Search found 101 matches
- Sat Mar 14, 2020 6:15 pm
- 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: Entropy and complexity
- Replies: 2
- Views: 274
Re: Entropy and complexity
Larger, more complex molecules would have more atoms in the molecule. This means that there are more electrons floating around which can result in more intermolecular forces between them and other species nearby. All the atoms would require more bonds to keep everything held together, and thus resul...
- Sat Mar 14, 2020 5:59 pm
- Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
- Topic: Half/Rxn & Balanced Equations for galvanic cells.
- Replies: 8
- Views: 572
Re: Half/Rxn & Balanced Equations for galvanic cells.
Platinum is the most common electrode used in electrochemical cells when none of the species present are solid metals because it is resistant to oxidation and won't easily react in redox reactions.
- Sat Mar 14, 2020 4:57 pm
- Forum: First Order Reactions
- Topic: First order rxns
- Replies: 6
- Views: 429
Re: First order rxns
You can look at the graph, the rate law expression (exponent = 1), the rate constant units (s-1), and the equation (if there's one reactant and its stoichiometric coefficient = 1).
- Sat Mar 14, 2020 4:54 pm
- Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
- Topic: Adding a Catalyst
- Replies: 6
- Views: 1586
Re: Adding a Catalyst
A catalyst only serves to speed up the rates of the forward/reverse reactions, but those would still be equal, and since catalysts don't change any equilibrium concentration and isn't a reactant since it can be regenerated and reused, the equilibrium constant K would not be affected. Also, K is the ...
- Sat Mar 14, 2020 12:35 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Equilibrium Constants
- Replies: 15
- Views: 950
Re: Equilibrium Constants
You should always make sure the equation is balanced before trying to do any calculations which require the correct stoichiometric ratios of reactants and products. Since the stoichiometric coefficients are crucial in things like exponents and fractions, and the equilibrium constant K is dependent o...
- Sun Mar 08, 2020 6:31 pm
- Forum: Zero Order Reactions
- Topic: Zero Order reaction rate constant
- Replies: 8
- Views: 501
Re: Zero Order reaction rate constant
The coefficients do not affect the rate constant, it will still be K.
- Sun Mar 08, 2020 6:27 pm
- Forum: Balancing Redox Reactions
- Topic: Oxidizing and Reducing
- Replies: 5
- Views: 372
Re: Oxidizing and Reducing
Since the half-reactions are typically written as reduction reactions, you have to use the cell potentials to understand which one is being oxidized and which one is being reduced.
More positive - reduction, cathode
More negative - oxidation, anode
More positive - reduction, cathode
More negative - oxidation, anode
- Sun Mar 08, 2020 6:24 pm
- Forum: General Rate Laws
- Topic: derivations?
- Replies: 5
- Views: 433
Re: derivations?
It would probably be helpful to at least understand the derivations and why/how they were done to achieve the equations we will use, but we probably would not have to do that whole process on paper for the test, rather just be able to use those equations correctly when required.
- Sun Mar 08, 2020 6:22 pm
- Forum: Reaction Mechanisms, Reaction Profiles
- Topic: Reaction Profile
- Replies: 2
- Views: 240
Re: Reaction Profile
If you can plot the graph then I think you should be able to go backwards and determine the rate of reaction and reaction order from a given graph by looking at the axes and linearity/curve of the line of the graph.
- Sun Mar 08, 2020 6:20 pm
- Forum: Method of Initial Rates (To Determine n and k)
- Topic: 7A.15
- Replies: 5
- Views: 400
Re: 7A.15
Don't worry about C, it's a zero order reaction - it will have no effect on the rate. Just focus on solving for A and B.
- Mon Mar 02, 2020 12:07 am
- Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
- Topic: salt bridge
- Replies: 9
- Views: 644
Re: salt bridge
Since electrons move from the anode to the cathode, the cathode eventually becomes very negatively charged and would stop electrons from moving from anode to cathode because like charges repel. The salt bridge allows ions to move between the anode and cathode to maintain both solutions in a neutral ...
- Sun Mar 01, 2020 11:59 pm
- Forum: Balancing Redox Reactions
- Topic: Anode and Cathode
- Replies: 9
- Views: 588
Re: Anode and Cathode
Electrons are lost from the anode (which is where oxidation occurs) and travel to the cathode (where reduction occurs).
- Sun Mar 01, 2020 10:58 pm
- Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
- Topic: Cathode/Right & Anode/Left
- Replies: 7
- Views: 1076
Re: Cathode/Right & Anode/Left
Oxidation happens at the anode and reduction happens at the cathode. Electrons leave the anode and go to the cathode.
- Sun Mar 01, 2020 10:51 pm
- Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
- Topic: Degree symbol
- Replies: 10
- Views: 1022
Re: Degree symbol
In things like ΔH° and ΔG°, the degree symbol just means that those are the standard ΔH and ΔG values, aka the values under "standard conditions" (STP = 1.0 atm and 25°C).
It's used for temperature for degrees Celsius/Centigrade (°C) and degrees Fahrenheit (°F).
It's used for temperature for degrees Celsius/Centigrade (°C) and degrees Fahrenheit (°F).
- Sun Mar 01, 2020 10:40 pm
- Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
- Topic: Reducing/oxidizing agent
- Replies: 8
- Views: 577
Re: Reducing/oxidizing agent
The reducing agent is the species that does the reducing - the reducing agent will reduce the other species by losing its electrons and giving them to the other species so that the other species gets reduced. Thus the reducing agent itself gets oxidized. Vice versa is true for oxidizing agents - the...
- Sat Feb 22, 2020 6:37 pm
- Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
- Topic: Electrochemical Cells
- Replies: 2
- Views: 161
Re: Electrochemical Cells
Electrical potential is the ability of an electrochemical/voltaic cell to produce an electric current, while voltage is the difference in electrical potential across different areas/points.
- Sat Feb 22, 2020 6:08 pm
- Forum: Balancing Redox Reactions
- Topic: Cell Diagrams
- Replies: 5
- Views: 314
Re: Cell Diagrams
Platinum is the most common electrode used in electrochemical cells because it is resistant to oxidation and won't easily react in redox reactions.
- Sat Feb 22, 2020 6:05 pm
- Forum: Balancing Redox Reactions
- Topic: Charge of oxygen
- Replies: 15
- Views: 769
Re: Charge of oxygen
Shouldn't the oxidation state of oxygen in O2 be zero? The oxidation state of each individual oxygen in compounds that have other elements of different electronegativity is -2, except in peroxides where it's -1. In O2, where there's no polarity in the bonds shared due to the fact that both oxygen a...
- Sat Feb 22, 2020 5:53 pm
- Forum: Administrative Questions and Class Announcements
- Topic: Curve?
- Replies: 5
- Views: 358
Re: Curve?
I don't think he curves tests, but I know that if you get a 50% in the class that's a C.
- Sat Feb 22, 2020 5:52 pm
- Forum: Balancing Redox Reactions
- Topic: Redox in Acidic/Basic Solutions
- Replies: 3
- Views: 272
Re: Redox in Acidic/Basic Solutions
When a redox reaction takes place in an acidic or basic solution, there would be an excess of H+ or OH- ions respectively. You need to use H+ to balance the half reactions in acidic solutions, and OH- to balance the half reactions in basic solutions. Also be sure to balance charges on both sides of ...
- Sun Feb 16, 2020 1:03 am
- Forum: Balancing Redox Reactions
- Topic: half reaction
- Replies: 8
- Views: 479
Re: half reaction
A half reaction is either of the reduction (RED) or oxidation (OX) reaction components of a redox reaction.
- Sun Feb 16, 2020 12:51 am
- Forum: Entropy Changes Due to Changes in Volume and Temperature
- Topic: memorize
- Replies: 14
- Views: 868
Re: memorize
I'm pretty sure most entropy, enthalpy, and gibbs free energy values will be given to us, either in the problem or the constants/values/equations sheets. And I mean, know that ΔH of all elements in their standard states is 0, and know the trends for ΔH, ΔS, and ΔG (<0 is spontaneous, decrease in ent...
- Sun Feb 16, 2020 12:42 am
- Forum: Balancing Redox Reactions
- Topic: How do you combine half reactions?
- Replies: 4
- Views: 323
Re: How do you combine half reactions?
Yes, but you may need to multiply the half reactions by constants in order to get electrons or repeating reactants and products equal in order to cancel out completely.
- Sun Feb 16, 2020 12:36 am
- Forum: Van't Hoff Equation
- Topic: T1 and T2
- Replies: 7
- Views: 572
Re: T1 and T2
The concentrations of reactants and products at equilibrium changes when temperature changes, so the value of K will also change when temperature changes.
- Sun Feb 16, 2020 12:35 am
- Forum: Van't Hoff Equation
- Topic: Van't Hoff Equation
- Replies: 4
- Views: 265
Re: Van't Hoff Equation
The temperature gets cancelled out:
ΔG = ΔH − TΔS = -RTlnK
lnK = (ΔH − TΔS)/(-RT) = ΔH/(-RT) − TΔS/(-RT) = -ΔH/(RT) + ΔS/R
ΔG = ΔH − TΔS = -RTlnK
lnK = (ΔH − TΔS)/(-RT) = ΔH/(-RT) − TΔS/(-RT) = -ΔH/(RT) + ΔS/R
- Tue Feb 11, 2020 3:02 am
- Forum: Calculating Standard Reaction Entropies (e.g. , Using Standard Molar Entropies)
- Topic: Delta H and Delta S
- Replies: 3
- Views: 320
Re: Delta H and Delta S
∆S is related to ∆H by ∆S=∆H/T (from ∆G = ∆H - T∆S, when ∆G = 0)
- Tue Feb 11, 2020 2:59 am
- Forum: Phase Changes & Related Calculations
- Topic: Heat of fusion and vaporization
- Replies: 1
- Views: 110
Re: Heat of fusion and vaporization
I believe that's correct - heat of fusion is the enthalpy when something changes state from solid to liquid, so the sign would be switched for the heat of solidification (liquid to solid) but still the same magnitude.
- Tue Feb 11, 2020 2:54 am
- Forum: Gibbs Free Energy Concepts and Calculations
- Topic: Go=0
- Replies: 7
- Views: 413
Re: Go=0
ΔG = 0 means that the system is at equilibrium - the forward and reverse reactions are occurring at the same rate at the same time.
- Tue Feb 11, 2020 2:52 am
- Forum: Administrative Questions and Class Announcements
- Topic: Memorizing acids and bases
- Replies: 2
- Views: 171
Re: Memorizing acids and bases
I'm pretty sure we need to have the small list of strong acids and bases memorized. The list was provided to us last quarter or you can just find it online. You'll know if something is a weak acid/base if it's not something from that list - you don't need to memorize weak acids and bases because it ...
- Tue Feb 11, 2020 2:49 am
- Forum: Gibbs Free Energy Concepts and Calculations
- Topic: Spontaneity
- Replies: 3
- Views: 293
Re: Spontaneity
△G < 0 means that the forward reaction is spontaneous, exothermic
△G = 0 means that the reaction is at equilibrium, reversible
△G > 0 means that the forward reaction is not spontaneous, endothermic
△G = 0 means that the reaction is at equilibrium, reversible
△G > 0 means that the forward reaction is not spontaneous, endothermic
- Sat Feb 01, 2020 3:14 pm
- Forum: Concepts & Calculations Using First Law of Thermodynamics
- Topic: Is U equal to delta Eth
- Replies: 2
- Views: 256
Re: Is U equal to delta Eth
Yes, Delta E and Delta U are essentially the same thing and can be used interchangeably.
- Sat Feb 01, 2020 3:10 pm
- Forum: Phase Changes & Related Calculations
- Topic: Internal Energy, U
- Replies: 6
- Views: 316
Re: Internal Energy, U
ΔH = ΔU + PΔV
ΔU is only equal to ΔH when the pressure is constant and the change in volume ΔV = 0.
ΔU is only equal to ΔH when the pressure is constant and the change in volume ΔV = 0.
- Sat Feb 01, 2020 3:07 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Test 1 #5
- Replies: 3
- Views: 249
Re: Test 1 #5
From the pKb you can find the value of Kb. Kb = 10^(-pKb) From the Kb you can find the value of Ka. Ka = Kw/Kb You can find the equation of Ka using the reaction and ICE table, and solve for the missing x values of the substances at equilibrium using the value of Ka and the equation. From there, you...
- Sat Feb 01, 2020 3:01 pm
- Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
- Topic: Enthalpy of Rxn
- Replies: 9
- Views: 435
Re: Enthalpy of Rxn
You multiply 300kJ/mol by 0.05 mol to get the mol units to cancel out and get a result of 15 kJ for the enthalpy of reaction.
- Sat Feb 01, 2020 2:43 pm
- Forum: Thermodynamic Systems (Open, Closed, Isolated)
- Topic: Isolated systems
- Replies: 4
- Views: 257
Re: Isolated systems
Yeah, I think for now we can assume that reactions in calorimeters suggest that the system is isolated. According to Dr. Lavelle's examples of open, closed, and isolated systems, he said that the combustion of glucose in a bomb calorimeter is an example of an isolated system where no energy or matte...
- Sun Jan 19, 2020 8:27 pm
- Forum: Calculating pH or pOH for Strong & Weak Acids & Bases
- Topic: Molar concentration of acids & bases
- Replies: 8
- Views: 409
Re: Molar concentration of acids & bases
If you're asked for the molar concentration of H3O+ or OH- you can leave your answer in terms of mol/L. Only when they ask for the pH or pOH do you have to think about taking the logarithms of those values.
- Sun Jan 19, 2020 8:25 pm
- Forum: Ideal Gases
- Topic: ph
- Replies: 10
- Views: 516
Re: ph
At different temperatures, the pH scale can go beyond the standard 0 to 14, because at different temperatures the autoprotolysis value of water is different from 10-14, but we do not need to worry about this in this class (for now).
- Sun Jan 19, 2020 7:55 pm
- Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
- Topic: Strong Acids/Bases vs. Weak Acids/Bases
- Replies: 9
- Views: 261
Re: Strong Acids/Bases vs. Weak Acids/Bases
Strong acids and bases completely dissociate in water, while weak acids and bases only partially dissociate. There's a fairly small/easy to learn list of strong acids and bases that you can memorize (that was provided to us last quarter or you can just find online). You'll know if something is a wea...
- Sun Jan 19, 2020 7:38 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Buffer
- Replies: 6
- Views: 364
Re: Buffer
A buffer is an aqueous solution that is a mixture of a weak acid/base and its conjugate base/acid, and it can resist change in pH when an acid or base is added to it. It is able to (mostly) maintain the pH of the solution because it is able to neutralize small amounts of the added acid or base becau...
- Sun Jan 19, 2020 7:34 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: ice boc
- Replies: 7
- Views: 258
Re: ice boc
The x is only negligible when adding/subtracting if the K value is very small (<10 -3 ) or when the change in the concentrations/partial pressures is less than 5% of the original concentration/partial pressure. You will not always have a small K value, and the stoichiometric coefficients will not al...
- Sun Jan 19, 2020 7:22 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: K for Gases
- Replies: 12
- Views: 395
Re: K for Gases
It probably depends on what you are given in the problem (the partial pressures or the concentrations). You could do either Kp or Kc, as long as you keep track and do not confuse the two because the values will not be the same. And in Wednesday's lecture Lavelle showed us how to convert between Kp ...
- Wed Jan 15, 2020 11:41 am
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: What is K
- Replies: 6
- Views: 246
Re: What is K
I'm pretty sure K c , K p , K w , K eq , K a , K b , etc are all different ways to clarify K, the equilibrium constant, by what is being used to calculate that value. K c is the equilibrium constant that is calculated using the concentrations of aqueous substances or gases of a system at equilibrium...
- Wed Jan 15, 2020 11:28 am
- Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
- Topic: delta H
- Replies: 5
- Views: 161
Re: delta H
I think last class Dr. Lavelle mentioned that there are three(?) ways of calculating delta H and that he'd teach us how to do it (if not now then eventually). However, for now it is important to know that positive delta H means that the reaction is endothermic and that heating the system will shift ...
- Wed Jan 15, 2020 11:17 am
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: ICE Table
- Replies: 8
- Views: 323
Re: ICE Table
Yes, ICE tables can be set up to determine the Initial, Change in, and Equilibrium concentrations (of aqueous substances or gases) or partial pressures (of gases).
- Wed Jan 15, 2020 11:09 am
- Forum: Non-Equilibrium Conditions & The Reaction Quotient
- Topic: Calculating Q
- Replies: 16
- Views: 793
Re: Calculating Q
You calculate Q the same way as you'd calculate K, using the gases and aqueous substances involved in the reaction. The only difference between Q and K is that Q can be different values since it can be calculated at any point during the reaction, while the K for a reaction at a specific temperature/...
- Wed Jan 15, 2020 10:57 am
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Writing K for heterozygous reactions
- Replies: 5
- Views: 190
Re: Writing K for heterozygous reactions
You would only use the gases to write the one (1) Kc equation. Liquids and solids are not included. For calculating Kc, you only take gases and aqueous solutions into consideration.
- Thu Jan 09, 2020 12:52 am
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: K being small or large
- Replies: 4
- Views: 136
Re: K being small or large
If K is small, there are more reactants present at equilibrium, which means that the system sits/lies to the left at equilibrium and strongly favors the reactants. If K is large, there are more products present at equilibrium, which means that the system sits/lies to the right at equilibrium and str...
- Thu Jan 09, 2020 12:49 am
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: K for Gases
- Replies: 12
- Views: 395
Re: K for Gases
It probably depends on what you are given in the problem (the partial pressures or the concentrations). You could do either Kp or Kc, as long as you keep track and do not confuse the two because the values will not be the same. And in Wednesday's lecture Lavelle showed us how to convert between Kp a...
- Wed Jan 08, 2020 9:45 pm
- Forum: Ideal Gases
- Topic: K and Q
- Replies: 13
- Views: 383
Re: K and Q
K is the equilibrium constant which is calculated when the system is at equilibrium, and Q is the reaction quotient that can be calculated at any point in the reaction. They are both calculated in the same manner though and by comparing the Q and K values you can determine where the reaction lies.
- Wed Jan 08, 2020 9:31 pm
- Forum: Ideal Gases
- Topic: Units for Pressure
- Replies: 6
- Views: 185
Re: Units for Pressure
It doesn’t matter what units of pressure you use as long as you use the appropriate value of R that works with those units.
- Wed Jan 08, 2020 8:41 pm
- Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
- Topic: Le Chatelier's Principle
- Replies: 6
- Views: 667
Re: Le Chatelier's Principle
Le Chatelier's principle states that if the equilibrium of a system is disturbed (caused by changes in temperature, pressure, volume, or concentration) the position of equilibrium will “shift” to counteract the changes and reestablish equilibrium in ways that we can predict.
- Sat Dec 07, 2019 3:13 pm
- Forum: Lewis Acids & Bases
- Topic: neutralization
- Replies: 6
- Views: 578
Re: neutralization
When a weak acid reacts with an equivalent amount of a weak base, it won't neutralize completely -- it depends on the equilibrium constant K for the reaction. But if the concentrations of a weak acid and strong base are equal then more volume of the weak acid would be needed to neutralize that stron...
- Sat Dec 07, 2019 3:09 pm
- Forum: Bronsted Acids & Bases
- Topic: weak bases
- Replies: 2
- Views: 282
Re: weak bases
Some weak bases include ammonia (NH 3 ), ammonium hydroxide (NH 4 OH), pyridine (C 5 H 5 N), and conjugate bases of weak acids. I think you determine which weak base is weaker/stronger in a similar manner to how you would determine which acid is stronger/weaker --> based on bond length and resulting...
- Sat Dec 07, 2019 3:04 pm
- Forum: Naming
- Topic: (en), (dien), etc.
- Replies: 6
- Views: 382
Re: (en), (dien), etc.
Yes, you can use the abbreviations when naming the compound and also when writing out the formula.
- Sat Dec 07, 2019 3:03 pm
- Forum: Significant Figures
- Topic: pH sig figs
- Replies: 9
- Views: 625
Re: pH sig figs
For pH and pOH, you worry about sig figs after the decimal point. Don't worry about it though until you have your answer.
- Sat Dec 07, 2019 3:01 pm
- Forum: Conjugate Acids & Bases
- Topic: how to figure out?
- Replies: 12
- Views: 730
Re: how to figure out?
The conjugate base is what is left of an acid when an H+ is removed, and the conjugate acid is what becomes of a base when an H+ is added.
- Mon Dec 02, 2019 9:41 am
- Forum: Naming
- Topic: Coordination Compound: Cation or Anion
- Replies: 3
- Views: 347
Re: Coordination Compound: Cation or Anion
Usually the cation is written first before the anion, it's just standard convention. I don't think there's anything wrong with switching that order other than it would look weird.
Re: oxidation
You add the oxidation number in parentheses after the transition metal if they have multiple oxidation states. Ex: iron(II) oxide and iron(III) oxide
- Mon Dec 02, 2019 8:55 am
- Forum: Calculating pH or pOH for Strong & Weak Acids & Bases
- Topic: pH calcuations
- Replies: 8
- Views: 474
Re: pH calcuations
That and pH+pOH=14, and perhaps equations relating to Ka.
- Mon Dec 02, 2019 8:54 am
- Forum: Calculating the pH of Salt Solutions
- Topic: pH formula?
- Replies: 69
- Views: 4130
Re: pH formula?
You just need to know how to calculate pH and pOH from the [H+] and [OH-] given, and vice versa. pH = -log([H+]) and pOH = -log([OH-]) = 14 - pH
- Thu Nov 28, 2019 3:00 pm
- Forum: Properties & Structures of Inorganic & Organic Acids
- Topic: Pka vs Ka
- Replies: 10
- Views: 608
Re: Pka vs Ka
Ka is the acid dissociation constant. pKa is the -log of this constant.
- Sun Nov 24, 2019 8:09 pm
- Forum: Determining Molecular Shape (VSEPR)
- Topic: 2.63
- Replies: 2
- Views: 122
Re: 2.63
I believe there are 2 lone pairs of electrons around the O, making that part bent, not trigonal planar, which is why it would be <109.5 degrees not 120 degrees.
- Sun Nov 24, 2019 7:59 pm
- Forum: *Molecular Orbital Theory (Bond Order, Diamagnetism, Paramagnetism)
- Topic: diamagnetism
- Replies: 5
- Views: 392
Re: diamagnetism
Diamagnetic atoms/compounds (and atoms) have paired electrons and are repelled from magnetic fields. (Paramagnetic atom/compounds are the opposite)
- Sun Nov 24, 2019 7:55 pm
- Forum: *Molecular Orbital Theory (Bond Order, Diamagnetism, Paramagnetism)
- Topic: paramagnetism
- Replies: 8
- Views: 707
Re: paramagnetism
Paramagnetic atoms/compounds have unpaired electrons, and are attracted to magnetic fields. (Examples: Cu2+,Fe3+)
- Sun Nov 24, 2019 6:47 pm
- Forum: Hybridization
- Topic: Strength of sigma vs pi bonds
- Replies: 6
- Views: 188
Re: Strength of sigma vs pi bonds
Sigma bonds are stronger because the bonding pair of electrons in sigma bonds is localised closer to the nuclei of the bonded atoms (on average). There is greater overlap.
- Sun Nov 24, 2019 6:44 pm
- Forum: Determining Molecular Shape (VSEPR)
- Topic: Bent vs linear
- Replies: 56
- Views: 4312
Re: Bent vs linear
Linear will have ONLY those two bonded atoms around the central atom, or the two bonded atoms and enough lone pairs around the central atom that would cause the dipole moments created from the lone pairs to cancel out, while bent would have the two bonded atoms around the central atom AND lone pairs...
- Sat Nov 16, 2019 10:23 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: Hydrogen Bonding
- Replies: 5
- Views: 158
Re: Hydrogen Bonding
Yes, a hydrogen bond is a strong dipole-dipole interaction between a slightly positive hydrogen on one molecule and a slightly negative O, N, or F on another molecule.
- Sat Nov 16, 2019 10:19 pm
- Forum: Determining Molecular Shape (VSEPR)
- Topic: What is VSPER
- Replies: 14
- Views: 1019
Re: What is VSPER
VSEPR stands for "Valence shell electron pair repulsion" but we do not need to memorize the full form of that acronym. However, we need to understand the theory and molecular geometries.
- Sat Nov 16, 2019 10:17 pm
- Forum: Determining Molecular Shape (VSEPR)
- Topic: Subscript on E
- Replies: 5
- Views: 316
Re: Subscript on E
You can put the subscript 1 on the E, but you don't have to. E1 and E are the same thing, so the 1 is pretty unnecessary, but if it helps you, it's okay.
- Sat Nov 16, 2019 9:52 pm
- Forum: Determining Molecular Shape (VSEPR)
- Topic: Bond Angles
- Replies: 8
- Views: 347
Re: Bond Angles
You should just memorize the generic ones: linear=180 degrees, trigonal planar=120 degrees, tetrahedral=109.5 degrees, trigonal bipyramidal=90 and 120 degrees, and octahedral=90 degrees. However, you should also know that having lone pairs will cause the bond angles to be less than the basic amounts...
- Sat Nov 16, 2019 9:50 pm
- Forum: Determining Molecular Shape (VSEPR)
- Topic: polar or non polar?
- Replies: 7
- Views: 551
Re: polar or non polar?
You can somewhat tell whether molecules are polar or nonpolar by whether or not their Lewis structures are symmetrical or not. Symmetrical = nonpolar, asymmetrical = polar (in general) Polar molecules must have polar bonds (bond between two different elements) with dipoles that do not cancel. Non-po...
- Sun Nov 10, 2019 11:12 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: London Forces
- Replies: 3
- Views: 170
Re: London Forces
Yes, London dispersion forces are intermolecular forces that occur between all atoms/molecules. They occur due to the temporary attraction that results from temporary dipoles due to electron movement within the clouds.
- Sun Nov 10, 2019 11:08 pm
- Forum: Electronegativity
- Topic: Atom size
- Replies: 22
- Views: 3310
Re: Atom size
Electronegativity is affected by the size of the atom, not the other way around. In fact, they're somewhat inversely proportional - as atom size increases, electronegativity decreases because it is easier for smaller atoms to attract electrons since the nucleus would be much closer to the electron c...
- Sun Nov 10, 2019 11:04 pm
- Forum: Formal Charge and Oxidation Numbers
- Topic: How to know where a double bond should go?
- Replies: 10
- Views: 1201
Re: How to know where a double bond should go?
Cl only has one unpaired electron in its valence shell and would thus typically and ideally only form a single bond with other elements, so if possible, a double bond with Cl is avoided.
- Sun Nov 10, 2019 11:03 pm
- Forum: Electronegativity
- Topic: Electron affinity
- Replies: 6
- Views: 756
Re: Electron affinity
Electronegativity and electron affinity are not the same thing. The difference between the two is that electronegativity is the chemical property that shows how well an atom can attract electrons, while electron affinity is the amount of energy released when an electron is added to a neutral atom to...
- Sun Nov 10, 2019 6:05 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: Temporary vs. Permanent Dipole
- Replies: 3
- Views: 244
Re: Temporary vs. Permanent Dipole
Permanent dipoles form when the electronegativity differences between the atoms bonded in a molecule is very great that some atoms are slightly positively charged and some are slightly negatively charged - for example, in water, there's a permanent dipole between the bonded hydrogens and oxygen such...
- Sun Nov 03, 2019 3:57 pm
- Forum: Properties of Light
- Topic: MeV
- Replies: 2
- Views: 110
Re: MeV
MeV is mega-electron volts. This is a unit of energy equal to 1000000 eV.
- Sun Nov 03, 2019 3:55 pm
- Forum: Quantum Numbers and The H-Atom
- Topic: 1D questions
- Replies: 4
- Views: 345
Re: 1D questions
11d. " How many orbitals are in subshells with l equal to (a) l = 0 --> s --> 1 orbital (b) l = 2 --> d --> 5 orbitals (c) l = 1 --> p --> 3 orbitals (d) l = 3 --> f --> 7 orbitals N = shell number, you can figure that out by what period (row) the element is in (EX: Na has 3 shells, n = 3. it's...
- Sun Nov 03, 2019 3:46 pm
- Forum: Student Social/Study Group
- Topic: Midterm
- Replies: 17
- Views: 913
Re: Midterm
I think the fundamentals are the main high school review topics, so I'd say it's pretty important to be confident with that for the midterm. But the midterm most likely will include everything we've learned so far as well from the quantum and chemical bonds sections.
- Sun Nov 03, 2019 3:32 pm
- Forum: Resonance Structures
- Topic: Drawing Resonance Structures
- Replies: 4
- Views: 297
Re: Drawing Resonance Structures
I think you just need to redraw the structures with the different double bonds. If the question asks to, then you would find the most ideal structure using formal charge and just draw that one.
- Sun Nov 03, 2019 3:25 pm
- Forum: Electronegativity
- Topic: Ionic or covalent?
- Replies: 17
- Views: 829
Re: Ionic or covalent?
An ionic compound is usually made from a metal and a non-metal, and a covalent/molecular compound is usually made from two non-metals. Sometimes you can determine ionic or covalent bonds by how far apart horizontally the elements are placed on the periodic table - the farther they are suggests great...
- Sat Oct 26, 2019 5:58 pm
- Forum: Trends in The Periodic Table
- Topic: Ionization energy
- Replies: 12
- Views: 638
Re: Ionization energy
It's pretty important to understand the ionization energy trends when looking at a periodic table - ionization energy increases from left to right across a period and decreases move down groups. It is measured in joules (J) or electron volts (eV), and is calculated by subtracting 1 from the atomic n...
- Sat Oct 26, 2019 5:48 pm
- Forum: Bond Lengths & Energies
- Topic: Bond length strength
- Replies: 6
- Views: 318
Re: Bond length strength
Bond strength and length will typically be given to you in the problem, on an information sheet, and certain ones might be required to be memorized. However, it's important to remember that triple bonds are stronger than double bonds, which are stronger than single bonds, and triple bonds are shorte...
- Sat Oct 26, 2019 5:43 pm
- Forum: Ionic & Covalent Bonds
- Topic: Resonance (all bonds are a hybrid of different bonds)
- Replies: 10
- Views: 415
Re: Resonance (all bonds are a hybrid of different bonds)
All the resonance structures of compounds that have resonance structures are equally accurate, but you would most likely have to draw all the resonance structures when asked to draw the Lewis structures for those compounds. However, you also use formal charges to determine which Lewis structure is m...
- Sat Oct 26, 2019 5:35 pm
- Forum: Ionic & Covalent Bonds
- Topic: Cation
- Replies: 23
- Views: 1831
Re: Cation
Cations are positively charged ions - these are atoms which have lost one or more electrons. Some examples of cations include K + , Na + , and Ca 2+ . Anions are negatively charged ions - these are atoms which have gained one or more electrons. Some examples of anions include F - , Cl - , and O 2- ....
- Sat Oct 26, 2019 5:29 pm
- Forum: Ionic & Covalent Bonds
- Topic: Covalent Bonds
- Replies: 5
- Views: 374
Re: Covalent Bonds
Nonmetals do not form cations because they are more electronegative than metals and attract electrons more strongly/readily, since they want to gain electrons to fill their octet. Metals also hold their valence electrons more loosely (which is why they're better conductors of electricity), so it is ...
- Sun Oct 20, 2019 6:31 pm
- Forum: Wave Functions and s-, p-, d-, f- Orbitals
- Topic: Tips for Subshells
- Replies: 4
- Views: 183
Re: Tips for Subshells
You use the noble gas from the period above the element you're writing the electron configuration for because noble gases have a full octet of electrons, and so the remaining electrons of the element you're configuring would be valence electrons. Noble gases have a full octet of electrons, so the no...
- Sun Oct 20, 2019 6:10 pm
- Forum: Heisenberg Indeterminacy (Uncertainty) Equation
- Topic: Heisenberg Uncertainty Principle
- Replies: 2
- Views: 172
Re: Heisenberg Uncertainty Principle
I think there is a maximum size, but I don't think we know what it is. Not going by the Heisenberg Uncertainty Principle and just going by nuclear attractive forces, bigger nuclei are unstable, which is why they are short-lived and decay quickly. There will be a point where if you keep adding proton...
- Sun Oct 20, 2019 5:39 pm
- Forum: Wave Functions and s-, p-, d-, f- Orbitals
- Topic: Atomic orbitals
- Replies: 5
- Views: 202
Re: Atomic orbitals
It's the probability of an electron being present at a specific location, aka in a specific orbital. The reason this is uncertain and not exact is because the exact position and momentum of an electron cannot be determined at the same time. Electrons are just too small and fast, man.
- Sun Oct 20, 2019 5:18 pm
- Forum: DeBroglie Equation
- Topic: DeBroglie Equation
- Replies: 11
- Views: 375
Re: DeBroglie Equation
Objects that have a rest mass behave like waves. That is the big concept of the De Broglie equation. So this equation is used to solve for the wavelength (or mass or velocity, depending on what the question is asking for and how the equation is rearranged) of any object that has momentum, or a mass ...
- Sun Oct 20, 2019 5:10 pm
- Forum: Photoelectric Effect
- Topic: 1B19
- Replies: 3
- Views: 248
Re: 1B19
Using the De Broglie equation λ = h/mv and the masses of a proton (1.6726*10^-27 kg) and a neutron (1.6750*10^-27 kg) that you find by looking them up (I think, unless it's given or you've memorized them)
- Sun Oct 13, 2019 12:11 am
- Forum: Significant Figures
- Topic: rounding in sig figs
- Replies: 5
- Views: 344
Re: rounding in sig figs
For rounding numbers that end in 5 in chemistry you want to try to round it to the nearest even number. 0.55 would round up to 0.6, 0.65 would round down to 0.6, etc. Usually when you have many numbers like this, rounding in this manner can somewhat "average" everything out. You would not ...
- Sun Oct 13, 2019 12:08 am
- Forum: Properties of Light
- Topic: Frequency vs. Wavelength
- Replies: 15
- Views: 718
Re: Frequency vs. Wavelength
Frequency is the number of waves per a unit of time (usually seconds), and wavelength is the length of one wave from crest to crest or trough to trough. Frequency times wavelength equals the speed of the wave, and in the case of light, we have c = λν. Frequency and wavelength are inversely proportio...
- Sun Oct 13, 2019 12:00 am
- Forum: Photoelectric Effect
- Topic: threshold energy
- Replies: 6
- Views: 323
Re: threshold energy
if the light energy is not great enough then electrons will not be excited. And if they aren't excited, then they can't escape from the pull of the metal.
- Sat Oct 12, 2019 11:53 pm
- Forum: Properties of Light
- Topic: Large Objects
- Replies: 7
- Views: 1121
Re: Large Objects
All matter has wavelike properties, but the wavelike properties are only noticed for moving objects with an extremely small mass (like electrons). This can be proven with the De Broglie equation, λ = h/mv --> if the mass is too large, the wavelength will be really small and thus the wavelike propert...
- Sat Oct 12, 2019 11:04 pm
- Forum: Balancing Chemical Reactions
- Topic: F.3
- Replies: 5
- Views: 382
Re: F.3
a) I think this is supposed to be something that we have memorized, perhaps from the polyatomic ions (nitrate = NO3-). I know for me in AP Chem we had to memorize strong acids and bases and polyatomic ions, but I'm sure it wouldn't matter if you looked up the formula --> Nitric acid = HNO3 b) For th...
- Sat Oct 05, 2019 4:19 pm
- Forum: Limiting Reactant Calculations
- Topic: Order of atoms in molecules
- Replies: 6
- Views: 268
Re: Order of atoms in molecules
It usually doesn't really matter what order the elements are in a compound, as long as the subscripts are correct. According to the Hill system, in compounds with carbon and hydrogen, you typically write carbon first, and then hydrogen, and then the remaining elements in alphabetical order. Another ...
- Sat Oct 05, 2019 4:10 pm
- Forum: SI Units, Unit Conversions
- Topic: E.23 Part B
- Replies: 3
- Views: 207
Re: E.23 Part B
The question is asking for how many moles of SO3 are in 7.00 x 10^2 mg of SO3. It's easier to look at everything in grams so 7.00 x 10^2 mg is the same as 7.00 x 10^2 x 10^-3 g, which is the same as 7.00 x 10^-1 g, or 0.700 g. Converting that into moles using the molar mass of SO3, which is 80.06 g/...
- Sat Oct 05, 2019 3:51 pm
- Forum: SI Units, Unit Conversions
- Topic: Series of Reactions Question
- Replies: 2
- Views: 119
Re: Series of Reactions Question
I'm also not completely sure what you mean, but if given a series of reactions, I'd assume that those reactions are like intermediate steps that would get you from the reactants in the first reaction to the products in the last reaction. As long as you're being careful and are able to keep everythin...
- Sat Oct 05, 2019 3:41 pm
- Forum: Significant Figures
- Topic: Question about significant figures and rounding a number
- Replies: 4
- Views: 342
Re: Question about significant figures and rounding a number
Yes, it's usually a lot easier to understand and use even numbers, so for rounding numbers that end in 5 in chemistry you want to try to round it to the nearest even number. 0.55 would round up to 0.6, 0.65 would round down to 0.6, etc. Usually when you have many numbers like this, rounding in this ...