CHEMISTRY COMMUNITY

WYacob_2C

How were you able to figure out that Q is [anode]/[cathode]?

WYacob_2C

Are we supposed to use the instantaneous rates when looking at the rates of reactants and products? If so, why?

WYacob_2C

If the original equation is the Arrhenius equation, what happens to the lnA when you derive the equation used to calculate rate constants at different temperatures (the one written in the original question)?

WYacob_2C

The equilibrium constant is equal to k(forward)/k(reverse). This is helpful when converting the concentration of intermediate species into concentrations of reactants of the overall reaction when given elementary reactions.

WYacob_2C

When do the orders of the rate equal the stoichiometric coefficients of a reaction, and when do they not? Thank you in advance.

WYacob_2C

Generally, time is in seconds, so it would be easier to convert all units to seconds.

WYacob_2C

Another good way to determine whether a reaction is in the zeroth, first, or second order is to look at the units of k, the rate constant. If the units of k is M/s, it is in the zeroth order; if k is 1/s, it is in the first order; if k is 1/M*s, it is in the second order.

WYacob_2C

In kinetics, n refers to the order of the reactants in a reaction. If n=1, this tells us the rate is directly proportional to the concentration of [reactant].

WYacob_2C

For the units of k, the zeroth order is M/s, the first order is 1/s, and the second order is 1/M*s. A good way to remember this is to divide by M when going from zeroth to first to second order.
zeroth order: M/s --> divide by M --> first order: 1/s --> divide by M --> second order:1/M*s

WYacob_2C

Also if given a chemical equation, does the coefficient in front of the reactant automatically translate into the exponent in the rate law? The coefficient does not automatically translate into the exponent in the rate law. The exponent in the rate law is the order of the reaction which is found us...

WYacob_2C

Could someone explain why species that undergo oxidation are called the reducing agent, as species that undergo reduction are called the oxidizing agent? Thank you in advance.

WYacob_2C

CynthiaLy4F wrote:I believe it will only cover topics from the midterm up until the end of kinetics.

Would it be up until the end of kinetics or the end of electrochemistry?

WYacob_2C

How can you derive ln(K1/K2)= -delta H/R (1/T1 - 1/T2) from the Van't Hoff equation given on the formula sheet: lnK=-delta H/RT + delta S/R ? Thank you in advance.

WYacob_2C

In acidic solutions, you balance redox reactions using H2O and H+. The hydronium ions produce the acidic solution.

WYacob_2C

When the cell potential is positive, the reaction is spontaneous. When you are given the standard cell potentials of different reduction reactions, typically the more positive value is more spontaneous, and therefore the reduction reaction.

WYacob_2C

After looking at the overall net charge of all the species on both sides of the reaction, you determine how many electrons you need to add in order to have the charges equal on both sides of the reaction. From here, you need to multiply the oxidation half reaction by 3 to turn the 2 electrons into 6...

WYacob_2C

If the net charge is not indicated on the upper right hand corner of the species, then the species have an overall net charge of zero.

WYacob_2C

How do we go about balancing redox reaction in basic solutions? How different is it from having a redox reaction in acidic reaction? Thank you in advance.

WYacob_2C

After balancing the oxidation half-reactions by adding 2H+ ions, the two side of the half-reactions have unequal charge. By adding the 2 e- on the right side of the reaction, it balances out the 2+ charge from the H+ ion.

WYacob_2C

n refers to the number of moles of e-

WYacob_2C

You can use this equation when you are trying to calculate K at different temperatures if delta H is known.

WYacob_2C

Could someone explain the how and why redox reactions occur? Thank you in advance.

WYacob_2C

Can someone explain how the K value can impact the sign of delta G. Thank you in advance.

WYacob_2C

At equilibrium, delta G will be zero, but I don't believe that always mean that delta H and delta S will also be zero.

WYacob_2C

Typically, when you are dealing with an ideal gas and need to find lets say the work, but certain components of the equation are missing, you can use PV=nRT. This will allow you to solve for what you're missing and use it to find the work, for example.

WYacob_2C

How can you tell whether a system is spontaneous, non-spontaneous, or reversible based off the change in entropy? Thank you in advance.

WYacob_2C

In what ways are microstates important in biological processes? Thank you in advance.

WYacob_2C

I believe the correct statement is: -(heat given off by system)=(heat gained by surroundings). This statement is true if the system is isolated because the heat given off my a system must be transferred to the surroundings.

WYacob_2C

A car engine is an open system because it allows for the exchange of matter and energy between the system and the surroundings.

WYacob_2C

I was wondering which conditions should we know for our midterm? So far I know we should understand an isothermal system and an adiabatic system; are there any other important conditions we should know and could you give a small description of it as well. Thank you in advance.

WYacob_2C

A state function is a property that is independent of how the substance was created; it only depends on the initial and final state. Some examples include: pressure, density, temperature, volume, enthalpy, internal energy, Gibbs free energy, and entropy.

WYacob_2C

An open system can exchange energy and matter with its surroundings. A closed system can exchange energy but not matter with its surroundings. An isolated system cannot exchange energy and matter with its surroundings. Therefore, an insulated system is an isolated system.

WYacob_2C

Can someone explain the relationship between work and the ideal gas law? I believe a problem was done in class where work was found using the ideal gas law. Thank you in advance.

WYacob_2C

Can someone explain the main difference between enthalpy and the change in internal energy?

WYacob_2C

What is the difference between a calorimeter and a bomb calorimeter? Thank you in advance.

WYacob_2C

Kp is used when dealing with partial pressures, so typically gases. Kc is used when dealing with concentration, so aqueous species.

WYacob_2C

Due to an activity of 1, solids and liquids are not included since they would have no impact on the equilibrium constant. Knowing this, you only include (aq) and (g) species to calculate the equilibrium constant.

WYacob_2C

Q is also equal [products]/[reactants]. If Q is less than K, that means the concentration of reactants is too much, causing the ratio between products and reactants to be small. In order to fix this, the chemical reaction will favor the formation of products to increase this ratio, in hopes of meeti...

WYacob_2C

To calculate percent ionized, you would first perform an ICE table on a chemical reaction. Typically, the equilibrium concentration of hydronium is represented by x. Solve for x using the Ka value and formula. The formula for percent ionized is = [x]/[acid(initial)] x 100%.

WYacob_2C

When dealing with liquids and solids, you completely disregard those species in the chemical reaction when doing an ICE table.

WYacob_2C

Test 1 will cover chemical equilibrium calculations, equilibrium shifts (Le Chatelier's), and weak acid/base calculation. Essentially, content covered in the first two weeks.

WYacob_2C

In order to go from molarity to mass, you would need to convert molarity to moles. This requires you to be given the volume so the units can cancel out. From the number of moles, you can use molar mass (g/mol) to obtain the mass.

WYacob_2C

If you are given moles or grams, you can first convert into molarity, and from there you can use the equation, P=(n/v)RT to find the partial pressure of each gas in the reaction. Then, these numbers can be used to calculate Kp.

WYacob_2C

The question to the problem is: "Consider the following reaction - PCl5 (aq) ⇌ PCl3 (aq) + Cl2 (aq) Given that 1.0g of PCl5 is placed in a 250 mL reaction vessel, determine the molar concentration in the mixture at equilibrium." How would I start off this question? Should I first find the ...

WYacob_2C

I'm having trouble figuring out how to do this homework problem. Any help is appreciated.

6B.5: "Calculate the pH and pOH of each of the following aqueous solutions of a strong acid or base: (a) 0.0146 M HNO3(aq); (b) 0.11 M HCl(aq); (c) 0.0092 M Ba(OH)2(aq)"

WYacob_2C

In class, we discussed finding the equilibrium constant while ignoring species in a reaction at the solid or liquid phase. If all species in a chemical reaction are solids/liquids what would the value of K be? Would there be a value of K? Thank you in advance.

WYacob_2C

What is the cut off for the value of K to say that the reaction strongly favors the formation of reactions and the reaction strongly favors the formation of products? Thank you in advance.

WYacob_2C

If in a reaction, all species are in the gas phase, typically you would use their partial pressures, meaning you would use Kp. If the species in a reaction are aqueous, you would use the concentrations and Kc.

WYacob_2C

If you increase the concentration of the products, and then proceed to find the reaction quotient, you'll see that Q>K, meaning the concentration of products > concentration of reactants. As a result, the reverse reaction is favored.

WYacob_2C

In the video module, Lavelle says that when Q>K, the reaction hasn't reached equilibrium yet because there is too much product, so it goes from right to left (reverse reaction) to reach equilibrium. My question is: how is it possible to have more product than reactant without going against the idea ...

WYacob_2C

Why is H2O a monodenate ligand? When you draw the lewis structure of H2O, the oxygen has two lone pairs, but the molecule as a whole is classified as a monodenate. Could someone explain this to me. Thank you in advance.

WYacob_2C

If something is a chelate what does that tell us and how would we identify it? Is there more to know other than just the definition of it? I think a good way to see if something is a chelate is to ask yourself "does this central atom have multiple polydentate ligands attached to it?" If t...

WYacob_2C

Why is it colbalt (III)? What is the oxidation number of the metal? Cobalt has an oxidation number of 3+ because we see that there is an overall charge of 2-, there are 5 CN- molecules and 5 OH2 molecules. Because CN has a charge of -1, there is a total -5 charge from them alone. OH2 has no charge ...

WYacob_2C

For [Co(CN)5(OH2)]2-,
why is it called aquapentacyanocobaltate(III) ion instead of aquapentacyanocobalt(III) ion?

WYacob_2C

Will we be expected to know the latin names of metals in coordination compounds?

WYacob_2C

When are we supposed to substitute metals with their latin name when naming coordination compounds?

WYacob_2C

How much information are we expected to know on the biological importance of coordination compounds?

WYacob_2C

Is CH2BR2 polar or nonpolar? Do the dipole moments cancel out?

WYacob_2C

Let's say a structure has resonance structures due to delocalized electrons, but each structure has different hybridizations. Which hybridization would be considered correct?

WYacob_2C

I think it's the same thing, but with the energy level, it's more specific for an atom.

WYacob_2C

The question for 2F.11 says, "White phosphorus, P4, is so reactive that it bursts into flame in air. The four atoms in P4 form a tetrahedron in which each P atom is connected to three other P atoms. (a) Assign a hybridization scheme to the P4 molecule." As I was drawing the lewis structure...

WYacob_2C

Dipole-dipole in the gas phase is also equal to induced dipole - induced dipole, so dipole-dipole in the solid phase would have stronger IMFs.

WYacob_2C

I'm assuming 9C, but I haven't heard anything from my TA.

WYacob_2C

A dipole moment is formed due to a significant enough difference in electronegativity between two atoms. Remember that electronegativity is the ability to attract electrons.

WYacob_2C

Could someone explain the coordination sphere. Thank you in advance.

WYacob_2C

The CN- ions are considered the ligands, and these ions provide the electron pairs that form bonds to Fe2+

WYacob_2C

Can someone explain the different bond angles within the trigonal bipyramidal shape? Thank you in advance.

WYacob_2C

I was wondering the same thing. In the textbook they use NH3 as an example where its electron arrangement is considered tetrahedral, but its shape is trigonal pyramidal. Can anyone explain this?

WYacob_2C

In lecture, Lavelle said that repulsion strength follows this pattern:
lone-lone pair>lone-bonding pair>bonding-bonding pair.
Could someone please explain this. Thank you in advance.

WYacob_2C

Do hydrogen bonds also have dipole moments? Could you characterize a molecule that has hydrogen bonds as it also having dipole forces?

WYacob_2C

Can someone help me with this problem? It states, " (a) What is the shape of a ClO2+ ion? (b) What is the expected OClO bond angle?"

WYacob_2C

What are instantaneous dipoles? Can someone please explain this to me.

WYacob_2C

Why does nitrogen have a lower ionization energy than nitrogen if ionization energy increases across a period?

WYacob_2C

Electronegativity is the ability to pull in an electron. It increases across a period because the nuclear charge of atoms increase, meaning its ability to pull in an electron is greater. It increases up a group also because the nuclear charge of atoms increase.

WYacob_2C

It depends on the difference in electronegativity. If the difference between the molecules' electronegativity values is larger than 2.0, the molecule is polar. Polarity is simply the unequal pull of electrons. If electronegativity is the ability to pull an electron, two molecules with very different...

WYacob_2C

Large anions are more polarizable because their electron cloud is larger and their nuclear charge is smaller, allowing the outermost electrons to get distorted easier. Larger atoms are more polarizable.

WYacob_2C

Can someone explain the lewis dot structure of BF3 please. Thank you.

WYacob_2C

It's important to know that
the energy of a photon - threshold energy = electron's kinetic energy.

WYacob_2C

You would need to find the mass. The molar mass is given in grams/mol, so first you would need to convert into atoms using (6.022 x10^23 atoms/mol). Then, convert grams into kilograms. Anything with mass and velocity has a wavelength, so it will work out, you just need to use dimensional analysis to...

WYacob_2C

How could we draw the lewis structures for ionic bonds? Can someone explain how that would work since the atoms wouldn't be sharing electrons. Thank you.

WYacob_2C

The best/most stable lewis structures come from a structure that has the most atoms with a formal charge of zero, the lowest magnitude of formal charges, and if there is a negative formal charge, it's on the most electronegative atom.

WYacob_2C

In lecture, Lavelle said "charged delocalization tends to be more stable." Could someone please explain this?

WYacob_2C

APatel_4A wrote:How do we know what the formal charge for the molecule should add up to? Is it always most stable if it adds up to 0?

Yes, the goal is to get a formal charge of 0. This tells us this is when it's most stable, and the lewis structure will best describe its real structure.

WYacob_2C

Electron affinity can be either negative or positive. It is defined as the energy associated with the release or addition of an electron. When an electron is added, electron affinity will be negative. On the other hand, when an electron is released, electron affinity will be positive.

WYacob_2C

Can someone further explain the idea of having a "partial bond" character? It was discussed in lecture when we were going over the nitrate ion.

WYacob_2C

Can someone explain electronegativity and its relationship to ionization energy, if there is one.

WYacob_2C

Hund's rule says that electrons at the same energy level occupy different orbitals before pairing up. This is due to the fact that electrons are all negatively charged, meaning they repel each other, so they would rather be in a separate, empty orbital if it's available. Once each orbital has an ele...

WYacob_2C

The Aufbau principle basically says that electrons fill the lowest energy levels before they move onto the next energy level. Notice how every time we move down the period table (and into a new energy level) or even across the periodic table (and into a new orbital), the previous energy levels / orb...

WYacob_2C

1.B.7 says "Sodium vapor lamps, used for public lighting, emit yellow light of wavelength 589 nm. How much energy is emitted by (a) an excited sodium atom when it generates a photon; (b) 5.00 mg of sodium atoms emitting light at this wavelength; (c) 1.00 mol of sodium atoms emitting light at th...

WYacob_2C

On the homework, problem 1.E.7 asks to "Determine whether each of the following electron configurations represents the ground state or an excited state of the atom given." part (c) has Be as the element along with the electron configuration diagram. I'm confused as to why they placed one e...

WYacob_2C

Can someone further explain why Cr and Cu are exceptions for the electron configuration rules we talked about in lecture.
The correct configuration:
Cr: [Ar] 3d^5 4s^1
Cu: [Ar] 3d^10 4s^1
Why aren't they:
Cr: [Ar] 3d^4 4s^2
Cu: [Ar] 3d^9 4s^2

WYacob_2C

Which equations apply to electromagnetic radiation and which ones would not work?

WYacob_2C

When the threshold energy is met, will electrons be emitted? Or does the energy of the photon have to exceed the threshold energy in order for electrons to be emitted?

WYacob_2C

Why is it that wavelike properties are only noticed in electrons? It was discussed in lecture, but I didn't get all the information, so I'm having trouble understanding.

WYacob_2C

Can someone explain the difference between constructive and destructive interference, and how larger waves are created in constructive interference while smaller waves are created through destructive.

WYacob_2C

From my understanding, in order for the electrons to be ejected, we need a specific frequency (or kinetic energy) to meet the threshold energy of the metal. This kinetic energy is found in particles. Therefore, light is also a particle.

WYacob_2C

A tip to make sure you are on your way to correctly calculating the percent yield is to see if your actual yield is less than your theoretical yield. Generally, this is the case due to measuring discrepancies.

WYacob_2C

Do you think we will have to memorize the Avogadro's Number for test? I am wondering if I will be given the Avogadro's Number when I get the questions that ask for atoms' number. I'm not that sure if we will need to know it for this class, but I heard that Lavelle does give constants on exams, but ...

WYacob_2C

How do you know when to multiply using Avogadro's number and when to divide? Generally, you use Avogadro's number (6.022 X 10^23 atoms/mol) when you are trying to do a mole-to-molecules/atoms/formula units conversion. When solving a problem, it always helps me to write out the units to see where th...

WYacob_2C

H.7 part (d) says "Write a balanced chemical equation for each of the following reactions...(d) The reaction of ammonia gas with oxygen gas at high temperatures in the presence of a copper metal catalyst produces the gases water and nitrogen dioxide." I've got the chemical equation but I n...

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