CHEMISTRY COMMUNITY

Ruby Richter 2L

What's the difference between the collision model and the activated complex model?

Ruby Richter 2L

Is there a case where the instantaneous rate increases with time?

Ruby Richter 2L

So the spontaneity of a reaction does not have anything to do with kinetics?

Ruby Richter 2L

I'm a little confused so catalysts are consumed in a reaction?

Ruby Richter 2L

The questions about the ozone layer and its breakdown could be important to know for the final

Ruby Richter 2L

I don't understand how lnQ=15 gives you Q=10^6. Could someone explain?

Ruby Richter 2L

Why is it that in a lot of answers in 6L it would say "at the anode after reversal"? What does it mean for it to be reversed and does this change the potential?

Ruby Richter 2L

how exactly do you determine n or the number of electrons transferred

Ruby Richter 2L

When asked to provide half-reactions should you include electrons in transit or wait until the final balanced equation addition to do so?

Ruby Richter 2L

When adding reactions and in the final state how do you determine what physical state everything is in?

Ruby Richter 2L

If there is no difference in efficiency then when would you use a porous disk instead of a salt bridge?

Ruby Richter 2L

What does the current refer to in terms of electrochemistry? Energy?

Ruby Richter 2L

What would indicate that corrosion is taking place in a certain metal?

Ruby Richter 2L

So the equation is essentially the same but without the naught at standard conditions?

Ruby Richter 2L

If you use it in your calculations for each term when it applies and the units cancel I don't think you'd need to use it.

Ruby Richter 2L

Are there any other common forms of inert conductors that might be helpful to know besides platinum or graphite?

Ruby Richter 2L

What exactly is the standard reduction potential and why does it have to be positive for the reaction to be spontaneous?

Ruby Richter 2L

So just to clarify because Fe is the one that's being reduced by the reaction it is gaining electrons but its oxidation number goes down?

Ruby Richter 2L

What are some examples of polyatomic ions that would be helpful to know?

Ruby Richter 2L

Why is oxygen generally -2 oxidation state and hydrogen generally +1?

Ruby Richter 2L

Ok figured it out. Since you are looking at the change in temperature of the solution, you need to use its mass, not the mass of zinc (8.5g). The question tells you that the density of the hydrochloric acid solution is the same as that of water, which is 1g/1ml. Since there are 800ml HCl, mass is th...

Ruby Richter 2L

I had the same question about where the 800g came from

Ruby Richter 2L

Can someone explain what it means to calculate hydrogenation? I'm confused about what the equation should be when you're trying to find the hydrogenation of ethyne to ethane.

Ruby Richter 2L

So you only use this equation and ignore mass or moles for a calorimeter problem?

Ruby Richter 2L

How do you find the determine the different combinations for the arrangement of the molecules from just looking at the lewis structure or the element itself?

Ruby Richter 2L

Just for clarification then the only case where entropy would not be calculated as delta is in the Boltzmann equation S=kBlnW?

Ruby Richter 2L

So since the pressure is constant in an open system does that mean it is not constant in closed and isolated systems?

Ruby Richter 2L

What exactly does it mean for a reaction to be spontaneous? I know it involves an increase in entropy but what are other determinants?

Ruby Richter 2L

What would be the change in volume for this problem then if final is what you get from finding how much the pump was compressed?

Ruby Richter 2L

How do you know when to use Cv vs Cp?

Ruby Richter 2L

When do you need to change the temperature from celsius to kelvin and when is it okay to leave T as celsius in an equation?

Ruby Richter 2L

So, for example, the specific heat of water will always be 4.186 J/gram °C under all conditions because it is fixed?

Ruby Richter 2L

What is the most accurate way to calculate enthalpy?

Ruby Richter 2L

Lavelle also said he would go into more detail about this next lecture on Wednesday.

Ruby Richter 2L

Bonds being broken and bonds forming also have different energies, as one is exothermic and one is endothermic i believe

Ruby Richter 2L

In a constant-volume calorimeter the system will be sealed and therefore isolated from its surroundings which is why the volume stays the same and there is no change in pressure. In a "bomb" calorimeter the process takes place at constant volume, so the reaction will have varying pressure ...

Ruby Richter 2L

So it would be the same because the path or the details don't matter in the equation?

Ruby Richter 2L

Under constant pressure or constant volume when the temperature of a system increases, the internal energies of the system (ie atoms and molecule energy) increase which means that the enthalpy of the system increases.

Ruby Richter 2L

805097738 wrote:
MingdaH 3B wrote:No, you can touch it.

wait what this a serious response lol

Today in class he did say that if you're using a calorimeter and you touch the outside before and after the experiment you can determine if heat was lost or gained. So yes I think?

Ruby Richter 2L

Does that mean enthalpy accounts for the change in heat?

Ruby Richter 2L

What would be an example of a question where you would use Hess law to answer?

Ruby Richter 2L

So just to clarify something being amphiprotic means its specific to the donation and accepting of protons, while autoprolysis means a hydrogen atom is removed from one molecule and given to the other same molecule?

Ruby Richter 2L

If you do the quadratic equation and get a positive and negative number would you just discredit the negative number? Why?

Ruby Richter 2L

What helps me visualize this is to treat the energy almost like a product or reactant. So if the reaction is exothermic, energy is a "product" and vice versa. If you increase the temp, you would increase the delta H, so whichever side it is on will end up decreasing. This is helpful, but ...

Ruby Richter 2L

When the pressure of the system decreases the reaction goes toward the side with more moles to restore equilibrium in the system. If the pressure of the system increases the reaction will favor the direction with fewer moles. Any inert gas will not change the reactant and product concentrations and...

Ruby Richter 2L

Maya Beal Dis 1D wrote:A change in temperature is the only factor that can change K, but a change in concentration or pressure will shift Q.

How does that change in concentration or pressure shift Q while not altering K?

Ruby Richter 2L

CMaduno_1L wrote:In regards to the activity of each ion, I believe they are referring to the ion's respective concentration. I hope this helps!

That makes sense, in a problem would that value be given or is there a way to calculate it?

Ruby Richter 2L

I'm confused as to why Le Chatelier's principle really matters in predicting which way the equilibrium will shift. Why does this tell us about the reaction and its components?

Ruby Richter 2L

So basically you're just multiplying the molarity times RT which gives you P?

Ruby Richter 2L

If the reactants or products are favored does that mean that more of them are present or produced in the reaction?

Ruby Richter 2L

How do you use the net ionic equation to find the equilibrium constant for reactions? The textbook says it should be written using the activity for each type of ion but I'm not sure what that means.

Ruby Richter 2L

So, in this case, the difference in electronegativity would dominate over the difference in bond strength?

Ruby Richter 2L

Does the sulfur from dirty coal or SO2 contribute to acid rain or are they different concepts entirely?

Ruby Richter 2L

What would be some of the environmental impacts of acid rain. Will we be asked about its effects or do we just need to know the reaction.

Ruby Richter 2L

For number 21) you need to essentially "give back" an electron pair to the ligands bonded to the central atom to find their formal charge. Does this apply to all ligands and coordination compounds? Like B12 for example?

Ruby Richter 2L

The same question asks you to use either the cation or anion, whichever is a weak acid or weak base in water. How do we determine which is weak in water?

Ruby Richter 2L

Since you know that nitrate has a negative charge, it would most likely be bonded to a hydrogen and act as an acid. Vice versa for zinc, because of its positive charge. Thus, this reaction takes into consideration that zinc hydroxide (a base) reacts with nitric acid (an acid) and forms a salt (zinc...

Ruby Richter 2L

The question asks you to select an acid and base for a neutralization reaction that results in the formation of (b) zinc nitrate. I'm confused as to how you know whether the N or Zn makes up the acid or base and how you would write the equation. Can someone explain please?

Ruby Richter 2L

What exactly does it mean when a compound is a chelate?

Ruby Richter 2L

What is a coordination complex? A complex is defined as "a species consisting of a central atom or ion to which a number of molecules or ions are attached by coordinate covalent bonds" and a coordination compound is basically a compound where at least one of the ions present is a complex....

Ruby Richter 2L

I believe CO3 2- was said to be mono or bidentate because either one or both of the oxygen atoms can bind to the central atom. Oxalate is a bidentate ligand because two oxygen atoms bind to the central atom. There are four oxygen atoms but the ion is planar and so the oxygen atoms are pointing in di...

Ruby Richter 2L

Does that mean that any polydentate ligand has the ability to form chelates if it can rotate into a ring configuration that allows binding at more than one site?

Ruby Richter 2L

I'm not sure about tm vs organometallic, but a complex is defined as "a species consisting of a central atom or ion to which a number of molecules or ions are attached by coordinate covalent bonds" and a coordination compound is basically a compound where at least one of the ions present i...

Ruby Richter 2L

Yes. Lone pairs have a stronger repelling effect than bonds because the electron cloud can spread over a larger volume. This means that the lowest energy/most stable structure is achieved when atoms bonded to the central atom are furthest from lone pairs, and when lone pairs are furthest from each o...

Ruby Richter 2L

In lecture today, Lavelle did an example concerning CH4 and its hybridization. I'm confused as to why the structure is "better explained" by mixing one 2s and three 2p orbitals to form four equivalent sp3 orbitals. What exactly does it mean to "mix" orbitals and why does it happen?

Ruby Richter 2L

I believe so. It would probably also be helpful to know how lone pairs affect the bond angles in those shapes.

Ruby Richter 2L

Atoms and ions with the same number of electrons are considered isoelectronic. They have the same electron configuration, but different properties due to the varying nuclear charge. F-,O2-, and Ne, for example, are isoelectronic.

Ruby Richter 2L

For molecules like ethene, you would analyze each central atom individually to reach a conclusion about the arrangement of electron density for the molecule as a whole. The shape of ethene then would be classified as trigonal planar.

Ruby Richter 2L

What is the difference or what distinguishes a coordinate covalent bond from a regular bond?

Ruby Richter 2L

I'm a little confused about what ionization energy has to do with the fact that it is very unlikely for an extremely electronegative element (such as O, N, F, Cl) to have a positive charge?

Ruby Richter 2L

Just for clarification, how exactly does an atom having an incomplete octet make it more stable?

Ruby Richter 2L

I think you can turn in 3F and then anything from the Molecular Shape and Structure topic that we just started.

Ruby Richter 2L

He will probably go over it in more depth next lecture, but the introduction of lone pairs onto the central atom of a molecule changes the shape. A good example of this is the tetrahedral shape, which is altered to a seesaw with the introduction of a lone pair on the central atom, as in TeCl4.

Ruby Richter 2L

The midterm covered all material up until Focus 2D in the Chemical Bonds outline, so the next topic should be 2E which is molecular shape.

Ruby Richter 2L

I think we will be expected to know those additional VSEPR shapes because most are exceptions that arise when lone pairs are introduced onto central atoms, which is an idea Lavelle will likely go over in further depth next lecture.

Ruby Richter 2L

The tetrahedral shape always refers to a central atom with 4 bonding pairs, though if the central atom has lone pairs the shape is an exception and the molecular geometry will change.

Ruby Richter 2L

For 2E.15 b I think TeCl4 is actually seesaw shaped not trigonal planar so it should have bond angles of approximately 90 and 120 degrees

Ruby Richter 2L

I believe question 2E.5 asks about the ClO2 cation, so in total it would have 18 valance electrons due to the positive charge and subtraction of one electron. This would cause the shape to be trigonal planar due to the lone pair on the central Cl atom.

Ruby Richter 2L

What would be another example of a radical having an incomplete octet because of unpaired spins?

Ruby Richter 2L

Why does the fact that charged subatomic particles (protons and electrons) are in closer proximity to each other make the bond sstronger?

Ruby Richter 2L

You probably don't need to memorize specific values and only need to know periodic trends in order to answer the questions.

Ruby Richter 2L

How would a double bond help stabilize a structure?

Ruby Richter 2L

I believe covalent character in bonds is determined by electronegativities. The smaller the difference in electronegativities the more covalent a bond. The greater the difference in electronegativity, the more ionic a bond is.

Ruby Richter 2L

Yes, extra electrons do affect radius of an atom because compulsion forces among electrons push them away from each other. However, this information is not relevant to this question. In this case, S^2-, Cl^1-, P^3- all have the same electron configuration of [Ar], meaning that they have the same nu...

Ruby Richter 2L

jvera4b wrote:The thrid quantum number tells us the specific orbital in a subshell, such as whether the electron can be foud in px py or pz.

What do px py and pz correspond to?

Ruby Richter 2L

What is the significance of the direction in which an electron spins?

Ruby Richter 2L

I know ionic and atomic radius follow the same trend in the periodic table increasing down the group and decreasing across a period, but does the covalent radius also follow this trend? Lavelle mentioned it in class but I was confused about the trend it follows.

Ruby Richter 2L

isoelectronic atoms have the same number of electrons. Na+, Mg2+, and F-, O2- and Ne all have 10 electrons which means they are isoelectronic, though they do not have the same chemical properties due to varying nuclear charges.

Ruby Richter 2L

In lecture he said it's helpful to think of orbitals as functions opposed to a tangible path. So because H atoms only have one electron in an s orbital there would be no difference in energy levels and therefore only one orbital

Ruby Richter 2L

I understand that nodal planes are areas where there is zero probability of electron density, but how does this relate to symmetry?

Ruby Richter 2L

As has been mentioned, since the number of protons increases, the nucleus gets bigger and attracts more electrons, so it's essentially pulling in the electrons that surround it which makes the atom as a whole smaller.

Ruby Richter 2L

Do the positive and negative values relate to the arrows he draws in class? I'm confused as to how that relates to the spin state.

Ruby Richter 2L

If I understood correctly the 4s sublevel is lower in energy and that is why it is filled before the 3d sublevel because the 4s is lower in energy. However, after the 4s state is occupied the 3rd state becomes lower in energy. Because the 4s orbital then behaves as the outermost, highest energy orbi...

Ruby Richter 2L

So does that mean that De Broglie's wave equation works for any particle with momentum or would the particle also need to have wavelength properties?

Ruby Richter 2L

He also mentioned that spectroscopic analysis of light given off by excited atoms shows only photons of particular energy are given off. This can be used to identify elements because like the above comment says, frequencies of light emitted and absorbed are unique for each element.

Ruby Richter 2L

Does that mean that if the energy of a photon is greater than or equal to the energy needed to eject an electron, then increasing intensity results in more ejected electrons?

Ruby Richter 2L

A helpful way to think of it is to consider light as photons of energy where one photon interacts with one electron. Each photon must have enough energy to remove an electron.

Ruby Richter 2L

It was also explained in class that waves, in general, show diffraction patterns and that when the electrons in the experiment passed through a crystal, they also showed diffraction. Since diffraction patterns result from interacting waves, it was concluded that electrons must also have wavelike pro...

Ruby Richter 2L

You should probably use as many decimal places as possible when you're working through the problem in order to get the most accurate result. Sometimes the answer might be off by a tenth or so depending on earlier rounding.

Ruby Richter 2L

It should be only on the fundamentals review so Balancing Equations, Limiting Reactants, Molarity, and Empirical and Molecular Formulas

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