CHEMISTRY COMMUNITY

BritneyP- 2c

Last chem community post ever!

BritneyP- 2c

A catalyst is not used up in the reaction, an intermediate is used up in the next step

BritneyP- 2c

usually in a concentration cell they provide the molarity of the the individual components, so just find what is reduced and what is oxidized and you can use the molarity to find Q

BritneyP- 2c

How are we going to be able to show our work for the test, does this mean we no longer get the partial credit for the work we do?

BritneyP- 2c

If the process has a high delta S and a high delta H, it can become spontaneous with a high temperature.

BritneyP- 2c

Thank you so much Dr. Lavelle!
These last 2 quarters have been amazing and I am so thankful to have you as my professor.

BritneyP- 2c

H+ has one charge to it and H2 has no charge to it, meaning each individual H has a 0 charge. So only one electron is transferred to lose away the H+ charge. The reaction is also a concentration cell, so the electron change is the same on both sides, so only 1 mole of electrons are transferred.

BritneyP- 2c

You add inert electrodes where there is no solid in that compartment.

BritneyP- 2c

The cell diagrams typically just write out the half reactions as it is in the Appendix. However, with oxidation you have to reverse it because the 1/2 reactions in the book are written as reduction potentials.

BritneyP- 2c

The reaction is a concentration cell which means the electron transfer has to be the same on both sides. H+ has to transfer 1 electron to lose its charge to become H2, so the moles of electron transferred would be 1

BritneyP- 2c

It should be spontaneous most of the time because you are releasing heat, and gas has more disorder to it. But i wouldn't say it is spontaneous all the time.

BritneyP- 2c

I usually just do all the homework questions, especially the ones at the end because they take all the topics and put it in 1 question

BritneyP- 2c

You use H20 to balance out all of the oxygens and then you use the OH- to balance out the hydrogens, if the solution is basic. If it is not, then you will use the H+ to balance out all of the hydrogens.

BritneyP- 2c

The cathode is reduced and the anode is oxidized. You can decipher this when you look at the charges in the equation.

BritneyP- 2c

its gonna cover the last part of thermodynamics and electrochemistry. We aren't gonna have kinetics on the test.

BritneyP- 2c

The species that are oxidized are called reducing agents because the other species related to them is getting reduced. Just as how if one is reduced something else is oxidized. So it aids in oxidation.

BritneyP- 2c

It depends on the units of your other constants. If you use 8.314 j/mol*K, then you have to convert to kelvin. If you are finding the difference between them though it doesn't matter because the end result is the same number

BritneyP- 2c

The battery is dead when there is no more flow between the anode and the cathode, but this can be prevented with a salt bridge.

BritneyP- 2c

Delta G* means that the conditions are at standard state.
Delta G means that the conditions aren't at standard state

BritneyP- 2c

The anode is always oxidized, so it loses electrons. The cathode is reduced so it gains electrons. Electrons will always move from anode to cathode. The cell potential only switches signs when you are balancing and equation and you flip one of the equations.

BritneyP- 2c

Using a salt bridge just allows for charges to balance on both sides, preventing battery death. If you didn't have the battery, the cathode would accumulate e- charges while the anode is depleted and then the battery would not work anymore.

BritneyP- 2c

This was really helpful! Thanks a ton

BritneyP- 2c

At equilibrium, the forward and reverse reactions are at the same rate. This means that no reaction is favored as G is not positive or negative, meaning that the reaction is not spontaneous

BritneyP- 2c

Lavelle doesn't curve his tests, but he curves the overall class grade which can help you or completely mess you up.

BritneyP- 2c

The standard entropies will be given to us and we do not have to memorize them.

BritneyP- 2c

A half reaction is when a chemical equation is broken up into 2 pieces. One is the substance that is oxidized, and the other is the one that is reduced. When you add both together, they should add up to the original equation.

BritneyP- 2c

Yes, when delta G is negative the reaction is spontaneous which is more favorable that when it is positive and not spontaneous.

BritneyP- 2c

Entropy is typically J/K, and if you have V2/V1 or T2/T1, the units would cancel out because they are dividing the same units over each other.

BritneyP- 2c

For a given initial and final volume,more expansion work is done when the temperature is high than low. For a given volume and amount of gas- phase molecules, a higher temperature corresponds to a higher gas pressure, and so the expansion takes place against a stronger force and therefore has to do ...

BritneyP- 2c

Having a larger delta S would make delta G smaller meaning it is spontaneous. If the delta S x T is still smaller than H, then that means the delta G is positive and not spontaneous, which is not favorable.

BritneyP- 2c

Reversible reactions mean that there is an infinitely small change in a certain variable that can affect the system

BritneyP- 2c

Technically there can be a few isolated systems, but it has a much smaller amount than closed and open systems.

BritneyP- 2c

you would use q=ncdeltaT, and set copper to equal the negative value for the q for water. Whatever heat is lost be one system is absorbed into the other system.

BritneyP- 2c

When you are calculating for the specific heat you should be using Kelvins.

BritneyP- 2c

Constant pressure means that there is not change in pressure, deltap=0 same as with constant volume

BritneyP- 2c

The textbook explains that the number comes from converting L*atm to Joules.

BritneyP- 2c

Entropy is the amount of disorder there is in a system. Enthalpy is part of the function that is used to determine enthalpy, which is DeltaG= Enthalph- TdeltaS

BritneyP- 2c

Hess' law states that enthalpy is a state function which also means that it is additive, meaning 2 or more chemical reactions can be added together.

BritneyP- 2c

Usually you do not get a negative square root term, but you get a negative number or a positive number. You ignore the negative number for the positive number when you are looking for the concentration .

BritneyP- 2c

Steam releases a lot more energy when it touches your skin, so it can cause more severe burns than water would. The phase change from steam to water to a lot steep than when hot water hits you.

BritneyP- 2c

if the concentration of reactants increase then the reaction will move towards the products, and if the concentration of products increase then the reaction will move towards the products.

BritneyP- 2c

You can use Kc with gases, but then they would usually provide the Kc for the gas already so that you can find one of the products or reactants, or they give you the molarity of the products and reactants. If they don't, then typically you use Kp

BritneyP- 2c

You should test each value, and rule out the one that is unreasonable in the situation. Usually you will end up with a positive and negative number, so it can immediately rule out.

BritneyP- 2c

The factors that affect equilibrium are concentration, pressure based on Volume, and temperature.

BritneyP- 2c

When you are looking for K is is molarity over molarity, which can cancel out all units. And if it doesn't cancel out all units, imagine the reactants changing to products or products changing to reactancts as activity, and activity is unitless.

BritneyP- 2c

If it gives you the K and provides you either the initial values of molarity or moles, you will have to do the ice table so you can find the equilibrium concentration or moles. Remember to only stick with one, and convert if you have to.

BritneyP- 2c

solids are not considered because they don't have a concentration, they have density. Liquids do not affect the reactant amount at equilibrium, so they are not considered in the equilibrium constant.

BritneyP- 2c

K doesn't have units because because the products and reactants have the same units so they can cancel out. But if it doesn't cancel out, instead of thinking of concentration or partial pressure, consider transition of reactants to products as activity, which is unitless, so K is unitless

BritneyP- 2c

Just solve Q the way you would for K. K is at equilibrium and Q is at any time.

BritneyP- 2c

You can use the aqueous solution and also gases, but solids don't have a concentration so they cannot be used, and liquids cannot be used either.

BritneyP- 2c

You use the Q to find whether the reaction is reactant favored or product favored. By using the concentrations of the compounds, if Q<K then it is reactant favored and the forward reaction is favored. If Q>K then it is product favored and the reverse reaction is favored.

BritneyP- 2c

Stablility makes it a stronger acid.

BritneyP- 2c

intermolecular forces affect the melting point not the amount of bonds it has.

BritneyP- 2c

none of them are radicals.

BritneyP- 2c

sp just demonstrates the amount of atoms around the central atom not the amount of bonds it has. There can be a unhybridized p orbital that is completely full to demonstrate the triple bond.

BritneyP- 2c

HClO4 is stronger because Cl has a higher electronegativity than P and so the oxide is overall more stable. As a result of its stability, it is more acidic than H3PO4

BritneyP- 2c

You need to know the charges of the other molecules and the charge of the overall molecule so that you can find the charge of the cation.

BritneyP- 2c

Ionization energy is the energy it takes to remove and electron, while electronegativity is the attraction of the electron to the atom.

BritneyP- 2c

A lewis acid is and electron acceptor and a lewis base is an electron donor

BritneyP- 2c

Long bonds are weaker than short bonds because they have less attraction to each other in contrast with short bonds. The atoms are either larger in size or the electrons are repelling each other away making it easy to break the bonds.

BritneyP- 2c

pKa is preferred because it is the log version of Ka, which is easier to compare than using Ka.

BritneyP- 2c

You don't have to memorize how to name them but you should know when to put the prefixes and when to change the metal cation into an -ate.

BritneyP- 2c

In a pi bond the p orbitals overlap above and below the atom, localizing the electrons above and below the plane of the bond—a higher energy state compared to the overlap of a sigma bond. You can also conceptualize that pi bonds are weaker because their electrons are in a higher energy state.

BritneyP- 2c

I don't think you will need to know that because with coordinate compounds you are just naming things out. But if you are asking about the ligands then you might need to

BritneyP- 2c

He curves at the end of the year so we never know what the final grade is until after the final.

BritneyP- 2c

It should be around 50 points according to the syllabus

BritneyP- 2c

They do occur in nature if it requires less energy which is more favorable.

BritneyP- 2c

Vsepr is just AXE, and you have to memorize the shapes each configuration makes bc it will be on test 2

BritneyP- 2c

Look at the atom.
Count the number of atoms connected to it (atoms – not bonds!)
Count the number of lone pairs attached to it.
Add these two numbers together.

BritneyP- 2c

It depends on the molecule.

BritneyP- 2c

The increase of surface area increases the ability of individual molecules to attract each other. Branching in molecules decreases the surface area thereby decreasing the attractive force between individual molecules. As a result, the boiling point decreases.

BritneyP- 2c

just say if it is 1/2 or -1/2

BritneyP- 2c

The 2 exceptions are copper and chromium

BritneyP- 2c

ionization energy increases as it goes up and to the right. Up because the radius is much smaller so that the energy of removing an electron is higher and to the right because there are more protons to attract the electrons so the energy to remove an electron is much higher.

BritneyP- 2c

Yea he is giving us past exam questions and we won't learn anything new.

BritneyP- 2c

oxygen does not follow the trend and the noble gases.

BritneyP- 2c

NH3 bonded to BF3

BritneyP- 2c

You might have to but Dr. Lavelle never really mentioned it.

BritneyP- 2c

I don't think it is everything in chemical bonds because he said that one of the slides he covered will not be on the midterm but on final.

BritneyP- 2c

double bonds are typically shorter than single bonds.

BritneyP- 2c

Because the electrons could be shared among the other atoms so it resonates around

BritneyP- 2c

I just memorize them

BritneyP- 2c

With lewis dot structures, you are dotting out the number of valence electrons you have for each element. With molecules you put the atom with the least amount of electronegativity in the middle and then all the others around it. Then you just have to count out the total electrons and make sure they...

BritneyP- 2c

I think it is because the 3d orbitals have more energy to them so we fill the 4s orbitals first

BritneyP- 2c

So, according to Pauli Exclusion Principle, it is better to fill up electron going in the same direction first as they would have lower energy potentials. So instead of filling up the 1px orbital completely, he added the other electron to the 1py orbital, as there is less energy.

BritneyP- 2c

I don't think so, I think you have to just assume that when electrons are in the same orbital pattern, one is 1/2 and the other is -1/2. If they were going in the same direction, they would go against Hund's Law

BritneyP- 2c

I think the reason why electron potential energies are higher the further they are from the nucleus is because if the atom loses the electron it would be more unstable. The fewer valence electron there are the more unstable they can become.

BritneyP- 2c

I think typically in the test they say what units o put the answer in but m/s is always safe.

BritneyP- 2c

The midterm should be everything from week one to chemical bonding

BritneyP- 2c

I don't know if we were given, but the mass of an electron is 9.109 x 10^-31 kg.

BritneyP- 2c

So light is a photon, which can move as both a particle and a wave. The particles individually move in a wave like motion, so I think you can consider them interchangeably.

BritneyP- 2c

The way I see it, small subatomic particles have a wave like property to them, which helps them move and repel around. As the object gets larger, they move less and have less of a wavelength property.

BritneyP- 2c

For test one, it is all the fundamental things we did. You don't have to do all the homework problems but you should have a general idea of the concept. A lot of constants are provided for us so you should be fine if you do light studying.

BritneyP- 2c

Because they already gave you the frequency, you can use E=Hf to find the energy, with h being planck's constant, and the frequency already being provided for.

BritneyP- 2c

the 0 after the decimal before the 7 is not significant, however the 0 after the 7 is

BritneyP- 2c

The theoretical yield should be the same as the limiting reactant, but remember that the theoretical yield will always be more than the actual yield due to outside factors such as solutions being stuck on the side of the beaker.

BritneyP- 2c

I just made sure to label each part of the problems and to put my name and id number on it. Also put a title on it and discussion section so that they know who you are and where to put your grade.

BritneyP- 2c

Yeah i might join if there is one! I am not the best at chemistry so it would be nice to hear other peoples understanding of the subject. Hopefully there will be a study group soon.

BritneyP- 2c

I think that if they don't give you a unit to convert to then just keep it the same. However, if they do give you something to convert to, then just stick with the moles of the converted element.

BritneyP- 2c

So I was reading through some online posts, but I think that formula units are only applied to salts such as NaCl. Molecular formulas are typically covalently bonded and so because salts like NaCl are ionic bonds they aren't molecules. I don't know if that helps but that is just what I think

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