CHEMISTRY COMMUNITY

Farah Abumeri 3F

Hi, in today's last lecture/review session :( , Dr. Lavelle was going over an incorrect cell diagram that was missing a conducting electrode. I'm curious about AgBr(s). He said that it was insoluble, therefore it wouldn't dissociate, right? But I thought the oxidation half cell reaction would only i...

Farah Abumeri 3F

Galvanic cells are batteries and they conduct electricity, so for that reason, the cell potential is positive. Galvanic cells generate electricity through spontaneous chemical reactions (hence the positive cell potential so that delta G will be negative) and consist of electrodes separated by aqueou...

Farah Abumeri 3F

Does anyone know if we will be tested on the difference in STP and SATP for the final?

Farah Abumeri 3F

The anode half-cell reaction, Au3+ + 3e- →Au(s), was flipped in order to cancel the electrons from the cathode half-cell reaction, resulting in Au3+ on the opposite side of Au(s).
I hope that answered your question!

Farah Abumeri 3F

4C.3 Calculate the final temperature and the change in enthalpy when 765 J of energy is transferred as heat to 0.820 mol Kr(g)at 298 K and 1.00 atm (a) at constant pressure; (b) at constant volume. Treat the gas as ideal. I'm confused on how to find delta H for part b when the reaction is at constan...

Farah Abumeri 3F

In the example that you chose, there are two electrodes: Cu(s) and Pt(s). Pt(s) is used when the half-cell reaction itself doesn't have a conducting solid. For the oxidation reaction with Cu(s) and Cu2+ (aq), there is already a conducting solid, Cu(s), and therefore no need for the Pt(s). But for th...

Farah Abumeri 3F

Can someone explain the relationship or, better put, why there isn't a relationship between the activation energy of a reaction and the enthalpy of a reaction?

Farah Abumeri 3F

A reaction intermediate doesn't appear in the overall chemical reaction, but it can sometimes appear in the overall rate law for a reaction if it is a part of the slow elementary reaction step. I think you might be confusing what is the intermediate in 7C.9: II) Step 1 NO2+NO2→NO+NO3 (slow) Step 2 N...

Farah Abumeri 3F

What is the difference between an activation complex and a transition state? From what I understand, both are arrangements that could possibly form products or revert to reactants....

Farah Abumeri 3F

Hello, I'm confused as to when we do or don't factor in the products into rate laws. I remember Dr. Lavelle stating that for aA+bB→cC, the unique rate=(-1/a)*(d[A]/dt)=(-1/b)*(d[B]/dt=(1/c)*(d[C]/dt. But for rate laws (that are functions of concentrations) and integrate rate laws (that are functions...

Farah Abumeri 3F

6N.3 Predict the potential of each of the following cells: (c) Pt(s)|Cl2(g, 250 Torr)|HCl(aq, 1.0 mol⋅L−1)||HCl(aq, 0.85 mol⋅L−1) |H2(g, 125 Torr)|Pt(s) I'm having troubling understanding how to set up the half-reactions. I don't know what ions cancel for which reaction. How do you determine when to...

Farah Abumeri 3F

Because this is a galvanic cell, the standard potential has to be positive. With this in mind, when you look up the standard potential in appendix 2B or elsewhere for chromium and copper, you want to arrange (meaning flip the chemical reaction) based upon if the addition of the cathode and anode is ...

Farah Abumeri 3F

A hydrate is a solid compound that contains bonded water molecules. I think that even though we haven't explicitly studied hydrates this quarter, we may be expected to apply concepts of electrochemistry to hydrates, but I'm not sure. Someone please correct me if I'm wrong!

Farah Abumeri 3F

You should have 8 electrons instead of 10 because the overall charge on the product's side is a total of -8.

Farah Abumeri 3F

Can someone explain how to balance redox reactions according to basic or acidic conditions? Are there particular steps that we need to follow in a certain order?

Farah Abumeri 3F

This problem is asking us to determine how the oxidation numbers have/haven't changed across the reaction. Starting with KClO2, we know that the oxidation number of O is 2- (from the periodic table) and that the oxidation number of K is +1 (from the periodic table). From that we can deduce an equati...

Farah Abumeri 3F

I find it helpful to look at which species are either gaining or losing the electrons. For example, if Fe has an oxidation number of 3+ on the reactant side of the reaction and an oxidation number of 2+ on the product side of the reaction, Fe has gained an electron and therefore Fe is being reduced....

Farah Abumeri 3F

What is the difference between an electrode and an anode?

Farah Abumeri 3F

Also, for this problem, how did you find the deltaH values to calculate deltaH of the reaction? I couldn't find it in appendix 2A.

Why does the solution manual use 800 grams (is this a combination of HCl and Zn)?

Farah Abumeri 3F

I also had a question about this problem too. How do we know that the 3H2O in the chemical equation is a liquid and not a gas? I know that the products for any combustion reaction is CO2 and H2O, does anyone know how to determine their phases?

Farah Abumeri 3F

In today's lecture (2/17/21), Dr. Lavelle mentioned that the cathode plate will become thicker as a charged species accepts electrons and the anode plate will become thinner as a species loses electrons. Is that the right way of understanding it or am I missing something? Also, is it possible for th...

Farah Abumeri 3F

for part a and b, use 3/2*R*T, plugging in the values that were given. and for part c, subtract b from a in order to calculate the difference.

hope this helps!

Farah Abumeri 3F

You would multiply the products/reactants. For example, for the reaction N2 +3H2 yields 2NH3, the Q equation equal (PNH3)^2/(PN2)*(PH2)^3.

Farah Abumeri 3F

Why does deltaG decrease more sharply with temperature for a gas phase than for a liquid phase? (textbook section 4J.1)

Farah Abumeri 3F

Can the equation, deltaS=n*R*ln(V2/V1), be used for both reversible and irreversible expansions/compressions? If so, why?

Farah Abumeri 3F

Which equation, deltaS=qrev/T or deltaS=n*C*ln(V2/V1), do we use during the phase changes, and which do we use during the time where the temperature is increasing? I think Dr. Lavelle mentioned in today's lecture (2/8/21) but I'm not sure I understand why.

Farah Abumeri 3F

For step 1, use the equation w=-nRTln(Vf/Vi) and for step 2, use the equation w=-PdeltaV. This is because step 1 is an isothermal, reversible reaction meaning that temperature is constant while step 2 is an irreversible reaction meaning that the system is pushing against constant external pressure. ...

Farah Abumeri 3F

The change in internal energy should equal n*Cv*deltaT, number of moles*specific heat constant*change in temperature. Remember Cv= Cp - R, meaning you should be able to solve for Cv based on the information given. Hope this helps!

Farah Abumeri 3F

Why will there be an increase in entropy anytime there is a positive q (that is going into the system) while the temperature is constant?

Farah Abumeri 3F

A reaction is considered spontaneous, meaning it can occur by itself without additional input of energy. I think Dr. Lavelle is going to explain next lecture how we need both the change in internal energy (or change in enthalpy) and entropy in order to determine if a reaction is favorable/spontaneou...

Farah Abumeri 3F

What does it mean if work is negative or if work is positive? And what's the explanation behind it?

Thanks in advance!

Farah Abumeri 3F

I would recommend thinking of this problem as a puzzle, you have to manipulate the reactions given in order to get the reaction 2M(s) + 3Cl2(g) → 2MCl3(s). 2M(s) + 6HCl(aq) → 2MCl3(aq) + 3H2(g) Change in enthalpy=-579 kJ (this rxn doesnt need to be changed because you want 2M(s) on the reactant side...

Farah Abumeri 3F

The question is:

6D.15 Calculate the pH of (a) 0.19 M NH4Cl(aq); (b) 0.055 M AlCl3(aq).

I know that Al3+ will act as an acid because it is small and highly charged. I'm confused as to how you set up the chemical equation for this problem. Also, where do you find the Ka for Al3+?

Thanks in advance!

Farah Abumeri 3F

For this problem and the other problems in 6D, you have to refer to tables 6C.1 and 6C.2 for Ka and Kb values. For this particular problem, you can find the Kb for NH3, the Kb for NH2OH, and the Kb for (CH3)3N in table 6C.2 in section 6C.1 of the textbook. On the midterm tomorrow, I believe we will ...

Farah Abumeri 3F

The only factor (that we have learned in this class) that will change the K, equilibrium constant is temperature. Changing the pressure or the concentration of reactants/products won't change the K (this is assuming the reaction is at constant temperature!).

Farah Abumeri 3F

An extensive property is a property that depends on the size of the sample such as volume. An intensive property is a property that is independent of the size of the sample such as density. Extensive properties aren't as useful as intensive properties because extensive properties' abilities are limi...

Farah Abumeri 3F

First, calculate the bond enthalpy of benzene as if there were no resonance, meaning 3 carbon carbon double bonds, 3 carbon carbon single bonds, and 6 carbon hydrogen bonds. This equates to 3(612) + 3(348) + 6(412)= 5352 kJ. Then, calculate the bond enthalpy of benzene with the resonance, meaning 6 ...

Farah Abumeri 3F

I would recommend starting by first arranging the reactions given in a way that will leave you with N2O5, dinitrogen pentoxide. To do this, we have to multiply 2 NO(g) + O2(g) --> 2 NO2(g) H°= -114.1 kJ by 2 so that the NO2 (g) will cancel. This leaves us with 4 NO(g) + 2O2(g) --> 4 NO2(g) H°= 4(-11...

Farah Abumeri 3F

Use standard enthalpies of formation from Appendix 2A to calculate the standard reaction enthalpy for each of the following reactions: (c) the formation of a sulfide by the action of hydrogen sulfide on an aqueous solution of a base: H2S(aq)+2KOH(aq)→K2S(aq)+2H2O(l) I got the same expression as the ...

Farah Abumeri 3F

In today's lecture (1/22/21), Dr. Lavelle explained that the bond enthalpies of diatomic molecules are more accurate than the bond enthalpies of other molecules. I know that the diatomic molecules are Br2 I2 N2 Cl2 H2 O2 F2, but what characteristics of the diatomic molecules make them have an accura...

Farah Abumeri 3F

Why is the energy required to break a hydrogen bond or the energy released to form a hydrogen bond such a great value when a liquid is vaporizing/vapor is condensing compared to when a solid is melting/liquid is freezing? Does it have something to do with the number of H bonds? I think we talked abo...

Farah Abumeri 3F

I think you might be doing a calculation error because pH and pOH range from 1 to 14, all positive values. For example, if given that the concentration of H3O+ is 2.0 x 10^-6, the pH=-log(2.0 x 10^-6)= 5.7. If given the concentration of OH- is 1.5 x 10^-9, then pOH=-log(1.5 x 10^-9)=8.8. Maybe you'r...

Farah Abumeri 3F

Percent ionization refers to the percent of molecules that were ionized, or gained an electron. Percent protonated refers to the percent of molecules that were protonated, or gained a proton (hydronium ion). I hope that helps!

Farah Abumeri 3F

Percent ionization is solved by dividing the concentration of the ionized molecule by the concentration of the initial molecule (prior to ionization). To check if the approximation is valid, divide the equilibrium concentration by the initial concentration, and if it is less than 5% of the initial m...

Farah Abumeri 3F

Your Q equation should be Q= [NH3]^2/ [N2]* [H2]^3 because the coefficient of H2 in the balanced chemical equation is 3. I believe that should help you get the right answer as long as you plug in the correct concentrations.

Farah Abumeri 3F

You're correct, since NH4(NH2CO2) is a solid, you can disregard it in your calculations to determine Kc. The next step is as you said, to convert the 17.4 mg of CO2 into moles of CO2. Then, to convert this value into concentration divide it by the volume, 0.250 L. When I did those calculations, I go...

Farah Abumeri 3F

I think it's helpful to determine if more products or reactants are going to be produced based on the change in temperature first. If products are more favored, then K will increase because the products are in the numerator. If reactants are more favored, then K will decrease because the reactants a...

Farah Abumeri 3F

A negative delta H means that the reaction is giving off heat, exothermic. A positive delta H means that the reaction requires heat, endothermic. I think Dr. Lavelle has mentioned that the enthalpy, H, of the reactants and products is going to become significant in future lectures in determining the...

Farah Abumeri 3F

From what I understand, both terms refer to the same thing. A question that asks for the composition of equilibrium mixture or the equilibrium composition of the mixture or some variant of those terms, all want you to solve for the concentration of the reactants and products at equilibrium.

Farah Abumeri 3F

For both endothermic and exothermic reactions, does heating favor the component that has the most enthalpy? For instance, endothermic reactions when heated favor the products, which have a greater enthalpy than reactants. Exothermic reactions when heated favor the reactants, which have a greater ent...

Farah Abumeri 3F

5I.15 When solid NH4HS and 0.400 mol NH3(g)were placed in a vessel of volume 2.0 L at 24 °C, the equilibrium NH4HS (s)⇌NH3(g)+H2S(g), for which Kc=1.6×10−4, was reached. What are the equilibrium concentrations of NH3and H2S? This question throws me off because I don't understand how NH3, a product, ...

Farah Abumeri 3F

Boric acid is acting like a lewis acid in this example because it's accepting an electron pair, OH-. From what I understand, not all acids have to accept a proton to be considered an acid. In this case, Boric acid accepts an electron pair rather than donating a H+ because I think it's more energetic...

Farah Abumeri 3F

This question asks: Decide whether an aqueous solution of each of the following salts has a pH equal to, greater than, or less than 7. If pH > 7 or pH < 7, write a chemical equation to justify your answer. I'm particularly confused about part e, AlCl3. I understand that the chloride ions won't affec...

Farah Abumeri 3F

When I was answering this question, I didn't have the values of pKb on hand. But I chose BrO- as the stronger base because it is more likely to accept a proton than morphine because BrO- is a negative polyanion and wants to attain a neutral charge. Someone correct me if I am wrong!

Farah Abumeri 3F

I believe hard water is alkaline (meaning more basic) and soft water is more acidic. Hard water had a soapy feel and soft water has an almost dry feel.

Farah Abumeri 3F

The thing to remember here is that the greater the number of oxygen atoms attached to the central atom, the stronger is the acid. This is because each oxygen pulls the electron density toward itself and therefore diffuses the charge of the anion I04-, I03-, IO2-, IO-. This stabilizes the anion, whic...

Farah Abumeri 3F

I would recommend "splitting" each salt into their anions and cations and then determining from those ions if they typically form strong/weak acids or strong/weak bases. For LiClO4 and KCl, both have a cation and anion that are part of a strong base and a strong acid. This means that they ...

Farah Abumeri 3F

Can someone explain why atoms with a greater electronegativity stabilize an acid? In Professor Lavelle's lecture on Friday, he showed the example with CLO-, BrO-, and IO-. From what I understand, because chlorine has the greatest electronegativity, it pulls the electrons the greatest toward itself, ...

Farah Abumeri 3F

pKa is the -log[Ka]. Ka is the equilibrium constant of a weak acid. I think Professor Lavelle was trying to highlight how the lower the pKa the lower the pH, which is a stronger acid. I'm pretty sure we don't have to know about equilibrium in depth for 14A. Someone correct me if I am wrong!

Farah Abumeri 3F

In today's lecture (Dec 2nd), Dr. Lavelle was comparing the strength of two strong acids: HBr and HCl. Is an acid with a weaker bond (which in this case is HBr, since it is larger) a stronger acid because it can give away a H+ to form H3O+ more easily? I was confused whether HCl or HBr was the stron...

Farah Abumeri 3F

What is the difference in purpose of hemoglobin and myoglobin? Do both transport oxygen but just in different amounts?

Farah Abumeri 3F

I would agree that a multidentate would be more stable than an unidentate. I think it depends on the central atom if it's more energetically stable for there to be more bonds or one bond. Correct me if I am wrong..

Farah Abumeri 3F

My guess is that it has to do with the strength of the electrostatic attraction between guanine and platinum. Is it because it's more energetically stable for cisplatin to lose the the chlorine while it's more energetically stable for NiCl2 to retain the chlorines while bonding to H20? I'm not sure ...

Farah Abumeri 3F

What was the explanation for why the DNA of healthy cells are more compact than that of the unhealthy cells? For that reason, there is a preferential impact of the drug on the unhealthy cells, right?

Farah Abumeri 3F

Does a tetradentate also form a chelate? Also, do the terms bidentate, tridentate, and hexadentate describe a ligand or a compound?

Farah Abumeri 3F

I had the same question. But, I don't understand what lone pairs you're referring to. Was Dr. Lavelle saying that the nitrogen was bidentate because it had two bonds? I'm still confused.

Farah Abumeri 3F

I think we just have to understand the patterns of bond angles and how bond angles change slightly based upon the number of lone pairs. If you have a basic understanding of for example, the tetrahedral arrangement, which has bond angles of 109.5, then you can adjust that number based upon how many e...

Farah Abumeri 3F

Hi, can someone explain why we can still determine the correct molecular shape from a lewis structure that is not the most stable? And, is this always the case or are there exceptions? Thank you in advance!

Farah Abumeri 3F

I think it's because flourine is the most electronegative element in this molecule, and so it will pull the electrons toward it.

Farah Abumeri 3F

I think what's really helpful is just doing the homework and sapling problems. The more practice you do, the more easily the names and bond angles will come to you. Also, for even more practice, attend the workshops/step-up sessions!

Farah Abumeri 3F

I also think those VSEPR notations are correct. I'm not sure if we have to memorize them because I think Dr. Lavelle wants us to be able to recognize that molecules with the same formula have the same general shape. But, memorizing might be a good start to understanding!

Farah Abumeri 3F

From what I understand, when you're drawing lewis structures of ions that have a negative charge of some sort, you want to make sure that the negative charge is placed on the most electronegative atom. So in the case of PO4 3-, the negative formal charges should go on the 3 oxygens, while phosphorou...

Farah Abumeri 3F

Hi, could someone explain the question below? I'm having a hard time understanding the explanations of what makes a molecule stronger/weaker than another. 3F.19 Account for the following observations in terms of the type and strength of intermolecular forces. (a) The melting point of solid xenon is ...

Farah Abumeri 3F

The stronger the intermolecular forces, the greater the boiling point of a molecule, since more energy is needed to break the bonds completely (this is called the dissociation energy). I believe in order of decreasing strength the IMFS are ion-ion, hydrogen bonding, ion-dipole, dipole-dipole = dipol...

Farah Abumeri 3F

Induced dipole-induced dipole interactions occur in all molecules. It refers to the temporary fluctuation of electrons that results in a partially negative charge and a partially positive charge. In other words, the temporary induced dipole induced another molecule to have a temporary dipole because...

Farah Abumeri 3F

One example is due to a large electronegativity difference, like in the molecule HF. Because F is very electronegative, it has this "electron pulling power" and pulls the electrons toward it, making the flourine side partially negative and the hydrogen side partially positive.

Farah Abumeri 3F

Electron affinity is the energy released when an electron is added to a gas-phase atom. Electronegativity is the ability of an atom to attract electrons to itself when it is part of a compound. Ionization energy is the energy needed to remove electron from atom in gas phase. Electron affinity and io...

Farah Abumeri 3F

I think it's more energetically stable for chlorine to have -1 fc and not oxygen because this way the majority of atoms have a fc of 0.

Farah Abumeri 3F

How do you know when to follow the layout of the atoms given by the chemical notation and when to follow what is energetically stable (formal charge rules)? For instance, ClNO2, the answer given by the book is a resonance structure with chlorine singly bonded to nitrogen and the two oxygens singly/d...

Farah Abumeri 3F

In lecture 16, Dr. Lavelle was explaining how ionic bonds have covalent character due to electrons being pulled into the bonding region. I'm confused on the terminology of it all. Is high polarizability and highly polarizable the same thing for an anion? And the lower the polarizability of the anion...

Farah Abumeri 3F

The electron configuration for Mn is [Ar]3d^5 4s^2 and to show Mn has been excited, Mn 2+, the electron configuration becomes [Ar]3d^5. Why do we fill the 4s orbital first and then the 3d orbital, but then for an excited state of an atom, we remove from the 4s orbital first? I might be overthinking ...

Farah Abumeri 3F

Hi Eliana! The electron configuration for a chromium atom is [Ar]3d^5 4s^1 (remember the special rule about how the electron orbitals have to be all half full or all full). The electron configuration for a chromium ion with a +3 charge would be [Ar]3d^3 (removing 3 electrons). The electron configura...

Farah Abumeri 3F

I would think that 3d would feel a greater effective nuclear charge because since it has less energy than 4s, 3d would be closer in distance to the nucleus. This is because as the energy levels increase, the energy of an electron decreases (becomes more positive). And due to the electrostatic potent...

Farah Abumeri 3F

How do you determine the magnetic quantum numbers specifically? For instance, if l=2, I understand that there are 5 options for a magnetic orientation quantum number because there are 5 d-orbitals. Those 5 numbers are -2,-1,0,1,2. How do we know that it goes from -2 to 2?

Farah Abumeri 3F

Hi Chloe! To start this problem, I would reference the periodic table. The shell n=1 is represented by the first group. For n=1, 2 electrons can occupy this shell as seen by the 1s orbital that is represented by the 2 elements, H and He. For n=2, 8 electrons can occupy this shell because 2 electrons...

Farah Abumeri 3F

Hi! Oxygen has a lower ionization energy than nitrogen and fluorine because in the 2p subshell, out of the total of 4 electrons, there are 2 electrons that occupy the 2px orbital. Keeping in mind the electrostatic attraction guidelines, there exists electron-electron repulsion in this 2px orbital an...

Farah Abumeri 3F

The EΨ means the energy of the wave function. This value also corresponds to the orbitals (since the second derivative of the wave function = the probability of finding an electron). In other words, the Hamiltonian (the double or second derivative) of the wave function = the energy of the wave funct...

Farah Abumeri 3F

Hi Melody! A wave function (trident symbol) is a math model that describes an electron's position, momentum, and wavelike properties in an atom. I think Dr. Lavelle is referring to how a wave function can be positive or negative or 0 according the phase of the wave when he says change in wave functi...

Farah Abumeri 3F

From what I understand, the circular standing wave model explains why electrons have quantized energy states in atoms and that electrons are bound to the atom. I think the important aspect to note is that the waves are all continuous, as in there is no break in the wave, further demonstrating how el...

Farah Abumeri 3F

Great, that makes a lot of sense! Thank you all!

Farah Abumeri 3F

Dr. Lavelle prefers that we use E=(-hR)/n^2 rather than the frequency=R(1/(n1)^2 - 1/(n2)^2) because it's a better conceptual application. On the midterm, are we allowed to use the Rydberg Equation rather than the fundamental equation, because I've notice it's much quicker to attain an answer that w...

Farah Abumeri 3F

A. is false because the speed of light (electromagnetic radiation) is constant, c=3x10^8 m/s. B. is false because frequency and wavelength are inversely proportional as c=wavelength x frequency. So if frequency decreases, then wavelength would have to increase. C. is true because since the electrica...

Farah Abumeri 3F

Catie Donohue 3I wrote:I'm looking at my notes right now and I believe you would plug in delta x as 10 rather than 5. One of the examples he gave was "x = 20m +/- 1m, delta x = 2 m," so that's essentially the same thing here except instead of 2 it would be 10. Hope this helps!

Thank you Catie!

Farah Abumeri 3F

Hi! Δv = 10.0 m/s not 5.0 m/s because when the problem states that the velocity of the bowling ball is 5.00 ± 5.0 m/s, the indeterminacy ranges from 5 m/s below and 5 m/s above, which is a total of 10m/s. I hope that helps!

Farah Abumeri 3F

I'm confused on how to solve this problem. I believe where I am going wrong is in regards to the plus or minus 5 meters. Are we supposed to plug in 5 directly for delta x? Or do we plug in 10? If someone could please explain, that would be extremely helpful! Thank you!!

Farah Abumeri 3F

^^^ My apologies, 5.51x10^-9 meters should be 5.51x10^-7 m!

Farah Abumeri 3F

If you were writing the wavelength as 5.51 then it would be 5.51x10^-7 m. Professor Lavelle wrote the wavelength as 551 with no decimal, so it would be 551x10^-9 m. I think that because we are using scientific notation the correct answer would be 5.51x10^-7 m. But 5.51x10^-7 m and 551x10^-9 m are te...

Farah Abumeri 3F

Hey Jessica! Good question. From what I understand, intensity is the brightness of electromagnetic radiation. The intensity of a wave of electromagnetic radiation is proportional to the square of its amplitude. Energy of light, on the other hand, is proportional to the frequency, which is shown by t...

Farah Abumeri 3F

Hi Alessia! First, you are given that the energy to remove an electron =3.61x10^-19 J. Then, you are told that there is no kinetic energy, which means the energy of the photon equals the energy to remove an electron ( remember E(photon)=E(remove)+E(Kinetic) ). Next, you have to rearrange the equatio...

Farah Abumeri 3F

I understand that if the energy of the photons from the light source is not equal to or greater than the energy to remove electrons, the electrons won't be ejected from the metal. I'm curious as to what happens to the energy of the photons from the light source if it is less than the energy to remov...

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