CHEMISTRY COMMUNITY

Adam Kramer 1A

Based on Lewis structures, we know that it takes energy to break a bond, and energy is released to form bonds, so if bonds are being made then the reaction is endothermic, since it is taking in energy, and it bonds are being broken then it is exothermic, since energy is being released.

Adam Kramer 1A

If the graph of 1/[A] vs time is linear, or if the exponents of the rate law add up to two, then the reaction is second order.

Adam Kramer 1A

the X-axis would be time and the y-axis would be 1/[A]

Adam Kramer 1A

The order is the sum of the exponents in the rate law. You simply add them and whatever the sum is is the order of the reaction

Adam Kramer 1A

to find the half life of the zero order reaction, you need to use the equation [A.5]=-kt+[A0], where A.5 is half the concentration of A0
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Adam Kramer 1A

It has to do with the log rules, if it is organized in a way that the negatives cancel when subtracting the ln[A]t over, then you get t=(1/k) ln[A]o/ln [A]t. If you change it, you can rearrange the equation so t=-(1/k) ln[A]t/ln[A]o, and the ln[A]t is divided by the ln[A]o.

Adam Kramer 1A

You write out the rate law for the first-order reaction, then you find that [A] decreased by .068M over 115 seconds as the rate, then you can plug in all the information you know, leaving the k constant as the only unknown since you know [A], the rate, and that the reaction is first-order, and solve...

Adam Kramer 1A

from there you can take the log of both sides and use log rules to move the B to the front, then divide and isolate the B. From there you just plug it into your calculator and find what B equals.

Adam Kramer 1A

The instantaneous rate of change is the average rate of change as the difference in time approaches 0. It is basically average rate of change over a really tiny time.

Adam Kramer 1A

You know that B increased . 018M in 3 minutes, so A decreased by 0.06M in the same time. You can then calculate the rate and you know it's first order, so you can then plug in the variables into the rate law equation and solve for the k rate constant.

Adam Kramer 1A

this is the half-reaction for the cathode. We know this because there are electrons being added to the reactants, reducing the Fluorine.

Adam Kramer 1A

The two gases never equal each other because the K constant is greater than one. At the start of the reaction, Q is larger than K, so the backward reaction is favored to go to equilibrium. Because of this, the pressure for 2I is much larger, and it will come down to equilibrium levels as I2 increase...

Adam Kramer 1A

Yes, electrolysis is a process used to use outside electric current to drive non-spontaneous reactions.

Adam Kramer 1A

You compare the ratio of the rate 1 and rate 2, versus the concentrations of the reactants in reaction 1 and reaction 2. Each reactant should be to an exponential power, so comparing the ratios of the rates and concentrations should allow you to isolate the exponent and determine the value of the n....

Adam Kramer 1A

the order is the dependence on the concentration of reactants. This typically corresponds to the exponent value. to find the order of a reaction, you simply add all the exponents of the reactants.

Adam Kramer 1A

The Boltzmann equation relates microstates of a system to a macroscopic quantity called entropy. It measures the possible microstates to give a quantity of the entropy of a system.

Adam Kramer 1A

The electrode potential is typically given in reduction potential. You would need to check signs to make sure you balance REDOX reaction correctly based on if the compound is reduced or oxidized.

Adam Kramer 1A

ampere is a measure of current, which is equivalent to a coulomb per second, coulomb is a measure of charge. an ampere is basically a coulomb per unit of time.

Adam Kramer 1A

I am unsure what the first question is asking, but as for the second, as long as you have cell potential, you can find out the voltage. You may need to use the Nernst equation if it is under non-standard conditions.

Adam Kramer 1A

I believe it does not matter. As long as there is ion flow, the reaction will be okay. The reaction just needs to transport electrons.

Adam Kramer 1A

is the oxidation number just the charge? If so, why do we now call it the oxidation number?

Adam Kramer 1A

For reversible reactions you know that the energy from the surroundings is equal to the negative of the energy of the system because there is no energy loss in the universe, so it must be equal.

Adam Kramer 1A

When entropy approaching 0, the value of TdeltaS is nearly 0, meaning Delta H is very very close to delta G, since the second term in the Gibbs Free Energy Equation goes to 0 and becomes less and less significant.

Adam Kramer 1A

You cannot really find the enthalpy at nonisobaric conditions, you would need to find the constant pressure to find the value with the equations we use. Because of this we would need to find heat instead.

Adam Kramer 1A

When do we use the standard enthalpy of formation? I feel like I always see it but I never use it, so when would we?

Adam Kramer 1A

The entropy would be different based on the different phases. This can be understood mathematically as at various temperatures, the phase would change for the substance, causing a change in entropy due to the change in the temperature.

Adam Kramer 1A

I believe that it has the same relationship as Hess's law because they are both state functions (entropy and enthalpy), but they are not exactly the same because Hess's law only applies to enthalpy. There is a very similar relationship, but they are different because we cannot track H alone. It is u...

Adam Kramer 1A

Yes, it requires much more energy to completely separate the molecules (vaporizing) than to just separate slightly, as with melting a substance. The molecules are much further apart, so there must be more energy to separate these molecules greater than the energy to melt the solid.

Adam Kramer 1A

I believe we use this equation when we are finding molar kinetic energy. I do also remember a homework question, I believe 4.c.3 or something, where we needed this to find the change in energy with constant pressure.

Adam Kramer 1A

He used the density of the liquid to find the mass. He did this because specific heat capacity has grams in the units, so it can be interpreted as the amount of energy needed to raise the temperature of one gram of a substance one degree. If he used molar heat capacity, then he would need to find th...

Adam Kramer 1A

Can somebody explain why for part A we would say that there is no work done to the system but for part B we would use nRT as the work portion of the enthalpy equation?

Adam Kramer 1A

Can someone explain the difference between the two work equations and when we would use each one?

Adam Kramer 1A

It may differ depending on if they ask for heat capacity, specific heat capacity, or molar heat capacity. Depending on the wording, it may ask for different values.

Adam Kramer 1A

I believe since it is at constant pressure, you use the w=-PV equation.

Adam Kramer 1A

Can someone explain the question on the test asking which direction the reaction will favor if there was an increase of pressure? How does the pressure change the equilibrium of the reaction?

Adam Kramer 1A

Entropy is a measurement of how much disorder there is in a system. If you think of increasing pressure as decreasing the volume, there is less available space for atoms to be disorderly. Because of this, there is less entropy, so a higher pressure will give a smaller entropy.

Adam Kramer 1A

Protonation is when a molecule gains an H+ proton, whereas ionization refers to any event in which an electron is added or removed to change the charge. Protonation involves changing the number of protons, and ionization refers to changing the number of electrons.

Adam Kramer 1A

Bond enthalpy is the change in energy of a certain bond when broken or formed, not being strict about the form of the reactants or products. Standard enthalpy is the change in energy when all reactants and products are in their "standard state", meaning they are at 1 atmosphere, and 1 mola...

Adam Kramer 1A

Can someone remind me what Lavelle was saying about having to add enthalpy if the phase changes? How do we calculate the change of enthalpy this way?

Adam Kramer 1A

Can someone explain what a state property is exactly and what this means in the context of enthalpy?

Adam Kramer 1A

Using Ka and Kb, you can find the concentration of hydronium ions and hydroxide ions. Using this information, you can find the pOH by taking the negative log of the concentration of Hydroxide ions, or the pH by taking the negative log of hydronium ions.

Adam Kramer 1A

When finding the percent protonated, the molecule giving off the H+ ion is the one becoming protonated. This is necessary to make sure the calculations are precise and the error in rounding is not too large. You will need to know if the questions ask for this.

Adam Kramer 1A

If the problem is asking about pH, then you will most likely know you are dealing with Ka or Kb. If the solution is a base, you will most likely be dealing with Kb to find the concentration of OH-, but if it is an acid, you will most likely use Ka to find the concentration of H+ ions. Furthermore, y...

Adam Kramer 1A

How do I solve for pH when a salt is dissolved? How do I know if the ion changes the pH of a solution or not?

Adam Kramer 1A

Temperature changes the amount of energy in a reaction, altering the overall thermodynamics of the reaction. Changing the concentrations of reactants or products would only change the Q, not the overall equilibrium constant.

Adam Kramer 1A

Endothermic reactions cause energy to be taken in during the reaction, causing the reaction to favor the products when temperatures are higher. Exothermic reactions give off energy, meaning they would favor the reactants when temperatures are higher.

Adam Kramer 1A

Dr. Lavelle earlier mentioned that we never use liquids or solids in calculating the K or Q values, but in the last lecture I remember him mentioning a few times that we would use the concentration of the liquid or something like that... Can someone explain why he was saying that we find that liquid...

Adam Kramer 1A

Chatelier's principle can be used to see which direction a reaction will proceed in response to a change in concentration or pressure. For example, if more reactants are added, therefore increasing concentration, Le Chatelier's principle tells us that the reaction will move forward in order to mini...

Adam Kramer 1A

When K is greater than 1, the mixture will contain mostly products, and vice versa for when it is less than 1. When it is about equal to 1, the mixture will have an intermediate mixture that is about equal with products and reactants.

Adam Kramer 1A

What does ICE stand for and how do we use it efficiently in calculating concentrations? I missed this lecture and I don't completely understand why it is useful.

Adam Kramer 1A

K will tell the proportion of concentrations needed between products and reactants in a reaction at equilibrium, or in the case of Kp, the partial pressures that will allow the reaction to be at equilibrium.

Adam Kramer 1A

kevinchang_4I wrote:
Jessica Tejero 3L wrote:For number 21 what is the oxidation state of iron?

The oxidation state of iron will be 2+ because two of the nitrogens have lone pairs making their formal charges -1 each.

Which two nitrogens have this formal charge? I am having trouble seeing this.

Adam Kramer 1A

What is the difference between Hemoglobin and myoglobin? If we were shown a picture of the molecule, how do you tell the difference?

Adam Kramer 1A

I believe the porphyrin ligand is chelating because it is polydentate. As for the shapes, I do not know if we need to know that or not.

Adam Kramer 1A

When you get rid of the first proton, there is more of a negative charge, holding the rest of the protons in a stronger bond, therefore making it harder to dissociate. This makes it take more energy to break the bond and therefore makes the Ka smaller for each successive dissociation.

Adam Kramer 1A

At one of the reviews, the UA said to memorize the strong acids, but do we also need to memorize strong bases? How can we tell if it is a strong base or acid if we don't specifically memorize them?

Adam Kramer 1A

For 1 a and b for the Marshmallow review, is K and Na not accounted for in the equilibrium solution because group 1 and 2 atoms do not affect pH?

Adam Kramer 1A

How can you tell that the polyprotic acid or base is polyprotic by looking at the formula?

Adam Kramer 1A

Are all Bronsted bases Lewis acids, and are all Lewis acids Bronsted bases? And why would Lewis acids and bases be important?

Adam Kramer 1A

Strong acids and bases will completely dissociate in a solution. They have long, weaker bonds and can easily dissociate to donate protons or accept protons in the solution.

Adam Kramer 1A

Like the reply above, you can look at the structure, but for the bronsted definition of acid or base, you would look to see if the structure is likely to donate a proton, or a hydrogen ion. This would make it a bronsted acid. If it were to be able to accept a proton, or hydrogen ion, it would be a b...

Adam Kramer 1A

How can we find the conjugate acid or base in a solution?

Adam Kramer 1A

What exactly is a ring structure and how do we know it is present?

Adam Kramer 1A

I believe the question is asking the same thing as in 2F.5. The question wants to know the hybridization orbitals, which is the same as the hybridization of the atom.

Adam Kramer 1A

The negative sign is because the energy is always negative, pulling the two masses together, I believe.

Adam Kramer 1A

I saw another chemistry community post where people were saying it doesn't matter what order the elements in the molecular formula were written, but I thought Lavelle had mentioned that the molecular formula was written in an order that put connected atoms next to each other so you could draw the st...

Adam Kramer 1A

What is the dentate that Lavelle was describing in class?

Adam Kramer 1A

Can someone explain what a chelate is and why it is important to molecule structure?

Adam Kramer 1A

It prefers equatorial because, in the full shape, the closest angle is 90 degrees, so you would want to remove one of the closest atoms to maximize the repulsion of the electrons and create the lowest energy.

Adam Kramer 1A

An octahedral with two lone pairs is a square planar, and with one lone pair, it is a square pyramid.

Adam Kramer 1A

You need to draw the dipoles with the shape to see how they would cancel. If every area of electron density is filled with an atom of equal electronegativity, there is probably no dipole since all the pull is the same and would cancel; if there is a missing atom and lone pairs instead, or a differen...

Adam Kramer 1A

I remember Lavelle mentioning that interaction potential energy is proportional to -q1q2/r^6, but when I looked online, I found a lot of sources saying it was actually equal to kq1q2/r. Can someone explain the difference in the equations and why they are different, as well as which is more correct?

Adam Kramer 1A

Lavelle mentioned that the potential energy is proportional to -q1q2/r^6, when q is the polarizability of an atom (dependent on the number of electrons and the size of the atom), and r is the distance between the atoms or molecules. I think this measures how strong the energy is that is pulling the ...

Adam Kramer 1A

I may be wrong, but I believe dipole-dipole is stronger, and this can be calculated by finding the dissociation energy of the bond. If it has lower dissociation energy, it has a weaker bond.

Adam Kramer 1A

potential energy is always negative because the force is pulling to objects together. If it was a force pushing the two atoms apart, it would be positive.

Adam Kramer 1A

The larger the radius of the atom, the more easily an atom can be polarized because the electron clouds are further from the nucleus and can distort more easily. The polarizability will decrease across a period because the increasing Z eff that is pulling the electrons closer to the nucleus.

Adam Kramer 1A

Why is an atom that donates a pair of electrons known as a Lewis base, and vice versa with the Lewis acid, and why does it matter?

Adam Kramer 1A

What causes different polarizability of molecules, and why does that affect a molecule being solid or liquid at room temperature?

Adam Kramer 1A

Visually, the resonance structure would look like the average of the different structures drawn. It would have bond lengths that average the different possibilities, but it cannot be drawn like that realistically on paper.

Adam Kramer 1A

Lewis structures with expanded octets would have lower charges than octet structures because they are forming the structure that would provide the lowest possible energy, allowing the molecule to go to larger subshells to reach that lower energy level. They are going into the d-subshell which provid...

Adam Kramer 1A

What is the difference between sigma and pi bonds and why are they important in chemistry? What purpose do these bonds serve in real life chemistry?

Adam Kramer 1A

Can somebody please explain what exactly Lavelle meant by ionic bonds having "covalent character"?

Adam Kramer 1A

Is there an easy way to determine if there is an octet rule exception for a given atom? How can we tell just by looking at the periodic table which atom can have more than 8?

Adam Kramer 1A

The spin number is the Pauli exclusion principle says you cannot have two of the same thing in the same orbital, so they must have opposing spin to counteract each other's magnetic forces. Up and down are the two different directions.

Adam Kramer 1A

Orbitals tell how far the valence electrons are from the nucleus, which can be useful when determining the ionic energy and how easily it can be used to make different compounds.

Adam Kramer 1A

You can tell in situations like when Dr. Lavelle was writing out the quantum numbers and shells and he wrote out lines above the subshells with arrows pointing up or down to fill the subshell. First all the electrons will fill in spinnning up and then they will fill in spinning down when denoted in ...

Adam Kramer 1A

When we are writing quantum numbers such as 2Px2, does it matter if we put x or y or z, or are those just chosen at random when we are writing them?

Adam Kramer 1A

So I get that these different orbitals correspond with the different blocks of the periodic table, but what does it mean in a more real-life sense? Like how can I picture this difference in my head when I am talking about the different orbitals?

Adam Kramer 1A

Can someone explain the difference between Balmer and Lyman series, and when would we see this? How does this display itself on a nonmolecular level in the real world?

Adam Kramer 1A

Radiation is a form of light, just not visible light. The speed will not change in a vacuum, but it will change as it passes through a different medium, such as glass.

Adam Kramer 1A

You should be able to figure this problem out by knowing the general order of wavelengths, or checking a chart with the frequencies. Higher frequencies, or shorter wavelengths, correspond to higher energies, and vice versa. So, by checking a chart in the book with the frequencies of different forms ...

Adam Kramer 1A

So for this problem, I had deduced that C was the right answer because the other three options did not make sense, but I do not understand what "The extent of change in the electrical field at a given point" means. Could someone explain how this relates to the frequency of electromagnetic ...

Adam Kramer 1A

The Schrodinger equation determines the probability amplitude, which is related to the probability, of a certain system being in a certain state. This eigenvalue equation relates a certain state of a system to its corresponding energy, relative to the other levels of the system. It often takes a wav...

Adam Kramer 1A

Yes, since the question asks for increasing energy, you would need least to most energy, meaning longest wavelength to shortest wavelength. Short wavelengths correspond to higher energy, and long wavelengths correspond to lower energy.

Adam Kramer 1A

I am confused by the concept of quanta and photons. Can someone explain how to measure a quanta and/or a photon and what it is exactly?

Adam Kramer 1A

Theoretical yield can be in moles or grams, depending on the question. The question may ask for the answer in one form or the other, or it may accept either answer.

Adam Kramer 1A

In lecture, Dr. Lavelle kept mentioning the intensity of light versus frequency. I understand that the frequency of light depends on the wavelength, but how does the intensity change? And how is intensity measured exactly?

Adam Kramer 1A

The density is mass/volume. Gas is unique because it does not have a fixed volume. The density of gas can change if you change the amount of gas but keep the volume of the container the same. If you add more gas to a container of a fixed volume, it will increase the density, for example.

Adam Kramer 1A

The units in Hertz is cycles/second, so the Hertz is just how many times the wave oscillates in one second.

Adam Kramer 1A

I would begin by converting 25.2 kg to grams, or 25.2 x 10^3 grams. From there I would find the moles of the UF6 by dividing the grams of UF6 by the molar mass. From there multiply the moles by 6 because there are 6 F- ions in each molecule of UF6, so you can get the number of moles of F- ions in th...

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