CHEMISTRY COMMUNITY

Tarika Gujral 1K

Unless the problem specifies that it is average rate, in general, rate is instantaneous.

Tarika Gujral 1K

It would be in terms of the compound that is being consumed. For example,

A —> B + C
R = k[A]

Tarika Gujral 1K

Ions for both oxidation and reduction are placed closest to the salt bridge
generally in the order reactants, products

Tarika Gujral 1K

Order is essential to calculate kr, half life, change in concentration, or time needed to get to a particular concentration. There are different equations for each order. You’ll either be given order of reaction, or if you are given elementary reactions (and need to determine order of overall reacti...

Tarika Gujral 1K

Both reactions are important in determining overall reaction. However, pertaining to rate law, the slow step (AKA the rate determining step) is the one that is used.

Tarika Gujral 1K

For precipitates in general the form is: REDUCTION: Precipitate + e — ions OXIDATION: Ions — Precipitate One ion will not change charge, (for AgCl) Cl- retains an oxidation number of -1, so the other ion is the one that is undergoing oxidation or reduction (the one that is going from solid to +1) Th...

Tarika Gujral 1K

First balance O with H2O.
Then balance H — add h2o equal to the number of hydrogens and for every h2o, add an oh- on opposite side

So if you have 4 extra hydrogens on one side, add four h2o on opposite side to balance, and add 4 oh- on the original side

Tarika Gujral 1K

Unless the reaction specifically states for 1 mole of formation/combustion,
to my understanding, G is either in J or kJ

Tarika Gujral 1K

1) With gaseous and nonconducting solid compounds, is the order Inert|Gas/solid|Chg || Chg|Gas/solid|Inert? Or does it follow the order of reactants to products? Inert|Ox Reactant|Ox Product || Red Reactant|Red Product|Inert 2) With a positive Ecell, reduction is always on the right. Is this order r...

Tarika Gujral 1K

Reduction occurs at the cathode. For reduction to occur, electrons must be present at the cathode for the reaction to “pick up” electrons.

Oxidation occurs at the anode. Oxidation thus releases electrons at the anode, which are then transported to cathode.

Tarika Gujral 1K

At the anode, oxidation occurs, which leads to the buildup of positively charged ions. At the cathode, reduction occurs, which leads to the buildup of negatively charged ions. As Lorena said, the buildup of these charges will eventually stop e- flow from anode to cathode. To maintain this flow, the ...

Tarika Gujral 1K

Mn is determined by the oxidation state of oxygen as well as the overall charge of the compound.
Oxygen = -2
Because there are 4 Oxygens and overall charge is -1, we need a +7 to balance it out.
Thus, Mn is +7

Tarika Gujral 1K

That also means that you must use the Cv value for ideal gases

MONOATOMIC: 3/2*R
LINEAR: 5/2*R
NONLINEAR: 7/2*R

Tarika Gujral 1K

When calculating change in entropy for systems that have a change in both volume and temperature: S = nRln(V2/V1) + nCvln(T2/T1) Because entropy is a state function: you can add change in volume to change in temperature. For change in temperature, you use Cv. Cv and Cp can also be found for linear a...

Tarika Gujral 1K

^^ Adding onto Faith’s answer:

For reversible, the question will also state that system is isothermal.

Also, Ssys is the same for irreversible and reversible work.
The only difference is Ssurr.

Tarika Gujral 1K

Heat capacity (neither specific nor molar) is used if no mass/moles are given.

An example is using a calorimeter calibration.
q = Ccal * delta T
Then plug in Ccal to determine q for a different reaction.

Tarika Gujral 1K

You can also use bond enthalpies to determine delta H:
Delta H = H bonds broken (reactants - H bonds formed (products)

But this is not always accurate, as it uses average enthalpy values for the bonds.

Tarika Gujral 1K

8.314 J/K*mol

.082 L*atm/K*mol

^^ Like Josephine said, it depends on the units in the question.

Tarika Gujral 1K

Not necessarily: Water SHC = 4.184 Benzene SHC = 1.74 Benzene has more atoms than water, yet its SHC is less than water. SHC depends on the types of bonds, not necessarily the amount of atoms. Molar heat capacity is dependant on amount of each substance, but again, the types of bonds mostly determin...

Tarika Gujral 1K

^^ Like Gwyn said, heat is not only needed to raise the temperature of the substance, but it is needed to convert it from solid to liquid and liquid to gas. Heat is applied in order to break the intermolecular forces between molecules. Since more heat is required to completely sever bonds (liquid to...

Tarika Gujral 1K

A perfect system would involve no loss of energy to surroundings. This by definition is an isolated system, which though exists in theory, there is no completely isolated system in reality.

Tarika Gujral 1K

Equilibrium constant would be equal to
1/[r] — if concentrations are given or reactants are aqeous
1/(Pr) — if reactants are gases

Tarika Gujral 1K

Different units of measurement
Thus entails use of different value for R constant.

Tarika Gujral 1K

The 5% approximation technique can be used for any K calculation, provided

K < 10-3 — Very little product formed, R-x = R
K > 103 — Very little reactant remaining, P+x = P

Tarika Gujral 1K

Small Ka = high pKa = weak acid
Big Ka = low pKa = strong acid

Tarika Gujral 1K

I believe a substance can be leveled by a solvent.

So in the case of a strong acid, if it is dissolved with a solvent that is a strong base, it is “leveled off.”

Both solute and solvent become more neutral

Tarika Gujral 1K

The 5% approximation can be used for values of K that are very large or very small.

If K is large — P+x = P
If K is small — R-x = R

But the verification must be computed after calculating equilibrium values.

Tarika Gujral 1K

The change in concentration of pure liquids and solids are insufficient — they essentially remain constant.
Thus, they are not included in equilibrium calculations.

Tarika Gujral 1K

Pressure and volume are inversely related, according to Boyle’s law.

Thus increasing pressure implies a decrease in volume.
Decreasing volume causes reaction to move to side with fewer moles of gas.
So increasing pressure causes reaction to move to side with fewer moles of gas.

Tarika Gujral 1K

Concentration is n (mol) / V (L)

Given the ideal gas law: PV = nRT
We write P = (n/V)RT
Thus P = (Conc)RT

Then to determine concentration, we divide P by RT
And get P/RT = Conc

Tarika Gujral 1K

KOH + HC2H3O2 >> KC2H3O2 + H2O

Net ionic: OH- + HC2H3O2 >> H2O + C2H3O2-

Acetic acid donates a proton, which makes the conjugate base C2H3O2-
KOH is a base, which means it accepts a proton to form water,

Because KOH is a strong base and acetic acid is a weak acid: the salt is basic.

Tarika Gujral 1K

Electronegativity follows a diagonal trend: increasing towards the upper right: however, period is more important than group. This is because a lower period is associated with fewer energy shells, and thus a higher Zeff. Higher Zeff implies greater electronegativity: because the stronger the nuclear...

Tarika Gujral 1K

Bronsted acids are more specific than Lewis acids. Bronsted acids are compounds that can donate a proton, where Lewis acids are electron pair acceptors. So all Bronsted acids are Lewis acids, but not all Lewis acids are Bronsted acids.

Tarika Gujral 1K

One way of determining charge of complex is through the presence of anions or cations outside []. Basically, the overall charge of the complex equals the charge on the anion or cation present.

Tarika Gujral 1K

From my understanding, we do not need to do calculations involving weak acids or bases. In general, however, the value of the constant remains the same: the concentrations of the conjugate acids and bases will decrease. This is because for weak acids and bases, there is incomplete disassociation, he...

Tarika Gujral 1K

Sigma bonds refer to overlap of s orbitals: since there is only one s orbital, there can only be one sigma bond. Pi bonds, on the other hand, refer to overlap of p orbitals. Since there are multiple p orbitals, multiple pi bonds can form.

Tarika Gujral 1K

Because the two chlorines are closer together on the first molecule, they create a strong negative pull. In the second molecule, they are a bit farther apart, and because of this the negative pull created by the individual chlorines partially cancel each other, creating a weaker overall pull.

Tarika Gujral 1K

Hybridization depends on regions of electron density. While VSEPR does help visualize these regions, it is not necessary to determine hybridization.

Tarika Gujral 1K

A bond is only formed if it is energetically favorable, meaning that electrons in a bond have a lower energy then free electrons. Thus, it is more energetically favorable to fill 1 d orbital and have all electrons in a bond, as opposed to having electrons in a free orbital.

Tarika Gujral 1K

Sigma bonds = overlap of two s orbitals, overlap of s and one lobe of p, overlap of 2 p orbitals (one lobe only)
Pi bonds = both lobes of p orbitals overlap — atoms cannot rotate

Single bonds = sigma bond
Double bond = sigma and pi bond
Triple bond = sigma and 2 pi bonds

Tarika Gujral 1K

By instantaneous interactions, I assume you are referring to induced dipole interactions. Polarazability (the amount an electron field can be distorted) is directly proportional to atomic radius: the larger the radius, the more distortion, Greater polarizability allows for stronger induced dipole in...

Tarika Gujral 1K

Electron promotion allows for bond formation. In most cases, forming bonds equates a lower energy state. Lower energy states are most favorable: Pauli Exclusion Principle is less favorable.

Tarika Gujral 1K

If there is an equivalent Lewis structure that can be formed (overall formal charge value remains the same)
simply by exchanging positions of atoms — then a molecule has resonance.

Tarika Gujral 1K

In terms of bond strength: type of bond is more important than size of molecule A larger radius, as you said, implies greater electron distortion Greater distortion of electrons means that the atom is more easily polarizable: will more easily form a dipole Since LDF forces are based on the formation...

Tarika Gujral 1K

Hydrogen bonding and Van der Waal forces are both intermolecular forces. VDW forces are present in all molecules H-bonding is typically characterized by H-NOF bonds From my understanding, because VDW forces is a bond between induced dipoles (which arise from a “temporary” dipole formation), hydrogen...

Tarika Gujral 1K

Taking antioxidants (vitamins) can help offset some of the damage.

Tarika Gujral 1K

Alkali — (no d electrons) s1
Grp 15 — if period 3+: (n-1)d10ns2np3
Grp 5 — (n-1)d3ns2
Coinage metals — acheive greater stability with a partially or completely filled d subshell
(n-1)d5ns1 OR (n-1)d10ns1

n = principal quantum number

Tarika Gujral 1K

Delocalized electrons are electrons spread over multiple atoms: they do not belong to a single atom. This usually occurs in double bonds or triple bonds.

Tarika Gujral 1K

It depends on information given. If given kinetic energy and energy/wavelength/frequency of incoming light, you can just subtract the energy of the incoming light from the value of kinetic energy to obtain the work function. Another way is if you are given the value of energy of photon at 0KE (maxim...

Tarika Gujral 1K

n = principle energy level (shell), l is angular momentum (subshell), and ml = magnetic quantum (orbital).
The highest value of l is equal n-1
Values of l correspond to subshells: 0-s, 1-p, 2-d, 3-f

Tarika Gujral 1K

l is angular momentum quantum number.
It is the number of subshells per principal energy level
l = n-1

ml is magnetic quantum number, and refers to the number of orbitals per subshell
ml = 2l + 1

ms is spin quantum number, and refers to spin of electron. It is either positive or negative one half

Tarika Gujral 1K

Atoms prefer to be in the lowest energy state possible. A half-filled or fully-filled d-subshell has a lower energy, which is why electron configurations that should be written as 3d4-4s2 or 3d9-4s2 are instead written 3d54s1 and 3d104s1

Tarika Gujral 1K

Nuclear charge refers to the strength of nuclear pull on electrons of an atom. However, the presence of more electrons creates shielding, which lowers the nuclear pull. Z-eff refers to the value of nuclear charge - shielding.

Tarika Gujral 1K

I believe frequencies in absorption and emission spectra would be different. For example, if red light is absorbed, green light would be given off, and red and green have different frequencies.

Tarika Gujral 1K

Since other atoms have more than one electron, determining energy would depend on both distance from nucleus and electron-electron repulsion.

Tarika Gujral 1K

Is there a way of mathematically calculating intensity/amplitude via the photoelectric effect equation:
KE electron = Energy of photon - Threshold energy?

Tarika Gujral 1K

More information would need to be provided, unless the problem specifies kinetic energy is 0 (i.e. longest wavelength). In this case, set threshold energy equal to energy of photon (velocity does not need to be calculated).

Tarika Gujral 1K

More information would need to be provided, unless the problem specifies kinetic energy is 0 (i.e. longest wavelength). In this case, set threshold energy equal to energy of photon (velocity does not need to be calculated).

Tarika Gujral 1K

When we have a repeating decimal number, such as 1/3, do we simply follow “normal” (lowest decimal point value for addition/subtraction and lowest number of sig figs for multiplication/division)? Or are there special rules? Also, how does rounding work?

Tarika Gujral 1K

Technically, don’t molar mass and molecular weight refer to the same concept: the total weight (in grams) of the molecular formula?

Tarika Gujral 1K

Theoretically, doesn’t it also refer to mass percent composition of the molecule?

Tarika Gujral 1K

Does the empirical formula represent the relative number of atoms of a compound or the relative mass ratio of the atoms in a compound?

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