CHEMISTRY COMMUNITY

Brian Hom 2F

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.

Brian Hom 2F

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.

Brian Hom 2F

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...

Brian Hom 2F

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...

Brian Hom 2F

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...

Brian Hom 2F

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.

Brian Hom 2F

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...

Brian Hom 2F

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.

Brian Hom 2F

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.

Brian Hom 2F

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.

Brian Hom 2F

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.

Brian Hom 2F

When delta G is equal to 0, the reaction is at equilibrium and it is neither spontaneous nor unspontaneous.

Brian Hom 2F

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.

Brian Hom 2F

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).

Brian Hom 2F

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 ...

Brian Hom 2F

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.

Brian Hom 2F

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...

Brian Hom 2F

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.

Brian Hom 2F

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.

Brian Hom 2F

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...

Brian Hom 2F

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...

Brian Hom 2F

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.

Brian Hom 2F

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.

Brian Hom 2F

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.

Brian Hom 2F

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 ...

Brian Hom 2F

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.

Brian Hom 2F

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.

Brian Hom 2F

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.

Brian Hom 2F

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.

Brian Hom 2F

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.

Brian Hom 2F

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.

Brian Hom 2F

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.

Brian Hom 2F

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...

Brian Hom 2F

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.

Brian Hom 2F

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

Brian Hom 2F

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...

Brian Hom 2F

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.

Brian Hom 2F

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.

Brian Hom 2F

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...

Brian Hom 2F

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...

Brian Hom 2F

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.

Brian Hom 2F

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.

Brian Hom 2F

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=...

Brian Hom 2F

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.

Brian Hom 2F

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).

Brian Hom 2F

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...

Brian Hom 2F

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 ...

Brian Hom 2F

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.

Brian Hom 2F

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...

Brian Hom 2F

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...

Brian Hom 2F

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...

Brian Hom 2F

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

Brian Hom 2F

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...

Brian Hom 2F

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.

Brian Hom 2F

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...

Brian Hom 2F

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.

Brian Hom 2F

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...

Brian Hom 2F

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.

Brian Hom 2F

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.

Brian Hom 2F

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...

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