CHEMISTRY COMMUNITY

Joshua Swift

When he said I₂ he was talking about Iodine.

Joshua Swift

All enthalpy values will usually be given in kJ/mol unless it is for the overall reaction.

Joshua Swift

I think it will all come down to how the problem is structured and what is given to you. I don't think you will be able to just choose one of the methods but you will have to calculate using equations or enthalpies given.

Joshua Swift

Endothermic reactions will always have a + $\Delta$ H and exothermic reactions will have a - $\Delta$ H. if heat is showed in the reaction on the reactants side it is endothermic and if it is present on the products side it is an exothermic reaction.

Joshua Swift

Vapor and gas are interchangeable. So when they say enthalpy of vaporization, they mean the phase change from a liquid to the gas state.

Joshua Swift

Autoprotolysis : A proton (hydron) transfer reaction between two identical molecules (usually a solvent), one acting as a Brønsted acid and the other as a Brønsted base

Joshua Swift

In this case it does not really matter for your calculations, but it will in other questions .

Joshua Swift

Liquids and Solids from the reaction are not included, you only need to account for the moles of gas

Joshua Swift

K is the equilibrium constant and can only be calculated at equilibrium.
Q is the reaction quotient and can be calculated the same way as K, but at any point in the reaction.
If T is not given, it is implied the reaction is at 25 degrees C.

Joshua Swift

All K are equilibrium constants and are calculated the same way, but the letters are used to specify which it needed for a certain situation. The a means it is for an acid, b is for a base, c is for concentration, p is for pressure, and w is for water.

Joshua Swift

R is the universal gas constant and it = 8.3144598 J/mol·K

Joshua Swift

There is no need to have the H₂O because you don't include any solids or liquids.

Joshua Swift

P=pressure
V=volume
n=moles
R=universal gas constant
T=temperature

Joshua Swift

K will always be the same value because it is the equilibrium constant and will only be relevant at equilibrium. At any point the reaction is not at equilibrium you want to solve for Q, the reaction quotient.

Joshua Swift

Q_p and Q_c are just more specific ways to account for Q, the reaction quotient. This is the same for K, K_p and K_c.

Joshua Swift

If the complex contains a negative charge, you add the suffix -ate to it.

Joshua Swift

They are connected because the regions of electron density correspond directly to the hybridization. Two regions = sp. Three regions = sp2. Four regions = sp3. And so forth. Double/triple bonds still only count as one region of electron density.

Joshua Swift

Depending on the question, the units can either be J/photon or J/atom.

Joshua Swift

When the question asks for a conjugate acid of a certain molecule, you just add a proton (H+) to it. The conjugate acid of HSO4- should have been H2SO4

Joshua Swift

For the conjugate acid you want to add a proton to the molecule. For the base, you want to take one away.

Joshua Swift

Yes, if a solution is basic it can be referred to as alkaline. The definition for alkaline : having the properties of an alkali, or containing alkali; having a pH greater than 7.

Joshua Swift

Amphoteric means the molecule can act as an acid or a base.
Amphiprotic means it can either donate or accept an H+

Joshua Swift

Fluorine's atomic radius is not very large meaning the molecule's bond is stronger compared to HCl, HBr, or HI. The bigger the atom, the weaker the bond and the stronger the acid.

Joshua Swift

If the molecule has different atoms bonded to each other, it will be polar. However, the geometry of a molecule can cancel out these polar bonds and make it nonpolar due to its symmetry.

Joshua Swift

Yes, a molecule may have polar bonds within it, but based on the geometry these dipoles may cancel out and result in a nonpolar molecule.

Joshua Swift

Not exactly, but Lavelle mentioned a few trends. The first two columns, the alkali metals and alkaline earth metals, produce bases while most of the elements on the right hand side of the table produce acids. There is also a diagonal band of amphoteric oxides that matches the diagonal band of metall...

Joshua Swift

For your conjugate acid you take the original formula and add a hydrogen. You take a hydrogen out of it to find your conjugate base.

Joshua Swift

In this sapling question, it asks to give the oxidation state of the metal species in the complex [Co(NH3)5Cl]Cl
The answer turns out to be +2 but I am not too sure why. Any help?

Joshua Swift

Equatorial bonds are those that stick out of the sides of the central atom and lie in the same plane, creating shapes like trigonal planar or square planar. The axial bonds are the ones that stick up or down from the central atom, creating 180 degree bond angles with each other and 90 degree bond an...

Joshua Swift

when you take a look at each individual carbon atom, it contains 4 bonding regions, making the shape tetrahedral.

Joshua Swift

Remember that double and triple bonds don't matter in hybridization, only regions (so any type of bond counts as 1) and lone pairs are counted. Oxygen has two bonds and two lone pairs which gives it an sp3 hybridization.

Joshua Swift

Yes, lone pairs are significant because they count as bonding regions. Lone pairs cause more repulsion between atoms in a molecule which alter the shape and bond angles. However, lone pairs in regions usually occupied by atoms will produce a different shape.

Joshua Swift

No, the type of bond doesn't matter, only bonding regions are counted when determining shape.

Joshua Swift

CO2 assumes a linear geometry and since the atoms are the same on each side, the electronegativity cancels and the molecule is nonpolar.

Joshua Swift

Yes, bonds and lone pairs count as regions of electron density and contribute to the overall shape of the molecule.

Joshua Swift

I recommend always drawing your lewis structure first, then determining how many bonding regions there are. From there, you can use the VSEPR model to find out what the specific shape is.

Joshua Swift

When lone pairs are present in the VSEPR model, it often uses for the approximation of less than 109.5 degrees. Since you got the angle correct, you were correct, but we technically don't need to know the exact angle, just that it is less than 109.5 degrees.

Joshua Swift

I feel like specifically understanding why certain shapes are named the way they are helps you memorize them more easily. Shapes like linear, bent, trigonal planar, and trigonal pyramidal all describe the shape given, so try not to get worked up by all the new terms just try to figure out why they h...

Joshua Swift

It has a maximum of 8 water molecules because it is accounting for each hydrogen as well as available lone pairs in the molecule that could potentially exert these attractions.

Joshua Swift

Yes, they are Lewis Bases because they are electron donors. Electron acceptors aka proton donors are the Lewis Acids

Joshua Swift

The central atom should be the one with the lowest electronegativity.

Joshua Swift

Hydrogen bonding only occurs in atoms containing Nitrogen, Oxygen, and Flourine.

Joshua Swift

The brackets are used when the molecule has an overall charge. This charge results from adding up all of the formal charges of each atom in the molecule.

Joshua Swift

The closer the formal charge is to 0 the more stable it is.

Joshua Swift

L represents the number of lone pairs around an atom. Lone pairs on lewis dot structures just look like two dots which aren't bonded to anything. When calculating formal charge of an atom, you just count how many pairs are located around that atom.

Joshua Swift

The trend in electronegativity is closely related with ionization energy and electron affinity. If the both of these are high, then the atom will have high electronegativity and will pull shared electrons towards it, and vice versa. Elements in the top right experience the highest electronegativity.

Joshua Swift

A coordinate covalent bond is when one element provides both of the electrons necessary in creating the bond.

Joshua Swift

A lone pair is a set of two valence electrons that belong to one atom that are not bonded or shared with another.

Joshua Swift

All ionic bonds have some covalent character because when bonding, the cation exerts an electrostatic attraction on the electrons surrounding an anion and the anion's electrons are being pulled into the bonding region, they are not just taken or given away, they end up in the middle, similar to the ...

Joshua Swift

p stands for momentum
p=mv
where m=mass and v=velocity

in Heisenberg uncertainty problems you will sometimes have $\Delta$ p
$\Delta$ p=m $\Delta$ v

Joshua Swift

Atomic radius gets larger as you move toward the bottom left of the periodic table.

Electronegativity is highest as you move toward the top left of the periodic table.

Electron affinity and ionization energy both increase as you move from left to right on the table.

Joshua Swift

For the most part you just want to remember that atoms get bigger as you move toward the bottom left and smaller towards the top right and as you move right along a period due to higher nuclear charges and more protons pulling the electrons closer to the center.

Joshua Swift

You want to use Avogadro's number hen you are given moles but the question asks for an answer in terms of one atom, molecule, formula unit, etc.

Joshua Swift

The last two are not compatible because the waves ends do not perfectly match up if you were to model them on an orbit around the atom. If there is a break in the wave, it won't be compatible.

Joshua Swift

In the photoelectric experiment, the threshold energy is the minimum amount of energy needed to remove an electron from the metal surface. Not overcoming this threshold results in an electron reaching its excited state, but not to the point where it can be removed.

Joshua Swift

In the photoelectric experiment, the threshold energy is the minimum amount of energy needed to remove an electron from the metal surface. Not overcoming this threshold results in an electron reaching its excited state, but not to the point where it can be removed.

Joshua Swift

Once you have the moles of each reactant, you want to use the coefficients you found in the balanced chemical equation and using stoichiometry determine which makes less product. The one which creates less is the limiting reactant because it is hindering the potential amount of the substance created.

Joshua Swift

You do not necessarily need to convert your mL to L if both units correspond, however I recommend converting to liters for the most part because when calculating molarity in other cases you will need to convert. This will just make you accustomed to making liters the norm

Joshua Swift

950000 only has two significant figures because trailing zeroes do not count. The only time trailing zeroes become significant is when a decimal point is present (950000.)

Joshua Swift

The frequency is the number of waves that pass a point in space during any time interval, usually per one second. The wavelength is the distance between two crests. A higher frequency results in a shorter wavelength and vice versa.

Joshua Swift

Showing all of your conversions helps you cancel out the unnecessary units along the way leading you to the desired units in your final value. I also think Prof. Lavelle mentioned partial credit, so showing all of your work would definitely help especially if you do end up with the wrong answer but ...

Joshua Swift

You usually want to end up with the same amount of sig figs as you started. Once you find how many are in the initial value you use to start your calculations you want to preserve that amount.

Joshua Swift

You have to use the grams which are given and solve for the moles for each reactant. Depending on the coefficients in the balanced equation, the limiting reactant is what is constricting the amount of product. If you had the same amount of moles of each substance but you need one mole of one yet two...

Joshua Swift

The theoretical yield is basically what you would end up with if you did a reaction in a perfect world. This means all of your numbers would be 100% spot on with no human error. Because there is no way around human error in a real experiment, we have the theoretical yield which we calculate based on...

Joshua Swift

I am quite confused on this question as well. The rest were all straight forward however this one I found myself having to look up additional information just to get the answers wrong still. I am using the same numbers as Rachel mentioned but ended up at incorrect answers nonetheless. Not really sur...

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