CHEMISTRY COMMUNITY

SVajragiri_1C

For the equation aA + bB -> cC + dD, where a,b,c,d are coefficients, the rate of absorption of A and the rate of formation of C are related as such:
(1/a)(d[A]/dt) = (1/c)(d[C]/dt)

SVajragiri_1C

You use Kelvin, because the unit for R in this equation has K in it.

SVajragiri_1C

Concentration cells have two cells where the same half-reactions occur, so when calculating the Ecell, the Ecells of each half-reaction would cancel each other out, since they are for the same reaction (except reversed).

SVajragiri_1C

Strong acids disassociate almost completely into hydronium ions, while weak acids only partially disassociate into hydronium ions. If the two acids are at the same concentration, the concentration of hydronium ions will be less for the weak acids. Since pH is the -log of the concentration of hydroni...

SVajragiri_1C

Degeneracy is exponentially related to microstates.

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The oxidizer equation is where the reaction breaks apart electrons from the reactant. The reduction equation adds electrons to the reactant.

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You don't include any reactant or product in the liquid of solid form when writing out the equation, including H2O.

SVajragiri_1C

Because electrode mass is always in excess, changing the mass doesn't do anything to cell potential.

SVajragiri_1C

As Ea increases, the reaction rate is more strongly dependent on the temperature, so with an increase in temperature, the rate will have a greater change than reactions with a lower Ea.

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Isochoric means constant volume throughout the process, where isometric means the measurements and dimensions stay constant throughout the process.

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Galvanic and voltaic cells are the same thing; they are spontaneous electrolytic cells.

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For a zero order reaction, the units for k is M/s. The general formula for units of k based on the order, where p is the order of the reaction, is M^(1-P)/s.

SVajragiri_1C

The general units for k is M^(1-p)/s, where p is the order number. So for 0 order, p=0, M/s. For 1st order, p=1, s^-1. For 2nd order, p=2, M^-1/s.

SVajragiri_1C

So first, you have to figure out which elements are being reduced and oxidized. Then write out the skeletal reactions for the oxidation and the reduction reactions. Then, balance the O's in the reaction by adding H2O. Then balance the H by adding H+ or OH- depending on if it is in acidic or basic so...

SVajragiri_1C

We get Test 2 grades back this week in discussion.

SVajragiri_1C

H is +1, O is -2. The sum of oxidation numbers is equal to the overall charge of the compound, so do some backwards calculations to figure out oxidation numbers of other compounds.

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Pt(s) is for when you only have a gaseous substance, or aqueous only.

SVajragiri_1C

The oxidizer gains electrons bc they reduce the other agent, and vice versa.

SVajragiri_1C

You have to use commas instead of | to separate the two phases.

SVajragiri_1C

Separate species are separated with a comma if they are in the same phase, and | is used for when they are in different phases.

SVajragiri_1C

n in the equation you are referring to is the number of moles of electrons that are transferred. If you balance the half-reactions, the amount of moles of electrons that are lost or gained is n. Some common oxidation rules: H is +1. O is -2. Ions' oxidation numbers are their charges. The sum of oxid...

SVajragiri_1C

If both species are decreasing in oxidation state then a functioning galvanic cell is not possible.
A cathode is the electrode where electrons are added (reduced).
An anode loses electrons (is oxidized).

SVajragiri_1C

When the cell potential is positive it means the forward reaction will be favored as it is spontaneous. If the cell potential is negative, then the reverse reaction is spontaneous and will be favored.

SVajragiri_1C

You add H+/OH- ions and H2O to balance out the hydrogens and oxygens in the half reactions. For acidic reactions you add the H+, and for basic reactions you add OH-.

SVajragiri_1C

Electrons only flow from anode(-) to cathode(+), which makes sense since electrons have a negative charge so it will move towards the cathode to try to balance out the charge.

SVajragiri_1C

If the standard reduction potential is positive, then the reduction is spontaneous.

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The equation represents the relationship between the equilibrium constant and the thermodynamic properties enthalpy, temperature, and entropy. This means that we can observe how K changes based on a change in temperature, enthalpy, or entropy.

SVajragiri_1C

When hydrogen is in a compound with elements that are less electronegative than it, like a cation or a metal, then its oxidation number will be -1.

SVajragiri_1C

The oxidation number of Group 1 elements is +1, it is +2 for Group 2 elements, halogens are -1 (in binary compounds). The oxidation number of H is usually +1. Using these facts combined with the rule that the sum of oxidation numbers of ions in a compound has to equal the total charge of that compou...

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The posts are checked after midnight every Sunday; so you have to submit 5 posts between Monday to the end of Sunday.

SVajragiri_1C

The pH is always calculated when the solution is at equilibrium, unless specifically said otherwise (but this doesn't happen). So yes, you can always calculate the H+ concentration from the given pH, but it will be the H+ concentration at equilibrium.

SVajragiri_1C

When G is negative, the reaction is spontaneous and thermodynamically stable, and if G is positive the reaction is non-spontaneous and thermodynamically unstable. You can calculate this using the equation G = H - TS.

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A reaction is thermodynamically stable when delta G (change in Gibbs free energy is less than 0). This usually means that delta H is negative and delta S is positive, but depending on the temperature of the reaction, it can be thermodynamically unstable or stable.

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The second law of thermodynamics is that the entropy (chaos) of the universe is always increasing.

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You can just memorize the charge for the basic elements like oxygen, nitrogen, carbon, hydrogen, etc. And the others are pretty similar to their ion charge, so just know that.

SVajragiri_1C

Entropy is not an intensive property; it is an extensive property and state function that depends on the mass and the current state of the substance.

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The midterm will be 6-8 PM, the locations are on the Chem 14B page.

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State functions are Enthalpy, Pressure, Volume, Temperature, density, and heat capacity, internal energy, Gibbs free energy, and entropy.

SVajragiri_1C

An extensive property is a property that changes depending on the mass of the substance involved, such as heat capacity. An intensive property is one that stays constant no matter the amount of substance, such as density or specific heat capacity.

SVajragiri_1C

Cv refers to the molar heat capacity of a gas at constant volume. Cp refers to the molar heat capacity of a gas at constant pressure. The two are different because in order to maintain the same pressure throughout a reaction the volume would have to be changing, and maintaining volume would require ...

SVajragiri_1C

The universe does not exchange matter or energy with anything surrounding it (as far as I know), which is why it fits the definition of an isolated system. I don't think it is a closed system because there isn't any surrounding to exchange energy with.

SVajragiri_1C

Work is equal to the pressure times the volume.

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Yes, it does matter if its a bomb calorimeter versus a regular calorimeter. A bomb calorimeter is an isolated system so you would have to solve accordingly. All other calorimeters are regular, and it doesn't matter otherwise.

SVajragiri_1C

Both are forms of heat capacity. Specific heat capacity is the amount of heat required to raise one gram of the substance by one degree Celsius/Kelvin. Molar heat capacity is the amount of heat required to raise one mole of substance by one degree Celsius/Kelvin. Both are intensive properties.

SVajragiri_1C

A closed system by definition goes cannot exchange matter with its surroundings. If the car is the system and the environment is the surrounding, then a car cannot be a closed system because it released exhaust (which is matter) into the environment.

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The different gas constants account for the different unit forms of pressure, volume, and temperature. Basically, you have to choose the R value that matches the units provided to you in the problem. Or you can just figure out which R, when used in calculations, will cause all the units to cancel out.

SVajragiri_1C

An intensive property is a characteristic of a substance that does not change no matter the amount or quantity of the substance. An example would be density or specific heat capacity. An extensive property is a characteristic of a substance that does change based on the amount or mass of the substan...

SVajragiri_1C

An isolated system doesn't exchange mass or energy/heat with the surroundings, like an insulated thermos with the lid screwed on. A closed system doesn't exchange matter with the surroundings; but it can exchange energy. So for example heating liquids in a pot with the lid closed is a closed system ...

SVajragiri_1C

Forming bonds is usually is the most stable form of the molecules; which is why energy is released when the bonds form. However I'm pretty sure there are a few very rare cases when bond formation is more unstable, in which case it would be endothermic.

SVajragiri_1C

Heat capacity is the amount of heat needed to raise a mass of a substance by one degree Celsius/Kelvin. Specific heat is a variation of heat capacity in that specific heat is the amount of heat needed to raise one unit of mass of a substance by one degree Celsius/Kelvin. Specific heat remains the sa...

SVajragiri_1C

By definition an isolated system does not exchange matter or energy/heat with its surroundings. Most systems cannot be perfectly isolated, but can come very close. An insulated thermos with the lid screwed on tightly is an example of an isolated system, because the insulated prevents almost no heat ...

SVajragiri_1C

You can use this equation to find partial pressures of the components of the reaction (P) if you know the volume, temperature and molar concentration. Then you could find the equilibrium constant Kp by plugging in the partial pressures into the formula for Kp.

SVajragiri_1C

Q and K are solved in the same way, however, K is the equilibrium constant by definition, while Q is the reaction quotient which can be found at any point in the reaction timeline, and based on whether Q is less than, greater than, or equal to K predictions about the reactions future can be made.

SVajragiri_1C

Weak acids disassociate into a less concentrated solution of hydronium ions in comparison to strong acids. Since pH is the negative log of hydronium ion concentration; weak acids would have higher pH values (negative log is basically the logarithm of 1/[hydronium ion])

SVajragiri_1C

Test 1 will be on chemical equilibrium and acids and bases. Everything on outlines 1 and 2 will be covered.

SVajragiri_1C

You simply need to multiple the K values for the two equations; if by chance one of the equations has to by multiples by a factor, take K to the power of that factor and continue normally.

SVajragiri_1C

The rule is to include all aqueous solutions and gases, just like you would to calculate K.

SVajragiri_1C

There is no unit for K, it is a constant for equilibrium. You can prove this because when you solve for K, all the units cancel out.

SVajragiri_1C

Concentration does have a unit (moles/liter). But, equilibrium constants do not have units.

SVajragiri_1C

Both are equilibrium ocnstants, but Kc is calculated from concentrations, and Kp is calculated from partial pressures.

SVajragiri_1C

K is a constant because when calculating it all the units cancel out, so there is no unit for it.

SVajragiri_1C

R is the ideal gas constant, 8.3145 J*mol^-1*K^-1

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When the complex is an anion, you use the latin prefix (only if there is one) for the metal, and end it in -ate.

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Yes the two terms are used interchangeably.

SVajragiri_1C

Amphiprotic means that the molecule can either accept or donate a proton in a reaction.
Amphoteric means that the molecule can react as either an acid or base in a reaction.
Normally, there is overlap.

SVajragiri_1C

A molecule is amphoteric if it can react as an acid or a base in an acid-base reaction.

SVajragiri_1C

The Lewis structure has 8 electrons, and when drawing the Lewis structure there are three bonds to the oxygen, with one lone pair. So there are 4 electron domains, so the molecular geometry is tetrahedral. But one electron domain is a lone pair, so the actual shape is trigonal pyramidal.

SVajragiri_1C

Delta x signifies the change in position of the electron.

SVajragiri_1C

By definition the pH is the -log of the concentration of hydronium atoms. It is simply a mathematical representation of the hydronium ion concentration.
The pOH is the -log of the concentration of hydroxide ions.

SVajragiri_1C

You use platinate instead of platinum because the charge of the overall complex is negative, so its an anion. The rule is that when the charge of the complex is an ion, you end the metal with -ate.

SVajragiri_1C

Sigma bonds are stronger than pi bonds because if you look at the 3D diagram of the orbitals, the heads of the two p orbitals in a sigma bond overlap, where as a pi bond is simply the attraction of two parallel p orbitals. This overlap is why sigma bonds are stronger.

SVajragiri_1C

A conjugate acid of a base is basically the base attached to a proton (hydrogen ion). Likewise, the conjugate base of an acid is the acid without a proton (hydrogen ion). It is basically a reaction of the addition/removal of a hydrogen ion, and the reactant and product are conjugates of each other.

SVajragiri_1C

Strong acids dissociate far more than weak acids do, which means that they release more hydrogen ions into the solution; this makes the solution more pH, since pH by definition is related to the inverse of the measure of hydrogen ions (the more hydrogen ions there are, the lower the pH is).

SVajragiri_1C

When writing the formulas for coordination compounds, you should start with the complex cation and put that in brackets, then follow it with the anion. Putting it the other way, while it may not be wrong, is abnormal so you should just avoid writing the formula that way.

SVajragiri_1C

The most general difference is that an acid gives off hydrogen ions in water, whereas bases give of hydroxide ions in water. If you are talking about Lewis acids and bases, however, then the difference is that Lewis acids accept electrons from other molecules, while Lewis bases donate electrons to o...

SVajragiri_1C

No, sigma and pi bonds do not influence a molecule's shape (in other words, the type of bond doesn't affect the shape).

SVajragiri_1C

Yes we will need to know how to determine polarity of all kinds of molecules, including the example you gave. That would be polar because of the presence of oxygen bonds and a non-symmetrical arrangement.

SVajragiri_1C

When you draw the Lewis structure, a signle bond has one sigma bond, a double bond has one sigma and one pi bond, and a triple bond has one sigma and two pi bonds.

SVajragiri_1C

We will get them in discussion next week most likely.

SVajragiri_1C

H3O+ is tetrahedral because when drawing the lewis structure, there are a total of 8 electrons, and so oxygen should have 3 bonds (to hydrogens) and then one lone pair, which means there are four regions of electron density about the central atom, which means the molecular geometry is tetrahedral, b...

SVajragiri_1C

To determine shape all you need to know is the number of lone pairs and the number of bonds about the central atom, so if you draw the Lewis structure right then that's all you need to know.

SVajragiri_1C

Like other elements with n=3 or higher, xenon has an empty d-orbital, specifically the 5d orbital, which can fill up with the extra electrons.

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Resonance structures are the multiple Lewis structures a single molecule can have.

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For example, in the molecule CO2, the bond C-O itself is polar, but since the molecule CO2 is linear (O-C-O), the polarity of each bond cancels each other out due to the symmetric shape of the molecule. This concepts applies to most types of molecules.

SVajragiri_1C

Yes, the final exam includes everything we've learned this quarter.

SVajragiri_1C

The first part of Monday's lecture will be the newest information on the test. Other than that its everything since the midterm.

SVajragiri_1C

A radical is considered a region of electron density and affects bond length as other lone electron pairs do.

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The only requirement is for the sum of the formal charges to add up to the overall charge.

SVajragiri_1C

You can underline the formal charges or something to distinguish them from the atom and the electron dots.

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It is only allowed when the the central atom with the expanded octet is in the 3rd row of the periodic table or below, because only these elements have a d-orbital.

SVajragiri_1C

No, fluorine has the highest electronegativity in all the periodic table; the noble gases have a complete octet so they would not want another electron.

SVajragiri_1C

I don't think it will be pushed back.

SVajragiri_1C

It's because more electrons are involved in the bond so the pull is stronger bringing in the atoms closer together.

SVajragiri_1C

A dipole moment is the measure of polar covalence of a bond in molecule.

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You only have to check the formal charge if they ask you to, other than that you do it just to verify your answer.

SVajragiri_1C

It will always be plus or minus 1/2, and there's no specific way to find out the answer, they normally dont ask you to determine it.

SVajragiri_1C

Normally ionic bonds happen between elements far from each other on the periodic table, with a metal and nonmetal. Covalent bonds are everything else

SVajragiri_1C

Just make sure the formal charges are as close to 0 as possible.

SVajragiri_1C

If its a little hard to find practice problems, I would replace numbers of the problems and redo the problem, and just like alter the data a little bit.

SVajragiri_1C

First convert the 5.15 ounces to grams using the conversion factor that is provided. Then you have to convert the 92 mph to meters per second by using the miles to meters conversion factor and the hours to minutes to seconds conversion factors (you might have to look this up online). Then plug the d...

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