its equilibrium it must make more of the product.
- Mon Dec 03, 2018 8:32 pm
- Forum: Shape, Structure, Coordination Number, Ligands
- Topic: Ligands and Lewis bases
- Replies: 3
- Views: 539
Re: Ligands and Lewis bases
A ligand is a type of Lewis base. Ligands donate a pair of their electrons to a central metal ion to form a coordinate covalent bond.
- Mon Dec 03, 2018 8:30 pm
- Forum: Bronsted Acids & Bases
- Topic: Bronsted Acids and Bases
- Replies: 2
- Views: 512
Re: Bronsted Acids and Bases
Bronsted acid are molecules that give off a hydrogen ion. Lewis acids are molecules that accept an electron pair. In the reaction HCl+water= H3O+ + Cl-, HCl is the Bronsted acid, while H+ is the Lewis acid since it accepts electrons from the O on H2O.
- Mon Dec 03, 2018 8:23 pm
- Forum: Air Pollution & Acid Rain
- Topic: ACID RAIN
- Replies: 5
- Views: 848
Re: ACID RAIN
Acid rain is bad for the environment because it changes the pH of a lot of things that depend on a certain pH level. For instance, plants prefer soil at a certain pH and acid rain disrupts this pH. This means the plants' enzymes will not be at a preferred environment, leading to less activity or den...
- Mon Nov 26, 2018 2:48 pm
- Forum: Shape, Structure, Coordination Number, Ligands
- Topic: labeling hybridization
- Replies: 3
- Views: 335
Re: labeling hybridization
To do hybridization, look at the number of areas of electron density because this indicates the number of hybrid orbitals. BF3 has three areas of electron density so the hybrid orbitals must be sp2.
- Mon Nov 26, 2018 2:45 pm
- Forum: Hybridization
- Topic: Bond Angles and Hybridization
- Replies: 2
- Views: 368
Re: Bond Angles and Hybridization
Basically, as we move from sp to sp2 to sp3 to etc, the bond angles are shrinking. sp has the greatest s-character since there is only one p and it has a bond angle of 180 while sp3 has a smaller s-character and has a bond angle of 109.5
- Mon Nov 26, 2018 2:43 pm
- Forum: Shape, Structure, Coordination Number, Ligands
- Topic: linear vs bent question
- Replies: 7
- Views: 1207
Re: linear vs bent question
When there are five areas of electron density and only two bondings pairs, the molecular shape is linear since the unbonded electrons are in the equatorial plane and they cancel each other's repulsion, leaving the bond angle to be 180. For the tetrahedral and trigonal planar geometry, when there are...
- Mon Nov 19, 2018 3:24 pm
- Forum: Hybridization
- Topic: Hybridized vs. Unhybridized Orbitals
- Replies: 4
- Views: 4401
Re: Hybridized vs. Unhybridized Orbitals
Unhybridized orbitals are the regular atomic orbitals that we have always known. Hybridized orbitals are orbitals that represent a mixture of unhybridized orbitals. These orbitals show what actually happens in bonding and help determine the molecular shape.
- Mon Nov 19, 2018 3:22 pm
- Forum: Determining Molecular Shape (VSEPR)
- Topic: Lone pairs and bonding
- Replies: 4
- Views: 443
Re: Lone pairs and bonding
Lone pairs on bonding pairs have a larger repulsive force that bonding pairs or bonding pairs, so the lone pairs will push bonding pairs closer together for the molecule to reach its lowest energy state.
- Mon Nov 19, 2018 3:20 pm
- Forum: Hybridization
- Topic: Hybridization
- Replies: 3
- Views: 326
Re: Hybridization
Hybridization is the concept that normal atomic orbitals of different types (s,p,d) can hybridize or join together to meet at a middle energy where the electrons are able to form bonds and meet the molecular geometry of the molecules. Different hybridizations describe different shapes and the region...
- Mon Nov 12, 2018 7:04 pm
- Forum: Determining Molecular Shape (VSEPR)
- Topic: Molecular Shape Affects Strength of Interaction
- Replies: 3
- Views: 214
Re: Molecular Shape Affects Strength of Interaction
The shape of a molecule contributes to the strength of the interaction because they interaction is stronger where there is more surface area where the dipoles are as close as possible. Two rods gives a stronger interaction as the dipoles are closer together. When the molecules are spheres, the oppos...
- Mon Nov 12, 2018 7:01 pm
- Forum: Polarisability of Anions, The Polarizing Power of Cations
- Topic: Polarizing Power
- Replies: 5
- Views: 538
Re: Polarizing Power
Polarizing power refers to the power of an atom to induce a dipole in another atom. It is the opposite of polarizability, which is how easy it is for an atom to turn into a dipole.Atoms with high polarizing power are light cations.
- Mon Nov 12, 2018 6:49 pm
- Forum: Dipole Moments
- Topic: Hydrogen Bonds
- Replies: 20
- Views: 1574
Re: Hydrogen Bonds
Hydrogen bonds are very strong and this explains why it takes a very hot temperature to boil water. For water to evaporate, you need all the hydrogen bonds broken. They are -20kJ/mol.
- Mon Nov 05, 2018 2:16 pm
- Forum: Lewis Structures
- Topic: SO2 Lewis Structure
- Replies: 4
- Views: 1424
Re: SO2 Lewis Structure
Sulfur is one of those elements in the 3rd row p-block that can form an expanded octet as it can use its d-orbitals to fit more electrons.The goal of a lewis structure for atoms that have an expanded octet is to ensure that all the formal charges of each atom is zero, especially the central atom. S=...
- Mon Nov 05, 2018 2:12 pm
- Forum: Lewis Structures
- Topic: Lewis Structures for Ionic Bonds
- Replies: 5
- Views: 524
Re: Lewis Structures for Ionic Bonds
Lewis structures for ionic bonds are just the cations and anions put side by side with the charges of each ion put to the side of the respective ion. Make sure that each atom has an octet.
- Mon Nov 05, 2018 2:10 pm
- Forum: Formal Charge and Oxidation Numbers
- Topic: Formal charges in charged molecules
- Replies: 5
- Views: 324
Re: Formal charges in charged molecules
When I look for formal charges, I usually just subtract the number of valence electrons by the number of bonds and electrons surrounding an atom. You could also use the formula FC=valence-(lone pairs+shared/2).
- Mon Oct 29, 2018 2:59 pm
- Forum: Trends in The Periodic Table
- Topic: 1F3 Periodic Table Trends [ENDORSED]
- Replies: 2
- Views: 280
Re: 1F3 Periodic Table Trends [ENDORSED]
They are different sizes in ionic radius because they have a different nuclear charge. All these ions have the same number of electrons, but Cl- has more protons so these protons will pull on the electrons closer to the nucleus, while the extra electrons in P-3 help shield the effective attraction o...
- Mon Oct 29, 2018 2:57 pm
- Forum: Lewis Structures
- Topic: Expanded octet
- Replies: 3
- Views: 299
Re: Expanded octet
Some atoms contain D orbitals, and when one uses these orbitals for electrons, the central atom in the lewis structure can have more than an octet. The D orbital allows for the atom to have more than an octet as it can fill electrons in its d orbitals once its s and p orbitals are filled.D orbitals ...
- Mon Oct 29, 2018 2:55 pm
- Forum: Resonance Structures
- Topic: Delocalized
- Replies: 2
- Views: 368
Re: Delocalized
In chemistry, delocalized electrons are electrons in a molecule, ion or solid metal that are not associated with a single atom or a covalent bond. The term is general and can have slightly different meanings in different fields. Basically, it means that the electron is equally shared among the atoms.
- Mon Oct 22, 2018 3:47 pm
- Forum: *Particle in a Box
- Topic: Test 2
- Replies: 9
- Views: 1380
Re: Test 2
We do not have to know electron configuration for Test 2. The topics we need to know are the Atomic World, the photoelectric effect, atomic spectra, Bohr frequency condition,De Broglie Equation, Heisenberg Uncertainty, energy levels, Schrodinger's wave function, and quantum numbers. Now that I am ty...
- Mon Oct 22, 2018 3:42 pm
- Forum: Heisenberg Indeterminacy (Uncertainty) Equation
- Topic: Heisenberg Uncertainty Question
- Replies: 3
- Views: 552
Re: Heisenberg Uncertainty Question
You should not worry too much about the derivation of the Heisenberg Uncertainty equation. Just know that at an atomic scale, the measurement process influences outcome so there is a limit to the accuracy to which the momentum and position of a particle can be known simultaneously. Know Delta p x de...
- Mon Oct 22, 2018 3:38 pm
- Forum: Properties of Electrons
- Topic: Difference between electron's particle like and wave like characteristics
- Replies: 5
- Views: 391
Re: Difference between electron's particle like and wave like characteristics
All matter has wavelike properties, but some wavelengths are too small to be measurable in classical objects like cars, pens, etc. Electrons on the other hand are very small and fast, so they exhibit wavelike properties. The photoelectric effect shows the electrons have both wavelike and particle li...
- Mon Oct 15, 2018 3:16 pm
- Forum: Bohr Frequency Condition, H-Atom , Atomic Spectroscopy
- Topic: Planck's constant
- Replies: 7
- Views: 1498
Re: Planck's constant
As others have said, Plank's constant (h) is a number we use to calculate many different things relating to quantum mechanics. We use this constant in E=hv, wavelength=h/p, E=hv/wavelength, etc
- Mon Oct 15, 2018 3:12 pm
- Forum: Properties of Light
- Topic: Momentum of Photon
- Replies: 4
- Views: 388
Re: Momentum of Photon
In classical electromagnetic theory, light turns out to have energy (E) and momentum (p), and these happen to be related by E = pc. Quantum mechanics introduces the idea that light can be viewed as a collection of "particles": photons. Even though these photons cannot be brought to rest, a...
- Mon Oct 15, 2018 3:05 pm
- Forum: Properties of Light
- Topic: 6th Edition homework 1.37 wavelength of protons and neutrons
- Replies: 2
- Views: 137
Re: 6th Edition homework 1.37 wavelength of protons and neutrons
The wave lengths of a proton and a neutron are identical to 3 significant figures as the lengths are 1.44x10^-12m. To solve this problem, you should use De Broglie's wave equation.
- Thu Oct 11, 2018 2:43 pm
- Forum: Properties of Light
- Topic: Why Short Wavelengths Can Eject e-
- Replies: 6
- Views: 991
Re: Why Short Wavelengths Can Eject e-
For an electron to be ejected from a metal, there is a threshold energy that each photon must meet. For every one photon that meets the threshold energy, one electron will be emitted from the metal. If the wavelength is longer than the threshold energy, then there would not be enough energy for each...
- Thu Oct 11, 2018 2:40 pm
- Forum: Bohr Frequency Condition, H-Atom , Atomic Spectroscopy
- Topic: Bohr frequency condition
- Replies: 2
- Views: 2751
Re: Bohr frequency condition
Basically the Bohr frequency condition is saying that for an electron to be excited, the energy difference between the two energy levels must meet the same energy as the incoming photon. Only the frequencies that correspond to the energy of the electrons will be absorbed.
- Thu Oct 11, 2018 2:34 pm
- Forum: Properties of Light
- Topic: Memorizing wavelengths and frequencies
- Replies: 5
- Views: 1800
Re: Memorizing wavelengths and frequencies
In class, Dr. Lavelle never really stresses the need to memorize the different wavelengths and frequencies, but I would agree that memorizing that 400-700 nm is visible light and the order of different types of wavelengths would be extremely helpful. I think it is much more important to stress the k...
- Mon Oct 01, 2018 4:27 pm
- Forum: Limiting Reactant Calculations
- Topic: Percent yield
- Replies: 10
- Views: 988
Re: Percent yield
In an ideal scenario the actual value would be 100%, but because of side reactions and experimental error, the theoretical is always greater than the actual yield.
- Mon Oct 01, 2018 4:25 pm
- Forum: SI Units, Unit Conversions
- Topic: Naming Compounds
- Replies: 8
- Views: 625
Re: Naming Compounds
Calcium Sulfide is CaS. There is not really a trick to naming this since you should just look at the valence electrons and see how many calciums and sulfurs you need to fulfill the valence ring. You want the compound to have 8 valence electrons and no negative or positive charge for ionic bonds.
- Mon Oct 01, 2018 4:20 pm
- Forum: Molarity, Solutions, Dilutions
- Topic: Question G5 7th Edition
- Replies: 1
- Views: 203
Re: Question G5 7th Edition
So to solve part A, we want to find out what volume of solution is needed to have 2.15mmol Na+. First we want to find out the concentration of Na+. 2.111g Na2CO3 divided by 105.99g Na2CO3 (molar mass). Then take that and multiply it by 2 since for every one Na2CO3 there are 2 Na+. Finally divide thi...