CHEMISTRY COMMUNITY

Radha Patel 4I

You can use platinum or graphite. Most people will probably use platinum if nothing else is stated in the question.

Radha Patel 4I

The question asks to explore the rocket fuel by calculating its enthalpy density. How do you know 1/4th or 3292 kj/mol of energy will be released per mole of TNT consumed? Where did they get 3292 kj / mol in the solutions manual ?

Radha Patel 4I

What are the differences between rate constant and equilibrium constant when temperature is increased or decreased? How do either of these functions affect activation energy?

Radha Patel 4I

Yes, you would use that equation by plugging in all the givens provided and find out that 10% of the initial concentration is in the body. Then you would multiply the mass times 0.10 to get the total mass of drugs remaining in the body.

Radha Patel 4I

The question says Substance A decomposes in a first order reaction and its half life is 355s. How much time must be elapsed for the concentration of A to decrease to a) one-eight of its initial concentration; b) one fourth of its initial concentration; c) 15% of its initial concentration ; d) one-ni...

Radha Patel 4I

In section 7B, why are the rate constants for first order reactions positive ? If the plot of the first order reaction has a negative slope then shouldn't k be negative in the solutions?

Radha Patel 4I

When K>>>>1 then the products are favored and K in the forward direction is larger than K' in the reverse direction. This occurs in an energy profile with an exothermic reaction. Vice Versa, when K<<<1 then it is in an energy profile that is endothermic.

Radha Patel 4I

When the reactants activation energy is higher than the products, then it is exothermic. In this case, potential energy is higher for reactants than products. When the products activation energy is higher than the reactants, then it is endothermic. In this case, the potential energy of the reactants...

Radha Patel 4I

If the standard cell potential is given then you will know the half reaction is an anode if it is more negative than the half reaction of the cathode. In other words, the more positive Ecell is the cathode and the more negative Ecell is the anode.

Radha Patel 4I

What is the difference between positional disorder and thermal disorder when there is a change in entropy to a system ?

Radha Patel 4I

Are there any other ways of saying "reaction rate constant" or will every problem just say "reaction rate constant"? And what is the difference between the rate constant and the reaction rate constant?

Radha Patel 4I

I would simplify after you add both reactions together, so you won't make any mistakes and can double check that all of the right coefficients and molecules are in the balanced equation.

Radha Patel 4I

You can identify an anode or cathode based on the values of the standard cell potential. If it is more positive then it is a cathode, if it is more negative than the cathode then it is an anode.

Radha Patel 4I

How would we be able to recognize that oxygen is the oxidizing agent and that the Fe is the reducing agent? How would the redox reaction look ?

Radha Patel 4I

In Table 6M.1 the reaction is written as the reduction reaction O2 +4H+ +4e- --> 2H2O with E ^o= +1.23V. In the answers they wrote it as the oxidation reaction by flipping the reaction to 2H2O->O2 +4H+ +4e- (E=+1.23). When we flip the reaction, the value of E^o becomes negative. When we pick an anod...

Radha Patel 4I

For problem 6N.5 a you are given a cell diagram : Pt(s)|H2(g,1.0 bar)|H+(pH=?)||Cl- (aq,1.0 mol*L^-1)|Hg2Cl2(s)|Hg(l), Ecell= +0.33V and they want you to find the pH of H+. My confusion in this problem is how to solve the algebraic part. I was able to reach 0.33V=0.27V - (0.0129 V)*ln[H+] ^2, but I ...

Radha Patel 4I

Zeroth Order plot is negative (-k). First order plot is negative (-k). Second order plot is positive (+k). Also Lavelle hasn't discussed it yet I believe, but the units of the rate constant k in Zeroth Order is M/s, in First Order is 1/s, and Second Order is M^-1* s^-1

Radha Patel 4I

If you were given an image then I heard that typically the left side is the anode (oxidation) and the right side is cathode (reduction). In a cell diagram , the oxidation is always written on the left side and the reduction is always on the right. You can also look at the half reactions to determine...

Radha Patel 4I

When you have a +E naught , it means that you will get a -deltaG , which means that k>1. A -deltaG is spontaneous.
When you have a -E naught, it means that you will get a +deltaG , which means that k<1. A +deltaG is non spontaneous.

Radha Patel 4I

I think it is best to look at the oxidation numbers of the atoms that are being reduced or oxidized so you can see what is happening to the reaction. In this case the Mn in MnO4^- is +7 because the x+4(-2)=-1 where -1 is the overall charge of the molecule and 4 times -2 is the oxidation number of ox...

Radha Patel 4I

Oxidizing agents remove electrons from a substance in a redox reaction. Reducing agents donates electrons in a redox reaction. In a reaction, the oxidizing agent goes through reduction while the reducing agent goes through oxidation. Reducing agents also have a lower electronegativity than oxidizing...

Radha Patel 4I

A salt bridge has an electrolyte between the anode solution and cathode solution in a galvanic cell. Without the salt bridge, the solutions would increase in positive charges in one cell and increase negative charges in the other. the salt bridge can reduce this from occurring and prevent the electr...

Radha Patel 4I

What steps do we need to know in order to balance a basic solution with its half reactions. How does it differ from balancing an acidic solution ?

Radha Patel 4I

I like to set it up as if it were an algebraic expression. For example, if we want to find the oxidation number of S in SO4^2-we can set it up algebraically. We know that the overall molecule has to equal -2 and that oxygen has an oxidation number of -2. There are 4 oxygens so we multiply 4 by -2 to...

Radha Patel 4I

When we know that the left side of || is oxidation and the right of || is reduction, we can then determine how to design the half reaction. For example we see that in order for H to be oxidized it needs to lose electrons, so it would go from
H2-->H+ with a balanced reaction of H2-->2H+ +2e-

Radha Patel 4I

I think it is sufficient enough to mention how it is being reduced, so in this case it is reduced from 6+ to 4+ electrons

Radha Patel 4I

The difference in deltaH naught of reactants and products are not temperature dependent, but because Gibbs Free Energy is temperature dependent since at equilibrium K is constant and K is affected by temperature change, so deltaG is not a constant due to temperature change.

Radha Patel 4I

There are multiple steps because there are different phases occurring. For example when ice goes from solid to liquid, the bonds are breaking as heat is rising. And then at deltaH fusion the temperature is at 0 because heat is being added to the system.

Radha Patel 4I

a) I2 has a lower mass so I2 has a higher molar entropy b) the gases of both structures are not going to change, but pentane has more entropy because it is flexible and rotational versus cyclopentane which has less mobility since the bonds are stuck together c) ethylene has higher molar entropy beca...

Radha Patel 4I

Lavelle mentioned on Friday that Gibbs Free Energy is related to spontaneity and nonspontaneity. In lecture he showed a graph that shows the decrease in Gibbs free energy to increasing Gibbs free energy. When deltaG decreases, it is called a spontaneous reaction. One way to represent this reaction i...

Radha Patel 4I

They both represent change in internal energy. I think deltaU is used a lot in lecture and in the textbook, but deltaE is on the constants sheet

Radha Patel 4I

What is the difference between an intensive and extensive property? Why is entropy an extensive property ?

Radha Patel 4I

If we look back at equilibrium reactions, we could predict which way a reaction must go in perspective of negative heat or positive heat energy. Exothermic processes involve the exertion of heat energy which makes the q a -q the same way -deltaH indicates an exothermic process. The same goes for end...

Radha Patel 4I

The heat of the bonds to break the substance are being supplied while the temperature does not change to allow the phase change to occur

Radha Patel 4I

If the system is thermally insulated then the temperature is equal to 0,making deltaS=0 If the thermally insulated system is at equilibrium then the state variable entropy is stationary so deltaS=0

Radha Patel 4I

The reaction is mixing with the products so heat will transfer to the insulated chamber of the calorimeter, causing the internal energy to decrease.

Radha Patel 4I

It would be irreversible and it would be referring to external pressure so w=0

Radha Patel 4I

DeltaU is change in internal energy
DeltaH is change in enthalpy
The basic formulas that they derive from :
DeltaU= q + w
DeltaH=DeltaU + P*DeltaV

Radha Patel 4I

I don't really know why they are those particular numbers but I know that Cv = 3/2 R and Cp = 5/2R for Monoatomic molecules while Cv=5/2 and Cp=7/2 for diatomic molecules

Radha Patel 4I

This is what I found on the web. http://chemed.chem.purdue.edu/genchem/topicreview/bp/ch21/chemical.php "The change in the enthalpy of the system in a reaction is equal to the change in internal energy plus the change in the product of the pressure times the volume of the system. DeltaH= DeltaE...

Radha Patel 4I

Closed systems are not complete sealed away from its surroundings. There is still heat that can be transferred. The way I think of isolated systems, is that there is no heat transfer and energy can not be exchanged with the surroundings.

Radha Patel 4I

Depending on the problem, you gotta think about what they are describing so you know what equation to derive off of it. Sometimes you will need more than one equation to get through a question. But it is best to think about the process and then look back at the thermodynamic equations to see which o...

Radha Patel 4I

There is a lot, but some formulas are used interchangably depending on the question being asked. To calculate internal energy : DeltaU= q + w sometimes you will need to make q or w negative depending on what the question is saying : when q (heat) is negative , the system is loses heat when q is posi...

Radha Patel 4I

open system - can exchange energy and matter with its surroundings. Ex. Coffee in a cup without a lid closed system - can exchange energy but not matter with its surroundings Ex. Coffee in a cup with a lid on it Isolated- cannot exchange energy and matter with its surroundings Ex. Hydroflask or seal...

Radha Patel 4I

Could anybody kindly send me the lecture notes from last Friday 1/17/20? My email is radhapatel777@me.com. Or could anyone explain the main components from that lecture?

Radha Patel 4I

A reversible process is a process that can be being reversed by an infinitesimal change in a parameter of the system. The process does not increase entropy.

Radha Patel 4I

Hess's Law states that the total change in enthalpy in a reaction is the sum of all energy changes in the reaction. It does not depend on the pathway needed to reach the end point of the reaction, as Professor Lavelle had explained with the mountain example, the enthalpy change does not depend on th...

Radha Patel 4I

Yes, it is an exothermic process because as a liquid converts to a solid, pressure and heat are being released. Heat has to be removed from the liquid in order for it to become solid.

Radha Patel 4I

Celsius and Kelvin are not the same, to keep your answer accurate, it is best to use Kelvin when you are given Celsius.

Radha Patel 4I

Exothermic reactions release heat when temperature increases, that heat is then favored towards the reactants where the heat is being absorbed. It also increases the product, so the reactants must increase to compensate for the rise in products.

Radha Patel 4I

pka = -log(ka)
pkb=-log(kb)
pka+pkb=pkw
pkw = 14.00 at 25 degrees celsius
ka= 10^-pka
kb=10^-pkb
ka x kb = kw

Radha Patel 4I

In addition to what the previous person had said, adding gases in a solution can change K when the temperature changes

Radha Patel 4I

yes, solids and liquids are excluded from ice tables as they add no significance to the solutions equilibrium

Radha Patel 4I

(changed concentration/ initial concentration ) (100%)

Radha Patel 4I

25 degrees celsius

Radha Patel 4I

Kc is the equilibrium constant for aqueous solutions. kc=[P]/[R]. Kp is the equilibrium constant for gas phases. kp= (P)/(R)

Radha Patel 4I

Both are applicable because they are units of pressure. On google it says that bars is smaller than atmospheric pressure, so keep your units consistent (: .

Radha Patel 4I

I think Lavelle suggested ICE tables as a way for you to keep your work organized, but i don't think it matters as long as you show your work.

Radha Patel 4I

I think the question will provide a value for K then you would have to find the value of Q or it will provide Q and you would have to find K. And then you would use the values of K and Q to determine if they are at equilibrium if both K and Q are the same.

Radha Patel 4I

When Q < K at the same time during the reaction then R > P and the forward reaction is favored
When Q > K at the the same time during the reaction , then P > R and reverse reaction is favored.
When Q = K at the same time during the reaction then it is at equilibrium.

Radha Patel 4I

kc refers to aqueous solutions and kp refers to the gas phase. One thing to highlight is that when you use kc, the general way to indicate that it is an aqueous solution is with brackets ( kc= [P]/[R] ) and with kp you indicate it with parentheses ( kp=(P)/(R) )

Radha Patel 4I

All anionic complexes have the transition metal ending in "ate" The complex [Fe(CN)6] 4- has an anionic charge of 4- making the Fe--- Ferrate. Im not absolutely sure about cyano, but I think it is because it is a charge of -1, making it also an anion. And for neutral atoms it would be cyan...

Radha Patel 4I

Tip : do not consider prefixes when naming the coordination compound alphabetically, but still include the prefixes in the name.

Radha Patel 4I

Oxygen is more electronegative than Cl because electronegativity decreases down the columns and increases across. Thus, O is more electronegative than P

Radha Patel 4I

Lewis Acid : electron pair acceptor
Lewis : electron pair donor

Say if you draw the lewis structure NH3 + BF3 , you will notice that the lone pair on N from NH3 will be accepted by BF3, making NH3 the base and BF3 the acid

Radha Patel 4I

Can someone explain how you can tell if a ligand is a monodentate , bidentate, triedentate ligand etc... ?

Radha Patel 4I

Molecular Geometry : bonds

Electronic Geometry/ arrangement : Bonds and lone pairs

Radha Patel 4I

Typically acids have a hydrogen atom. For instance HCl and HPO+
Also acids can typically gain a hydrogen atom for solutions involving water for instance NH3 + H2O (double arrows in both directions) NH4^+ OH^-
H2O is the acid and NH4^+ is the conjugate acid

Radha Patel 4I

F-Cl would be more covalent because they share an equal amount of valence electrons thus having it be nonpolar while P-O would be less strong as a covalent bond because they share a different amount of valence electrons. Some things to keep in mind is that ionic bonds are atoms are metal + nonmetal ...

Radha Patel 4I

They help give us the shape of the molecule by giving a 3D interpretation.
Pi bonds are perpendicular to the plane of hybrid orbitals which are sigma bonds.

Radha Patel 4I

Bronsted Acids - Proton donor
Bronsted Bases - proton acceptor
Lewis Acids- electron pair acceptor
Lewis Bases - electron pair donor
Arrhenius Acids - forms H+ / H3O+ ions in (aq) solution
Arrhenius Bases - forms OH- ions in (aq) solution

Radha Patel 4I

The central atom is restricted to the element that has the lowest ionization energy. Fluorine (as far as I know) has the highest ionization energy, so whatever element that has a higher ionization energy than Fluorine would allow Fluorine to be the central atom.

Radha Patel 4I

I might not be able to answer this question correctly, but I think because pi bonds do not allow bound atoms to rotate, so I think the electron densities would be pointed in one direction instead of both in and out.

Radha Patel 4I

Intra means within, this is one dipole
Intermolecular is between two dipoles that make a bond and can be easily broken.

ClH----ClH

ClH is the intramolecular force

The dashed lines are the intermolecular force

Another example is

H2O-----H2O

Radha Patel 4I

High Polarizing Power: Smaller cations that have higher positive charges, cations with the same radius, the higher the charge is
Li+ is the highest of polarizing power among alkali metal ions

Radha Patel 4I

Valence electrons because you need to know the number of valence electrons for a certain structure in order to make bonds and lone pairs before you start adding formal charges.

Radha Patel 4I

Radicals are unequal pairs of electrons that can be found when you are given a compound. For instance, the compound OF has 13 valence electrons. This is an unequal pair of electrons because 13 does not make an equal pair of electrons since it is an odd number, one electron will be left by itself.

Radha Patel 4I

Polarizability -
- Generally for anions, are electrons that are further away from the nucleus
- more energy shells = more polarizability
Polarizing power- Generally for cations, are less electrons closer to the nucleus
- less electron shells = more polarizing power

Radha Patel 4I

Intermolecular forces : Forces that hold molecules in a substance

Intramolecular forces: Forces that hold atoms in a molecule

Intramolecular forces are stronger because they contain covalent, ionic, and metal bonds.

Radha Patel 4I

I think you are absolutely true because electrons can jump to higher energy levels when excited which means they can also jump to higher energy orbitals. On the contrary, if you want an electron to remain in the g orbital or beyond, you probably need a significant amount of energy and the ability to...

Radha Patel 4I

Elements in the d block are transition metals, so they normally express valence electron from the s orbital. For example, Fe has 2 valence electrons because the electron configuration is 1s^2 2s^2 2p6 3s2 3p^6 4s^2 3d^5. Notice that both ns^2 have 2 electrons so we have 2 valence electrons. Another ...

Radha Patel 4I

According to what I found from google, depending on what Al reacts with, makes the reaction as a base or acid. For instance when Al(OH)3 s + 3HCl aq ==> AlCl3 aq + 3H2O reacts as a base in acidic conditions. This is possible as we know that anything with -OH is a base. However, I think it may be bec...

Radha Patel 4I

I think the reason for this is because there are more elements beyond what the periodic table provides, but those elements remain unknown. I read somewhere that there are elements beyond 121 that make up the g orbital. However, maybe it is possible to compute them based on the patterns given from th...

Radha Patel 4I

So Copper can't have a d-orbital 3d^9 because any atom written as 3d^9 or 3d^4 has to have its electrons evened out in the d orbital subshell, so it becomes [Ar] 3d^10. If you set up a d orbital sub shell for 3d^10 , you will be able to fill 2 electrons for each of the 5 orbitals to make 10 electron...

Radha Patel 4I

De Broglie's equation proves that all matter has wavelike properties. Thus, it can be used to to find the wavelength of a proton or an electron by simply using the mass of a proton or electron and velocity.

Radha Patel 4I

Aside from the speed of light, if you were given the variables from the de Broglie's equation, you can solve for the wavelength and therefore use this wavelength in the equation c = wavelength x frequency.

Radha Patel 4I

The speed of light is constant, it helps maintain the equation c= wavelength x frequency by allowing wavelength and frequency to be inversely related.

Radha Patel 4I

The vacuum prevents air molecules from electrons emitted from being mixed.

Radha Patel 4I

Why do energy levels have to be integers without decimals. For instance, the principle quantum number of an electron moves from energy level n=1 to n=2 when it absorbs light. Why couldn't this electron have moved to n=1.5? How do we know energy levels exist?

Radha Patel 4I

Question M9 on the section for Limiting Reactants asks to write the net ionic equation for the reaction?
How do we determine what is "net"? Will be asked on Test 1 to set up a net ionic equation?

Radha Patel 4I

So do we still include NaOH in this equation, what do you mean by net molecule?

Also, how exactly do we approach this problem to set up a balanced equation?

Radha Patel 4I

I normally do these: review homework problems, ask questions about things I don't understand, and try my best to comprehensively understand the word problems we are given.

Radha Patel 4I

The limiting reactant is only when there is little of a certain molecule in the reactant that limits how much there should be in the end product. In this case both sides of the equation are equivalent.

Radha Patel 4I

There will be chemical formulas and equations given on the exam, including a periodic table.

Radha Patel 4I

Does dilution mean you are adding or subtracting the amount of liters in a solution ?

Radha Patel 4I

Could someone explain how you are supposed to understand stoichiometric reactions. For instance, in the chemical equation N2(g) +3H2(g) -> 2NH3 (g), how and why is 1 mol N2 chemically equivalent to 3 mol H2 and 2 mol NH3?

Radha Patel 4I

The homework question for E29 b says "How many moles of Cl- ions are present in the sample?" The sample is 8.61g of CuCl2 x 4H20 , the moles of this sample is 0.0417. The answer to this problem is .0834 mol Cl- Why do we have to multiply 0.0417 mols twice? Doesn't 0.0417 represent the enti...

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