Search found 63 matches
- Sat Mar 16, 2019 12:08 am
- Forum: Entropy Changes Due to Changes in Volume and Temperature
- Topic: 9.13
- Replies: 1
- Views: 437
9.13
During the test of an internal combustion engine, 3.00 L of nitrogen gas at 18.5 C was compressed suddenly (and irreversibly) to 0.500 L by driving in a piston. In the process, the temperature of the gas increased to 28.1 C. Assume ideal behavior. What is the change in entropy of the gas? How can yo...
- Thu Mar 14, 2019 11:08 pm
- Forum: Arrhenius Equation, Activation Energies, Catalysts
- Topic: A in the Arrhenius Equation
- Replies: 4
- Views: 371
Re: A in the Arrhenius Equation
it is the frequency factor, and basically gives the frequency with which reactants will collide in the correct orientation in order to form product.
- Thu Mar 14, 2019 11:01 pm
- Forum: General Rate Laws
- Topic: Final
- Replies: 9
- Views: 1028
Re: Final
I don't think so, but on previous exams/midterm sig figs weren't counted for every problem, only for 1-2
you always need the correct units though!
you always need the correct units though!
- Thu Mar 14, 2019 11:00 pm
- Forum: Kinetics vs. Thermodynamics Controlling a Reaction
- Topic: Overall Order
- Replies: 5
- Views: 691
Re: Overall Order
you can use it to determine how the overall rate will change with a change in reactant concentration
- Mon Mar 11, 2019 11:36 am
- Forum: General Rate Laws
- Topic: Are coefficients in rate laws?
- Replies: 2
- Views: 271
Re: Are coefficients in rate laws?
They don't affect the rate law itself, but do effect the value of k as you need to know the ratio of moles produced/used during the reaction to find k.
- Mon Mar 11, 2019 11:34 am
- Forum: Ideal Gases
- Topic: Ideal gases
- Replies: 5
- Views: 413
Re: Ideal gases
For the most part, yes. The questions should say "assume ideal behavior."
- Mon Mar 11, 2019 11:32 am
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Equilibrium Constanst
- Replies: 3
- Views: 361
Re: Equilibrium Constanst
the units on the rate constant k must ensure that the overall units for the rate is (g/mol)/s.
- Mon Mar 04, 2019 4:22 pm
- Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
- Topic: Nernst Equation (log vs. ln)
- Replies: 5
- Views: 6425
Re: Nernst Equation (log vs. ln)
do both yield the same results?
- Mon Mar 04, 2019 4:19 pm
- Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
- Topic: Nernst
- Replies: 6
- Views: 523
Re: Nernst
also, log is used when dealing with pH
- Mon Mar 04, 2019 4:15 pm
- Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
- Topic: 6th edition example 14.8
- Replies: 1
- Views: 235
Re: 6th edition example 14.8
No. Ecell = Ecath - Eanode, where the E values are for the reduction reaction (so you don't make anything negative), which is the method used in the book. Ecell = Ecath + Ean when you add the actual potentials for each half-reaction. Either method will yield the same answer.
- Sun Feb 24, 2019 9:07 pm
- Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
- Topic: Spontaneous?
- Replies: 13
- Views: 1464
Re: Spontaneous?
Enthalpy doesn't really show spontaneity, except that exothermic reactions are generally spontaneous because delta S is usually positive for these reactions.
A positive entropy generally indicates a spontaneous process, but only with a negative delta G can you be sure.
A positive entropy generally indicates a spontaneous process, but only with a negative delta G can you be sure.
- Sun Feb 24, 2019 9:05 pm
- Forum: Balancing Redox Reactions
- Topic: Hydrogen?
- Replies: 3
- Views: 289
Re: Hydrogen?
Hydrogen has only 1 valence electron. When combined with a less-electronegative element (eg. a metal), it gains another to complete its p-orbital, giving it an oxidation state of -1. In other cases, it loses its electron, giving it an oxidation state of +1. Since there is only 1 electron to begin wi...
- Sun Feb 24, 2019 9:02 pm
- Forum: Balancing Redox Reactions
- Topic: Balancing Redox Reactions
- Replies: 1
- Views: 214
Re: Balancing Redox Reactions
First, write out the half-reactions and balance each as you normally would. Then, balance it so the charges on both sides add up to the same number.
- Sun Feb 24, 2019 12:36 pm
- Forum: Gibbs Free Energy Concepts and Calculations
- Topic: Spontaneous with Temperature Increase?
- Replies: 2
- Views: 400
Spontaneous with Temperature Increase?
Can a nonspontaneous process with a positive deltaS become spontaneous if the temperature is increased (assuming that deltaH and deltaS are both independent of temperature)?
- Wed Feb 20, 2019 4:18 pm
- Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
- Topic: Salt Bridge
- Replies: 3
- Views: 318
Re: Salt Bridge
what is the difference between a salt bridge and porous disk?
- Wed Feb 20, 2019 4:12 pm
- Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
- Topic: Anode v. Cathode
- Replies: 9
- Views: 905
Re: Anode v. Cathode
what is the difference between an anode and cathode?
- Wed Feb 20, 2019 4:11 pm
- Forum: Balancing Redox Reactions
- Topic: Separating the equation
- Replies: 5
- Views: 474
Re: Separating the equation
Why would you separate the equation? Like how would this make it easier?
- Sun Feb 10, 2019 6:27 pm
- Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
- Topic: when to use kj and kj.mol^-1
- Replies: 2
- Views: 1753
Re: when to use kj and kj.mol^-1
enthalpies of formation are always given /mol. As for reaction enthalpies, I believe that they're generally given in just kJ because it's for the entire reaction (so there are multiple moles of substances used).
- Sun Feb 10, 2019 6:26 pm
- Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
- Topic: Enthalpy of Phase Changes
- Replies: 4
- Views: 381
Re: Enthalpy of Phase Changes
More and more energy (heat) is required to attain higher energy phases because you have to separate the molecules more. in terms of energy, solids < liquids < gases. Therefore, the enthalpy of fusion is less than that of vaporization.
- Sun Feb 10, 2019 6:23 pm
- Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
- Topic: Problem #8.59 (Sixth Edition)
- Replies: 3
- Views: 371
Re: Problem #8.59 (Sixth Edition)
The standard enthalpy of formation for N2 is 0! All elements in their standard states (N2, O2, etc.) have a standard enthalpy of formation of 0
- Sat Feb 02, 2019 9:26 pm
- Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
- Topic: Compression of Gas
- Replies: 4
- Views: 411
Re: Compression of Gas
why does work being done correlate to heat being added?
- Sat Feb 02, 2019 9:25 pm
- Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
- Topic: delta H vs q
- Replies: 9
- Views: 856
delta H vs q
What is the difference between and q? How are they related?
- Sat Feb 02, 2019 9:21 pm
- Forum: Concepts & Calculations Using First Law of Thermodynamics
- Topic: U=q+w
- Replies: 3
- Views: 392
Re: U=q+w
Delta U is the change in internal energy of a system. The equation states that Delta U is equal to the heat lost/gained (q) plus the work done on or by the system (w). This is because the only way for a system to lose internal energy is through heat or work.
- Sun Jan 27, 2019 9:18 pm
- Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
- Topic: Ph and Pka
- Replies: 5
- Views: 378
Re: Ph and Pka
You could use Pka and an ICE table if necessary to find [H3O+].
- Sun Jan 27, 2019 9:15 pm
- Forum: Phase Changes & Related Calculations
- Topic: Steam v. Boiling Water
- Replies: 4
- Views: 372
Re: Steam v. Boiling Water
The energy to boil water is (energy to melt) + (energy to boil).
The energy to have steam is (energy to boil) + (energy to vaporize)
Therefore, more energy (and thus, more heat) is required to form steam, which is why the burns are more severe.
The energy to have steam is (energy to boil) + (energy to vaporize)
Therefore, more energy (and thus, more heat) is required to form steam, which is why the burns are more severe.
- Sun Jan 27, 2019 9:12 pm
- Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
- Topic: Standard Enthalpy
- Replies: 1
- Views: 176
Re: Standard Enthalpy
Dr. Lavelle said in class that those values will be given.
- Mon Jan 21, 2019 12:21 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: buffer questions on test
- Replies: 7
- Views: 485
Re: buffer questions on test
What exactly do we need to know about them?
- Mon Jan 21, 2019 12:21 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Kp vs Kc
- Replies: 7
- Views: 694
Re: Kp vs Kc
If all the reactants/products are gases, it doesn't matter which you use. However, Kc and Kp are not always equal! This is due to concentration and Pressure being related via the Ideal Gas Law (PV = nRT) This link explains the technicalities of it well: https://chem.libretexts.org/Bookshelves/Physic...
- Mon Jan 21, 2019 12:17 pm
- Forum: Non-Equilibrium Conditions & The Reaction Quotient
- Topic: Buffer Solutions
- Replies: 2
- Views: 229
Re: Buffer Solutions
Buffer solutions are used to keep the pH constant. To my understanding, you don't "ignore" the salt, but because it is a buffer, it doesn't affect pH / affect [H3O+] and factor into the ICE table.
- Sun Jan 13, 2019 6:37 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: ICE Tables
- Replies: 2
- Views: 286
Re: ICE Tables
For A\rightleftharpoons B + C To make an ICE table, first enter all the numbers you are given into the table, and add in 0 in the "Initial" column if they're not given and there's no way to calculate it (you would be able to calculate it if you have Q, for example). If you're given an equi...
- Sun Jan 13, 2019 6:12 pm
- Forum: Ideal Gases
- Topic: Definition of an Ideal Gas [ENDORSED]
- Replies: 2
- Views: 243
Definition of an Ideal Gas [ENDORSED]
What are the conditions for an Ideal Gas in terms of Temperature/Pressure/Volume etc?
- Sun Jan 13, 2019 6:11 pm
- Forum: Ideal Gases
- Topic: Pressure and Temperature [ENDORSED]
- Replies: 2
- Views: 409
Pressure and Temperature [ENDORSED]
According to the Ideal Gas Law, P = nRT/V. Therefore, P and T are directly proportional. My question is, conceptually, how/why does an increase in Pressure cause and increase in Temperature and vice-versa?
- Sun Dec 09, 2018 4:38 pm
- Forum: Properties & Structures of Inorganic & Organic Acids
- Topic: Why HF is a weaker acid than HCl
- Replies: 17
- Views: 15974
Re: Why HF is a weaker acid than HCl
By that same logic, would HClO2 be weaker than HClO3?
- Fri Dec 07, 2018 12:17 am
- Forum: Calculating pH or pOH for Strong & Weak Acids & Bases
- Topic: pH for strong acids [ENDORSED]
- Replies: 2
- Views: 267
Re: pH for strong acids [ENDORSED]
It can be assumed that given a strong acid, it completely dissociates in solution, and therefore the pH is -log[H3O+] (we don't have to worry about the Ka values or anything like that).
- Fri Dec 07, 2018 12:14 am
- Forum: Amphoteric Compounds
- Topic: Definition
- Replies: 6
- Views: 575
Re: Definition
Yes -an amphoteric substance like water would act like a base or an acid depending on what it is reacting with.
- Tue Dec 04, 2018 9:21 pm
- Forum: Shape, Structure, Coordination Number, Ligands
- Topic: Denticity from lewis structure or VSEPR
- Replies: 1
- Views: 146
Denticity from lewis structure or VSEPR
Is there a way to tell denticity of a ligand from its lewis structure or VSEPR shape? How do you find denticity otherwise?
- Sun Dec 02, 2018 10:50 pm
- Forum: Properties & Structures of Inorganic & Organic Acids
- Topic: Acid + Base Reaction
- Replies: 1
- Views: 206
Acid + Base Reaction
Do all bases neutralize acids and vice-versa? Or does the strength of the acid/base affect how they react?
- Sun Dec 02, 2018 10:49 pm
- Forum: Properties & Structures of Inorganic & Organic Acids
- Topic: Water
- Replies: 4
- Views: 491
Water
Does water have a neutral pH because it can act as an acid or base depending on the situation?
- Sun Dec 02, 2018 10:45 pm
- Forum: Properties & Structures of Inorganic & Organic Acids
- Topic: "Bronsted" and "Lewis" Interchangability
- Replies: 2
- Views: 256
Re: "Bronsted" and "Lewis" Interchangability
But both Bronsted and Lewis acids dissociate into Hydronium ions in water, correct?
- Sun Dec 02, 2018 10:39 pm
- Forum: Properties & Structures of Inorganic & Organic Acids
- Topic: "Bronsted" and "Lewis" Interchangability
- Replies: 2
- Views: 256
"Bronsted" and "Lewis" Interchangability
Are all Lewis acids bronsted acids and vice-versa? Is the same true for Bases?
- Sun Dec 02, 2018 10:34 pm
- Forum: Properties & Structures of Inorganic & Organic Acids
- Topic: Biological Compounds
- Replies: 3
- Views: 301
Re: Biological Compounds
it wouldn't make sense for a Nitrogen lone pair to act as an acid, as acids are e- pair acceptors by definition, not donors.
- Sun Dec 02, 2018 10:33 pm
- Forum: Properties & Structures of Inorganic & Organic Acids
- Topic: Acids for final
- Replies: 2
- Views: 205
Re: Acids for final
Probably the ones mentioned in class -- Carboxylic as the most common Organic acid, HBr/HCl/etc as strong acids, and CH3COOH (acetic) as an example of a weak acid
For bases, you should probably know the Alkali/Alkaline Earth metals as strong bases and NH3/Ammines as weak bases
For bases, you should probably know the Alkali/Alkaline Earth metals as strong bases and NH3/Ammines as weak bases
- Wed Nov 21, 2018 11:28 am
- Forum: Hybridization
- Topic: Hybrid orbitals pointing to corners?
- Replies: 4
- Views: 252
Re: Hybrid orbitals pointing to corners?
Because of electron repulsion, to maximize distance the orbitals end up "pointing to the corners."
- Wed Nov 21, 2018 11:24 am
- Forum: Hybridization
- Topic: Sp3
- Replies: 2
- Views: 267
Re: Sp3
there are 3 p-orbitals, each holding up to 2e-, for a total of 6 electrons, not 6 orbitals.
- Wed Nov 21, 2018 11:22 am
- Forum: Hybridization
- Topic: What is s-character of an orbital? (6th ed, 4.43)
- Replies: 1
- Views: 203
What is s-character of an orbital? (6th ed, 4.43)
The question reads, "Noting that the bond angle of an sp3 hybridized atom is 109.5 and that of an sp2 hybridized atom is 120, do you expect the bond angle between two hybrid orbitals to increase or decrease as the s-character of the hybrids is increased?" What is the s-character of a hybri...
- Sun Nov 11, 2018 12:51 pm
- Forum: Bond Lengths & Energies
- Topic: Bond Length
- Replies: 9
- Views: 936
Re: Bond Length
I don't think so. By definition, single bonds are generally longer than double bonds, especially between the same elements.
- Sun Nov 11, 2018 12:50 pm
- Forum: Dipole Moments
- Topic: Polarizable vs Polarizing Ability
- Replies: 3
- Views: 489
Polarizable vs Polarizing Ability
What is the difference between these two terms, and what they have to do with electronegativity?
- Sun Nov 11, 2018 12:32 pm
- Forum: Bond Lengths & Energies
- Topic: VSEPR Model for Water
- Replies: 3
- Views: 374
VSEPR Model for Water
Why isn't H2O a linear molecule, but CO2 (for example) is? How do we know the bond angle isn't 180?
- Sat Nov 03, 2018 10:26 am
- Forum: Lewis Structures
- Topic: Resonance Structures
- Replies: 1
- Views: 122
Resonance Structures
I'm still a little confused on how to find resonance structures. How can you tell how many resonance structures a molecule has / which structure is the most stable?
- Sat Nov 03, 2018 10:22 am
- Forum: Ionic & Covalent Bonds
- Topic: Delta Negative
- Replies: 2
- Views: 170
Re: Delta Negative
When atoms covalently bonded unequally share electrons (occurs in any bond with atoms of different elements), the more electronegative atom "pulls" the shared e- towards them, giving that side of the molecule a slight negative charge. Similarly, the less electronegative atom ends up with a...
- Sat Nov 03, 2018 10:17 am
- Forum: Electron Configurations for Multi-Electron Atoms
- Topic: Nickel/Vanadium alternate configuration
- Replies: 1
- Views: 241
Nickel/Vanadium alternate configuration
I understand why Chromium and Copper don't follow the electron configuration pattern, but my question is, why do Vanadium and Nickel? Their electron configurations are [Ar]3d3 4s2 and [Ar]3d8 4s2 respectively, but wouldn't [Ar]3d5 and [Ar]3d10 be more stable? Or is it because they need electrons in ...
- Sun Oct 28, 2018 9:45 pm
- Forum: Lewis Structures
- Topic: Lewis Structure for Compounds
- Replies: 6
- Views: 413
Lewis Structure for Compounds
In Class, Dr. Lavelle mentioned that you should not draw 2 cations next to each other when drawing the lewis dot structure of an ionic compound. Why is that?
- Sun Oct 28, 2018 9:40 pm
- Forum: Ionic & Covalent Bonds
- Topic: Variable Valence
- Replies: 2
- Views: 84
Re: Variable Valence
Why do they have a tendency to form multiple ions? Also, are elements that form ions w/ variable valence all transition metals?
- Sun Oct 28, 2018 9:37 pm
- Forum: Ionic & Covalent Bonds
- Topic: Atomic Radius Decreasing
- Replies: 2
- Views: 196
Atomic Radius Decreasing
I'm still confused as to why atomic radius decreases across a period. Shouldn't more electrons being added to new orbitals increase the size?
- Sat Oct 20, 2018 5:59 pm
- Forum: Properties of Light
- Topic: Photoelectric Effect result
- Replies: 2
- Views: 357
Photoelectric Effect result
How was the fact that long wavelengths, regardless of intensity, could not eject an e-, but shorter wavelengths could used to determine that light can be quantized as photons? What is the reasoning behind this conclusion?
- Sat Oct 20, 2018 5:57 pm
- Forum: Bohr Frequency Condition, H-Atom , Atomic Spectroscopy
- Topic: energy difference vs. E subscript n
- Replies: 2
- Views: 1221
Re: energy difference vs. E subscript n
So to calculate deltaE from, for example, the second to the first energy level, it would be E(subscript)2 - E1?
- Sat Oct 20, 2018 5:52 pm
- Forum: Properties of Light
- Topic: Atomic Spectra
- Replies: 3
- Views: 257
Re: Atomic Spectra
Do emission and absorption spectra look the same? Or are they "opposites" of each other?
- Sun Oct 14, 2018 3:58 pm
- Forum: Properties of Light
- Topic: Speed of Light
- Replies: 41
- Views: 2596
Re: Speed of Light
the speed of light changes with the medium, in air it is 3.0x10^8m/s.
- Sun Oct 14, 2018 3:52 pm
- Forum: Bohr Frequency Condition, H-Atom , Atomic Spectroscopy
- Topic: Balmer Series
- Replies: 2
- Views: 159
Re: Balmer Series
For the Balmer series, the lowest energy level (the final energy level) is n=2. The electron is falling from a higher energy level to n=2, but since it hasn't reached ground state, it is still excited. Energy is still given off.
- Sun Oct 14, 2018 3:47 pm
- Forum: Properties of Electrons
- Topic: Diffraction Patterns/Slit experiment
- Replies: 1
- Views: 114
Diffraction Patterns/Slit experiment
Do all dark bands correlate to destructive interference/light bands correlate to constructive interference? Why does this happen?
- Fri Oct 05, 2018 5:34 pm
- Forum: Limiting Reactant Calculations
- Topic: When to use H vs H2
- Replies: 7
- Views: 994
Re: When to use H vs H2
I also have a question: when you have a reaction in the form of MgSO4.7H2O where the 7 is in front of the H2O, would you have to do 7x(molar mass of H2) + the molar mass of O or 7x(the molar mass of H20)? Because 2 hydrogens are Bonded to 1 oxygen (to form water), the "7" is the coefficie...
- Fri Oct 05, 2018 5:29 pm
- Forum: Properties of Light
- Topic: Behavior of small objects - clarification
- Replies: 3
- Views: 172
Re: Behavior of small objects - clarification
I don't think it would be continuous. Because only 1 molecule is entering at a time, the amount of water is so small that the scale (as Leela said) would have "jumps" as it recalibrates. Another analogy would be when you don't close the sink tap fully, and one droplet at a time comes out -...
- Fri Oct 05, 2018 5:20 pm
- Forum: SI Units, Unit Conversions
- Topic: formula units [ENDORSED]
- Replies: 69
- Views: 31801
Re: formula units [ENDORSED]
Are salts the only compounds for which you use Formula Units as opposed to Molecule? Or is any compound with 2 different elements a Formula Unit?