CHEMISTRY COMMUNITY

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- Unimolecular reaction: only 1 reactant molecule participates, molecularity =1
- Bimolecular reaction: two reactant species come together to react, molecularity=2
- Termolecular reaction: the collision of 3 molecules & uncommon

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You can determine molecularity by looking at the number of molecules/ions/atoms that are participating in the rate determining step of a reaction.

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When you are looking at the elementary reactions, catalysts are in the very first step as a reactant and as a product in the very last step too. Catalysts create a different, faster pathway for the reaction, but it is not used. Intermediates are not present as reactants in the first step but are pro...

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The catalyst provides a completely different pathway, which speeds up the reaction; it does not speed up the original pathway. You usually base the rate law on the slowest, rate determining step. But when a catalyst is introduced, you can base it upon the new, different pathway the catalyst provides...

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deltaStot = deltaSsys + deltaSsurr
When a reaction is at equilibrium & is reversible.
Then, deltaSsurr=-deltaSsys

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First, focus on balancing the reactants and products of each half reaction. Next, to get the overall reaction, add the two half-reactions together. At this step, you would multiply a factor to a half reaction if needed so that electrons/spectators are canceled as needed for the overall rxn.

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A weak acid has less % dissociation (less of the acid, or the [HA] is breaking down), so that means when you take the pH, the value will be higher.

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If we are asked to find the frequency factor, A, it tells us how often molecules collide when the concentration is [1] and whether or not the molecules are properly oriented.

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Like the others said k' is the rate constant for the reverse reaction. In addition to applying it to the K=k/k', you can also see k' in elementary reaction rates that are used to find net rate of formation.

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I think dimerization is referring to an addition reaction where two molecules of the same compound react. For example, molecule A + molecule A reacts to form molecule A2.

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This list really helped me determined oxidation numbers!

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Both the salt bridge and the porous disk have the same purpose in a cell. They facilitate ion transfer, which stops charge buildup within the cell. I don't think we have to know when/why either is used for this class; it will be either be stated in the problem or it won't be significant.

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They are the same; there are just two names for it. Both are names for an electrochemical cell in which a spontaneous redox reaction is induced to create electrical charge flow.

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Yes, F is the Faraday constant. The Faraday constant represents the # of colombs per mole of elections. I think it is given to us on the equation sheet!

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Because entropy is a state function, it doesn't matter what "path" you take, as long as you correctly get from point A to point B. Therefore, you calculate the change in volume, then you can calculate the change in temperature (or vice versa, it doesn't what order you do it in). Then you a...

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They are different because their C value is different depending on the structure of the molecule you're looking at and whether or not the system is at constant pressure or constant volume. Cv,m=3/2R for a monatomic molecule Cv,m= 5/2R for a diatomic or linear molecule Cp,m=5/2R for a monatomic molec...

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Using the ideal gas law, or Boyle's law, where PV=nRT, P and V are inversely proportional which is why V2/V1=P1/P2.

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Le learned this in discussion today and these are from my notes!
- For a reversible, isothermal expansion of an ideal gas:
w=-nRTln(Vfinal/Vinitial) OR w=-nRTln(Pinitial/Pfinal)
- For constant pressure:
w=-PdeltaV=-deltanRT
- For constant volume:
w=0

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The constant C in (ΔS = nC ln (T2/T1)) stands for the heat capacity at constant volume or constant pressure, depending on the problem.

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Degeneracy refers to the multiple ways that energy can be configured. Entropy refers to the "uncertainty" or "disorder" of a system. They have a proportional relationship; as degeneracy increases, entropy increases too, vice versa.

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Heat (q) is negative when the amount of heat is being released/reaction is exothermic. The equation for entropy includes delta q, or the change in q; this is how q and entropy are related.

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Here's the worked out problem!

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Temperature is the only thing that affects the equilibrium constant (K). Therefore, when temperature changes, so does K. Q is used to calculate the current state or a hypothetical state of a reaction to compare to the K for the temperature to see whether the reaction will favor reactants or products.

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We don't have to always convert to K for every calculation in chemistry, but most of the equations we use right now have units that use K in them. The best course of action is to look at the units used in the equation/problem and adjust accordingly.

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More work is down in a reversible expansion because they move very slowly and work against external pressure. Think about the equations; the equation for reversible expansion uses an integral for accuracy because the expansion is slower and does more work whereas the equation for irreversible equati...

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Microstates are specific ways in which the energy of a system can be arranged. The multiple ways the energy can be arranged depends on the atom/molecule arrangements. Entropy is the measure of uncertainty in a system, so the more microstates there are, the higher the entropy.

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DeltaU describes the change in internal energy of a system and DeltaH describes the change in total heat content of the system. Entropy is the measure of uncertainty, which is very significant in describing a system.

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A thermos is technically an isolated system because there is no exchange of matter or energy between the system (thermos) and surroundings. However, a cold or hot drink in the thermos will eventually get to room temperature. It's very difficult to achieve and build a true, isolated system, but the t...

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Steam hurts a lot more than just hot water because of the energy difference. Looking at the heating curve, steam (water in gas form) lies higher than hot water (water in liquid form; although it is hot water and "holds" more energy, it is still a liquid). When the steam hits your hand, the...

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Extensive properties depend on the quantity of material being measured. An example of an extensive property is mass. The higher the quantity of the material, the higher the mass will be. On the other hand, intensive properties don't depend on the quantity of material being measured. For example, an ...

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Hess's Law states that the heat of a specific reaction is equal to the sum of the heats of reaction. This depends on the fact that enthalpy is a state function because state function values do not depend on the path that is taken to reach that specific value. Therefore, it is okay to add/subtract th...

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Isolated systems are important because there is no energy or matter transfer between the system and its surroundings. An open system allows both energy and matter to transfer between the system and its surroundings & a closed system allows energy to be transferred between the system and its surr...

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ClF3 is T-Shaped, and so the dipole movement between the Cl and F atoms do not evenly cancel each other out. This means the ClF3 molecule is polar. However, the BF3 molecule is trigonal planar, so the dipole movement between the B and F atoms cancel each other out. The dipole movement points to the ...

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You don't have to draw wedges/lined triangles in a trigonal planar shape. The wedges and such indicate that the bond is 3D (either "coming out" of the paper or "going into" the paper), but all four atoms in a trigonal planar molecule lay flat.

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Here!

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Yes, the relationship between the strength of an acid/base and the strength of its conjugate base/acid is inversely proportional. The stronger the base is, the stronger its conjugate acid & vice versa.

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First, add together the number of bonds in the molecule (the number following X). In this case, it is 3. Then add the number of lone pairs (the number following E). In this case, it is 1. 3 + 1 = 4. Therefore, we know that the shape is tetrahedral, but since there is a lone pair, the geometry is tri...

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When we increase the temperature, water's ability to ionize increases, so [H+] increases, which means pH decreases. Essentially, a record of a pH value without a corresponding temperature value is not enough information in something like a lab report. If it is just water by itself, I don't think tem...

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Looking at salt as the product of an acid-base reaction, we can determine how the salt would act. For example, a popular neutral salt is table salt, or NaCl. We know the Na+ ion comes from NaOH. NaOH is a strong base, dissociating fully. Once dissociated, Na+ does not want to turn back into NaOH. We...

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Water is left out of the equation because it doesn't change in concentration. These equations are determining the strength of an acid/base, so the constant H2O concentration does not play a role.

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For example, we are given that the molarity of a solution is 0.1M NaOH. Since we know that NaOH is a strong base, we know that it will fully dissociate. Therefore,
0.1 M NaOH --> 0.1 M OH-
pH = 14 - pOH = 14 - (-log([OH-])) = 14 - (-log([0.1M)) = 14 - 1 = 13

So, the final answer is pH = 13.

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They aren't exactly the same, but they are related. The PKa/PKb is used to measure the strength of an acid or base in solution whereas pH is specifically the measure of the concentration of hydrogen ions in solution.

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In an acid-base reaction, the conjugate acid/base are on the products side of the equation. Essentially, the conjugate acid is the base with a hydrogen ion added to it. The conjugate base what is remaining after the original acid has donated a proton during the acid-base reaction.

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Polar compounds are often nonsymmetrical as well. The lack of symmetry is what causes dipole moments. Nonpolar molecules do not have dipole moments because either the bonded atoms do not have a great enough electronegativity difference or the molecule is symmetrical and the dipole moments cancel.

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I agree with the others who have responded. I feel that it is always best to start out with a Lewis structure and then go from there. You can determine the shape/structure and then observe how the intermolecular forces affect molecule interaction.

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It seems a little bit counterintuitive, but forming bonds requires energy. Creating a bond is bringing 2+ atoms into a more stable position. Thus, breaking the bond is where energy is absorbed whereas forming bonds is where energy is released.

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Determining when the bond angle is a "little less" or "slightly less" greatly depends on the existence of lone pairs and how it creates repulsion against one another and thus, against the other atoms within the molecules. I like to try to imagine the molecule and picture how cert...

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Essentially, the question is asking the following: Of CF4, CCl4, and CBr4, which is the strongest bond? The strongest bond would be the shortest bond; the pull between the two atoms is the strongest. Therefore, the strongest C-X bond would be predicted to be CF4.

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It isn't necessary to memorize exact bond angles for specific molecules. Dr. Lavelle mentioned that we just need to know how lone pairs affect repulsion and nearby bond angles (i.e. a lone pair will push against adjacent bond angles, making them less than the standard degree for that specific shape).

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Electronegativity is how efficient an atom can attract electrons and electron affinity is the energy released when an electron is added in the gaseous state to form an anion. Electronegativity increases and electron affinity gets more negative from left to right, and from bottom to top.

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An easy way to memorize how the atomic radius trends are to consider how electrons and protons are attracted to each other.

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I don't think Dr. Lavelle said anything specific about naming ionic compounds, but an easy way to remember is to name the cation first and then name the anion second, changing the suffix of the nonmetal to "-ide."

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The Balmer and Lyman series are just named for series with a specific final resting energy quanta level (n). Lyman's final resting spot is n=1 whereas Balmer ends at n=2.

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The use of Roman numerals in chemical nomenclature is to indicate the charge of the ion. Usually, the transitional metal has multiple possible ion charges. For example, Fe (II) stands for Fe2+ and Fe (III) stands for Fe3+; the charge changes according to the number of electrons on the atom.

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The center atom is most likely the one with the lowest ionization/electronization energy.

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When determining the shape of a molecule, I like to draw a basic Lewis dot structure model and then use the VSEPR (Valence Shell Electron Pair Repulsion) theory, which states that the repulsion of the valence electron pairs is what gives the molecules their shape.

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Essentially the Pauli exclusion principle doesn't allow the electrons to have the same exact quantum numbers. So to occupy the same orbital, the spin has to be different.

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There are two exceptions because a completely full/half full d sub-level is more stable than when partially filled, so an electron from the 4 oribital is excited and moves to a 3d orbital. They are more stable configurations. And I agree, I think we should memorize these exceptions.

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I usually try to keep as many sig figs as I can during the calculations so that the final answer is more accurate. Then, I do all the rounding and cut down to the appropriate number of sig figs at the final step.

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I think Dr. Lavelle mentioned this in lecture! From what I remember, he said there is no specific wavelength where a moving object is considered to have "measurable wave-like properties." I don't think we will have to worry about this on any tests/quizzes though, it's just something to kee...

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Can someone explain how to do Ch.1 6th edition 57?

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Yes, they are asking for the empirical formula.

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It gives you the radius, but you need the diameter to get the length of the chain. So 2 x 144 pm = 288 pm. 1 mol of Ag means there are 6.022 x 10^23 atoms of Ag. Then you multiply (6.022 x 10^23 atoms of Ag)(288 pm)= 1.73 x 10^26 pm. Then, you convert to km, which is 1.73 x 10^11 km.

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Whenever there is a decimal, you count from left to right starting with the first nonzero number, which is why 400.0 and 400.00 have a different amount of sig figs.

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