CHEMISTRY COMMUNITY

Mina Tadros 3L

The rate constant, k, just like the equilibrium constant, K, is affected by a temperature change.

Mina Tadros 3L

If Q>K, then the reaction will progress towards the reactants since more products formed. If Q<K, the reaction will progress towards the products since there are more reactants present.

Mina Tadros 3L

The slowest step is typically given to you. If you are given a diagram, the slow step would be the one with the greatest activation energy.

Mina Tadros 3L

Dear Dr. Lavelle,

Thank you for an amazing quarter! I know this has been a challenging year for all of us, but you were able to keep me motivated and engaged. I learned so much from you, which I am forever grateful for. Thanks again for everything, and have a great spring break!

Mina Tadros 3L

n is the number of electrons that are transferred in a redox reaction. Make sure you balance your redox reactions before plugging in a value for n in the Nernst equation.

Mina Tadros 3L

Intermediates are produced in one step and later used in another step to help the reaction progress. Catalysts, on the other hand, are introduced into reactions to lower the activation energy and speed up the reaction.

Mina Tadros 3L

Our chemistry-related posts will most likely remain here, and I believe that we will still have access to our accounts, which I like since one day, years into the future, I would love to log back in and reminisce about my college days (sounds corny, I know haha).

Mina Tadros 3L

Yes, the anode is where oxidation occurs (loss of electrons), and the cathode is where reduction occurs (gaining of electrons). Thus, the electrons will always flow from the anode to the cathode.

Mina Tadros 3L

For a zero-order reaction, the rate of the reaction is independent of the concentration of the reactants.

Mina Tadros 3L · Re: Final Exam Time The final is on March 14th from 9:30 AM -11 AM.

The final is on March 14th from 9:30 AM -11 AM.

Mina Tadros 3L

Intermediates cannot be in the rate law because they are produced in one reaction and then used up in another reaction. Thus, when looking for the reaction's overall rate, the intermediates ending up canceling each other out since they are on opposite sides.

Mina Tadros 3L

When the plot of [A] vs. time is linear, then it is zero-order. When the plot of ln[A] vs. time is linear, then it is first-order. When the plot 1/[A] vs. time is linear, then it is second-order.

Mina Tadros 3L

Kc is the equilibrium constant for molar concentrations, whereas K is a more general equilibrium constant.

Mina Tadros 3L

As long as the units cancel and you end up with the correct unites you are looking for, then it does not matter.

Mina Tadros 3L

Q is the reaction quotient, which is the ratio of products to reactants that are not at equilibrium. In contrast, K is the equilibrium constant, which is also the ratio of products to reactants, but they have already reached equilibrium.

Mina Tadros 3L

n is the number of moles of electrons that are being transferred after balancing the redox reaction.

Mina Tadros 3L

The higher the atomic number, the greater the number of microstates, which increases the disorder.

Mina Tadros 3L

When work is done on the system, the work is positive, but when the system does work, the work is negative.

Mina Tadros 3L

The anode is where oxidation occurs (releasing electrons), whereas the cathode is where reduction occurs (the gaining of electrons). I don't really know of a mnemonic that could help you easily differentiate between the two.

Mina Tadros 3L

If Q>K, then there are more products present than is needed for equilibrium; thus, the reaction will proceed to the reactants until equilibrium is established. If Q<K, then there are more reactants present than is needed for equilibrium to be established; thus, the reaction will proceed towards the ...

Mina Tadros 3L

I also learned this acronym in AP chem, haha! It honestly is very helpful.

Mina Tadros 3L

To be honest, I usually just take a nap after a stressful midterm/week. It helps me recharge and be prepared for the next week.

Mina Tadros 3L

You would use delta H fusion when you are dealing with a phase change from a solid to a liquid.

Mina Tadros 3L

When you are dealing with the ideal gas law, PV=nRT, you would use 0.08206 since its units are (atm)(L)/(mol)(K). This matches every aspect of the ideal gas law. However, it depends on the units you are given. For instance, one of the R values is 8.314 J/(K)(mol). This is typically used when you are...

Mina Tadros 3L

Delta U = q + w, delta U being the change in internal energy, q being the heat added or released from the system, and w is the work the system does. When q = 0, then you are dealing with an isothermal system, meaning delta U = 0 and therefore, q = -w. When the system does not work due to constant vo...

Mina Tadros 3L

Whenever you are dealing with state properties such as enthalpy and entropy, you can add every process and calculation conducted. This is because it does not matter what path the system undertook. All we care about is the final and initial states.

Mina Tadros 3L

Dr. Lavelle usually updates them after every midterm, so the chem community posts will most likely be updated soon since our 2nd midterm is coming up.

Mina Tadros 3L

When the system is compressed, work is positive, but when the system expands, work is negative since it is doing work by pushing against external pressure.

Mina Tadros 3L

Attack on Titan and Jujutsu Kaisen! Highly recommend both!

Mina Tadros 3L

Heat, which is not a state function, is denoted by q, while enthalpy, which is a change in heat at constant pressure, is a state function, and thus, it is denoted by delta H.

Mina Tadros 3L

Exothermic reactions are a release in heat and, thus, they have a negative value associated with them. An absorption in energy/heat is an endothermic process, and, therefore, it will always be positive.

Mina Tadros 3L

Dr. Lavelle included this week in the grading, but don’t worry, once you complete your posts for this week, it will automatically update. As long as you have 50 posts by the end of the quarter, you’ll be fine.

Mina Tadros 3L

Vapor and gas are the same thing.

Mina Tadros 3L

Heat capacity cannot be negative because it is the amount of energy required to raise a substance's temperature by 1 degree Celsius.

Mina Tadros 3L

To go from pKa or pKb to Ka or Kb, you would do 10^-(pKa or pKb).

Mina Tadros 3L

Just like everyone has been saying, you would assume it is a liquid unless stated otherwise. Also, since liquid water is in large excess in a reaction, it is disregarded from the equilibrium constant.

Mina Tadros 3L

The larger the pKa, the weaker the acid and the weaker the acid, the stronger is its conjugate base.

Mina Tadros 3L

Endothermic is when heat is absorbed, so there is sufficient energy to break the bonds within a molecule. Exothermic, on the other hand, is when energy is released, which typically occurs when bonds are being formed. You would know it is exothermic for this reaction because it appears to be a combus...

Mina Tadros 3L

HClO3 is a strong acid.

Mina Tadros 3L

Dr. Lavelle said that we should assume 1 bar=1 atm since they are relatively close in amount to be considered equivalent in our calculations.

Mina Tadros 3L

Do as many practice problems as you can, read the textbook, review your notes, and attend review sessions. Hope this helps :)

Mina Tadros 3L

You would use the ICE box when you are given an initial concentration of a weak acid or base, and you are trying to calculate the equilibrium concentration of both the products and the reactants.

Mina Tadros 3L

You have to check if and see if it truly is negligible or not. The way you do that is by calculating the percentage protanated or deprotonated. If the percentage is less than 5%, it is fine to disregard the x in the denominator in your calculation. However, if it is greater than 5%, you will have to...

Mina Tadros 3L

Steam burns at 100 degrees Celcius are more severe than water burns at 100 degrees Celcius because you have to consider the amount of energy required for the phase change. Thus, when steam begins to condense when it touches a colder surface, you have to add the energy released from the phase change ...

Mina Tadros 3L

The smaller the pKa, the stronger the acid. Also, the greater the Ka, the stronger the acid.

Mina Tadros 3L

Q is the reaction quotient, which is essentially the ratio of products to reactants of a reaction that is not at equilibrium. K, on the other hand, is the equilibrium constant, which is the ratio of products to reactants at equilibrium. You can relate Q to K to find out which direction the reaction ...

Mina Tadros 3L

You have to complete 5 posts every week for a total of 50 posts by the end of the quarter.

Mina Tadros 3L

You should also know atmospheres and torr (1 atm=760 torr) when dealing with partial pressures.

Mina Tadros 3L

Ka is the acidity constant, whereas Kb is the basicity constant. They are both solved in the same way: [P]/[R]. You would use them whenever a question asks for you to solve for the equilibrium constant or you are trying to calculate the equilibrium concentration of a reactant or product that is pres...

Mina Tadros 3L

Whatever is reacting to form something else will be the negative one. That is because as the reaction proceeds, the reactant's concentration will begin to decrease while the product(s) it is forming will be increasing. That is why it would be positive for products, and for reactants, it would be neg...

Mina Tadros 3L

Temperature is the only factor that affects K. For instance, if you are dealing with an endothermic reaction, and you increase the temperature, the system will try to offset this increase in temperature by shifting towards the products. This will cause the product's concentration to increase and, th...

Mina Tadros 3L

When dealing with the ideal gas law, you must always use kelvin for temperature.

Mina Tadros 3L

When you are given the concentration of the reactants and products, you use Kc. However, if you are given the partial pressures of the reactants and products, you would use Kp.

Mina Tadros 3L

Pretty sure we will be only dealing with ideal gasses in this course.

Mina Tadros 3L

Correct. Whenever you take the ratio of the concentration (or partial pressure) of products over reactants when it is not at equilibrium, you are solving for Q, the reaction quotient. If the reaction is at equilibrium, then the ratio of products to reactants is the equilibrium constant, K.

Mina Tadros 3L

You only include H2O in the equilibrium constant if it is a gas. If it is a solid or a liquid, you do not include it.

Mina Tadros 3L

Yes. Dr. Lavelle has designed this course to flow smoothly, with every new topic covered being built upon the previous topics discussed. Since we ended with an introduction to acids and bases in Chem 14A, I believe we will begin with a more detailed explanation of acids and bases in Chem 14B.

Mina Tadros 3L

Polyprotic acids are acids that are able to be deprotonated more than once. For instance, H2SO4: 1) H2SO4 + H2O ----> HSO4^- + H+ 2) HSO4^- + H20 ----> SO4^2- + H+.

Mina Tadros 3L

Coordination numbers are the number of ligands that are attached to the central metal cation. These are only for the ligands within the coordination sphere. Since [NiCl4] has 4 ligands attached to the central metal cation, then it has a coordination number of 4. [Ag(NH3)2] has two, thus, it has a co...

Mina Tadros 3L

Lewis acids and bases deal with electrons, whereas Bronsted acids and bases deal with protons. A Lewis acid is any atom that can accept a pair of electrons from a lewis base, forming a coordinate covalent bond. A Bronsted acid is a compound that is able to release a proton (H+). A Bronsted base is a...

Mina Tadros 3L

50% of all the points you can earn (250/500) would give you a C-, which is considered a passing grade.

Mina Tadros 3L

The longer the bond, the stronger the acid. This is because longer bonds are weaker in strength, and thus, are easier to deprotonate.

Mina Tadros 3L

The number of ligands is the number of lewis bases (electron-pair donors) attached to the central metal cation. This would also be the coordination number for the coordination compound.

Mina Tadros 3L

I always do all the calculations first, and then I look for sig figs at the very end. This allows my answer to be as accurate as possible, with very minimal to no rounding error.

Mina Tadros 3L

Yes, if the molecule has polar bonds, but the dipole moments cancel, it would be a nonpolar molecule.

Mina Tadros 3L

Stressed. Studying for finals and finishing up remaining assignments has been exhausting. I cannot wait for break.

Mina Tadros 3L

Correct.

Mina Tadros 3L

Lone pairs do not automatically make a molecule polar. Only if the lone pairs are located in one particular section of the molecule (thus, they're not canceling each other) will the molecule be polar.

Mina Tadros 3L

Certain resonance structures have a more stable formal charge since they are closer to 0. Structures with the least amount of formal charge tend to be the most stable, and thus, they are the resonance structures that contribute the most to the molecular structure.

Mina Tadros 3L

Polar molecules are molecules that have dipoles that do not cancel. Nonpolar molecules have dipoles that do cancel. Also, if there are differences in electronegativity because the atoms bound to the central atom are not uniform, then it will be a polar molecule.

Mina Tadros 3L

Yes, since it is a resonance structure, they are delocalized.

Mina Tadros 3L

I usually make a plan for the day that I follow. For example, I have to study for chem from time X to time Y, and only after I completed this schedule, will I take a break. I also like to put my phone away, so I don't get distracted if I get a call or a text.

Mina Tadros 3L

Bond angles are not calculated. They are experimentally determined.

Mina Tadros 3L

Repulsion occurs between lone pairs and bonding pairs. However, the strength of the repulsions are different: lone pair-lone pair repulsion > lone pair-bonding pair repulsions > bonding pair-bonding pair repulsions.

Mina Tadros 3L

Carbon and Hydrogen have similar electronegativities, and thus, have a small electronegativity difference. However, since Fluorine, Oxygen, and NItrogen are more electronegative than Carbon, there is a greater electronegativity difference. This is why hydrogen bonds are only present in bonds with Ni...

Mina Tadros 3L

I believe we may still have lectures on our break. We had one during Veterans day, so I don't see why this would be any different.

Mina Tadros 3L

Don't stress about it too much. There is still a lot of time left for you to make up for any bad score. Keep your head up. You got this!

Mina Tadros 3L

When drawing Lewis Structures, you should always draw the most stable and plausible structure, which would be the one with the least amount of formal charge.

Mina Tadros 3L

Since it is an exception, Ag has an electron configuration of [Kr]4d^10 5s^1 (it is more stable to have all the d orbitals paired than having 4 paired orbitals and 1 unpaired orbital). Thus. for Ag^+1, the electron configuration would be [Kr]4d^10 since we are removing an electron from the valence s...

Mina Tadros 3L

We will be tested on the material we did not cover in outline 2 and all of the material in outline 3.

Mina Tadros 3L

Elements in the 3p block can have expanded octets because in the n=3 shell, there are s,p, and d orbitals present (n=3 l=2). The presence of empty d-orbitals allows for expanded octets since they can hold additional electrons.

Mina Tadros 3L

The most stable structure would be the one with the atoms having a formal charge closest to 0. Also, you should always make sure that the most electronegative atom holds the negative formal charge since it is the most capable of holding the electrons. If the most electronegative atom has a + formal ...

Mina Tadros 3L

The least electronegative atom will go in the center.

Mina Tadros 3L

I am not trying to die, so I would help shut off the reactor.

Mina Tadros 3L

No, they are omitted. This is due to noble gases having a full octet. A full octet means that the element or compound is not reactive. If these full octet elements were to add an electron, it would require energy and, thus, the electron affinity for it would be negative.

Mina Tadros 3L

As you move across the periodic table, you are increasing in the number of protons in the nucleus. This increase in the number of protons causes the effective nuclear charge to increase since the more protons there are, the greater the pull on the electrons.

Mina Tadros 3L

I'm doing alright. A little stressed here and there, and I barely have any time to relax :(. But overall, I am still hanging in there...at least for now.

Mina Tadros 3L

When calculating empirical formulas, you will have to have them as whole numbers. Thus, when calculating empirical formulas, you would have to multiply every single element in a way that gets rid of any fraction.

Mina Tadros 3L

It depends on what the question is asking. If the question asks for the long hand electron configuration, you will write every aspect of that element's electron configuration. If it asks for the shorthand, you will write the noble gas that is right above the element you are writing the electron conf...

Mina Tadros 3L

I believe the TAs check the date and time you make a post. Therefore, to receive all 5 points for a week, you would have to make sure you make 5 posts before midnight every Sunday.

Mina Tadros 3L

Avogadro's number is 6.022 x 10^23, and you would use it when looking for formula units, atoms, photons, and any particle (just not moles or grams).

Mina Tadros 3L

Yes, c will always be the speed of light. It is constant, after all. The reason why it is a constant is due to the inverse relationship between wavelength and frequency. Whenever you double wavelength, you are halving the frequency, and when you multiply these two values together, you will always ob...

Mina Tadros 3L

I'm not sure about the number of problems in the midterm, but I know how to prep. The best way to prep would be to read from the textbook and do as many practice problems as possible. This will allow you to apply your knowledge and gain practice on how to tackle particular problems. I hope this help...

Mina Tadros 3L

If you are given a wavelength that is less than 400nm, then you would use the Lyman series (n=1) because the Lyman series absorbs or emits energy in the UV region. However, if you are dealing with the visible region, you would use the Balmer series (n=2).

Mina Tadros 3L

The electron density distribution is the arrangement of electrons within an orbital. It is essentially the probability of finding an electron at a particular position in the (wave function)^2. If you are at a peak or a trough, you will have a high probability of finding an electron. However, if you ...

Mina Tadros 3L

Since it gives you nitrogen by itself, it would be N2, but you would have to convert moles of N2 to N when dealing with empirical formulas.

Mina Tadros 3L

Whenever an excited electron falls back down to its ground state, it will emit photons that release energy. This electron can continuously release photons at every energy level until it has reached its ground state, where the electron becomes relaxed.

Mina Tadros 3L

When doing conversions, I usually use 10^x (x being all real numbers). This simplifies my conversions since I do not have to waste my time writing out the full value.

Mina Tadros 3L

I usually change my sig figs at the very end to ensure that my calculations are as close to the real value as possible. If you keep rounding midway, your answer begins to deviate from the final actual value.

Mina Tadros 3L

1)Attend as many sessions as possible. This will allow you to get extra practice problems, not in the textbook nor the Chem 14A website. Also, they go over how to do them, so if you are ever stuck, they explain the problems step-by-step. 2) Do as many practice problems as you can. It is common that ...

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