CHEMISTRY COMMUNITY

Julie Park 1G

Rate is generally described as $\frac{mol}{L\cdot s}$
The zeroth order is described by $k_{0}[A]^0=k_0$ and since $[A]^0=1$ , the units remain as $\frac{mol}{L\cdot s}$

This video helps with finding the units for any-order reactions
https://www.youtube.com/watch?v=1g-vDSWYins

Julie Park 1G

Not sure which discussion section you're in, but here's the link to a few of them!
viewtopic.php?f=160&t=62122&p=237630&hilit=test+2&sid=398e06555d588269350912837d954689#p237630

Julie Park 1G

You can use example 7A.7 from the book to see exactly the units for k change based on the reaction order! A easy way to find out the units is to use $M^{n-1}\cdot t^{-1}$ where M = mol/L and n is the reaction order

Julie Park 1G

Because $U = q+w$ ,
$U = \Delta H-P\Delta V$ ,
which can be rearranged as
$\Delta H=U+P\Delta V$

Julie Park 1G

We don't have to worry about the steady state approach in this class!
We'll rather be focusing on the pre-equilibrium approach.

Julie Park 1G

Exactly! The catalyst will have "disappeared" from the final reaction equation because it has been cancelled out (since it's in the reactant side of the first equation) and the product side of another equation

Julie Park 1G

You would take the half reactions: 2H+ (aq,1.0M) + 2e- --> H2 (g,1atm) // E cathode = 0.00V H2 (g,1atm) --> 2H+ (aq,0.075M) + 2e- // E anode = 0.00V Add them together: 2H+ (aq, 1.0M) + H2 (g,1atm) --> 2H+ (aq,0.075M) + H2 (g,1atm) and get Ecell = 0.00V Then use the nernst equation to get: E=E^\circ ...

Julie Park 1G

Expansion will usually lead to an increase in volume (because the internal pressure is greater than the external pressure); likewise, compression will lead to a decrease in volume (because external pressure is greater than the internal pressure)

Julie Park 1G

A catalyst will be present in the beginning of the reaction (in reactants) but will be consumed in the reaction and thus will not appear in the final product. In 7E.5, the hydroxide ion (OH-) serves as the catalyst since it's present in the reactant of step 1 and in the product of step 2 (cancelling...

Julie Park 1G

You might want to know how nitric oxide (homogeneous catalyst -- meaning the catalyst is in the same phase as the reactants) catalyzes the conversion of oxygen to ozone in the lower atmosphere.
In this process, NO serves as the catalyst while NO2 is an intermediate.

Julie Park 1G

An elementary reaction is an individual, single step reaction in a proposed reaction mechanism. An elementary reaction can be described by a unimolecular reaction, where one molecule forms one or more products, bimolecular reaction, where two molecules collide at the same place and time, termolecula...

Julie Park 1G

The Arrhenius equation, $k=Ae^{\frac{-Ea}{RT}}$ , can be used to find the reaction rate based on the temperature or presence of a catalyst.

Julie Park 1G

The term "Ideal gas" is often used to describe the Ideal Gas Law PV=nRT, which describes the relationship between pressure, volume, temperature, and the number of moles of a gas. It's also used to transform equations -- for example, \Delta H=\Delta U+P\Delta V can be rewritten as \Delta H=...

Julie Park 1G

Since the entire reaction, in order to come to a completion, has to wait for the slowest step to finish, the overall reaction rate is pretty much reliant on the rate of the slowest step. That's why the slowest step is called the rate-determining step.

Julie Park 1G

You'll have to add Pt(s) to whichever side (or both sides) of the cell diagram (anode or cathode) doesn't have metal solid.

Julie Park 1G

I believe professor Lavelle provided an example along the lines of something like this: Imagine there are two students sitting across from each other with the goal to throw their crumpled piece of paper and have them collide mid-air. The likelihood of success is not that low! It's certainly possible...

Julie Park 1G

The overall reaction rate is pretty much reliant on the rate of the slowest step, since the entire reaction has to wait for it. That's why the slowest step is the rate-determining step.

Julie Park 1G

Reaction profiles describe the variation in potential energy as two reactants meet, form an activated complex, and separate as products.

Julie Park 1G

The Arrhenius equation also takes into account the presence of a catalyst when determining the reaction rate. A catalyst will lower the activation energy (Ea), therefore affecting the rxn rate.

Julie Park 1G

The total number of moles is 0.045mol after you add the 0.030mol of SO3 and 0.015mol of O together. The reason why only 0.015mol of O2 is involved is because of the presence of a limiting reactant. Basically, for every two moles of SO2, only one mol of O2 can react (according to reaction equation). ...

Julie Park 1G

Correct!

Julie Park 1G

Temperature and catalyst presence can affect the rate constant, as seen in the Arrhenius Equation

Julie Park 1G

Both are used to find entropy (S), but in this class, their usage will depend on the context (info given) The equation involving the boltzmann constant (kB), S=k_blnW should be used when you're given the number of states and species, while equations such as \Delta S = nRln\frac{V2}{V1} , which invol...

Julie Park 1G

In most of the example problems we've encountered, Ecell is positive. However, in this question, Ecell is negative!
When Ecell is positive, the cathode is on the right side and the anode is on the left side
When Ecell is negative, the anode is on the right side and the cathode is on the left side

Julie Park 1G

The problem mentions that this is an acidified solution of potassium permanganate and Iron (III) Chloride. With this information, I wonder if the H+ in the left side of the half-reaction symbolizes the protons existing in the acidified solution while the 5e- represent how acids gain electrons (accor...

Julie Park 1G

Exactly! You don't have to add the coefficients in the cell diagrams.

Julie Park 1G

The reduction half-reaction involved is 2H+ + 2e- --> H2 And the final cell reaction is described by H+ (aq, 1x10-3M) --> H+ (aq, 1x10^-4M) When you add the reduction half-reactions together (by reversing one of the equations), you will get 2H(aq, 1x10^-3M) --> 2H+ (aq, 1x10^-4M) I wonder if they us...

Julie Park 1G

The potential involving Cr2+ and Cr3+ is provided in appendix 2B of the textbook! (:
According to the textbook, the standard reduction potential of Cr3+ + e- = Cr2+ has a value of of -0.41V

Julie Park 1G

You can take these two equations that we already know: \Delta G = \Delta G^{\circ} + RTln\frac{[P]}{[R]} and \Delta G=-nFE and combine them to get -nFE = \Delta G^{\circ} + RTln\frac{[P]}{[R]} when you solve for E, you will get E=-\frac{\Delta G^{\circ}}{nF} - \frac{RT}{nF}ln\frac{[P]}{[R]} Since -\...

Julie Park 1G

You may be asked to balance an equation (involving acids/bases) by using oxidation and reduction half-reactions. First, you would identify the reduction and oxidation components of the reaction. Then, you would balance the two equations, except for the number of H and O. To balance the number of O, ...

Julie Park 1G

14B-1, 11am class: Last name A-L in Moore 100. Last name M-Z in Dodd 147. 14B-2, 1pm class: Last name A-L in Broad 2160E. Last name M-Z in Franz 1178. 14B-4, 3pm class: Last name A-Z in CS24. You can find this under "Midterm Exam: Review Sessions and Exam Venues" on the Chem. 14B page! (:

Julie Park 1G

Partial pressure refers to the pressure component of a particular, individual gas in a mixture of gases. Regular pressure might then refer to the total pressure of a mixture of gases.

Julie Park 1G

Take the heat change (to raise the temperature of water), which you found in part a, and divide it by the sum of the heat changes (for copper and water), which is your final answer from part a.

Julie Park 1G

According to $\Delta S = nRln\frac{V_1}{V_2}$ , the amount of expansion from volume V1 to V2 can affect entropy.

Julie Park 1G

$P\Delta V$ becomes insignificant because there is no expansion work and the volume of the reactants = volume of the products. This means that $\Delta U$ , which normally would be $q_{p} + w$ , now only equals $q_{p}$ , which in other words, is described as $\Delta H$

Julie Park 1G

You'll want to use the standard enthalpies of formation and the coefficients of the balanced equation to find the enthalpy of the reaction. \Delta H = 2(-395.72kJ\cdot mol^-1)-2(-296.83kJ\cdot mol^-1)=-197.78kJ\cdot mol^-1 Since the question says that 0.030mol of SO2 are consumed, yo...

Julie Park 1G

Enthalpy is a state function/property because its value is independent of how the sample was prepared. Instead, it's value is determined by its current state. In other words, a state property (enthalpy) is not dependent on the path taken to obtain that state.

Julie Park 1G

Using bond enthalpies is the least accurate method because they are represented by averages from many different molecules (method 2)

Julie Park 1G

The standard state of a substance describes its pure form of at 1bar, and for a solute, at a concentration of 1mol/L.

Julie Park 1G

It's saying that since enthalpy is a state property (not dependent on the path taken to obtain that state), enthalpies can be added (and subtracted).
For example, Hproducts - Hreactants = Change in H

Julie Park 1G

The conjugate seesaw basically describes how...
The stronger an acid, the weaker its conjugate base will be
The stronger a base, the weaker its conjugate acid will be

From this concept, you can derive equations such as
Kw = Ka x Kb
Kw = [H3O+][OH-]
pKw = pKa + pKb

Julie Park 1G

For solubility, the equilibrium constant is represented as Ksp. Ksp represents the level at which a solute can dissolve in a solution. The greater the Ksp, the more soluble the solid is an the aqueous solution.

Julie Park 1G

In example 5I.1, they want you convert the partial pressures PH2 and PCl2 from mPa (which is given) to bar. Partial pressure of H2 = 4.2 mPa and Cl2 = 8.3 mPa It's also given that 1 bar = 10^5 Pa However, we are given partial pressures in mPa. Knowing that there are 1000 mPa in 1 Pa, you can convert...

Julie Park 1G

Yes, I believe that you should look up the Ka. I think that questions such as these are supposed to provide the Ka in the problem unless previously stated in a table of Ka, but I can't seem to find the Ka for HClO in the textbook. After finding Ka, set up the Ka expression using information deduced ...

Julie Park 1G

Once you find the concentration of the hydroxide ion in the original solution, you'll want to take other given info -- volume of NaOH (0.200L) , ratio of moles of Na2O and NaOH (1mol Na2O and 2mol NaOH according to the balanced reaction equation), and the grams of Na2O per mole (61.98g/mol) -- to us...

Julie Park 1G

You're correct in that we don't put units, but I believe the parentheses indicate gas pressure (not concentration).

Julie Park 1G

K describes the equilibrium constant (the ratio of products and reactants at equilibrium). By comparing Q (the ratio of products and reactants at a specific instant, not necessarily at equilibrium) with K, you can tell which way the reaction will proceed to get closer to equilibrium. For example, wh...

Julie Park 1G

For the ICE table, you should have something that looks like.... SO2(g) + NO2(g) --> NO(g) + SO3(g) 0.0200, 0.0400, 0.0200, 0.0300 -x , -x , +x , +x 0.0200 -x, 0.0400 - x, 0.0200 + x, 0.0300 + x Were you able to get to this step? Remember that you first have to convert the moles of each substance in...

Julie Park 1G

They'll be available for pickup beginning week 3 from 3034 Young Hall

Julie Park 1G

Yes, you can include everything except for solids(s) and liquids(l)! Anything denoted as "aq" or "g" should be used when writing out K

Julie Park 1G

https://www.youtube.com/watch?v=BNYz5EKXVeI This video does a pretty good job at explaining the concepts behind the Heisenberg Uncertainty Principle, and it also provides examples using the uncertainty equation (including an example that translates \Delta p from the uncertainty equation to m\Delta v )

Julie Park 1G

E describes the # of lone pairs on the central atom. For example, SO2 consists of an S bonded to two O with double bonds. In addition, one lone pair (2 electrons) exists on S. Therefore, the formula would look like: AX2E

Julie Park 1G

Well-known strong acids are often put into a list of seven different molecules called the "7 Strong Acids" HClO_{4}, HClO_{3}, HCl, HBr, HI, HNO_{3}, and H_{2}SO_{4} The well-known strong bases are usually categorized by the name "8 Strong Bases" They are the Group 1A metal hydro...

Julie Park 1G

Myoglobin:
x1 O2 possible bonding
Transports O2 in muscle cells

Hemoglobin:
x4 O2 possible bonding
Involved in red blood cells

Also, the lone pair on CO can bind to hemoglobin. These leads to "suffocation at the molecular level", and explains why CO is toxic

Julie Park 1G

In addition, it's useful to know that the Arrhenius definition of acids/bases surround the idea that acids ionize in aqueous solutions to produce H+ ions while bases produce OH- ions

Julie Park 1G

Formal charge: # ve- a neutral atom of the element would have - (sum of unpaired electrons + bonds) Note: a. count each unpaired electron attached to the atom as a single value b. count each bond as a single value For example, say that Nitrogen was surrounded by 1 double bond and 2 unpaired valence...

Julie Park 1G

You'll first want to find the # of electron densities surrounding the atom in question. In (a), BF3, B is bonded to three F atoms in single bonds. According to the chart, the three bonds (electron densities) would give the B in BF3 to a s1p2 (sp2) hybrid orbital. 1 --> s1 2 --> s1p1 3 --> s1p2 4 -->...

Julie Park 1G

Consider the number of atomic and hybrid orbitals involved in each of these When there are 2 atomic/hybrid orbitals and the hybridization of the central atom is sp, the electron arrangement is linear. When there are 3 atomic/hybrid orbitals and the hybridization of the central atom is sp2, the e- ar...

Julie Park 1G

You'll probably want to know the definitions of both and be able to identify them based on a reaction equation or when given a certain experimental context, but it's likely that the question will explicitly ask you to state whether something is a bronsted/lewis component. By the Bronsted definition,...

Julie Park 1G

Since pH is found by using the equation -log(x), where x is the concentration of hydrogen ions, pH will be negative as long as the hydrogen ions have a molarity greater than 1 (due to the behavior of the -log function). Because a negative pH is really hard to calculate experimentally due to lack of ...

Julie Park 1G

The well-known strong acids are commonly put into a list of seven different molecules: HClO_{4}, HClO_{3}, HCl, HBr, HI, HNO_{3}, and H_{2}SO_{4} These are known as the "7 Strong Acids" The well-known strong bases are categorized by the name "8 Strong Bases" They are the Group 1A...

Julie Park 1G

When figuring out hybrid orbitals, first identify the number of electron densities surrounding the atom in question. In (a), BF3 is characterized by B bonded to three F atoms in single bonds. According to the chart, the three bonds (electron densities) would allow the B in BF3 to use a s1p2 (sp2) hy...

Julie Park 1G

I believe that the deprotonation has to do with the ability of weak/strong acids to dissociate. Weak acids, such as acetic acids, are known to not dissociate completely while strong acids can dissociate fully in water/aqueous solutions. This means that strong acids can ionize and release a lot of pr...

Julie Park 1G

I would say that week 9 is coordination compounds and week 10 homework would be Lewis acids and bases

Julie Park 1G

Most oxidation states of elements in molecules/compounds can be found by looking at the groups of the periodic table (PT). The oxidation number represents the # of electrons that an atom can gain, lose, or share when chemically bonding with an atom of another element. Ex: NaCl Na (in first group) ha...

Julie Park 1G

They are compounds that contain a coordination complex, which is the product of a Lewis acid-base reaction where neutral molecules/anions (ligands) bond to a central metal atom/ion by coordinate covalent bonds (bonds formed when one donor atom supplies both electrons).

Julie Park 1G

Electron affinity describes a neutral atom's likelihood of gaining an electron. Here are some explanations for why electron affinity increases as you go up a group and to the right side of the periodic table. Down the group: Electron affinity decreases. Increased shielding + greater distance between...

Julie Park 1G

I think that this question is asking if there are different numerical values of bond angles in OSCl. It's true that there are technically two OSCl bonds, but the actual angle degrees for each of them are the same. Therefore, there's only one "bond angle".

Julie Park 1G

When it comes to trends across the periodic table, it would be a good idea to know the general reasoning as to why those trends occur. Since electronegativity measures an atom's tendency to attract and form bonds with electrons, electronegativity increases up and to the right on a periodic table (wh...

Julie Park 1G

The difference between a molecule's "energy" when the lone pairs (e-) are put on the axial or equatorial planes can help you identify the molecule's most stable structure. A more stable structure would be one with lower "energy" (less e- repulsion) For example, in I{F_{4}}^{+} , ...

Julie Park 1G

It's important to know that an axial or equatorial lone pair (e-) placement can determine the most stable structure. Ideally, you would want a structure with lower "energy" (less e- repulsion) For example, in IF_{4}^+ , there are two possible places (orientations) where the lone pair can e...

Julie Park 1G

If you look at the lewis structure of SO2, you'll be able to see that while there are two sets of double bonds between S and O, there is still a lone pair of e- on S. This creates two dipole moments between S and each O where the S atom is a partial positive and O is partially negative.

Julie Park 1G

Neopentane's structure consists of four C atoms attached to a center C atom in a "+" shape, with CH3 stemmed out from each of the four surrounding C atoms. The structure is symmetrical and kind of spherical. I recommend looking at the imagine on the right-hand side of this page: https://en...

Julie Park 1G

Looking at the lewis structures may help, and examining the general types of the compound might further clarify which substance has a higher melting point. For example, in (a), between HCl and NaCl, NaCl will have a higher melting point because it's an ionic compound. In (b), Butanol is stronger bec...

Julie Park 1G

Yes, the textbook (2.D.2) says that when the distortion of the e- cloud on the anion increases, the covalent character of the bond also increases.

Julie Park 1G

ms (spin quantum number) describes the magnitude and direction that an electrons spins
ms only has two possible values: +1/2 and -1/2

therefore, there is no such thing as ms = 0

Julie Park 1G

It would probably help to be able to know the general definition as well as the periodic trends for these traits (and why they generally follow those trends). They both follow the same periodic trends: Both increase from left to right Both increase from the bottom to the top In a late quantum review...

Julie Park 1G

Shortcut for formal charge: # ve- (a neutral atom of the element would have) - (sum of # unpaired electrons + bonds) Note: a. count each unpaired electron attached to the atom as a single value b. count each bond as a single value For example, say that Nitrogen was surrounded by 1 double bond and 2 ...

Julie Park 1G

Formal charge: # ve- a neutral atom of the element would have - (sum of unpaired electrons + bonds) Note: a. count each unpaired electron attached to the atom as a single value b. count each bond as a single value For example, say that Nitrogen was surrounded by 1 double bond and 2 unpaired valence ...

Julie Park 1G

You should also probably know the relative strengths of bonds based on their length.
For example, triple bonds, which are shorter than single or double bonds, are typically stronger than the latter two bonds.
Likewise, double bonds are shorter but stronger than single bonds.

Julie Park 1G

The conservation of energy concept refers to this equation:
$E_{photon} - \Phi= E_{kinetic}$
aka
Energy of photon - threshold energy = electron kinetic energy

Julie Park 1G

i think the question was mistyped but just for reference: Write the subshell notation (3d, for instance) and the number of orbitals having the following quantum numbers: a. n=5, l=2 (5d, five) b. n=1, l=0 (1s, one) c. n=6, l=2 (6f, seven) d. n=7, l=3 (2p, three) Know that l = 0 corresponds to the s-...

Julie Park 1G

I've yet to check with my TA but I assume that any material we learn until the day of the midterm is "fair game" :)

Julie Park 1G

This probably isn't an official rule, but it's often easiest to think that the atoms are attached in order as presented by the name of the molecule or compound. For example, by looking at H2CSO, you can assume that 2 hydrogen atoms will be attached to C, which is attached to the S atom, which is att...

Julie Park 1G

In Acetic Acid, CH_{3}COOH or CH_{3}CO_{2}H , you can see two groups: CH3 and COOH. Elements like C and O usually take the "inside" of the structure while atoms of hydrogen will take the exterior as they bond with C and O. In CH3, you can assume that C takes the center and that it's surrou...

Julie Park 1G

For Cr, instead of writing: Cr: [Ar] 3d^4 4s^2 You would write: Cr: [Ar] 3d^5 4s^1 The second version presents a more stable e- configuration (d subshell becomes half full, instead of being "almost half full") For Cu, instead of writing: Cu: [Ar] 3d^9 4s^2 You would write: Cu: [Ar] 3d^10 4...

Julie Park 1G

Two electrons are paired if the have opposite spins ↿⇂ Two electrons are parallel if they have the same spin ↿↿ This describes the way electrons fill subshells For example, the diagram for Carbon would look like: 2p ↿ ↿ _ (parallel) 2s ↿⇂ (paired) 1s ↿⇂ Carbon's electronic configuration = 1s^2 2s^2 ...

Julie Park 1G

I believe that we're supposed to write the electron configuration such that it is in a least-to-most energy order Example from slides: Sc: [Ar] 3d^1 4s^2 Once the 4s orbital has been occupied and electrons begin to fill the 3d state, the 3d state is considered to have less energy than 4s That's why ...

Julie Park 1G

You would first convert the wavelength of 420nm to meters
Then use E=hc/lamba to find the energy in J/photon
Then find the number of photons by dividing the energy from 64J
Then find the moles of photons by multiplying the number of photons by (1mol/6.022x10^23 photons)

Julie Park 1G

For Cu, instead of writing: Cu: [Ar] 3d^9 4s^2 You would write: Cu: [Ar] 3d^10 4s^1 This is simply because the latter version presents a more stable electron configuration where the d subshell remains completely full I believe the two exceptions are that half full d5 and full d10 subshells have lowe...

Julie Park 1G

You would use it to describe the relation between the change in energy of an atom (as it transitions between two states) or molecule & the frequency of radiation emitted or absorbed.

The equation $\Delta E=hv$ or $E_{upper}-E_{lower}=hv$ describes this relation.

Julie Park 1G

A photon, in simple terms, is "...a packet of energy" of electromagnetic radiation. The equation for the energy of a photon is E=hv where E is energy, v=frequency, and h=planck's constant.

Julie Park 1G

In constructive interference, interactions between waves lead to a greater amplitude. This occurs when the peaks of waves coincide. On the other hand, in destructive interference, interactions between waves lead to a smaller amplitude. This happens when the peak of one wave coincides with the trough...

Julie Park 1G

You can use...
1/2mv^2 = hv - work function

1/2mv^2 refers to the kinetic energy of an ejected e-
hv refers to the energy supplied by a photon
the work function (threshold energy) is the energy required to eject an electron

Julie Park 1G

Given that E=mc2 and E=hv
Substitute E to get mc2=hv
Rearrange to get mc = (hv)/c = p
Note: If E=pc, and E=hv, then p=E/c can be rearranged to p=hv/c

Given that c=λv and p=(hv)/c, p=h/λ
Which can be rearranged to λ=h/p (De Broglie)

Julie Park 1G

For this question, you'll probably have to have known the formula for nitric acid beforehand. Nitric acid is one of the seven strong acids. a. Nitric acid = HNO_{3} b. While knowing that... H = 1.008 grams/mol N = 14.01 grams/mol O = 16.00 grams/mol you can estimate that O has the greatest mass perc...

Julie Park 1G

1.0molAg\cdot \frac{6.02\times 10^{23}AgAtoms}{1.0molAg}\cdot \frac{288pm}{1AgAtom}\cdot \frac{1m}{10^{12}pm}= 1.73\times 10^{14}m Step 1: Find the number of Ag atoms in 1.00mol Ag atoms. Step 2: Multiply the # of Ag atoms by the length (diameter is 144 x 2 = 288pm) of each atom. Step 3: Convert to...

Julie Park 1G

Here is how you would find the amount of moles of (a) Cu2+ ions ins 3.00g of CuBr2: 1. Find the molar mass of CuBr2: 223.5g/mol CuBr2 2. Perform dimensional analysis to convert known units to mol Cu2+. (3.00gCuBr_{2})\cdot (\frac{1molCuBr_{2}}{223.5gCuBr_{2}})\cdot (\frac{1molCu^...

Julie Park 1G

If you set the mass of the compound at 100g and you know that 88.8% of the compound is M (Metal), you can conclude that the metal weighs 88.8 grams (100g x 0.888). If the compound weighs 100g in total, then subtracting the amount of metal from it should give you the weight of the leftover component,...

Julie Park 1G

In all cases, subscripts only apply to elements inside the parentheses. In this case, the subscript of 2 only applies to $N_{3}$ . Therefore, you can look at $Mg(N_{3})_{2}$ as $MgN_{6}$ .

Another example: $Ca(OH)_{2}$ translates to $CaO_{2}H_{2}$

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