CHEMISTRY COMMUNITY

Daria Azizad 1K

Since 14B acids and bases builds upon info from the 14a section, I think it would be useful to review it if necessary.

Daria Azizad 1K

I think based on the information you are given. If it isn't as standard temp, use g= delta h - t delta s.

Daria Azizad 1K

We can predict a potential pathway, but not verify any elementary steps as being the correct ones.

Daria Azizad 1K

The reverse reaction will be. Since concentration of a reactant decreases as a rxn progresses, 1/[R] will increase.

Daria Azizad 1K

The angular dependence is taken into account by the pre-exponential factor, A, which you can think of as the likelihood/probability of a rxn happening based on a collision. So when A is large, k is larger, and when A is smaller, k is smaller because k and A are directly related thru the Arrhenius eqn.

Daria Azizad 1K

The relationship btwn K and the constants is K= k/k', which means that when k is high, the rxn favors the products and when k' is high, the rxn favors the reactants.

Daria Azizad 1K

Thermodynamic stability can be identified by looking at delta G. Something stable will be in its lowest energy form and will therefore be unlikely to react.

Daria Azizad 1K

They are based on the reaction with the standard hydrogen electrode.

Daria Azizad 1K

It will decrease the concentration. To find out how this affects cell potential, you can plug numbers into E=-RT/nF lnQ with alterations to Q. For instance, if the cathode's concentration decreases, cell potential will increase.

Daria Azizad 1K

They are in the same solution when they are all at either the anode or cathode. Commas denote same side and state. The straight line refers to different phases.

Daria Azizad 1K

If you increase the mass of electrodes the battery will have a longer lifetime. Cell potential will not change

Daria Azizad 1K

Au (s) is the electrode. Even though it is submerged in solution, it has not dissociated and is therefore is solid.

Daria Azizad 1K

Based on Q in the Nernst equation. If [P] > [R] then Ecell is negative. If [P] < [R] then Ecell is positive

Daria Azizad 1K

Balance the electrons in the oxidation reaction because the stoichiometric coefficient applies to the # of e- as well

Daria Azizad 1K

An electrolyte is a salt like KOH or NaCl. It completely ionizes in solution

Daria Azizad 1K

Yeah I was a bit confused about how the oxidation numbers don't change, but it can be broken down to reduction and oxidation half reactions: reduction: 4e- + O2 + 2H2O --> 4OH- oxidation: 2H2O --> 4H+ + O2 + 2e- How do we know that O2 is involved? Like why is it not Red: 2H+ + 2e- -> H2 Oxid: 2OH- ...

Daria Azizad 1K

I believe we will be given that information.

Daria Azizad 1K

Platinum is inert and won't interfere w the redox rxn. Other inert materials could be used as well, such as graphite.

Daria Azizad 1K

Which eqn are you referring to? N is the number of moles, not R.

Daria Azizad 1K

all solutes present at 1 mol/L and all gases at 1 bar

Daria Azizad 1K

Yes, because its positive value means that delta G will be negative, therefore the rxn is spontaneous. If the standard potential is negative, that means the reverse rxn is spontaneous.

Daria Azizad 1K

Elements in Groups 1, 2, 6, and 7 generally will carry the same oxidation state as the charge of the cation/anion they form. Therefore, assigning their oxidation states first allows us to find the oxidation state of an unknown oxidation state. Also, knowing the charges of polyatomic cations and anio...

Daria Azizad 1K

A state function relies on initial and final values, not the pathway taken.

Daria Azizad 1K

In a vacuum, there is nothing to push against, therefore no work is performed.

Daria Azizad 1K

The T cancels because it is in both numerator and denominator

Daria Azizad 1K

A good way to figure out which R to use it to see what units you need to cancel in order to get the desired units

Daria Azizad 1K

A salt will dissociate into its constituent ions in water, so the ion that is an acid or base will act the same way as a normal acid/base and you will solve it the same way.

Daria Azizad 1K

At equilibrium, the system does not have a preference for the forward or reverse rxn, so neither would spontaneously occur

Daria Azizad 1K

Reactants have their bonds broken, which is endothermic, so it is positive. Products have their bonds formed, which is exothermic, thus negative.

Daria Azizad 1K

they give you the value for q, you can find Cv and Cp from the ideal gas heat capacity eqn, and you're given Ti, so you're just solving for Tf.

Daria Azizad 1K

Heat capacity is an intensive property because it depends on the amount of matter that you start with. Heat capacity is defined as the energy that it takes to raise 1mol of substance by 1 degree c, and it takes more energy to raise 1 mol of a complex molecule by 1 degree C than it does a simple one...

Daria Azizad 1K

Use the qcal= Ccal x delta T to get q, which is delta U because delta U is equal to q at constant volume

Daria Azizad 1K

For gases, the change in enthalpy is defined by that equation. This is because when gas is produced work is done to clear the other gases so the enthalpy is lower than the internal energy. This is explained in detail on pg 274 in the textbook (4D.2) Where does that formula come from? Shouldn't nRT ...

Daria Azizad 1K

Flipping the sign accounts for flipping the equation because we have changed from an endo to exo or exo to endo rxn.

Daria Azizad 1K

Use the gas constant that properly aligns with those units.

Daria Azizad 1K

standard entropy is entropy at standard conditions, which is at a chosen temp (generally 25)

Daria Azizad 1K

would the enthalpies for the reactants and products in steps 1 and 3 be both positive? or would reactants be positive and products be negative? if the calculation for q in step 1 is positive because final temp is higher than initial and in step 3 it is negative because final temp is lower than init...

Daria Azizad 1K

Calculate the amount of H+ and divide by orginal amount of acid then multiply by 100

Daria Azizad 1K

351.5K is the BP temp of ethanol, so you only have to calculate the entropy at the phase change, so delta S = delta H of vap / T at BP

Daria Azizad 1K

Yes because all atoms that form diatomic molecules are in those molecules under standard conditions.

Daria Azizad 1K

P and V have an inverse relationship

Daria Azizad 1K

microstates/degeneracy is the number of positions a molecule/atom can occupy.

Daria Azizad 1K

Maggie Eberhardt - 2H wrote:can someone explain to me how the answer to this problem (0.341 J/Kxs) is positive even though the equation you use to solve it is -(rate of heat generation)/temperature = -100/293???

The body is generating heat, so delta H is positive for the surroundings.

Daria Azizad 1K

No, other units can represent it, but we use kJ by convention.

Daria Azizad 1K

When volume is not constant, the gas is either expanding or compressing, so there is some work done. Therefore, that energy from work contributes to the delta H and must be factored in.

Daria Azizad 1K

Reaction enthalpy is the enthalpy of the overall reaction, while enthalpy of formation corresponds to a specific element.

Daria Azizad 1K

The heat released by the chemical reaction will be equal to the heat absorbed by the calorimeter. So,
(mass of calorimeter) x (C of calorimeter) x (change in temp) = (mass of substance) x (Cs) x (change in temp)

Daria Azizad 1K

Since energy is used to do work, the system is losing energy, and that loss is represented by the minus sign.

Daria Azizad 1K

Since Ka is the ratio of products to reactants, and a product is H3O+, when the concentration of H3O+ is higher, the Ka will be higher.

Daria Azizad 1K

Endothermic:
R + heat <-> P

Exothermic:
R <-> P + heat

Adding heat in an endothermic rxn will push it right, and adding heat in an exothermic rxn will push it left

Daria Azizad 1K

There is also Pa or kPa, which has a more significant difference. I think if it is necessary to convert we will be given the conversion factor.

Daria Azizad 1K

I think they want us to have a non-programmable calculator, so any scientific calculator would be safe to bring.

Daria Azizad 1K

Yes, whenever the H+/OH- concentration is greater than 1, pH/pOH will be negative

Daria Azizad 1K

Both, as they refer to the same thing.

Daria Azizad 1K

We should be able to approximate in binomials as well. If you approximate it or solve it fully out, you get the same value.

Daria Azizad 1K

ELu 1J wrote:It occurs naturally and emphasizes the amphoteric nature of water (the ability to both give and accept a proton).

The ability to accept and donate a proton is amphiprotic, while amphoteric is the ability to react with both acids and bases. :)

Daria Azizad 1K

You would multiply the Ks of the two reactions that form the given reaction since you can think of their separate eq constants being combined into one equilibrium constant.

Daria Azizad 1K

To solve this problem, you need to make an ICE table. The initial concentrations of H2 and I2 can be found by dividing the number of moles by the volume of the flask. Then, we can find H2's equilibrium concentration by multiplying its initial value by 0.6. If we say that the concentration of H2 chan...

Daria Azizad 1K

When pressure is increased due to compression (volume of container being changed), the equilibrium will shift to the side with less moles. If pressure is increased by adding a gas not involved in the reaction, the equilibrium will not change (as the concentrations of the gases involved in the rxn ar...

Daria Azizad 1K

The concentration is the real reason why it is affected. When pressure increases, volume decreases, so concentration increases. For example, if pressure is doubled, then volume is Concentration=moles/(1/2)V=2mol/V. So, in this case, concentration would be doubled.

Daria Azizad 1K

A quick way to determine which is more stable is to compare the K values: if K is high products are favored, and when K is low, reactants are favored. Whichever has a lower K value would favor the reactants more so than the other.

Daria Azizad 1K

There would be different amounts of O2 and O3 because of the different concentrations. This ratio does not refer to the eq. constant, so they would not be the same.

Daria Azizad 1K

Most likely the value we need will be provided, just check that the units in the constant match up with the pressure unit.

Daria Azizad 1K

Yes, there is a periodic trend insofar as electronegativity and atomic size play a role. Larger atoms bonded to H have weaker bonds, so they are stronger acids.

Daria Azizad 1K

A ligand is polydentate if it can bind to a metal atom at more than one location. The best way to figure this out would be looking at the Lewis structure and seeing if it could orient itself in such a way that makes multiple bonds possible. For example, H2O is monodentate because its bent structure ...

Daria Azizad 1K

When it is a strong acid or base, use a one-way arrow because it completely dissociates. With weak acids and bases, there is both dissociation and formation occurring, so use a two way arrow.

Daria Azizad 1K

carbon dioxide + water -> carbonic acid
CO2 (g) + H2O (l) -> H2CO3 (aq)

sulfur dioxide and nitrogen oxides can also lead to acid rain:
SO2 + H2O -> H2SO4

2NO2 + H2O -> HNO3 + HNO2

Daria Azizad 1K

Not necessarily, removal of one hydrogen is the conjugate base of an acid. For instance, H2CO3 has the conjugate bases HCO3- and CO3 2-

Daria Azizad 1K

I generally approach these problems by first identifying what ligands are in the coordinate sphere, so for (a), the ligand is chlorine. Since we know that Cl has a -1 charge and that there are four of them, that means the charge of nickel plus the charge of the chlorines will equal the charge of the...

Daria Azizad 1K

The strength or weakness of an acid depends on how much it dissociates in solution. When it does not 100% dissociate, it is not a strong acid or strong base.

Daria Azizad 1K

A conjugate acid is when a base takes a H+ ion and a conjugate base forms when an acid loses its H+ ion

Daria Azizad 1K

Yes, if a lone pair is covalently bonded to another atom, then both electrons being shared come from the same atom, and therefore it is a coordinate covalent bond.

Daria Azizad 1K

We can find the pH of a weak acid or base using its Ka or Kb value. Use the equilibrium equation to solve for the concentration of H+. Then, take the -log of that concentration.

The equilibrium expression would look like this:
Ka= [H+][A-] / [HA]

Daria Azizad 1K

The Bronsted definition refers to the donation or acceptance of a H+ ion while the Lewis definition refers to the donation or acceptance of an electron pair. In this way, the Lewis definition is much broader and can include other species like transition metals being oxidized and reduced, while the B...

Daria Azizad 1K

Also, the unhybridizied orbital is lower energy than the hybridized orbital, and electrons will go to the lowest energy state possible.

Daria Azizad 1K

The OH2 is just to emphasize that the lone pair on the oxygen atom is what is coordinate to the central metal atom. Both are technically correct though.

Daria Azizad 1K

Tetrahedral shapes will never be nonpolar if there are different atoms bonded, even though the way we draw it in 1D makes it seem like it.

Daria Azizad 1K

I think that both the structure w/ two double bonds and the structure w/ one double bond and one single bond are acceptable, so they are just giving answers for both.

Daria Azizad 1K

Formal charge is an indicator of stability, so considering the formal charge of a bonded atom is useful in determining whether or not it will break the octet rule. If breaking the octet rule results in a FC=0, it is likely more stable, and therefore more likely to be the correct lewis structure.

Daria Azizad 1K

Yes, solids have higher intermolecular forces, which is why we can think of the molecules composing a solid as being held together more tightly than those of a liquid or gas. A good way to remember this is to think about the Halogens and how F, the least polarizable of the group, is a gas, while Iod...

Daria Azizad 1K

Yes, because of the alcohol group, there is H-bonding. For a molecule to have H-bonding, hydrogen must be bonded to O, N, or F, and those atoms must also have a lone pair.

Daria Azizad 1K

Since Iodine is bigger, it has more electrons and outer valence electrons experience shielding from the positively charged nucleus. Thus, iodine is more polarizable than chlorine. This trend holds true as you move down the group. For BP, intermolecular attractions are more important than intramolecu...

Daria Azizad 1K

You can make a visual model of the intermolecular attractions by drawing the Lewis structures. Based on how close the electrons or nucleus of one molecule/atom can get to another nucleus or electron pair, you can distinguish what will be stronger. For instance, H forms Hydrogen bonds with lone pairs...

Daria Azizad 1K

Emma Joy Schaetz 1E wrote:Is this always true?

Yes, this is always true, as electrons will always be negatively charged and thus repel one another. Minimizing repulsion will always result in more stability.

Daria Azizad 1K

Yes, molecular shape affects intermolecular interactions, as it influences how closely together they can get, or how close another molecule or atom can get to the central atom. For example, linear molecules can pack more closely together than tetrahedrals. Also, if a central atom is attached to four...

Daria Azizad 1K

Dipole moments are describing intermolecular forces. As the electron distribution in one molecule forms areas of partial negative charge and areas of partial positive charge, it influences the partial charges in another molecule due to repulsive forces. Polar molecules have a permanent dipole, there...

Daria Azizad 1K

Number of electrons and shape of the molecule are often interrelated, as a molecule with more electrons will be larger. When comparing electrons with similar numbers of electrons, then shape will likely be a determining factor.

Daria Azizad 1K

Usually, it is best to have differing FC side by side (like a -1 next to +1) rather than the same FC side by side (like +1 next to +1) because it is unlikely that there would be two same charge centers in close proximity due to repulsive forces.

Daria Azizad 1K

The central Se atom is single bonded to two OH groups and double bonded to two O. The OH groups will be polar w/ partial positives on H and partial negatives on O. Also, since the electron distribution is different for the single and double bonds, some areas on the molecule will “concentrate” more e...

Daria Azizad 1K

Since it is bonded to N, O, or F, which are highly electronegative, H’s one electron will be pulled away from it. So that means H is basically just a proton and therefore negatively charged atoms will be highly attracted to it.

Daria Azizad 1K

Larger atoms in bonds have more covalent character than smaller atoms (due to shielding and distance from nucleus increase). Since Iodine is larger, HI will have more covalent character.

Daria Azizad 1K

If we are expected to use exact electronegativities, I believe the values will be provided. Without those values, we can make assumptions as to the electronegativities of atoms based on periodic trends. As you move up and right, electronegativity increases. Therefore, we can assume the electronegati...

Daria Azizad 1K

Multiply the percent of KNO3 by the total mass of the solution:

510 x 0.0545 = 27.8 g KNO3

Since the components of the solution are KNO3 and water, the remaining mass will be that of water.

510-27.8= 482.2g H2O

Daria Azizad 1K

No, charge will always be a whole number. Whenever we divide by two in the FC equation, the numerator will be an even number, as it refers to pairs of electrons.

Daria Azizad 1K

Using formal charge is a helpful way to confirm the identity of E, as we know that an element w/ 5 VE is likely to be the central atom. We could also subtract the electrons accounted for by Cl and O from the total # of electrons and be left with 5 electrons. Since we are told that E is in period 3, ...

Daria Azizad 1K

Species with an odd number of electrons have an unpaired electron. Take CH3 for example: there are 7 electrons total, so carbon will have 3 pairs and 1 single electron. This, by definition, makes it a radical. The converse is true, as even numbers of electrons form pairs.

Daria Azizad 1K

I believe the same thing happens for part d because the 6 s and p orbitals are farther from the nucleus and are therefore more "loosely" held. So when it becomes an ion, electrons are lost from there first.

Daria Azizad 1K

Electronegativity also decreases down the periodic table because as more shells are added, the more distant the positive nucleus is from other electrons it would attract; thus the electrostatic forces of attraction are weaker.

Daria Azizad 1K

Electron diffraction gives evidence that EM radiation acts like a wave instead of a particle. Black body radiation and the atomic spectra both give evidence that energy is emitted/absorbed discretely (thus evidence of particle nature), however the photoelectric effect is what confirmed that EM radia...

Daria Azizad 1K

Elements in the third period and after generally have exceptions to the octet rule where they can take on more electrons than eight. However, prior to that, H and He will not follow the octet rule, but rather the "duet rule" because they will only try to fill up their s orbital. Boron also...

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