CHEMISTRY COMMUNITY

Ben Zhang 2H

In the reaction C(s) + O2(g) into CO2 (g), does entropy decrease or increase? It goes from two moles to one so that would decrease entropy but carbon also goes from solid to gas so I'm not sure.

Ben Zhang 2H

Gibbs free energy and entropy are related by the equation deltaG = deltaH - TdeltaS. That means when there is an increase in entropy there is a decrease in Gibbs free energy. A process becomes more spontaneous the more disordered it becomes in a way.

Ben Zhang 2H

For the most part the catalyst will appear in the first step of the reaction. However, it is possible for it to pop up in a later elementary reaction I believe. The important to differentiate a catalyst that appears later and an intermediate is that an intermediate will be a product first while the ...

Ben Zhang 2H

Molecularity is the number of reactants that you have and not the total number of substances you have. So the number of moles you have on the reactant side is the molecularity that you have in an elementary step.

Ben Zhang 2H

I don't think it does. For the equation k = Ae^(-Ea/RT). Raising the temperature of a lower activation energy would increase the rate constant more than if you were to do it at a higher activation energy. In this equation, e is raised to the negative (Ea/RT) so lower activation energies result in hi...

Ben Zhang 2H

How can you tell if entropy change is positive or negative based on the chemical equation? Is it based on the change of states or number of moles?

Ben Zhang 2H

Why is the steady-state approach more general than the pre-equilibrium approach? Also, is there a better one to use?

Ben Zhang 2H

It technically is possible. However, these reactions happen when all these molecules collide with each other at the same time. The more molecules needed to collide or the higher the order of reaction, the less likely the collision happens. If the collision doesn't happen then the reaction doesn't re...

Ben Zhang 2H

If a reaction can have two different products and one product has a lower activation energy than the other one, does that mean one product doesn't form at all?

Ben Zhang 2H

How is it possible for a reaction to be zero order? Why can changing the concentration of a reactant have no effect on the rate of reaction?

Ben Zhang 2H

When calculating initial reaction rate, we only focus on the initial reaction concentration and not the product concentration because the reaction has not technically started. The initial reaction rate is when t=0 so at that time there are only reactants and no products formed yet. This also makes c...

Ben Zhang 2H

I feel like a reaction can be controlled by both kinetics and thermodynamics. Thermodynamics tells us what direction the reaction is going. It tells us if the reaction will form products or reactants. Kinetics controls how fast the reaction reaches equilibrium. So you can control a reaction by makin...

Ben Zhang 2H

It means that the reverse reaction is spontaneous.

Ben Zhang 2H

Combustion itself should be exothermic. Maybe in lecture there was something else to that problem or explanation where the heat released is balanced out by something so that the overall temperature stays the same.

Ben Zhang 2H

A reversible reaction work is done in infinitesimal increments. As a result, the change is really close to 0 and the overall system doesn't really change, so temp is constant. A irreversible reaction has a noticeable change in the system especially in volume. That's why temperature changes.

Ben Zhang 2H

If entropy is negative, this means that the disorder of the system goes down. In other words, the system becomes more organized. Since the entropy of the universe is always increasing, this means that the entropy of the surroundings must increase and the increase has to be bigger than the decrease o...

Ben Zhang 2H

So for delta S and delta G, the change is larger in the gas phase of a substance than the liquid or solid phase. Is this also true for enthalpy or delta H?

Ben Zhang 2H

Why is it that a heavier atom will have more thermally accessible vibrational energy levels and thus higher entropy?

Ben Zhang 2H

Why is a metal like Platinum a good material to use in the batteries?

Ben Zhang 2H

S is just the entropy of the reaction or whatever you're looking at. S with the degree is the entropy under standard conditions. This means it is the entropy under a specific set of conditions. S is more general. It could be the same value as S with the degree if it has the same conditions as the st...

Ben Zhang 2H

Non-spontaneous processes do have a decrease in entropy. I may be wrong. but I'm pretty sure that the entropy of the universe is always increasing. As a result, the entropy of the system can decrease if the increase in entropy of the surroundings is greater than the decrease so there is an overall i...

Ben Zhang 2H

To find the enthalpy of vaporization, you divide the amount of energy produced by the heater by the difference in moles of the molecule. It's good to know that a watt is 1J/sec. To find the entropy of vaporization, you take what you got for enthalpy of vaporization and divide that by the boiling poi...

Ben Zhang 2H

For the Achieve Week 5 problem 19, why do we use the R=8.314 gas constant if we are dealing with bars?

Ben Zhang 2H

Enthalpy (H) is talking about the total heat content of the system. Entropy (S) is the disorder of the system or the number of possible positions the molecules can be in. They do have a direct relationship with each other but they aren't the same. DeltaS = deltaH/Temperature.

Ben Zhang 2H

Why is Gibb's free energy a good thing to use to determine the spontaneity of biological reactions?

Ben Zhang 2H

Entropy has a direct relationship with temperature. Change in entropy has an inverse relationship with temperature.

Ben Zhang 2H

Why is Gibbs free energy the maximum for work?

Ben Zhang 2H

Entropy is 0 when K=0 and there are no impurities. I understand why K needs to be 0 but why can't there be any impurities? Since K=0, does everything kind of stop and entropy would be 0 regardless if there were impurities?

Ben Zhang 2H

You would use PV=nrT to calculate the change in volume of this reaction. I'm pretty sure you assume initially the volume is 0 so whatever you get from that equation is the deltaV. You use that to find work(w) using w=-PdeltaV. Then to find specific heat you use the 5R/2 with the R they give you, thi...

Ben Zhang 2H

I don't believe we will use any other equation for reversible reactions because integrals are really the only thing that can measure the infinitely small difference in volume of the system.

Ben Zhang 2H

I think entropy increases when energy increases as well. Entropy is a measure of disorder. When you put energy into molecules they get excited and move around more, thus causing more disorder. However, if you are talking about a system losing energy, the entropy of the surroundings will increase but...

Ben Zhang 2H

Internal energy is at a minimum because there is no net exchange of energy anymore. If internal energy was above its minimum, the system would probably lose energy until it no longer can.

Ben Zhang 2H

You can't always assume [H30+]=[OH-]. However, for ex 6A.21 in the textbook, it tells you that you are dealing with water. Water has a pH of 7 which means that water is neutral and [H30+]=[OH-]. However, acids and bases have unequal concentrations and you would need to use ICE tables and have a litt...

Ben Zhang 2H

A negative pH just means that the solution is really, really acidic. Its [H30+] is so high that the log of it is positive, thus resulting in the negative pH.

Ben Zhang 2H

I know that entropy is always increasing. However, is it possible for entropy to decrease for a system?

Ben Zhang 2H

Breaking bonds require energy because the bonds are already in a stable place and don't want to change. You have to force them to change by putting energy into them. Forming bonds release energy because the molecule is going to a stable place so a lower potential energy. By going to a lower potentia...

Ben Zhang 2H

No, the specific heat changes based on state of matter and what type of compound it is.

Ben Zhang 2H

How do scientists measure entropy? I don't quite get how people can measure disorder.

Ben Zhang 2H

Yeah you're right that all chemical reactions have a reverse reaction. It's just that some reaction's reverse reaction is so small that we can pretty much say the reaction goes to completion.

Ben Zhang 2H

The temperature remains constant during the phase change because the energy being added isn't being used to increase the kinetic energy of the particles. Instead, the energy is being used to break the bonds between the molecules and make them move more freely.

Ben Zhang 2H

When you change something from one state of matter to another, you need energy. The energy being added to water when it is being evaporated doesn't increase the temperature of the water but instead is used to break the bonds of the water molecules. As a result, boiling water and steam have about the...

Ben Zhang 2H

If it's protonation percentage, it should be concentration of conjugate divided by initial concentration of the molecule because we want to know how much of that initial concentration actually protonated.

Ben Zhang 2H

I think the biggest difference is that free expansion is a type of irreversible reaction, so it is different from a reversible reaction.

Ben Zhang 2H

How can the entropy of a system decrease?

Ben Zhang 2H

If you're talking about concentration, then you use the concentration you found of BH+ and OH- to find the concentration of B. Since H20 is a liquid, it isn't used to find the equilibrium constant. As a result the equilibrium constant is equal to ([OH-]*[BH+])/[B]. The equilibrium constant is alread...

Ben Zhang 2H

Enthalpy values are needed to see if the reaction is endothermic or exothermic. You could also maybe tell if the reactions is two reactants combining to form one product then it's exothermic because bond formation releases energy. If the reactions is one reactant splitting apart to form two products...

Ben Zhang 2H

Yeah the rule is that if Ka is less than 10^-3 you can approximate. I think Lavelle mentioned you could do 10^-4 to be safe because some instances of 10^-3 it might not be <5%. If it's greater than 5% than you need to redo the problem without the approximation and hope it doesn't get too ugly.

Ben Zhang 2H

You generally use ice boxes when you want to find the concentration of reactants or products after equilibrium. You can usually identify the type of problem when they give you the molecules in the reaction, the Ka, and the initial concentration of at least one molecule.

Ben Zhang 2H

Polyprotic bases can accept multiple protons. Usually this means they have a neg charge greater than one so that they can accept those protons. You can also check their conjugate acid and see if that is also polyphonic.

Ben Zhang 2H

Whatever is being consumed or used to make the other molecules is -nX. Whatever is being made is +nX.

Ben Zhang 2H

The reason why the reactants are favored is because H20 is a liquid. When calculating these problems, we don't include solids and liquids. As a result, there are two moles of gas on the products side and only one mol of gas on the reactants side.

Ben Zhang 2H

When you have k={products]/[reactants] and you multiply it out, if there is a x^2 then you use the quadratic formula to find the possible values of x.

Ben Zhang 2H

If it's a reactant, it will be -X because it is being used up in the reaction. If it is a product, it will be +X because the molecule is being formed. However, you have to check the stoichiometric coefficients of the balanced reaction. That coefficient will determine whether it is a -1X or a -2X or ...

Ben Zhang 2H

I think limiting reagents are really only a thing when the reaction goes to completion. So the reaction would have to pretty much use up all the available reactants to form products. In that case, there wouldn't be an equilibrium because equilibrium doesn't have the reaction go to completion.

Ben Zhang 2H

I believe because water is the solvent. It is there to help with the process and assumed to be in excess. As a result, we don't really need to know the concentration of water.

Ben Zhang 2H

I believe so. It also deals with the fact that strong acid or base would have a very stable cation or anion. That's why it is strong because the resulting cation or anion doesn't want to react, so there barely is a reverse reaction. As a result, the resulting cation or anion is probably going to be ...

Ben Zhang 2H

A Lewis acid accepts an electron pair. A Bronsted acid donates a proton, usually a H+. An Arrhenius acid is just a compound that increases the H+ concentration in solution. I think we mainly just focus on Lewis and Bronsted in 14a. The Lewis definition is more general than the Bronsted definition

Ben Zhang 2H

Yeah we assume that they completely dissociate in water. That's why we don't see a Ka or Koh value with them.

Ben Zhang 2H

I believe a coordinate complex is just a metal center with ligands around it. The coordinate compound is the overall neutral molecule that is made up of coordinate complexes. The complexes can have charges but the compound is neutral.

Ben Zhang 2H

The spectator ion will usually be a component of a strong acid or base. For example in KF, K+ ends up being the spectator ion because KOH is a strong base while HF is a weak acid.

Ben Zhang 2H

Is the n=1 level the same distance away from the nucleus for all atoms?

Ben Zhang 2H

When an acid is called strong, it doesn't mean that the molecule itself has strong bonds. A strong acid is one that will dissociate completely or almost completely which is why they have longer, weaker bonds. A weak acid actually has the strong acids because it doesn't dissociate completely, thus ma...

Ben Zhang 2H

I believe the number of binding sites is equal to the number of electron pairs the molecule has to bind because each site the ligand donates one electron pair.

Ben Zhang 2H

Does bond length/bond strength or the stability of the anion matter more when determining the relative strengths of acids?

Ben Zhang 2H

How is an anion stabilized by resonance?

Ben Zhang 2H

What does it mean when a nodal plane contains the internuclear axis?

Ben Zhang 2H

Yep, hybridization is just two atoms bonding and sharing their electrons at the most stable level. This level ends up being between the 2p and 2s level so the two levels hybridize and we get the most stable hybridized orbital.

Ben Zhang 2H

A weak acid typically has strong intramolecular forces while a strong acid has weak intramolecular forces. So typically acids that have longer bonds or some other weaker bonds are going to be the stronger acid. This is because the weaker the bond, the more the molecule dissociates in solution. Stron...

Ben Zhang 2H

There are some ways to tell if a molecule is an acid or a base. The two main ways I know are that if there is a OH at the end of a molecule it is probably a base, because that oxygen can receive an electron pair. If there is just an H at the end of the molecule, it is probably an acid. There may be ...

Ben Zhang 2H

What exactly is the difference between an aqueous solution and a liquid?

Ben Zhang 2H

Why is it that compounds with different size atoms still have the same shape as other compounds? For example, a molecule that has 6 hydrogen atoms is octahedral and a compound with 3 hydrogen and 3 chlorine atoms have the is also octahedral. Wouldn't the different size of the chlorine atom push the ...

Ben Zhang 2H

Why exactly are the experimentally proven bond lengths of a molecule the average of the different bond lengths it has? So why doesn't the electron pair in a double bond stay there and not influence the other bond lengths in a molecule?

Ben Zhang 2H

I believe they have similar chemical properties since they share the same number of electrons.

Ben Zhang 2H

In this problem there are 8 possible hydrogen bonds because each N can form 2 because there is a pair of lone electrons and the oxygen can form 4 more because it has two pairs of lone electrons. Each lone electron on N or O can form a hydrogen bond.

Ben Zhang 2H

A coordinate covalent bond is when two atoms create a bond together by sharing two electrons. However, instead of each atom sharing one of its atoms, a coordinate covalent bond involves one atom donating two electrons in the electron sharing while the other atom doesn't have any to share. An example...

Ben Zhang 2H

Dipole-dipole movements usually are associated with non polar molecules. Polar molecules still experience them but we don't really talk about them because polar molecules have much stronger bonding such as covalent or ionic bonding. Induced dipole movement is the same as London Dispersion Forces. Th...

Ben Zhang 2H

Electronegativity is the measure of an atom's tendency to attract an electron during bonding. So as you move across a period, an electron has more electrons and gets closer to completing its octet. As a result, its electronegativity increases because it wants to attract an electron to complete the o...

Ben Zhang 2H

I think it is because the further away the two atoms are, the more prominent the charges on each atom are. There is a bigger separation or difference in charge in the atoms are more spread out.

Ben Zhang 2H

Yeah, you can think of it that atoms with a larger atomic radius will have its electrons farther away from the nucleus, so the pull from the nucleus is less. In addition, there are probably more electrons in between the valence electrons and nucleus so the electron-electron repulsion is also going a...

Ben Zhang 2H

If the difference is between 1.5 and 2, I think you need to conduct experiments to see if the molecule has more covalent or ionic bonds.

Ben Zhang 2H

I think when making Lewis Dot Diagrams, you prioritize giving electron pairs to the atoms with smaller ionization energies. So we would give Nitrogen its electron pairs first and then any excess electrons that need to be made into double bonds would be with atoms with higher ionization energy like t...

Ben Zhang 2H

I think they use x-ray spectroscopy to find the diffraction patterns. The patterns are then used to find exactly how long the bond lengths are.

Ben Zhang 2H

I used De Broglie's equation to find the momentum of the electron. Then I found the velocity of the electron since we already know the mass of the electron. Then kinetic energy is 0.5mv^2. Then convert that answer from joules to eV.

Ben Zhang 2H

Yeah the 4s orbital will be filled before the 3d orbital. A helpful thing to look at for this is the periodic table. If you read it from left to right, it will tell you the order that the orbitals get filled above. For example, in the 4th row, the s comes before the d so that tells us that the 4s is...

Ben Zhang 2H

I believe this is partly due to the shape of the orbitals and the order they come in. S orbitals are spherical in nature, while the other orbitals have specific shapes which might make them higher in energy. In addition, there is electron to electron repulsion. The p orbital comes after the s orbita...

Ben Zhang 2H

Since it is talking about a nitrogen atmosphere, I think it means that the nitrogen is just in the air. Nitrogen as a gas only appears as N2 and not N. So in this situation it would be N2. As long as it talks about nitrogen being a gas or in the atmosphere, it should be N2. The problem will probably...

Ben Zhang 2H

It is the same for molecules and compounds.

Ben Zhang 2H

How does electron shielding affect the properties of the element or atom?

Ben Zhang 2H

When do you know if the next level s series is lower in energy than the current level's d series?

Ben Zhang 2H

It is 3d^5 4s^1 instead of 3d^4 4s^2 because it is more stable for the electrons to fill out the 3d series instead of fill out 4s and partially fill out 3d.

Ben Zhang 2H

Why do some things like light travel in a wavelike shape instead of a different shape?

Ben Zhang 2H

I'm pretty sure any equation we need to know will be on the equation sheet Dr. Lavelle provided for us. If it's not there, we probably don't need to know that equation.

Ben Zhang 2H

Electrons with stationary energy can only exist at discrete energy levels. Since electrons can only stay in these level, only certain wavelengths are allowed inside an atom. Do the certain wavelengths that are allowed inside an atom vary between each individual atom? Or are the same certain wavelen...

Ben Zhang 2H

A good way to know what orbital an element is in is to see what block the element is in. Check to see to see if it is in the s, p, d, or f block. Once you know which block, you have to figure out what level that s, p, d, or f is in. To do this, check which row of the periodic table the element is in...

Ben Zhang 2H

Are wavelengths smaller than 10^15 undetectable to us currently with our technology or is this as small as theoretically possible that humans can detect wavelengths?

Ben Zhang 2H

Electrons with stationary energy can only exist at discrete energy levels. Since electrons can only stay in these level, only certain wavelengths are allowed inside an atom.

Ben Zhang 2H

I think it is possible for the waves of larger masses to be detected, maybe not from the technology we currently have, with a smaller velocity. The only problem I could see with this is that once you have a large enough mass, the wavelength it produces is so tiny that I doubt it could ever be detect...

Ben Zhang 2H

All matter has wavelike properties. It's just that these wavelike properties are only noticeable for moving objects with extremely small mass such as an electron. Since the electron is small enough to display wavelike properties, it has diffraction patterns just like waves.

Ben Zhang 2H

Does anyone know how to tell if a molecule is an acid or a base just by looking at its molecular formula?

Ben Zhang 2H

What are some of the ways/reasons the actual yield might end up being smaller than the theoretical yield? The main ways why actual yield might end up being smaller is that there are side reactions that happen along with the main reaction because it is nearly impossible to create a perfect space in ...

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