Search found 63 matches
- Sun Mar 10, 2019 10:12 pm
- Forum: Reaction Mechanisms, Reaction Profiles
- Topic: Pre-equilibrium reaction mechanisms
- Replies: 1
- Views: 285
Pre-equilibrium reaction mechanisms
What is meant by approximated concentrations for pre-equilibrium reaction mechanisms? How does this differ from the steady state? How are intermediates involved?
- Sun Mar 10, 2019 10:09 pm
- Forum: Reaction Mechanisms, Reaction Profiles
- Topic: Rate and equilibrium constant
- Replies: 1
- Views: 259
Rate and equilibrium constant
What is the relationship between rate constant and equilibrium constant?
- Thu Mar 07, 2019 9:31 pm
- Forum: Balancing Redox Reactions
- Topic: Balancing Redox Reactions
- Replies: 5
- Views: 713
Re: Balancing Redox Reactions
Balance the same as an acidic solution, just add an OH- to balance out every H+. If there are H+ and OH- on the same side, add them to form H20.
- Thu Mar 07, 2019 9:20 pm
- Forum: General Rate Laws
- Topic: Average rate
- Replies: 2
- Views: 309
Re: Average rate
The average rate is obtained by taking the slope of the line connecting any two points on the curve during that period. Ie amount of change/time taken. The instantaneous rate is obtained by taking the slope of the line tangent to the curve at a given time (t). The instantaneous rate is essentially t...
- Thu Mar 07, 2019 8:50 pm
- Forum: Zero Order Reactions
- Topic: Zero Order Reaction- how to identify
- Replies: 2
- Views: 330
Re: Zero Order Reaction- how to identify
A reaction is zero-order if concentration data is plotted versus time and the result is a straight line.
- Sat Mar 02, 2019 7:19 pm
- Forum: Second Order Reactions
- Topic: Pseudo-first-order reaction
- Replies: 4
- Views: 494
Re: Pseudo-first-order reaction
A reaction which is made first order by increasing or decreasing the concentration of a reactant is a pseudo first order reaction.
- Sat Mar 02, 2019 7:15 pm
- Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
- Topic: H+ in cell diagrams
- Replies: 5
- Views: 608
Re: H+ in cell diagrams
Include H+ in cell diagrams when it is used to balance out the H2O on the opposite side of reaction
- Sat Mar 02, 2019 7:14 pm
- Forum: General Rate Laws
- Topic: Kinetics
- Replies: 3
- Views: 368
Re: Kinetics
The average rate is obtained by taking the slope of the line connecting any two points on the curve during that period. Ie amount of change/time taken. The instantaneous rate is obtained by taking the slope of the line tangent to the curve at a given time (t). The instantaneous rate is essentially t...
- Tue Feb 26, 2019 9:14 am
- Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
- Topic: Finding K using standard potential
- Replies: 1
- Views: 198
Finding K using standard potential
Is there a way to use cell potential to calculate Ka without using Nernst? Can you go about this by finding Ecell, using that to find dG and then solving for K usuing -RTlnK?
- Tue Feb 26, 2019 9:09 am
- Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
- Topic: Changes in cell potential
- Replies: 1
- Views: 220
Changes in cell potential
How would you predict the effect of changes in concentration of reactants and products on the cell potential?
- Mon Feb 25, 2019 5:05 pm
- Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
- Topic: Anode and Cathode
- Replies: 6
- Views: 610
Re: Anode and Cathode
In a galvanic (voltaic) cell are the cathode and anode the same as in an electrolytic cell?
- Mon Feb 25, 2019 4:44 pm
- Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
- Topic: Anode and Cathode
- Replies: 6
- Views: 610
Re: Anode and Cathode
Cations (positively charged molecules) gain electrons from the cathode, which is where reduction takes place. Contrarily, anions (negatively charged molecules) lose electrons at the anode, which is where oxidation takes place. Remember OIL RIG. Electrons always flow from the anode to the cathode or ...
- Mon Feb 25, 2019 2:04 pm
- Forum: Balancing Redox Reactions
- Topic: Adding H+, OH- and H20
- Replies: 4
- Views: 923
Re: Adding H+, OH- and H20
H2O and H+ are used to balance out the numbers of oxygen and hydrogen atoms in the reaction, look at 14.1 in textbook for an example
- Mon Feb 25, 2019 1:46 pm
- Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
- Topic: Test topics
- Replies: 1
- Views: 177
Test topics
Wondering how much the second test will cover, up to where in the textbook/homework problems and how far into electrochemistry
- Mon Feb 18, 2019 8:46 pm
- Forum: Gibbs Free Energy Concepts and Calculations
- Topic: Delta G
- Replies: 3
- Views: 391
Re: Delta G
Exergonic processes release energy. The change in Gibbs free energy (ΔG) is a negative value because energy is lost,
whereas an endergonic processes absorbs energy and their products are of greater free energy than the reactants.
whereas an endergonic processes absorbs energy and their products are of greater free energy than the reactants.
- Mon Feb 18, 2019 8:20 pm
- Forum: Gibbs Free Energy Concepts and Calculations
- Topic: standard Gibbs Free Energy
- Replies: 4
- Views: 524
Re: standard Gibbs Free Energy
Standard state being 1atm and at 25°C. The standard Gibbs free energy of formation of a compound is the change of Gibbs free energy that occurs when 1 mole of a substance in its standard state is formed from its constituent elements which are also in their standard states
- Mon Feb 18, 2019 8:13 pm
- Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
- Topic: Positive vs Negative E value
- Replies: 5
- Views: 5516
Re: Positive vs Negative E value
The Ecell value is obtained from the two half reactions or the balanced chemical equation. Ecell is E(cathode) minus E(anode). For deltaG to be negative, which indicates that the reaction is a spontaneous one, E cell must be positive.
- Mon Feb 11, 2019 11:48 am
- Forum: Thermodynamic Definitions (isochoric/isometric, isothermal, isobaric)
- Topic: delta U [ENDORSED]
- Replies: 10
- Views: 3001
Re: delta U [ENDORSED]
Recall that dU=q+w. For an isothermal expansion q=-w. Also, temperature does not change (hence isothermal), therefore q=0. If q=0 then w=0. Thus, dU=0+0=0.
- Mon Feb 11, 2019 11:39 am
- Forum: Calculating Work of Expansion
- Topic: Reversible vs Irreversible
- Replies: 10
- Views: 984
Re: Reversible vs Irreversible
W for reversible isothermal expansion of an ideal gas W=-nRTln(V2/V1)
- Mon Feb 11, 2019 11:37 am
- Forum: Entropy Changes Due to Changes in Volume and Temperature
- Topic: deltaS=nCvln(t2/t1) what is Cv?
- Replies: 7
- Views: 2766
Re: deltaS=nCvln(t2/t1) what is Cv?
If a gas is compressed suddenly and irreversibly, treat it as a two step process where the dS from dT and dS from dV need to be accounted for. In this case, you would do dS=nCvln(T2/T1) if v was constant + deltaS=nRln(V2/V1).
- Mon Feb 11, 2019 11:29 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: 4G. 2B 7th edition
- Replies: 2
- Views: 385
Re: 4G. 2B 7th edition
T=0 ie absolute zero does not necessarily mean that there is zero entropy. It does, however, mean that entropy and enthalpy will be at their minimum values.The Third Law of Thermodynamics states that as the temperature of a system approaches absolute zero, its entropy approaches a constant- for pure...
- Thu Jan 31, 2019 11:19 pm
- Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
- Topic: Enthalpy
- Replies: 6
- Views: 563
Re: Enthalpy
Bond breaking is an endothermic process ie a process that requires energy. For endothermic reactions, the products of the reaction have a greater enthalpy than the reactants, and heat is absorbed by the system from its surroundings. Therefore, the delta H b must be positive because the energy is bei...
- Thu Jan 31, 2019 11:14 pm
- Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
- Topic: U:Internal Energy
- Replies: 4
- Views: 435
Re: U:Internal Energy
They are essentially the same. It just depends which values you are given in the question, and which you can plug into the equation.
- Thu Jan 31, 2019 11:10 pm
- Forum: Thermodynamic Systems (Open, Closed, Isolated)
- Topic: q=-q
- Replies: 4
- Views: 2075
Re: q=-q
no heat is transferred between two objects in thermal equilibrium
- Thu Jan 31, 2019 11:04 pm
- Forum: Phase Changes & Related Calculations
- Topic: Phase change and temperature
- Replies: 3
- Views: 378
Re: Phase change and temperature
Temperature of a substance does not change during a phase change. If heat is coming into a substance during a phase change, then this energy is used to break the bonds between the molecules of the substance.
- Thu Jan 31, 2019 10:59 pm
- Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
- Topic: Bonds and energy release
- Replies: 2
- Views: 353
Re: Bonds and energy release
To break the bond, you have to fight against the bond, so energy is required in bon breaking. Potential energy is stored in molecules and this energy is released when bonds forms. Things tend to go to the lowest energy state possible
- Sun Jan 20, 2019 7:40 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Concentrations Effect on K
- Replies: 8
- Views: 528
Re: Concentrations Effect on K
Out of the various stresses, only temperature changes Kc
- Sun Jan 20, 2019 7:37 pm
- Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
- Topic: Temperature's effect on Kc
- Replies: 2
- Views: 260
Temperature's effect on Kc
According to Le Chatelier's Principles, how and why does temperature impact Kc?
- Sun Jan 20, 2019 7:31 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: ICE calculation sig figs
- Replies: 5
- Views: 427
Re: ICE calculation sig figs
You should always refer to the question, and go by the number of sig figs used there.
- Wed Jan 09, 2019 10:04 am
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Kc vs. Kp
- Replies: 7
- Views: 638
Re: Kc vs. Kp
for Kc, you use the square brackets to denote concentration
- Wed Jan 09, 2019 10:02 am
- Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
- Topic: Catalysts
- Replies: 3
- Views: 278
Catalysts
Do catalysts act as a stressor in a reaction? Do catalysts favor a particular direction ie the forward or the reverse?
- Wed Jan 09, 2019 10:00 am
- Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
- Topic: Applying Le Chatelier's principle
- Replies: 2
- Views: 140
Applying Le Chatelier's principle
What would happen if one were to increase the temperature of a reaction, and why?
- Wed Jan 09, 2019 9:58 am
- Forum: Ideal Gases
- Topic: Units
- Replies: 5
- Views: 353
Units
What are the units for P=(nRT)/V? And what is the ideal gas constant?
- Thu Jun 07, 2018 8:23 pm
- Forum: Calculating the pH of Salt Solutions
- Topic: How temperature affects pH
- Replies: 3
- Views: 2553
Re: How temperature affects pH
Technically temperature should have no real effect on pH, however, since water undergoes deconstruction of some sort from H2O -> OH- + H,
and there are 2x H. Since pH quantifies the quantity of H+ in a solution, the pH would be slighlty lower/more acidic in higher temperatures.
and there are 2x H. Since pH quantifies the quantity of H+ in a solution, the pH would be slighlty lower/more acidic in higher temperatures.
- Thu Jun 07, 2018 8:17 pm
- Forum: Amphoteric Compounds
- Topic: Identifying an amphoteric compound
- Replies: 3
- Views: 2932
Re: Identifying an amphoteric compound
If something has the ability to act as BOTH an acid and a base then it is amphoteric, so when looking at a reaction/equation, test if the compound has the ability to be a proton donor AND an hydroxide donor. One of the most common amphoteric substances out there is water as it behaves in this way.
- Thu Jun 07, 2018 8:05 pm
- Forum: Calculating pH or pOH for Strong & Weak Acids & Bases
- Topic: Calculating the difference between two pH values
- Replies: 2
- Views: 500
Calculating the difference between two pH values
How do you calculate the difference between two pH values of the same acid, just diluted. 12.9 is an example of a question that asks you to do this.
Thanks
Thanks
- Wed May 30, 2018 4:50 pm
- Forum: Determining Molecular Shape (VSEPR)
- Topic: Resonance structure effect on molecular shape
- Replies: 3
- Views: 456
Resonance structure effect on molecular shape
ClO2+ has 4 different resonance structures so I am wondering if each structure would warrant a different molecular shape.
Thanks
Thanks
- Wed May 30, 2018 4:37 pm
- Forum: Lewis Structures
- Topic: Electrons in Valence Shell
- Replies: 4
- Views: 821
Re: Electrons in Valence Shell
You can also use the principle quantum numbers of the element to determine how many electrons it can hold. Typically, the highest number of electrons that can fit in any given shell = 2n².
- Thu May 24, 2018 3:34 pm
- Forum: Resonance Structures
- Topic: 3.47
- Replies: 3
- Views: 597
Re: 3.47
Hydrocarbons often form structures like this, with carbon as the central atom and hydrogens branching off- for example benzene rings. So just predict such structures for molecules with multiple carbons and hydrogens.
- Thu May 24, 2018 3:29 pm
- Forum: Bond Lengths & Energies
- Topic: Dissociation Energy
- Replies: 3
- Views: 620
Re: Dissociation Energy
Dissociation energy is a measure of the strength of a bond. Therefore, it can be measured by breaking bonds, and recording how much energy was required to do so.
- Thu May 24, 2018 3:25 pm
- Forum: Determining Molecular Shape (VSEPR)
- Topic: Regions of electron density
- Replies: 7
- Views: 738
Re: Regions of electron density
electron density counts for both bonding and unshared electron pairs around the central atom
- Tue May 15, 2018 1:56 pm
- Forum: Lewis Structures
- Topic: Lewis Structures
- Replies: 4
- Views: 579
Re: Lewis Structures
The central atom is the atom that has the lowest electronegativity or the highest valence. You expand from there.
- Mon May 14, 2018 11:17 pm
- Forum: Lewis Structures
- Topic: Identifying elements in Lewis structures [ENDORSED]
- Replies: 2
- Views: 727
Identifying elements in Lewis structures [ENDORSED]
For question 3.37, why would the answer be phosphorus specifically and not, say nitrogen, or any of the other period 3 elements. Would they not all work due to having 5 valence electrons. In general, how does one figure out an unknown element from a lewis structure?
- Mon May 14, 2018 10:32 pm
- Forum: Formal Charge and Oxidation Numbers
- Topic: Oxidation Number & Bonds
- Replies: 6
- Views: 2570
Re: Oxidation Number & Bonds
Seeing as the question asks for a maximum and a minimum oxidation number, can there be an intermediary oxidation number or must the answer be +7 and/or -1?
- Wed May 09, 2018 12:50 am
- Forum: Photoelectric Effect
- Topic: Work function and kinetic energy
- Replies: 1
- Views: 319
Work function and kinetic energy
If the work function of A is 6x10^-19 J per atom and the work function of B were let's say 7x10^-19, wouldn't you expect A to eject a slower electron than B if the same light source shines on both. Why is this NOT the case??
- Tue May 08, 2018 10:50 pm
- Forum: Properties of Electrons
- Topic: Wave-like properties
- Replies: 1
- Views: 338
Re: Wave-like properties
Yes, all matter has both wave-like and particle properties- including protons and neutrons. The concept is just typically used with quantum mechanics due to the small scale because large scale matter has a wavelength that is far too short to be detected.
- Tue May 08, 2018 10:45 pm
- Forum: Trends in The Periodic Table
- Topic: Ionization exceptions [ENDORSED]
- Replies: 8
- Views: 1652
Re: Ionization exceptions [ENDORSED]
Yes and we should know how to explain why the exceptions occur, for example because a full shell OR half full shell are most stable. Nitrogen's half full shell is what makes it more stable than oxygen, resulting in a higher ionization energy.
- Tue May 08, 2018 9:46 pm
- Forum: Heisenberg Indeterminacy (Uncertainty) Equation
- Topic: Uncertainty calculation
- Replies: 1
- Views: 337
Uncertainty calculation
If a proton is accelerated in a cyclotron to a very high speed that is known to within 3.0x10^2km*s^-1. So you know the speed, you can find out the momentum, but how do you find out the minimum uncertainty in the position.
- Sun May 06, 2018 11:45 pm
- Forum: Quantum Numbers and The H-Atom
- Topic: Difference between the quantum number for particle and electron
- Replies: 3
- Views: 495
Re: Difference between the quantum number for particle and electron
when we talk about the principle quantum number for a particle, we are referring to electrons
- Sun May 06, 2018 11:16 pm
- Forum: Wave Functions and s-, p-, d-, f- Orbitals
- Topic: Energy difference between 4s and 3d
- Replies: 3
- Views: 1285
Re: Energy difference between 4s and 3d
The 4s shell is only lower in energy if there than 3d when there aren't electrons in 3d, which is why atoms lose the 4s electrons before they lose the 3d electrons. Those in the 3d shell would be the highest energy electrons due to the repulsive forces of electrons already in the 3d shell.
- Sun May 06, 2018 10:59 pm
- Forum: Trends in The Periodic Table
- Topic: Electron Affinity
- Replies: 3
- Views: 458
Re: Electron Affinity
electron affinity is the energy released when an atom acquires an electron (ie these would be negative values). So yes, a high electron affinity would mean the energy released when an electron is added would technically be very low.
- Sun Apr 29, 2018 10:32 pm
- Forum: Quantum Numbers and The H-Atom
- Topic: Orientation of Lobes
- Replies: 3
- Views: 520
Re: Orientation of Lobes
You would describe the magnetic quantum number (m) which labels different orbitals of a subshell including nodal planes ie symmetric density distribution or not
- Sun Apr 29, 2018 10:28 pm
- Forum: Wave Functions and s-, p-, d-, f- Orbitals
- Topic: orbitals/lobes
- Replies: 3
- Views: 392
Re: orbitals/lobes
I believe we should be able to identify and draw different orbital according to information given about the planes and quantum values (n,l and m)
- Sun Apr 29, 2018 10:26 pm
- Forum: Wave Functions and s-, p-, d-, f- Orbitals
- Topic: PROBLEM 2.1
- Replies: 4
- Views: 455
Re: PROBLEM 2.1
The orbital that hydrogen's electron is in is the 1s orbital, the 1 meaning that the electron is in the energy level closest (1st energy level) to the nucleus. If an electron is in a 2 orbital (2nd energy level) it just means that there is a greater chance that the electron will be further away from...
- Thu Apr 26, 2018 5:22 pm
- Forum: Photoelectric Effect
- Topic: Question 1.33, part b
- Replies: 1
- Views: 235
Question 1.33, part b
The velocity of an electron that is emitted from a metallic surface by a photon is 3.6x10^3 km/s. No electrons are emitted from the surface of the metal until the frequency of the radiation reaches 2.50x10^16Hz. How much energy is required to remove the electron from the metal? I know you eventually...
- Thu Apr 26, 2018 4:03 pm
- Forum: DeBroglie Equation
- Topic: Calculating wavelength of an electron
- Replies: 4
- Views: 601
Calculating wavelength of an electron
When you know the velocity of an electron, how do you then calculate the wavelength?
Thanks
Thanks
- Wed Apr 25, 2018 7:32 pm
- Forum: Photoelectric Effect
- Topic: Calculating kinetic energy of an emitted electron [ENDORSED]
- Replies: 3
- Views: 722
Calculating kinetic energy of an emitted electron [ENDORSED]
I'm wondering how you go about calculating the kinetic energy of an ejected electron when you are only given the speed at which it is ejected. What would you would put for mass of electron in the KE equation.
Thanks
Thanks
- Thu Apr 12, 2018 2:44 pm
- Forum: SI Units, Unit Conversions
- Topic: Correct Units?? [ENDORSED]
- Replies: 8
- Views: 897
Re: Correct Units?? [ENDORSED]
you would normally use grams unless the question uses or states otherwise or if the calculated number is very large, making it more convenient or logical to use kg. Typically, you'll be able to tell what is appropriate.
- Thu Apr 12, 2018 2:11 pm
- Forum: Photoelectric Effect
- Topic: Original Photoelectric Experiment
- Replies: 3
- Views: 406
Re: Original Photoelectric Experiment
I believe the aim was to observe how the transfer of energy from light to an electron in the metal results in the emission of said electron from the metal
- Tue Apr 10, 2018 4:46 pm
- Forum: Balancing Chemical Reactions
- Topic: Fastest way to balance chemical equation
- Replies: 9
- Views: 16514
Re: Fastest way to balance chemical equation
start by balancing the atoms with the highest number of atoms in the reaction. Typically you leave balancing oxygen and/or hydrogen until last
- Tue Apr 10, 2018 4:41 pm
- Forum: Accuracy, Precision, Mole, Other Definitions
- Topic: rounding [ENDORSED]
- Replies: 10
- Views: 950
Re: rounding [ENDORSED]
you should always use the number of sig figs of the number with the lowest number of sig figs in the question and subsequent calculations
- Tue Apr 10, 2018 4:37 pm
- Forum: Molarity, Solutions, Dilutions
- Topic: Mixtures and Solutions
- Replies: 2
- Views: 423
Re: Mixtures and Solutions
Hi so n is moles, m is mass and M is molar mass. Thus, moles is equal to mass divided by molar mass. You would get the molar mass from the periodic table. Also, c is concentration, n (again) is moles and V is volume.Thus, concentration is equal to moles divided by volume of solution. In each equatio...
- Tue Apr 10, 2018 4:30 pm
- Forum: Molarity, Solutions, Dilutions
- Topic: G.11 / Volumes for Solutions
- Replies: 2
- Views: 332
Re: G.11 / Volumes for Solutions
Volume is equal to moles/concentration, so you would do 4.5x10^-3 mols divided by 0.278M.
Hope this helps
Hope this helps