CHEMISTRY COMMUNITY

Christine Honda 2I

I know that on a previous test they were asked to derive Van't Hoff's equation! But it is always useful to understand derivations so you know how to apply the equation.

Christine Honda 2I

I remember seeing somewhere that certain salts are not ideal for salt bridges... does anyone have an idea of what salts these include?

Christine Honda 2I

A catalyst is always regenerated!

Christine Honda 2I

Thank you so much, Lyndon! Thank you for your dedication, patience, compassion, and hard work. I've been going to your workshops every week since 14A and I honestly could not have passed this class without you! Good luck in your future endeavors!

Christine Honda 2I

Even though both are given on the equation sheet I think it would be safe to know the derivations just in case anything is asked on the final.

Christine Honda 2I

The reaction will only happen if a catalyst is added and therefore the activation energy is lowered so the reaction can proceed

Christine Honda 2I

The higher Ecell value is usually reduced!

Christine Honda 2I

A catalyst is always regenerated! So if you see it on the reactants and products side then it is a catalyst!

Christine Honda 2I

Yes! I believe they said answers will still be posted on chemistry community.

Christine Honda 2I

Depending on the order of the reaction, the straight line (whether it is a positive or negative slope and the graph axis labels itself) will tell you the order of the reaction.

Christine Honda 2I

You can always solve for the units by knowing the rate reaction equation (rate=k[A]^2) and solving for k!

Christine Honda 2I

This is such a good idea and thank you for organizing this!

Christine Honda 2I

They are the exact same equations just the very last equation has been raised to the e.

Christine Honda 2I

In addition, the y-intercept is the initial concentration!

Christine Honda 2I

You use the Nernst equation to quantitatively determine the direction of the electron transfer under non-standard conditions. We use it when there's a dependence of cell potential on concentration.

Christine Honda 2I

I believe that because it is a Halogen, it's natural state is in X2 form (Cl2, F2, etc.) and therefore the reaction X2=2X is endothermic because it takes energy to pull the two atoms apart. Therefore we know the reaction will shift right towards the products when the temperature is increased.

Christine Honda 2I

Yes, I believe the substance has to be in a solid state. It must be a perfect crystalline to have zero disorder and therefore have zero entropy.

Christine Honda 2I

Voltage is the amount of energy being produced by the electrodes. It is the potential difference between two electrodes.

Christine Honda 2I

MnO4- is being reduced because when we calculate the oxidation of state of Mn in this compound it is +7 (do this knowing that O is -2, multiplying it by 4 and knowing that the entire molecule has a charge of -1). But in the products, Mn has a charge of +2. This shows that Mn has gained 5 electrons a...

Christine Honda 2I

When the standard reduction potential is positive that means the reduction is spontaneous!

Christine Honda 2I

You look at how many electrons are being transferred!

Christine Honda 2I

What does it mean when a redox reaction takes place in an acidic or basic solution? How do you balance a redox reaction when it takes place in an acidic or basic solution?

Christine Honda 2I

Using Le Chatelier's principle which takes into account the increase in either products or reactants concentrations, the Ecell will either decrease or increase. If the concentrations of the reactants are increased, then Ecell will be greater than Estandard. If the concentrations of the products are ...

Christine Honda 2I

As Dr. Lavelle mentioned at the end of the lecture today, the test will cover the second page of the Thermodynamics outline and all of the Electrochemistry Outline. But the test will NOT include Chemical Kinetics.

Christine Honda 2I

It is conventional to put the anode on the left and the cathode on the right. That being said it would be smart to double-check that this is true in a problem or on a test (if possible) by seeing which is being reduced and which is being oxidized.

Christine Honda 2I

G* means that all the substances are in their standard states

Christine Honda 2I

Br is both the oxidizing and reducing agent.
We balance it assuming using the fact that it is an aqueous solution so H2O.

3Br2 + 6OH- --> 5Br- + BrO3- + 3H2O

Christine Honda 2I

The absence of the flow of electrons or charge between the anode and cathode can also be solved by using a salt bridge!

Christine Honda 2I

One thing my high school teacher taught me to remember oxidation/reduction is L.E.O (loses electrons oxidation) the lion goes G.E.R (gaining electrons reduction)! Hope this helps make memorization easier :)

Christine Honda 2I

Qreaction=-Qcalorimeter and so that is why the answer is negative 1.19kJ!

Christine Honda 2I

As someone else said I think it would be a good thing to familiarize yourself with the Constants and Equations sheet that's on Dr. Lavelle's website and it is likely that you will be able to deduce what each variable is!

Christine Honda 2I

Can someone explain to me why steam causes worse burns than boiling water? I know he went over it in great detail during lecture but I want to be sure that I have the concepts solidified.

Christine Honda 2I

A bomb calorimeter is completely sealed and insulated, making it an isolated system. It maintains a constant volume.
A constant pressure calorimeter gives enthalpy values.

Christine Honda 2I

It should be in terms of Joules whether that is J or kJ. It can also be in J/mol or kJ/mol depending on the context.

Christine Honda 2I

Make sure to familiarize yourself with the Constants and Equations sheet on Dr. Lavelle's website, therefore, you know what you should and shouldn't memorize!

Christine Honda 2I

Typically a substance is in its standard state when a gas is at 1 atm and 1M. For a pure liquid or sold it is most stable at 1 atm and a temperature of interest or about 25C.

Christine Honda 2I

In Method 2 you use each individual bond enthalpies to calculate delta H. Using the Lewis structures you look at which bonds are broken in the reactants and which bonds are formed in the products. The bonds broken are positive enthalpies and bonds formed are negative. Then you add the enthalpies of ...

Christine Honda 2I

If the substance is not in the most stable/standard phases then you must use the total of the enthalpy of the phase change and the bond enthalpy when calculating.

Christine Honda 2I

I would definitely start with 4D because that's what addresses enthalpy!

Christine Honda 2I

The small percent ionization indicates the change in molar concentration or x is so small that it becomes negligible and this makes the approximation acceptable.

Christine Honda 2I

No, you do not need to raise it to the stoichiometric coefficients because when you take the pOH you are taking the -log of the concentration of OH- ions, not the ratio of them.

Christine Honda 2I

It means that the reaction has to shift towards the reactants or products in order to achieve the same ratio and the same K value.

Christine Honda 2I

The 5% rule applies to when you use the ICE table. If K is less than 10^-3, then you can assume that X is so small that it will not make a difference. For example if you have K=X^2/(0.3-X), then you can change it to X^2/0.3 because the X in the denominator becomes negligible. The 5% rule is if you f...

Christine Honda 2I

If it asks for molar concentrations I believe it is asking for mol/L. pH or pOH will be asked for specifically.

Christine Honda 2I

In discussion, my TA mentioned these as strong acids and bases! I think they would be helpful to memorize so that you know which acids or bases completely dissociate.
Strong Acids: HCl, HNO3, H2SO4, HBr, HI, HClO4
Strong Bases: LiOH, NaOH, KOH, Ca(OH)2, Ba(OH)2, Sr(OH)2

Christine Honda 2I

The 5% percent rule is used to check if our "X is small" approximation is valid or not. We check to see if the X we solve for is less than 5% of the initial concentration. If it IS less than 5% then the approximation is valid.

Christine Honda 2I

H2O is often not included because it is a liquid, or solvent in the solution. Therefore, it is not included in the K expression or in the ICE table.

Christine Honda 2I

I don't think ICE tables are necessary to get full credit on tests as long as you get the right answer. Although I would suggest using one because there's possible partial credit.

Christine Honda 2I

You still need to include the H2O in the equilibrium expression. You can only disregard it if it is a solid or liquid!

Christine Honda 2I

Since we know that 60% of the H2 reacted, then at equilibrium we can use the fact that there will be 40% left when solving for the equilibrium concentrations. Therefore, when we use the ICE table, we can set the change in H2 (0.133-x) equal to the equilibrium value of H2 (0.4 x 0.133) and solve for X!

Christine Honda 2I

Using the reaction given, set up an ICE table. You should get a Kp equation that looks like x^2/(0.22-2x)^2 and set this equal to the Kp given. Because the equilibrium constant is small, we can assume that X is negligible compared to 0.22, therefore we can ignore it in the denominator. We end up hav...

Christine Honda 2I

For the purpose of this class, K is unitless. But in higher classes, it refers to the "activity" of the reactants and products.

Christine Honda 2I

Yes! The diameter is the uncertainty in position.

Christine Honda 2I

Polydentate is referring to anything that can bind in two or more places. I would describe EDTA as a hexadentate to be more specific!

Christine Honda 2I

Yes, CH3COOH is the acid and CH3NH2 is the base!

Christine Honda 2I

The triple bond between C and N has one sigma bond and two pi bonds.
The sigma bond is written as sigma(Chybridization,Nhybridization)
Then you will have two pi bonds are written as pi(C2p,N2p)

Christine Honda 2I

For 14A we will not have to calculate the Ka for weak acids. We will learn that in 14B. I would know how to calculate the pKa of a weak acid when given Ka though assuming that it is given to us.

Christine Honda 2I

Yes, polar molecules possess a permanent dipole moment.

Christine Honda 2I

(Greek Prefix) Ligand names in alphabetical order, Transition Metal Cation Name (Roman Numeral). If there are anions, then add it to the end. If there is water then add (Greek Prefix) Hydrate.

Christine Honda 2I

A paramagnetic electron is an unpaired electron. An atom is considered paramagnetic if even one orbital has a net spin. Diamagnetic electrons are whenever two electrons are paired together in an orbital, or their total spin is 0. Also, diamagnetic atoms/compounds (and atoms) have paired electrons an...

Christine Honda 2I

Since this is a coordination compound the lewis structure would have the transition metal in the middle and the ligands in bonded to it, all in square brackets.

Christine Honda 2I

Crystal field theory (CFT) is a bonding model that explains many important properties of transition-metal complexes, including their colors, magnetism, structures, stability, and reactivity. It qualitatively describes the strength of the metal-ligand bonds in transition-metal complexes. Based on the...

Christine Honda 2I

To figure out the charge of the metal you can look at the ligands and overall charge of the complex. Since there are 6 CN- and the overall charge is 4-, that means the charge of Fe is 2+. To name the compound, you should write out the name for it by beginning with each ligand, in alphabetical order,...

Christine Honda 2I

A sigma bond is stronger. Sigma bonds result from the head-on overlap of the orbitals of the two atoms, which has more area of overlap than pi bonds which result from the parallel overlap of orbitals. That is why sigma bonds are stronger.

Christine Honda 2I

Any time two electrons share the same orbital, their spin quantum numbers have to be different. Whenever two electrons are paired together in an orbital, or their total spin is 0, they are diamagnetic electrons.

Christine Honda 2I

A paramagnetic electron is an unpaired electron. An atom is considered paramagnetic if even one orbital has a net spin.

Christine Honda 2I

Sigma bonds result from the head-on overlap of the orbitals of the two atoms, which has more area of overlap than pi bonds which result from the parallel overlap of orbitals. That is why sigma bonds are stronger.

Christine Honda 2I

A heme complex forms when an iron ion binds to the porphyrin ligand. The porphyrin ligand is a tetradentate ring structure, meaning the fact that there are four nitrogens facing inward that can can form coordination complexes with the iron. When this complex binds with another protein they make up m...

Christine Honda 2I

The characteristic tetravalence of carbon is due to the small promotion energy of a carbon atom. This energy is small because a 2s-electron is transferred from an orbital that it shares with another electron to an empty 2p-orbital. Although the promoted electron enters an orbital of higher energy, i...

Christine Honda 2I

The VESPR theory applies to radicals, and they can be counted as electron densities. For example, in CH3 you have 7 total electrons it's going to be a trigonal planar you're going to have the Carbon as the central atom that is bonded to 3 H's and then you have one electron (unpaired lone pair) on th...

Christine Honda 2I

The VSEPR model is used to determine the molecular geometry and the electron-group geometry. The Lewis structure helps us identify the bond pairs and the lone pairs.

Christine Honda 2I

The one with the bond angle as 120 degrees must have lone pairs. The one that is 180 degrees may have lone pairs.

Christine Honda 2I

Typically, cations will have less polarizability because there are less electrons and therefore the effective nuclear charge on the electrons are stronger and pulled in closer to the nucleus. Therefore, it is harder to "distort" the electron cloud making it less polarizable. The opposite i...

Christine Honda 2I

Yes, hydrogen bonds are the strongest IMF. The δ+ hydrogen is so strongly attracted to the lone pair on the other atom that it is almost as if you were beginning to form a covalent bond. It doesn't go that far, but the attraction is significantly stronger than an ordinary dipole-dipole interaction.

Christine Honda 2I

In the see-saw shape the axial and equatorial positions are not chemically equivalent. If the lone pair is in the axial position, we have three LP–BP repulsions at 90°. If the lone pair is in the equatorial position, we have two 90° LP–BP repulsions at 90°. With fewer 90° LP–BP repulsions, we can pr...

Christine Honda 2I

Electronegativity is a measure of the tendency of an atom to attract a bonding pair of electrons. Electron affinity is defined as the change in energy (in kJ/mole) of a neutral atom (in the gaseous phase) when an electron is added to the atom to form a negative ion.

Christine Honda 2I

Since there are two electrons in the first orbital of the O sublevel, there is greater electronic repulsion in the 2p sublevel for O than N. Therefore, it is easier to remove an electron from the O than the N, and the ionization energy of O is lower than N. Also nitrogen has a lower ionization energ...

Christine Honda 2I

Yes, dipole moments is referring to the fact that one atom is more electronegative. The larger the difference in electronegativity, the larger the dipole moment. It is conventional to draw a dipole moment arrow from positive to negative.

Christine Honda 2I

305416361 wrote:
Victoria Otuya 4F wrote:I learned an easier way to remember the formal charge equation: valence electron -(dots + line).

does this count "dots" as pairs of dots or individual ones?

Count each dot as one electron each.

Christine Honda 2I

Professor Lavelle uses boiling points to indicate which dipole interactions are stronger because the stronger the interactions between molecules, the more energy/heat required to separate them from each other, which raises the boiling point of the molecule.

Christine Honda 2I

When polarizability of molecules increases, it takes more energy to break the stronger bonds between molecules resulting higher melting and boiling points.

Christine Honda 2I

The magnetic quantum number tells you how many orbitals there are in a subshell and it tells you the orientation of the orbital.

Christine Honda 2I

Use 0.5 for the uncertainty!

Christine Honda 2I

You can use c=(lambda)(nu) for electromagnetic radiation, or light.
You can use lambda=h/p or lambda=h/mv for electrons because they have mass.

Christine Honda 2I

Electronegativity is a measurement of a neutral atom's likelihood of gaining an electron.
Ionization energy is the minimum energy required to remove a valence electron.
Both of these have the trend of increasing going towards the right and increasing going up the periodic table.

Christine Honda 2I

I think it is important to write the ground state first so that we can see which orbital has the highest energy so we can easily see where to remove or add electrons. It may not be totally necessary though, more just useful.

Christine Honda 2I

I'm assuming they will be given to us because Dr. Lavelle's Constants and Equations sheet on his site has all three of these equations on it!

Christine Honda 2I

kJ/mol!

Christine Honda 2I

Cations are smaller than their parent ions because cations lose electrons and when an atom loses electrons, the positively charged nucleus pulls the electrons more closely making it smaller.

Christine Honda 2I

The spins of two electrons are said to be paired if one is ↑ and the other ↓. Paired spins are denoted ↑↓, and electrons with paired spins have spin magnetic quantum numbers of opposite signs. No two electrons in an atom can have the same set of four quantum numbers.

Christine Honda 2I

Atomic size decreases from left to right across a period of elements. This is because protons are being added to the nucleus making it more positively charged as well as the fact that electrons are added to the same shell. This creates greater nuclear attraction and therefore the electrons are pulle...

Christine Honda 2I

The two main exceptions are Chromium ([Ar]3d^5 4s^1) and Copper ([Ar] 3d^10 4s^1)

These are exceptions to the general rule because a completely full or half full d sub-level is more stable than a partially filled d sub-level.

Christine Honda 2I

Frequency = -R [(1/n*2) - (1/N*2)]
in which "n" is the initial energy level, and "N" is the final energy level and we are supposed to solve for "n"

1.14x10^14 = -3.29x10^15 [(1/n^2) - (1/4^2)]

Solving for n, I ended up with n=6!

Christine Honda 2I

As others have said, a cation loses electrons and anions gain electrons. Therefore, cations have a positive charge and anions have a negative charge.

My high school teacher told us to think that a cat has "paws" so therefore CATions are "pawsitive"

Christine Honda 2I

A completely full or half full d sub-level is more stable than a partially filled d sub-level, so an electron from the 4s orbital is excited and rises to a 3d orbital. It is easier for them to remove a 4s electron and bring it to the 3d subshell, which will give them a half-filled or completely fill...

Christine Honda 2I

You can calculate it using the distance between two nuclei of touching identical atoms, but as far as trends for atomic radius,
The size of an atom will decrease as you move from left to the right of a period.
The radius of atoms increases as you go down a certain group.

Christine Honda 2I

In a ground-state atom, all electrons are in the lowest possible energy levels.

Christine Honda 2I

They both apply to the Hydrogen atom. Emission or absorption processes in hydrogen give rise to series, which are sequences of lines corresponding to atomic transitions, each ending or beginning with the same atomic state in hydrogen. For the Lyman series, which corresponds to UV light, the electron...

Christine Honda 2I

In the photoelectric experiment, a certain light was used to attempt to eject an electron from a metal. The experiment showed that if the light were a wave, then simply increasing the intensity would increase energy. But, increasing the intensity of the light did not result in ejection. Scientists t...

Christine Honda 2I

You need to convert nm to m then use the equation: E=hc/lambda. E = [(6.626 x 10^-34 Js)(3.0 x 10^8 m/s)]/(420 x 10^-9 m) = 4.7 x 10^-19 J Doing this gives us how much energy in Joules each photon has. Then multiply 32 W by 2, so 64 J are generated in 2.0 seconds. Use the answer we found above to ge...

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