CHEMISTRY COMMUNITY

Andre_Galenchik_2L

Whichever value that leads to no negative concentrations when plugging back in to the ICE table.

Andre_Galenchik_2L

They can be found on the Constants and Formulas sheet.

0 order: t1/2 = [A]o/2k

1st order: t1/2 = 0.693/ k

2nd order: t1/2 = 1/k [A]o

Andre_Galenchik_2L

Either way is fine as they are equivalent.

Andre_Galenchik_2L

Average rate: Total Change/Total Time
Instantaneous rate: The rate of change at a particular moment
Unique rate: The rate of change of a species divided by its stoichiometric coefficient. For reactants it's negative, as it is disappearing.

Andre_Galenchik_2L

If there is water on both sides, just cancel them out till there is only water on one side. The solutions manual most likely just wants you to see how much water they added to both sides while trying to find the answer.

Andre_Galenchik_2L

For simplicity, only flip the sign when you have the two reduction equations in front of you and you want to make the anode equation. Like in Hess's Law examples, you just add the two reduction potentials. That is what the equation Eºcell = Eºcathode - Eºanode is basically doing. So make sure to not...

Andre_Galenchik_2L

Just to confirm, does order matter when drawing a cell diagram (with regard to on the anode or cathode side, does it matter which species goes first?)

Andre_Galenchik_2L

Why is the reverse reaction very unlikely to occur?

Andre_Galenchik_2L

But why in the textbook solutions there occasionally is platinum on both sides of the salt bridge, even though one side has a solid?

Andre_Galenchik_2L

Using the equation Delta G = Delta H - T Delta S, knowing that the reaction is exothermic would increase the chances of Delta G being negative and thus spontaneous.

Andre_Galenchik_2L

They are connected by the equation Delta G = Delta G with a degree + RTlnQ.

Andre_Galenchik_2L

I believe that Gibbs Free Energy is a term that scientists defined based solely on enthalpy and entropy. For example, a machine cannot directly find the delta G of a reaction on its own. The machine will look at the change in enthalpy and entropy to calculate delta G.

Andre_Galenchik_2L

How large the molecule is. An easy way to do this is by calculating the molar mass. In what state the molecule is in (gaseous has the most entropy). How many unique atoms are within the molecule to allow for more states.

Andre_Galenchik_2L

The best way to understand this is by looking at an energy diagram as water goes from solid to gas. During vaporization, you can see that there is a plateau during 100C as liquid water must convert into water. The energy of water only increases once it gets into the gaseous form.

Andre_Galenchik_2L

Why do we not add in units when calculating for Kp or Kc? We are plugging in the partial pressures and concentrations, yet we simply ignore the units?

Andre_Galenchik_2L

Are you referring to the specific heat capacity of water?

Andre_Galenchik_2L

Don't we need to know that the Cp for a single atom is 5R/2 and the Cv for a single atom is 3R/2?

Andre_Galenchik_2L

The units always depend on what specific term the question is looking for.

Andre_Galenchik_2L

W < 0 when work is done by the system
W > 0 when work is done to the system

Andre_Galenchik_2L

With a larger molecule, there are more possibilities to where the electrons/atoms position themselves in relation to each other.

Andre_Galenchik_2L

Delta U is equal to 0 when the work done by the system is equally replaced by heat being added into the system.

Andre_Galenchik_2L

If pOH and pH always add up to 14, is it possible to have a negative pH? What about a pH higher than 14?

Andre_Galenchik_2L

pH can be used to find the amount of hydronium ions in a certain reaction. pKa allows you to solve for reaction quantities by giving you the equilibrium constant of the reaction.

Andre_Galenchik_2L

What happens to the mol/L when calculating K? For example if there are three reactants on the products side and two reactants on the reactants side with stoichiometric coefficients of 1.

Andre_Galenchik_2L

Make sure to always remember that the mole proportion is very important when inserting "x" (the change in molarity). C part of ICE!

Andre_Galenchik_2L

K is the actual equilibrium constant of a reaction at a certain temperature. Q is called the reaction quotient and is just used as a reference point when the reaction you have at hand is not yet at equilibrium. They both have the same formula, it is just that K uses the formula when the reaction is ...

Andre_Galenchik_2L

He mentioned this detail in order for you to not be confused when you end up with a pH over 7 (basic) while calculating the pH of a solution mixed with a very very weak acid (that means you did it wrong). When calculating for pH, always remember that the hydronium concentration of the water you begi...

Andre_Galenchik_2L

Yes, when temperature is increased, it allows for molecules to move around faster and thus interacting with each other more to create new molecules which proceeds the reaction forward.

Andre_Galenchik_2L

Basically in a question you are given the K value of the reaction when it is at equilibrium. The reaction that you have to work with is not at equilibrium so by finding the reaction quotient, you can figure out which way the reaction will be favored.

Andre_Galenchik_2L

As you can see by the reactions Samantha pointed out, when they are added together the Cl2 cancel out, making the reaction asked about in question 5H.3. When you add reactions, the K of the new reaction is the product of the K's of the reactions that were added together.

Andre_Galenchik_2L

For the 7th edition, it is on page 724.

Andre_Galenchik_2L

The ones you should memorize for sure:

Strong Acids: HCl, HBr, HI, H2SO4, HClO4, HNO3, HClO3

Strong Bases: All alkali metals with OH and the larger alkaline metals (Ca,Sr,Ba) with OH

Andre_Galenchik_2L

As HCl is a strong acid, it will stay dissociated as H+ and Cl- (an acid is stronger the more likely it dissociates and releases a H+). On the other hand, as HF is a weak acid, it will more likely go back into HF as it does not like to be in its dissociated form of H+ and F-.

Andre_Galenchik_2L

I think it relates to the fact that a greater electronegativity difference would result in more electrons being further away from the hydrogen giving it a stronger positive partial charge. It will then form stronger hydrogen bonds because of the charge difference.

Andre_Galenchik_2L

Most likely, as it would not make sense otherwise. Perhaps the setting of the problem will hint on whether it is used as an acid or base.

Andre_Galenchik_2L

It may be because bromine is a bigger element than fluorine.

Andre_Galenchik_2L

First draw the lewis structure. You see that BeCl2 only has two regions of electron density around it. Thus, its hybrid orbital will be sp. If it had three regions of electron density around it, the hybrid orbital would be sp2. Regions of electron density is equal to the number of hybrid orbitals.

Andre_Galenchik_2L

Just try to remember the demonstration that Dr. Lavelle did during class. He put two sticks between his two index fingers and tried to turn his index fingers. From rotating his fingers, the sticks fell out of their formation.

Andre_Galenchik_2L

I believe that knowing the name of molecules is not necessary for our course. If you are really worried, just ask your TA for the basic molecules that someone should always know like water and carbon dioxide.

Andre_Galenchik_2L

You need to use the conversation of energy equation expressed during the photoelectric effect: Energy of photon = Work Function + Kinetic Energy of released electron. You were able to find the energy of the photon correctly, you just forgot to find the KE of the electron through using the equation K...

Andre_Galenchik_2L

Yes, they do. They are considered to simply count as one of the total number of electron densities surrounding a central atom.

Andre_Galenchik_2L

Yes, symmetric molecules tend to be nonpolar. For instance, carbon dioxide (linear shape) is nonpolar as the dipole moments cancel each other out.

Andre_Galenchik_2L

Just always make sure to first have all the atoms have an octet. After all the atoms have an octet, check the formal charges of each atom and adjust accordingly (usually by adding double bonds).

Andre_Galenchik_2L

You can also look where the particular element is on the periodic table. Metals and nonmetals tend to form ionic bonds and two nonmetals tend to form covalent bonds.

Andre_Galenchik_2L

If it did ask for Cu 2+ then it is most likely a textbook error.

Andre_Galenchik_2L

Most likely, as we do not need to memorize each element's value, but rather the trend across a group and period.

Andre_Galenchik_2L

With more dispersion forces, there is more attraction between atoms meaning they will be less likely to move freely. States of matter are based on the movement of atoms/molecules.

Andre_Galenchik_2L

The atomic radius increases down a group as another shell of electrons is being added (energy level). Once the second period hits 8 electrons, its shell becomes full and a new shell (the n=3 shell) begins. Across a period the radius decreases because as the shell remains the same, the number of prot...

Andre_Galenchik_2L

No, you do not multiply by 2. Uncertainty is what becomes delta v.

Andre_Galenchik_2L

For an electron, you would most likely be given info to complete the equation E - work function = KE to find the frequency.

Andre_Galenchik_2L

I do not believe so. Just remember to take away the 4s electrons before the 3d electrons.

Andre_Galenchik_2L

I am not exactly sure about a and c, but for d, a +3 charge means the element is losing 3 electrons. Knowing this, phosphorus if it lost 3 electrons would have the configuration of magnesium which has 2 valence electrons.

Andre_Galenchik_2L

Whichever one has a higher electronegativity (a want for electrons), that element will gain the negative charge.

Andre_Galenchik_2L

I am pretty sure there is one exception dealing with half filled sub-shells but he has not gone over them specifically. At least I believe so.

Andre_Galenchik_2L

For nodal planes I am pretty sure p has 1, and then as you go up each subshell it increases by 2. So d has 3 nodal planes and f has 5 and so on. Is there a difference between nodal and radial planes?

Andre_Galenchik_2L

An element has an octet if it has 8 valence electrons. Yes, an orbital does need a full octet before moving to the next orbital (at least for the level we are learning).

Andre_Galenchik_2L

Where do you find the corrections to the textbook problems? I only see the solution manual corrections.

Andre_Galenchik_2L

For part c I keep getting 12nm and not 8.8nm (the answer). What am I doing wrong as I am plugging in the exact formula for speed of light?

Andre_Galenchik_2L

Which element of each of the following pairs has the higher electron affinity: a) tellurium or iodine; b) beryllium or magnesium; c) oxygen or sulfur; d) gallium or indium? So why is the answer for c) sulfur and for b) and d) the answer is that they are equal. All these scenarios show one element on...

Andre_Galenchik_2L

In the ultraviolet spectrum of atomic hydrogen, a line is observed at 102.6 nm. Determine the values of n for the initial and final energy levels of the electron during the emission of energy that leads to this spectral line. I understand how to solve this question it is just that I am confused why ...

Andre_Galenchik_2L

By octet exceptions are you referring to the half d block and full d block exceptions we learned in class today?

Andre_Galenchik_2L

I am unsure to your question (I assume you would include the f orbitals), but I wanted to make sure that all we need to know for electron configurations are the s-block, p-block, and 1st row of d-block.

Andre_Galenchik_2L

All you have to know conceptually is that at the atomic level, one can never exactly determine the position and velocity of a particle because when they are that small, they exhibit both wavelike and particle like properties. It becomes uncertain whether to find their features through formulas we us...

Andre_Galenchik_2L

Sorry I am still confused about this rule. For single problems is it not fine to just round up at 5 as it is in the upper half of 0-9?

Andre_Galenchik_2L

I think it always depends on the situation you put it in. For example, with the photoelectric effect it will act as a particle but when testing for interference it will act as a wave.

Andre_Galenchik_2L

I believe that with very small particles such as electrons, it is just a natural occurrence that they must be quantized (for electrons being between energy levels).

Andre_Galenchik_2L

When asked questions about comparing atoms, grams, or moles in this case, just always take the time to use Avogadro's number and the molar mass to get the unit that you want. Using dimensional analysis can help you cross out units and see if the unit that is remaining is the one you want (such as th...

Andre_Galenchik_2L

So is the molecular formula for magnesium sulfate heptahydrate MgS7H2O? I am not even sure if that is how the formula is written, for example is the 7 supposed to be distributed like so: MgSH14O7?

Andre_Galenchik_2L

It is not possible due to the Law of Conservation of Matter/Mass. In a reaction, mass does not suddenly disappear or appear such as when liquid water evaporates, the water is still there just in a gaseous form. Thus, reactants totaling a mass of 12 grams will form products that total 12 grams - no l...

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