Search found 17627 matches

by Chem_Mod
Thu Aug 25, 2011 9:57 am
Forum: Photoelectric Effect
Topic: work function, why do we divide by Avogadro's number?
Replies: 1
Views: 338

work function, why do we divide by Avogadro's number?

Question: For problems using the work function, why do we divide by Avogadro's number?
by Chem_Mod
Thu Aug 25, 2011 9:56 am
Forum: Photoelectric Effect
Topic: E=hv-phi application
Replies: 1
Views: 5108

Re: E=hv-phi application

Answer: The main equation is that E(photon)=Phi+KE, where phi is the work function which is the minimum energy required to remove an electron and KE is the kinetic energy of an electron. Basically the equation is using conservation of energy. The energy given by the photon is used to remove an elec...
by Chem_Mod
Thu Aug 25, 2011 9:56 am
Forum: Photoelectric Effect
Topic: E=hv-phi application
Replies: 1
Views: 5108

E=hv-phi application

Question: The kinetic energy equation E=hv-(work function) can be written E=hv(photon)-hv(ejected). Why is it that if a problem states "Radiation of X Hz is required to eject an electron...," you plug X into the ejected half, whereas if it states "Radiation of X Hz strikes Cs and eje...
by Chem_Mod
Thu Aug 25, 2011 9:55 am
Forum: Photoelectric Effect
Topic: Energy level and Photons
Replies: 1
Views: 369

Re: question on energy level and photon match

Answer: In the first case of excitation of H atom, the energy of the incoming photon is smaller than the ionization energy of H atom. The photon can only excite the electron in H atom from lower energy state to higher energy state. Thus H atoms can only absorb photons with fixed energy. But if the ...
by Chem_Mod
Thu Aug 25, 2011 9:55 am
Forum: Photoelectric Effect
Topic: Energy level and Photons
Replies: 1
Views: 369

Energy level and Photons

Question: How does the energy difference between two energy level and the energy of the incoming photon match in order for the electron in the hydrogen atom to absorb and be excited to the next energy level? If the energy of the photon was greater than (but not great enough to excite the electron i...
by Chem_Mod
Thu Aug 25, 2011 9:51 am
Forum: *Black Body Radiation
Topic: What is "black body radiation?"
Replies: 8
Views: 1079

Re: What is "black body radiation?"

Answer: "Black body radiation" refers to the radiation that originates from the thermal energy of the body that is heated.
by Chem_Mod
Thu Aug 25, 2011 9:51 am
Forum: *Black Body Radiation
Topic: What is "black body radiation?"
Replies: 8
Views: 1079

What is "black body radiation?"

Question: What is "black body radiation"?
by Chem_Mod
Thu Aug 25, 2011 9:50 am
Forum: Einstein Equation
Topic: steps in finding the max wavelength that can break a bond?
Replies: 1
Views: 1094

Re: steps in finding the max wavelength that can break a bon

Answer: First, figure out how much energy is in a single C-C bond because one photon will interact with one bond. To do this, take the energy per mole and divide it by Avogadro's number since there are that many C-C bonds in one mole. From there, set this energy to find a wavelength using the expre...
by Chem_Mod
Thu Aug 25, 2011 9:50 am
Forum: Einstein Equation
Topic: steps in finding the max wavelength that can break a bond?
Replies: 1
Views: 1094

steps in finding the max wavelength that can break a bond?

Question: What are the steps in finding the maximum wavelength needed to break a bond (a C-C bond for example)?
by Chem_Mod
Thu Aug 25, 2011 9:49 am
Forum: Properties of Electrons
Topic: Nuclear charge and electron energies
Replies: 1
Views: 224

Re: Nuclear charge and electrons

Answer: If the electrons are strongly attracted, then the tendency for them to escape deceases. This means that the system becomes more stable and the more stable the system is the lower is its energy. Remember that nature favors stability and low energy.
by Chem_Mod
Thu Aug 25, 2011 9:45 am
Forum: Properties of Electrons
Topic: Nuclear charge and electron energies
Replies: 1
Views: 224

Nuclear charge and electron energies

Question: The greater charge of a nucleus in a many-electron atom, the stronger it attracts the electrons and therefore lowers their energy. Why would an increase in nuclear charge result in lower energy?
by Chem_Mod
Thu Aug 25, 2011 9:44 am
Forum: Properties of Electrons
Topic: What is the formal definition of the "Quantized Property"?
Replies: 1
Views: 1684

Re: What is the formal definition of the "Quantized Property

Answer: Property that has only certain discrete values, and values in between discrete values are not possible.
by Chem_Mod
Thu Aug 25, 2011 9:44 am
Forum: Properties of Electrons
Topic: What is the formal definition of the "Quantized Property"?
Replies: 1
Views: 1684

What is the formal definition of the "Quantized Property"?

Question: What is the formal definition of the "Quantized Property"?
by Chem_Mod
Thu Aug 25, 2011 9:44 am
Forum: Properties of Electrons
Topic: excited state from n=1 to n=3, do they come back down?
Replies: 1
Views: 301

Re: excited state from n=1 to n=3, do they come back down?

Answer: Upon relaxation, both cases are possible for the electron.
by Chem_Mod
Thu Aug 25, 2011 9:43 am
Forum: Properties of Electrons
Topic: excited state from n=1 to n=3, do they come back down?
Replies: 1
Views: 301

excited state from n=1 to n=3, do they come back down?

Question: When electrons come back down from an excited state, say from n=1 to n=3, do they come back down to n=1 after they emit the energy? Can they fall incrementally from n=3 to n=2 to n=1, thereby emitting 2 different frequencies of light?
by Chem_Mod
Thu Aug 25, 2011 9:41 am
Forum: Properties of Light
Topic: Constant c value?
Replies: 1
Views: 249

Re: Constant c value?

Answer: 3.00 X 10^8 m/s is fine.
by Chem_Mod
Thu Aug 25, 2011 9:41 am
Forum: Properties of Light
Topic: Constant c value?
Replies: 1
Views: 249

Constant c value?

Question: In the textbook the value of C (the speed of light) is given as 3.00 X 10^8 m/s, but in the solutions manual it is written as 2.99792 X 10^8 m/s. Which value of c should we use in our calculations?
by Chem_Mod
Thu Aug 25, 2011 9:40 am
Forum: Properties of Light
Topic: What is the wavelength for 300MHz? , What is the SI units
Replies: 1
Views: 431

Re: What is the wavelength for 300MHz? , What is the SI unit

Answer: Use (wavelength)=(speed of light)/(frequency)=(2.998*10^8 ms^-1)/(300*10^6 s^-1)=1m. Remember that the unit Hz is just s^-1, so MHz is 10^6 s^-1. The SI unit is meter for distance; however, you do not always need to convert to this unit when solving problems, although in this problem it is ...
by Chem_Mod
Thu Aug 25, 2011 9:40 am
Forum: Properties of Light
Topic: What is the wavelength for 300MHz? , What is the SI units
Replies: 1
Views: 431

What is the wavelength for 300MHz? , What is the SI units

Question: What is the wavelength for 300MHz? , What is the SI units used to find wavelength?
by Chem_Mod
Thu Aug 25, 2011 9:39 am
Forum: Limiting Reactant Calculations
Topic: How do we find the amount of oxygen in combustion?
Replies: 1
Views: 339

Re: how do we find the amount of oxygen in combustion?

Answer: The amount of oxygen in CO2 and H2O after combustion is the sum of the amount of O from both the substance and the reactant O2. But by subtracting the mass of C, H and any other additional element, you can get only the mass of O present in the starting substance.
by Chem_Mod
Thu Aug 25, 2011 9:39 am
Forum: Limiting Reactant Calculations
Topic: How do we find the amount of oxygen in combustion?
Replies: 1
Views: 339

How do we find the amount of oxygen in combustion?

Question: In a combustion reaction, how do we find the amount of oxygen?
by Chem_Mod
Thu Aug 25, 2011 9:02 am
Forum: Balancing Chemical Reactions
Topic: Balance the equation Cu(NO3)2 + NaOH --> Cu(OH)2
Replies: 1
Views: 1044

Re: balance the equation Cu(NO3)2 + NaOH --> Cu(OH)2

Answer: Include Na(NO)3 in the product. Remember that this is a double displacement reaction. so this product has to be there. After you add this on the product side you can balance the reaction easily.
by Chem_Mod
Thu Aug 25, 2011 9:02 am
Forum: Balancing Chemical Reactions
Topic: Balance the equation Cu(NO3)2 + NaOH --> Cu(OH)2
Replies: 1
Views: 1044

Balance the equation Cu(NO3)2 + NaOH --> Cu(OH)2

Question: How would you balance the initial equation Cu(NO3)2 + NaOH --> Cu(OH)2 ?
by Chem_Mod
Thu Aug 25, 2011 9:02 am
Forum: Empirical & Molecular Formulas
Topic: 6C,6H,6Cl how should i write the molecular formula
Replies: 1
Views: 423

Re: 6C,6H,6Cl how should i write the molecular formula

Answer: 6CHCl means 6 x CHCl. The molecular formula must be written as: C6H6Cl6. The main difference is that C6H6Cl6 is one molecule, while 6CHCl is six CHCl molecules.
by Chem_Mod
Thu Aug 25, 2011 9:01 am
Forum: Empirical & Molecular Formulas
Topic: 6C,6H,6Cl how should i write the molecular formula
Replies: 1
Views: 423

6C,6H,6Cl how should i write the molecular formula

Question: When a molecular formula has 6C, 6H,and 6Cl, can I write 6CHCl, or do I have to write C6H6Cl6?
by Chem_Mod
Thu Aug 25, 2011 9:01 am
Forum: Empirical & Molecular Formulas
Topic: Why is the empirical formula for sodium hydroxide NaOH
Replies: 1
Views: 748

Re: Why is the empirical formula for sodium hydroxide NaOH

Answer: Since NaOH is not a molecule we don't really think of empirical and molecular formulas for it. We generally write formula units in the same order as their bond order. In this case Na+ is interacting with the O and not the H, hence NaOH.
by Chem_Mod
Thu Aug 25, 2011 9:00 am
Forum: Empirical & Molecular Formulas
Topic: Why is the empirical formula for sodium hydroxide NaOH
Replies: 1
Views: 748

Why is the empirical formula for sodium hydroxide NaOH

Question: Why is the empirical formula for sodium hydroxide NaOH and not NaHO? (The former formula had OH at the end while in the latter formula, it was HO).
by Chem_Mod
Thu Aug 25, 2011 9:00 am
Forum: Empirical & Molecular Formulas
Topic: Why is NO called nitric oxide not nitrogen oxide?
Replies: 1
Views: 727

Re: Why is NO called nitric oxide not nitrogen oxide?

Answer: Nitric oxide is the common or historical name. Nitrogen oxide is the modern name. Both are correct and I tend to use the modern names.
by Chem_Mod
Thu Aug 25, 2011 9:00 am
Forum: Empirical & Molecular Formulas
Topic: Why is NO called nitric oxide not nitrogen oxide?
Replies: 1
Views: 727

Why is NO called nitric oxide not nitrogen oxide?

Question: Why is NO called nitric oxide and not nitrogen oxide?
by Chem_Mod
Thu Aug 25, 2011 8:59 am
Forum: Empirical & Molecular Formulas
Topic: Why is Cu2O named copper(I)oxide?
Replies: 1
Views: 2951

Re: Why is Cu2O named copper(I)oxide?

Answer: In the name copper(I)oxide, the (I) stands for the charge of the copper cation. Since oxygen anion carries 2 negative charges, the two copper cations each carries one positive charge, i.e. Cu+.
by Chem_Mod
Thu Aug 25, 2011 8:59 am
Forum: Empirical & Molecular Formulas
Topic: Why is Cu2O named copper(I)oxide?
Replies: 1
Views: 2951

Why is Cu2O named copper(I)oxide?

Question: Why is Cu2O named copper(I)oxide?
by Chem_Mod
Thu Aug 25, 2011 8:58 am
Forum: Empirical & Molecular Formulas
Topic: Combustion of caffeine, why have oxygen in it?
Replies: 1
Views: 446

Re: combustion of caffeine, why have oxygen in it?

Answer: The problem only tells you that C, N and H is found in the compound. It does not say that they are the ONLY elements in the compound. As stated in the solution manual, the sum of the percentages of C, N and H is smaller than 100%, so there must be another element in the compound. And the co...
by Chem_Mod
Thu Aug 25, 2011 8:58 am
Forum: Empirical & Molecular Formulas
Topic: Combustion of caffeine, why have oxygen in it?
Replies: 1
Views: 446

Combustion of caffeine, why have oxygen in it?

Question: In the combustion of caffeine, it says the compound contains carbon, nitrogen, and hydrogen, but why does the answer have oxygen in it?
by Chem_Mod
Thu Aug 25, 2011 8:57 am
Forum: Molarity, Solutions, Dilutions
Topic: Dilutions (how much water is needed)
Replies: 3
Views: 338

Re: dilution (how much water need to added in )

Answer: The resulting volume will be 5x the original volume (4 + 1). Since 2.5 mol/L is 5x (0.50 mol/L) it will give the correct dilution.
by Chem_Mod
Thu Aug 25, 2011 8:54 am
Forum: Molarity, Solutions, Dilutions
Topic: Dilutions (how much water is needed)
Replies: 3
Views: 338

Dilutions (how much water is needed)

Question: When you make dilution of 2.5 mol/L solution to make 0.50 mol/L solution, I don't understand why 4 volumes of water are needed to be added to 1 volume of the 2.5 mol/L.
by Chem_Mod
Thu Aug 25, 2011 8:53 am
Forum: Molarity, Solutions, Dilutions
Topic: Total volume for both species are the same?
Replies: 1
Views: 253

Re: total volume for both species are the same?

Answer: Assume that you add 3 mL of sulfuric acid to 3 mL of water. Each component in the mixture has a total volume of 6 mL. That is how the final volume for the two species are known to be the same. The moles can then be calculated using the given volume/concentration.
by Chem_Mod
Thu Aug 25, 2011 8:52 am
Forum: Molarity, Solutions, Dilutions
Topic: Total volume for both species are the same?
Replies: 1
Views: 253

Total volume for both species are the same?

Question: How does one know that the final total volume for both species is the same, and how is this used to determine the number of moles required?
by Chem_Mod
Thu Aug 25, 2011 8:51 am
Forum: Molarity, Solutions, Dilutions
Topic: How should we approach dilution problems?
Replies: 1
Views: 289

Re: How should we approach dilution problems?

Answer: Dilutions just creates a change in concentration. The number of moles of a species remains the same, only the volume changes. Since molarity = moles/volume, this means that the molarity changes as well, but it can be calculated with the equation.
by Chem_Mod
Thu Aug 25, 2011 8:51 am
Forum: Molarity, Solutions, Dilutions
Topic: How should we approach dilution problems?
Replies: 1
Views: 289

How should we approach dilution problems?

Question: How should we approach dilution problems?
by Chem_Mod
Thu Aug 25, 2011 8:45 am
Forum: Significant Figures
Topic: Significant figures for numbers without a decimal
Replies: 1
Views: 248

Re: significant figures for numbers without a decimal

Answer: Always use the lowest sig fig that appears in the question. In this case, the answer should be in 1 sig fig as 200 has 1 sig fig and that is the lowest sig fig that appears in the question.
by Chem_Mod
Thu Aug 25, 2011 8:45 am
Forum: Significant Figures
Topic: Significant figures for numbers without a decimal
Replies: 1
Views: 248

Significant figures for numbers without a decimal

Question: For significant figures, say a question includes 2 different values, 7.884 and 200 (instead of 200.) Should we pay attention to the 7.884 when figuring out the significant figures for our result, thus rounding to 4 sig-figures? (since 200 is ambiguous and does not include the "."...
by Chem_Mod
Thu Aug 25, 2011 8:44 am
Forum: Significant Figures
Topic: Significant figure rules
Replies: 4
Views: 503

Re: Significant figure rules

Answer: Use the lowest significant figure that is used in the values in the question. Be careful when handling integers such as 400 (which by rules is considered to only have 1 significant figure), but could also be 4.00*10^2 and in that case it has 3 significant figures.
by Chem_Mod
Thu Aug 25, 2011 8:43 am
Forum: Significant Figures
Topic: Significant figure rules
Replies: 4
Views: 503

Significant figure rules

Question: What is the rule for significant figures when solving a problem?
by Chem_Mod
Thu Aug 25, 2011 8:42 am
Forum: Significant Figures
Topic: Round up or down?
Replies: 1
Views: 228

Re: Round up or down?

Answer: Round to the nearest even number. 10.25 would become 10.2.
by Chem_Mod
Thu Aug 25, 2011 8:42 am
Forum: Significant Figures
Topic: Round up or down?
Replies: 1
Views: 228

Round up or down?

Question: In regards to significant digits, if I have to round off a number, do I round up or round off to the nearest even number when there is a 5. For example if three significant digits are required and my answer in my calculator is 10.25, will it be 10.3 or 10.2?
by Chem_Mod
Thu Aug 25, 2011 8:41 am
Forum: Significant Figures
Topic: Question #9 - Winter Final 2000
Replies: 1
Views: 220

Re: Question for 2000 winter final

Answer: Since 5.0g was used, X should have 2 sig figs, which means the pH should have two decimal places. Please see sig figs handout on VOH and other VOH Q&A.
by Chem_Mod
Thu Aug 25, 2011 8:41 am
Forum: Significant Figures
Topic: Question #9 - Winter Final 2000
Replies: 1
Views: 220

Question #9 - Winter Final 2000

Question: For the Winter 2000 Final exam, number 9, why are there three significant figures for the pH instead of 2?
by Chem_Mod
Thu Aug 25, 2011 8:40 am
Forum: Significant Figures
Topic: Question #7 & #10 - Fall 2000 Final
Replies: 1
Views: 206

Re: Question 10 for 2000 fall final

Answer: X should have 2 sf and pH will have two decimal places. Q10 answer should have 3sf (two decimal places). See SF handout online.

The Q7 answer should have 3 sf.
by Chem_Mod
Thu Aug 25, 2011 8:40 am
Forum: Significant Figures
Topic: Question #7 & #10 - Fall 2000 Final
Replies: 1
Views: 206

Question #7 & #10 - Fall 2000 Final

Question: When solving for X (concentration of OH-), how many sig figs does X have? Since the question only has two sf, does X also only have 2 sf? If yes, then will the pH only have one sf?

Also in Q7, why does the answer only have two sf?
by Chem_Mod
Thu Aug 25, 2011 1:50 am
Forum: Trends in The Periodic Table
Topic: Why is there a decrease of atomic mass from Te to I?
Replies: 1
Views: 280

Re: Why is there a decrease of atomic mass from Te to I?

Answer: Atomic mass is the sum of protons + neutrons. Generally, atomic mass increases from left to right. Te has more neutrons so its atomic mass is higher than I.
by Chem_Mod
Thu Aug 25, 2011 1:50 am
Forum: Trends in The Periodic Table
Topic: Why is there a decrease of atomic mass from Te to I?
Replies: 1
Views: 280

Why is there a decrease of atomic mass from Te to I?

Question: If atomic weight increases as the protons increase, then why is there a decrease from Te to I?
by Chem_Mod
Thu Aug 25, 2011 1:45 am
Forum: Resonance Structures
Topic: Does SClO2 have resonance structure?
Replies: 1
Views: 402

Re: Does SClO2 have resonance structure?

Answer: Yes, the product can be drawn with another resonance structure with a double bond between the sulfur and the oxygen, resulting in S having 12e- in its valence shell. The oxygen is more likely, than the Cl, to form a double bond.
by Chem_Mod
Thu Aug 25, 2011 1:45 am
Forum: Resonance Structures
Topic: Does SClO2 have resonance structure?
Replies: 1
Views: 402

Does SClO2 have resonance structure?

Question: In the molecule SClO2, Sulfur is in the middle of two Oxygen atoms, each bonded to the Sulfur with a double bonds. The S atom also has a lone pair. The S is also linked to a Cl atom with a single bond. I want to know why the S doesn't maintain its other double bond with the second O atom,...
by Chem_Mod
Thu Aug 25, 2011 1:43 am
Forum: Trends in The Periodic Table
Topic: Why is aluminum not a metalloid?
Replies: 1
Views: 2178

Re: Why aluminum not metalloid?

Answer: The physical & chemical properties of aluminum are more similar to the general properties of metals. Since the energy of the valence e- in the d-orbitals are very similar to the transition metals it can have various oxidation states. The oxidation state is determined by what they are bo...
by Chem_Mod
Thu Aug 25, 2011 1:42 am
Forum: Trends in The Periodic Table
Topic: Why is aluminum not a metalloid?
Replies: 1
Views: 2178

Why is aluminum not a metalloid?

Question: Why isn't aluminum classified as a metalloid? How do you find the oxidations states of the transition state metals? What would happen if you passed gaseous CO2 through liquid NaOH?
by Chem_Mod
Thu Aug 25, 2011 1:38 am
Forum: Bond Lengths & Energies
Topic: Is there any element never form double or triple bond?
Replies: 1
Views: 1006

Re: Is there any element never form double or triple bond?

Answer: In chemistry there are compounds that can be made under unusual conditions. So one should never say "never". However I have not heard of H forming a double bond.
by Chem_Mod
Thu Aug 25, 2011 1:37 am
Forum: Bond Lengths & Energies
Topic: Is there any element never form double or triple bond?
Replies: 1
Views: 1006

Is there any element never form double or triple bond?

Question: Are there elements that are unable to form double or triple bonds no matter what? And if so which elements are they?
by Chem_Mod
Thu Aug 25, 2011 1:34 am
Forum: Formal Charge and Oxidation Numbers
Topic: Molecule is the most stable when FC close to 0?
Replies: 1
Views: 214

Re: Molecule is the most stable when FC close to 0?

Answer: You are correct FC = 0 is the most stable, so the wording should be FC as close to 0 are the most stable.
by Chem_Mod
Thu Aug 25, 2011 1:34 am
Forum: Formal Charge and Oxidation Numbers
Topic: Molecule is the most stable when FC close to 0?
Replies: 1
Views: 214

Molecule is the most stable when FC close to 0?

Question: The molecule is most stable when the FC is closest to zero, correct? Because in one part of the book, it said the lower the FC, the more stable/covalent... this would mean that negative formal charges were the most stable.
by Chem_Mod
Thu Aug 25, 2011 1:33 am
Forum: Octet Exceptions
Topic: Which atoms can have incomplete octets?
Replies: 1
Views: 1080

Re: Which atoms can have incomplete octets?

Answer: Many atoms have incomplete octets in compounds may have an incomplete octet. They are H, He, Li, Be, B, and sometimes Al.
by Chem_Mod
Thu Aug 25, 2011 1:32 am
Forum: Octet Exceptions
Topic: Which atoms can have incomplete octets?
Replies: 1
Views: 1080

Which atoms can have incomplete octets?

Question: Which atoms can have incomplete octets, as in less than 8 electrons surrounding them?
by Chem_Mod
Thu Aug 25, 2011 1:31 am
Forum: Sigma & Pi Bonds
Topic: Why 1 sigma and 2 pi bonds for CO?
Replies: 1
Views: 5059

Re: Why 1 sigma and 2 pi bonds for CO?

Answer: CO is the same as NO except that C has 1 less valence e-. Look at the molecular orbital diagram for NO but using 10e- instead of 11e-. Since the pi 2px and pi 2py and sigma 2pz bonding molecular orbitals are all filled there are 3 bonds. 1 sigma and 2 pi.
by Chem_Mod
Thu Aug 25, 2011 1:30 am
Forum: Sigma & Pi Bonds
Topic: Why 1 sigma and 2 pi bonds for CO?
Replies: 1
Views: 5059

Why 1 sigma and 2 pi bonds for CO?

Question: Why does the molecule CO form one sigma and two pi bonds? Doesn't this indicate that it is a triple bond, and if so wouldn't that leave the carbon atom with 1 unpaired electron and the oxygen atom with 3 unpaired electrons.
by Chem_Mod
Thu Aug 25, 2011 1:27 am
Forum: *Molecular Orbital Theory (Bond Order, Diamagnetism, Paramagnetism)
Topic: HOMO for bonding and LUMO for antibonding?
Replies: 1
Views: 921

Re: HOMO for bonding and LUMO for antibonding?

NO is an example of HOMO to LUMO transitions. HOMO and LUMO can be any type of molecular orbitals, with HOMO being the Highest Occupied Molecular Orbital and LUMO being the Lowest Unoccupied Molecular Orbital. The bond order is the number of bonds that stabilize the two bound atoms. So the higher th...
by Chem_Mod
Thu Aug 25, 2011 1:27 am
Forum: *Molecular Orbital Theory (Bond Order, Diamagnetism, Paramagnetism)
Topic: HOMO for bonding and LUMO for antibonding?
Replies: 1
Views: 921

HOMO for bonding and LUMO for antibonding?

Does HOMO have to be a bonding molecular orbital? And does the LUMO have to be an anti- bonding molecular orbital? Also: Higher bond order means greater bond strength, right? But what does bond order actually mean/ signify?
by Chem_Mod
Thu Aug 25, 2011 1:15 am
Forum: *Molecular Orbital Theory (Bond Order, Diamagnetism, Paramagnetism)
Topic: For 2 different elements, which element has lower line?
Replies: 1
Views: 201

Re: For 2 different elements, which element has lower line?

In correlation diagrams of hetronuclear diatomic molecules, the energy levels of the more electronegative atom are lower.
by Chem_Mod
Thu Aug 25, 2011 1:15 am
Forum: *Molecular Orbital Theory (Bond Order, Diamagnetism, Paramagnetism)
Topic: For 2 different elements, which element has lower line?
Replies: 1
Views: 201

For 2 different elements, which element has lower line?

When drawing molecular orbital diagrams with two different elements, what determines which element is lower down: the electronegativity or the atomic number?
by Chem_Mod
Thu Aug 25, 2011 1:10 am
Forum: Conjugate Acids & Bases
Topic: Why CH3CO2- not strong base as it's weak acid?
Replies: 1
Views: 4103

Re: Why CH3CO2- not strong base as it's weak acid?

The pKa for acetic acid is 4.75. Therefore pKb = 14 - 4.75 = 9.25 for the acetate ion and comparing to the pKb values, it is not that strong a base. The higher the pKb, the weaker the proton accepting power of the base.
by Chem_Mod
Thu Aug 25, 2011 1:10 am
Forum: Conjugate Acids & Bases
Topic: Why CH3CO2- not strong base as it's weak acid?
Replies: 1
Views: 4103

Why CH3CO2- not strong base as it's weak acid?

Why is CH3CO2- is a weak base? Shouldn't it be a strong base because its conjugate acid lies below H2O, in which the book clearly states that any base with a conjugate acid lying below H2O strong.
by Chem_Mod
Thu Aug 25, 2011 1:02 am
Forum: Properties & Structures of Inorganic & Organic Bases
Topic: Alternative to figure out base' strength except look at Kb?
Replies: 1
Views: 469

Re: Alternative to figure out base' strength except look at

Generally speaking yes, the Group 1 & 2 metal oxides and hydroxides form strong bases in aqueous soln. Going across a period, the less basic the compound. Also the greater the negative charge on an anion, the more likely it will pick up a proton and increase the [OH-].
by Chem_Mod
Thu Aug 25, 2011 1:02 am
Forum: Properties & Structures of Inorganic & Organic Bases
Topic: Alternative to figure out base' strength except look at Kb?
Replies: 1
Views: 469

Alternative to figure out base' strength except look at Kb?

Is there a way to figure out the strength of bases other than from looking at Kb and pKb values?( a way similar to figuring out the strength of acids?
by Chem_Mod
Thu Aug 25, 2011 12:13 am
Forum: Ideal Gases
Topic: How R be determined?
Replies: 1
Views: 271

Re: How R be determined?

Experimental values for a gas that is most similar to an ideal gas can be used to determine this number. Helium is a good example. One would measure the P, V, T and n and then calculate R.
by Chem_Mod
Thu Aug 25, 2011 12:12 am
Forum: Ideal Gases
Topic: How R be determined?
Replies: 1
Views: 271

How R be determined?

When discussing the individual gas laws, it was determined that V=constant*nT/P. From there we said that constant=PV/nT=8.314 J/(K*mol). How was that number determined? How was the number for the universal gas constant, R, figured it out
by Chem_Mod
Thu Aug 25, 2011 12:05 am
Forum: *Indicators
Topic: End point, stoichiometric point, and equilibrium point
Replies: 1
Views: 2792

Re: End point,stoichiometric point and equilibrium poin

Answer: Stoichiometric point: # moles H3O+(OH-) added = # moles OH-(H3O+) in a sample at the stoichiometric point in the solution contains a salt in water. End point: [HIn] = [In-] the end point of a titration is defined as the point at which the concentrations of the acid and base forms of the ind...
by Chem_Mod
Thu Aug 25, 2011 12:04 am
Forum: *Indicators
Topic: End point, stoichiometric point, and equilibrium point
Replies: 1
Views: 2792

End point, stoichiometric point, and equilibrium point

Question: What is the difference between the end point, the stoichiometric point, and the equilibrium point, and how are they related to one another?
by Chem_Mod
Thu Aug 25, 2011 12:01 am
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: When reactant-product and product-reactant?
Replies: 1
Views: 307

Re: When reactant-product and product-reactant?

The question was: Calculate the reaction enthalpy for the combustion of methane from the data below. Is the reaction exothermic or endothermic? DHB (O-H) = 463 kJ/mol DHB (C-H) = 412 kJ/mol DHB (C=O) = 743 kJ/mol DHB (O2) = 496 kJ/mol The above are bond enthalpies, that is, the energy required (+ve ...
by Chem_Mod
Thu Aug 25, 2011 12:00 am
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: When reactant-product and product-reactant?
Replies: 1
Views: 307

When reactant-product and product-reactant?

We do reactants - products when finding the reaction enthalpy. Before that we were instructed to do products - reactants. How come it is different in this question?
by Chem_Mod
Wed Aug 24, 2011 11:55 pm
Forum: Trends in The Periodic Table
Topic: Why atomic radius decreases while ionic doesn't from R to L?
Replies: 1
Views: 237

Re: Why atomic radius decrease while ionic doesn't from R to

Answer: Reading from L to R across a period, the nuclear charge increases by +1 and the number of e- increases by one. But since the e- are added to the same principle shell the atomic radius decreases. For anions, it is very different, the nuclear charge is constant while the number of e- increase...
by Chem_Mod
Wed Aug 24, 2011 11:54 pm
Forum: Trends in The Periodic Table
Topic: Why atomic radius decreases while ionic doesn't from R to L?
Replies: 1
Views: 237

Why atomic radius decreases while ionic doesn't from R to L?

Question: Atomic radius increases down a group and from right to left across a period. However, in ionic radius, cations have a smaller radius than their parent atoms because they lose e- and now occupy a shell lower in energy but how come anions have a larger ionic radius when they gain an e-. In ...
by Chem_Mod
Wed Aug 24, 2011 8:50 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Difference between reaction enthalpy & enthalpy of formation
Replies: 1
Views: 19896

Re: Difference between reaction enthalpy & enthalpy of forma

Yes there is a difference. The reaction enthalpy is the heat given off or taken up for the rxn, i.e., the enthalpy difference between the reactants and products. The enthalpy of formation of a compound is the enthalpy change between the elements in their standard state (reactants) and the compound (...
by Chem_Mod
Wed Aug 24, 2011 8:49 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Difference between reaction enthalpy & enthalpy of formation
Replies: 1
Views: 19896

Difference between reaction enthalpy & enthalpy of formation

Is there a difference between the reaction enthalpy and the enthalpy of formation? Why is the formula for the enthalpy of formation=products-reactants and the formula for the reaction enthalpy through the use of bond enthalpies (+ve for bonds broken i.e.reactants and -ve for bonds formed i.e.product...
by Chem_Mod
Wed Aug 24, 2011 12:16 am
Forum: Resonance Structures
Topic: Can we vary bonds between different elements in resonance?
Replies: 1
Views: 222

Re: Can we vary bonds between different elements in resonanc

Answer: They can be with different elements. The Cl with a double bond has a higher formal charge.
by Chem_Mod
Wed Aug 24, 2011 12:15 am
Forum: Resonance Structures
Topic: Can we vary bonds between different elements in resonance?
Replies: 1
Views: 222

Can we vary bonds between different elements in resonance?

Question: When writing resonance hybrid structures, can we vary the bonds between different elements or do they have to be between the same element? For example, can a resonance hybrid structure with a double bond between Nitrogen and Oxygen and then another structure between Nitrogen and Chlorine?
by Chem_Mod
Wed Aug 24, 2011 12:14 am
Forum: Lewis Structures
Topic: Single and triple bond in molecule
Replies: 1
Views: 260

Re: Single and triple bond in molecule

Answer: The more electronegative oxygen with a negative charge (FC=-1) is more stable than the N with a negative charge (FC=-1).
by Chem_Mod
Wed Aug 24, 2011 12:13 am
Forum: Lewis Structures
Topic: Single and triple bond in molecule
Replies: 1
Views: 260

Single and triple bond in molecule

Question: Why is the NCO- Lewis structure most stable when there is a triple bond and a single bond?
by Chem_Mod
Wed Aug 24, 2011 12:11 am
Forum: Naming
Topic: How to write chemical formula of a complex?
Replies: 1
Views: 361

Re: How to write chemical formula of a complex?

The rules are much less systematic. For example, [Co(en)2 Cl2] is more common than [CoCl2(en)2].
by Chem_Mod
Wed Aug 24, 2011 12:11 am
Forum: Naming
Topic: How to write chemical formula of a complex?
Replies: 1
Views: 361

How to write chemical formula of a complex?

How is the chemical formula for a complex written? What are the rules for the ordering of the atoms/molecules in the chemical formula?
by Chem_Mod
Wed Aug 24, 2011 12:09 am
Forum: Properties & Structures of Inorganic & Organic Acids
Topic: Why acetic acid is weaker acid than formic acid?
Replies: 1
Views: 397

Re: Why acetic acid is weaker acid than formic acid?

In the -CH3 each H is delta + which makes the C delta - which makes acetic acid slightly weaker than formic acid.
by Chem_Mod
Wed Aug 24, 2011 12:09 am
Forum: Properties & Structures of Inorganic & Organic Acids
Topic: Why acetic acid is weaker acid than formic acid?
Replies: 1
Views: 397

Why acetic acid is weaker acid than formic acid?

In what reaction does the -CH3 in acetic acid have proton donating capabilities that would make it weaker than formic acid?
by Chem_Mod
Tue Aug 23, 2011 11:33 pm
Forum: Octet Exceptions
Topic: Why expanded octet?
Replies: 1
Views: 297

Re: Why expanded octet ?

Answer: They are in the 3rd period and they do have empty 3d orbitals.
by Chem_Mod
Tue Aug 23, 2011 11:33 pm
Forum: Octet Exceptions
Topic: Why expanded octet?
Replies: 1
Views: 297

Why expanded octet?

Question: Why do S, Cl and P have expanded octets?
by Chem_Mod
Tue Aug 23, 2011 11:32 pm
Forum: *Making Buffers & Calculating Buffer pH (Henderson-Hasselbalch Equation)
Topic: Approximate Ka for ICE
Replies: 1
Views: 206

Re: Approximate Ka for ICE

Answer: Its definitely ok if K < 10-5. It's never ok if K > 10-3. If it's in between, you need to check your answer.
by Chem_Mod
Tue Aug 23, 2011 11:31 pm
Forum: *Making Buffers & Calculating Buffer pH (Henderson-Hasselbalch Equation)
Topic: Approximate Ka for ICE
Replies: 1
Views: 206

Approximate Ka for ICE

Question: When using the ICE chart, how small does K have to be in order to approximate it?
by Chem_Mod
Tue Aug 23, 2011 11:28 pm
Forum: Dipole Moments
Topic: Why is COCl2 polar?
Replies: 1
Views: 542

Re: Why is COCl2 polar?

Answer: Yes, since the dipoles do not cancel, it makes the molecule polar.
by Chem_Mod
Tue Aug 23, 2011 11:27 pm
Forum: Dipole Moments
Topic: Why is COCl2 polar?
Replies: 1
Views: 542

Why is COCl2 polar?

Question: Why is COCl2 polar? Are the electric dipoles of Cl signifigantly larger than O?
by Chem_Mod
Tue Aug 23, 2011 11:24 pm
Forum: *Indicators
Topic: Is Cu2+ acidic or basic? What indicator should be used?
Replies: 1
Views: 2070

Re: Is Cu2+ acidic or basic? What indicator should be used?

Answer: Since the oxidation state is Cu2+ it is expect to be basic. For indicators, the pK of the indicator should be equal to the stoichiometric point.
by Chem_Mod
Tue Aug 23, 2011 11:24 pm
Forum: *Indicators
Topic: Is Cu2+ acidic or basic? What indicator should be used?
Replies: 1
Views: 2070

Is Cu2+ acidic or basic? What indicator should be used?

Question: Transition metals act as Lewis acids and make hydronium ions, but O2- is also a very strong base, making hydroxides, so is CuO acidic or basic? How is an indicator chosen?
by Chem_Mod
Tue Aug 23, 2011 11:20 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: What is the geometry of CO2H2 ?
Replies: 1
Views: 424

Re: What is the geometry of CO2H2 ?

Answer: There are only three regions of electron density around C, so it is trigonal planar.
by Chem_Mod
Tue Aug 23, 2011 11:19 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: What is the geometry of CO2H2 ?
Replies: 1
Views: 424

What is the geometry of CO2H2 ?

Question: What is the geometry of CO2H2 around C? wouldn't it be trigonal planar?
by Chem_Mod
Tue Aug 23, 2011 10:50 pm
Forum: Ideal Gases
Topic: How to find delta n?
Replies: 1
Views: 19171

Re: How to find delta n?

Delta n is the difference in the number of moles of gas between reactants and products.

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