CHEMISTRY COMMUNITY

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The activated complex I believe is what forms when molecules in a reaction collide in the right orientation to form products. How temperature affects this is that with increasing temperature, there are more collisions, with higher energy (and are able to overcome the energy barrier/activation energy...

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I'm pretty sure you can always add Platinum if you're missing an inert conductor on one side of the cell. I think you can add any solid metal as your conductor, but Platinum is what is standard. I hope this helps!

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I'm pretty sure voltaic and galvanic cell are the same (convert chemical energy to electrical energy, standard cell potential is always positive). Electrolytic cells convert electrical energy to chemical energy, and use spontaneous reactions to drive nonspontaneous reactions, the standard cell poten...

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Maybe it is because when we are looking at reaction rates, we are looking at initial concentrations, when a reaction first starts. At this point in time no products have been formed, so they would not be included in the rate law, since they are not affecting the rate.

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You use the equation delta G = delta H - Tdelta S, and by plugging in your known values of delta H and S, you make G equal to zero and solve for T. That temperature, T (when G = 0) is when the reaction changes from nonspontaneous to spontaneous and vice versa.

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I believe that by lowering the activation energy of a reaction, catalysts increase the speed of a reaction.

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Athena L 1B wrote:Is Pt(s) the only other substance you would add in any scenario?

I think you can add any inert conductor (I think any solid metal), but Pt(s) is just the most commonly used.

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delta G standard is equal to zero when K=1, which I believe is very rare.

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I would assume 50-72% or so would be a C- and then the rest of the grading would be on a normal scale. I'm sure you could ask your TA though, or professor Lavelle.

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Does anyone know if we will be asked to draw a cell diagram for Test 2?

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Can someone explain how to balance redox reactions in acidic or basic conditions? How do you know what to use to balance out everything???

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Can someone please explain what inert conductors are, and why they are helpful in redox reactions? Thank you

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The internal energy of an isolated system is constant, and the entropy of an isolated system increases in the course of any spontaneous change, according to the first and second laws of thermodynamics.

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The equation is called the Van't Hoff Equation, and it helps show temperature dependence of K! It can be used to find K at different temperatures.

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I think Dr. Lavelle also mentioned that when K<1, enthalpy dominates over entropy, and the reaction will be non-spontaneous

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If K = 0, is the reaction at equilibrium?

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Because at the freezing temperature is when it goes from liquid to solid, so it's also the melting point, where it goes from solid to liquid. So you use the same temperature.

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dgerges 4H wrote:I also got that the other part of w=9.12 from w=-pdv. so i got a total of 11.45kj or 1.145x10^5j for w. is this correct?

I also got that for work

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It only doesn't change temperature when the phase change is occurring, because the energy being provided to or leaving the system is going towards breaking /forming bonds, not increasing or decreasing the temperature. Once the phase change is finished, then the energy will go towards changing temper...

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Definitely doing all the homework problems assigned, because I know sometimes textbook problems are put on the midterm / final verbatim.

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I know in the textbook sometimes just the final equation is given and not the intermediate equations that must be be set up and manipulated to solve for the final equation, but I'm pretty sure for this class that the intermediate equations and their enthalpies will be given in the problem so that al...

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In addition to that, sometimes you'll need to multiply one of the delta H's if the final reaction requires two moles of one of the substances, and the given delta H is for one mole. So you have to make sure that the reactions match with the amount of moles required in the final reaction, if that mak...

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How do you know which of the three methods to use when given a specific problem? Like when would you use Hess's Law vs. Bond Enthalpies vs. Standard Enthalpies of formation?

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Why are bond enthalpies the least accurate way of measuring reaction enthalpies?

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I believe the only way to change K is to change the temperature of a reaction.

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bars I believe is a unit of pressure, like atm, so if given this, you would be finding Kp, versus when given molarity, that is the concentration of a molecule, and you would find Kc.

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The easiest way to tell if a reaction is endothermic or exothermic is by the change in enthalpy (delta H), which I believe will be given for these types of reactions.

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I believe it is because the molar concentration of a pure substance, such as a liquid or solid, does not change in a reaction! So, since it doesn't change, it wouldn't affect the ICE table!

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I believe so.

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I'm pretty sure brackets indicate concentration so for Kc [H20] indicates the concentration of water, but with Kp you have (PCl2). You don't need brackets to indicate concentration for this because the P indicates the pressure of the gas. I hope this helps!

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I would say the easiest way is just to draw out the compound, especially if it is not too large of a molecule. It's also probably the easiest way to check your answer.

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I think in class it was stated that either definition will work for this class, and both sufficiently cover what we need to know.

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I don't think you have to memorize the different energy values of the different orbitals. Just know that s is always the lowest energy, and then p. Once you get to the fourth row, s fills up first because its a lower energy, but then once one electron is in the 3d orbital, that becomes your lowest, ...

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Hydrogen bonding is a type of dipole-dipole bond, that is stronger than other dipole-dipole bonds, as well as ion-dipole, dipole-induced dipole, and van der Waals / London dispersion forces. Hydrogen bonds can only occur between a hydrogen atom and a N, O, or F atom, because these atoms have very hi...

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molecules held in a polar covalent bond have dipoles. An induced dipole can happen to an element in a nonpolar covalent bond, when near a polar molecule, because the partial charge of that molecule will repel the electrons in the nonpolar molecule

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I think you would have to draw out the Lewis Structures and then add in the arrows for the dipole moments, making the arrows larger or smaller depending on the difference in electronegativity between the atoms being bonded. From that image you would look at the directions the arrows are pointing, an...

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I think for molecules like that, it is possible for it to have different isomers which are both polar and nonpolar. My TA did an example in discussion with C2F2H2, a similar molecule, and there were three isomers, one of which was nonpolar because the polarities cancel each other out. This isomer th...

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The first bond that two atoms make is a sigma bond. If two atoms have a double bond (i.e O=O) then they will have one sigma bond and one pi bond. If two atoms have a triple bond, like Nitrogen with Nitrogen, then there will be one sigma bond, and two pi bonds. So if two atoms are bound by more than ...

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I think it would be given, but in general you should just know conceptually that single bonds are the longest (and weakest), and then double bonds are shorter, and triple bonds are the shortest (and the strongest).

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I think if another molecule/element was nearby it would only shift the electrons within the molecule, through repulsion of charges, but not affect the actual angles within the molecule.

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I think if it involves cations and anions its an ionic bond, and polar bonding refers to covalent bonds between elements in their neutral states. The bond is only polar because elements have different electronegativities.

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The intensity of the light will decrease (i.e. the lamp will be dimmer). This is because there are now atoms that have a higher threshold energy in the lamp. So, the voltage energy being emitted is not sufficient enough to excite these atoms with a higher threshold energy, to the next energy level, ...

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Ionization energy is the energy it takes to remove an electron from an element. Once one electron is removed, the element has an overall positive charge. Electrons are negative, so they are therefore more attracted to this positively charged element, making them harder to remove.

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It does have access to its d and f subshells, those shells just aren't filled. This is why elements after row 2 can have an expanded octet (more than 8 electrons), because n=3, which means that l can equal 0,1, or 2 (s, p, and d orbital). Even though none of the elements in row three have any electr...

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I believe that going down a group has more significance than across a period for the trends. For example, with atomic radius, Arsenic would have a larger radius because it has the 4s 3d and 4p orbitals in addition to the orbitals in fluorine. The same goes for Selenium and Iodine. Although Iodine's ...

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I don't think we would be able to tell. If a question were to come up on quantum numbers, I think all you would need to know about ms is that it can only be +1/2 or -1/2. Whether it is + or - I believe is arbitrary for this class.

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I think that if the question was assigned, it would be better just to understand it, in case a question on molecules comes up. I believe all of those compounds are salts, so it would make sense that the Lewis structures were written like ionic compounds.

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Once there is an electron in the 3d orbital, it has a lower energy than the 4s orbital, meaning that the electron configuration would be written as 3d1 4s2. Copper's neutral state electron configuration is 3d10 4s1. Since electrons are removed from the highest energy level first, the electron in the...

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Zn+ having an electron removed from the 4s orbital isn't an exception to a rule. Once an electron is in the 3d orbital, that orbital has a lower energy than 4s, which would mean the electron configuration is written as 3d1 4s2. Since electrons are removed from the highest energy level (the level wri...

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I believe r is the radius and R is the radial wavefunction, which indicates how the wavefunction varies as a particle moves away from the nucleus in any direction. It is a part of the wavefunction equation where Ψ(r, θ , ф) = R(r) x Y(θ, ф)

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I believe there is an example in the textbook (6th edition) on page 23. It goes through how to calculate the energies of a particle in a box.

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When an electron is removed, the atom becomes a cation, or a positively charged ion. This positive charge in the atom makes the electrons more attracted to it, and therefore harder to remove.

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Intensity is increasing the amplitude of the wavelength, so making it larger or smaller. When light is acting as a particle, increasing the intensity is just increasing the amount of photons (not the energy per photon). The reason why intensity was significant was because in the photoelectric experi...

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Wavelength is measured in meters, so always convert to meters! Energy is in Joules. eV, Watts, and cal can all be converted into Joules (the conversion are in the back of the book). So yes, always convert back to meters or Joules

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Black body radiation is an object that absorbs ALL radiation at all wavelengths. To the extent of my knowledge, it has no real equivalent in everyday life, and the closest example would be something like a black hole. I do not believe that we need to know about black body radiation for this course.

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If the threshold energy is given in Joules/mole, you just have to divide by Avogadro's number (6.022x10^23) in order to cancel the units. Then you will just have Joules and can use that number in your equations.

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Tamera Scott 3L wrote:I've also seen E=hf once, does anyone know if that is the same as E=hv?

v is frequency, so I believe f would just be another way to denote frequency.

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the equation shows that the energy per photon is proportional to frequency. As frequency increases, so does the energy per photon. Planck's constant, h, is the proportionality constant that equates v to E.

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In one of the module's Professor Lavelle mentions that light's affect on electrons is more noticeable because they have a much smaller mass than protons/neutrons. However, would the position of the electron's in the atom also be significant, because they are located in orbitals outside the nucleus?

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I believe it is more standard to round up with numbers ending in 5

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So when asked for atoms of a molecule we can multiply by the mols by Avogadro's number to get number of atoms, but I do not understand how to get molecules from mols? You can do the same thing to get molecules, because moles is just a unit of "something" not just an atom, but also molecul...

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When professor Lavelle was talking about the oscillation of electric and magnetic fields, are both important when looking at electromagnetic radiation / light? Like what is the significance of each? I know he addressed the speed of the electric field, and it's importance in different ranges of visib...

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