Search found 68 matches

by K Stefanescu 2I
Mon Mar 12, 2018 10:31 am
Forum: Balancing Redox Reactions
Topic: Half-reactions
Replies: 4
Views: 195

Re: Half-reactions

In most cases, yes. Just focus on flipping the reactions so you have the correct overall reaction equation (one half-reaction must be a reduction, the other an oxidation, and when added together, they must be equivalent to the original reaction).
by K Stefanescu 2I
Mon Mar 12, 2018 10:27 am
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Steady State vs. Pre-Equilibrium
Replies: 2
Views: 112

Steady State vs. Pre-Equilibrium

I am still a bit confused regarding these two ways of determining the reaction mechanism. What would a problem/question involving a steady state calculation look like? How is the pre-equilibrium approach "less flexible" than the steady-state approach?
by K Stefanescu 2I
Mon Mar 12, 2018 10:12 am
Forum: *Nucleophiles
Topic: Final Exam Topics [ENDORSED]
Replies: 1
Views: 332

Final Exam Topics [ENDORSED]

Which organic topics will be present on the final? The syllabus does not explicitly include any such topics, but we covered nucleophiles in class. What should we know for the final exam?
by K Stefanescu 2I
Sun Mar 11, 2018 10:15 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Slow Step
Replies: 3
Views: 150

Re: Slow Step

The slow step determines the rate because regardless of how fast the other steps are, the total time of the reaction can never be less than the time that has already been "spent" on the slowest step. For example, consider a reaction that has the following steps and times: Step 1- 12 second...
by K Stefanescu 2I
Sun Mar 11, 2018 10:11 pm
Forum: *Enzyme Kinetics
Topic: Enzymes
Replies: 8
Views: 587

Re: Enzymes

This is a very basic model of an enzyme in action: https://www.youtube.com/watch?v=V4OPO6JQLOE (It's a short video and has pretty nifty animation.) This demonstrates one way that enzymes can lower the activation energy, in this case by bringing the substrates together in the correct orientation so t...
by K Stefanescu 2I
Sun Mar 11, 2018 10:01 pm
Forum: *Nucleophiles
Topic: What is a nucleophile? [ENDORSED]
Replies: 6
Views: 471

Re: What is a nucleophile? [ENDORSED]

I believe Dr. Lavelle mentioned this helpful way to remember the definition in class: a nucleophile likes the (positively charged) nucleus. (This is clearly shorthand and does not go into details regarding the charge of the nucleophile, as mentioned in other posts, but can be useful in case you forg...
by K Stefanescu 2I
Sun Mar 11, 2018 9:59 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Reading a Cell Diagram
Replies: 4
Views: 266

Re: Reading a Cell Diagram

I found this resource to be incredibly useful: https://chem.libretexts.org/Core/Analyt ... taic_Cells
Open source textbooks are pretty great (and I found this one to be more concise than our textbook).
by K Stefanescu 2I
Mon Mar 05, 2018 2:02 pm
Forum: General Rate Laws
Topic: When to Use Avg. vs Instantaneous
Replies: 5
Views: 146

Re: When to Use Avg. vs Instantaneous

Dr. Lavelle has said that the instantaneous rates are used most often, so I think we are to use them on most questions, unless the question explicitly requires that we use the average rates. Can anyone confirm this?
by K Stefanescu 2I
Mon Mar 05, 2018 1:58 pm
Forum: Administrative Questions and Class Announcements
Topic: Test 3 - Chapter 15 homework
Replies: 3
Views: 174

Test 3 - Chapter 15 homework

Which questions from the homework on chapter 15 will be included on test 3? (As in, numbers a-b.)
by K Stefanescu 2I
Mon Mar 05, 2018 1:35 pm
Forum: General Rate Laws
Topic: Useful Resource
Replies: 1
Views: 87

Useful Resource

I found this simulation from Phet to be useful (and pretty fun to use):
https://phet.colorado.edu/en/simulation ... -and-rates
by K Stefanescu 2I
Mon Feb 26, 2018 6:31 pm
Forum: Student Social/Study Group
Topic: Post All Chemistry Jokes Here
Replies: 7582
Views: 1017164

Re: Post All Chemistry Jokes Here

Coming up with new material for this thread is difficult... all of the good chemistry jokes Argon.
by K Stefanescu 2I
Mon Feb 26, 2018 6:27 pm
Forum: Student Social/Study Group
Topic: Post All Chemistry Jokes Here
Replies: 7582
Views: 1017164

Re: Post All Chemistry Jokes Here

Since we are studying half-life/radioactivity....
Are you Polonium-210?
Because your ambient glow is to die for.
by K Stefanescu 2I
Mon Feb 26, 2018 4:19 pm
Forum: General Rate Laws
Topic: Examples
Replies: 3
Views: 156

Examples

What is an example of a first order rate reaction? Are there any types of reactions that we should generally know are likely to be first order ones?
by K Stefanescu 2I
Tue Feb 20, 2018 11:29 am
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: 14.15
Replies: 1
Views: 113

Re: 14.15

Reduction occurs at the cathode, while oxidation occurs at the anode. So, the metal that gains electrons is the cathode. Thus, the anode is the source of electrons (the metal loses electrons). When calculating E, remember to reverse the sign of the reduction reaction's E before adding it to the E of...
by K Stefanescu 2I
Tue Feb 20, 2018 11:22 am
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Porous Membrane vs. Salt Bridge
Replies: 1
Views: 170

Re: Porous Membrane vs. Salt Bridge

As a follow-up question, would the use of a porous membrane be written differently using IUPAC notation, compared to a salt bridge?
by K Stefanescu 2I
Tue Feb 20, 2018 11:19 am
Forum: Balancing Redox Reactions
Topic: Oxidation Agents
Replies: 4
Views: 141

Re: Oxidation Agents

The agents and what is being done to them is reversed/opposite.

oxidizing agents are themselves reduced
reducing agents are themselves oxidized
by K Stefanescu 2I
Tue Feb 20, 2018 11:18 am
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: IUPAC Notation
Replies: 1
Views: 95

IUPAC Notation

Could anyone explain the IUPAC cell notation, in a nutshell? I am still lost on where to place the different substances and when to include another metal on the outside (usually Platinum).
by K Stefanescu 2I
Thu Feb 15, 2018 7:41 pm
Forum: Balancing Redox Reactions
Topic: 14.5 d
Replies: 2
Views: 109

14.5 d

Original reaction: P4 -> H2PO2(-) + PH3 In balancing the half reaction of P4 -> H2PO2(-), why do we add OH- to the left hand side instead of beginning by adding water molecules to that side? In all of the other reactions, the standard process for balancing the number of Os has been to add water firs...
by K Stefanescu 2I
Mon Feb 12, 2018 4:53 pm
Forum: Calculating Work of Expansion
Topic: Free Expansion
Replies: 2
Views: 144

Re: Free Expansion

The condition of free expansion only tells us that w=0. q and U are not necessarily also zero in all cases of free expansion.
by K Stefanescu 2I
Mon Feb 12, 2018 4:51 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: Trouton's Rule
Replies: 1
Views: 121

Re: Trouton's Rule

Trouton's rule states that the standard entropy of many liquids is approximately 85 J/Kmol. So, to use it to determine, for example, the enthalpy of a substance, we could do the following: If liquid bromine evaporates at 59*C, what is its standard enthalpy of vaporization? Using dS=dH/T, rewrite to ...
by K Stefanescu 2I
Mon Feb 12, 2018 9:03 am
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Gibbs and Stability
Replies: 1
Views: 83

Gibbs and Stability

Why are positive G values representative of instability for the given molecule?
by K Stefanescu 2I
Mon Feb 12, 2018 8:58 am
Forum: Gibbs Free Energy Concepts and Calculations
Topic: 9.99
Replies: 1
Views: 79

9.99

How is bond energy related to Gibbs free energy, based on part b of this question involving graphs?
by K Stefanescu 2I
Mon Feb 05, 2018 7:50 am
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: Heat Capacity Value
Replies: 2
Views: 132

Heat Capacity Value

Why is the heat capacity for a monoatomic gas at constant volume C=(3/2)R? How was this derived?
by K Stefanescu 2I
Mon Feb 05, 2018 7:50 am
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: Formula
Replies: 2
Views: 123

Formula

Where did U=(3/2)nRT come from? How was it derived?
by K Stefanescu 2I
Mon Feb 05, 2018 7:48 am
Forum: Calculating Work of Expansion
Topic: Naming Question [ENDORSED]
Replies: 5
Views: 218

Naming Question [ENDORSED]

Why is reversible expansion called “reversible”?
by K Stefanescu 2I
Sun Feb 04, 2018 4:47 pm
Forum: Administrative Questions and Class Announcements
Topic: Midterm Content Question
Replies: 4
Views: 223

Midterm Content Question

What will the midterm cover (as in, up until which section of the homework)? Also, will we be asked to derive any of the equations, or just apply them?
by K Stefanescu 2I
Mon Jan 29, 2018 11:48 am
Forum: Third Law of Thermodynamics (For a Unique Ground State (W=1): S -> 0 as T -> 0) and Calculations Using Boltzmann Equation for Entropy
Topic: Degeneracy (w)
Replies: 1
Views: 143

Degeneracy (w)

On an exam, will we be given the degeneracy of a system? Or would we be asked to determine the degeneracy from a diagram/drawing of a system?
by K Stefanescu 2I
Mon Jan 29, 2018 11:42 am
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: Graphs of H and S
Replies: 2
Views: 134

Graphs of H and S

I understand why S is at a minimum at equilibrium, but why is H at a maximum when this occurs?
by K Stefanescu 2I
Mon Jan 29, 2018 11:39 am
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: Possible Question Type
Replies: 1
Views: 94

Possible Question Type

On an exam, will we ever be asked to identify the conditions of a process from the PV diagram? (Isobaric, isothermal, adiabatic, etc.?)
by K Stefanescu 2I
Mon Jan 22, 2018 12:15 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Memorizing Enthalpies [ENDORSED]
Replies: 5
Views: 166

Re: Memorizing Enthalpies [ENDORSED]

Is this also true of bond enthalpies? Or will we have to memorize common bond enthalpies (C-C, O-H, etc.)?
by K Stefanescu 2I
Mon Jan 22, 2018 12:13 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: Difference between U and H? [ENDORSED]
Replies: 3
Views: 192

Re: Difference between U and H? [ENDORSED]

Also, don't forget that U= q+ w (and any other substitutions for q and w)! So, U is the overall internal energy due to heat and work, whereas q only reflects energy due to heat.
by K Stefanescu 2I
Mon Jan 22, 2018 12:08 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Standard enthalpies of formation [ENDORSED]
Replies: 2
Views: 132

Re: Standard enthalpies of formation [ENDORSED]

In general, the complexity of the chemical formulas given on homework problems indicates that for most answers, this would not be the case. However, even though bond enthalpies are averages and not specific to the given compounds, if you have time (or want more practice), you can check your answers ...
by K Stefanescu 2I
Sun Jan 21, 2018 1:43 pm
Forum: Phase Changes & Related Calculations
Topic: Equations to know
Replies: 6
Views: 218

Re: Equations to know

Will we also be given all of the enthalpy values needed to solve a problem? Are there ANY enthalpy values we should memorize (besides which ones are zero)?
by K Stefanescu 2I
Sun Jan 21, 2018 1:37 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Exam Questions on Reaction Enthalpies [ENDORSED]
Replies: 1
Views: 141

Exam Questions on Reaction Enthalpies [ENDORSED]

When asked to calculate the reaction enthalpy for a particular reaction, will we be given the reactions prior to it (as in question 8.61) or will we be expected to write the preceding reactions for each reactant and product (as in 8.57)?
by K Stefanescu 2I
Fri Jan 12, 2018 2:57 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Question 8.117
Replies: 1
Views: 129

Question 8.117

What is the rationale behind the solution manual's answer? The original question is as follows: One step in the production of hydrogen as a fuel is the reaction of methane with water vapor: CH4(g) + H2O(g) --> CO2(g) + 3H2(g)   H=- 318 kJ What is the change in internal energy for the production of 1...
by K Stefanescu 2I
Thu Jan 11, 2018 9:18 am
Forum: Phase Changes & Related Calculations
Topic: General Question
Replies: 3
Views: 192

General Question

What is the difference between q and H? When is each used?
by K Stefanescu 2I
Thu Jan 11, 2018 9:16 am
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Standard Enthalpies vs. Bond Enthalpies Equations
Replies: 1
Views: 85

Standard Enthalpies vs. Bond Enthalpies Equations

Why does solving problems involving standard enthalpies take the form of H= H(products)-H(reactants) while problems involving bond enthaplies take the form of H= H(bonds in reactants)- H(bonds in products)?
by K Stefanescu 2I
Mon Jan 08, 2018 5:07 pm
Forum: Phase Changes & Related Calculations
Topic: Temperature and Exothermic Reaction [ENDORSED]
Replies: 4
Views: 218

Re: Temperature and Exothermic Reaction [ENDORSED]

If the vessel/beaker holding the reaction is placed in a temperature-controlled tub, then as the exothermic reaction is giving off heat, the sensor controlling the temperature of the tub will make it so the tub itself always remains at the same temperature. It will adjust to make up for the extra he...
by K Stefanescu 2I
Mon Jan 08, 2018 3:47 pm
Forum: Phase Changes & Related Calculations
Topic: Question 8.25
Replies: 4
Views: 226

Question 8.25

Quesiton: A constant-volume calorimeter was calibrated by carrying out a reaction known to release 3.50 kJ of heat in 0.200 L of solution in the calorimeter (q=-3.50 kJ), resulting in a temperature rise of 7.32 degrees C. In a subsequent experiment, 100.0 mL of 0.200 m HBr(aq) and 100.0 mL of 0.200 ...
by K Stefanescu 2I
Mon Jan 08, 2018 3:14 pm
Forum: Phase Changes & Related Calculations
Topic: Question 8.11
Replies: 1
Views: 121

Question 8.11

I understood how to calculate the different values for work required to answer the problem. However, I was wondering: is there a purely theoretical reason why a reversible reaction would do more work than an irreversible one?
by K Stefanescu 2I
Mon Dec 04, 2017 9:49 am
Forum: Bronsted Acids & Bases
Topic: Donating protons versus electrons [ENDORSED]
Replies: 1
Views: 133

Re: Donating protons versus electrons [ENDORSED]

It is the inverse of what you stated. A Bronsted acid is a specific type of Lewis acid. Consider the reaction NH3+HCl<-> NH4+ +Cl- A Bronsted acid is a proton donor, so it will donate H+. In this case, HCl is the acid, as it donates its H+ to NH3. A Lewis acid is an electron acceptor. For HCl to dis...
by K Stefanescu 2I
Mon Dec 04, 2017 9:29 am
Forum: Bronsted Acids & Bases
Topic: Proton donor/acceptor [ENDORSED]
Replies: 1
Views: 147

Re: Proton donor/acceptor [ENDORSED]

A molecule can be a proton donor if, when interacting with another molecule of a different substance, it gives away an H+ (a hydrogen atom without its electron, so the only charge in the atom is the + charge of the proton in the nucleus). These molecules are considered Bronstef acids. When in an aqu...
by K Stefanescu 2I
Mon Nov 27, 2017 9:45 am
Forum: Non-Equilibrium Conditions & The Reaction Quotient
Topic: Endothermic vs. Exothermic [ENDORSED]
Replies: 1
Views: 149

Endothermic vs. Exothermic [ENDORSED]

If the question does not tell us, how are we to identify if a reaction is exothermic or endothermic?
by K Stefanescu 2I
Mon Nov 27, 2017 9:43 am
Forum: Equilibrium Constants & Calculating Concentrations
Topic: 11.14
Replies: 1
Views: 143

Re: 11.14

Either one should be correct. I believe that you would want to use the concentration (Kc), given that it is in a liquid.
by K Stefanescu 2I
Mon Nov 20, 2017 9:49 am
Forum: Lewis Structures
Topic: Question 4.5
Replies: 2
Views: 135

Question 4.5

The question asks us to determine the shape of ClO2+ and determine its bond angle. However, my question pertains only to determining the Lewis structure of the compound. The book lists the following as the correct Lewis structure- .. .. .. :O - Cl - O: .. .. Why wouldn't it be the following? .. .. ....
by K Stefanescu 2I
Mon Nov 20, 2017 9:40 am
Forum: Naming
Topic: 17.31d
Replies: 4
Views: 246

Re: 17.31d

For sodium bisoxalato(diaqua)ferrate (III), start with the first part of the name. Sodium's separation from the name of the compound implies that it is outside of the brackets. Na [ Then, inside of the brackets, start with the first portion of the name (this will be rearranged later). Bis implies th...
by K Stefanescu 2I
Mon Nov 13, 2017 12:12 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: VSEPR for four electron densities
Replies: 2
Views: 124

Re: VSEPR for four electron densities

Trigonal pyramidal structures have 4 regions of electron density, but one of those regions is a lone pair instead of a bonded atom. In contrast, tetrahedral structures have 4 regions of electron density that are all "attached" to a bonded atom. I believe that hybridization of the central a...
by K Stefanescu 2I
Mon Nov 13, 2017 12:09 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Question 4.25
Replies: 2
Views: 248

Re: Question 4.25

1) Draw the Lewis structures of the molecules in the question. 2) Determine which bonds have the greatest difference in electronegativity (for example, C-Cl has a greater difference than C-H). 3) Draw the dipole moments for those bonds of greatest electronegativity difference. 4)Compare the directio...
by K Stefanescu 2I
Mon Nov 06, 2017 9:15 am
Forum: Trends in The Periodic Table
Topic: Electron Affinity [ENDORSED]
Replies: 6
Views: 455

Re: Electron Affinity [ENDORSED]

Regarding electronegativity and electron affinity, don't forget that if both of these values are high for an element, it will also have a high ionization energy. Ionization energy also follows both of these trends: increasing left to right and up each group.
by K Stefanescu 2I
Mon Nov 06, 2017 9:11 am
Forum: Administrative Questions and Class Announcements
Topic: Midterm Materials [ENDORSED]
Replies: 7
Views: 415

Midterm Materials [ENDORSED]

Are we to purchase a blue book for the upcoming midterm, or will it be similar to previous exams when all answers were written on the exam?
by K Stefanescu 2I
Mon Oct 30, 2017 5:13 pm
Forum: Electron Configurations for Multi-Electron Atoms
Topic: Ground state vs. Excited State
Replies: 2
Views: 226

Re: Ground state vs. Excited State

Most questions I've seen so far tell you if it is excited or not. From an Aufbau diagram, if there is an electron in a shell of higher energy than expected for the element (which you can determine from the electron configuration), then it is excited. Also, if unpaired electrons in a shell do not exh...
by K Stefanescu 2I
Mon Oct 30, 2017 5:08 pm
Forum: Lewis Structures
Topic: 3.39
Replies: 2
Views: 151

Re: 3.39

It is because they are ionic bonds, not covalent.
by K Stefanescu 2I
Mon Oct 23, 2017 9:23 am
Forum: Wave Functions and s-, p-, d-, f- Orbitals
Topic: Orbitals and quantum numbers
Replies: 1
Views: 106

Re: Orbitals and quantum numbers

If n=3, then l can be any integer less than and including n-1, including 0. So, the allowed values for l are 0, 1, and 2. In this case, l cannot be 3. If you are asked to give the allowed values for l, list them as follows: 0, 1, 2. These l values correspond to orbitals s, p, and d, as you said. If ...
by K Stefanescu 2I
Mon Oct 23, 2017 7:53 am
Forum: Electron Configurations for Multi-Electron Atoms
Topic: EC Order Clarification
Replies: 2
Views: 146

Re: EC Order Clarification

Assume that the lower shells are filled first. I have also always used that chart and find it helpful- just remember to reorganize the levels so they increase at the end. And if there is an instance in which electrons can fill either a high 4 sub shell or a low 5 subshell, fill the high 4 subshell f...
by K Stefanescu 2I
Tue Oct 17, 2017 8:16 pm
Forum: DeBroglie Equation
Topic: CHAPTER 1 QUESTION 33!!!
Replies: 8
Views: 433

Re: CHAPTER 1 QUESTION 33!!!

E=hv only applies to photons, since it uses the definition of v that is consistent with vw=c (with w=wavelength, v=frequency, and c=speed of light). This equation does not apply to electrons. E=0.5mV^2 applies to particles that have mass, such as electrons. It is the same with deBroglie's equation, ...
by K Stefanescu 2I
Tue Oct 17, 2017 7:48 pm
Forum: Photoelectric Effect
Topic: Photoelectric Effect as Proof of Particle Qualities of Light
Replies: 3
Views: 254

Re: Photoelectric Effect as Proof of Particle Qualities of Light

Electrons will not be emitted from the metal unless EACH photon of light has sufficient energy. This was proven by the fact that simply increasing the intensity of a light source did not result in more electrons being emitted. If light had been acting as a wave, increasing the intensity (and therefo...
by K Stefanescu 2I
Mon Oct 16, 2017 9:15 pm
Forum: Bohr Frequency Condition, H-Atom , Atomic Spectroscopy
Topic: Identifying radiation based on a wavelength
Replies: 3
Views: 183

Re: Identifying radiation based on a wavelength

We must know the visible light spectrum (700-400 nm). Anything greater than 700 is infrared, values slightly below 400 fall into the UV spectrum. I don't believe we need to know the spectrum to the extent of differentiating microwaves and x-rays...
by K Stefanescu 2I
Mon Oct 16, 2017 9:13 pm
Forum: Photoelectric Effect
Topic: Hey I stumbled upon these questions. Please help!
Replies: 4
Views: 387

Re: Hey I stumbled upon these questions. Please help!

23. C- photons must change to from a wave model to a particle model. If they had been consistent with waves, increasing the intensity (I) would have caused more electrons to be emitted from the metal, given that I is proportional to A^2 (amplitude squared). However, despite increasing the intensity ...
by K Stefanescu 2I
Mon Oct 16, 2017 9:10 pm
Forum: Bohr Frequency Condition, H-Atom , Atomic Spectroscopy
Topic: Atomic Spectra Module Q 29
Replies: 2
Views: 267

Re: Atomic Spectra Module Q 29

This question is similar to 1.27, for further practice/reference. a) The words "energy per photon" should bring to mind the formula E=hv. Because we have been given the wavelength instead of frequency, we must rewrite the formula by substituting v=c/w. (I am using w to denote wavelength.) ...
by K Stefanescu 2I
Wed Oct 11, 2017 9:26 am
Forum: Heisenberg Indeterminacy (Uncertainty) Equation
Topic: Post Module Q. 14
Replies: 3
Views: 264

Re: Post Module Q. 14

I think the answer should be D rather than C because Heisenberg's uncertainty equation inherently requires some movement (given that p= mass* velocity of some sort) in order to solve for the position of the particle in question. If the position is given and momentum is being solved for, velocity/spe...
by K Stefanescu 2I
Mon Oct 09, 2017 7:55 pm
Forum: Properties of Light
Topic: Amplitude of the wave [ENDORSED]
Replies: 7
Views: 516

Re: Amplitude of the wave [ENDORSED]

Yes, the light will be brighter. Intensity is a measure of brightness. However, with regard to the photoelectric effect, as others have stated, a brighter light does not result in a greater number of electrons being ejected from a metal. Rather, the energy of each photon will determine a light sourc...
by K Stefanescu 2I
Mon Oct 09, 2017 12:54 pm
Forum: Bohr Frequency Condition, H-Atom , Atomic Spectroscopy
Topic: Using the Rydberg Equation
Replies: 4
Views: 255

Using the Rydberg Equation

On question 1.15, I understood how to solve for n1 and n2 in every respect besides why we assume that n1=1. The way the textbook solves it requires that we assume n1=1 in order to find n2=3. Why is this the case? Does this apply in every scenario?
Thank you in advance.
by K Stefanescu 2I
Thu Oct 05, 2017 10:35 pm
Forum: Accuracy, Precision, Mole, Other Definitions
Topic: #of molecules/atoms/formula units
Replies: 3
Views: 238

Re: #of molecules/atoms/formula units

It depends heavily on the question. You must read carefully, particularly when the question is specifying that it wants a particular number of atoms as opposed to molecules (H vs. H2O, for example). Depending on the ratio of atoms within a given compound, reading the question carefully can save you ...
by K Stefanescu 2I
Tue Oct 03, 2017 7:07 pm
Forum: Significant Figures
Topic: Sig Figs in 0.0380 [ENDORSED]
Replies: 5
Views: 388

Re: Sig Figs in 0.0380 [ENDORSED]

The last 0 is considered significant. For further clarification, here are a few examples: 0.05 = 1sf (the 5) 0.00478 = 3sf (the 478, so any zeroes before these non-zero numbers are not counted) 678.0 = 4sf (the 0 after the decimal point is considered significant because it came after non-zero number...
by K Stefanescu 2I
Tue Oct 03, 2017 10:56 am
Forum: Empirical & Molecular Formulas
Topic: F.23 Question [ENDORSED]
Replies: 5
Views: 421

Re: F.23 Question [ENDORSED]

Yes. For example, for ethene, the mass percentage of carbon would be calculated as follows: ((2* 12.011)/(2*12.011 + 2*1.008)) * 100= 92.3% I think that most questions requesting mass percentage require that the answer be given as a percentage. I would do so in any case, just to be safe. Don't forge...
by K Stefanescu 2I
Mon Oct 02, 2017 8:08 pm
Forum: Molarity, Solutions, Dilutions
Topic: Help with G13 Homework Problem
Replies: 2
Views: 228

Re: Help with G13 Homework Problem

Your solution is correct in terms of molarity (M), which is 0.050M NH4NO3. However, the question requires that you calculate the amount of N atoms received in moles. To do this, start by determining the moles of NH4NO3 received by each plant. As n=MV, plug in your final values for these (I prefer to...
by K Stefanescu 2I
Mon Oct 02, 2017 1:44 pm
Forum: Limiting Reactant Calculations
Topic: Question M.1 [ENDORSED]
Replies: 5
Views: 753

Re: Question M.1 [ENDORSED]

You are correct that you must calculate the mass of hydrazine produced from 35.0g of ammonia. You will find that this resultant theoretical yield does not match the 25.2g of hydrazine actually produced. Thus, you must determine percent yield by dividing the actual yield (given) by the theoretical yi...

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