CHEMISTRY COMMUNITY

Sofia Ban

It is also important to distinguish between a catalyst and an intermediate in that one (the catalyst) is consumed by a step but regenerated by a later step; the other (intermediate) is created by a step but consumed by a later step.

Sofia Ban

When given values for standard enthalpy of reaction and value for K at one temperature, how do you find the K at another temperature (assuming that the standard enthalpy and entropy of the reaction stay constant over this temperature change)

Sofia Ban

Can someone explain the effect of changing the mass of the electrode on the cell potential?

Sofia Ban

When finding the initial rate or initial concentrations, is it possible that there'll be a case where you won't have constant initial concentrations to figure out each of the order of reactants? I think I came across this scenario once, so how would you approach the problem? This applies to problems...

Sofia Ban

Yeah, A in the equation is the frequency factor or pre-exponential factor, which also includes # of collisions with the correct orientation!

Sofia Ban

The maximum work is done under conditions of constant T &P so Gibbs free energy, which is the amount of energy that is free to do work, is the same as maximum work. The equation for Gibbs free energy=-nFE so we see the same equation for max work.

Sofia Ban

temperature and rate constant have a directly proportional relationship. When t2>T1, the right-side is +, so ln of the ratio of the two constants is +, which means that k2>K1. This makes sense conceptually too because increasing temperature increases the speed of molecules which increases the chance...

Sofia Ban

before you write down ur values, just doublecheck the numbers that appear and make sure you're writing the same number and right decimal points. Also, despite the sig figs needed for the end value, it's best not to use this to write down numbers during the actual calculation process.

Sofia Ban

value of what? If you are referring to the standard reduction potential of the anode and cathode, then yes.

Sofia Ban

Adding on to that, the higher to the top of the electrochemical series, the more favorable the rxtn is for reduction. Conversely, the bottom of the list favors oxidation (giving away electron).

Sofia Ban

What is the significance of changing a differential rate law into an integrated rate law?

Sofia Ban

The purpose of a salt bridge is to maintain a balance of charges, since the electrons are moving from one half cell to another. This allows for the continuation of electron flow.

Sofia Ban

anode left; cathode right -separate anode and cathode with a salt bridge denoted by 2 lines - separate different states with a single line but if it's the same state but different species, denote it with a comma - solids are on the outside (solid metal electrode) and if no metal in the reaction, use...

Sofia Ban

Since n is the number of electrons, you would use the half reactions to determine how many electrons were lost or gained (same #) and this is your value for n.

Sofia Ban

It means Carbon in the form of solid graphite.

Sofia Ban

In the cell diagrams, what does "Pt(s)" mean? And how does this change how we set up the diagram or chemical reaction equations?

Sofia Ban

Changing the concentration of the reactants or products would make Ecell either > or < E°cell, and we know from the Nernst Equation that the ratio of the concentration of products and reactants (Quotient value) is considered when calculating the value for cell potential (Ecell).

Sofia Ban

Yes, there is that equation, but this equation can also be changed to include values for R constant, temperature, and the concentration of the products and reactants. Well, based on the equation, the spontaneity of the reaction would affect E since having a negative value for delta G (spontaneous) w...

Sofia Ban

When the chemical reaction is multiplied by a factor, delta G and delta°G is increased by that factor, but Ecell and E°cell stays the same. This is also because cell potential is independent of the cell size.

Sofia Ban

When Ecell>E°cell, you are favoring product formation. AN increase in product concentration leads to an increase in delta G. Based on the equation, an increase in delta G would yield an increase in E cell so they are directly related! As for Ecell<E°cell, you are favoring reactant formation, which t...

Sofia Ban

There are rules in determining the oxidation numbers and here are a few: 1)The oxidation number of a free element is always 0. 2)The oxidation number of a monatomic ion equals the charge of the ion. 3) There are some elements that already have a set oxidation number unless it is present in a compoun...

Sofia Ban

Since delta S of the system is 3.84 Joules per Kelvins (from an isothermal, reversible expansion), and if we assume that delta S of the surroundings is also 0, the total delta S is 3.84 Joules per Kelvins as well. Both delta U and w is equal to 0, so the value of q is also 0, which accounts for the ...

Sofia Ban

There is also delta S (standard), however, we can assume this value is constant and just take in values of enthalpy and temperature

Sofia Ban

This equation is for residual or positional entropy where you take into consideration the degeneracy value to determine the entropy value (as opposed to the other equation that takes in values for heat and temperature)

Sofia Ban

In the equation 0=standard delta G+RTlnQ, why is the value of Q the equilibrium constant of the reaction?

Sofia Ban

Yes, at constant volume, delta U=qv and at constant pressure, delta U=qp+w (using qp=delta H, we can rewrite it as delta U=delta H-P*deltaV.

Sofia Ban

Yes, you would make sure the reaction is balanced first so that you can multiply the standard enthalpies of formation of each product/reactants by the corresponding stoichiometric coefficient. Then proceed with the equation where you subtract the sum of these values (reactants) from that of products.

Sofia Ban

When calculating the standard delta G, we can use the standard enthalpy of formation and standard molar entropy values of the reactants and products. However, are these values given to us in the question/table or do we have to compute these values separately as well?

Sofia Ban

Is there an easier way to think about the relationship of G, H, S, and temperature in the Gibbs free energy equation and how increasing/decreasing one variable will result in a positive/negative value for delta G?

Sofia Ban

For question 4G.5, how would you calculate the entropy value for the cis molecule? I still don't quite understand how to draw this out and determine the degeneracy value...

Sofia Ban

Why is heat capacity an extensive property and specific heat capacity an intensive property? What does this mean?

Sofia Ban

yes, I believe heat capacity can be negative and this would indicate that when a system loses energy, its temperature increases.

Sofia Ban

Lavelle mentioned that there were 3 ways of changing the energy of a system, but can someone explain a little bit more about each?

Sofia Ban

You would multiply 300kJ/mol by the 0.05 mol since we are trying to get rid of the mol unit. Keep in mind we are trying to find the enthalpy of the reaction which the units are in joules.

Sofia Ban

The dog bones he had up there were representations of the various micro states that 2 atoms can be in. Degeneracy is the number of ways of achieving a given energy state, and for 2 particles, there are 4 micro states that can fulfill this (the 4 dog bones with different combos of A/B positioning).

Sofia Ban

What is the relationship between high/low heat capacity and overall transfer of energy?

Sofia Ban

I still don't understand when it says that internal energy, volume, pressure, enthalpy, temp, density etc are state functions and the significance of this? Can someone explain it in the simplest terms with examples as well?

Sofia Ban

yes, pressure and volume are inversely proportional (this is called Boyle's Law)

Sofia Ban

the two reactions can be "fused" together to yield the end reaction, where if the reactant for one reaction is the same as the product for the other reaction, they cancel each other out. Also, you can have the product of one reaction as the reactant for the second reaction to yield the fin...

Sofia Ban

why is it that decreasing volume (and conversely increasing pressure) and having more moles of gas on the reactant side, favors product formation? viceversa?

Sofia Ban

What is the relationship between standard reaction enthalpy and standard enthalpy of formation?

Sofia Ban

What is bond enthalpy and why is it always a positive value?

Sofia Ban

In the textbook, it stated that water is amphiprotic but that this was different than being amphoteric. Can someone explain the difference between the two?

Sofia Ban

work=opposing force x distance moved and work(w) is usually reported in joule (J).
This equation reflects the definition of work, which is the process of achieving motion against an opposing force

Sofia Ban

What is a conjugate acid/base and what is its relationship to the acid/base in the same reaction?

Sofia Ban

Can someone explain more thoroughly the concept, autoprotolysis? I understand that its constant of water at 25 degrees celsius is 1x10^-14 (Kw), but how do we come to this value and what does it mean?

Sofia Ban

What is Ka and Kb? and what is its relationship to pKa/pKb and the strength/weakness of the acid/base?

Sofia Ban

we don't include those two states because molar concentration of a pure substance doesn't change in a reaction

Sofia Ban

P= pressure
V=volume
n=# of moles
R=gas constant
T=temperature

Sofia Ban

K is used to calculate the concentration or pressure of a species at equilibrium while Q is used to predict the direction of a non-equilibrium reaction (whether the forward or reverse reaction is favored or if Q=K, reaction is at equilibrium). The equilibrium constant (K) is the ratio of the equilib...

Sofia Ban

It doesn't really matter where the Cl atoms are located. If the other two atoms surrounding the central atom are not chlorine, the molecule will be polar.

Sofia Ban

No, oxidation numbers can be negative,too. For example, the element Fluorine always has an oxidation number of -1.

Sofia Ban

I believe that sp3 would be just fine.

Sofia Ban

When a ligand binds at 1 site, it is monodentate, 2 sites it is bidentate, etc, but what is a chelate and how does it differ from the other ligands? What is its significance?

Sofia Ban

What is the coordination number and how do you find it?

Sofia Ban

I have a general idea of what a ligand is, but what is its significance and how does it relate to the lewis acids/bases?

Sofia Ban

If two ions have the same charge, why is the smaller one the one with higher polarizing power?

Sofia Ban

What is the different between polarizability, polarizing power, and polarization?

Sofia Ban

A pi bond has most of its electron density between the atomic nuclei.
Why is this statement false? Also, where is most of its electron density located at then?

Sofia Ban

A molecular is polar if it has a partial negative charge on one side and a partial positive side on the other. The molecular shape shows the final shape of the molecule (since it accounts for the least amount of repulsion from lone pairs too). Molecules in which all of the atoms surrounding the cent...

Sofia Ban

I think that when asked for the arrangement, it's asking for all single, double, triple bonds as well as lone pair electrons (Lewis Structure). For molecular shape, it may want just the positioning of the atoms without showing what kinds of bonds are attached (almost like a simple 3D drawing) and th...

Sofia Ban

The relative strength of the intermolecular forces helps determine the boiling points. Stronger intermolecular bonds require more energy to break, so substances with stronger bonds will have a higher boiling point.(vice versa) Furthermore, more branched particles have LESS surface area compared to a...

Sofia Ban

Polarization is the partial or complete separation of the positive and negative electric charges in a nuclear, atomic, molecular, or chemical system. The polarity depends upon the electronegativity of the bonding atoms; most electronegative atoms pull the electronic cloud towards itself. Polarizatio...

Sofia Ban

Can someone clarify for me the relationship between polarizability, dipole moments, and fluctuating electron distribution. Also, how does the dissociation energy and interaction potential energy relate to them?

Sofia Ban

Dipole moments occur when there is a separation of charge. They can occur between two ions in an ionic bond or between atoms in a covalent bond. They also arise from differences in electronegativity, and the larger the difference in electronegativity, the larger the dipole moment.

Sofia Ban

What does it mean to have delocalized electrons or bonds?

Sofia Ban

It wouldn't be correct or rather very unlikely (as said by the comment above) because the boron atoms obey a sextet rule. In this compound, the boron atom only has six valence shell electrons, but the octet rule is satisfied by the fluorine atoms around it.

Sofia Ban

Formal Charge of an atom indicates the gain or loss of an electron while forming covalent bonds. An easy way to understand this concept of formal charge and stability is to think about attaining the lowest formal charge for a given Lewis structure because the one with the lowest formal charges is th...

Sofia Ban

It is also important to note that when counting electrons, negative ions should have extra electrons placed in their Lewis structures and positive ions should have less electrons than the uncharged molecule. After the Lewis structure of the ion is written, place the entire structure in brackets, and...

Sofia Ban

There is definitely a relationship between trends and electron configurations. For example, as the period goes from left to right, the electron configuration changes so that more electrons are added to the levels. This reflects the increase in Ionization Energy, since IE increases going left to righ...

Sofia Ban

H and He are exceptions to the Octet Rule because for them, a full shell contains only 2 electrons (1s shell). Li and Be are metals, so they're likely to lose electrons, therefore becoming cations (Li+, Be2+). When this happens, they revert to the "noble gas" configuration of He, which is ...

Sofia Ban

#29 How many electrons can have the following quantum numbers in an atom? (a) n=2, l=1 (b)n=4, l=2, m1=-2 (c)n=2 (d)n=3 l=2 m1=+1

Thought I knew how to solve this question until I came upon the magnetic quantum number in (b). Can someone please explain what the question is asking and how to start it?

Sofia Ban

I understand how to calculate the wavelength of radiation generated by the transition of n=1 to n=2, but how do you use this value to determine the series it belongs to and the color of light that will be emitted?

Sofia Ban

After doing a few of Chapter 2's homework problems, I have a couple questions: 1. What is the key difference between ground state and excited state and how does this change the electron configuration of that atom? 2. How do you obtain the magnetic quantum number from quantum number l or any other va...

Sofia Ban

As the frequency decreases, the waves broaden (wavelength increases). The extent of the change is the slope of the wave; therefore, the extent of the change also decreases.

Sofia Ban

First, use the equation c=wavelength x frequency(v). Rearrange this equation so that you are looking for the value of v, so v= c/wavelength. Then, convert nm to m. We know that the SI unit for nm is 1x10^-9m, so 2.5nm will be 2.5x10^-9m. Plug in this value as well as the speed of light constant (3.0...

Sofia Ban

It means that energy is only available in discrete (individual and separate) and small packets called quanta.

Sofia Ban

In the visual, you see that there are a total of 9 Gallium atoms. Divide 9 by Avogadro's constant; this is the mole amount of Gallium on that balance. Multiply this number by 70 grams/mol (molar mass of Gallium) in order to find the mass of Gallium. Your value should come out to be 1.05x10^-21 Since...

Sofia Ban

I believe you start by first converting the mL to L because Molarity uses the units mol/L. Since the Molarity and volume is given to you, you can find the amount in moles. After finding this value, find the molar mass of the pentahydrate and multiply this value with the mole amount. This should give...

Sofia Ban

To find the amount (in moles), start by calculating the molar mass of the compound and then divide the given mass by this value. In order to find the number of molecules and formula units, multiply the mole amount by Avogadro's constant.

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