CHEMISTRY COMMUNITY

KHowe_1D

I find that OIL RIG is useful:
Oxidation is Loss
Reduction is Gain

KHowe_1D

Usually in a cell diagram anode is on the left and cathode is on the right.

KHowe_1D

Since Kelvin would be canceled out by the units of R, you should convert all temperatures to K.

KHowe_1D

Kp is in terms of pressure while Kc is in terms of molarity (concentration). I would say just during calculations to specify with the subscript.

KHowe_1D

H2O decreases the concentration of the solution. A cathode being diluted would decrease the cell potential but an anode being diluted would increase the cell potential.

KHowe_1D

if the concentration of the products is greater than the concentration of the reactants, K>1 and if the concentration of the products is lower than the concentration of the reactants, K<1. This helps you determine which side the reaction favors.

KHowe_1D

n is the number of electrons transferred in a reaction.

KHowe_1D

When reactant energy is higher than the product it is exothermic because energy is being released but if the reactant energy is lower than the product, it is endothermic because energy is required.

KHowe_1D

K (the equilibrium constant) has no units.

KHowe_1D

K depends on the concentration of the products and the concentration of the reactants in an equilibrium equation.

KHowe_1D

The agents are what cause the oxidation or reduction so it will be, by definition, the opposite.

KHowe_1D

You will need to be able to determine it yourself. The anode is oxidized and the cathode is reduced.

KHowe_1D

You should know outline 5 and the last page of outline 4 for test 3. I don't believe current is mentioned but you could go through the objectives again to double check.

KHowe_1D

It maintains the charge of electrons between the cathode and anode.

KHowe_1D

An oxidizing agent is being reduced and the reducing agent is being oxidized.

KHowe_1D

I think it's safer to just be as specific as possible. It is being reduced because it is gaining the electron while Cu is being oxidized because it is losing the electrons.

KHowe_1D

Work will be negative when it is done by the system and will be positive when work is done on the system.

KHowe_1D

Voltage is the potential difference between two electrodes.

KHowe_1D

You use whichever R will cancel out the units given.

KHowe_1D

Faradays constant represents the charge of one mole of electrons.

KHowe_1D

A reaction is spontaneous where deltaG is negative. When deltaG is positive the reaction is non spontaneous.

KHowe_1D

You include gases and aqueous solutions but exclude liquids, such as water, and solids.

KHowe_1D

The heat lost by the water has been gained by the ice so you have negative q_water and a positive q_ice.

KHowe_1D

Isobaric systems are systems with constant pressure so you would use an equation that works with the variables you are given as long as pressure is constant. A common equation is deltaH = q

KHowe_1D

When delta U is zero that means the equation deltaU = q+w is now 0=q+w so you can now change the equation to be q=-w w is negative because you can have negative work but you can't have negative heat energy. It essentially just means that the heat added to the system is the same as the work being don...

KHowe_1D

A bomb Calorimeter has a constant volume.

KHowe_1D

A spontaneous reaction will have a negative delta G. A non spontaneous reaction will have a positive delta G.

KHowe_1D

X is too small when K<10^-3

KHowe_1D

Yes, the energy is converted and will be conserved throughout reactions.

KHowe_1D

If you didn't have K you wouldn't be able to solve for x. So I think we can assume that we either have to solve for K or for x but not both so in a scenario where you solve for x, K should be given.

KHowe_1D

Partial pressure is the pressure of each individual gas while the total pressure is the pressure of the entire system.

KHowe_1D

A negative delta H is exothermic because heat is being released into the surrounding environment.

KHowe_1D

The total energy within the closed system is U which is internal energy.

KHowe_1D

Heat, mass flow, and work are the ways to change the energy of a system.

KHowe_1D

Delta H would be positive because the molecules are absorbing energy to "loosen" the bonds.

KHowe_1D

You use an ICE table to solve for concentrations so usually you will be given K.

KHowe_1D

No the standard state depends on the element is the state at which the element is the most stable.

KHowe_1D

when x is less than 10^-3 it can be assumed to be small and disregarded from the denominator.

KHowe_1D

partial pressure is the pressure of each individual gas and total pressure is the pressure of the entire system.

KHowe_1D

K changes because temperature affects the rate at which the reaction occurs.

KHowe_1D

I don't think you get marked off for not using an ice table as long as you get the right answer. However I recall Lavelle gives partial credit for correct procedures so if you did use the ice table but got the answer wrong, you would probably get partial credit.

KHowe_1D

K will not change if you add more reactants or products because it is the concentration at equilibrium however Q may change because Q is the reaction quotient that can be calculated at any point during the reaction.

KHowe_1D

Protons and electrons have opposite charges (Proton + and electron -) so they attract each other.

KHowe_1D

The topics covered will be acids and bases as well as equilibrium.

I find the best way to study for Lavelle's tests are to do the practice problems because some of the questions are directly out of the homework problems.

KHowe_1D

Question 5.H.5 from the homework asks

Evaluate Kc for each of the following equilibria from the value of K:
(a) 2NOCl(g) ∆2NO(g)1Cl2(g),K51.831022 at500K
(b) CaCO3(s) ∆ CaO(s) 1 CO2(g), K 5 167 at 1073 K

Is K different from Kc? and how do you calculate K from Kc?

KHowe_1D

Yes partial pressure is only used for gases with the units of atm.

KHowe_1D

They have different values because K is only at equilibrium and Q can be calculated at any time during the reaction.

KHowe_1D

They aren't calculated in equilibrium expressions because they are considered pure substances which don't affect the equilibrium concentration.

KHowe_1D

Yes I believe Q can be applied to both concentration and partial pressure.

KHowe_1D

The difference between K and Q is K is the concentration at equilibrium and Q is the reaction quotient which is calculated the same as K and can be calculated at any time during the reaction.

KHowe_1D

You would use those when the ligand already has a prefix so for example en has a prefix already so if it was (en)2 it would be bisethylenediamine.

KHowe_1D

Sig figs for pH will be the same as doing sig figs for any other question! If you are given a concentration to calculate pH with 3 sig figs then your answer should have 3 sig figs.

KHowe_1D

the units for c are in meters per second.

KHowe_1D

You need to know how a salt can affect the pH of a solution whether it is making it more basic or acidic.

KHowe_1D

sigma bonds are the first bonds to form and can rotate. pi bonds are double and triple bonds and cannot rotate.

KHowe_1D

When it asks you to do the Calcium ion it is referring to the most common ion which would be Ca2+. This is apparent when referencing the periodic table because this would be the most stable Calcium ion.

KHowe_1D

An amphoteric compound can both accept and donate protons/hydrogen atoms.

KHowe_1D

It is because chlorine has a higher electronegativity than Hydrogen.

KHowe_1D

Acids are the proton donors while bases are the proton acceptors.

KHowe_1D

Only one proton is lost per reaction so over several reactions, multiple protons can be lost.

KHowe_1D

Lewis acids accept electron while bronsted give electrons.

KHowe_1D

After a little googling, I believe it is an amino acid that helps the molecule stabilize after oxidation.

KHowe_1D

We are on Outline 5 so we are doing section 9C for the homework.

KHowe_1D

Why is it that humans can consume (and enjoy consuming) relatively acidic things but can't consume most bases? It it like this for most species?

KHowe_1D

I believe an example in class was myoglobin (FeN4) which is what builds up hemoglobin in the blood.

KHowe_1D

Stronger bonds lead to higher boiling/melting points because it takes more energy to break this bonds.

Weaker bonds are easier to break and therefore will have a lower boiling and melting point.

KHowe_1D

I would refer to the bond as angular because it is the more formal way of referring to the bond.

Either should be fine but to be safe, I would refer to it as angular as stated in the textbook.

KHowe_1D

It doesn't matter what atom you start with because you are finding the individual charges for each atom. To find the charge of the molecule you would add up the charges of each individual atom.

The most favorable formal charge is zero because it means the molecule is stable.

KHowe_1D

Everything not covered on the midterm will be on the test. This includes dipole moments and the shapes/structures that we are doing now. I'm not sure what else though.

KHowe_1D

I would assume that we need to know the shapes that are gone over in lecture.

KHowe_1D

Resonance structures are the different ways the bonds can be done on the same molecule.

For example if there is a double bond on 3 oxygens and a single bond on 1 oxygen, the resonance structure would be the different positions of the single and double bonds on the molecule.

KHowe_1D

The angular momentum quantum number is l which is 0 to n-1

KHowe_1D

Ion - Ion interactions are the interactions between anion and the cation.

KHowe_1D

Covalent character is where atoms or molecules share electrons and ionic character is when electrons are "transferred" from one atom to another.

KHowe_1D

Yes they will follow the octet rule even if that makes the formal change not equal to 0 because having 8 electrons in the outer shell is where an atom is most stable.

KHowe_1D

Yes some of the elements can use the d orbital which can help reach the formal charge of zero.

KHowe_1D

Yes you should always try to have a half-filled or completely full orbital because it is more stable.

KHowe_1D

Most of the time, the central atom is the atom that can form the most bonds with other atoms.

KHowe_1D

Shorter bonds are stronger than longer bonds.

KHowe_1D

You want to calculate the formal charge to ensure that you have the most stable molecule.

KHowe_1D

Helium probably wouldn't bond with other elements because it is already stable as a noble gas. Noble gasses are known not to react with other elements.

KHowe_1D

Yes it can tell you the electron configuration. The number indicates how many electrons the element has. You can find the orbitals/subshells by looking at what group and period the element is in.

KHowe_1D

A lone pair is a pair of electrons not bonding two elements together.

KHowe_1D

Cu and Cr are the only exceptions because the half full and full d shell is more stable than a full 4s shell.

KHowe_1D

They are the exceptions because a full d orbital and a partially full 4s shell is more stable than an almost full d orbital and a full 4s shell.

KHowe_1D

I was taught the same thing in high school but I think that it was because it was easier to remember.

Dr. Lavelle said that the 3d was written before the 4s because the 3d subshell has less energy than the 4s subshell.

KHowe_1D

You pick the noble gas before the element. Those are the ones on the far right of the periodic table. These are chosen because they have filled electron shells.

KHowe_1D

A nodal plane is an area where the probability of finding an electron is zero. It relates to electron distribution because you know that electrons are not within the nodal planes.

KHowe_1D

There are two electron in the first s shell so you have 1s^2 In the second s shell you also have 2 electrons so you have 2s^2 The p shell can hold 6 electrons in its 3 orbitals but since carbon only has 6 total electrons there is one in 2px and one in 2py. The x and the y indicate which orbitals are...

KHowe_1D

I believe in this case the answers would be similar with c=frequency*wavelength being 12*10^-9m and frequency=hc/E being 9*10^-9m. However I believe you're supposed to use the frequency=hc/E because the E is factoring in the given velocity (when calculating for kinetic energy) which isn't being fact...

KHowe_1D

Constructive interference is when waves are in sync with each other and produce a larger amplitude.

Destructive interference is when they waves are out of sync resulting in a smaller amplitude.

KHowe_1D

This example shows diffraction patterns because the x ray is being or split when it goes through a crystal. The beam is going to enter at one angle, and exit at another.

KHowe_1D

I'm not entirely sure either. But I think you could just plug in values for n. I'm not sure if there is a more efficient way of doing this.

KHowe_1D

If you weren't given ANY numbers to work with, I would simply round to 3 decimals. That's what I normally do. But remember not to round until the final answer.

There are a few resources that are on the website that include the rules for sig figs.

KHowe_1D

Amplitude is just how high and low the wave goes but this isn't present in the equations we were given in class. I don't think it is as important as wavelength and frequency in this class. From physics, the amplitude could be calculated using sine, but I don't think we are going to use that in this ...

KHowe_1D

I used the Broglie relationship because you just need to mass of an electron (which is provided in the book) to calculate the answer.

I modeled my work after the example 1B.4

KHowe_1D

He didn't specify but that is what we covered in the last 2 lectures so I have been doing problems from the Quantum World homework. EDIT: An email was just sent out and it stated: "Since students want to focus on the high school review topics for test 1 they can hand in homework #2 covering rev...

KHowe_1D

What exactly is the Rydberg equation and how do you know when to use it?

KHowe_1D

My TA said that for the first test we should know a few basic ones but most chemical formulas will be provided.

KHowe_1D

You have to find the mass composition of each substance.

First you find the total molar mass.

Then you take the molar mass of each substance and divide it by the molar mass. Multiply by 100% to get each percentage.

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