CHEMISTRY COMMUNITY

Laura Gong 3H

You can solve for the units of the rate constant by making sure your units at the end equal to M/s (which are the units for rate).

Laura Gong 3H

The units of the rate constant is M-1*s-1 or 1/(M*s) where M is the concentration mol/L.

Laura Gong 3H

It differs in the Y axis.
Zero order is simply [A] vs time.
First order is ln[A] vs time.
Second order is 1/[A] vs time.

Laura Gong 3H

1/2 dNO2/dt is the unique reaction rate of the chemical equation given.
It follows the aA+bB-->cC+dD example given a few lectures ago where -1/a*d[A]/dt = -1/b*d[B]/dt = 1/c*d[C]/dt = 1/d*d[D]/dt.

Laura Gong 3H

Lower case k is the rate constant. (units vary)
Upper case K is the equilibrium constant. (no units)

Laura Gong 3H

The Arrhenius equation k=Ae^(-Ea/RT) demonstrate how temperature and activation energy can affect K.

Laura Gong 3H

You would order the metals by highest SRP value to lowest SRP value because they lower they are on the SRP table, the better they are at being reducing agents/getting oxidized.

Laura Gong 3H

I would use the method of initial rates that we learned about in Friday's 3/1 lecture. An example would be to set (rate 1)/(rate 2)= (k1*[A]^x*[B]^y*[C]^z)/(k2*[A]^x*[B]^y*[C]^z) to solve for the order of reactant A in this particular where x,y,z=order of the reactants. Just plug in the values from ...

Laura Gong 3H

So for C, I think you'll find that your work will get you:
1^z/2^z = 1 where z=the order in relation to reactant C.
This just means that z=0 so the reaction is zero order for reactant C.

Hope this helps!

Laura Gong 3H

n if the number of moles of electron transferred in the redox reaction. You can find n by balancing the redox reaction.

Laura Gong 3H

I believe the convention on the left would be to write it in the order of oxidation (anode) and on the right would be to write in the order of reduction (cathode) if that makes any sense.
So if Cu2+ were to be oxidized to Cu4+, you would write Cu2+,Cu4+.

Laura Gong 3H

Platinum won't react in the redox reaction (and affect the voltage reading) but it can still conduct electricity (the flow of electrons from the anode to the cathode) which can helpful when your reaction involves gases or aqueous solutions.

Laura Gong 3H

Standard Gibbs free energy occurs under standard conditions (1M, 1atm, 298K or 25C). I think reaction Gibbs free energy is just referring the free energy of a particular reaction which may or may not occur under standard conditions.

Laura Gong 3H

O2 is probably not included in the calculations for delta H and delta G because standard enthalpy of formation of O2 and the free energy of O2 are both 0.

Laura Gong 3H

When change in enthalpy and entropy are both negative, raising the temperature would make the change in free energy more positive. (less spontaneous)
When change in enthalpy and entropy are both positive, raising the temperature would make the change in free energy more negative. (more spontaneous)

Laura Gong 3H

If the system is at equilibrium, its free energy is not changing. Therefore, Delta G = 0.

Laura Gong 3H

How do you calculate deltaH of a reaction occurring at a different temperature given deltaH of a reaction at another temperature?
Will we need to know this for the midterm?

Laura Gong 3H

COF2 has greater molecular complexity compared to BF3 which means it has a greater number of possible positions/orientations which makes its entropy greater than BF3 which has lesser number of possible positions.

Laura Gong 3H

It tell you that there is 1mol of the substance. W= number of possible orientation^number of particles in 1 mol (which is Avogrado's number)
Then use S=kB*lnW to find the entropy of the sample.

Laura Gong 3H

At least for the 6th edition, this particular question is 9.13 and on the website, the solution manual errors page says that the answer you got was correct because like you predicted, because N2 is a diatomic gas we need to use Cv=5/2R not 3/2R.

Laura Gong 3H

One is used when the system is at constant pressure (irreversible expansion) (w=-pdeltaV) and the other is used when pressure is not constant (usually isothermal reversible expansion) (w=-nRT*ln(Vf/Vi)).

Laura Gong 3H

During phase changes, the temperature does not changem so instead of using the equation q=mCdeltaT, use q=ndeltaHfus or q=ndeltaHvap depending on which phase change.

Laura Gong 3H

Work is usually in J but if its value is large enough, it can also use kJ.
1 L.atm = 101.325 J. This is the conversion found in the constant and formula sheet.

Laura Gong 3H

Degeneracy refers to number of microstates in a system that have the same energy level.

Laura Gong 3H

Isothermal expansion occurs when the temperature stays constant. It usually refers to reversible expansion where you would use the equation w=-nRT*ln(Vf/Vi).

Laura Gong 3H

Knowing when the reaction is occurring under constant pressure can help you solve problems involving work. It can help you determine which equation to use (either w=-PdetlaV or w=-nRTln(Vf/Vi)).
Also at constant pressure we can determine that qp=deltaH.

Laura Gong 3H

I used a similar method to answer this question. Using the First Law of Thermodynamics, I know that q(ice)=-q(water) where q(ice) is equal to the enthalpy of the phase change of ice (q=n*deltaH(fus)) and the enthalpy of the unknown temperature change (q=50.0*4.184*(Tf-0)). q(water) is equal to the e...

Laura Gong 3H

For this question you need to know that for an ideal gas Cp(specific heat at constant pressure) = (5/2) R and at constant volume is Cv = (3/2) R where R is equal to 8.312 J*K-1*mol-1.

You can find these values on the constant and formulas sheet.
Hope this helps!

Laura Gong 3H

Fusion (melting) occurs when a solid becomes liquid. In order to make that transition, intermolecular bonds between the substance need to be broken. Breaking bonds is an endothermic process that takes in heat, so enthalpy is positive. Freezing occurs when a liquid becomes a solid. In order to make t...

Laura Gong 3H

Relative heat capacities can give us an idea of how well the substance can act as an insulator. The greater the value of C, the better it is at insulating heat. Greater heat capacities may also point to greater molecular complexity, because there are more atoms and bonds to store energy. These are f...

Laura Gong 3H

It just means that the most stable form (its standard state) of a pure liquid or solid is liquid or solid.

Laura Gong 3H

Heat capacity is just the amount of heat required to raise of an object by 1C. It does not specify the amount of the object. The units are usually kJ*C-1 or kJ*K-1. Specific heat capacity is the heat required to raise the temperature of 1 gram of a substance by 1C. Molar heat capacity is the heat re...

Laura Gong 3H

By definition, the standard enthalpy of formation of an element in its most stable form is 0. This could include the diatomic molecules, H2, N2, O2, F2, Cl2, Br2, and I2 and transition metals in their solid form, and C in graphite form.

Laura Gong 3H

In addition to what was said above, exothermic reactions tend to make the surroundings warm as it gives off heat, while endothermic reactions tend to make the surrounds cool as it absorbs heat.

Laura Gong 3H

I think we will use Hess's Law solve for the total enthalpy of a reaction. It proves that enthalpy is a state function. (It can be added or subtracted easily because it is not dependent on the reaction's pathway.)

Laura Gong 3H

Knowing the Ka or Kb can help you solve for H+ or OH- concentrations (using ICE tables) that can then help you solve for pH or pOH.

Laura Gong 3H

To solve for the percentage of PCl5 decomposed, I found the percentage of PCl5 remaining and divided it by the initial amount of PCl5. Once I found that percentage, I subtracted that value from 1 to get the percentage of PCl5 decomposed.

Laura Gong 3H

I haven't done this question yet, but since you you know the balanced equation and the partial pressures of each species in the reaction at equilibrium, I would write out the K expression for the reaction and plug in the values of their partial pressures at equilibrium.
Kp= P(B)*P(C)^2/P(A)^2

Laura Gong 3H

If a reaction "sits" toward the product side, it implies that K is large. If a reaction "sits" toward the reactant side, it implies that K is small (less than 1). The word "shift" is used when the reaction is not at equilibrium or when equilibrium is disturbed (Le Chatl...

Laura Gong 3H

When Q=K, the reaction is at equilibrium; neither the product or reactant side is favored.

Laura Gong 3H

In this question, you will have to set up an ICE table. [H2]=0.400mol/3.00L=.133mol/L and [I2]=1.60mol/3.00L=.533 mol/L If 60.0% of hydrogen gas reacted than X (change in molarity of reactants and products) will be equal to .133mol/L * (.60)=0.08 From there you can calculate the equilibrium concentr...

Laura Gong 3H

Pressure and concentration are related by the ideal gas law: PV=nRT. When you rearrange the equation, P=(n/V)RT where (n/V) is equal to concentration (mol/L).
When you increase pressure by decreasing pressure, the value of V in the denominator decreases, thereby increasing the concentration.

Laura Gong 3H

The quadratic formula is used most commonly in problems where changes to the initial molarity of the reactant are significant and usually when K is greater than 10^-3. When we get to acid and base equilibria, some K values will be so small that we will be able to use the assumption rule, which allow...

Laura Gong 3H

Catalysts are not consumed in a chemical reaction, meaning that they appear in the reactant and product side, so though you could include it into your chemical reaction it is redundant and usually not.

Laura Gong 3H

You can calculate equilibrium concentrations if you know the value of K and by using ICE tables.

Laura Gong 3H

When the question asks you to write the Kc expression, it is just looking for the form, Kc=[P]/[R].
The equation K=KcRT^delta(n) is the equation used to convert Kc to Kp (or the equilibrium constant using partial pressures).
For some reason, it appears the textbook does not include the subscript p.

Laura Gong 3H

I think you can either Kc or Kp as long as you follow the conventions for either. So if you were to write Kc expressions, remembering to put the brackets symbolizing concentration around the products and reactants or for Kp expressions, using P (representing partial pressure) and the subscript of ei...

Laura Gong 3H

For acids we can also look at the strength/length of a bond between H-A as well as the characteristics of oxoacids which depend on the electronegativity of the atoms in an acid.

Laura Gong 3H

No, I believe they are asking you to specify which species were involved in the proton transfer. For example NH4+Cl- in water, the NH4+ (an acid) loses the proton and water gains the proton to become [H3O+]. NH4+ would be the acid, the resulting NH3 would be the conjugate base. H2O would be the base...

Laura Gong 3H

I believe it's in the acids and bases outline, so it should be important to know.

Laura Gong 3H

A pi bond can have delocalized electrons if the molecule has other resonant structures.

Laura Gong 3H

An easy way that usually helps me remember if the intermolecular forces are dipole or induced dipole is that:
Dipole moments occur with polar molecules where induced dipole occur with non polar molecules.

Laura Gong 3H

Lewis acids are electron pair acceptors and Lewis bases are electron pair donors.
Bronsted Lowry acids are proton donors and Bronsted Lowry bases are proton acceptors.

Laura Gong 3H

It doesn't say in Outline 3, but I think it's best if you familiarize yourself with all VSEPR formulas and the corresponding molecular shapes. There are numerous charts you can find online for the VSEPR model. I've attached one here: http://web.gccaz.edu/~kimld88531/vsepr%20handout.pdf Hope this hel...

Laura Gong 3H

For drawing the lewis structure of a molecule: count the number of valence electrons of each of the atoms and then arrange the molecules so that Sb is the central atom. From there fill in the octets and make sure there are the same number of valence electrons you counted from before. Check formal ch...

Laura Gong 3H

I believe that we will most frequently encounter sp3, sp2, and sp hybridization, but in Monday's lecture, Dr. Lavelle also mentioned that sp3d and sp3d2 hybridized orbitals exist when the central atom has an expanded octet.

Laura Gong 3H

Sigma bonds have their electron density along the bond axis and cylindrical in shape which allow for rotation. Pi bonds have their electron density above and below the bond axis. Their orbitals overlap side by side which makes them rigid, trying to rotate that bond would result in breaking that bond.

Laura Gong 3H

I believe Dr. Lavelle mentioned that they are experimentally measured.

Laura Gong 3H

One possible reason is when there are nonbonding electron pairs or lone pairs that occupy more space due to electron to electron repulsion. The extra space they occupy would push the bonded atoms to be closer and decrease the bond angles between the two atoms.

Laura Gong 3H

I think one example that showcases how high electron densities repel each other is looking at molecules that have a tetrahedral shape: molecules with 4 bonded pairs, 3 bonded pairs and 1 lone pair or 2 bonded pairs and 2 lone pairs. For instance, the bond angles for CH4 is 109.5 where as for NH3 it ...

Laura Gong 3H

The neutral electron configuration of Cd is [Kr]4d105s2.
When the question asks you for the +2 cation of the element, you just have to remove the 2 valence electrons which will get you: [Kr]4d10.

Laura Gong 3H

delta X (uncertainty in position) would be 1% times the radius of the atom multiplied by two (which would give you the diameter of the atom).

Laura Gong 3H

One easy way too tell if a molecule is non polar is if the atoms surrounding the central atom are all the same. For example CH4 is non polar.
Granted if there is a lone pair on the central atom and the atoms are the same around it, it will actually polar. For example, SO2.

Laura Gong 3H

There should be double bonds from S to O since this gives us the lowest formal charges. Remember, S can have an expanded octet, so S would have have a double bond with each of the Os and one lone pair and each of the Os would have two lone pairs to fill their octets.

Laura Gong 3H

Elements in the third row and below. Some common ones are P, S, and Cl.

Laura Gong 3H

What works for me is: Formal Charge = Valence Electrons - (Dots + Dashes). Dots representing number of electrons that are unbounded and dashes representing the number of bonds.

Laura Gong 3H

Notable hypervalent (expanded octets) atoms are usually elements below row 2, especially S, P, Cl, Br, I, and Xe. This is because the electrons can occupy the 3d orbital in bonding.

On the other hand, notable octet deficient atoms are usually in column 3A (B, Al, Ga, etc.).

Laura Gong 3H

Most molecules or ions that have resonant structures usually have more than one oxygen. Some examples include SO42- and NO3- which we did in class and CO32-.

Laura Gong 3H

The most stable lewis structure usually has the least number of formal charges and when the negative formal charges are on the most electronegative atom in the molecule. Hope this helps!

Laura Gong 3H

No, there isn't a difference. I think lines are easier to read in a lewis drawing and make it more easy to understand that there is a bond, that way the dots can represent nonbonding electrons more easily.

Laura Gong 3H

Delocalized electrons are present when a molecule can do resonance, meaning the electrons are equally distributed across the bonds of a molecule even though the lewis drawing may indicate otherwise. (This is a limitation of drawing lewis structures.) The electron distribution will be the same across...

Laura Gong 3H

Calculating the formal charges of each atom can help you determine the best lewis structure for a particular molecule and like Elias said, confirm the overall charge of the atom.

Laura Gong 3H

F cannot make double bonds because it has 7 valence electrons and only has room to make one single bond to form an octet.
It is more like that the nitrogen and oxygen will form a double bond.

Laura Gong 3H

The reason is because when those elements are ionized, the electrostatic attraction experienced between the electrons and the nucleus change. Chlorine has the greatest amount of protons compared to S and P which means that when it loses an electron, it will pull the remaining electrons in even tight...

Laura Gong 3H

Shielding causes electron to electron repulsion, which increases the value of r which decreases the electrostatic attraction. So electrons in the p orbital compared to the s orbital experience less electrostatic attraction but their energy is not getting close to zero. I find that the electrostatic ...

Laura Gong 3H

Today we covered writing electron configurations as well as Pauli Exclusion Principle, Hund's Rule, and the Aufbau Principle. We practice writing the electron configurations for elements Carbon, Silicon, Scandium. We need to know the s-Block, p-Block, and 1st row of the d-Block and that after 4s sta...

Laura Gong 3H

Sometimes the question with give you a plus/minus value for deltaX (say +/-5) which means you have to double that value (deltaX=10) before plugging it into the equation.

Laura Gong 3H

The probability density is a measure of the likelihood (probability) that a particle will be found at a particular location in space. In this case, where you would likely find an electron in the electron cloud.

Laura Gong 3H

+1/2 represents spin up and -1/2 represents spin down of the electrons. The numbers basically distinguish how the electron is spinning.

Laura Gong 3H

Each unique atom and molecule, I believe, absorb and emit only certain wavelengths of light, that's why spectroscopy is useful in detecting what a substance could be; each element has a specific fingerprint. The actual line that shows up is spectrum emission.

Laura Gong 3H

How do you calculate deltaV from this problem? You are caught in a radar trap and hope to show that the speed measured by the radar gun is in error due to the Heisenberg uncertainty principle. If you assume that the uncertainty in your position was +/- 5 m when your speed was measured, and that the ...

Laura Gong 3H

The reason why we can't determine the precise value of position and momentum is because when the light (photon) is shown onto an electron, it will alter the course of the path the electron is traveling on. The light scattered from the electron will affect the electron's momentum and position because...

Laura Gong 3H

The longer wavelength of light has a lower frequency that does not carry enough energy to eject one electron, even when you increase the intensity (amplitude) of the wave. That is what they discovered in the photoelectric experiment, pointing to the fact that light also has properties of particles. ...

Laura Gong 3H

It's also important to note that increasing the intensity (or number of photons) of a particular wavelength to increase the number of electrons ejected a particular metal only works when the frequency of the wavelength is already high enough to eject electrons. Otherwise, increasing the intensity of...

Laura Gong 3H

Quantized and discrete are intended to have the same definition here. It just means that the variables in a system has a only a number of distinct values it can be. For example, when we talk about principle energy levels, n, n can only equal to 1, 2, 3 or 4--never 1.2 or 2.4234, etc.

Laura Gong 3H

To answer your second question first, I noticed that for the pre-assessment it doesn't tell you how many you got correct/wrong. However, after submitting the post-assessment, they do tell you how many you got correct/wrong. For #14, you need to use the idea of conservation of mass to find the mass o...

Laura Gong 3H

To answer the second part of your question with respect to (aq), knowing whether or not a substance is aqueous in water will also tell you whether or not the compound dissociates, or separates into ions when dissolved in water. This can be important for when you're writing net ionic equations and on...

Laura Gong 3H

The answer I got was the answer in the back of the textbook (aside from the mistake of mol C instead of mol N.) Since you originally have 1.0L of 0.20 M of the fertilizer solution, by adding 3.0L of water, your new total volume of solution is 4.0L. The new concentration of fertilizer would be .20mol...

Laura Gong 3H

I think the purpose of this question is based more on the concepts of dilution rather than applying the concepts. To find the concentration of a solution, I would still use mol/L where L is the total volume of the solution. So here, since the question tells you that the solution is doubled each time...

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