CHEMISTRY COMMUNITY

Ai-Tan La 1K

It takes the ln2 because of how the equation is derived from first order rate equations. A first order reaction has a rate in proportion with its concentration of reactant and the ln is used to relate it to the rate constant k.

Ai-Tan La 1K

so the molarity of the solution that you start with will change by a factor of x. And the products will grow by a factor of x. This would get you the Ka=x^2/(.199--x). Then you set up your quadratic equation of x^2+0.00336x-7.164x10^-4=0. Then you solve for x using the quadratic formula where you wo...

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In the Arrhenius equation what is A in it and how do we get it?

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Including water in the equilibrium constant is not what we do because usually the concentration of water is very large and does not change that much throughout the reaction.

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In first order reactions the rate of the reaction is directly linked to the concentrations of the reactants. So if the concentration is halfved the rate is halved and if its doubled the reaction is doubled.

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The reason the standard cell potential does not change is because the direction that the electrons flow throughout the cell during the reaction because it is a thermodynamic property. Thermodynamic properties depend not on the concentrations of the reactant in the reaction but rather the chemicals t...

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On Achieve week 9 question 4 how do we determine the reaction order given 1/s M/s etc?

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What it means by the first order is for every one of reactant one product is created.

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You need to add the same amount of OH- to both sides. This would balance out the oxygens that you are adding. And since you are adding OH- to balance out H+ ions those would be combined to form neutral H2O.

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You know how to write these diagrams by the solutes that are in the solutions and by knowing which are in the cathodes and anodes. The cathode is usually on the left and the intermediate ions are in the middle. Then the anode element is on the right. Make sure not to include stoichiometric coefficie...

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Reduction potential is the tendency for an object to gain electrons. Voltage is the amount of energy per electrical charge.

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The oxidizing agent in a reaction is the thing that is getting reduced. So once you have determined the oxidation numbers you can look at the change of it and see which ones charge is getting lower. That would be your oxidizing agent.

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I believe that only redox reactions are the only reactions that can power voltaic cells.

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Delta H is greater than Delta U when there is work done by the reaction to the surroundings. This is because delta U is = q + w, and if work is done by the system to the surroundings w is -.

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you can use this formula when the conditions are under constant pressure. Since it has the value of delta H given you do not need other measurements like volume.

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A positive delta s means that the reaction makes the system more chaotic. This would affect the Gibbs Free Energy by having the -TdeltaS portion more negative. And the opposite is true for the negative delta S which would mean the system becomes more ordered by the reaction. This would make the Gibb...

Ai-Tan La 1K

Can someome explain how we can have water vapor at 27 degrees celsius. It doesn't quite make sense since the boiling point of water is at 100 degrees celsius, wouldn't water at 27 C be in the liquid state?

Ai-Tan La 1K

The use of the different formulas to calculate delta G are through the different things you are given in the problem. If you are given partial pressures or concentrations in an equilibrium reaction you would need to use delta G= G0 + RT lnQ. And you would have to be given G0 or delta G. If you are g...

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Ok so for this equation is you need to look up the delta h value of fusion for water which is 6.01 KJ/mol. Then you would multiply by the amount of mols you have in the reaction (80.0/18.02=4.439 mols). This would give you the delta H that is needed to melt the ice which is 26.7KJ. How you need to h...

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On Achieve question 9 it says to calculate delta s surroundings you do -delta H/T. But in the equations sheet it says delta S can be calculated by qrev/T. So how do we know to use this equation verses another equation to calculate the delta s of surroundings.

Ai-Tan La 1K

How come in the solutions it multiplies R by 5/2. I don't really understand how they know to do this and why they do this.

Ai-Tan La 1K

How come for certain equations we have q=mC delta T, q=nC delta T, and q= C delta T.

Ai-Tan La 1K

Can someone explain the difference of the work functions like w=-PdeltaV vs w=-nRTln(V2/V1). Like why do we have two different equations and when would we use either one.

Ai-Tan La 1K

You would need to multiply the 6.01x10^3 j/mol of H2O by the mols of ice to get the amount of energy for the delta H fusion. Then you would add this to the q ice and set them equal to the -q of water. Since heat goes from hot to cold the energy would be leaving the water and going into the ice. And ...

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We know that V2/V1=2 in a given system usually when the problem is asking what would happen when the volume is doubled.

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-w means that the system is releasing work or in other words energy. So in this instance it would be doing work on something else. If w was positive it would be gaining work so it would be having work done on itself.

Ai-Tan La 1K

You would have to convert the amount of grams of the substance into amount of moles of the substance. Then from that mol amount and then you multiply the amount of mols C by delta H/ how many mols of C are in your reaction. So for me it was 358.8kJ/4 molC. This is because the rxn uses 4 mols of C to...

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A closed system is like a plastic water bottle that is shut closed. The water cannot get out but the heat energy from the surroundings can still heat up the water since the plastic doesn't insulate the water. So therefore it is a closed system since matter cannot get in and out but energy can. An is...

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This is because we only measure gasses in pressure typically. We don't measure solids and liquids in pressure we measure them in volume, mass, or molarity.

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when you are amplifying a delta H of a reaction by a certain factor do you raise the delta H to the power of 3 or do you multiply it by three and what is the reasoning?

Ai-Tan La 1K

when you are amplifying a delta H of a reaction by a certain factor do you raise the delta H to the power of 3 or do you multiply it by three and what is the reasoning?

Ai-Tan La 1K

Enthalpy changes relate to other thermodynamic quantities such as entropy and Gibbs free energy since enthalpy is the heat of the system which essentially is the energy within the system. The more enthalpy the more GIbbs free energy since there is more energy available to the system.

Ai-Tan La 1K

We do not consider solids or liquid (H2O) during an equilibrium reaction or ICE table because the change they have on the equilibrium reaction is negligible.

Ai-Tan La 1K

Can someone explain how to determine whether an equilibrium reaction would be charged or neutral based on the Ka and pH or Kb and pOH respectively. I know it has to do with something about which is greater but I am just a little confused.

Ai-Tan La 1K

Can someone explain how to determine whether an equilibrium reaction would be charged or neutral based on the Ka and pH or Kb and pOH respectively. I know it has to do with something about which is greater but I am just a little confused.

Ai-Tan La 1K

Usually when setting up the ICE table for these acid base reactions the products will be increasing by x and the reactants will be decreasing by -x. You would know by looking at the chemical equation of B+ H2O = BH + OH-. The concentration of BH and OH will go up since you start out with 0 concentra...

Ai-Tan La 1K

I believe the reasoning is because since you are increasing the partial pressure of one product which would eventually make more of the reactants. By making more reactants this would cause an increase of products as well in order to achieve equilibrium.

Ai-Tan La 1K

partial pressure is apart of of the total pressure that is associated with the gas that we are observing. Total pressure is the sum of all the partial pressures in the system. Partial pressure affects equilibrium the same way that affecting concentrations of reactants or products does. If you increa...

Ai-Tan La 1K

Kw changes according to the increase or decrease of temperature. So if temperature increases Kw increases and if temperature decreases Kw decreases.

Ai-Tan La 1K

What determines the changes in K is the type of reaction that we have. The K value for one reaction is the only K value that you can have for that reaction since it will eventually come to equilibrium. However temperature does change K which we learned during exo and endothermic reaction.

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By adding more acid or base into the solution the equilibrium of water would be disrupted from its original pOH or pH. By adding a strong acid it would increase the [OH3+] and vice versa with a strong base and [OH-]. This would change the reaction quotient (Q) which would then change which direction...

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There really isnt a difference between the two. When comparing the Q value to the K value when it says the forward reaction is favored it means the the concentration of reactants will go down and the concentration of products will go up and vice versa. When the reaction shifts towards the forward re...

Ai-Tan La 1K

I think where you went wrong is with the NH2 equation. You do need to reverse the reaction like you said but you also need to multiply the reaction by a factor of two since you have two NH2's in your equation.

Ai-Tan La 1K

There are four assumtions for a gas to be "ideal". The first is that the gas has negligible volume. The second is the gas particles have no intermolecular attraction and are equally sized. The third is the gas particles have collisions with no energy loss. And lastly the gas particles move...

Ai-Tan La 1K

I am confused about the question because I feel like I've been doing it correctly but I cannot get the right answer. I used the KC reaction and inversed it so 2NH3 is a reactant and N2 and 3H2 are products. Which gives the new Kc of 27.7. I then used the Kb reaction and multiplied it by three which ...

Ai-Tan La 1K

You should be using minus 2x since the NO would be changing at a rate of -2x.

Ai-Tan La 1K

Does anyone know if we go to discussion for week 1?

Ai-Tan La 1K

This question is tieing back to the relation between pKa and pH. If the pH is lower than the pKa value then the solution is more acidic so the predominant species would be the protonated version of the molecule. If the protonated version of the molecule is neutral then the solution would be neutral,...

Ai-Tan La 1K

Cl2 means that there would be Cl bonded to Cl. So if you have one mol of Cl2 its 6.022x10^23 Cl-Cl molecules. H2 is the same thing. Its H bonded to H. 2H is different. 2H indicates that its two molecules of H but they are not bonded together.

Ai-Tan La 1K

I forgot to add im in discussion 1C

Ai-Tan La 1K

I believe it is better to take 14B then 14BL because you would have the knowledge of B going into BL. It is also good to take both at the same time, but it is warned not to take 14BL by itself and not have taken 14B.

Ai-Tan La 1K

Hi I am looking to swap my Chem 14B because it conflicts with another class I have. Is someone willing to switch?

Ai-Tan La 1K

If the pH value is above the pKa then that means that the solution is not very acidic. Which along with the higher pH would indicate that the solution is more basic.

Ai-Tan La 1K

Does anyone know if Lavelle posts practice finals from previous years?

Ai-Tan La 1K

That did not work sadly. I dont know what else it could be.

Ai-Tan La 1K

I am having trouble naming my chemical compound. The formula is [Co(NH3)5 Cl] Cl2. I named it penta ammine chloro cobalt(III)dichloride but it wrong. I have tried so many other variations and I cannot get it. Can someone help?

Ai-Tan La 1K

There is no complete rule as to how many ligands can bind to the TM central atom. But the TM's oxidation state and overall charge of the molecule does determine how many anions can bind to the TM.

Ai-Tan La 1K

An easy way to determine the oxidation number is to see the overall charge of the molecule and how many anions are bonded to the transition metal. If a compound has 3 Cl bonded to it and it is neutral that would mean that the -1 charge of the Cls would have to cancel out with the charge of the trans...

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Ion-Ion IMFS are due to two opposing charge ions, like Na+ and Cl-. This attraction is due to the drastic difference in charge between the two molecules. Dipole-Dipole IMFS are between molecules that have opposing dipoles (these molecules are polar), like H2O. H2O has a dipole pointing towards oxyge...

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Are we expected to know the Transition metal biological functions for the class? Dr. Lavelle went over it in lecture today but I am just wondering if we are going to be tested on it.

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It helps them to get a lower energy electron arrangement by averaging the orbitals of the atom. So instead of the p orbitals reaching out so far outside of the atom, the electrons are held closer to the atoms nucleus.

Ai-Tan La 1K

I am pretty sure they are the same and are written differently to show the orientation of water. Since it is written OH2 it would show that the oxygen is arranged closer rather than the hydrogens.

Ai-Tan La 1K

Yes a single bond has one sigma, a double bond has one sigma one pi, and a triple bond has one sigma and 2 pi bonds.

Ai-Tan La 1K

For an sp3 molecule it would mean that the atom would have bonding in four different areas. Having a double bond with an atom does not hybridize it in an additional orbital.

Ai-Tan La 1K

I know we have been talking about the molecular shapes in class and how they come about based on the maximum distance between the atoms to minimize repulsion. So how do rings come about? Wouldn't the shape of least repulsion be a line?

Ai-Tan La 1K

I believe in a triple bond the orbitals would overlap just like in the double bond. And since a triple bond could only occur through the outermost electron cloud the bonding would take place in the p orbital, since the s orbital is not large enough and the d orbital is not the valence shell. So a tr...

Ai-Tan La 1K

I think only in certain cases can the type of atom cause a distinct change in the molecules shape. But for the most part I think that the atom type does not change the shape, the electron cloud is what affects the molecule shape.

Ai-Tan La 1K

The strongest bond between two atoms would be an ionic bond. This is because of the large electronegativity difference between the two atoms which would strip one atom of their valence electrons. This would make the atom charged and the opposite charges causes a strong attraction between the two ion...

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The larger the atom or molecule the stronger its LDF will be. This is because with the increase of size of the electron cloud the weaker the nucleus can hold onto the electrons. You determine the LDF by the temporary slight negative or positive charge of the atom based on the position of the electro...

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I believe at that point to find the most favorable lewis structure you would need to be given clues or told characteristics of the molecules structure.

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The reason for this is because covalent bonding between two atoms is a mutual sharing of an electron between the two. This intertwines the two electron orbitals in the molecule. However, hydrogen bonding occurs when a slightly negative N,O,or F atom is in close proximity to a slightly positive H ato...

Ai-Tan La 1K

I was wondering how we know what atoms are able to break the octet rule? I know its atoms in the P block but how far down the p block is required until the element can violate octet?

Ai-Tan La 1K

I believe there is no class friday since it is a holiday.

Ai-Tan La 1K

A resonance structure is a lewis structure that has different ways to write how the atoms bond with one another. So yes, it does mean that the lewis structure is just written in a different way. You know which to change when writing it in a similar way because usually they would be between one atom ...

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The light comes from a light source that the researchers can manipulate the intensity and wavelength of the light. It proves for the wave particle duality that photons have both particle and wave like characteristics. Photons interact to cause this effect by supplying enough energy to the electron t...

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To determine the most ionic to least ionic you would have to use the periodic table. You would see the distance between the two elements and the further apart they are on the periodic table the more ionic the bond would be. For example K-F would be the most ionic because it has the greatest distance...

Ai-Tan La 1K

To determine the wavelegnth range you would find the wavelength from the largest spectral from n=5 to n=1 with the equation v=R[1/n1^2-1/n2^2]. Then you would do the same for the smallest spectral line from n=5 to n=4. Then you would take these two wavelengths and find the difference between them to...

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A lewis acid is an atom that gains an electron, whereas a lewis base is an atom that "donates" an electron.

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The Lewis Dot Structures are decently accurate when looking at the skeletal structure of an atom. However what Lewis Dot Structures lack is the three-dimensional shape of the molecule. It is a simplified structure of a molecule but it still shows which atoms are bonded with others and whether they a...

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The easiest way to understand electron configuration is to memorize where the s, p, and d block are. The s block will be on the left side of the periodic table with the two collums corresponding to s1 and s2. The right side of the periodic table would be the p block with the collums corresponding to...

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If you have 2p4 and 2p5 then the distribution of electrons between the two orbitals would be unequal. However, this is fine. So the distribution of electrons between the orbitals would be 2px2 2py1 2pz1, for 2p4 and 2px2 2py2 2pz1 for 2p5. This just means in one or two of the three orbitals would ha...

Ai-Tan La 1K

I believe you would use the wavelength from part b to answer part c by finding the frequency of the light. Which then you would just multiply the frequency of the photon by Phlanks constant in the equation E= hv to get the energy of the photon.

Ai-Tan La 1K

I believe you are using the wrong equation to find the frequency. You should be using the v=R[1/n2^2-1/n1^2]. Then you will plug in the Rydberg constant and the corresponding n2 and n1 values. v=R(1/4^2)-(1/2^2)] This will give you the frequency of the photon emitted by the hydrogen atom when an ele...

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I always set up equations like fractions (so if it were converting molar mass to kg per mol it would be like g/m times 1kg/1000g). And have the same measurements on opposite sides of the fraction so that the units cancel out. If it were in scientific notation 1000g=1kg, or 1x10^3g=1kg. And the rest ...

Ai-Tan La 1K

I have a question about question 15 from the new hw. It says we need to convert to eV but on the equations sheet there is no conversion from Joules to eV. Are we expected to know the conversion between the two measurements?

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You use de Broglie's equation to find either the wavelength or velocity of things with mass. To find the energy of the electron you would need to use the equation E=hv.

Ai-Tan La 1K

Since c is referring to the speed of light in a vacuum, c should not change and it should always be 2.99x10^8 m/s.

Ai-Tan La 1K

I believe we have to take the absolute value of the equation because there is no such thing as emitting negative energy.

Ai-Tan La 1K

I like to think of it like this. Phi is the path that the wave is actually taking. But when you multiply the path that the wave is taking by the path again it would square the area that the wave can be in. Therefore it would give you the possible area that the electron could be in, thus giving the p...

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In order to count how many hydrogens there are in a compound the simplest way is to count the hydrogens shown in the compound structure. Since C has to have 4 bonds if the carbon is just by itself it would have 4 hydrogens. But if it is bonded to more things like another carbon for example, it would...

Ai-Tan La 1K

I agree with you that the wording to the question is confusing and I believe you are correct with the fact that you would need to know the frequency for this new burt of electrons. But how I solved this question is by dividing the new total energy by the work function to find the number of electrons.

Ai-Tan La 1K

I would assume the change in work function would affect the amount of energy needed to eject the electron from the metal since the work function determines the amount of energy needed to eject an electron.

Ai-Tan La 1K

To convert wavelegnth to frequency you would use the C=LamdaV equation. Where you would divide the speed of light by v to get the wavelegnth.

Ai-Tan La 1K

For this question you would need to take the enthalpy or amount of energy it takes to melt one gram of ice. Multiply that amount by the total mass of ice you have in this question (407g). That would be the total amount of energy you would need to melt all of the ice. Then by utilizing the equations ...

Ai-Tan La 1K

To my knowledge the correct way to determine the limiting reactant is by finding the amount of moles of both regants. Then by utilizing the balanced equation multiply the amount of moles by the molar ratio between the two reactants. So yes you did do it correctly!

Ai-Tan La 1K

The enthalpy of ice can be used to determine the number of jouled required to melt a certain amount of grams of ice by multiplying the J needed to melt one gram of ice by the mass of the ice we want to melt. That is the total amount of Joules needed to melt the total ice we have. We take that amount...

Ai-Tan La 1K

From the description of how you solved the problem you are actually supposed to solve it by dividing 10.95 J by what you got (1.857x10^-21). That would give you the number of photons required.

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In order to write the balanced equation for the reaction you need to know what makes Boron Oxide. I do not know how to determine the chemical formula but after searching it up it is B2O3. With that information you can figure out the rest of the balanced equation by writing B2O3 + 3Mg -> 2B + 3MgO by...

Ai-Tan La 1K

I believe with this type of question you would go with the given amount of significant figures of the original amount of HF. Since they state 25.92mg of HF you would round to 4 sig figs. Since all the other numbers are constants from the periodic table their amount of sig figs would not affect the a...

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I believe it is 2 answers every week should grant you the points that you need for that week.

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