CHEMISTRY COMMUNITY

Isaiah Little 1A 14B

Catalysts are usually shown in the reaction equation above the "======>" arrow. For example, if potassium iodide is the catalyst in a reaction then "KI" will be written above the "======>" reaction arrow.

Isaiah Little 1A 14B

Cell potential is the potential voltage that a galvanic cell can exhibit based on the reduction potentials of its redox reactions. A substance with a higher reducing power is more likely to be oxidized, meaning that it is most "willing" to give up electrons in order to reduce other substan...

Isaiah Little 1A 14B

It depends on which side needs to be balanced in terms of excess hydrogen. If the solution is acidic, H+ would be added to whichever side that needs more hydrogen atoms to balance the redox equation, whereas OH- would be added in redox equations in basic solutions.

Isaiah Little 1A 14B

Raising the temperature in a reaction typically increases the rate at which the reaction proceeds (k) since the increased average kinetic energy of the particles in the reaction causes more reactants to collide with other reactants to form products.

Isaiah Little 1A 14B

Typically, k increases as the temperature increases because heat increases the average kinetic energy of the particles in a reaction, increasing the likelihood that two reactants will meet and thus react.

Isaiah Little 1A 14B

Activation energy is the main determinant in the kinetic stability of a reaction. For instance, a reaction is kinetically stable if the activation energy is exceedingly high (i.e.; the conversion of carbon (diamond) into carbon (graphite) since said reaction would take a high amount of energy to und...

Isaiah Little 1A 14B

For reactions with multiple reactants, we also tend to use a small amount of one reactant and excess of the other reactants in order to study the order of each reactant. For example, in a reaction A + B + C ====> D, we would use A and C in excess and a small amount of B to determine its order with r...

Isaiah Little 1A 14B

Countless biological chemical reactions are also catalyzed by proteins, such as the metabolization of lactose using lactase.

Isaiah Little 1A 14B

Half-life deals with finding the time it takes one reactant to decompose to half of its original mass, so there cannot be "multiple reactant" half-life problems.

Isaiah Little 1A 14B

Christy Zhao 1H wrote:How do you know when to use Pt or graphite?

It usually specifies whether platinum or graphite is used, but both serve the same purpose. However, a Pt(s) electrode is more commonly used.

Isaiah Little 1A 14B

Most chemical experiments occur at STP, or Standard Temperature and Pressure, where the reaction occurs at 25 C (298 K) and 1 atm of atmospheric pressure. The reason for using STP is to allow other scientists to easily reproduce the conditions for the experiment.

Isaiah Little 1A 14B

I believe that there is no advantage to using a salt bridge over a porous membrane. Both work by allowing the charged ions to move from one solution to another in order to keep the charge flowing. If there was no salt bridge, the charged ions (say, Fe3+) would accumulate in one beaker and no electri...

Isaiah Little 1A 14B

It shouldn't matter; they're both the same thing. I just use H+ for the sake of saving time and ink.

Isaiah Little 1A 14B

You would only add H2O to balance out the number of oxygen atoms in a reaction. Otherwise, to balance the number of hydrogen atoms in a redox reaction, you would add H+ ions to whichever side as needed. Then to balance the charges, you would add electrons as necessary. In this case, the reaction wou...

Isaiah Little 1A 14B

A greater volume (lower pressure) allows for more room for the molecules to occupy, increasing the potential for degeneracy in the system. Think of it in terms of one mile of crowded freeway; the more lanes there are for cars to move about, the more combinations of different cars there can be in tha...

Isaiah Little 1A 14B

I doubt that we would have to know any other equation other than those provided on the equation sheets. The derivations are taught most likely to provide a basis of understanding on where the equation came from and how they relate to one another, rather than just name dropping a formula.

Isaiah Little 1A 14B

This is because in an isothermal reversible expansion process all energy is converted into useful work, whereas in isothermal irreversible expansion some energy is lost in the form of entropy; therefore, the work value of the latter would be less than the former.

Isaiah Little 1A 14B

The delta S (surroundings) for irreversible expansion is zero because some of the energy was lost in the form of entropy (whereas in reversible expansion, all energy is converted into useful work), so the overall change in entropy (delta S (total)) has to be a positive number. The system is also iso...

Isaiah Little 1A 14B

Think of 0 K as a theoretical limit, where entropy is a function of the temperature in Kelvin. As T approaches 0 K, so would entropy; but since we cannot achieve 0 K, we can only approach zero entropy.

Isaiah Little 1A 14B

I believe that we assume ideal gas behavior for the sake of understanding the basis of the concept. Calculating for non-ideal gas behavior before understanding the ideal gas behavior would most likely be more confusing because the former requires more to be taken into account.

Isaiah Little 1A 14B

Without the weight pulley controlling the gas's volume, the gas would expand throughout the container because of the positive pressure it exerts against the vacuum. Adding weight to the pulley will counteract the pressure exerted by the gas, compressing said gas in the container -- whereas removing ...

Isaiah Little 1A 14B

I've heard that Dr. Lavelle's office hours may be busy at times, so seeing a TA or making use of the Peer Learning Sessions may be viable options as well. All of these hours can be found on the 14B website!!

Isaiah Little 1A 14B

As Clarisse said, the heat of fusion/vaporization should be given. You would then need to determine which value to use (heat of vaporization for phase changes between liquids and gases, and heat of fusion for phase changes between liquids and solids), where you would then multiply the value by the m...

Isaiah Little 1A 14B

It helps to consider whether the phase change is exothermic or endothermic, because then you'll know if heat is being absorbed or released. The heat of vaporization from a liquid to a gas is positive because it is an endothermic phase change that requires energy, whereas the heat of fusion from a li...

Isaiah Little 1A 14B

Because W (work) = PdV (pressure times a change in volume), work cannot be done if there is no change in volume since the dV value would equal 0.

Isaiah Little 1A 14B

I doubt that we will have to memorize any enthalpy values or heats of vaporization/fusion, but it may be helpful to have the 4.18 j/gc value handy when doing heat calculations involving water.

Isaiah Little 1A 14B

To convert L/atm to Joules, you would multiply the L/atm amount by 101.325 joules, since 1 L/atm = 101.325 joules.

Isaiah Little 1A 14B

A change in degrees Celsius would be equivalent to the change in degrees Kelvin.

Isaiah Little 1A 14B

It probably varies from TA to TA, but I don't see why pencil would be a problem! Tests should be in pen, though.

Isaiah Little 1A 14B

I believe that it is covered in 14BL, however.

Isaiah Little 1A 14B

The way I remember them is that I remember the shapes that have the largest number of bonding atoms, like octahedral and tetrahedral. If lone pairs replace the bonding atoms in a molecule, I picture the shape without a bonding atom at a point (ex; tetrahedral + 1 lone pair in place of an atom = trig...

Isaiah Little 1A 14B

A symmetrical molecule cannot be polar, regardless if the bonds within the molecule are polar or not.

Isaiah Little 1A 14B

Dipole moments usually pertain to an unequal distribution of electrons in a molecule. This unequal distribution arises as a result of highly-polar bonds and asymmetry within the molecule, where the charged electrons of a molecule reside together on one end of the molecule. For instance, water has a ...

Isaiah Little 1A 14B

It shouldn't be on the final because it was not covered in any class or discussion section as far as I'm concerned

Isaiah Little 1A 14B

A delocalized bond usually involves resonance between different bond types. For example, the double and single bonds of each carbon in a benzene ring resonate between double in single bonds; therefore, the double bonds are delocalized because they are not defined to a certain region.

Isaiah Little 1A 14B

Think of it in terms of polarity; if a charge is concentrated on one side of the molecule and not the other, then the molecule will be polar, but if the charges are evenly distributed then the molecule's polarity will cancel out.

Isaiah Little 1A 14B

That structure with a double bond would work IF nitrogen broke the octet rule, but it cannot since its principle quantum number is 2 and there is no 2d orbital.

Isaiah Little 1A 14B

I really found the whole TM and biological significance section interesting. What are some other examples of vital TM complexes other than the ones we learned in class?

Isaiah Little 1A 14B

For the sake of simplicity and this class, complete combustion always results in the production of gaseous H2O and CO2. In reality, combustion produces many other compounds, such as CO.

Isaiah Little 1A 14B

SiO2 is polar based on the electronegativity differences between Silicon and Oxygen, which can be interpreted from the periodic table. Although the SiO2 molecule itself is non-polar due to symmetry, the bonds between the Si and O atoms are polar.

Isaiah Little 1A 14B

To add to the previous statement (which also added to its previous statement), atoms bond to achieve noble gas configuration, which is considered low-energy and stable.

Isaiah Little 1A 14B

Unless the object of interest is a photon, then said object's velocity should be slower than the speed of light. Any velocity that exceeds the speed of light would be unreasonable.

Isaiah Little 1A 14B

Generally speaking, bonds between metals and nonmetals form ions when they bond, so a metal/nonmetal bond is an ionic bond. A covalent bond occurs between nonmetals, and a metallic bond is a bond between metal elements.

Isaiah Little 1A 14B

In my high school we were required to memorize a list of polyatomic ions, which included the formulas for compounds such as ammonium and sulfate. I haven't heard much about having to do the same here at UCLA yet, but it would only be beneficial to know the formulas.

Isaiah Little 1A 14B

Generally speaking, electron affinity increases up a group and across a period. This is mainly due to the shielding of electrons and an electron's "desire" to achieve noble gas configuration. For instance, fluorine has a higher electron affinity than oxygen because the former only needs on...

Isaiah Little 1A 14B

It'd probably be beneficial to know that a photon with a wavelength of 400-700 nm lies in the visible light spectrum, that a photon with a wavelength shorter than 400 nm is typically ultraviolet or higher energy particles (x-rays, gamma rays), and that 800 and above corresponds to infrared or lower-...

Isaiah Little 1A 14B

Wavelength is given instead of frequency most likely because the creators of the book wished for you to do an extra step to make the problems more complex. However, you can find the frequency from wavelength using c=lambda*nu, where lambda is the wavelength and nu is the frequency. Just rearrange th...

Isaiah Little 1A 14B

S2- is larger than O- because S2- has more protons and thus a stronger pull on its electrons than O- does, so it has a smaller atomic radius.

Isaiah Little 1A 14B

I was gonna make a funny chemistry joke.
But they argon.

Isaiah Little 1A 14B

Generally speaking, cations (positive ions) are typically metals which lose their electrons in an ionic bond, while anions (negatively charged ions) are typically nonmetals which gain electrons in an ionic bond. For example, in KCl, the metal K loses it's electron based on the aforementioned rule, w...

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