CHEMISTRY COMMUNITY

Olivia Young 1A

Why is it that when the activation energy increases, k decreases?

Olivia Young 1A

What is the difference between elementary steps and all other steps? Is there a significance in this difference?

Olivia Young 1A

Another definition of microscopic reversibility that Dr. Lavelle mentioned in lecture was when one assumes that the reaction has the same intermediates (same pathway) in both the forward and reverse reactions.

Olivia Young 1A

Is there a specific reason both zero order reactions and first order reaction graphs have a slope of -k, while the slope of a second order reaction is k?

Olivia Young 1A

Is the equation t1/2 = 0.693/k valid for all first order reactions? And if so, it it because the initial concentration of A cancel out and leave ln(1/2)?

Olivia Young 1A

I am confused as to the meaning of n and m concerning the overall reaction order. In lecture, we used an examples with NH4+ and NO2-, and we determined that rate 2/rate 1 = 2 = 2.0^m, therefore m is 1. I don't know where the 2.0 value came from, or how to determine n.

Olivia Young 1A

Why is oxidation called that? Is there a specific reasoning that the loss of electrons is called oxidation (is it related to oxygen)?

Olivia Young 1A

Is the oxidation number of oxygen always -2? My teacher in high school told me that, but I am not sure if that is always true because difference molecules can affect the oxidation number of oxygen differently.

Olivia Young 1A

In addition to what the other comments say, you can typically determine the oxidizing and reducing agent by first determining which molecules are oxidized and reduced. Therefore, the molecule that is being reduced is also the oxidizing agent for the other, and the molecule that is being oxidized is ...

Olivia Young 1A

In lecture we discussed how if K is less than 1, then deltaG is positive, and visa versa. When K is less than one, there are more reactants than products at equilibrium, so would the reaction always shift right/favor the forward reaction when deltaG is positive?

Olivia Young 1A

I am a little confused on the meaning of temperature dependence of K in the Van't Hoff equation. Does is just mean that the value of K can change depending on the temperature?

Olivia Young 1A

Another way of telling if the reaction is spontaneous is if the change in entropy of the universe is positive (deltaS universe). This is because deltaS universe is equal to -(deltaG)/T. As long as deltaG is negative, the resulting value which equals deltaS universe will be positive, since the temper...

Olivia Young 1A

When calculating the change in entropy, do you always have to analyze the heat flow to determine if it is positive or negative? So, if the surroundings gain heat while the system loses it, would deltaS of the system be negative and deltaS of the surroundings be positive?

Olivia Young 1A

This equation, called the Boltzmann formula, is used to calculate deltaS (statistical entropy). kB is Boltzmann's constant, 1.381 x 10^-23 J/K, which is multiplied by the natural logarithm of W, degeneracy. Degeneracy is the number of ways that atoms/molecules can be arranged with the same total ene...

Olivia Young 1A

This question was recently answered in the same topic, but the answer is that the degeneracy of COF2 allows for a greater disorder and more possible arrangements of atoms, compared to BF3 since there is only one arrangement for that. Since there is higher degeneracy is COF2, it has a higher molar en...

Olivia Young 1A

When the energy of a system changes by doing work on it, is it only possible for gases, or also liquids and solids?

Olivia Young 1A

Is there a relationship between work and degeneracy because they both use the same variable, w, or is this just a coincidence?

Olivia Young 1A

Why don't deltaU or deltaH fully describe the system? So, why is entropy necessary to describe the system and what information does it provide?

Olivia Young 1A

In lecture, it said that Cp > Cv. Is this always true, or was that just for one example? If it is always true, why?

Olivia Young 1A

If Cv or Cp is not specified, it helps to know that Cv (molar heat capacity of a gas at constant volume) often uses a bomb calorimeter in which the volume remains constant and there is pressure buildup, hence the name. Cp (molar heat capacity of a gas at constant pressure) uses a constant pressure c...

Olivia Young 1A

So far in lecture, we have gone over most of 4D and 4C. 4D goes over standard reaction enthalpies, combustion, and Hess's Law, so the homework from that section should be helpful. 4C goes over some of what we covered today in lecture, such as heat capacities.

Olivia Young 1A

You only ignore X when it is being added or subtracted from a number, because X is so small that it barely makes any difference to the resulting value. This occurs when K is less than 10^-3. If X is by itself or being squared on the numerator of a fraction, don't assume X is 0 and instead continue s...

Olivia Young 1A

Is there any difference in the direction of the reaction when pressure is changed by altering the volume compared to adding inert gas?

Olivia Young 1A

Jordan Lo 2A wrote:Is test 1 the entire outline 2? I could be wrong but I don't remember going over polyprotic acids (last couple exercises in 6th edition) or examples (last bullet points under concepts)

At office hours this morning, my TA said we did not need to know polyprotic acids for Quiz 1.

Olivia Young 1A

What does Kw represent? We used this term in lecture today concerning water, but I didn't know the specific meaning of Kw.

Olivia Young 1A

In lecture, why was a change in temperature described as a change in K, while a change in concentration and a change in pressure is described as no changes in K?

Olivia Young 1A

When the volume decreases and the number of moles of gas on both sides of the reaction are equal, the reaction does not shift and it is unaffected. This is because the number of moles of reactants and products are equal, so the reaction does not favor either the forward or reverse reaction. If the v...

Olivia Young 1A

Is there a certain significance to when K is equal to 1? In the lecture it was discussed that it is rare when K = 1, but I was not sure if it meant anything specific concerning reactants and products.

Olivia Young 1A

The partial pressure of a gas is not the same thing as finding the equilibrium concentration, but they are related. Partial pressure = (concentration)*R*T because it is derived from the ideal gas law, PV=nRT. When solving for pressure, P, you divide both sides by V, volume, and n/V equates to concen...

Olivia Young 1A

Why is it that solids and liquids are not included in the K expression? Is there a specific reason or is it a general rule?

Olivia Young 1A

In lecture we discussed how HCl in an aqueous state is hydrochloric acid. So, if we do not specify that HCl is aqueous, is it not considered an acid?

Olivia Young 1A

When looking at the formula for coordinate compounds, part of the formula is inside brackets while other parts are not. I was wondering what the difference is between those two parts and how to distinguish between them. Thanks!

Olivia Young 1A

Ligands are ions or molecules that bind to a central atom which makes up the coordination sphere. Ligands are the Lewis base in the interaction because they supply both electrons within the coordinate bond. They are significant because when the ligands are bound with the central atom, the transition...

Olivia Young 1A

At the end of lecture today, we went over how an unhybridized p-orbital is at a perpendicular angle to the hybridized orbital. Do 90 degree bond angles always form between pi-bonds and an unhybridized p-orbital, or was it just this one example?

Olivia Young 1A

Hybridization is related to bond strength such that the bond strength increases as the s character increases in the bond. Therefore, the sp hybridization has a stronger bond strength than sp2, sp2 is stronger than sp3, and etc. This is because the s-orbital is closer to the nucleus than p or d-orbit...

Olivia Young 1A

In lecture today, Dr. Lavelle mentioned that, based on electron density, the shape of ammonia is trigonal pyramidal. But, this is not actually considered the molecule's shape. Can someone please explain this? Thanks!

Olivia Young 1A

Do lone pair electrons influence the name of the molecular shape? In the molecular geometries such as seesaw, don't lone pairs affect the name given to it, or is it just the bound electrons that influence it?

Olivia Young 1A

London Dispersion forces can have multiple names including induced dipole-induced dipole and Van der Waals forces. These forces are always present and attractive and occur when fluctuating electron distribution results in fluctuating dipoles. London Dispersion forces are the weakest because they inv...

Olivia Young 1A

The order of repulsion strength in bonds from strongest to weakest is: lone-lone pair, lone-bonding pair, bonding-bonding pair. Therefore, lone pairs have the most repulsion strength among electrons. This causes bond angles to decrease because the strength of the lone pairs force the bound pairs to ...

Olivia Young 1A

I am a little confused as to the relationship between a molecule's polarizability and its state of matter (solid, liquid, gas). In class we discussed how molecules with high polarizability boil at a higher temperature, but I don't know why this happens. Could someone please explain?

Olivia Young 1A

An induced dipole results from the interaction between a nonpolar molecule and another molecule, which can be very polar depending on the type of interaction. As the polar molecule moves closer to the non polar molecule, the distribution of charge in the polar molecule causes the arrangement of elec...

Olivia Young 1A

A covalent bond is when two atoms share electrons to achieve a noble gas electron configuration, because that is the most stable state for molecules. Typically in covalent bonds, one shared electron comes from one atom and the second shared electron comes from the other atom. Meanwhile, a coordinate...

Olivia Young 1A

When you are trying to determine the lewis structure of a compound, how does the formal charge affect it? I remember learning that a compound is most stable when there is a neutral charge among all atoms, but I wasn't sure if the correct lewis structure is always the one with as many atoms having a ...

Olivia Young 1A

Removing a second electron from an atom is much harder than removing the first electron because there is a higher electrostatic attraction. This is represented through ionization energies; the first ionization energy is the energy required to remove an electron, and the second ionization energy is t...

Olivia Young 1A

The lewis structure of BrF3 permits Br to have 10 valences electrons, which is above the octet rule of 8 valence electrons, because it is in period 3 or higher of the periodic table. Because Br is in period 4, it has an n value of n = 4. Therefore, l can be equal to 0, 1, 2, or 3. The l value of 2 c...

Olivia Young 1A

Electron affinity and electronegativity are different, but they have a very similar trend across the periodic table. Electron affinity refers to the energy released when electrons are added to a gas phase atom, while electronegativity describes the the ability of an atom to attract a pair of bonded ...

Olivia Young 1A

What is the difference between the Pauli Exclusion Principle and Hund's Rule? I was confused as to how these two rules affect the electron configuration of atoms and if we need to include these rules when writing out electron configurations. Thanks!

Olivia Young 1A

The shielding effect is how the inner electrons (in the lower energy levels) decrease the attractive pull of the nucleus on the outer electrons (in the highest energy levels). Therefore, the electron-electron repulsion between electrons on different energy levels reduces the electrostatic attraction...

Olivia Young 1A

The variable 'l' represents the orbital angular momentum quantum number, therefore it relates to the shape and type of orbital. The values of 'l' define the subshell that an electron belongs to, and there are 'n' different values of 'l' such that 'l' ranges from 0 to n-1. So, in the n=1 shell, 'l' i...

Olivia Young 1A

In the problem we went over in class, the uncertainty in the electron's velocity was calculated, through the Heisenberg Indeterminacy equation, to be greater than the speed of light. This results in us recognizing that the model is incorrect because atoms only exist based on their physical parameter...

Olivia Young 1A

I believe I remember Dr. Lavelle saying that the 'd' atomic orbital has two nodal planes, but the mention of the cone-shaped nodal plane confused me. Is the cone nodal plane in the d-orbital considered one of the two basic nodal planes or is it a separate, third nodal plane in the d-orbitals? Also, ...

Olivia Young 1A

We have to account for the difference in position and momentum because electrons have such small mass that the presence of electromagnetic radiation, or light, causes the electron to alter its path and momentum. We use the symbol delta p and delta x because delta represents change which shows that t...

Olivia Young 1A

Planck's constant, which has a rounded value of 6.626 x 10^-34 Joules (or kg.m^2.s^2), is often used in quantum mechanics when determining the energy of a photon. We are currently using Planck's constant as it relates to the equation, E=hv, in which the energy of a photon (E) is equal to Planck's co...

Olivia Young 1A

The threshold energy is the minimum amount of energy needed to eject an electron from a specific metal. The threshold energy is not used to calculate the energy of a photon, E=hv, but it is used in calculating the kinetic energy of the ejected electrons. The kinetic energy can be calculated by subtr...

Olivia Young 1A

Electron affinity is the energy that is released when an electron is added to a gas-phase atom. Generally, the trend for electron affinity is that it increases left to right across a period until it reaches the noble gases and decreases going down a group. Of course there are exceptions to this tren...

Olivia Young 1A

I am also unsure of which book edition you are referring to, but if your question is on the 7th Edition Topic 1A.3 exercise, then you would need to use the E=hv equation and the c=v*wavelength equation. For part (a), you would only need to use c+v*wavelength, yet remember that all electromagnetic ra...

Olivia Young 1A

Classical mechanics describes how large objects act and their corresponding behavior. Classical mechanics typically represents a continuous function because the object is so large that it can be present in a continuous field. Quantum mechanics, meanwhile, describes the behavior of small objects whic...

Olivia Young 1A

When calculating the moles of an element using the molar mass, I believe its best to be as accurate as possible and use the value given to you in the periodic table with that number of significant figures unless otherwise stated. When you reach the final answer through division, though, your end res...

Olivia Young 1A

If a problem is telling you that there is a combustion of a certain molecule, then it is essentially saying that the designated organic molecule combines with oxygen(O2) to form carbon dioxide(CO2) and water(H2O). Since the combustion of molecules occurs in air, there is an excess of O2 molecules, s...

Olivia Young 1A

As previously mentioned, aqueous solutions are solutions such that the solvent is water. In solutions, there is a solvent and a solute, and the solvent is the dominant substance. Therefore, in aqueous solutions, the main component of the mixture is water and the compound is dissolved in water. Aqueo...

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