CHEMISTRY COMMUNITY

Rachel Bartley 2B

k refers to the rate constant, which represents the speed and direction of the reaction.

Rachel Bartley 2B

In chemistry, we look at enzymes and catalysts to see how they affect the speed at which reactions occur.

Rachel Bartley 2B

The nernst equation is E=Eº - (RT/nF)lnQ and is used to calculate the cell potential.

Rachel Bartley 2B

Eo is an intensive property that is important because it is the potential an electron experiences in a cell. Its value always stays the same.

Rachel Bartley 2B

Salt bridges allow anions to flow towards the anode and cations towards the cathode to help balance the charges.

Rachel Bartley 2B

Platinum is added to whatever side needs a conducting solid. So if only one side needs a conducting solid, then it is added to that side, but if both need one then it is added to both.

Rachel Bartley 2B

Catalysts can lower the activation energy to speed up the forward and reverse reactions.

Rachel Bartley 2B

To calculate the overall order of a reaction, just add up all of the rate orders for each reactant.

Rachel Bartley 2B

Yes, rate laws are always positive even if the rate of the concentration of reactants decreases.

Rachel Bartley 2B

The graph of a second-order reaction will show a linear, positive line with the axis labeled 1/[A] over time.

Rachel Bartley 2B

The order of a reaction refers to the relationship between the concentrations of the reactants taking part in the reaction and the rate of the reaction. To tell what the order of a reaction is, take the sum of the order of each reactant.

Rachel Bartley 2B

No, they are actually the most rare because they are independent of concentration of any of the reactants.

Rachel Bartley 2B

Yes, k’ refers to the rate constant of the reverse reaction.

Rachel Bartley 2B

No, they are not related, but if you have the unique rate, then the coefficients of the reaction and products do relate to the reaction rate.

Rachel Bartley 2B

Fast enzymes have high k values, which means they convert substrate to products faster than enzymes with lower k values.

Rachel Bartley 2B

Both intermediates and catalysts cancel out in a series of reaction mechanisms, but intermediates are species that are formed in one step and then used up in another, while catalysts are are never used up. So intermediates will first appear in the products of one step and then in the reactants of an...

Rachel Bartley 2B

Catalysts decrease the activation energy in both the forward and reverse reactions.

Rachel Bartley 2B

The overall rate law is the rate law of the slowest step because it determines what the rest of the steps are limited by. Even the fastest step is limited by the slowest one.

Rachel Bartley 2B

Since thermodynamics is about stability in one state versus another and kinetics is about the speed at which a species reacts, I believe that a reaction does always need to be controlled by one.

Rachel Bartley 2B

Hi, for my problem I have: "For a particular redox reaction, MnO2 is oxidized to MnO−4 and Fe3+ is reduced to Fe2+ . Complete and balance the equation for this reaction in basic solution. The phases are optional." I believe that I've balanced the charges right, but I don't know how to bala...

Rachel Bartley 2B

pKa measures the strength of an acid, so a low pKa indicates a strong acid with a low pH, while a high pKa indicates a weaker acid with a higher pH that is still below 7 on pH scale because 7 and below refers to acidity.

Rachel Bartley 2B

While molar entropy is dependent on the state of the molecule, you can also determine which has the higher molar entropy typically by looking at the size of each molecule because larger molecules have less order. This means that HBr would have a higher molar entropy than HF because it is larger than...

Rachel Bartley 2B

Typically, larger molecules have higher entropies because they have less order and increased molecular motion. This means you would compare the entropies of HF and HBr by comparing the sizes of the two molecules using periodic trends. With this, HBr is larger and has higher entropy than HF.

Rachel Bartley 2B

Spontaneous reactions aren’t always exothermic, as a reaction can still have a negative delta G if TdeltaS is positive and greater than deltaH.

Rachel Bartley 2B

Entropy is the measure of disorder within a system. Gases typically have a high entropy because there is very little order among molecules as they are more free to move around as a gas than in a liquid or solid.

Rachel Bartley 2B

I understand it is the entropy of a system being related to the heat and temperature in that system, in which an increase in heat, increases the entropy, while a larger temperature than heat decreases the entropy. This can be understood when observing phase changes from water vapor to liquid water t...

Rachel Bartley 2B

qrev refers to the amount of heat in a reversible reaction. (rev coming from reverse)

Rachel Bartley 2B

The change in entropy is actually always zero for reversible reactions, not irreversible reactions. It is zero because no heat is being exchanged between the system and its surroundings.

Rachel Bartley 2B

An example of an open system is if you have a glass of water out on a table, in which the water can evaporate. An example of a closed system is if you have a closed cup of water, in which the water can’t evaporate. And an example of an isolated system, which we were given in class, is the combustion...

Rachel Bartley 2B

The three ways of changing the energy of a system are: add or remove the amount of substance, heat or cool the system, and do work on the system.

Rachel Bartley 2B

It would be the other way around. When work is negative, the system is doing work, and when it is positive, then work is being done on the system.

Rachel Bartley 2B

For a reaction to be spontaneous means that it can occur naturally on its own without requiring energy or heat. If a reaction is spontaneous, it tends to have a negative G, while a non-spontaneous reaction will have a positive G.

Rachel Bartley 2B

In this equation it is Q because it is under conditions in which the system is not at equilibrium. If the system is at equilibrium, then a different equation using K would be used.

Rachel Bartley 2B

Yes, they are all state functions.

Rachel Bartley 2B

Spontaneous reactions have a negative delta G because they can occur on their own, while non-spontaneous reactions require some input of energy or work, so its delta G would be positive.

Rachel Bartley 2B

delta G=0 at equilibrium because there is no change in free energy because the forward and reverse reactions are occurring at the same rate.

Rachel Bartley 2B

Cp and Cv are different at constant volume because no work is being done on the system, while at Cp, some work is being done on the system. This means that Cv will be smaller than Cp.

Rachel Bartley 2B

In terms of work, a negative sign indicates that a system is doing work, while a positive sign means that work is being done onto the system. In terms of heat, a negative sign indicates the system is losing heat energy, while a positive sign indicates it is gaining heat energy.

Rachel Bartley 2B

By saying the copper is placed in a vessel of negligible heat capacity, this means that the vessel isn’t absorbing any energy, so now you can calculate how much energy the copper itself is absorbing or releasing.

Rachel Bartley 2B

The equilibrium constant will increase because the added heat will favor the formation of products, and a favored forward reaction will have a higher K value than one that favors the reverse.

Rachel Bartley 2B

If the change in enthalpy is equal to the amount of heat entering or leaving the system, then this means that the pressure is constant and and no non-expansion work is done on the system. In this case, then the variable q gets replaced by delta H.

Rachel Bartley 2B

To find the standard enthalpy of formation, you subtract the sum of enthalpies of formation of the reactants from the sum of enthalpies of formation of the products.

Rachel Bartley 2B

Enthalpy can be negative when a system is losing heat, while it is positive when heat is gained. Therefore, if a system is losing more heat than it is gaining, then its enthalpy will be negative.

Rachel Bartley 2B

When delta H is negative, that means heat is leaving a system. When it is positive, heat is entering the system.

Rachel Bartley 2B

The difference between boiling point and heat of vaporization is that boiling point is the temperature at which vaporization occurs, whereas heat of vaporization is the amount of energy required to allow a system to vaporize.

Rachel Bartley 2B

I remember it as exo- exit, so exothermic means heat is exiting the system. And endo- as enter, so endothermic would mean heat enters the system.

Rachel Bartley 2B

Yes, H2O would still be a liquid while boiling because the temperature is still the same boiling temp. Not all liquid water molecules are broken into water vapor molecules yet.

Rachel Bartley 2B

R is a constant, but there are different values of it for different units, so you would use the R value specific to the units given in each problem.

Rachel Bartley 2B

Since they are different units, you would use different values of R based on whichever unit you are working with.

Rachel Bartley 2B

The R values are given in different units, so the value depends on what you are trying to calculate and convert to and from with. First look at the units given and understand what units you should end with to determine which R value you should proceed with while working through dimensional analysis.

Rachel Bartley 2B

pKa is the -log(kA), and a low Ka indicates a high ph. So a low pKa means the Ka is high, making the pH low. A high pKa means the Ka is low, making the pH high.

Rachel Bartley 2B

The coordination number of a compound gives the number of bound atoms, which can assist in naming the molecular geometry. If a compound's coordination number is 4, then you know that there are 4 atoms bound to a central atom, giving the molecular shape of AX4 (tetrahedral).

Rachel Bartley 2B

No, empirical formulas always have whole numbers.

Rachel Bartley 2B

Chelating ligands attach to the central atom by donating their lone pair electrons to it.

Rachel Bartley 2B

The larger anions get, the more polarizable they become, while the smaller a cation gets, the more polarizable it becomes. This means polarizability trends diagonally from the top left of the periodic table to the bottom right.

Rachel Bartley 2B

Elements in Period 3 and below are capable of having expanded octets because they all have d-orbitals. You'll likely know when the exceptions take place as an expanded octet helps stabilize the compound by decreasing the formal charge of the central atom.

Rachel Bartley 2B

The 2 coefficient just specifies what period the sp^3 hybridization is in, which in this case is the 2nd period.

Rachel Bartley 2B

The work function is the minimum energy needed to eject an electron. It's given in units of J.

Rachel Bartley 2B

It first helps to look at the full neutralization equation for the salt, where the salt and water are the products. Then you can find the acid and base that would be the reactants for the neutralization. A strong base and acid suggest a neutral salt because the conjugate of each acid and base would ...

Rachel Bartley 2B

H2O's molecular geometry is bent because it has two bound atoms and two lone pairs on oxygen, the central atom. The two lone pairs on the oxygen atom push the two hydrogen atoms down further away from the oxygen atom and closer to each other, creating a bent shape and 104.5 degrees angle between the...

Rachel Bartley 2B

Bond lengths are contingent on the atomic size of each atom because logically, two smaller atoms bonded together will have a shorter bond than a large atom bonded to a smaller atom or two larger atoms bonded together because the two smaller atoms can be closer in proximity without interfering with e...

Rachel Bartley 2B

Electron affinity is the amount of energy released when an electron attaches to another atom, while ionization energy is the amount of energy required to remove an electron from an atom. With this, the two cannot be interchanged despite them following the same periodic trends.

Rachel Bartley 2B

Yes, the two are the same and can be interchanged. They are the weakest intermolecular forces that can be found whenever any atom is bound to another.

Rachel Bartley 2B

Double bonds are shorter than single bonds because they have more shared electrons between two atoms, meaning there is a greater attraction pulling the two atoms closer together.

Rachel Bartley 2B

The concept of resonance structures is that they are supposed to be the same molecule with the same arrangement of atoms, but with just a different arrangement of bonds. This means that double or triple bonds can rotate around resonance structures, creating a mirrored version of the first structure.

Rachel Bartley 2B

I've never been so stressed and overwhelmed but going into Week 10, I'm looking forward to almost being done with my first quarter.

Rachel Bartley 2B

I get really bad anxiety as well and am super stressed for the upcoming final, but one thing I've been doing so far to help keep me calm is listening to music that makes me feel really happy and upbeat, even if it's only one or two songs at a time. Sometimes just listening, dancing, and singing alon...

Rachel Bartley 2B

Hydrogen bonding only occurs when the H atom is bound to another highly electronegative atom such as N,O, F. Since the H in CHO is not bound to the O, there is no hydrogen bonding here. However, if another positive H atom binds to the partially negative O atom in CHO, then hydrogen bonding can occur...

Rachel Bartley 2B

Amphoteric compounds have both acid and base properties. Metals such as zinc, beryllium, etc. can form amphoteric compounds. With this, some examples are zinc oxide and beryllium hydroxide.

Rachel Bartley 2B

H+ and H3O+ are the same and can be used interchangeably. H3O+ just refers to H+ bonded to a water molecule.

Rachel Bartley 2B

Yes, when the central atom has a lone pair, you can expect the molecule to be polar because that lone pair will push the surrounding bound atoms further away from the central atom.

Rachel Bartley 2B

Formal charge doesn't influence intermolecular forces, but it is considered when understanding the structure of molecules because it indicates stability. Stable molecules are those with a nonzero (or as close to zero) formal charge on each molecule or those that spread out evenly the little charges ...

Rachel Bartley 2B

A radical is an atom or molecule with at least one unpaired electron. Because of this, radicals are usually very reactive.

Rachel Bartley 2B

As you move across a period, elements gain an electron and proton, which increases the nuclear charge within the same electron shell. This means that the electrons have a greater nuclear charge pulling them closer to the nucleus, reducing the atomic radius as you move along a period. And as you move...

Rachel Bartley 2B

When comparing melting/boiling points between two compounds, it is important to look at both the size of the compounds as well as the difference in electronegativities depending on the type of compounds you are comparing. So when looking at ionic compounds, such as NaF and KCl, the difference in ele...

Rachel Bartley 2B

Hydrogen bonds are one of the strongest intermolecular forces, meaning they require more energy to break them apart, giving them both a higher boiling and melting point than other intermolecular forces, such as ion-dipole, dipole-dipole, and LDFs.

Rachel Bartley 2B

Delocalized pi bonds are found in compounds that have resonance structures because the resonance structures indicate that the electrons are not fixed to a single bond and are therefore free to move around.

Rachel Bartley 2B

When naming atoms outside of [], cations always come before the coordination compound, while anions come after.

Rachel Bartley 2B

Myoglobin is a monomer that stores oxygen in muscle cells, while hemoglobin is a polymer made of 4 of the myoglobin structures that transports oxygen throughout the blood.

Rachel Bartley 2B

We use bis-, tris-, tetrakis-, pentakis-, and so on when di-, tri-, tetra-, penta- prefixes are already used in the naming of the coordination compound in order to prevent confusion and the double naming of any ligands.

Rachel Bartley 2B

Hi! I keep getting the name of this compound [Co(NH3)6]Cl3 : wrong, but I can't figure out what is wrong. I don't know why hexaamminecobalt(III) trichloride is wrong. Can someone please help?

Rachel Bartley 2B

You're right about how to find the coordination number by looking for the number of ligands bonded to the central metal and only accounting for what is inside the brackets, but you're overlooking something in the Co(SO4)(NH3)5. In this Co is the central metal with 6 bonded ligands: one SO4 molecule ...

Rachel Bartley 2B

I did the exact same thing as you, but once I read that I had to account for the counterion, I realized I didn't think about the negative charge on Cl when calculating the oxidation number for Co. The compound as a whole isn't charged, but the -1 charge on Cl means the charge of Co is now +3 instead...

Rachel Bartley 2B

Hi! I saw on another reply that en in is bidentate and the molecule I have is [Co(en)2(CO)2]Br : I know that this means that en attaches twice to the metal, meaning it adds two to the coordination compound, but my question is how do you know when a molecule is bidentate? I wouldn't have known this w...

Rachel Bartley 2B

Hi! I'm pretty sure the two correspond to each other because when you know the coordination number of a compound, then it is easier to deduce what the geometry is for that compound. This is because the coordination number is the number of ligands bound to a central atom, which that number is then us...

Rachel Bartley 2B

Hi! The coordination number in metals is the number of ligands that can bond to the given metal. With that, ligands are atoms, molecules, or ions that are bonded to a central atom, and in this case, a metal.

Rachel Bartley 2B

Hi! I was stuck on the third structure for a while too until I figured out that the structure would require the carbon atoms to form a ring in order for there to be a double and single bond between the three atoms. The H atoms are then placed accordingly to fill each octet.

Rachel Bartley 2B

Hi! The problem is regarding which molecules have the higher boiling/melting points between a) HCl vs. NaCl b) C2H5OC2H5 vs. C4H9OH c) CHI3 vs. CHF3 and d) C2H4 vs. CH3OH. I thought I was doing it correctly until I checked the answer and realized I did it all completely wrong, so I was wondering wha...

Rachel Bartley 2B

Generally, polar substances will have a higher melting point because of the existence of dipole forces.

Rachel Bartley 2B

I was wondering this same thing as I was doing this problem. I believe AX4E2 is a typo in the textbook, and the VSEPR formula is actually AX3E2 because there are only 3 bound electrons in ICl3.

Rachel Bartley 2B

Hi! The problem is to draw the lewis dot structure of BrF3, which I started by finding the total number of electrons, which is 28e- and drawing 3 Fl atoms around the Br atom. I then put the respective 6 valence e- around each Fl atom but then got confused on how to complete the Br octet. When I look...

Rachel Bartley 2B

Hi! I'm a little confused on question 13 in the textbook problems from section 2A on ionic bonding. The question is: For each of the following ground-state atoms, predict the type of orbital (1s, 2p, 3d, 4f, etc.) from which an electron will need to be removed to form the +1 ions: (a) Zn; (b) Cl; (c...

Rachel Bartley 2B

Chlorine is going to be more electronegative than Berilium because it is further right on the periodic table, which indicates more electronegativity than if you were to look at elements above and below each other.

Rachel Bartley 2B

So while resonance does always imply delocalized electrons, the two cannot be interchangeable because resonance structures are a case of delocalized electrons while delocalized electrons do not exist solely within resonance structures.

Rachel Bartley 2B

The atom with the lowest ionization energy is put at the center because it requires the largest number of e- to complete the octet. So as you go across a period, ionization energy increases because as you move across a period, elements gain electrons.

Rachel Bartley 2B

A stimulant in coffee and tea is caffeine, a substance of molar mass 194 g/mol. When 0.376 g of caffeine was burned, 0.682 g of carbon dioxide, 0.174 g of water, and 0.110 g of nitrogen were formed. Determine the empirical and molecular formulas of caffeine, and write the equation for its combustion...

Rachel Bartley 2B

For textbook Problem M11, I found O2 to be the limiting reactant for a, but I am still confused for how to solve b and c despite reading past responses for the questions! I don't know where to start, and anything will help!

Rachel Bartley 2B

For Question 32.B: In a second experiment a shorter wavelength light source is used resulting in ejected electrons with a kinetic energy of 4.200 x 10-19 J. What is the energy of this incident light? What is the wavelength of this incident light? I don't know exactly where to start because I am conf...

Rachel Bartley 2B

Thanks for the idea Rio, my answer to a is 1.99x10^-19 J, and my answer to b is 9.069x10^28.
For a, I used E(k)=1/2mv^2.
And for b, I converted the work function given in kJ to J and then multiplied by Avogadro's number.

Rachel Bartley 2B

For Question 30.C: What is the frequency of the incident light on the sodium metal surface? the given is: Light hits a sodium metal surface and the velocity of the ejected electron is 6.61 x 105 m.s-1. The work function for sodium is 150.6 kJ.mol-1. I tried solving the question by adding the work fu...

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