CHEMISTRY COMMUNITY

Michael Nguyen 1E

If you see a graph of [A] v. t and it is linear with a negative slope, you know that the reaction is zero-order with respect to that reactanct. The rate constant k is equal to the negative of the slope.

Michael Nguyen 1E

A first-order reaction will have a straight-line graph of ln[A] v. t A second-order reaction will have a straight-line graph of 1/[A] v. t A zero-order reaction will have a straight-line graph of [A] v. t The first-order and zero-order graphs will have negative slopes while the second-order graph wi...

Michael Nguyen 1E

I believe that if we need to determine the order of a reaction based on graphs, then they will most likely provided the graphs that we need.

Michael Nguyen 1E

The unit for the rate constant will depend on the overall reaction order. The rate will always be in units of M/s and each concentration will be in M. So the rate constant will always be in units so that when multiplied with the concentrations, the result will be in M/s.

Michael Nguyen 1E

An intermediate will first appear as a product and then appear again as a reactant. Catalysts are the opposite. They will first appear as a reactant and then appear again as a product. Note than neither intermediates nor reactants will show up in the overall balanced equation.

Michael Nguyen 1E

Generally, I believe the maximum amount of work able to be done (w_max) is equal to deltaG. This is for all reactions under any conditions I believe.

Michael Nguyen 1E

A table of values of standard reduction potentials should be provided if they are needed to solve a particular problem.

Michael Nguyen 1E

The cell potential will not change because the electrodes are solids, so increasing their masses will not impact the chemical equilibrium. However, as the previous post noted, increasing the mass of an electrode will prolong the battery's life while decreasing the mass will shorten the battery's life.

Michael Nguyen 1E

I don't think that knowing this is super important or essential, but it is good to know. The standard reduction potentials are all based on reactions with the standard hydrogen electrode as a common reference point.

Michael Nguyen 1E

An electrolytic cell has a negative cell potential. Therefore, if you know the two half-reactions, you can arrange them in a way that results in the cell potential being negative.

Michael Nguyen 1E

The species that is reduced is the one with the more positive standard reduction potential. The species that is oxidized is the one with the more negative standard reduction potential. This set-up will result in a positive cell potential.

Michael Nguyen 1E

You can find standard reduction potentials in the back of the book in Appendix 2B.

Michael Nguyen 1E

Yes, if you want to have a positive cell potential overall, the more positive E will be at the cathode and the less positive E will be at the anode.

Michael Nguyen 1E

Water is only included in the equilibrium constant expression when it is in the gas phase. Solids and liquids are not included when calculating equilibrium constants.

Michael Nguyen 1E

I believe that an electrode has to be solid metal, not just any solid. Some solids are not metal, and I do not think these would work as electrodes.

Michael Nguyen 1E

You need to use a platinum metal electrode for the cathode/anode when there is no solid metal conductor present in the redox reaction. The platinum electrode allows for electron transfer without affecting the actual redox reaction.

Michael Nguyen 1E

In that cell notation, the species on the right of the double line are reacting at the cathode. Since reduction occurs at the cathode end of the cell, you know that Cl₂ is the one being reduced.

Michael Nguyen 1E

A platinum electrode is needed when there is no solid metal conductor as an electrode already present. If there are already a metal anode and a metal cathode, then the platinum electrode is unnecessary. Whenever an inert electrode is needed, it is usually the platinum electrode, and I am unsure if t...

Michael Nguyen 1E

In addition, E^o is a value that has been found experimentally and is commonly found in tables, not requiring calculations. However, E is the cell potential at any condition and requires calculations to find. E^o is used in the Nernst Equation to find E.

Michael Nguyen 1E

The reason we had to include a platinum electrode in this example is because both Fe³⁺ and Fe²⁺ are in solution. This means that there is no solid metal electrode present. The platinum electrode was needed in order for electrons to flow from anode to cathode.

Michael Nguyen 1E

I'm sure there are some features in the batteries we use every day that allow for charged particles to move freely and prevent charge buildup. Even if it is not a salt bridge, the mechanism likely has the same purpose.

Michael Nguyen 1E

Platinum is commonly used as an electrode when the reaction at the cathode or anode does not have a conducting solid metal involved. Platinum is used because it is an inert metal and will not directly affect the redox reaction.

Michael Nguyen 1E

Yes, these topics will be covered on Test 2. Test 2 is on the second page of the thermodynamics outline and electrochemistry.

Michael Nguyen 1E

In a galvanic cell, a salt bridge allows charged particles to pass from one beaker to another to prevent charges from building up. If charges were allowed to build in the beakers, the redox reaction would stop prematurely due to charge buildup.

Michael Nguyen 1E

q is the same as deltaH under conditions of constant pressure. Enthalpy is defined as the amount of heat released or absorbed at a constant pressure.

Michael Nguyen 1E

Depending on if the question was dealing with a weak acid or a weak base, you would first need to calculate Ka (for an acid) or Kb (for a base). Then, you would need to set up and solve an ICE table using the reaction between the acid/base and water. After that, you should have either [H 3 O + ] or ...

Michael Nguyen 1E

Work will be negative when the system does work on the surroundings. This generally happens when the system expands in volume through work of expansion.

Michael Nguyen 1E

The "m" stands for molar, which means that the whole term refers to the entropy of one mole of the given substance.

Michael Nguyen 1E

I think when the temperature is not given explicitly, you can assume it is 298 K if it's needed for the problem. I think this also applies to pressure, and we assume it is 1.00 atm.

Michael Nguyen 1E

When temperature, pressure, and volume are given in a problem, you can solve for moles using the equation PV=nRT. The gas constant (R) is provided on the constants and equations sheet.

Michael Nguyen 1E

Yes, the equation will still have a negative sign in front. When work is done on the system, the change in volume is negative. This negative cancels with the one in the equation, resulting in a positive value for work. This makes sense because when work is done on the system, the value should be pos...

Michael Nguyen 1E

In the solution manual that I have, 490 J is the correct answer. It is written as 4.90*10² J, but it is still the correct answer.

Michael Nguyen 1E

This constant is used to convert between L*atm and Joules. It can be found on the provided constants & equations sheet.

Michael Nguyen 1E

If the heating curve is steeper, that means that the specific heat capacity for that material is low. Since the curve is steep, that means that it does not take much energy to raise the temperature of the material. Conversely, a curve that is not steep means that the specific heat capacity for that ...

Michael Nguyen 1E

The word "isothermal" refers to a system being at a constant temperature. In these situations, it is best to use the equations that involve a change in volume and pressure.

Michael Nguyen 1E

A reversible process is slow and efficient whereas an irreversible process is fast and inefficient. Also, irreversible gas expansions occur under conditions of constant external pressure while reversible gas expansions do not have constant external pressure.

Michael Nguyen 1E

It depends on what constants you are given in the problem. If you are given the molar heat capacity, you should use moles. If you are given the specific heat capacity, you should use grams.

Michael Nguyen 1E

The negative sign is there because the system loses energy by doing work of expansion. The system does work on the surroundings, and therefore it decreases in internal energy.

Michael Nguyen 1E

You would use the -P*deltaV equation when the external pressure is constant because you can pull a constant outside of the integral. However, if the external pressure is not constant, you would need to use the integral formula.

Michael Nguyen 1E

No, if the conversion is completely equal, you do not have to consider the sig figs. So in the example you provided, 1000 ml=1 L, you would not consider those sig figs. However, a conversion factor that is not completely equal, such as molar masses, would require you to consider those sig figs.

Michael Nguyen 1E

This constant is very commonly used because a lot of problems deal with a change in temperature of water. It can also be found on the constant and equations sheet on the class website.

Michael Nguyen 1E

Yes, that's correct. When the temperature of a system changes, its equilibrium constant will also change.

Michael Nguyen 1E

Depending on the information given in the question, you may have to use different equations to solve for [H₃O⁺]. An equation that relates [H₃O⁺] to K_w would be [H₃O⁺][OH^-]=K_w.

Michael Nguyen 1E

Celsius and Kelvin will never be the same number for a given temperature. You must always convert according to the problem. The conversion is K = C+273.15, which I believe is on the equations sheet.

Michael Nguyen 1E

From the graph that is provided, you can see that A goes down 10, B goes up 5, and C goes up 10. When you simplify this ratio, there are 2 units of A, 1 unit of B, and 2 units of C. Also, A is the reactant because it decreases while B&C are the products since they increase.

Michael Nguyen 1E

Buffers are different because there will be initial concentrations for both the weak acid/base and its conjugate. Often times, these concentrations are the same. However, the way the ICE table is used, the techniques, and the rules for approximation are still the same.

Michael Nguyen 1E

Other examples of state properties include energy, pressure, volume, temperature, density, and heat capacity.

Michael Nguyen 1E

Yes, you should consider the sig figs for the equilibrium constants because they are calculated from concentrations that have limits on their sig figs too.

Michael Nguyen 1E

There are different names for equilibrium constants because they provide a little bit more information about the system that is being studied. Kc means the system is dealing with concentrations, Kp means the system is dealing with partial pressures, Kw has to do with water, Ka is for weak acids, and...

Michael Nguyen 1E

Solids and liquids do not affect equilibrium or the equilibrium constant. Solids do not have concentration, which is why they do not affect equilibrium. Liquids are usually solvents and have insignificant changes in concentration, so they do not affect equilibrium either.

Michael Nguyen 1E

Different stresses that can be applied to a system at equilibrium include:
Adding/removing a reactant or product
Change the pressure of the system (by manipulation volume or by adding an inert gas)
Changing the temperature of the system

Michael Nguyen 1E

There is an announcement on the class website that says that the test is on chemical equilibrium & acid-base equilibria. I think a good way to study for the test is to do as much practice as possible to get exposed to a variety of different questions. If possible, try to do all of the problems t...

Michael Nguyen 1E

Although adding an inert gas will increase the pressure of a system, the partial pressures of the reactive gases are not changing because the volume has stayed the same. Therefore, K stays the same and there is no shift in the system.

Michael Nguyen 1E

Solids do not have concentration or pressure, which is why they are left out of K expressions.
Liquids are usually solvents and have a very insignificant change in concentration, which is why they are not included in K expressions either.

Michael Nguyen 1E

There are many units for pressure, and you should use the unit that is presented in the problem if possible. Otherwise, common units for pressure are: atmospheres (atm), torr, bar, and pascals (Pa). There may be more, but these are the common ones I think.

Michael Nguyen 1E

Kp can only be used for gases because only gases can exert pressure on a container. Therefore, if you only have aqueous solutions in your chemical equation, then you know you must calculate for Kc since there are no gases. If you have only gases in your chemical equation, you can solve for either Kc...

Michael Nguyen 1E

Solvents are not included in the equilibrium constant equation because the concentration of a solvent does not change significantly in equilibrium reactions. There is such a large excess of solvent in these reactions that their concentration is essentially constant throughout the reaction.

Michael Nguyen 1E

When the concentration of the products is increased in an equilibrium reaction, the reverse reaction will be favored and more reactants will be formed.

Michael Nguyen 1E

When Q<K, the reaction will proceed in the forward direction and favor the products.
When Q>K, the reaction will proceed in the reverse direction and favor the reactants.

Michael Nguyen 1E

Q and K are calculated in the same way by using the same equation. However, K is a constant that is calculated using the concentrations when the reaction reaches equilibrium while Q changes as the reaction proceeds. Often, we compare Q and K to determine which direction the reaction will continue ov...

Michael Nguyen 1E

Argon and Xenon are both nonpolar. Therefore, the only forces that they experience are induced-dipole induced-dipole forces. Since Xenon is a larger atom than Argon and has more electrons, these induced-dipole induced-dipole forces are stronger in Xenon than in Argon. Therefore, it would take more e...

Michael Nguyen 1E

The fact that there are more oxygen atoms is an explanation for anion stability. Since there are more oxygens, there is more electron-pulling power in the anion that will delocalize the charge more, making the anion more stable.

Michael Nguyen 1E

An oxoacid is an acid that contains one or more oxygen atoms. Generally, an oxoacid contains hydrogen, oxygen, and at least one other element. For example, H₃PO₄ and HNO₃ are both oxoacids.

Michael Nguyen 1E

Generally in a chemical equation, the Bronsted acid and base are both reactants. When they react, the products are a conjugate base and a conjugate acid.

Michael Nguyen 1E

When naming the ligands in a coordination compound, the -ide suffix is dropped and is replaced with -o.
Since CN^- is cyanide, the -ide is dropped and replaced with -o when used in naming for a coordination compound, and it becomes cyano.

Michael Nguyen 1E

Terminal atoms are the other atoms in a molecule that are not the central atom. For example, in methane (CH 4 ), the carbon atom would be the central atom and the four hydrogens are all terminal atoms. For the final, I guess you should know what it means, but it is something that shouldn't be too ha...

Michael Nguyen 1E

No, actually the -ide suffix means that they are ions. So chloride would be Cl^- and bromide would be Br^-.

Michael Nguyen 1E

Bronsted and Lewis acids/bases are just two different ways to define acids/bases. Neither is more correct, and there is no difference in the actual compounds. The Bronsted definition is based on the donation/reception of protons. The Lewis definition is based on the donation/reception of lone pairs ...

Michael Nguyen 1E

The electrostatic attraction between a cation and an anion is depended on the charges of the ions as well as the distance between them. The force is stronger if the charges of the ions are higher. In other words, the strength of the force is directly proportional to the charges of the ions. The forc...

Michael Nguyen 1E

I don't believe there is any difference between these terms. They are all different, interchangeable ways to identify the compounds we have been discussing in lecture.

Michael Nguyen 1E

When a ligand binds at multiple sites, it means that one single ligand donates multiple electron pairs to the transition metal cation and binds to it in multiple locations.

Michael Nguyen 1E

The acids found in biological systems tend to be weaker because many biological processes tend to be pH-dependent. A strong acid will decrease the pH of a system much more than a weak acid will. Therefore, organic acids tend to be weaker because they will not as drastically change the pH of a biolog...

Michael Nguyen 1E

Polar molecules tend to have higher boiling points than nonpolar molecules because of the presence of dipole-dipole interactions and potentially hydrogen bonding. Both of these forces are stronger than the induced dipole-induced dipole forces that are the only intermolecular forces in nonpolar molec...

Michael Nguyen 1E

Lone pairs on an atom are considered regions of electron density. Therefore, they are including in the hybridization of that atom.

Michael Nguyen 1E

In order for an f-orbital to be hybridized, there would have to be 10 regions of electron density around an atom (1 s-orbital, 3 p-orbitals, 5-d orbitals, and 1-f-orbital). I'm not sure if this possible, but it seems very unlikely. I don't think we will need to know about it for future assessments.

Michael Nguyen 1E

Pi bonds inhibit rotation in a molecule because the orbitals that are interacting to form the bond are arranged side-by-side, not end-to-end. Since they are arranged side-by-side, rotating the molecule would prevent the orbitals from overlapping, break the pi bond, and would require a chemical react...

Michael Nguyen 1E

When molecules are drawn using a ring structure, assume that all of the atoms have an octet (except for hydrogens). However, the lone pairs are often omitted in the drawing but are implied to be there. Since the lone pairs are still there, they are included in the hybridization.

Michael Nguyen 1E

Since the oxygen has one double bond and two lone pairs, there are a total of three regions of electron density around it. Three regions of electron density correspond with an sp2 hybridization for the oxygen.

Michael Nguyen 1E

Yes, I believe the two are the same thing. It is just the electrostatic attraction between a positively-charged cation and a negatively-charged anion.

Michael Nguyen 1E

Hydrogen can only form one bond in a molecule. So in order for hydrogen bonding to take place, H has to be bonded to N, O, or F, since those atoms would create the largest electronegativity differences.

Michael Nguyen 1E

Intermolecular forces occur between separate molecules while chemical bonds occur within one single molecule.

Michael Nguyen 1E

Bigger molecules have larger electron clouds, which make them more polarizable. This will lead to stronger dipole moments between the molecules and stronger attractive forces. This will increase the melting and boiling points of the compounds.

Michael Nguyen 1E

London dispersion forces act on all atoms and molecules. This includes polar molecules and nonpolar molecules.

Michael Nguyen 1E

I don't believe resonance structures really impact the VSEPR model. The model only depends on the number of atoms bonded to the central atom and the number of lone pairs on the central atom. Whether or not there is resonance, single bonds, or double bonds, it does not affect a molecule's shape accor...

Michael Nguyen 1E

The h stands for Planck's constant, which is provided on the constants sheet.
The v stands for the frequency of EM radiation that is being used in the calculation.

Michael Nguyen 1E

You should always account for all of the electrons in the Lewis structure. They could be as lone pairs or in bonds, but all of the electrons should be represented in the structure.

Michael Nguyen 1E

There are other exceptions that can have expanded octets beyond just P, S, and Cl. Any element that would have unfilled d-orbitals able to be used would be able to accommodate extra electrons and have an expanded octet. It's just that the first ones that are able to do this are P, S, and Cl.

Michael Nguyen 1E

Metals tend to have lower electronegativity values while nonmetals tend to have higher electronegativity values. Since the difference in electronegativity between a metal and a nonmetal is typically large, they form ionic bonds. Similarly, since the difference in electronegativity between two nonmet...

Michael Nguyen 1E

Covalent compounds are drawn using lines, which represent the sharing of electrons (covalent bonds).
Ionic compounds are drawn as separate ions that are close to one another because of their electrostatic attraction.

Michael Nguyen 1E

Elements that do not require an octet include:

The first four elements (H, He, Li, Be)
Boron (B), Aluminum (Al), and the rest of that group. These elements sometimes have only 6 valence electrons rather than a full octet.

Michael Nguyen 1E

Yes, if you are drawing a Lewis structure for an ion, the sum of all of the formal charges in the ion must equal the total charge of the ion.

Michael Nguyen 1E

Ionic bonds are typically stronger than covalent bonds since they involve two particles that have full positive/negative charges rather than just the sharing of electrons. Double bonds are stronger than single bonds because there are more electrons involved in the sharing. In addition, double bonds ...

Michael Nguyen 1E

The formal charge equation that Professor Lavelle provided in class is a little confusing to understand, but it is just the # of valence electrons of the atom minus the number of lone pair electrons minus half the number of bonding electrons: FC = V - (L +.5B) So for example, if you have a Lewis str...

Michael Nguyen 1E

Yes, I believe that those elements also follow the same pattern that chromium and copper have.

Michael Nguyen 1E

The central atom of a molecule is most typically an atom of the element with the lowest ionization energy. However, hydrogen is never central as it can only form one bond.

Therefore, for NHF2, the central atom would be nitrogen as it has the lowest ionization energy and is not hydrogen.

Michael Nguyen 1E

When a molecule has resonance, it means that a multiple bond (double bond, triple bond, etc.) can be placed in different locations within the molecule without having to move the individual atoms in the structure.

Michael Nguyen 1E

The central atom of a molecule is usually an atom of the element with the lowest ionization energy.

Michael Nguyen 1E

Once you've determined the l value, you can determine the possible ml values. The values ml can have are -l, -l+1, ..., 0, ..., l-1, l.
In simpler terms, the possible values of ml are the whole number values between -l and l.
For example, if l=2, ml can be -2, -1, 0, 1, 2.

Michael Nguyen 1E

Yes, you should aim for formal charges of 0 because that will give you the most accurate Lewis structure for the molecule you are modeling. However, achieving formal charges for every atom in the molecule may not be possible.

Michael Nguyen 1E

For an electron in the 3p subshell:
n=3 (3rd principal energy level)
l=1 (p subshell)

Since ml can have values of -l, -l+1,..., l-1, l, the only possible values of ml would be -1,0,1.

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