Search found 62 matches
- Sat Mar 16, 2019 2:21 pm
- Forum: First Order Reactions
- Topic: half life
- Replies: 3
- Views: 572
half life
Why is the half-life for first order reactions (t1/2=(ln2/k) independent of the initial reactant concentration [A]0, while the half-life of zero order and second order reactions are dependent? ([A]0 is included in both of their t1/2 formulas)
- Fri Mar 15, 2019 11:51 pm
- Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
- Topic: Salt bridge
- Replies: 1
- Views: 307
Re: Salt bridge
The electrolytes in a salt bridge need to be relatively unreactive with other chemicals in the cell and have cations and anions with similar migratory speed. KCl is often used because the ions K+ and Cl- are similar in size and transport numbers (.49 and .40, respectively). During the long time of o...
- Fri Mar 15, 2019 11:29 pm
- Forum: Concepts & Calculations Using First Law of Thermodynamics
- Topic: change in internal energy for isothermal process
- Replies: 1
- Views: 402
Re: change in internal energy for isothermal process
It is always true for ideal gasses. An ideal gas has no interactions between particles or intermolecular forces, so pressure change at constant temperature does not change internal energy.
- Fri Mar 15, 2019 11:28 pm
- Forum: Concepts & Calculations Using First Law of Thermodynamics
- Topic: free expansion
- Replies: 2
- Views: 500
Re: free expansion
Free expansion is an irreversible process in which a gas expands into an insulated evacuated chamber. Because it's insulated, there is no change in temperature and q=0. Because there is no external pressure and gas is moving freely, w=0 too.
- Fri Mar 15, 2019 11:24 pm
- Forum: Concepts & Calculations Using First Law of Thermodynamics
- Topic: U=0
- Replies: 6
- Views: 3164
Re: U=0
When dealing with an ideal gas (which we pretty much always are in this class), the ∆U is 0 for every isothermal process. In the case os isothermal reversible expansion, ∆U=q+w=0 so q=-w
- Fri Mar 15, 2019 10:52 pm
- Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
- Topic: H+ and OH- in cells
- Replies: 1
- Views: 195
Re: H+ and OH- in cells
Correct. If they are involved in the overall reaction they would be included in the cell diagram.
- Fri Mar 15, 2019 10:31 pm
- Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
- Topic: Most Stable Form
- Replies: 1
- Views: 493
Re: Most Stable Form
You can tell by calculating the formal charges of each bond ([# of valence electrons on atom] – [non-bonded electrons + number of bonds]). A molecule is most stable when the formal charge of as many of its bonds as possible are at or near 0.
- Fri Mar 15, 2019 10:23 pm
- Forum: Gibbs Free Energy Concepts and Calculations
- Topic: Test 2 Question 7
- Replies: 3
- Views: 553
Re: Test 2 Question 7
In both instances, they are approaching equilibrium with their surrounding temperature. It would require no input of energy for a cup of hot coffee to cool down (when it is hotter than its outside environment) or an ice cube to heat up (when it is cooler than its outside environment). Thus, both are...
- Fri Mar 15, 2019 10:16 pm
- Forum: Phase Changes & Related Calculations
- Topic: removing heat from system
- Replies: 4
- Views: 667
Re: removing heat from system
Exothermic/endothermic indicates a transfer of energy, but not always in the form of heat, so the temperature does not necessarily change.
- Fri Mar 15, 2019 10:13 pm
- Forum: Reaction Mechanisms, Reaction Profiles
- Topic: Pre-equilibrium Approach
- Replies: 2
- Views: 611
Re: Pre-equilibrium Approach
You don't account for solids or liquids in your equilibrium.
- Fri Mar 15, 2019 10:11 pm
- Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
- Topic: When to use Nernst
- Replies: 3
- Views: 370
Re: When to use Nernst
It's used to understand electron transfer when conditions aren't standard (so not occurring at 25ºC)
- Fri Mar 15, 2019 10:08 pm
- Forum: Thermodynamic Definitions (isochoric/isometric, isothermal, isobaric)
- Topic: Isometric/Isochoric
- Replies: 11
- Views: 1344
Re: Isometric/Isochoric
Yes. Bomb calorimeters are used as closed systems for constant-volume experiments.
- Fri Mar 15, 2019 10:05 pm
- Forum: General Rate Laws
- Topic: Rate laws
- Replies: 2
- Views: 352
Re: Rate laws
Yes, they are both written in terms of concentrations
- Fri Mar 15, 2019 9:59 pm
- Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
- Topic: Equation sheet
- Replies: 4
- Views: 474
Re: Equation sheet
It was for Test 2 so I'd strongly assume yes.
- Fri Mar 15, 2019 9:58 pm
- Forum: Arrhenius Equation, Activation Energies, Catalysts
- Topic: Effects of Temperature on Rate Constant
- Replies: 1
- Views: 303
Re: Effects of Temperature on Rate Constant
The source of the activation energy needed to push reactions forward is typically heat energy from the surroundings.
- Fri Mar 15, 2019 9:55 pm
- Forum: Gibbs Free Energy Concepts and Calculations
- Topic: Gibbs Free Energy
- Replies: 2
- Views: 446
Re: Gibbs Free Energy
haha yea
- Fri Mar 15, 2019 9:48 pm
- Forum: Gibbs Free Energy Concepts and Calculations
- Topic: Gibbs Free Energy
- Replies: 1
- Views: 424
- Fri Mar 15, 2019 9:47 pm
- Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
- Topic: Electrolytic cell
- Replies: 2
- Views: 264
Re: Electrolytic cell
Galvanic cells and electrolytic cells are the same thing. Problems would have to do with oxidation and reduction half reactions.
- Fri Mar 15, 2019 9:45 pm
- Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
- Topic: E equations and when to use them?
- Replies: 2
- Views: 251
Re: E equations and when to use them?
They're the same equation rearranged. You'd use one over the other depending on the information your given and the information you need to find.
- Fri Mar 15, 2019 9:40 pm
- Forum: Phase Changes & Related Calculations
- Topic: Specific heat capacity of ice
- Replies: 2
- Views: 1922
Re: Specific heat capacity of ice
Think of it as two reactions occurring, where the ice (gains heat and) is undergoing a phase change to water and water (loses heat and) is undergoing a phase change to water. Thus you would have two identical equations equal to each other except for the specific heat and enthalpies. ice: q(gain) = m...
- Fri Mar 15, 2019 9:31 pm
- Forum: Entropy Changes Due to Changes in Volume and Temperature
- Topic: Relationship b/w ∆H and ∆S
- Replies: 1
- Views: 413
Re: Relationship b/w ∆H and ∆S
Based of the Gibbs free energy equation (∆G = ∆H - T∆S) a spontaneous reaction will always occur when ∆H is negative and ∆S is positive, and a reaction will always be non-spontaneous when ∆H is positive and ∆S is negative.
- Fri Mar 15, 2019 9:28 pm
- Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
- Topic: Delta G of galvanic cells
- Replies: 2
- Views: 503
Re: Delta G of galvanic cells
Because it's a spontaneous reaction that converts electrical energy to chemical energy.
- Fri Mar 15, 2019 9:24 pm
- Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
- Topic: Oxidizing Power - Test 2
- Replies: 2
- Views: 287
Oxidizing Power - Test 2
The question asked to rank Pt, Pb, and Cu in order of increasing power going from their neutral to second oxidation state. I assumed this meant we had to switch the signs of each Eº, considering all of their reactions were listed backward. And since reducing power increases with a more negative Eº, ...
- Tue Feb 12, 2019 4:13 pm
- Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
- Topic: Bond Enthalpy and Resonance
- Replies: 1
- Views: 272
Bond Enthalpy and Resonance
For part (d) of #8.67 (6th edition) the problem is the same as part (c) except we take into account resonance. I would've assumed that we use the average of the bond enthalpies for a C--C bond (348 kJ/mol) and C==C bond (612 kJ/mol) and multiply that by 6 moles rather than add up 3 of each. However,...
- Sun Jan 27, 2019 8:02 pm
- Forum: Phase Changes & Related Calculations
- Topic: Knowing which work function to use
- Replies: 1
- Views: 155
Knowing which work function to use
How do we know when to use the work function with -P or -nRT?
- Sun Jan 27, 2019 8:01 pm
- Forum: Phase Changes & Related Calculations
- Topic: Memorizing unit conversions?
- Replies: 3
- Views: 341
Memorizing unit conversions?
The problems for chapter 8 consist of a lot of conversions between units (i.e. 1 Torr = 133.3 Pa). Should we be memorizing all of these conversions, some of them, or would they all be provided?
- Sun Jan 27, 2019 7:59 pm
- Forum: Phase Changes & Related Calculations
- Topic: 6th ed problem 8.3
- Replies: 1
- Views: 209
6th ed problem 8.3
The varieties of word table lists ∆V as being in units of m^3 but #8.3 calculates it in terms of L. Which unit should we try to use?
- Sun Jan 27, 2019 7:57 pm
- Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
- Topic: Variables affecting pH
- Replies: 2
- Views: 237
Variables affecting pH
Could someone explain which elements don't affect pH and why?
- Sun Jan 27, 2019 5:13 pm
- Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
- Topic: Factors related to acidity
- Replies: 2
- Views: 264
Factors related to acidity
Why is electronegativity proportional to acidity?
- Thu Jan 10, 2019 5:39 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: products to reactants ratio
- Replies: 1
- Views: 193
Re: products to reactants ratio
If the temperature and volume is the same in two containers, and they are undergoing the same reaction, their equilibrium constants will be the same even if they have different concentrations of reactant. If you are just looking at the ratio of product/reactant (not K, which takes into account stoic...
- Thu Jan 10, 2019 5:31 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Partial Pressure vs. Brackets
- Replies: 2
- Views: 603
Partial Pressure vs. Brackets
For problem 11.13 in the 6th edition, in the answer booklet, the quotients for (a) and (c) are written in terms of partial pressure (so P with the subscript). The answer for (b), however, is written with the molecules placed inside brackets. Is there a reason why (b) is formatted differently? Or is ...
- Wed Dec 05, 2018 11:56 pm
- Forum: Calculating pH or pOH for Strong & Weak Acids & Bases
- Topic: Sig Figs for pH
- Replies: 3
- Views: 379
Re: Sig Figs for pH
For pH, one sig fig corresponds to one decimal place (ex: 1.5) and two sig figs correspond to two decimal places (ex: 1.53) and so on. On the test, we will likely use three sig figs as per usual so answers would look like something like 1.532
- Wed Dec 05, 2018 11:52 pm
- Forum: Determining Molecular Shape (VSEPR)
- Topic: Molecular Shape
- Replies: 4
- Views: 510
Re: Molecular Shape
sorry, I meant trigonal bipyramidal, not pyramidal
- Wed Dec 05, 2018 11:43 pm
- Forum: Acidity & Basicity Constants and The Conjugate Seesaw
- Topic: Strength of Acids
- Replies: 1
- Views: 180
Re: Strength of Acids
Acids are stronger if they can more readily release H+ ions. Acetic acid is stronger because it has more to release than formic acid.
- Wed Dec 05, 2018 11:39 pm
- Forum: Naming
- Topic: Coordination Number and Central Atoms
- Replies: 1
- Views: 212
Re: Coordination Number and Central Atoms
Each atom would have their own coordination number, just like how each have their own VSEPR formula, shape, or formal charge. Any question you'd get would specify which atom it wants you to provide the coordination number for.
- Wed Dec 05, 2018 11:23 pm
- Forum: Shape, Structure, Coordination Number, Ligands
- Topic: 9C.5 (7th ed)
- Replies: 2
- Views: 313
Re: 9C.5 (7th ed)
It always helps to draw the Lewis structure for each of these molecules first. If there appears to be multiple lone pairs that a single metal ion could attach to, then it is polydentate. I've attached a drawing of what the first one would look like, which is tridentate.
- Wed Dec 05, 2018 11:16 pm
- Forum: Shape, Structure, Coordination Number, Ligands
- Topic: edta
- Replies: 1
- Views: 289
Re: edta
The extent we should know is that it's a hexadentate ligand that essentially forms a cage around metal ions by attaching to its 6 lone pair binding sites in an octahedral fashion.
- Wed Dec 05, 2018 11:06 pm
- Forum: Determining Molecular Shape (VSEPR)
- Topic: Molecular Shape
- Replies: 4
- Views: 510
Molecular Shape
IF5 has a VSEPR formula of AX5E but has a square pyramidal shape. Why doesn't it have a trigonal bipyramidal shape? Wouldn't the electron densities be more spaced out this way?
- Mon Nov 26, 2018 11:02 pm
- Forum: Hybridization
- Topic: problem 4.91
- Replies: 1
- Views: 237
problem 4.91
According to the textbook and solutions, benzyne (C6H4) is highly reactive because of the sp hybridization of two of the carbon atoms (there are two double bonds and one triple bond). Can someone explain to me how hybridization has an effect on how reactive a molecule is?
- Mon Nov 26, 2018 5:36 pm
- Forum: Sigma & Pi Bonds
- Topic: Sigma vs. pi
- Replies: 1
- Views: 214
Re: Sigma vs. pi
Their difference in strength has to do with their overlap. Sigma bonds are characterized by end-to-end overlap while pi bonds (which occur between "leftover" p-orbitals) overlap in a side-to-side fashion. As you can see in the image below, the head-on contact allows much more overlap and t...
- Mon Nov 26, 2018 5:29 pm
- Forum: Determining Molecular Shape (VSEPR)
- Topic: Bond Angles
- Replies: 1
- Views: 1050
Re: Bond Angles
When there is a lone pair present, its electron density will always cause a repulsion of the other densities, causing slightly smaller bond angles. A trigonal pyramidal molecule is essentially a tetrahedral (109.5º) where one of the bonds is replaced with a lone pair. This lone pair experiences repu...
- Mon Nov 26, 2018 5:21 pm
- Forum: Determining Molecular Shape (VSEPR)
- Topic: Octahedral
- Replies: 3
- Views: 1656
Re: Octahedral
The bond angles are all 90º. Your second guess is correct; when there are two lone pairs, the repulsions cancel out and the square planar also has 90º angles.
- Sun Nov 18, 2018 1:21 pm
- Forum: Determining Molecular Shape (VSEPR)
- Topic: Trigonal Pyramidal and it's consequences
- Replies: 1
- Views: 194
Re: Trigonal Pyramidal and it's consequences
The electron density around lone pairs are stronger than bonded pairs. Thus, the other pairs are repelled slightly from the lone pair, pushing them closer together and resulting in angles slightly less than the normal 109.5º that a tetrahedral has.
- Sun Nov 18, 2018 1:18 pm
- Forum: Determining Molecular Shape (VSEPR)
- Topic: Seesaw Bond Angles
- Replies: 3
- Views: 176
Re: Seesaw Bond Angles
The lone pair does affect the seesaw structure, actually. It pushes the linear pairs away and the trigonal planar pairs closer together. The resulting angles are slightly less than 90º and 120º.
- Wed Nov 07, 2018 4:03 pm
- Forum: Interionic and Intermolecular Forces (Ion-Ion, Ion-Dipole, Dipole-Dipole, Dipole-Induced Dipole, Dispersion/Induced Dipole-Induced Dipole/London Forces, Hydrogen Bonding)
- Topic: Bond length effect on bond strength
- Replies: 3
- Views: 512
Re: Bond length effect on bond strength
You got it! The larger an atom's radius, the longer its bond will be with another atom and the weaker the pull is between its protons and electrons.
- Wed Nov 07, 2018 2:21 pm
- Forum: Polarisability of Anions, The Polarizing Power of Cations
- Topic: Polarizing power/polarizability periodic trends
- Replies: 2
- Views: 1282
Re: Polarizing power/polarizability periodic trends
Smaller, more highly charged cations have greater polarizing power because they have a stronger pull on the electrons of ions. So you could generally say polarizing power increases up and across the periodic table in terms of cations. Polarizability increases as the anion gets larger and less electr...
- Wed Nov 07, 2018 2:12 pm
- Forum: Bond Lengths & Energies
- Topic: problem 3.85b
- Replies: 1
- Views: 310
problem 3.85b
How is it possible that SO2 and SO3 have the same bond length, as implied by the solutions manual? Doesn't SO3 have more bonds between atoms and thus longer bonds, since bond length is inversely related to the number of bonds between atoms?
- Sat Nov 03, 2018 6:45 pm
- Forum: Lewis Structures
- Topic: Memorizing chemical formulas from their names?
- Replies: 3
- Views: 342
Memorizing chemical formulas from their names?
One of the questions asks to draw the Lewis structure of a molecule but it gives the name and not the formula (i.e. ammonium chloride). Generally, will we need to know many formulas from their names? If so, which ones?
- Sun Oct 28, 2018 4:23 pm
- Forum: Ionic & Covalent Bonds
- Topic: Covalent Bonds
- Replies: 7
- Views: 675
Re: Covalent Bonds
Non-metals form anions. Their ionization energies are too high to form cations.
- Sun Oct 28, 2018 4:20 pm
- Forum: Electron Configurations for Multi-Electron Atoms
- Topic: Copper and Chromium Exception
- Replies: 1
- Views: 252
Re: Copper and Chromium Exception
When you are writing out the electron configuration for copper and chromium you'll notice their d-orbitals contain 9 electrons. It is much more stable to have the full 10 electrons, so we take away an electron from the valence s-orbital and add it to the d-orbital. Thus, instead of copper being writ...
- Sun Oct 28, 2018 4:13 pm
- Forum: Wave Functions and s-, p-, d-, f- Orbitals
- Topic: CH 3 problem 5 [ENDORSED]
- Replies: 1
- Views: 143
Re: CH 3 problem 5 [ENDORSED]
It would normally be expected for copper to have an electron configuration of [Ar]3d^9 4s^2, but since it would be a lot more stable to have a full d-orbital, it is rather written as [Ar]3d^10 4s^1. Thus, when an electron is taken away from the outermost orbital (s), it becomes a positively charged ...
- Tue Oct 23, 2018 11:58 pm
- Forum: Properties of Light
- Topic: Electromagnetic Spectrum
- Replies: 5
- Views: 631
Re: Electromagnetic Spectrum
You should have a general idea of the EM spectrum:
UV light = 100-400 nm
Visible light = 400-700 nm
Infrared = 700 nm-1 mm
UV light = 100-400 nm
Visible light = 400-700 nm
Infrared = 700 nm-1 mm
- Tue Oct 23, 2018 11:54 pm
- Forum: Bohr Frequency Condition, H-Atom , Atomic Spectroscopy
- Topic: Is there ever a negative frequency
- Replies: 1
- Views: 256
Re: Is there ever a negative frequency
There is no such thing as a negative wavelength or frequency. The negative sign you may calculate using Rydberg's equation is simply a representation of energy being either released or emitted and can be ignored in terms of frequency. Going from n=4 to n=2 emits energy, so the equation yields a nega...
- Thu Oct 18, 2018 1:48 am
- Forum: *Shrodinger Equation
- Topic: Shrodinger Equation;
- Replies: 1
- Views: 225
Re: Shrodinger Equation;
Basically... The Schrodinger Equation is used to understand the physical properties of a system. The wave function (psi) exists in three dimensions (x,y,z), so solving for psi yields three quantum numbers. These three numbers define the energy shell occupied by the electron, energy subshell, and ori...
- Wed Oct 17, 2018 8:47 pm
- Forum: Properties of Light
- Topic: Wave/particles
- Replies: 5
- Views: 440
Re: Wave/particles
As explained by wave-particle duality, light exhibits characteristics of both waves and particles. In the case of the photoelectric effect, light acts as particles, while in the case of the DeBroglie theorem, light acts as a wave. In sum, "wave" and "particles" are terms that can...
- Wed Oct 17, 2018 8:40 pm
- Forum: Bohr Frequency Condition, H-Atom , Atomic Spectroscopy
- Topic: Rydberg equation
- Replies: 4
- Views: 403
Re: Rydberg equation
It tells us how much energy is being released (as light) when an electron shifts from one energy level to another, with "n" representing the energy level. We can expect the answer to be negative when energy is being released (and the electron moves closer to the nucleus) and positive when ...
- Tue Oct 09, 2018 7:57 pm
- Forum: Properties of Light
- Topic: Do I need to memorize the Light Spectrum? [ENDORSED]
- Replies: 13
- Views: 902
Do I need to memorize the Light Spectrum? [ENDORSED]
I noticed in the homework a lot of problems asking which part of the spectrum a certain number of nm fell into (after doing a problem where you calculate the wavelength of something). For tests and such, will we need to have the spectrum memorized? Like, will I need to know that 340 nm falls in the ...
- Tue Oct 09, 2018 7:47 pm
- Forum: Properties of Light
- Topic: Problem 1.25 (c) 6th edition
- Replies: 1
- Views: 107
Re: Problem 1.25 (c) 6th edition
I'm replying to my own question because I just noticed what the issue was. Though it is not said in the manual, Avogadro's number and the photon energy are also being multiplied by 1.00 mol. This cancels out with the mol^-1.
- Tue Oct 09, 2018 7:45 pm
- Forum: Properties of Light
- Topic: Problem 1.25 (c) 6th edition
- Replies: 1
- Views: 107
Problem 1.25 (c) 6th edition
It asks to find how much energy is emitted by 1.00 mol of sodium atoms with a wavelength of 589 nm. The solutions manual says to simply multiply Avogadro's number by the energy it takes to emit a single photon of that wavelength. The units do not seem to add up, though. We just want an answer in jou...
- Thu Oct 04, 2018 3:41 pm
- Forum: Significant Figures
- Topic: Molar Mass
- Replies: 5
- Views: 415
Re: Molar Mass
I believe you always answer with 3 sig figs in it's scientific notation form. So if it's 1.201 * 10^(-1), then you would answer 12.01 for the molar mass.
- Thu Oct 04, 2018 3:35 pm
- Forum: Molarity, Solutions, Dilutions
- Topic: HW #L 11
- Replies: 1
- Views: 171
HW #L 11
For this problem, it asks to find the mass of HCl that can neutralize Mg(OH)2. In the solutions manual, it appears that we have to come up with our own formula, based on the given formula with CaCO3. How do I come up with this on my own? As in how do I know what pairs up with what?
- Thu Oct 04, 2018 3:28 pm
- Forum: SI Units, Unit Conversions
- Topic: SI Units
- Replies: 7
- Views: 517
Re: SI Units
I agree with Anushi. Whatever the given mass is in the problem is the unit you should give in your answer.