CHEMISTRY COMMUNITY

Tai Metzger 3K

I had a question about the answer to question 3 part a. Wouldn't the order of rxn with respect to HgCl2 and C204 ^2- be 1 and 1 because when the concentrations double, the rates also double? Thanks!

Tai Metzger 3K

A catalyst is present before and after a reaction. An intermediate is only present during the reaction. I hope this helps.

Tai Metzger 3K

It would not be possible for us to calculate A, however we could compare A for different collisions. For example, the collision of two H atoms would have a higher A than a more complex collision.

Tai Metzger 3K

I think a catalytic converter is used to convert toxic cases like carbon monoxide to something less toxic and is used by coating an exhaust engine with a catalytic converter (I think like platinum?) Can someone confirm Yep, this is correct. Additionally, catalytic converters would be considered het...

Tai Metzger 3K

It is to denote that it is not the same k as the k in the overall rate law. I hope this helps!

Tai Metzger 3K

Yes, in other words, catalysts are present before and after a reaction whereas intermediates are only present during the reaction.

Tai Metzger 3K

Brianna Becerra 1B wrote:If partial pressure is used in both the reactant and product, then converting it using Pv=nRT would make it so the conversion would not make a difference as you would be essentially canceling the conversion out.

Is it okay to use both concentration and partial pressure in the same Q expression?

Tai Metzger 3K

Hi! When the electrode's element is not specified in a question (i.e. only the dissolved ions are given), do we automatically assume that it is a Pt electrode when writing ell diagrams? Are there other materials that the electrode could be made of?
Thanks!

Tai Metzger 3K

n is the number of electrons transferred per reaction.

For example, in the reaction: Fe2+ + Cu --> Cu2+ + Fe n would equal 2.

I hope this helps!

Tai Metzger 3K

Hi! I was having trouble figuring out how to write the overall reaction equation for a concentration cell when give a figure of the concentration cell. Could someone help me with this? Thanks!

Tai Metzger 3K

Hi, I was working on a homework problem and in the question we are given concentrations for aqueous species involved in the reaction and the partial pressure of a gas that is a product of the reaction. When setting up the Q expression, should we convert the partial pressure to concentration using PV...

Tai Metzger 3K

let's say: rate = [A]^m * [B]^n

the order of reaction = m + n

I hope this helps!

Tai Metzger 3K

Hi! I was wondering why there is a negative at the start of this equation. Thanks!

Tai Metzger 3K

Both units can be used, however if the numbers are very large kJ are typically more convenient to use. However, when doing calculations, make sure that all units cancel which often depends on the units of the constants that you are given. I hope this helps!

Tai Metzger 3K

What is the difference between Galvanic and Concentration cells and which is more important? Thanks!

Tai Metzger 3K

In regards to terminology, why is the species that is oxidized called the reducing agent and vice versa. Thanks!

Tai Metzger 3K

Typically, the anode is on the left and the cathode is on the right, separated by a || . You are correct that solids typically go on the outside and are separated from aqueous solutions and gases by a single |

Tai Metzger 3K

Since the pKa is less than the pH at that point, the dissociation reaction will shift to the right, producing more CH3COO- ions. Thus the overall charge would be net negative. I hope this helps!

Tai Metzger 3K

removing NO would cause the rxn to shift left, decreasing the concentration of the products, NO2. Since P=nRT/V, as the concentration goes down, so does the partial pressure. I hope this helps!

Tai Metzger 3K

Hi everyone, I hope ya'll are doing well! I was wondering what salt bridges are made of. Is there a specific type of salt? Thanks!

Tai Metzger 3K

delta G for the reaction depends on what conditions the reaction is occurring at. When conditions are standard, we call the delta G delta G naught. I hope this helps!

Tai Metzger 3K

When Q is greater than 1, delta G is positive and thus the rxn is not spontaneous in that direction. When Q is less than 1, delta G is negative and thus the rxn is spontaneous in that direction.

Tai Metzger 3K

since we are talking about 3 diemsnions, you must raise the conversion factor to the 3rd power as well. this is because dm are being converted in all 3 dimensions, not just 1.

Tai Metzger 3K

q = deltaH when work=0. This occurs when volume is constant because w=P*deltaV

Tai Metzger 3K

What is irreversible expansion?

Tai Metzger 3K

PV is equal to nRT and is the ideal gas law. P*deltaV is used to find work.

Tai Metzger 3K

The delta H for a rxn does not necessarily have to have a coefficient of 1 for the compound being formed. However, for delta H of formation, the compound being formed must have a coefficient of one since the unit is J/mol of the compound being formed rather than J/mol of rxn.

Tai Metzger 3K

It entirely depends on which C you are given. If given molar heat capacity, use moles. If given specific heat capacity, use mass (g). When solving, make sure to check if the units cancel.

Tai Metzger 3K

Hello! Do we need to memorize Cp and Cv for gases or will they be provided? Thanks!

Tai Metzger 3K

Hi! I was wondering how solving bomb calorimetry problems differs from other heat exchange problems. Thanks!

Tai Metzger 3K

Insulation primarily affects enthalpy because it prevents the exchange of heat between the system and the surroundings. Entropy is more associated with changes in volume rather than insulation. I hope this helps!

Tai Metzger 3K

Hi! What does it mean for a reaction to be reversible? Thanks!

Tai Metzger 3K

Yes, U is a state property because changes in internal energy are a function of initial and final states. I.e. deltaU=Uf-Ui

I hope this helps!

Tai Metzger 3K

Can all the equations we have learned in class be used when dealing with any of the three types of thermodynamic systems? Thanks!

Tai Metzger 3K

Since closed systems do not allow flow of matter but do allow flow of energy, you are correct that they can be changed via changes in temperature and pressure. I hope this helps!

Tai Metzger 3K

W will be negative if the system is doing work (expansion) and will be positive when work is being done on the system (compression). I hope this helps!

Tai Metzger 3K

No, base the sig figs off of the accuracy of information given to you, not known constants. I hope this helps!

Tai Metzger 3K

A visual way to think of this is imagining the molecules floating around in a box. If the box shrinks, but there are still the same number molecules floating around, they will push harder on the box (i.e. larger pressure).

Tai Metzger 3K

the function p has a negative sign, resulting in larger inputs having smaller outputs. Thus, a larger Ka (and stronger acid) would have a smaller pKa.

Tai Metzger 3K

I believe endergonic and exergonic are more broad whereas exothermic and endothermic refer specifically to the change in enthalpy in a chemical reaction.

Tai Metzger 3K

Kp depends on the partial pressures of the reactants and products. Adding an inert gas would increase the overall pressure but would not affect any of the partial pressures, thus leaving Kp unchanged.

Tai Metzger 3K

I was doing some practice problems and for a couple I found that x was found to be so small that the concentrations for the reactants were the same at equilibrium as they were initially. Is this possible and/or common? Thanks!

Tai Metzger 3K

Hi, I was wondering when it is useful to use PV=nRT. Thanks!

Tai Metzger 3K

No, the Kw is not 10^-14 at all temperatures, just at 25 degrees C.

Tai Metzger 3K

When species are solid or liquid, they are generally left out of the K expression because we assume that the concentration does not change.

Tai Metzger 3K

In class today we went over the effect of adding heat to an equilibrium system. If the reaction is exothermic, adding heat will favor the reactants so K decreases. If the reaction is endothermic, adding heat will favor the products so K increases. In addition, we reviewed acid and base principles: K...

Tai Metzger 3K

In an electromagnetic gradient, there is no distinction between an electric force and a magnetic force. There is simply the electromagnetic force acting.

Tai Metzger 3K

K is essentially a ratio (between products and reactants) and so it does not have units.

Tai Metzger 3K

I was wondering what elements are more "ideal" and why. Thanks!

Tai Metzger 3K

substituting 1 for solids and liquids is the same thing as ignoring it since there is no effect on the calculation.

Tai Metzger 3K

If a reaction is at equilibrium and you add a product, the reverse reaction will be favored.
If a reaction is at equilibrium and you add a reactant, the forward reaction will be favored.

Tai Metzger 3K

I hope I can help you resolve this haunting question. I believe that it is a physical reaction because no bonds are broken.

Tai Metzger 3K

Yes, the dipoles would cancel if the Cl's are opposite each other, making it a nonpolar molecule.

Tai Metzger 3K

Mg 2+ is smaller than Na+ because they have the same number of e- but Mg has more protons, pulling the e- closer to the nucleus. O2- is smaller than N3- for the same reason. N3- is more polarizable than O2- because it is smaller. Br- is more polarizable than Cl- because it is larger, making it easie...

Tai Metzger 3K

When writing the hybridization of a molecule, for example 2sp, is the 2 indicating the energy level of the orbitals that are being hybridized? Additionally, is it always necessary to include this number or is it acceptable to simply write sp? Thanks!

Tai Metzger 3K

if you are given a molecule it will be indicated what its charge is. SO4 2- will generally be given.

Tai Metzger 3K

Ka = Products/Reactants and strong acids dissociate (almost) completely so the reactants would be equal to (almost) zero. Thus, the Ka of a strong acid would approach infinity and so strong acids cannot have a Ka.

Tai Metzger 3K

Generally, hybridization only occurs among the outermost orbitals.

Tai Metzger 3K

In the context of what we have been learning, a ligand is a lewis base (e- pair donor)that attaches to a central ion (generally a transition metal) to form a coordination compound.

Tai Metzger 3K

What are the strong acids and why are they so much better at donating protons than other molecules?

Tai Metzger 3K

Yes, a Bronsted base recieves a proton and a Bronsted acid donates a proton

Tai Metzger 3K

An amphoteric compound is a compound that can act as both an acid or a base. The best example of this is water, which donates H+ to become OH- and can receive H+ to become H3O+.

Tai Metzger 3K

Yes, polarity of the polar molecules induces polarity in the non-polar molecule. For example, the positive end of a polar molecule would induce a dipole in a nonpolar molecule, causing the positive end of the polar molecule to be attracted to the induced negative end of the nonpolar molecule.

Tai Metzger 3K

Yes, I was taught that ionic bonds are intramolecular forces, rather than intermolecular forces, and are much stronger than london forces, dipole-dipole interactions, and Hydrogen bonds.

Tai Metzger 3K

Hi Chloe! CHI3 had a higher boiling point because it has many more electrons and is much larger, causing the london dispersion forces to be greater than the dipole-dipole interactions of CHF3.

Tai Metzger 3K

Although calculations are not going to be tested, you should understand that Interaction potential energy is proportional to -(alpha1)*(alpha2)/(r^6)
where alpha is polarizability and r is the distance between the molecules.

Tai Metzger 3K

Dipole-induced dipole interactions are their own separate interaction and occur between a polar molecule and a non-polar molecule. This is different from London forces and Dipole-dipole interactions in that London forces occur between all molecules and dipole-dipole interactions occur between two po...

Tai Metzger 3K

They are separate (although related) things. A molecule may have dipole-dipole interactions but does not have hydrogen bonding.

Tai Metzger 3K

Induced dipole - induced dipole (aka london forces) are temporary and occur in all atoms/molecules. Dipole-dipole interactions are permanent and are caused by the uneven distribution of e- in the molecule, resulting in an area of relative positive charge and an area of relative negative charge. The ...

Tai Metzger 3K

Not 100% sure if this is correct, but I drew it with the Se in the middle and the O's surrounding it. For 2 of the O's I drew double bonds and 2 lone pairs, and for the other 2 O's I attached H's and 2 lone pairs.

Tai Metzger 3K

You can always write them to the side as long as long as you specify which formal charge goes with each atom.

Tai Metzger 3K

In general, hydrogen bonding is the strongest, followed by dipole-dipole interactions, and then London forces.

Tai Metzger 3K

Since the midterm questions primarily come from homework and other practice problems, it is unlikely that orbital shape will be a major part of the test. I think that what you have already stated is sufficient understanding for the midterm in regards to this topic.

Tai Metzger 3K

For Schrodinger's equation, the main thing we need to understand is the implications of the equation rather than the equation itself (because it requires very high level math). Essentially, the solutions to Schrodinger's equation are wavefunctions, from which we are able to understand orbitals as cl...

Tai Metzger 3K

Dr. Lavelle has never mentioned this so I would assume not.

Tai Metzger 3K

For solving the problem you will most likely have to convert to SI units. For the final answer you can use whatever unit you want unless the question specified what unit to give in your answer.

Tai Metzger 3K

Not necessarily. If the energy is negative, it means that energy has been released and the e- has fallen from a higher energy level to a lower one. If energy is positive, it means that energy has been absorbed and the e- has jumped to a higher energy level.

Tai Metzger 3K

I'm not sure if their the same thing but you should probably stick to the one Dr. Lavelle gave.

Tai Metzger 3K

valence electrons are the number of electrons in the outermost shell. For nonmetals, this is simply the group number. Transition metals always have 2 valence electrons since the electrons in their d orbitals are in a lower energy level than the 2 electrons in the outermost s orbital.

Tai Metzger 3K

Formal charges can be used whenever you are drawing lewis structures. However, the point of using it is to determine the most stable structure when there are multiple possible structures that can be drawn. When formal charges = 0, the structure is most stable.

Tai Metzger 3K

In terms of resonance structures, yes there will be multiple correct lewis structures (by definition). For other structures, I would guess that there is usually only one correct answer when we take into account formal charge.

Tai Metzger 3K

There will never be a situation where formal charge is a fraction because when dividing by 2 the numerator is always an even number (bonds are pairs of e-).

Tai Metzger 3K

You can pretty much use the noble gas configuration whenever you want (except for H and He since they have no preceding noble gas).

Tai Metzger 3K

Ionization energy is the energy required to remove an electron from the gas-phase atom. From left to right across a period, the ionization energy increases. Going down a period the ionization energy decreases. e- affinity is (kind of) the opposite in that it is the energy released when an e- is adde...

Tai Metzger 3K

When n=6, there are 6 possible values for l but these values of l start at 0. So the 6 possible values of l are 0,1,2,3,4,5.

Tai Metzger 3K

Remember that the maximum value of quantum number l is n-1. For a g-subshell, l= 4. Therefore, the earliest a g-subshell could exist is at n=5.

Tai Metzger 3K

I find it useful to know the order of frequencies for different types of EM radiation (e.g. radiowaves<microwaves<infrared<visible light<UV<xray<gamma rays).
Additionally, I think you are correct in thinking that we should know that visible light is 400-700 nm.

Tai Metzger 3K

Most constants will be given to us for the tests so just use whatever is on the sheet.

Tai Metzger 3K

It's also important to understand this is actually completely arbitrary so in reality we have no idea if it is Px, Py, or Pz.

Tai Metzger 3K

Atomic spectra are associated more with the quantum model. This is due to the fact that the spectral lines occur because the electrons can only exist at certain (quantized) distances from the nucleus.

Tai Metzger 3K

In general, the periodic table has the following trends for atomic radius:
As you move down a column, atomic radius increases.
As you move from left to right along a row, the atomic radius decreases.

Tai Metzger 3K

The equations involved here are:
wavelength*frequency = c(speed of light)
h*frequency = Energy
From what you are given, it seems like the first equation is all you need.

Tai Metzger 3K

A more mathematical way of describing this uses the following equations: If x*y = k (constant) than x and y are inversely proportional because y=k/x, where if x increases than y decreases. Conversely, if y/x = k than x and y are directly proportional because y=kx, where if x increases than y increas...

Tai Metzger 3K

Wavelength is inversely related to frequency, as seen in the equation: wavelength*frequency = c (speed of light) Additionally, frequency is directly proportional to energy in a photon, as seen in the equation: E=h*frequency Therefore, wavelength must be inversely proportional to energy in a photon.

Tai Metzger 3K

For an electron to be ejected, it must be hit with a photon that has enough energy (high enough frequency). This amount of energy is called "work function" and will generally be given in photoelectric question unless you are asked to solve for the work function. For problems like these, yo...

Tai Metzger 3K

Using the wave model of light, increasing intensity of light increased the amplitude of the wave, not the frequency. However, in the quantum model of light the intensity of light corresponds to number of photons (i.e. doubling the brightness doubles the number of photons but has no effect on frequen...

Tai Metzger 3K

A "Black Body" is a hypothetical object that can absorb all frequencies of radiation. This would theoretically make it "invisible" to us.

Tai Metzger 3K

In the number .020, is the first zero significant?

Tai Metzger 3K

I also had a question relating to this. What exactly are the roman numerals after some metals and when do we need to use them?

Tai Metzger 3K

Generally, it is easiest to start with the element that appears only once on each side of the equation and then move on to the more complex elements. In this case, I recommend starting with Fe.

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