Search found 86 matches

by Rachel Formaker 1E
Fri Mar 16, 2018 11:18 am
Forum: Arrhenius Equation, Activation Energies, Catalysts
Topic: Question 15.95
Replies: 1
Views: 82

Re: Question 15.95

Because the slow step is the rate-determining step, only changing the slow step will change the rate of the reaction.

Adding a catalyst to one of the fast steps will not affect the rate of reaction because the fast step does not determine the rate.
by Rachel Formaker 1E
Fri Mar 16, 2018 11:03 am
Forum: Reaction Mechanisms, Reaction Profiles
Topic: sketching reaction profiles
Replies: 2
Views: 92

Re: sketching reaction profiles

For a reaction profile, we mainly need to take into account the number of elementary steps, the activation energy of each step, and whether the reaction is exothermic or endothermic. For each elementary step, there is one energy barrier/"hill" in the reaction profile. The slow step will ha...
by Rachel Formaker 1E
Wed Mar 14, 2018 3:06 pm
Forum: Interesting Applications: Rechargeable Batteries (Cell Phones, Notebooks, Cars), Fuel Cells (Space Shuttle), Photovoltaic Cells (Solar Panels), Electrolysis, Rust
Topic: Electrolysis
Replies: 1
Views: 160

Re: Electrolysis

I think if you're told that it is an electrolytic cell, you should also be able to calculate standard cell potential by putting the reaction with the higher standard reduction potential at the anode rather than cathode. Basically, this would be the reverse of a Galvanic cell, so you could calculate ...
by Rachel Formaker 1E
Wed Mar 14, 2018 10:13 am
Forum: Arrhenius Equation, Activation Energies, Catalysts
Topic: Arrhenius when Temperature Changes
Replies: 3
Views: 108

Re: Arrhenius when Temperature Changes

Just make sure that you are consistent with which numbers you use. Keep track of which set of numbers is k1/T1 and which is k2/T2
by Rachel Formaker 1E
Sun Mar 04, 2018 11:48 pm
Forum: Zero Order Reactions
Topic: Slopes
Replies: 3
Views: 109

Re: Slopes

If you find experimentally certain points on the graphs we discussed in class, you can use the slope to find k. Since k is experimentally determined, this is the way to find k, not the other way around. I wouldn't say you necessarily need to memorize why certain orders correspond with certain graphs...
by Rachel Formaker 1E
Sun Mar 04, 2018 9:54 pm
Forum: Method of Initial Rates (To Determine n and k)
Topic: Little Product
Replies: 4
Views: 130

Re: Little Product

When there is product present, the product will also be reacting to form reactant. So this reverse reaction would occur in addition to reactant forming product, changing the overall rate at which reactant is consumed and product is formed. We therefore use initial rates to avoid having to calculate ...
by Rachel Formaker 1E
Sun Mar 04, 2018 2:49 pm
Forum: General Rate Laws
Topic: Rate Law
Replies: 3
Views: 92

Re: Rate Law

Rates are always given as positive values. Since the equation for rate is rate= d[]/dt and the concentration of reactants is decreasing, simply using the above equation for the rate of consumption of reactants would yield a negative rate. To correct this and give a positive rate for rate of consumpt...
by Rachel Formaker 1E
Sun Mar 04, 2018 2:43 pm
Forum: First Order Reactions
Topic: Significance of the order of a reaction?
Replies: 1
Views: 136

Re: Significance of the order of a reaction?

The order of a reaction tells us how the rate of reaction is affected by the concentration of the reactants. For a zero-order reaction, the rate of reaction is independent of the concentration of reactants, so changing the reactant concentration will have no effect on the reaction rate. For a first-...
by Rachel Formaker 1E
Sun Feb 25, 2018 2:36 pm
Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
Topic: swapping signs of E values
Replies: 8
Views: 248

Re: swapping signs of E values

I think Dr. Lavelle prefers that we use:
Eocell = Eocathode - Eoanode
so that we don't have to switch the sign of either standard reduction potential
by Rachel Formaker 1E
Sun Feb 25, 2018 12:21 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Galvanic cell set up
Replies: 8
Views: 178

Re: Galvanic cell set up

Since the reactions in Galvanic cells are spontaneous and Eocell = Eocathode - Eoanode, the reaction with the more positive (or less negative) standard reduction potential should be at the cathode so that Eocell > 0.
by Rachel Formaker 1E
Sun Feb 25, 2018 12:06 pm
Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
Topic: Finding Standard Potential Through Compiling Half-Reactions
Replies: 2
Views: 94

Re: Finding Standard Potential Through Compiling Half-Reactions

Even though ΔG of a final reaction will be the sum of the ΔGs of its composite reactions, it is important to note that this is not true of standard potential, E o . Since E o is not a state function, you must manipulate the equations to use ΔG, which is a state function. If reaction 1 + reaction 1 =...
by Rachel Formaker 1E
Mon Feb 19, 2018 8:35 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Cell Diagrams [ENDORSED]
Replies: 4
Views: 189

Re: Cell Diagrams [ENDORSED]

inert metal | reactant | product || reactant | product | inert metal The anode is typically on the left and the cathode is typically on the right. The double line represents the salt bridge, and will be replaced with a single line if there is a porous disk instead of a salt bridge. Lines are used to...
by Rachel Formaker 1E
Mon Feb 19, 2018 1:07 pm
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: Equilibrium constant
Replies: 3
Views: 125

Re: Equilibrium constant

Because ΔGo= -nFEo = -RTlnK,

-nFEo = -RTlnK

When standard cell potential is positive, K>1

When standard cell potential is negative, K<1

For positive Eo, larger the standard cell potential of a reaction, the larger the equilibrium constant.
by Rachel Formaker 1E
Thu Feb 15, 2018 11:36 pm
Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
Topic: Delta G=-nFE
Replies: 5
Views: 726

Re: Delta G=-nFE

Moles in the equation ΔG=-nFE is for moles of electrons, so even if the moles of a substance are not explicitly given, you should be able to figure out the moles of electrons through the redox half-reactions.
by Rachel Formaker 1E
Sat Feb 10, 2018 9:26 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: 9.15
Replies: 3
Views: 121

Re: 9.15

Heat is always required to melt a substance, so ∆H is positive.

Heat is released when a substance freezes, so ∆H is negative.

∆Hfreezing = ∆Hfusion, and since you are given ∆Hfusion from Table 8.3, you just reverse the sign of ∆Hfusion to get ∆Hfreezing = -6.01 kJ/mol
by Rachel Formaker 1E
Sat Feb 10, 2018 6:25 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: 9.5
Replies: 3
Views: 100

Re: 9.5

Since the problem says that the heat is being transferred from one reservoir to another, you can assume that the heat is leaving the first reservoir (-q) and entering the second reservoir (+q).
by Rachel Formaker 1E
Sat Feb 10, 2018 6:23 pm
Forum: Calculating Work of Expansion
Topic: Reversible vs Irreversible Work
Replies: 1
Views: 85

Re: Reversible vs Irreversible Work

If the external pressure is higher than the internal pressure, there will be compression rather than expansion of the gas, so you're not comparing it to reversible expansion anymore. However, I would assume that reversible compression would be more work being done on the system than irreversible com...
by Rachel Formaker 1E
Sat Feb 10, 2018 6:14 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: Irreversible expansion and entropy [ENDORSED]
Replies: 1
Views: 96

Re: Irreversible expansion and entropy [ENDORSED]

ΔS of the system will increase because in free expansion, the volume of the system will still increase, so the particles can occupy more microstates, representing an increase in entropy.
by Rachel Formaker 1E
Sat Feb 10, 2018 6:08 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: 9.13
Replies: 4
Views: 106

Re: 9.13

Although it does not specify 1 moleof N2 gas in the book, 9.13 is listed in the solutions manual errors on Lavelle's website. In the corrected answer, Lavelle says to assume both ideal behavior and 1 mol of N2 gas.
by Rachel Formaker 1E
Fri Feb 09, 2018 5:32 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: Homework problem 9.47
Replies: 2
Views: 91

Re: Homework problem 9.47

Isothermal means that the temperature does not change in the reaction. For all isothermal reactions, there is no change in internal energy, so ΔU=0. In this problem, we are told that ΔU=0 because the reaction is isothermal. Since no work is done in free expansion (w=0) and ΔU = q + w, when ΔU=0 and ...
by Rachel Formaker 1E
Sun Feb 04, 2018 10:40 pm
Forum: Thermodynamic Definitions (isochoric/isometric, isothermal, isobaric)
Topic: Exothermic and Spontaneous
Replies: 4
Views: 169

Re: Exothermic and Spontaneous

Exothermic and endothermic refer to ΔH, or the amount of heat absorbed or released in a reaction. Spontaneous and non-spontaneous refer to ΔG, or the free energy change of the reaction. Because ΔG = ΔH - TΔS, ΔG depends on both ΔH and ΔS. So not all exothermic reactions (ΔH < 0) will be spontaneous ...
by Rachel Formaker 1E
Sun Feb 04, 2018 10:33 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Measuring delta G
Replies: 4
Views: 95

Re: Measuring delta G

Since we cannot measure ΔG directly, we use equations with values that we can measure to calculate ΔG. We can measure equilibrium concentrations to calculate the equilibrium constant K, so we can calculate ΔG using K from measured concentrations: ΔG o = -RTlnK If the system is not at equilibrium, we...
by Rachel Formaker 1E
Sun Feb 04, 2018 10:29 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Gibbs free question
Replies: 2
Views: 65

Re: Gibbs free question

At equilibrium, the free energy of the products is equal to the free energy of the reactants.
Since ΔG = Gproducts - Greactants
When Greactants = Gproducts, ΔG = 0

Therefore, at equilibrium, ΔG = 0
by Rachel Formaker 1E
Sun Feb 04, 2018 10:26 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Difference between deltaG and deltaG*
Replies: 2
Views: 55

Re: Difference between deltaG and deltaG*

delta G o is for when the reactants and products are all in their standard states. This means that pressure is 1 atm and temperature is 25 o C (298 K). So if any of the given conditions violate these conditions, don't use delta G o . The general rule I use for homework and tests is that if the given...
by Rachel Formaker 1E
Sun Feb 04, 2018 6:22 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: Test Number 1
Replies: 9
Views: 268

Re: Test Number 1

There is heat transferred in this situation in order to keep temperature constant.
As a gas expands, it cools. Because the question tells us that temperature is constant, the gas must have absorbed heat from the surroundings to maintain its temperature and counteract the cooling from expansion.
by Rachel Formaker 1E
Sun Feb 04, 2018 5:01 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: Heat transfer to a liquefied gas.
Replies: 2
Views: 119

Re: Heat transfer to a liquefied gas.

When the pressurized liquid escapes as a gas, it undergoes a phase change where it changes from liquid to gas. Enthalpy of vaporization is always positive, meaning that heat is required to change the phase from liquid to gas. So heat is absorbed by the liquid as it changes into the gas phase while i...
by Rachel Formaker 1E
Sat Jan 27, 2018 10:25 pm
Forum: Thermodynamic Definitions (isochoric/isometric, isothermal, isobaric)
Topic: Degeneracy (W) [ENDORSED]
Replies: 8
Views: 379

Re: Degeneracy (W) [ENDORSED]

Degeneracy is the number of possible states that a system can have. For example, if one particle can be in one of two sides of a flask (similar to the example in class) the degeneracy is W=2 because the system has two possible states (the particle on either side of the flask). An equation for degene...
by Rachel Formaker 1E
Sat Jan 27, 2018 10:15 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: Enthalpy of Reaction at lower temperatures [ENDORSED]
Replies: 2
Views: 90

Re: Enthalpy of Reaction at lower temperatures [ENDORSED]

At lower temperatures, enthalpy of a reaction (ΔH or q P ) has a bigger influence on the entropy of a reaction because of this equation: \Delta S = \frac{q}{T} When T is lower, ΔS is larger, meaning that q had a larger effect on entropy. For example, if q=10 and T=1, ΔS =10, but if q=10 and T=10, th...
by Rachel Formaker 1E
Sat Jan 27, 2018 10:07 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: Ideal Behavior
Replies: 3
Views: 128

Re: Ideal Behavior

In general, when a problem says to assume ideal behavior, it is referring to the ideal gas law:
PV=nRT
by Rachel Formaker 1E
Sat Jan 27, 2018 1:26 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: Calculating degeneracy(W)
Replies: 3
Views: 144

Re: Calculating degeneracy(W)

To modify the equation above, W=2 N for a 2-state system, where N is the number of particles. The example we used was where each particle could be in one of two bulbs of a flask This equation can be used for any number of states, just by changing the base. For a 3-state system: W=3 N The number of s...
by Rachel Formaker 1E
Sat Jan 27, 2018 1:08 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: Internal energy as a state function
Replies: 3
Views: 117

Re: Internal energy as a state function

Internal energy is a state function because it depends only on the initial and final states of the internal energy. Although work is not a state function, as long as the sum of work done and heat transferred is the same, the change in internal energy will be the same regardless of the pathway taken ...
by Rachel Formaker 1E
Fri Jan 26, 2018 9:19 pm
Forum: Calculating Work of Expansion
Topic: Irreversible Pathway Picture
Replies: 3
Views: 127

Re: Irreversible Pathway Picture

The reason that no work is done in this picture is because the gas is expanding into a vacuum. There is no external pressure for in the vacuum, so since there is nothing for the gas to push against as it expands, it is not doing any work. The textbook calls this expansion against zero pressure "...
by Rachel Formaker 1E
Sun Jan 21, 2018 2:43 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: enthalpy of reaction
Replies: 1
Views: 53

Re: enthalpy of reaction

If the reaction is conducted at constant pressure , then heat transferred (q p ) will be equal to the enthalpy of the reaction (ΔH). Enthalpy is specifically the heat released or absorbed at constant pressure, so make sure that pressure is constant (reaction is not in a bomb calorimeter) before assu...
by Rachel Formaker 1E
Fri Jan 19, 2018 9:39 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Question 8.43
Replies: 2
Views: 87

Re: Question 8.43

The reason the answer is c) and not b) is because the slopes of the heating curve for the solid and gas phases must be steeper than the slope of the heating curve for the liquid phase. This is because the heat capacity of the liquid phase is higher than the heat capacities of the solid and gas phase...
by Rachel Formaker 1E
Fri Jan 19, 2018 8:43 pm
Forum: Phase Changes & Related Calculations
Topic: Closed Systems [ENDORSED]
Replies: 8
Views: 411

Re: Closed Systems [ENDORSED]

To increase the internal energy of a closed system, you can heat the system and/or perform work on the system.
You can heat the system using an external heat source, and you can perform work on a system by compressing the system (like compressing a bike pump).
by Rachel Formaker 1E
Fri Jan 19, 2018 8:28 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: Concept Clarification
Replies: 3
Views: 127

Re: Concept Clarification

Adding matter to an open system increases the internal energy of that system, and removing matter from an open system decreases the internal energy of the system.
by Rachel Formaker 1E
Fri Jan 19, 2018 8:22 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Question 8.49
Replies: 2
Views: 80

Re: Question 8.49

When a reaction produces heat (is exothermic), heat leaves the system. ΔH is negative because this represents heat leaving the system as it is produced.
by Rachel Formaker 1E
Fri Jan 19, 2018 7:58 pm
Forum: Thermodynamic Systems (Open, Closed, Isolated)
Topic: Isolated vs. Adiabatic system
Replies: 8
Views: 365

Re: Isolated vs. Adiabatic system

The internal energy of an isolated system will not change over time.

In an adiabatic system, energy is not transferred as heat, but the internal energy can still change if energy is transferred to or from the system as work.
For adiabatic systems, ΔU=w because q=0.
by Rachel Formaker 1E
Sun Jan 14, 2018 10:55 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: Born Habers Cycle [ENDORSED]
Replies: 4
Views: 180

Re: Born Habers Cycle [ENDORSED]

Just to note, on the outline for the unit on Thermochemistry and the First Law of Thermodynamics, Dr. Lavelle says to omit section 8.18 concerning the Born-Haber Cycle.
by Rachel Formaker 1E
Sun Jan 14, 2018 8:15 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: 3 Different Methods
Replies: 2
Views: 89

Re: 3 Different Methods

Adding onto the previous response, if you are given the standard enthalpies of formation for the reactants and products, you use the equation:
Σ ΔHorxn = Σ ΔHof(products) - Σ ΔHof(reactants)
by Rachel Formaker 1E
Sun Jan 14, 2018 6:23 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Standard Reaction Enthalpy
Replies: 1
Views: 92

Re: Standard Reaction Enthalpy

Some examples of reactants or products not in their standard states is carbon as diamond (instead of graphite) or oxygen as ozone (O3 rather than O2).

So a possible example of a reaction with reactants not in standard states is the conversion of ozone into oxygen:
2O3(g) --> 3O2(g)
by Rachel Formaker 1E
Fri Jan 12, 2018 2:47 pm
Forum: Phase Changes & Related Calculations
Topic: Heating Curve
Replies: 6
Views: 220

Re: Heating Curve

The length of the lines of the heating curves also represents the amount of heat needed to change the state of the substance. The longer the line, the more heat is required, indicating that the heat capacity is higher.
by Rachel Formaker 1E
Fri Jan 12, 2018 2:24 pm
Forum: Phase Changes & Related Calculations
Topic: qv vs qp
Replies: 4
Views: 475

Re: qv vs qp

Dr. Lavelle also specified that Qv is found using a bomb calorimeter, which keeps volume constant, while Qp is found using a coffee cup calorimeter, which allows gases to escape to keep pressure constant.
by Rachel Formaker 1E
Fri Jan 12, 2018 2:21 pm
Forum: Phase Changes & Related Calculations
Topic: Standard Reaction Enthalpy
Replies: 8
Views: 234

Re: Standard Reaction Enthalpy

Standard reaction enthalpy is specifically the reaction enthalpy for a reaction in which all the products and reactants are in their most stable forms and the pressure is 1 atm. Reaction enthalpy in general could be for a reaction in which ice is used instead of water, or ozone (O 3 ) instead of O 2...
by Rachel Formaker 1E
Sat Dec 09, 2017 8:51 pm
Forum: Properties & Structures of Inorganic & Organic Acids
Topic: Strong Bases? [ENDORSED]
Replies: 2
Views: 332

Re: Strong Bases? [ENDORSED]

Metal hydroxides are usually strong bases
Examples include NaOH, LiOH, KOH, etc.

Just as strong acids completely dissociate in water, strong bases also completely dissociate in water, so their conjugate acids are EXTREMELY weak, and you assume that none of the strong base remains in solution.
by Rachel Formaker 1E
Sat Dec 09, 2017 8:35 pm
Forum: *Molecular Orbital Theory (Bond Order, Diamagnetism, Paramagnetism)
Topic: Isoelectronic
Replies: 14
Views: 401

Re: Isoelectronic

Isoelectronic means that the two ions have the same number of valence electrons.

F- has valence 8 electrons
Because O- and N2- each have only 7 valence electrons, they are not isoelectronic with F-
by Rachel Formaker 1E
Sat Dec 09, 2017 8:32 pm
Forum: Acidity & Basicity Constants and The Conjugate Seesaw
Topic: Question 12.45
Replies: 3
Views: 290

Re: Question 12.45

The lower the pKb, the stronger the base.
Because pKa + pKb = 14 (so when pKa increases, pKb decreases), the larger the pKa value for an acid, the stronger the conjugate base.
by Rachel Formaker 1E
Sat Dec 09, 2017 8:21 pm
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: Pressure and Volume
Replies: 2
Views: 198

Re: Pressure and Volume

Increasing pressure by compression (decreasing volume) will cause the reaction to proceed toward the side with fewer moles of gas. Decreasing pressure by increasing volume will cause the reaction to proceed toward the side with more moles of gas. Dr. Lavelle specified in class that just saying that ...
by Rachel Formaker 1E
Sat Dec 09, 2017 8:09 pm
Forum: Naming
Topic: Test 4
Replies: 4
Views: 328

Re: Test 4

Diaquadifluoromercury(III)
by Rachel Formaker 1E
Sat Dec 09, 2017 8:05 pm
Forum: Calculating pH or pOH for Strong & Weak Acids & Bases
Topic: Relationship between pH, protanation and molarity
Replies: 5
Views: 185

Re: Relationship between pH, protanation and molarity

For an acid, when given the initial molarity and percent deprotonation, you multiply the initial molarity by the percent deprotonation (as a decimal, so over 100) to find the concentration of H 3 O + ions in solution. You then use this concentration to find pH in the normal way (pH=-log[H 3 O + ]) F...
by Rachel Formaker 1E
Sun Dec 03, 2017 6:10 pm
Forum: Non-Equilibrium Conditions & The Reaction Quotient
Topic: ICE table question
Replies: 5
Views: 1862

Re: ICE table question

If you are given initial concentrations and all of them are nonzero, calculate the reaction quotient Q. If Q<K, the reaction moves toward the products, so the ICE table would have +x on the products side and -x on the reactants side. If Q>K, the reaction moves toward the reactants, so the ICE table ...
by Rachel Formaker 1E
Sun Dec 03, 2017 6:02 pm
Forum: Non-Equilibrium Conditions & The Reaction Quotient
Topic: Notes on 11.37
Replies: 3
Views: 240

Re: Notes on 11.37

The rule in general is for a given equation, you raise K to the power of whatever value you multiplied the chemical reaction by.

So if you multiply the equation by 3, the new value of K would be the initial K3
by Rachel Formaker 1E
Sat Dec 02, 2017 8:55 pm
Forum: Hybridization
Topic: Pi Bonds
Replies: 2
Views: 156

Re: Pi Bonds

When a pi bond is delocalized, it is not restricted between two atoms. The electrons are spread out over several atoms in a molecule, giving the affected bonds characteristics (length and strength) between a double and single bond. For example, in benzene (C 6 H 6 ) there are 3 pi bonds delocalized ...
by Rachel Formaker 1E
Sat Dec 02, 2017 8:49 pm
Forum: Bronsted Acids & Bases
Topic: Bronsted Acid vs Lewis Acid [ENDORSED]
Replies: 3
Views: 163

Re: Bronsted Acid vs Lewis Acid [ENDORSED]

Another difference is that all Bronsted acids are Lewis acids, but not all Lewis acids are Bronsted acids. This is because when a molecule is a proton donor, that proton is an electron pair acceptor, making the molecule both a Bronsted acid(proton donor) and a Lewis acid (electron pair acceptor). So...
by Rachel Formaker 1E
Sun Nov 26, 2017 11:30 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Determining Molecular Shape
Replies: 3
Views: 154

Re: Determining Molecular Shape

Since the resonance structures are the same in terms of atom placement and differ only in electron placement, the shapes for different resonance structures will be the same. Shape depends on the number of regions of electron density, so whether there is a single, double, or triple bond has no effect...
by Rachel Formaker 1E
Sun Nov 26, 2017 11:16 pm
Forum: Hybridization
Topic: 3 regions of e- density
Replies: 3
Views: 177

Re: 3 regions of e- density

The coefficient when describing a hybridized orbital describes the energy level of the orbital being hybridized. So in general, when there are 4 regions of electron density, there will be sp 3 hybridization. Using the coefficient 4 in 4sp 3 means that the element with the hybridized orbitals is in P...
by Rachel Formaker 1E
Sun Nov 26, 2017 10:48 pm
Forum: Naming
Topic: Charges on Compounds
Replies: 1
Views: 103

Re: Charges on Compounds

To find the charge of a complex, you add the charges of the atoms/ions that make up the complex. In tetracyanonickelate(II): 4 x CN - = 4- 1 x Ni 2+ = 2+ Charge of complex = 2- You know that the nickel in this complex has a 2+ charge from the Roman numerals in the name. Since Table 17.4 is on the ou...
by Rachel Formaker 1E
Sun Nov 26, 2017 10:40 pm
Forum: Hybridization
Topic: HMK 4.91
Replies: 3
Views: 146

Re: HMK 4.91

The solutions manual also states that because the triple bonded carbons are strained in the ring formation, they may form a diradical in which the triple bond is replaced by a double bond with a single radical electron on each carbon. This would also result in a very reactive molecule because of the...
by Rachel Formaker 1E
Mon Nov 20, 2017 4:21 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Bond Angles
Replies: 2
Views: 107

Re: Bond Angles

We need to know the bond angles for the common VSEPR shapes (linear, trigonal planar, tetrahedral, trigonat bipyramidal, etc). However, we do not need to memorize the exact values for experimentally determined bond angles, like those resulting from lone pairs "pushing" the bonded atoms clo...
by Rachel Formaker 1E
Mon Nov 20, 2017 4:13 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Question 4.13 a
Replies: 3
Views: 140

Re: Question 4.13 a

The I 3 - molecule has the VSEPR notation AX 2 E 3 . Because it has 5 regions of electron density, begin by looking at the trigonal bipyramidal shape. The bond angles in trigonal bipyramidal are 120 o between the equatorial atoms, and only 90 o for the axial atoms. Because the lone pairs have more r...
by Rachel Formaker 1E
Mon Nov 20, 2017 4:01 pm
Forum: Properties of Electrons
Topic: Chem Midterm Question Q3C
Replies: 1
Views: 163

Re: Chem Midterm Question Q3C

If the performance of the supercomputer is only based on the speed of the electrons, the number of electrons is unrelated to performance. If you increase the number of electrons, all of the electrons will still have the same speed, there will just be more of them. This is similar to the results of t...
by Rachel Formaker 1E
Mon Nov 20, 2017 3:48 pm
Forum: Lewis Structures
Topic: Organic Lewis Structures
Replies: 2
Views: 145

Re: Organic Lewis Structures

Generally, with chemical formulas, atoms written next to each other are bonded to each other. So in HOCO, writing the formula this way tells you that the two oxygen atoms are bonded to the carbon, and the hydrogen is bonded to an oxygen. This can be especially helpful in hinting at the common groups...
by Rachel Formaker 1E
Mon Nov 20, 2017 3:41 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Lewis structure and Vsper
Replies: 2
Views: 117

Re: Lewis structure and Vsper

When drawing Lewis structures, the bonds can be placed at any angle around the central atom. We are not responsible for drawing VSEPR models, but it will help to understand the 3D shape, and you must know the bond angles for the given shapes.
by Rachel Formaker 1E
Mon Nov 20, 2017 3:38 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: KP versus KC
Replies: 3
Views: 172

Re: KP versus KC

Both types of equilibrium constant, whether in regard to molarity or partial pressure, refer to the composition of the equilibrium. Either constant will tell you if the equilibrium sits to the left or to the right.
by Rachel Formaker 1E
Sun Nov 12, 2017 11:32 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Lone Pair Placement
Replies: 3
Views: 168

Re: Lone Pair Placement

In general, since lone pairs have the greatest repulsion, put them wherever they will be farthest from each other or from other atoms. This will minimize the repulsion in the molecule and result in the most stable structure.
by Rachel Formaker 1E
Sun Nov 12, 2017 10:34 pm
Forum: Lewis Structures
Topic: Radicals
Replies: 7
Views: 257

Re: Radicals

As a general rule, yes, an odd number of valence electrons in a molecule means the molecule will be a radical.
by Rachel Formaker 1E
Sun Nov 12, 2017 10:18 pm
Forum: Trends in The Periodic Table
Topic: Hydrogen Electronegativity
Replies: 4
Views: 449

Re: Hydrogen Electronegativity

In addition, hydrogen is a very small atom, so its nuclear charge has a strong pull on the electrons in a bond. There is also very little to no shielding because hydrogen only has one electron, so the effective nuclear charge felt by the electron is very high.
by Rachel Formaker 1E
Sun Nov 12, 2017 9:47 pm
Forum: Octet Exceptions
Topic: Expanded Octet
Replies: 6
Views: 537

Re: Expanded Octet

The elements that typically have less than an octet are hydrogen, helium, lithium, and beryllium. Boron also may form molecules where it only has 6 electrons. For expanded octets, any element in period 3 or later with a d-orbital can have an expanded octet. This includes sulfur, phosphorus and chlor...
by Rachel Formaker 1E
Sun Nov 12, 2017 9:32 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Trigonal Bipyramidal with 1 lone pair and 4 bonds
Replies: 3
Views: 158

Re: Trigonal Bipyramidal with 1 lone pair and 4 bonds

In the equatorial plane, there are 3 regions of electron density, which can be separated by approximately 120 o bond angles. This is favorable compared to axial atoms above and below the equatorial plane, which have only approximately 90 o bond angles with equatorial atoms. Since lone pairs have mor...
by Rachel Formaker 1E
Sun Nov 05, 2017 9:21 pm
Forum: Lewis Structures
Topic: Lewis Structure Format
Replies: 2
Views: 122

Re: Lewis Structure Format

To clarify, when there is a bracket with a charge around a Lewis structure with multiple atoms, that means that the molecule shown is a polyatomic ion. The bonds between the atoms within the ion itself are covalent, but the ion will form ionic bonds with other ions. When there are bonds shown as lin...
by Rachel Formaker 1E
Sun Nov 05, 2017 1:33 pm
Forum: Resonance Structures
Topic: Homework problem 3.57
Replies: 1
Views: 143

Re: Homework problem 3.57

The atom in the center in the molecules here is always the one with the lowest ionization energy, so these do follow the guideline laid out in class. The guideline for ionization energies is that ionization energy decreases as you go down a group and increases right to left across a period. In the s...
by Rachel Formaker 1E
Sun Nov 05, 2017 1:18 pm
Forum: Lewis Structures
Topic: Lewis Acid/Base vs. Regular Acid/Base
Replies: 1
Views: 82

Re: Lewis Acid/Base vs. Regular Acid/Base

Lewis acids and bases are defined in terms of electrons, while regular (Bronsted) acids and bases are defined in terms of protons. A Lewis acid accepts an electron pair and a Lewis base donates an electron pair. A Bronsted acid donates a proton and a Bronsted base accepts a proton. If something is a...
by Rachel Formaker 1E
Sun Nov 05, 2017 1:06 pm
Forum: Trends in The Periodic Table
Topic: why carbon has a higher electron affinity than nitrogen.
Replies: 5
Views: 2407

Re: why carbon has a higher electron affinity than nitrogen.

Nitrogen has a half-filled 2p subshell, so that there is one electron in each orbital. This creates an unusually stable atom because of half-shell stability. Because nitrogen is relatively stable on its own, it has a relatively low electron affinity. It is similar to the reason that chromium has an ...
by Rachel Formaker 1E
Mon Oct 30, 2017 10:42 am
Forum: Formal Charge and Oxidation Numbers
Topic: Ionization energy vs. electron affinity [ENDORSED]
Replies: 5
Views: 320

Re: Ionization energy vs. electron affinity [ENDORSED]

Another way to think about this is that a low ionization energy corresponds to likelihood to form a cation (because it is easier to remove the electron) and a high electron affinity corresponds to likelihood to form an anion (because more energy is released when an electron is added). This is helpfu...
by Rachel Formaker 1E
Mon Oct 30, 2017 10:35 am
Forum: Trends in The Periodic Table
Topic: Exceptions to trends [ENDORSED]
Replies: 6
Views: 667

Re: Exceptions to trends [ENDORSED]

The ionization energies of the Group 15 elements is higher than that of the Group 16 elements because in Group 15, each p-orbital has one electron, which is relatively stable because it is a half-filled subshell. Group 16 elements have one set of paired electrons in the p-orbital, and the repulsion ...
by Rachel Formaker 1E
Sun Oct 22, 2017 3:46 pm
Forum: Electron Configurations for Multi-Electron Atoms
Topic: nodal planes [ENDORSED]
Replies: 3
Views: 349

Re: nodal planes [ENDORSED]

Nodal planes are planes on which there is no chance that an electron will be found. The s-orbitals have no nodal planes, but the p- and d- orbitals do. They are mainly of interest when we are trying to figure out the location of an electron in a given orbital. The electron will never be at the nucle...
by Rachel Formaker 1E
Sun Oct 22, 2017 1:31 pm
Forum: Wave Functions and s-, p-, d-, f- Orbitals
Topic: Magnetic Quantum numbers vs. Spin Magnetic
Replies: 2
Views: 126

Re: Magnetic Quantum numbers vs. Spin Magnetic

The magnetic quantum number of an electron tells us precisely which orbital within a subshell that the electron occupies. The spin magnetic quantum number has values of either +1/2 (spin up) or -1/2(spin down). This tells us if the electron spins counterclockwise (spin up) or clockwise (spin down). ...
by Rachel Formaker 1E
Sun Oct 22, 2017 1:11 am
Forum: Wave Functions and s-, p-, d-, f- Orbitals
Topic: electron configurations [ENDORSED]
Replies: 2
Views: 166

Re: electron configurations [ENDORSED]

To clarify, the 2p electron subshell has 3 orbitals, 2p x , 2p y , and 2p z , each of which can hold 2 electrons. According to Hund's Rule, if electrons in the same subshell can occupy different orbitals, then they will do so. So when an atom has 2 electrons in the 2p subshell, they will occupy the ...
by Rachel Formaker 1E
Sun Oct 15, 2017 1:20 pm
Forum: Bohr Frequency Condition, H-Atom , Atomic Spectroscopy
Topic: H-Atom Equation
Replies: 3
Views: 150

Re: H-Atom Equation

To elaborate on the last answer: When you calculate ΔE, you do final-initial. In this case, that means E n (final) - E n (initial) When the electron is moving from a higher energy state to a lower energy state, ΔE will be negative. When the electron is moving from a lower energy stat...
by Rachel Formaker 1E
Sat Oct 14, 2017 11:32 pm
Forum: Properties of Electrons
Topic: Speed/Energy of Electrons
Replies: 4
Views: 212

Re: Speed/Energy of Electrons

I think your confusion is mainly mixing up speed, energy, and frequency. The speed of light is constant (3.00 x 10 8 m/s), and is equal to the frequency times wavelength of light. The frequency(v) of light is different for different types of light, and the energy(E) of light is related to the freque...
by Rachel Formaker 1E
Sat Oct 14, 2017 10:40 pm
Forum: Bohr Frequency Condition, H-Atom , Atomic Spectroscopy
Topic: Question about Atomic Spectroscopy
Replies: 4
Views: 227

Re: Question about Atomic Spectroscopy

Because each element has a different number of protons, each element's nucleus has a different positive charge. This variation in positive charge for each element causes the electrons in each element to be bound to the atom by a different amount of energy. The slight differences in configuration cau...
by Rachel Formaker 1E
Sat Oct 14, 2017 8:22 pm
Forum: Einstein Equation
Topic: Planck's Constant
Replies: 3
Views: 234

Re: Planck's Constant

Constants usually have the units that they do because of the units of the quantities that they relate.
So in the equation E=hv, Planck's constant relates frequency(in seconds-1) and energy (Joules). In order for this equation to make sense, Planck's constant must have the units of Joule-seconds.
by Rachel Formaker 1E
Fri Oct 06, 2017 6:03 pm
Forum: Balancing Chemical Reactions
Topic: Determining States of Matter in Reactions
Replies: 7
Views: 677

Re: Determining States of Matter in Reactions

For the purposes of chemical equations, aqueous solutions and liquids are different, and it is important to make this distinction when writing out the equation.
An aqueous solution is indicated by the symbol (aq), while a liquid is indicated by the symbol (l).
by Rachel Formaker 1E
Fri Oct 06, 2017 1:32 pm
Forum: SI Units, Unit Conversions
Topic: Prefixes [ENDORSED]
Replies: 6
Views: 356

Re: Prefixes [ENDORSED]

As far as I know, the common prefixes need to be memorized.
The ones we went over in lecture are

giga: 109
mega: 106
kilo: 103
deci: 10-1
centi: 10-2
milli: 10-3
micro: 10-6
nano: 10-9
pico: 10-12
by Rachel Formaker 1E
Thu Oct 05, 2017 10:50 pm
Forum: Accuracy, Precision, Mole, Other Definitions
Topic: Formula Units
Replies: 2
Views: 188

Re: Formula Units

Discussing the formula unit of an ionic compound is equivalent to discussing a molecule of a covalently bonded compounds. It is technically incorrect to call a unit of NaCl a molecule, although that may be what you have heard in past chemistry classes. Call it a formula unit instead. Fundamentals Se...
by Rachel Formaker 1E
Thu Oct 05, 2017 10:10 pm
Forum: Balancing Chemical Reactions
Topic: Writing chemical formulas [ENDORSED]
Replies: 5
Views: 307

Re: Writing chemical formulas [ENDORSED]

When we are given the name of the compound in a problem and we are supposed to find the chemical formula for an equation with no other information, the compound is usually an ionic compound and we are supposed to be able to figure out the formula using the oxidation numbers of its elements. For exam...

Go to advanced search