CHEMISTRY COMMUNITY

Hazem Nasef 1I

That is the specific heat capacity of the Potion in terms of kilojoules. This is taken from part 1B, where it is mentioned in the question as 5.4 J/C.g. This is then converted to kilojoules.

Hazem Nasef 1I

I'll assume you are talking about heating curves since that is what is relevant to heat capacity. Since the x-axis is time, and the y-axis is temperature, a steep slope would mean it takes less time to reach a certain temperature than a slope that isn't steep. If something requires less time to reac...

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The change in internal energy for this problem is solely due to work from compression. There is no mention of using heat or increasing the temperature of the pump. Since the problem only speaks of compression work, it is assumed no heat was transferred.

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Two molecules have to collide in the correct orientation, meaning that specific places on one molecule must collide with another molecule in a certain location. The molecules can't just randomly collide in any location in order for the reaction to proceed. Think of it like plugging a plug into an ou...

Hazem Nasef 1I

Yes, you are correct. Starting with the original equation, if you move ln[A]0 to the other side, it becomes ln[A] - ln [A]0 and you are left with -kt on the other side. Dividing by the negative one will result in -ln[A] + ln[A]0, which can be rewritten as ln([A]0/[A]), which is equivalent to kt.

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A negative order means that as the concentration of that substance is increased, the rate of the reaction decreases. An example of this would be a product with a negative order. If the concentration of this product is increased, it participates in a reverse reaction, thereby slowing down the reactio...

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For a zero order reaction, a graph of [A] vs time will produce a straight line with a negative slope. For a first order reaction, a graph of ln([A]) vs time will produce a straight line with a negative slope. For a second order reaction, a graph of 1/[A] vs time will produce a straight line with a p...

Hazem Nasef 1I

When hydrogen peroxide decomposes into water and oxygen gas, the process is quite slow. Adding the catalyst potassium permanganate will speed up the reaction, causing it to proceed almost instantly by using an alternate energy pathway that requires a lower activation energy.

Hazem Nasef 1I

In the regular rate laws, it is assumed that the coefficients in front of the reactants and products are all 1. In this case, when the coefficient of the reactant is 2, then the differential rate law has a 1/2 in front of it. When this is integrated, there is now a 2 in front of the -k*t instead of ...

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The reaction rate is represented as change in concentration over change in time. Since the concentration of reactants decreases as time goes on, the change in concentration is a negative value. To make the reaction rate a positive value, we always place a negative sign in front of the change in conc...

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You add an inert platinum electrode whenever there is no solid substance in a half-cell. For example, for the standard hydrogen electrode, aqueous hydrogen ions are reduced to hydrogen gas, so since there is no solid substance to serve as the electrode, which is why an inert platinum electrode is ne...

Hazem Nasef 1I

There is no difference in using log versus using ln. The main reason log is preferred is because it is used in measuring pH, so it is easier to keep the logarithm the same base across chemistry, rather than switching from ln to log.

Hazem Nasef 1I

To balance in basic solution, first balance the half reactions as if they were in acidic solution and add them together. Then, add OH- ions to both sides in the same number which H+ions are present on one side. (i.e. if you have 6H+ ions, then add 6OH- ions to both sides) The side that has 6H+ and 6...

Hazem Nasef 1I

I understand that all values are for standard reduction potentials, but when using the Ecell=Ecathode-Eanode we plug in both values for the reduction potential of the equations from the anode and cathode even when we know the reaction at the anode is actually the reverse reaction since it is actual...

Hazem Nasef 1I

When balancing half-reactions, first balance all the elements except for hydrogen and oxygen. Then, balance any oxygens by adding the appropriate number of water molecules to the side opposite of the oxygens. Then, you balance the hydrogens from the water molecules by adding H+ ions to the side oppo...

Hazem Nasef 1I

Also, if you can find someone from previous years to buy the course reader from, it has all of the lecture slides in it.

Hazem Nasef 1I

An increase in disorder would correspond to an increase in entropy, since entropy is the number of different states a system can be in. For example, when a substance goes from a liquid to a gas, there is an increase in entropy of the system, since the collection of gas molecules can occupy a greater...

Hazem Nasef 1I

When Gibb's Free energy is negative, this means that the process is spontaneous, in other words, one that will occur without any energy input from the surroundings. There are many examples of spontaneous processes in everyday life. Two of these would be iron rusting or the decay of radioisotopes.

Hazem Nasef 1I

Heat capacity is a measured value of the amount of heat required to raise an object's temperature by 1 degree Celsius, it is not a calculated value. (there is no formula) Entropy refers to the likelihood a system will be in a particular state. I don't believe there is any connection between the two ...

Hazem Nasef 1I

will anything about knowing how the equations were made up as shown in todays lecture need to be rememberes I think it is fair game for the midterm since it was covered during lecture. Normally, we aren't asked questions about derivations of formulas, but I would still be familiar with it to be safe.

Hazem Nasef 1I

Degeneracy refers to the number of ways of achieving a given energy state. Disorder refers to the organization of atoms and molecules. They are similar in the fact that when either degeneracy (Boltzmann equation) or disorder increases, entropy also increases. Although they are similar properties, th...

Hazem Nasef 1I

You are correct in that reversible expansions do more work than irreversible expansions. Although internal energy is a state property, both work and heat depend on the path taken, so they are not state properties. Work for a reversible expansion is nRT*ln(V2/V1) and is -P*deltaV for an irreversible ...

Hazem Nasef 1I

I believe normally that the number of states possible in a system would be given to you, or you would be able to deduce it from information given (i.e. the number of arrangements of molecules that result in the same energy) and you would have to calculate degeneracy. The degeneracy is given by the n...

Hazem Nasef 1I

Increasing degeneracy results in an increase in entropy of the system. This is shown by the Boltzmann equation: S=kB*ln(W), where w is the degeneracy and S is entropy. Therefore, an increase in w increases the value of S, which is entropy. This also makes sense because degeneracy is the number of wa...

Hazem Nasef 1I

You can use the conversion of about 22.7 L being equivalent to one mole of gas ONLY because this question is occurring under standard temperature (0 C) and pressure (1 atm). You get the same answer if you use it for this question. However, if the reaction is not occurring under these conditions, the...

Hazem Nasef 1I

If you notice, in the original equation, it was just N2 reacting with 2.5 moles of O2 ( or 5 moles of O). In this second reaction, instead of N2, it is two moles of NO, which contains two moles of O, and then 1.5 moles of O2 (or 3 moles of O). So both equations essentially have 5 moles of O, but the...

Hazem Nasef 1I

That is how they calculated the enthalpy of vaporization because these values are always reported per 1 mole. If you divide the the heat by the number of moles, you'll get the enthalpy per mole, which is the standard way of reporting it.

Hazem Nasef 1I

McKenna disc 1C wrote:So it can be at any temperature, so long as the substances are existing in their standard state? Thanks!

Yes, that is correct. However, most of the time, the reported data is for 25 degrees celsius.

Hazem Nasef 1I

The Born Haber cycle is a way of breaking up the lattice enthalpy into smaller processes, whose values are known. The lattice enthalpy is equivalent to the sum of the enthalpy of atomization of the cation, enthalpy of atomization of the anion, the ionization energy of the cation, the electron affini...

Hazem Nasef 1I

No, my TA told us that any values like these necessary for a problem will be given to you.

Hazem Nasef 1I

It's not necessarily having more oxygens, but rather having more atoms that stabilize the anion by withdrawing delocalizing the negative charge. For example, as Dr. Lavelle discussed in class, trichloroacetic acid (an acetic acid molecule in which the three hydrogen atoms are replaced with chlorine ...

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A lewis acid is a species which accepts electron pairs. BF3 is electron deficient, because it only has 6 valence electrons. It has room to form a coordinate covalent bond, by accepting an electron pair from a lewis base, such as ammonia, which has a lone pair of electrons.

Hazem Nasef 1I

Yes, you are correct. Whenever a compound has resonance, this means that a double or triple bond can be found in multiple locations in the compound. That second or third bond is always a pi bond, and when there is resonance, that means that the electrons involved in the pi bond are delocalized.

Hazem Nasef 1I

Although if you count the number of atoms and molecules, it seems to have increased, no extra molecules have been inserted into the flask. All that happened was that 3 of the molecules have dissociated into atoms, so the actual amount of substance has not changed. Therefore, the pressure remains con...

Hazem Nasef 1I

It seems that for the anionic ligands in the table, they can be named without memorization as the same rule applies: change the -ide to -ido, the -ate to -ato, and the -ite to -ito. As far as the neutral ligands, we should definitely know the prefix for water and ammonia as those were on the homewor...

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When you draw the 2-D lewis structure, the chlorines can be placed opposite each other, and it appears that the dipoles cancel. However, CH2Cl2 is a 3-D molecule arranged in a tetrahedral shape. No matter how you arrange the chlorine atoms and hydrogen atoms, the dipoles will never be completely opp...

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The simplest coordination compounds are linear with a coordination number of 2. Coordination numbers as high as 12 are found with elements of the f-block, but are rare in the d-block.

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The d subshell consists of five orbitals. Three of them have 4 lobes of electron density located in the XY, YZ, and ZX planes. One of them has lobes of electron density along the X and Y axis. The last one has lobes of electron density along the Z axis and and a donut shape of electron density in th...

Hazem Nasef 1I

There's two conventions for drawing the dipoles. The classic convention is to draw the arrow pointing towards the negative partial charge. The modern convention is to draw the arrow pointing towards the positive partial charge. Both are valid, but since Dr. Lavelle showed us the classic convention, ...

Hazem Nasef 1I

I would say a good way to memorize them is to organize the shapes by electron domain geometry. Then, you should know that there are shapes whose molecular geometry matches its electron domain geometry, and shapes with one or more lone pairs replacing an atom. For example, for tetrahedral electron do...

Hazem Nasef 1I

Yes, you can look at the distance between the two elements on the periodic table. For example, sodium and chlorine are on opposite sides of the periodic table, so you can know that the electronegativity difference will be quite large and an ionic bond will form. As opposed to nitrogen and oxygen, wh...

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Formal charge is basically the charge that an atom would have if the bond it formed is perfectly covalent. Basically, that means it's the charge that the atom would have it "owned" its lone pair electrons and "owned" half the number of shared electrons. When formal charge is 0, t...

Hazem Nasef 1I

My homework points are inputted on MyUCLA. I think it just depends on your TA, and if they want to put them in weekly or at the end.

Hazem Nasef 1I

You should complete problems related to the topics covered in lecture this week. We've been finishing up chapter 2, so you should probably do problems from the end of the assigned problems of chapter 2 that we covered this week. The chapter 2 problems are: 1, 13, 17, 19, 21, 23, 25, 27, 29, 31, 33, ...

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The lower case "h" represents Planck's constant in equations like De Broglie's equation and the Bohr frequency condition. Frequency is represented by a lower case Nu, which looks like a lower case "v". Frequency doesn't tend to be represented by h.

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Essentially, electromagnetic radiation can act as both a wave or a particle, depending on the situation. This was shown for example in the photoelectric effect, when the incident UV radiation on the metal acted as photons of light, rather than waves, with each individual photon requiring enough ener...

Hazem Nasef 1I

They stopped selling them in order to cut down on costs for students.

Hazem Nasef 1I

The intensity of the light is essentially the amplitude. Increasing the intensity increases the number of photons hitting the metal. Originally, it was expected that if a certain intensity of UV light didn't remove electrons from the metal, then increasing the intensity of the light (or number of ph...

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What relationship do these series have with the elements? Do all elements have these series? Are the different series only referring to the electrons? The Balmer and Lyman series are specific only to the hydrogen atom, not other elements. They represent the transitions of hydrogen's electron betwee...

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If you were asking about how to find how much reactant is actually remaining, you would use the limiting reactant to find the moles of excess reactant actually used. Then, you would subtract how much was used from the amount of the excess reactant to find how much excess reactant is left over.

Hazem Nasef 1I

Whenever I click on the Chemistry 14A site at CCLE it goes directly to Professor Lavelle's website, and I cant find the link for media resources on his website anywhere. Where should I go? I joined the class late, so I missed three lectures. I also could not find the link for media resources since ...

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