CHEMISTRY COMMUNITY

Thomas Gimeno

if you want to test something like dropping 10% you can just use a hypothetical like plugging in your initial concentration as 1M and your final concentration as .9M. I'm not 100% sure cause I know the rate of change can be dependent on the morality for first order reactions so you mihgt have to kno...

Thomas Gimeno

because Cl2 is just an element, its gibbs free energy is 0. This means that while you can include it, it doesn't impact the calculations.

Thomas Gimeno

Oxidation number represents how electrons move. So for example, oxygen usually has and oxidation number of -2 which means its pulling two extra electrons and sorta holding onto them. This can be scene in water where the oxygen side of the compound becomes negatively charged and the hydrogen side of ...

Thomas Gimeno

a metal will dissolve in solution if it is loosing electrons and becoming an ion. This is oxidation and occurs at the anode. I think this means if a metal has a really low reduction potential (and in turn a really high oxidation potential), it's likely to dissolve into solution.

Thomas Gimeno

a single line means the two things are in contact at different phases (like solid and aqueous). A double line means the two things are not touching each other/are in different cells. A comma between two hings means they are in contact with each other and at the same phase. These rules can be apllied...

Thomas Gimeno

The activation energy of the reverse reaction is equal to the activation of the forward reaction minus the enthalpy.

Thomas Gimeno

Q is a representation of the ratio of products over reactants when not at equilibrium, K is a representation of the ratio of products over reactants when at equilibrium. If Q is bigger, that means the there are currently more products then there would be at equilibrium meaning the reactants are favo...

Thomas Gimeno

He talks about it in the lecture from Wednesday of week 4.

Thomas Gimeno

According to the second law of thermodynamics, the entropy naturally increases. So if you have a negative change in entropy, you must have done some type of work to get there meaning the reaction is not spontaneous. I don't think that all reactions with a positive delta s are spontaniouse but I thin...

Thomas Gimeno

Hemoglobin is important for gas transfer as it helps to move waste like CO2 out of the cell and helps to move necessary O2 into the cell. This allows for homeostasis of necessary metabolic compounds.

Thomas Gimeno

The second law essentially says that the total entropy is always increasing, in the case of freezing water, the water itself is becoming more ordered and therefore loosing entropy. However, freezing is an exothermic process meaning that heat from the water has entered the surroundings and therefor i...

Thomas Gimeno

If it is not specified in the question, I think you can look at things like if OH- or H+ was produced. However, I think there is also some common snse involved like if your doing a reaction with HCL its probably acidic.

Thomas Gimeno

I know it takes up so much paper but I write down every single step so there is no way to forget/miss something. Also it makes it really easy to check your work or find a mistake when you get a question wrong. Other than that, ALWAYS look at if something is in basic or acidic solution because I some...

Thomas Gimeno

A metal will dissolve into solution if it becomes an ion: EX: Zn(s)-->Zn2+(aq) + 2e- This ionization usually occurs during oxidation at the anode. You can figure out which metal will be oxidized by looking at the cell potentials for the two half cell reactions. Whichever one has a more favorable vol...

Thomas Gimeno

A salt bridge allows for the two parts of the cell to stay neutrally charged. If one were to become more negative or positive, it could hinder the flow of electrons. The way this is prevented is that if one part of the cell gets too positive or negative, ions will flow through the salt bridge to neu...

Thomas Gimeno

As electrons move from one part of the cell to the other, that builds a negative charge on one side. This charge can reduce the moment of electrons so the way this is mitigated is with the salt bridge. A salt bridge allows for charged ions to moved between the two sections of the cell so if for exam...

Thomas Gimeno

In accidic solutions you can balance your Oxegen with H2O and your hydrogen with H+ because there are excess H+ ions in acidic solution. In basic solution, you can do the same thing but at the end, you must neutralize the H+ with OH- because there are excess OH- ions in basic solution.

Thomas Gimeno

As electrons flow from one side of the cell to the other, they must come from somewhere and go to somewhere. The electrons are removed from the anode where the metal forms compounds with the salt in order to release electrons. The salt bridge helps to replenish the ions of the salt so the reaction c...

Thomas Gimeno

I think they'll always tell us. Or, there will be some information in the problem that will make it clear, like if the reaction is occurring in a solution of hydrochloric acid for example.

Thomas Gimeno

The oxidizing agent is the thing being reduced and the more easily it can be reduced, the better it oxidizes. Therefor you can look at the standard energy of reduction to determine it. The more negative that energy, the more easily something can be reduced and better it oxidizes.

Thomas Gimeno

The delta S does not represent the current entropy, but rather the entropy of changing from liquid to gas. If you have a high delta S, that means when you the substances changed it became a lot more disordered. Also, gasses can only get so disordered so if there is a really high delta S, it is proba...

Thomas Gimeno

One way to look at entropy is a measure of disorder, so the more disorder the more entropy. Liquids are not super orderly as they can slosh around and move, but the usually have a defined volume and won't for example expand to the size of their container. Gasses on the other hand are VERY disorderly...

Thomas Gimeno

When water freezes it goes from a not very orderly liquid to a relatively orderly solid, this means entropy has decreased. However, when water freezes it also looses heat energy which enters the surroundings. This heat released into the surrounding increases the entropy of the surroundings. This inc...

Thomas Gimeno

I think it may be specific to the problem. Cv is used when the volume is constant and the pressure is changing and Cp is used when the pressure is constant and the volume is changing. I think that means that you can use either one depending on the specifics of the problem. I'm not 100% sure though, ...

Thomas Gimeno

I think it is because Br is a larger atom than F meaning Br has more electrons that could have more possible states. For NH3 verses Ne, NH3 is a somewhat complex molecule and Ne is just a single atom, I think this means that Ne has less possible variation than NH3.

Thomas Gimeno

I have two strategies. The first is to write out all the variables given and what variable you're trying to find. With that information you can look on your equation sheet to help identify which equations will be useful. The second is unfortunately just to do a heck ton of practice problems. There a...

Thomas Gimeno

The Br- ion in water would form HBr however, HBr is a strong acid which fully dissociates in water. This means the Br- does not interact with the water which also means that it cannot affect pH because it does not change the concentrations of H+ or H3O+ ions.

Thomas Gimeno

I kind of think of q in a similar way as delta H. If delta H is negative for an equation it means heat is being released and if q is negative for a system, it also means heat is being released. The same goes for when the values are positive, it means heat is entering either the equation or the system.

Thomas Gimeno

I think its mostly about what variables that are given in the problem. For example if you don't have the pressure than you cant use w=-PdeltaV. Same with if you don't have the number of moles for the other equation.

Thomas Gimeno

Solids can't do work on their surroundings because they do not fill the space or create pressure. Therefore going from two mols of solids to one mol of gasses would do work because the gas now can create pressure and therefore do work.

Thomas Gimeno

It helps to think about it as a change in enthalpy. Enthalpy is just heat so steam has a high enthalpy and water has a low enthalpy (cause steam has more heat and energy than water). If something is moving from high enthalpy to low enthalpy, it has a negative change in enthalpy or a negative delta H...

Thomas Gimeno

liquid water is held together by hydrogen bonds and they are the reason water can stay liquid at relatively high temperatures. Similar molecules that cannot form hydrogen bonds tend to have boiling points much lower than that of water. Overall, when vaporizing water, you have to break those hydrogen...

Thomas Gimeno

I think when something goes from solid to liquid the change in volume is relatively small (especially for water where Ice actually takes up more space than liquid water) so fewer hydrogen bonds must be broken. Liquid water still has a very large number of hydrogen bonds as it still has surface tensi...

Thomas Gimeno

A phase change is when something changes from one phase to another. This can be something like melting where something goes from solid to liquid but it could also be something like deposition where a gas changes to a solid.

Thomas Gimeno

If a reaction goes from high to low enthalpy that would mean that is have a negative delta H meaning the reaction produces heat. If you heat a reaction where a product is heat, you will push it towards the reactants so yes.

Thomas Gimeno

This is used all the time because its an effective way of getting unfavorable reactions to occur. You used the energy produced by one reaction to make another reaction go. For example, this is how all of the electron transport chain works. An electron is given to a molecule which is favorable, and t...

Thomas Gimeno

This is when the hydrogen bonds which hold the two strands of DNA together break apart. This is an incredibly important function for life as it allows for DNA replication and RNA transcription. It is also an endergonic reaction which needs energy in order to proceed. The reaction is catalyzed by the...

Thomas Gimeno

The reaction in the fuel cell would have to be spontaneous (aka negative delta G)

Thomas Gimeno

Compounds like ethanol specifically are significantly cleaner than other non-renewables because when combusted they only produce CO2 and water compared to others which produce much more potent green house gasses. Also, the sun and wind are intermittent forms of energy and we do not have the energy s...

Thomas Gimeno

You can use almost any equation with an open system you just have to be cognoscente of how the open system affects your variables.

Thomas Gimeno

When looking at pressure, you only take into account gasses. Because of the left there is one mol of gas and on the right there are two mols of gas, increasing pressure would favor the right side.

Thomas Gimeno

Think of heat as just another product or reactant. If the reaction is endothermic (delta H is positive) then heat would be a reactant: heat + ab --> a + b If the reaction is exothermic (delta H is negative) then heat would be a product: ab--> a + b+ heat Then if you think about adding more heat or t...

Thomas Gimeno

Well if there was a reaction that was part way to equilibrium at 25 degrees and you can calculate a Q value. If at that moment the temperature jumped to 45 degrees, the Q value you then calculate would be the same as before because in that moment, the concentrations of reactants and products do not ...

Thomas Gimeno

This question is essentially asking what part of the reaction is favorable at this pH, products or reactants. This is because the reactants represent the nurtal atom: HA, and the products represent the charged atoms: A- and H3O+. To determine which side of the reaction is more favored you can compar...

Thomas Gimeno

Ice tables can be applied to any equilibrium problem and you should use the unites given in the problem. I think the only possible units are mols/L when looking at concentration and then various pressure units. For example, I believe there was a question on the sapling that used an ICE table with th...

Thomas Gimeno

I find ICE tables most helpful when the question gives the current concentration of the products and reactants as well as the K value. You can then use the ICE table to find the equilibrium concentrations.

Thomas Gimeno

Concentration is the ratio of solute to solvent meaning the amount of something in solution compared to the amount of the solution itself. This doesn't really make sense for a solid because if I just hold some salt for example, there is no solute or solvent. However, Density is a measurement similar...

Thomas Gimeno

A catalyst just facilitates a reaction and therefore causes it to reach equilibrium more quickly. This means that the k value is not changed but the time it takes to go from Q to K is reduced.

Thomas Gimeno

Temperature can be important if you have to convert anything between concentration and pressure because it is part of PV=nRT. Also, the K value of a reaction is different at different temperatures so a change in temperature could change that value.

Thomas Gimeno

I think it's because 1. the inert gas is not participating in the reaction and therefore does not effect the K value itself and 2. When you add the gas it will effect the partial pressures of both the products and reactants meaning while each individual value changes, they remain proportional which ...

Thomas Gimeno

You essentially count the number of ligands. Their is one SO4 and 5 NH3s. Add this together and you get six. The coordinate number is just a representation of how many bonds a central atom has.

Thomas Gimeno

En is a ring and contributes 2 to the coordinate number. The cl2 contributes another two to the coordinate number so the total number is 4. This is because the coordinate number is just the number of atoms/molecules the central metal is bound to.

Thomas Gimeno

It is true that within the brackets ligands are molecules or atoms that donate electrons to the central transition metal. This can get confusing however because outside the brackets this is not neccesarily true and therefore moliculs/atoms outside the brackets are not considered ligands.

Thomas Gimeno

The number in parenthesis is just the oxidation state of the central metal. This can be determined by adding up the oxidation number of all the individual components of the molecule and then subtracting that from the total charge of the molecule.

Thomas Gimeno

Everything is within the brackets so all compounds are ligands except the central cobalt. Because of this you have to list the chlorine before the cobalt as trichloro.

Thomas Gimeno

Localized electrons are what is seen in resonance structures. It is when, for example, there is technically two single bonds and one double but they all exist in a state similar to a 1 and 1/3 bond. This is because some of the electrons are delocalized and moving around among all the bonds not just ...

Thomas Gimeno

Yes and no. A double/triple bond will create the same angles as a single bond however replacement of two single bonds with a double bond will drastically change the shape. For example a carbon with four single bonds is tetrahedral while a carbon with two single bonds and one double bond would be tri...

Thomas Gimeno

The shape would be bent. Shape only looks at the position of bonds and not the position of lone pairs. Even though H2O only has two bonds, it is still sp3 because it has two bonds and two lone pairs, I think this may be why you thought it was tetrahedral.

Thomas Gimeno

Every bond has a sigma bond, double bonds add a pi and tripple bonds add 2 pi bonds. This means singles have a sigma, doubles have a sigma and a pi, and triples have a sigma and two pi.

Thomas Gimeno

What I do is count the number of bonds and lone pairs (double bonds still count as 1) then use that number to determine the hybridization. If you think about it as each letter in the hybridization having an invisible one in the superscript, then you can add the numbers in the superscript together an...

Thomas Gimeno

If its rod shaped then either end of the rod is likely partially charged and another charged rod can line up antiparallel making the dipole moment at either end of each particle very close to the dipole moments on the other particle. This means that both dipole moments on both molicules are interact...

Thomas Gimeno

Hydrogen bonds would occur because there is a hydrogen bonded to an oxygen. It doesn't matter what other atoms the oxygen would bind to because of how large the electronegativity difference is between hydrogen and oxygen. This means that the hydrogen would be partially positive and the oxygen would ...

Thomas Gimeno

While london dispersion forces always occur in groups of molecules, each individual molecule is not always participating in LDFs. Also LDFs can occur in one part of a molecule and not another part, all that is necessary is a sight where a difference in electron density can create a partial positive ...

Thomas Gimeno

Polarizability is how easily an electron can be pulled away from the cat ion and towards the anion. If the cation has a high polarizability then the molecule likely has high ionic character and low covalent character.

Thomas Gimeno

If it is dipole-dipole then the two molecules are polar and have a dipole at all times. If it is induced dipole that means that the molecule/s is/are non polar and only have a temporary dipole due to the random movement of electrons to one side of the molecule.

Thomas Gimeno

Well so ionic and covalent bonds are the opposite ends of the spectrum of electronegativity difference with ionic having a high difference and covalent having a small difference. A dipole moment occurs when a bond has a significant difference in electronegativity but the difference is not high enoug...

Thomas Gimeno

In class he said that if the difference is greater than 2 it is considered ionic and if the difference is less than 1.5 it is considered covalent.

Thomas Gimeno

Hydrogen usually exists in its H+ state and therefore generally will except electrons.

Thomas Gimeno

I think about it like this, I draw each atom and the number of valance electrons it "should" have (so for nitrogen there would be 5). Then I started pairing up the electrons from different atoms to form bonds. If I find that all the valance electrons have been used up and the only way to f...

Thomas Gimeno

Carbon and hydrogen have very similar electronegativities so when they are bonded together it is non polar. This means that their is no partial charges and it is these partial charges that cause hydrogen bonding to occur.

Thomas Gimeno

Generally we think of ionic bonds being strictly one atom giving an electron to another atom and covalent bonds as two atoms sharing two electrons equally. This is untrue because in reality the vast majority of bonds have electrons shared a little bit. The covalent character is a way of describing h...

Thomas Gimeno

The octet rule is just a representation of the fact that atoms in energy levels 1 and 2 want to fill their outer most s and p orbitals. When you start moving into higher energy states there are more orbitals and this results in the possibility of more than 8 valance electrons.

Thomas Gimeno

To preface, this is just the way I think about it. The nitrogen would normally have 5 valence electrons meaning it can form three bonds and then have a lone pair. In this case though, the central nitrogen is forming a fourth bond meaning that one of the electrons from the lone pair is being used in ...

Thomas Gimeno

I don't think vesper will be on the exam because it was taught after Wednesday. I think vesper is really helpful though especially for determining polarity. For example, it might look that h2o had an equal distribution of electrons but with vesper we know that it actually has a bent structure. This ...

Thomas Gimeno

The way i was taught in high school was that larger ions have more electrons which can contribute to london dispersion forces. The more electrons an atom has, the larger the temporary dipole can be because there will be a greater difference in electrons between the positive and negative end.

Thomas Gimeno

You're missing a possible partial positive charge on the nitrogen atom. This occurs because normally nitrogen only makes three bonds but if it looses one electron (making it +1) it can form a fourth bond.

Thomas Gimeno

London dispersion forces are always present and there would also be a dipole-dipole interaction due to the partial negative charge of the O in the OH group.

Thomas Gimeno

Double bonds have a greater interaction between electrons than single bonds. If you think about it in the electron cloud model, more of the electron clouds would have to overlap in odder to form a double bond when compared to a single bond. This increased overlap can be seen as the nuclei getting cl...

Thomas Gimeno

The formal charge is important because it shows where there are more or less electrons. For example, if an oxygen atom has three lone pairs of electrons and one bond, it would have a negative formal charge. This is because oxygen would normally only have two lone pairs of electrons along with two mo...

Thomas Gimeno

The 1s state is on the first energy level and the 2p state is on the second, if you remember the diagram he showed, the second energy level is father away from the nucleus making the overall radius larger.

Thomas Gimeno

The primary difference is energy of the light produced. Lynman has a large jump from the 2nd or higher to the 1st energy level which means that high energy light is release which will in turn be ultraviolet and invisible to the naked eye. Balmer has a smaller jump from the 3rd or higher to the 2nd e...

Thomas Gimeno

I wouldn't worry too much because usually the answer accounts for a slight bit of variation based on constants but i think if the text book is using 2.998*10^8 then it's probably your best bet.

Thomas Gimeno

Well solving for the energy of a photon is plank's constant times frequency and you can sub in the speed of light over the wavelength for frequancy. The equation you wrote has speed of light over frequency (Or i may have misread it cause you can't use greek symbols). But also, a question could ask a...

Thomas Gimeno

I really like to just go through my notes and collect all the equations we learned. Then I write out an equation sheet where I identify each part of the equation, explain its significance and when it is used, and then try and do one example problem with it. I find it really helpful because it prepar...

Thomas Gimeno

Wave length will usually be given in nm which is m*10^-9 however there was a problem that gave wavelength in um which is only m*10^-6. Frequency is in Hz which is just 1/seconds. You can think of it a per second if that helps. It makes sense because when wave length and frequency are multiplied you ...

Thomas Gimeno

The main purpose of Avogadro's number is to covert between # of particles and mols. The number itself, 6.022x10^23, represents the # of particles in one mole. It super helpful when you either have or need the # of particles but it also comes up in some equations (usually for the purpose of convertin...

Thomas Gimeno

It 100% for simplicity. When you have 45% of something, its a lot easier to just write it as 45g then as an obscure number representing a different total

Thomas Gimeno

The key is the last part of the name: heptahydrate. When hydrate is at the end of the name of a chemical it means water molecules are incorporated into the structure of that chemical. In this case there are seven molecules of water because the prefix hepta means seven. When it comes to writing this,...

Thomas Gimeno

Well the first step is to identify what the sulfide would look like. Because Ca would give up its two valence electrons it has a charge of +2. Sulfur wants to gain two electrons to fill its outer shell which makes it -2. This means the Calcium Sulfide is just CaS. To then find the molar mass you can...

Thomas Gimeno

Because there is one atom of Cu in CuBr2, for every mole of CuBr2 you have one mole of Cu. I think you might be looking at the Br2 and thinkcing that's why you divide by however the fact that there are 2 Br atoms does not change the ratio between Cu and CuBr2.

Thomas Gimeno

I took AP Chem in my junior year and I am a first year now. I'm finding that a good amount of the content is coming back but whenever I'm unsure about a basic, I really like to go n youtube and find someone explaining the topic. A lot of teachers will post lectures and practice problems online which...

Thomas Gimeno

Well logically, if you add the mass of the CaCl2 and the water, you should get the mass of the total solution. And, CaCl2 represents 32.5% then the water must represent 67.5% because water+CaCl2=100%. So if you multiply the total mass by the .325 and .675 to find the masses of the CaCl2 and water re...

Thomas Gimeno

I really like to write my units in my calculations for every problem. This allows me to make sure that all my units cancel and it's a nice little check to make sure I did the problem correctly because your units should match up with what the question is asking for.

Thomas Gimeno

It helps to take practice tests. Either ones you find online or one you make yourself, they give you confidence and help you to know what to expect out of the test. Its a lot less scary to do something for the 5th time than to do it for the first time.

Thomas Gimeno

For anyone who's interested in batteries, this article discusses the new development in charging lengths and long-term power storage. It's in the context of electric cars but the research could have really cool implications for clean energy. https://phys.org/news/2020-10-electrode-material-battery-c...

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