CHEMISTRY COMMUNITY

Arshiya

Because the units for the rate is Molarity/second, the different ordered reactions will have different units for k in order to have the M/s rate unit. Therefore for first-order reactions, k is 1/s. For second order reactions, k is 1/M*s.

Arshiya

For part c, we are calculating the certain temperature that changes the reaction from nonspontaneous to spontaneous. Therefore, we use the equation deltaG=deltaH-TdeltaS. Plugging in the values given for enthalpy and entropy we set this equation to 0>enthalpy-T*entropy and solve for T. You make the ...

Arshiya

I am not entirely sure if we need to know how to draw them. Lavelle never really addressed them in the lecture notes, so don't stress too much about them. They were present in today's review session, so just know how it was used in the problem that was given.

Arshiya

Pt(s) is put in the cell diagram when no solid is present in the redox reaction that is the metal electrode. Pt(s) is platinum and is added to the cell diagram to represent the inert metal electrode.

Arshiya

Like stated on his website, the final will be a cumulative test of what we have learned from the start of the quarter until the end.

Arshiya

If we were to solve for the rate or rate constant, Lavelle would probably specify what type of order the reaction is. Or, similar to the homework problems, he could provide a table of experiments using different concentrations and rates for us to figure out the order of each reactant or the overall ...

Arshiya

If it is not stated, find the rate of each of the elementary steps. The slowest rate should be the rate-determining step.

Arshiya

I don't think you would need to know calculus for kinetics. Just know what the integral and derivative signs mean when used in the equations.

Arshiya

Based on conceptual situations like these, you need to understand what is taking place in a reaction like ice melting. Since Gibbs is related to the change of enthalpy and entropy, see how these are changing when ice is melting. When ice melts, the entropy is increasing because ice is going from a s...

Arshiya

I don't think it matters which one you write first, however, make sure to use a comma since they are in the same phase.

Arshiya

For simple reactions involving elements like Zn/Zn2+ or Cu/Cu2+, it is easier to see which one is oxidized or reduced. However, for complex compounds or more complex reactions, it is better to identify the couple and then calculate the oxidation state for that half-reaction. Although it takes time, ...

Arshiya

There is no specific preference used when calculating Gibbs. Just make sure you are using the same units though through the calculation. Gibbs is usually reported as kJ/mol.

Arshiya

The driving force of dissolution can be determined by the dispersal of matter or energy.

Arshiya

He posted on his website and stated in lecture on Friday that the Nernst equation will not be on the test. All the content covered in class this week including Gibbs will be on the test.

Arshiya

In addition, if the question asks for the Gibbs free energy of formation of the reaction the units should be kJ/mol. Just pay attention to what the question is asking.

Arshiya

In addition, in an electrochemical cell, the anode is negative while an electrolytic cell the anode is positive. Most importantly, in an electrolytic cell, the reactions taking place are nonspontaneous, while electrochemical cells have spontaneous reactions.

Arshiya

In addition, when the entropy of the system is in equilibrium the entropy of the system is equal to the entropy of the surroundings.

Arshiya

You can assume work is equal to 0 in a vacuum where the external pressure is 0

Arshiya

No, I don't think so. You should know the equations on the constant and equations sheet provided. In addition, you should know the equations for derived equations for entropy and work like Lavelle showed us in class.

Arshiya

It doesn't matter which sign you attribute to the system or surroundings. As long as you understand the system and surroundings are equal but opposite in sign, you should get the correct answer.

Arshiya

You can find those values according to the equipartition theorem for an ideal gas and use U=3/2nRT to substitute and find the values for Cp and Cv. It's on the constant and equations sheet. Just remember to use those for monoatomic ideal gases.

Arshiya

In addition, in an isothermal irreversible reaction, the pressure is constant. Therefore, the amount of work done is -Pex*V. Because it is isothermal, no heat is lost or gained. In an isothermal reversible reaction, the pressure and volume are increasing or decreasing in small incremental steps. Bec...

Arshiya

I understand how to do the problems in order to get the enthalpy of a reaction. However, I am confused when the units should be J/mol or just J when calculating enthalpy.

Arshiya

I also recommend watching Youtube videos in order to review major concepts. In addition, I like doing the worksheets Karen posts on Chemistry Community. I also like to take notes down while reading the textbook. Reviewing my notes, doing as many problems I can, and attending the reviews sessions has...

Arshiya

As seen in the problems in the book, I noticed that most systems we will be dealing with are closed like pistons. However, work can be done on an open system such as taking a coffee stirrer and stirring coffee. This action represents a force being applied over a distance and it interrupts the moveme...

Arshiya

2. Internal energy is a state function, which means that it is a property that depends only on the current state and disregards how the system was prepared. The internal energy of an object is the sum of the potential and kinetic energy it possesses. You cannot measure the absolute or exact value of...

Arshiya

If a system is at equilibrium the external pressure is equal to the internal pressure. In an irreversible system, the external and internal pressures are different and therefore work must be done in order to restore the equilibrium. Because of this instability, the system will expand if the external...

Arshiya

Because this post will probably be really long if I explained everything, I would refer to Lavelle's lecture notes. His notes break down how to solve the enthalpy for the reactions. If you want a review, I love watching youtube videos. I will leave several links below if you want more examples. http...

Arshiya

In regards to equilibrium equations, you must see the K value when making an assumption. If the K value is less than 10^-3, then you can proceed using x. However, make sure you check your assumption with the 5% condition.

Arshiya

Because an inert gas does not react with the reactants or products, it is essentially not changing the concentration of the products and reactants. In addition, the volume is constant so the concentrations remain untouched. Therefore, this will not effect equilibrium.

Arshiya

Because polyprotic compounds can dissociate multiple times, there will be multiple pKa values for every reaction that occurs. Depending on the information given in the question u will be able to find Ka for a given step.

Arshiya

Just to be safe, I would use what we know. And kA*kb=kw is given so use that.

Arshiya

Depending on the significant figures of the data given in the problem, you will have that many sig figs after the decimal for pH. For example say if you were given a K value of two significant figures a potential pH value could be 2.88. You can double check on the website under everything about sig ...

Arshiya

Is Keq different from Kc, or does it represent the same thing? Also, will we be marked wrong if we wrote Keq instead of Kc for the chemical equilibrium equation?

Arshiya

These short notations in a chemical reaction represent the form or state of the compound in the equation. "Aq" stands for aqueous solution, "s" represents a solid, "g" represents a gas state, and "l" represents a pure liquid form. When you see a compound with ...

Arshiya

Because Kc measures the concentrations at equilibrium, it is a constant that remains unchanged even if more products or reactants are added as it is a fixed ratio. If there is a change in the initial concentration of reactants and products in a question, then you will be finding Q.

Arshiya

a weak conjugate base means a stronger acid

Arshiya

when Ka is given you can set up the formula of ka=product of the product concentrations/product of reactant concentrations and solve for the [H+] concentration. Then you would take the -log to find the pH.

Arshiya

Because an acid is a proton donor, it will lose the hydrogen. Therefore, the conjugate base will be H2B03.

Arshiya

The transition metals must have roman numerals that match the ion charge.

Arshiya

I've been memorizing the table in the book in order to remember the names of the molecules. In addition, another helpful source is quizlet. There are many flashcards created to memorize these formulas. I do believe that complicated acids will be provided on the final.

Arshiya

Transition metals have many oxidation states because they have the d shell where they can lose electrons from.

Arshiya

I know they have review sessions as Dr. Lavelle showed us the pdf in class. I just wanted to know if there would be a practice final like we had on the midterm?

Arshiya

When looking at the Lewis Structure of the molecule, you can see if that molecule has single, double, or triple bonds. Depending on that, you can see how tightly bound the atoms are to the central atom. The higher the bond strength, the harder it is to break the bonds apart or leading to a higher bo...

Arshiya

Will there be a practice final exam released on chemistry community like "garlic bread"? Or will we be doing practice during the review sessions this week?

Arshiya

The 2 and 3 represent the number of p orbitals that are being hybridized.

Arshiya

I may be wrong, but from what I understand is this means that the more electrons that are distorted or unevenly distributed within the cloud, the greater the separation of charge. This separation of charge makes the molecule highly polarizable.

Arshiya

As far as the examples we've done in class with Lavelle, I don't think we need to know that for the test. But, its good to know what they are.

Arshiya

I haven't gotten that far in the textbook, but I know hybridization can change the energy levels of the orbitals in molecules.

Arshiya

I believe it should also have an sp3 hybridization.

Arshiya

Like stated above, you can cancel the net dipole moments in order to determine if a molecule is polar or not. However, I think just basing it off the Lewis Structure might not be the best. For me, I like to know the shape of the molecule so I can visualize how the atoms are rearranged and how the di...

Arshiya

A dipole is when a molecule is separated by a partial positive charge and a partial negative charge. For example, H2O has a dipole moment. Oxygen is more electronegative and thus has a negative charge, while the two hydrogen carry a more positive charge. A dipole is quantified by its dipole moment w...

Arshiya

Polarizing power is the ability for a cation to distort an anion. On the other hand, polarizatibility is the tendency or the likelihood that the anion is becoming polarized.

Arshiya

A coordinate covalent bond is formed when two atoms share a pair of electrons, however those shared electrons come from one atom.

Arshiya

I am pretty sure we won't need to memorize all of them right now for the test. I remember Lavelle saying, the more we see them being used, the more we will remember. I wouldn't stress too much about that for the midterm.

Arshiya

As the number of orbitals increases, the s and d orbitals become very close in energy with s being slightly lower than d. Therefore, the 4s orbital will fill up first and then the 3d orbital will be filled. However, d becomes favorable when the electron has an uneven amount of electrons. Orbitals li...

Arshiya

For predicting the number of unpaired electrons, you can either write out the electron configuration in order to see how many electrons are left in the valence shell. Or you can locate the element on the periodic table, and see what block it occupies. If you know the block or orbital, you can see it...

Arshiya

Unfortunately, I think the only way to solve this question is by using the mass of the electron because kinetic energy has to do with the mass of the object that is moving at a speed. The equation would then be λ = 2(h*c)/m*v^2 and you would plug in all the numbers to get your value.

Arshiya

I'm not sure if you have taken chemistry or AP Chemistry in high school, but a good resource is the ap books as they supply some of the same information learned in class. I know the ap books break it down and are much easier to comprehend than some sections in this textbook. So for refreshers, you c...

Arshiya

Yes, valence electrons are only found in the s and p orbitals. So 2 electrons in the s orbital and 6 in the p orbital add up to the 8 valence electrons that are found in the elements.

Arshiya

For part a), I converted 3600 into meters and then multiplied it to the speed of light. The frequency found was 1.1*10^14 Hz. For part b), I used the equation E=hv, and solved for the E by using Plank's constant and the frequency found in part a. For part c), I used the energy in part b and multipli...

Arshiya

I don't think they have a correlation at all. I know diffraction is useful for studying the structure of molecules. The textbook doesn't relate the two, however, they do discuss how this interference relates to the wave-particle duality of electromagnetic radiation. Spectral lines are calculated whe...

Arshiya

I know from previous replies, many have stated not to worry about that topic for the midterm or test this Wednesday.

Arshiya

I understand that a photon must have a high enough energy to remove an electron? However, why can't two photons combine there energy to eject an electron?

Arshiya

In order to remove an electron, there has to be a photon and electron interaction. You can have a high intensity, meaning more photons interacting with electrons, however, this does not guarantee that electrons will be emitted. Instead, the photon must have greater energy than the electron in order ...

Arshiya

For one of the questions, it states in order to interpret the results of photoelectric experiments the model of light needs to change from a wave model to a particle model. I understand the experiment and how it works. However, is it wrong to say the light needs to change from a wave model to a phot...

Arshiya

If a question gives values with three significant figures and an answer is a whole number like 400, would I have to denote the answer with a decimal point like 400.?

Arshiya

You could also have two limiting reactants if there are two different reactions involved in the question.

Arshiya

When solving for the empirical formula, when do we know when to round up or down? For example, if it's 8.7 moles, should we round to 9 or multiply by a value to reach a whole number?

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