CHEMISTRY COMMUNITY

Goyama_2A

yes, for redox reactions in basic solution, you are supposed to add H2O to the side of the reaction that needs more hydrogens and then balance accordingly by adding an equal number of moles of OH- to the other side.

Goyama_2A

So, is a condition of a reaction having "arrhenius behavior" having constant activation energy?

Goyama_2A

ln A is based upon the variable A, which is called the pre-exponential factor. The pre-exponential factor represents the frequency of collisions between reactant molecules in a particular reaction.

Goyama_2A

yes, when determining the overall rate of reaction, you can use the slow step as the sole determinant of the rate by assuming that the other steps are so fast in relation to the slow step that their influence on the overall reaction rate is negligible.

Goyama_2A

Are activation energies always constant? If not, what variables change them?

Goyama_2A

The book explains that we sometimes need to specify the specific species our rate refers to or write our rate law as “rate of consumption/production of A” instead of just rate. When would we need to be specific with species/processes we are referring to?

Goyama_2A

The book mentioned that a good way to check your calculated rate constant when given experimental data is to plug it into the rate law with the given data and see if you get the given rate. I was wondering what some other quick ways there are to check our answers in this kinetics section?

Goyama_2A

n represents the order of the reactant, which in turn gives insight into the mechanism of the reaction. how do you know what the order is The order refers to the sum of all the exponents of the concentrations in the rate law. For example, if the rate law was rate=kr[A]^2[B]^3, the overall order wou...

Goyama_2A

I believe that reaction rate constant and rate constant mean the same thing and can pretty much be used interchangeably, they will most likely always be referred to as one of the two. However, it is important to distinguish this from the reaction rate, which is the rate at any given moment in the re...

Goyama_2A

the textbook gives units that your rate constants should be in for each reaction order, how do these work for non-whole number reaction orders?

Goyama_2A

The standard Gibbs of formation should only be used to calculate the delta G standard of a reaction at standard conditions (25C and 1 atm). If equilibrium isn't at those conditions, you should be using the given K to calculate the standard delta G of the reaction. In this case, they give you K so th...

Goyama_2A

to your first question, I believe that Cl is acting as both a reducing and oxidizing agent because one of the Cls is giving an electron while the other is accepting that electron.
to your second question, I think someone told me that the Cl2 reactant is a typo and that it should be 2Cl

Goyama_2A

If those topics are reflected in the homework and/or lecture notes, they are fair game for test 2 so long as it is within the relevant section of thermodynamics or in our electrochemistry unit. I think the homework is probably a good indicator of what you should know regarding these, or any, topics.

Goyama_2A

The question asks to find the standard cell potential of (M2+/M) in the cell M(s)|M+ (aq)||Cu2+(aq)|Cu(s). I figured that since the cell has copper written on the right, that it was the cathode. But, the solutions manual treats the copper half reaction as the anode. How do we determine this?

Goyama_2A

To do this, you need to look at the relative rates of the product and reactant. You can see that I is being formed doubly as fast as I2 is being used up, due to the 1:2 ratio. To graph this, you just need to demonstrate this relationship using a graph of time on the x axis and concentration being on...

Goyama_2A

At different temperatures, delta G changes, which means that you cannot use the standard Gibbs free energy values at 100 degrees C, as those are only the values at 25 degrees C. This means in order to find the delta G at a different temperature, you would need to use the equation that relates delta...

Goyama_2A

I think usually unless oxygen or hydrogen is written as it’s own molecule (I.e as shown in 6K.5A) we just put them as they are written in the half reactions of their respective molecules (I.e MnO4 - or H2SO3). They usually just allow us to determine the oxidation number of the species of focus.

Goyama_2A

The problems asks to balance the redox reaction in acidic solution of : Cl2 (g) —> HClO (aq) + Cl2 (g) I understand why they broke the two reactions into Cl2 —> HClO and Cl2 —> 2Cl- But, I’m wondering why they were able to write the product in the second half reaction as chlorine ions (2Cl-) rather ...

Goyama_2A

How do you know which method to use when balancing half equations? I.e. balancing Hydrogens by adding H+ to one side vs balancing hydrogens by adding H2O to one side and OH- to the other.
What tells are there in a reaction that lets you know which way to go?

Goyama_2A

The question asks to calculate the equilibrium constant at 23 C and 100 C for two reactions using the data from appendix 2A. Even though the standard Gibbs of formation for the molecules is given in the appendix, the solutions manual says we have to use the enthalpies of formation and entropies of f...

Goyama_2A

deltaS total is the sum of the delta S of the surroundings and the delta S of the system. Typically, when there is no subscript for a variable, as is the case with just delta S, that means it is referring to the system. So, deltaS is just the change in entropy of the system.

Goyama_2A

when a system is adiabatic, there is no heat flow meaning:
q=0
deltaU=w

Goyama_2A

pretty much anytime the substance is an ideal gas in a problem and the C isn't explicitly given to you, you'll use either (3/2)R or (5/2)R to calculate q. Under conditions of constant volume, you would use the (3/2)R and under conditions of constant pressure, you would use (5/2)R.

Goyama_2A

I believe you should know the meanings of the two terms as they might be used in an equation:
isobaric- constant pressure
isochoric- constant volume
isothermal- constant temperature

understanding these terms is important because they influence the values and calculations used in a problem

Goyama_2A

I believe this statement refers to the equation for gibbs free energy (deltaG=deltaH- TdeltaS). This means that the magnitude of influence the deltaS, entropy, has on the change in Gibb's free energy is dependent on T. This is because, as T increases, because it is being multiplied by deltaS, the ma...

Goyama_2A

Yes, you would use that method. The reasoning behind this is that entropy is a state function, so the value is only dependent on its final state rather than the path taken to get there. Because of this, you are able to add together the change in entropy from each step and find the change in entropy ...

Goyama_2A

I used the enthalpy of formation and gibbs free energy of H2O (l). The appendix doesn't even list an H2O aqueous. I see where you're looking, but the solutions manual used the values listed under H2O (l) despite writing H2O (aq) so it might've been a typo.

Goyama_2A

I know that work is different for reversible and irreversible reactions, so how does my calculation of work differ for a reversible vs. an irreversible reaction? Additionally, what other values/calculations differ for reversible vs. irreversible reactions and how do I accommodate those differences (...

Goyama_2A

The questions asks to find the enthalpy change per liter for the reaction TNT and O2 to form CO2, H2O, and N2. I understand how they used the enthalpies of formation to find the enthalpy of the reaction to be -13168 kJ/mol. But, when they divide that by 4 to get the delta H per mole of TNT, they mak...

Goyama_2A

As more atoms are in a molecule, the number of microstates (possible arrangements) increase and thus there are overall more ways to distribute the motional energy of the molecules within the gas sample. In lecture, Dr. Lavelle uses the number of microstates as the primary indication of change in ent...

Goyama_2A

Microstates are the varying possible arrangements for molecules. As motional energy (ie rotational, transitional, and vibrational energy discussed in the textbook pg.260) increases, the number of microstates tends to increase as well, which, in lecture, we take as a conceptual indication as a positi...

Goyama_2A

I believe so.
This is the case for most because no change is occurring in the reaction:
ie. O2–>O2
However, if you were to calculate the enthalpy change in a reaction such as:
2O—> O2
You would be calculating the heat of atomization(which is the heat released when the O2 bond is formed)

Goyama_2A

I was doing problem 4C.3 and in the solution they said that at constant pressure, change in enthalpy is equal to q. Why is this?

Goyama_2A

I had a different form but the gist should be the same. Use the given Molarity of hydrogen fluoride to set up an ICE table. Once that's set up, you should have equilibrium concentrations in terms of X. Use the equilibrium concentration values in terms of x to create an equation for the equilibrium c...

Goyama_2A

Since it wasn't addressed in lecture, you won't be expected to know it. But, I think it'll be helpful to understand the foundations that go into forming the theorem.

Goyama_2A

Unless the question specifically states that you're considering the calorimeter as a system or as surroundings, I think it isn't counted as either. The main contribution of a calorimeter in a problem is its measurements of heat absorbed or released by a system.

Goyama_2A

In lecture, Dr.Lavelle showed us that perfect system equation which states that q(system)+q(surroundings)=0, which in turn means that q(system)=-q(surroundings) or vice versa.

Goyama_2A

I think you would use the given molarity value of the triethylamine solution to make an ICE table. The equilibrium value for the N(CH3CH2)3, NH(CH3CH2)3+, and the OH- should come out to 0.2-x, x, and x respectively. Then use those equilibrium values to make an equation for the equilibrium constant t...

Goyama_2A

What do the vant hoff equation variables mean and what is it used for? Are we expected to use this equation? If so, in what scenario might we use it?

Goyama_2A

In the “skills you have mastered” section of 5J, it says we should be able to predict the value of K at one temperature from its value at another temperature. Lavelle excluded part of this section from the assigned reading, but I just wanted to make sure. Should we be able to do this? Have we addres...

Goyama_2A

X is assigned to Change in molarity based on the balanced equilibrium reaction. In 5I.15, the reaction is 1:1:1 meaning all changes should either be +x or -x. If the reaction had a different ratio then the changes would be reflective of that ratio. Consider the equation 1AB2C2 —> 1A + 2BC. Since the...

Goyama_2A

The 5% rule basically allows us to determine the validity of an approximation by looking at the percent of ionization of the acid. Consider the reaction: [HA] —> [H+] + [A-]. If you’re looking for the Ka value, you’d need to use the equation Ka= x^2/([HA] - x). But, if the Ka is very small (Lavelle ...

Goyama_2A

When talking about the effect of inert gases on a reaction at equilibrium, we are more focused on the fact that it is extremely stable and thus does not react. The inert gas wouldn’t interact significantly with the other reactants/products in the reaction and this has no net effect on the direction ...

Goyama_2A

So for these, you’re going to use your understanding of fundamental concepts and Le Chateliers to decide if they’ll stay the same or change: A) the amount of O2 will be different because there are different amounts of reactants and this different amounts of products B) the partial pressure of O2 sho...

Goyama_2A

A larger Ka indicates a stronger acid, meaning the acid ionizes more than if it had a smaller Ka. So, that means the bonds in the acid are weak because they are more inclined to dissociate.

Goyama_2A

At the end of the last lecture, Dr.Lavelle explained that if [H3O+]<10^-7 then the solution is considered neutral, could someone explain why this is?

Goyama_2A

I believe that that is just a typo on the part of the solutions manual because, in order to get the OH- concentration, you just need to divide Kw (1x10^-14) by the respective H3O+ concentration, which they did correctly in all of the other parts. The answer I got is 3.23x10^-15.

Goyama_2A

In the book, they give an equation for converting between Kc and K: $K=(RT)^{\Delta n(sub "r")} Kc$ . How do I use this equation? Does Lavelle expect us to be able to practice this equation?

Goyama_2A

The book mentions that, in reactions involving fully dissociated ionic compounds in solution, the equilibrium constant should be written for the net ionic equation by using the activity for each type of ion. First off, what does this fully mean in simpler terms? and is this something we should be do...

Goyama_2A

If the way the equilibrium constant was calculated is in no other way indicated, it is safe to assume that the K value was calculated using whatever form of given concentrations/partial pressures is in the question (meaning if they give you a partial pressure, it is probably Kp and vice versa). Plus...

Goyama_2A

Because the change in energy is negative, the reaction is exothermic. The answer is that the reaction shifts to the left because the reaction is exothermic and thus decreasing temperature would move the reaction in the forward. Therefore, increasing temperature would do the opposite.

Goyama_2A

when writing the K expression, you don't include it. But say the solid or liquid is the only product in the reaction, you'd still put a 1 in the numerator over your non-solid/liquid reactants.

Goyama_2A

First off, since the initial concentration of SO3 is 0 and you are adding 2X, the equilibrium concentration should only be 2X rather than c+2X. You would then proceed using your equilibrium equations you have set up (0.522-2X, 0.633-X, and 2X) in filling out your equation for K. With these equilibri...

Goyama_2A

What are the roles that CO2, H2CO3, and HCO3- play in maintaining blood at a pH of 7.4? Lavelle said to look for it in the textbook but I was unable to find it.

Goyama_2A

A bronsted acid is something that in it of itself is a proton donor. A conjugate acid is the acid resulting after a bronsted base accepts a proton. For example, NH4+ is the conjugate acid of NH3.

Goyama_2A

Why is oxalate bidentate and not tetradentate?

Goyama_2A

No, 14a no longer requires student to do calculations based on weak acids and bases. I think we’ll learn more about that in 14B.

Goyama_2A

You should know the reactions behind acid rain. Acid rain is largely contributed to the interactions of water with nitrogen and sulfur oxides. So, solutions to acid rain would pretty much be anything reducing human activity causing the excessive release of sulfur and nitrogen into the environment. T...

Goyama_2A

What make a coordinate covalent bond differ from an ionic or covalent? I understand that, in coordinate covalent bonds, both electrons are donated by the same atom, but if that’s the case, how do they differ from ionic bonds?

Goyama_2A

Unless you know by memorizing a specific coordination compound, I don’t think you can just determine by looking at the formula. Drawing it out helps because it shows you the placement of the atoms and the compound’s structure.

Goyama_2A

I don’t think there is any set steps to determining whether or not something is amphoteric. However, it is helpful to think about the conjugate base and/or acid of something in determine whether it is amphoteric. If something doesn’t have a Hydrogen atom, it obviously doesn’t have a proton to donate...

Goyama_2A

The trichloroacetic acid is stronger because the chlorine is an electron withdrawing group. This causes a withdrawal of electrons from both the carbon atom and the oxygen atom. Due to the withdrawal of electrons, the electron density in the O-H bond is diminished and this weakens the O-H bond, this ...

Goyama_2A

Bronsted acids/bases focuses on the protons:
-bronsted acids- proton donors
-bronsted bases- proton acceptors

Lewis acids/bases focus on the electrons:
-Lewis acids- electron pair acceptor
-Lewis bases- electron pair donor

Goyama_2A

I believe the rule is to write the neutral molecule first and then the anion. If there are multiple anions, they are listed in order of their atomic numbers.

Goyama_2A

What is the purpose of hybridization? Why does it occur?

Goyama_2A

When determining whether or not a ligand is polydentate, you need to look at the location of lone pairs on the ligand and the shape of the ligand. If the lone pair locations are spread out between several atoms on a ligand, it is likely to be polydentate rather than when they are all located on one ...

Goyama_2A

I believe it also should include hybridization because that wasn’t a topic covered on our most recent test.

Goyama_2A

The strength of an acid is based upon its ability to lose hydrogen ions (ionize) when dissolved in water. Inorganic compounds lose hydrogens ions much more easily than organic, making them considered stronger.

Goyama_2A

Yes I believe it can be any atom that has an empty p orbital and a paired s orbital.

Goyama_2A

How do electron repulsions relate to the Pauli exclusion principle?

Goyama_2A

No, depending on the bonds and number of lone pairs that are also arranged about the central atom, a molecule with lone pairs can hold a wide variety of molecular shapes.

Goyama_2A

Why in some molecular shapes (like square planar) are the lone pairs on opposite sides of the central atom but in other molecular shapes (like bent or t-shape) the lone pairs are next to one another? How do you determine where the lone pairs are in relation to one another about the central atom?

Goyama_2A

The valence shell electron repulsion theory is the model by which we determine molecular shapes by determining the form of the molecule which would minimize the electrostatic repulsion. This helps us to determine shapes because our Lewis structures tell us the bonds and line pairs in a molecule but ...

Goyama_2A

The lone pair causes the S-F bonds to not be directly symmetrical from one another and therefore their dipole moments don’t cancel out.

Goyama_2A

Usually it helps to know which atom will be the central atom. The central atom is the atom with the least electronegativity (except in cases where that atom is hydrogen). From there, you could just go about arranging the remaining atoms about the central.

Goyama_2A

What is a dipole moment and how do they affect intermolecular forces?

Goyama_2A

So for this problem, you could’ve used the rydberg formula to find energy at a specific level. I believe they gave us the change in energy, so you’d use the delta E= E(final) - E(initial). The only variable you should have left in the formula would be n(final) because they told us that it was a hydr...

Goyama_2A

I think I remember Lavelle explaining it as those larger molecule have more electrons, resulting in stronger London dispersion forces due to the fact that they have stronger instantaneous-induced dipoles.

Goyama_2A

If you were trying to determine the answer to this question using Lewis structures, you would have to look at the molecular shapes. The AsF3 molecule has lone pairs pushing the three bonds down, this giving it a pyramidal shape, which is polarized as the less electronegative atom is on one side whil...

Goyama_2A

Assuming you’re talking about the wavelength of light, you would use the E= Kinetic Energy + work function formula in order to find the energy of the photon. I believe I remember the question asking for the wavelength of the photon which emitted the electron. If you’re looking for the wavelength of ...

Goyama_2A

Can someone please explain the basic concepts we should know for schrodinger’s equation? It confuses me so much

Goyama_2A

What are the general exceptions to the octet rule we should know? And how many electrons can those exceptions hold when bonding?

Goyama_2A

Yes, as elements move to the right in a period, they have more protons, resulting in a high effective nuclear charge (in other words, a stronger pull) on each electron from the nucleus. This stronger pull leads to a smaller radius.

Goyama_2A

The energy of an orbital refers to the amount of energy required of electrons to be in that orbital. In order for an electron to be in a certain orbital, it must have the discrete amount of energy required of that orbital. This higher energy is due to the fact that the higher energy orbitals are fur...

Goyama_2A

Pauli’s principle states two things: there can be no more than 2 electrons in an orbital and electrons in the same orbital must be spin paired. This would be violated if you placed 3 electrons or more in an orbital or if your 2 electrons had the same direction of spin (ie both +1/2 or both -1/2). Hu...

Goyama_2A

The electron is usually placed in a way that would allow our structure to be the lowest energy structure, meaning the least formal charges possible. So, it’s mostly the same as any other situation where you’re trying to figure out the best structure for bonding, except this time you happen to have a...

Goyama_2A

Resonance is the blending of structures with the same arrangement of atoms but different arrangements of electrons. The actual structure is a hybrid of these resonant structures and is the most stable structure. The resonant structures all have the same energy and allow us to both visual and predict...

Goyama_2A

When counting the number of valence electrons an element has, you only count the number of electrons held in the outer shell. This usually doesn’t include those from the d-orbital because electrons aren’t placed in the d-orbital until there are some in the next shell s-orbital, but by then the s-orb...

Goyama_2A

When thinking about ionization energy comparisons between several elements, you have to take both the period and the group into account rather than just the groups. Therefore the ionization energy trends can’t just be described with one direction, such as down. The ionization energy increases in the...

Goyama_2A

Although most elements need exactly 8 electrons in a bond to be stable, there are some exceptions to the rule. Some elements, like Boron, can be stable with less than 8 electrons, while some other elements, like Sulfur, can be stable with more than 8 electrons. This is due to the expansion of valenc...

Goyama_2A

The topic hasn’t really been brought up yet in specifics as to the shapes, so as of what we have learned so far, probably not. But, if it’s addressed by the midterm then yes.

Goyama_2A

You use de Broglies equation to find the wavelength of an object with mass when given the mass and velocity of the object. The units for the equation are: Joules•seconds for plancks constant, kg for mass, meters/second for velocity, and meters for wavelength.

Goyama_2A

yes, our homework is to be done on the topic we are currently working on. So since we are still on quantum world, you just pick five other problems from the topic to turn in.

Goyama_2A

Wavelength is inversely proportional to mass. This means that, the higher the mass, the shorter the wavelength. For larger objects, the wavelength becomes so small (the rule is generally any wavelength less than 10^-15 m) that it is unnoticeable. We just have to assume that it have wavelike properti...

Goyama_2A

The uncertainty in velocity would be 10 m/s. The uncertainty is given by the total range of what it could be. So, in this case, since the velocity could be anywhere ranging from 0 m/s to 10 m/s, your uncertainty in velocity would be 10 m/s.

Goyama_2A

This is a set mass. Electrons don’t gain or lose mass through any process. It is given to us on our constant sheet.

Goyama_2A

Hund’s Rule basically states that, due to electron repulsion, each orbital in a sub shell is occupied by a single electron before any electrons within that orbital are paired. It also explains that each of the single electrons have the same spin. The rule helps us to figure out electron configuratio...

Goyama_2A

Why can’t electrons exist between energy levels? I remember Lavelle mentioning this in class but I’m confused as to why

Goyama_2A

On the class website, there’s a list of a bunch of helpful links and one of them is titled “everything you want to know about sig fig” which is a document with all of the sig fig rules and I’m assuming Lavelle accepts these rules.

Goyama_2A

Lavelle has chemistry constants and equation documents listed on the class website and they have helpful information for conversions and constants.

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