Search found 62 matches
- Thu Mar 14, 2019 10:59 pm
- Forum: Kinetics vs. Thermodynamics Controlling a Reaction
- Topic: Overall Order
- Replies: 5
- Views: 706
Re: Overall Order
Good question. The only thing I can think of is it would tell you the units of the equation as seen in the table below.
- Thu Mar 14, 2019 10:49 pm
- Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
- Topic: Porous Wall
- Replies: 4
- Views: 643
Re: Porous Wall
Hopefully this diagram will help depict it better than any words. The two solutions are separated by a porous barrier that prevents them from rapidly mixing but allows ions to diffuse through. https://chem.libretexts.org/Bookshelves/General_Chemistry/Book%3A_Chem1_(Lower)/16%3A_Electrochemistry/24.0...
- Thu Mar 14, 2019 10:36 pm
- Forum: Arrhenius Equation, Activation Energies, Catalysts
- Topic: catalyst vs intermediate
- Replies: 9
- Views: 855
Re: catalyst vs intermediate
A catalyst can be an intermediate in an equation, but not all intermediates are catalysts. I believe to be able to tell if it is a catalyst you would have to be given that it is a catalyst or that the activation energy was lowered.
- Fri Mar 08, 2019 3:27 am
- Forum: Kinetics vs. Thermodynamics Controlling a Reaction
- Topic: Reaction mechanisms
- Replies: 3
- Views: 466
Re: Reaction mechanisms
That is because the entire reaction must wait for the slowest step to proceed. That's why this would be the rate-determining step.
- Fri Mar 08, 2019 3:19 am
- Forum: First Order Reactions
- Topic: Second and Zero Order Units
- Replies: 2
- Views: 344
Re: Second and Zero Order Units
The units of kr depend on the overall order of the reaction and ensure that kr x (concentration) a has the same units as the rate, namely, concentration/time. Thus, when the concentration is expressed in moles per liter and the rate is expressed in mol*L -1 *s -1 , the units of kr are a follows: 1st...
- Fri Mar 08, 2019 3:07 am
- Forum: Zero Order Reactions
- Topic: definitions
- Replies: 2
- Views: 310
Re: definitions
I am also led to believe that these values have to be experimentally found, and are not just based off of something you can look at a chemical equation and tell. For example, if you have 1 mol of x that produces 1 mol of product then you have 2 mol of x that produces 2 mol of product you can see thi...
- Fri Mar 01, 2019 8:08 pm
- Forum: Kinetics vs. Thermodynamics Controlling a Reaction
- Topic: characterization of a reaction
- Replies: 3
- Views: 598
Re: characterization of a reaction
For thermodynamic favorability: ΔG>0, the reaction is nonspontaneous in the forward direction, not thermodynamically favorable ΔG<0, the reaction is spontaneous in the forward direction, thermodynamically favorable However, a reaction can be thermodynamically favorable yet still wont proceed due to ...
- Fri Mar 01, 2019 6:56 pm
- Forum: Balancing Redox Reactions
- Topic: Oxidation State
- Replies: 4
- Views: 542
Re: Oxidation State
For very easy problems typically involving just one element turning into an ion of itself where you can instantly tell if it was reduced or oxidized by balancing the charge by adding e- to one of the sides. Other than that you have to calculate the oxidation states of the molecules using the oxidati...
- Fri Mar 01, 2019 6:48 pm
- Forum: General Rate Laws
- Topic: Unique rate coefficients
- Replies: 2
- Views: 346
Re: Unique rate coefficients
I know you are referring to the example where 2NO2 -> 2NO + O2 turned into - d[NO2]/dt = d[NO]/dt = 2d[O2]/dt. However, it is much easier to just use fractions for more complicated problems where this problem and the unique rate would be -(1/2)d[NO2]/dt = (1/2)d[NO]/dt = d[O2]/dt where the 1/2 comes...
- Fri Feb 22, 2019 4:35 am
- Forum: Gibbs Free Energy Concepts and Calculations
- Topic: Spontaneous
- Replies: 2
- Views: 329
Re: Spontaneous
Basically we can just use Gibbs to relate all three terms and determine if something is spontaneous or not Remember the Gibbs equation is (delta)G = (delta)H - T(delta)S Gibbs Free Energy = if it is negative it is spontaneous Spontaneous = a reaction that favors the formation of products under the c...
- Fri Feb 22, 2019 4:26 am
- Forum: Balancing Redox Reactions
- Topic: Number of electrons
- Replies: 5
- Views: 587
Re: Number of electrons
In half reactions we just find the sum of the two halves (the reduction half-reaction + the oxidation half-reaction). First make sure all of the equations are balanced. Make sure in molecule compounds as well that you are taking note of the sign. For example, let's pretend that FeO 2 -2 is a thing. ...
- Fri Feb 22, 2019 4:13 am
- Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
- Topic: Standard hydrogen electrode
- Replies: 1
- Views: 289
Re: Standard hydrogen electrode
The standard hydrogen electrode is a measurement of the oxidation-reduction potentials for the thermodynamic scale. Basically it s a very good introduction to oxidation-reduction reactions. Here's a picture to help visualize the oxidation taking place on the left (Lose Electron Oxidized) and the red...
- Tue Feb 19, 2019 4:02 pm
- Forum: Gibbs Free Energy Concepts and Calculations
- Topic: What to do when temperature isn't given
- Replies: 8
- Views: 833
Re: What to do when temperature isn't given
Temperature should always be given for any Gibbs Free Energy problem, unless you have to solve for the temperature in the problem.
- Tue Feb 19, 2019 3:55 pm
- Forum: Gibbs Free Energy Concepts and Calculations
- Topic: Finding standard reaction for a reaction
- Replies: 3
- Views: 423
Re: Finding standard reaction for a reaction
The only reason I can think of is because O2 is already in its most standard state so this would be counted as 0 for those calculations. The textbook goes more into detail on which calculation to use standard state of elements = 0 for.
- Tue Feb 19, 2019 3:50 pm
- Forum: Gibbs Free Energy Concepts and Calculations
- Topic: Equilibrium
- Replies: 3
- Views: 347
Re: Equilibrium
This graph helps demonstrate the point if you are more visual or mathematical. Where you can see the forward and reverse reaction meet at a minimum. This minimum is equilibrium in this reaction and shows why since it is a minimum equilibrium would be 0.
- Mon Feb 11, 2019 2:43 pm
- Forum: Administrative Questions and Class Announcements
- Topic: Thermochemistry Review Packet
- Replies: 4
- Views: 585
Re: Thermochemistry Review Packet
Thank you for the great review session!
- Sat Feb 09, 2019 12:03 am
- Forum: Concepts & Calculations Using Second Law of Thermodynamics
- Topic: Motion and Entropy/Enthalpy
- Replies: 3
- Views: 430
Re: Motion and Entropy/Enthalpy
They relate because through this molecular motion in each one is how the molecule can store energy. This motion results in the greater the number of possible microstates which then leads to higher the entropy.
- Fri Feb 08, 2019 11:58 pm
- Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
- Topic: Calculating q
- Replies: 1
- Views: 270
Re: Calculating q
The equations are used for the same thing where q = mCT is used to find the heat of a particular substance with a mass, change in temperature, and specific heat capacity. The only difference is in a bomb calorimeter the mass is not that relevant for finding q so you can negate it and just use q (cal...
- Fri Feb 08, 2019 11:48 pm
- Forum: Concepts & Calculations Using First Law of Thermodynamics
- Topic: Molar entropy
- Replies: 2
- Views: 303
Re: Molar entropy
From the trend I believe there is a decrease in the entropy as the forces between the atoms, molecules, or ions increases. A good example is the three solid compounds NaF with the molar entropy 51.5, MgO at 26.8, and AlN at 20.2
- Sat Feb 02, 2019 11:53 am
- Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
- Topic: breaking double bonds?
- Replies: 6
- Views: 1260
Re: breaking double bonds?
Just to give some evidence to what everyone else is saying. A carbon-carbon single bond has a length of 154 and energy of 348, a carbon-carbon double bond has a length of 134 and energy of 614, while a carbon-carbon triple bond has a length of 120 and energy of 839. Here we can see that a double bon...
- Sat Feb 02, 2019 11:46 am
- Forum: Thermodynamic Systems (Open, Closed, Isolated)
- Topic: open system
- Replies: 8
- Views: 1311
Re: open system
This is because the open beaker is open to the entire atmosphere which is much bigger than the beaker so it makes the beaker's pressure irrelevant to any change and that is why pressure is constant. It is just like when you add a bucket of water into the Ocean it really does not make a difference on...
- Sat Feb 02, 2019 11:42 am
- Forum: Thermodynamic Definitions (isochoric/isometric, isothermal, isobaric)
- Topic: Heating Curve
- Replies: 2
- Views: 392
Re: Heating Curve
I would assume so yes just based off the assumption that you can't create heat without any work being done. So any heat released from the breaking of molecules would be from the exact energy stored in those bonds.
- Thu Jan 24, 2019 5:15 pm
- Forum: Phase Changes & Related Calculations
- Topic: Why steam causes severe burns
- Replies: 9
- Views: 1934
Re: Why steam causes severe burns
Here is a graph that could help supplement what everyone else is saying. Here, you can see that more energy is needed in order to make a gas a gas, so when it comes into contact with skin it releases the more heat it has stored.
- Thu Jan 24, 2019 5:08 pm
- Forum: Phase Changes & Related Calculations
- Topic: Enthalpy and States
- Replies: 8
- Views: 749
Re: Enthalpy and States
Yes the state of matter will affect the enthalpy. A liquid of a substance will have a different enthalpy than a gas of the same substance.
- Thu Jan 24, 2019 5:03 pm
- Forum: Non-Equilibrium Conditions & The Reaction Quotient
- Topic: Le Chateliers Priniciple
- Replies: 9
- Views: 912
Re: Le Chateliers Priniciple
An increase in pressure will cause the reaction to trend towards the side with less moles so lets say we have a reaction that is 2A + 3B -> 2C then an increase in pressure will cause more products to form. This is true unless the pressure is increased by adding an inert gas (a gas that is random and...
- Fri Jan 18, 2019 9:54 am
- Forum: Ideal Gases
- Topic: Q and K Graph Explanation
- Replies: 2
- Views: 248
Re: Q and K Graph Explanation
I know what graph you are talking about, and hopefully this one can help explain Q and K with respect to equilibrium.
- Fri Jan 18, 2019 9:48 am
- Forum: Acidity & Basicity Constants and The Conjugate Seesaw
- Topic: Ka Kb significance
- Replies: 3
- Views: 2329
Re: Ka Kb significance
So here is everything I have found p in front of anything means -log, so pKa = -log(Ka) pKb = -log(Kb) pH = -log(H+) pOH = -log(OH-) Other relationships at 25 degrees C… pH + pOH = 14 Kw (1 x 10^-14) = Ka * Kb pKa + pKb = 14 (this is a similar equation to the one above but by finding the -log we can...
- Fri Jan 18, 2019 9:34 am
- Forum: Administrative Questions and Class Announcements
- Topic: Studying for First Discussion Test
- Replies: 10
- Views: 783
Re: Studying for First Discussion Test
I'd say to try and use as many as possible of Dr. Lavelle's provided resources. Since they are created by him and he oversees them I am sure that they are all geared toward the subjects that he sees are most important for our success in the class. I'd definitely recommend going through the video mod...
- Thu Jan 10, 2019 5:54 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: How to use ICE tables
- Replies: 5
- Views: 694
Re: How to use ICE tables
This table may help to visualize it all, and is an example that uses Molarity.
- Thu Jan 10, 2019 5:49 pm
- Forum: Non-Equilibrium Conditions & The Reaction Quotient
- Topic: Solid and Liquids in reaction equilibrium situations
- Replies: 1
- Views: 198
Re: Solid and Liquids in reaction equilibrium situations
Water is the only thing that I know can possess this power, since it can act both as an acid and a base which is why it can form both hydroxide and hydronium ions. This also explains why it is such a powerful solvent.
- Thu Jan 10, 2019 5:41 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Partial Pressure vs. Brackets
- Replies: 2
- Views: 604
Re: Partial Pressure vs. Brackets
Square brackets [] denotes concentration and it is only used for Kc. Gases (Kp) however use parentheses (). So no they are not interchangeable. This is because Kc is used as an equilibrium constant, while Kp stands for partial pressure.
- Mon Dec 03, 2018 11:10 pm
- Forum: Determining Molecular Shape (VSEPR)
- Topic: Seesaw shape
- Replies: 3
- Views: 373
Re: Seesaw shape
Hopefully this visual will help to see where the bond angles are 180, 120, and 90 degrees.
- Mon Dec 03, 2018 11:03 pm
- Forum: Lewis Acids & Bases
- Topic: Acids?
- Replies: 2
- Views: 311
Re: Acids?
Some of the trends we see to tell the differences is stronger acids have lower pKa values, strong acids lose H+ easily and the resultant anion must be stable. With weaker (larger) bonds it is easier to remove the H+. Short bonds are stronger where we can see the smaller elements trend towards the up...
- Mon Dec 03, 2018 10:52 pm
- Forum: Lewis Acids & Bases
- Topic: Identifying Lewis acid
- Replies: 2
- Views: 313
Re: Identifying Lewis acid
Lewis acids accept pairs of electrons. Electronegativity is a measure of how strongly atoms attract bonding electrons to themselves. Therefore we can assume that if an atom is more electronegative than an atom then it will be the acid since it will be more likely to accept the pairs of electrons.
- Mon Dec 03, 2018 10:46 pm
- Forum: Properties & Structures of Inorganic & Organic Acids
- Topic: acids and bases
- Replies: 3
- Views: 337
Re: acids and bases
Some of the trends we see to tell the differences is stronger acids have lower pKa values, strong acids lose H+ easily and the resultant anion must be stable. With weaker (larger) bonds it is easier to remove the H+. Short bonds are stronger where we can see the smaller elements trend towards the up...
- Mon Dec 03, 2018 10:37 pm
- Forum: Lewis Acids & Bases
- Topic: Lone Pairs only on Central Atoms?
- Replies: 2
- Views: 322
Re: Lone Pairs only on Central Atoms?
A Lewis acid is an electron -pair acceptor as shown in the diagram
- Mon Dec 03, 2018 6:58 pm
- Forum: Properties & Structures of Inorganic & Organic Acids
- Topic: DNA
- Replies: 1
- Views: 247
Re: DNA
Looking at the picture we can see that is is a bronsted-lewis acid
- Thu Nov 22, 2018 12:22 pm
- Forum: Determining Molecular Shape (VSEPR)
- Topic: Seesaw vs Tetrahedral Bipyramidal
- Replies: 2
- Views: 843
Re: Seesaw vs Tetrahedral Bipyramidal
This should help distinguish between all of the shapes. I often find it's easier to see a visual for these kinds of problems.
- Thu Nov 22, 2018 12:14 pm
- Forum: Lewis Structures
- Topic: Complete Lewis Structures
- Replies: 4
- Views: 446
Re: Complete Lewis Structures
For drawing them either structure should be fine, but you should be able to know the name of the structure that is made from either of the drawings.
- Thu Nov 22, 2018 12:05 pm
- Forum: Dipole Moments
- Topic: London forces and dipole moments
- Replies: 4
- Views: 436
Re: London forces and dipole moments
London forces are the weakest of all intermolecular forces, and they increase in strength as the total number of electrons increase.
- Sat Nov 17, 2018 10:22 pm
- Forum: Determining Molecular Shape (VSEPR)
- Topic: Triple Bonds
- Replies: 2
- Views: 197
Re: Triple Bonds
A sigma bond is always the first bond between two atoms, while pi bonds are always the second
- Sat Nov 17, 2018 10:12 pm
- Forum: Hybridization
- Topic: Bond Angles
- Replies: 12
- Views: 1113
Re: Bond Angles
Something to keep in mind as well is when lone pairs are involved it changes the bond angle from the expected amount. For example NH3 has bond angles of 107 degrees instead of the expected 109.5 degrees. There is no way to know this since it needs to be tested in the lab since it's unique to each mo...
- Sat Nov 17, 2018 9:54 pm
- Forum: Determining Molecular Shape (VSEPR)
- Topic: Determining a Dipole Moment
- Replies: 2
- Views: 314
Re: Determining a Dipole Moment
The dipole charge has to do with electronegativity. The more electronegative atom has a partial negative charge since it pulls the electrons closer to itself. While, the less electronegative atom is partially positive since the other atom is holding the electrons more tightly.
- Thu Nov 08, 2018 10:44 am
- Forum: Polarisability of Anions, The Polarizing Power of Cations
- Topic: Electron distortion
- Replies: 3
- Views: 720
Re: Electron distortion
Basically to sum it up on how I see it is more electrons = greater ablity to bond and form stronger bonds.
- Thu Nov 08, 2018 10:34 am
- Forum: Ionic & Covalent Bonds
- Topic: Electron Distortion definition
- Replies: 2
- Views: 329
Re: Electron Distortion definition
Here's a post from 2016 that I think does a very good job of explaining the concept: Electron distortion is when the electrons of the anion are attracted to the cation, which causes the shape of the electron density to change slightly. When we talk about ionic bonds, we usually think it means a bond...
- Thu Nov 08, 2018 10:28 am
- Forum: Ionic & Covalent Bonds
- Topic: Periodic Trends
- Replies: 3
- Views: 381
Re: Periodic Trends
A TA told me that going up a column (group) means it is more electronegative than just going across a row. So in this case Na would be more electronegative than Ca. I would still ask a TA for a further explanation on why this occurs though.
- Thu Nov 01, 2018 12:59 pm
- Forum: Resonance Structures
- Topic: Definition of resonance
- Replies: 7
- Views: 872
Re: Definition of resonance
We use resonance in order to show the different options for different bonding molecules. For example, in NO3 Nitrogen can form a double bond with oxygen on any of the 3 oxygen molecules. This gives us three different possibilities for which one Nitrogen can be bonding too. Since we do not know which...
- Thu Nov 01, 2018 12:52 pm
- Forum: Trends in The Periodic Table
- Topic: Implications of ionization energy
- Replies: 2
- Views: 214
Re: Implications of ionization energy
This is typically because the elements with lower ionization energies have more open spaces (have more opportunity) for bonding. For example, Carbon can form 4 bonds and has a lower ionization energy than Fluorine who can only form 1 bond (we get these numbers by looking at how many valence electron...
- Thu Nov 01, 2018 12:46 pm
- Forum: Ionic & Covalent Bonds
- Topic: Removing the second electron
- Replies: 8
- Views: 643
Re: Removing the second electron
Here are some numbers to give some of the reasons above some more concrete evidence. For Al it takes 577.6 kJ/mol to remove the 1st electron, 1816.6 for the second, 2744.7 for the third, and 11,577 for the fourth. Looking at these numbers it makes sense why it is a lot easier to gain 4 electrons tha...
- Thu Oct 25, 2018 11:09 am
- Forum: Trends in The Periodic Table
- Topic: Ionization Energy
- Replies: 6
- Views: 1669
Re: Ionization Energy
Emmaraf 3K wrote:Are you referring to a specific question? Looking at a chart online for ionization energies, it says the ionization energy for sulfur is less than oxygen.
Here is the chart they were referring to. It may help to have a visual to better understand the concept:
- Thu Oct 25, 2018 10:57 am
- Forum: Student Social/Study Group
- Topic: Post All Chemistry Jokes Here
- Replies: 9651
- Views: 3008804
Re: Post All Chemistry Jokes Here
Sixteen sodiums walk into a room. Who's next? Na - Na - Na - Na - Na - Na - Na - Na - Na - Na - Na - Na - Na - Na - Na - Na - BATMAN
- Thu Oct 25, 2018 10:45 am
- Forum: Trends in The Periodic Table
- Topic: Ionization Energies
- Replies: 3
- Views: 332
Re: Ionization Energies
Losing four electrons would require a large amount of energy. The ionization energies for 4 electron removals with the elements of the group 14 would be very high. This way it would be more likely for them to gain 4 electrons to reach a stable state. That is a very good point. It is especially true...
- Fri Oct 19, 2018 3:38 am
- Forum: Bohr Frequency Condition, H-Atom , Atomic Spectroscopy
- Topic: Lyman vs Balmer
- Replies: 6
- Views: 776
Re: Lyman vs Balmer
This video does a pretty good job of explaining it and is nice since it includes animations: https://www.youtube.com/watch?v=VQJx6JAq_po
- Fri Oct 19, 2018 3:29 am
- Forum: Electron Configurations for Multi-Electron Atoms
- Topic: Tips and Tricks
- Replies: 4
- Views: 1390
Re: Tips and Tricks
Thank you! That makes a lot more sense and will definitely come in handy! I was wondering the same thing.
- Fri Oct 19, 2018 2:02 am
- Forum: Wave Functions and s-, p-, d-, f- Orbitals
- Topic: Video Modules
- Replies: 7
- Views: 732
Re: Video Modules
Hopefully he will be uploading a module for it. However in the mean time Khan academy is a great resource for learning Chemistry since they often provide examples and have a video on the topic here: https://www.khanacademy.org/science/physics/quantum-physics/quantum-numbers-and-orbitals/v/heisenberg...
- Thu Oct 11, 2018 12:30 pm
- Forum: SI Units, Unit Conversions
- Topic: Should Significant Figures be affected by constants?
- Replies: 10
- Views: 910
Re: Should Significant Figures be affected by constants?
I don't believe a constant would effect the number of sig figs you should round to in your answer, but rather it should be a given number such as 5.0g since that is a number that the person asking the question can change based off how many significant figures they are looking for in the answer. Ther...
- Thu Oct 11, 2018 12:24 pm
- Forum: Properties of Light
- Topic: Memorizing wavelengths and frequencies
- Replies: 5
- Views: 1556
Re: Memorizing wavelengths and frequencies
I believe it's important to know that visible light is in the range between 400-700 nanometers. I would also know that higher energy waves (gamma ray/x-ray/ultraviolet) have shorter wavelengths and higher frequencies. While lower energy waves (radio/microwave/infared) have longer wavelengths and low...
- Thu Oct 11, 2018 12:18 pm
- Forum: Limiting Reactant Calculations
- Topic: Limiting Reagent
- Replies: 10
- Views: 1577
Re: Limiting Reagent
Example #6 on this website does a great job of explaining it with a practice problem:
https://www.chemteam.info/Stoichiometry ... agent.html
https://www.chemteam.info/Stoichiometry ... agent.html
- Thu Oct 11, 2018 12:10 pm
- Forum: Limiting Reactant Calculations
- Topic: Percent Yield [ENDORSED]
- Replies: 13
- Views: 2833
Re: Percent Yield [ENDORSED]
You should be given the actual yield, and have to calculate for the theoretical yield. This is because we can't calculate for the disruptions that take place during an experiement (side-rections, molecules stuck to the side of the beaker, etc). The actual yield is also done in an experiment setting....
- Thu Oct 11, 2018 12:03 pm
- Forum: Properties of Light
- Topic: Electromagnetic Spectrum
- Replies: 2
- Views: 183
Re: Electromagnetic Spectrum
I believe it's important to know that visible light is in the range between 400-700 nanometers. I would also know that higher energy waves (gamma ray/x-ray/ultraviolet) have shorter wavelengths and higher frequencies. While lower energy waves (radio/microwave/infared) have longer wavelengths and low...
- Thu Oct 11, 2018 11:52 am
- Forum: Student Social/Study Group
- Topic: Studying techniques
- Replies: 12
- Views: 803
Re: Studying techniques
Dr. Lavelle provides a lot of great resources for studying. I'd definitely reccomend going through the video modules on the website, and reading the chosen sections in the book. Do the practice problems for homework and choose a wide range not just all from one section/topic. If you are confused on ...
- Thu Oct 11, 2018 11:41 am
- Forum: Accuracy, Precision, Mole, Other Definitions
- Topic: Naming Simple Coumpounds
- Replies: 2
- Views: 533
Re: Naming Simple Coumpounds
I don’t believe we need to know this quite yet, but if you want a head start here’s a few that have to do with polyatomic ions: -ate means it has more oxygen -ite means it has less oxygen Per- means it has one more oxygen Hypo- means it has one fewer oxygen These are from the video at https://www.kh...