Search found 50 matches

by Cooper1C
Wed Mar 14, 2018 3:12 pm
Forum: Phase Changes & Related Calculations
Topic: 15.85
Replies: 2
Views: 213

Re: 15.85

Unimolecular means that the reaction involves one molecule, bimolecular means the reaction involves two molecules, and termolecular means the reaction involves three molecules.
by Cooper1C
Wed Mar 14, 2018 3:09 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Catalyst and Intermediate
Replies: 5
Views: 310

Re: Catalyst and Intermediate

A catalyst does not change the reactants and products of a reaction - it just changes the pathway. So you should be able to have catalysts and intermediates in the same reaction.
by Cooper1C
Wed Mar 14, 2018 3:06 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: k' reverse reaction constant
Replies: 6
Views: 312

Re: k' reverse reaction constant

It's just the notation - it distinguishes k from k'. I don't think there's anything special about it.
by Cooper1C
Fri Mar 09, 2018 8:31 pm
Forum: Student Social/Study Group
Topic: Post All Chemistry Jokes Here
Replies: 7609
Views: 1019625

Re: Post All Chemistry Jokes Here

Q: What kind of fish is made out of 2 sodium atoms?
A: 2 Na
by Cooper1C
Fri Mar 09, 2018 8:31 pm
Forum: Student Social/Study Group
Topic: Post All Chemistry Jokes Here
Replies: 7609
Views: 1019625

Re: Post All Chemistry Jokes Here

Q: What do you call a wheel made of iron?
A: A ferrous wheel.
by Cooper1C
Fri Mar 09, 2018 8:30 pm
Forum: Student Social/Study Group
Topic: Post All Chemistry Jokes Here
Replies: 7609
Views: 1019625

Re: Post All Chemistry Jokes Here

Q: What do you call a clown who's in jail?
A: A silicon.
by Cooper1C
Wed Feb 28, 2018 4:41 pm
Forum: Method of Initial Rates (To Determine n and k)
Topic: When do we calculate for k
Replies: 3
Views: 146

Re: When do we calculate for k

k is based on experimental data, so if you're given data you are probably expected to calculate it. If not, I think you can use the table.
by Cooper1C
Wed Feb 28, 2018 2:26 pm
Forum: Zero Order Reactions
Topic: Using Half Life with Zero Order
Replies: 2
Views: 132

Re: Using Half Life with Zero Order

On page 631, the textbook also says that the half-life is not used for second order reactions. Maybe this is because the half-life depends on the initial concentration for zero and second order reactions? This would make it difficult to compare reactions.
by Cooper1C
Wed Feb 28, 2018 2:13 pm
Forum: Method of Initial Rates (To Determine n and k)
Topic: 15.19
Replies: 2
Views: 149

Re: 15.19

From experiment 2:

17.4 mmol/L*s = k(2.5 mmol/L)(1.25^2 mmol^2/L^2)(1.25^2 mmol^2/L^2)
k = 17.4 mmol/L*s /(1.25^2*1.25^2*2.5) mmol^5/L^5

The mmol and L cancel, so you have

k = 17.4/s /(1.25^2*1.25^2*2.5) L^4/mmol^4

1 mmol = 10^3 mol, so

k = 17.4/(1.25^2*1.25^2*2.5)* 10^12 L^4/mol^4*s
by Cooper1C
Thu Feb 22, 2018 7:45 pm
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: Nernst Equation to find pH
Replies: 6
Views: 1592

Re: Nernst Equation to find pH

At standard conditions, you can use the formula to find the pH. The formula for ph is pH = -log[H+}, so you can find the concentration of hydrogen ions by the Nearst equation.The formula above is already converted from ln to log.
by Cooper1C
Thu Feb 22, 2018 7:41 pm
Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
Topic: swapping signs of E values
Replies: 8
Views: 493

Re: swapping signs of E values

If you use the formula you do not need to change the sign of for either half reaction because the minus sign does it for you.
by Cooper1C
Thu Feb 22, 2018 7:38 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Homework 14.9
Replies: 1
Views: 104

Re: Homework 14.9

In order to use the formula , you can solve for n by writing out the oxidation and reduction half reactions and balancing them.
by Cooper1C
Wed Feb 14, 2018 1:13 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: Temperature Relation
Replies: 2
Views: 112

Re: Temperature Relation

Relationship between T and delta U: \Delta U = q (assuming no work is done) If you increase heat added (increase q) then delta U increases. Relationship between T and delta S: delta S \Delta S __{T_{1} \rightarrow T_{2}} = nC(\ln T_{2} - \ln T_{1}) If you look at the natural log graph: If T_...
by Cooper1C
Wed Feb 14, 2018 12:30 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: Difference between delta S and delta S naught
Replies: 2
Views: 1587

Re: Difference between delta S and delta S naught

The third law of thermodynamics says that the total entropy is always increasing, so delta S total must be positive. The standard enthalpy for a reaction can be positive or negative depending on the reaction. For example, building polymers from monomers has a negative delta S (the complexity is incr...
by Cooper1C
Wed Feb 14, 2018 12:29 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: 9.73 and delta S tot
Replies: 1
Views: 115

Re: 9.73 and delta S tot

The third law of thermodynamics says that the total entropy is always increasing, so delta S total must be positive. The standard enthalpy for a reaction can be positive or negative depending on the reaction. For example, building polymers from monomers has a negative delta S (the complexity is incr...
by Cooper1C
Wed Feb 07, 2018 7:02 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: K to Kc equation
Replies: 2
Views: 111

Re: K to Kc equation

Kc is the equilibrium constant in terms of molar concentrations. See section 11.6 in the textbook.
by Cooper1C
Wed Feb 07, 2018 6:59 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: 9.25
Replies: 2
Views: 120

Re: 9.25

The question says "what might its residual molar entropy be?" so you would use avogadro's constant.
by Cooper1C
Wed Feb 07, 2018 6:57 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: 9.19
Replies: 1
Views: 91

Re: 9.19

Because entropy is a state function and you know the vaporization at 100 degrees C, to find the standard entropy of vaporization at 85 degrees C you can heat the water to 100 degrees C, vaporize it, then cool it to 85 degrees C. This will give you the standard entropy of vaporization at 85 degrees C.
by Cooper1C
Thu Feb 01, 2018 6:33 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: Negative delta s value
Replies: 4
Views: 874

Re: Negative delta s value

A negative delta S corresponds to a spontaneous process when the magnitude of T * delta S is less than delta H (which must be negative). This is because delta G must be negative, and delta G = delta H - (T * delta S). A negative delta S would mean that the products have a lower entropy than the reac...
by Cooper1C
Thu Feb 01, 2018 6:29 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Spontaneous
Replies: 14
Views: 423

Re: Spontaneous

Reactions are spontaneous when delta G is negative. delta G = delta H - (T * delta S) Releasing heat is favored, and increasing entropy is favored (for example, liquid to gas - especially favored at higher temperatures). You have to consider both cases to make a conclusion about the spontaneity of a...
by Cooper1C
Wed Jan 31, 2018 4:22 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: State functions [ENDORSED]
Replies: 7
Views: 239

Re: State functions [ENDORSED]

Delta S is also a state function.
by Cooper1C
Tue Jan 23, 2018 8:09 pm
Forum: Phase Changes & Related Calculations
Topic: Phase Changes and Energy
Replies: 2
Views: 120

Re: Phase Changes and Energy

I think s->l->g requires energy and g->l->s releases energy.
by Cooper1C
Tue Jan 23, 2018 8:05 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Problem 8.51
Replies: 2
Views: 234

Re: Problem 8.51

You use the enthalpies of formation to calculate delta H, then you have to convert kJ/mol TNT to kJ/L, which is why you need to know the density of TNT.
by Cooper1C
Tue Jan 23, 2018 8:03 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: 8.51
Replies: 1
Views: 88

Re: 8.51

The first step is to balance the equation that they describe in the first sentence. CO + H2O -> CO2 + H2 Then you know that the heat absorbed by the calorimeter is equal to the heat released by the reaction. qcal = -qrxn And delta U = q because the reaction occurred in a bomb calorimeter (w = 0 beca...
by Cooper1C
Thu Jan 18, 2018 3:38 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: 8.51
Replies: 1
Views: 108

Re: 8.51

I believe that the sign is positive because the definition of enthalpy density is the enthalpy released per liter, so adding a negative sign would mean energy is absorbed.
by Cooper1C
Mon Jan 15, 2018 7:31 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: Q. 8.39
Replies: 2
Views: 149

Re: Q. 8.39

I would draw the phase change chart for water first. The first phase change is at 0 degrees and the second is at 100 degrees. If you start at 0 degrees (ice) and go to 20 degrees (liquid), you need to consider both the heat required to change ice to a liquid and the heat required to raise the temper...
by Cooper1C
Fri Jan 12, 2018 10:26 am
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: 8.61
Replies: 4
Views: 165

Re: 8.61

Like balancing chemical reactions, I recommend manipulating the equations that have the least number of the same molecule first, and the should build on it.
by Cooper1C
Fri Jan 12, 2018 10:22 am
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: 8.49
Replies: 5
Views: 198

Re: 8.49

What is the difference between internal energy and enthalpy? H = U + PV. Enthalpy is equal to internal energy plus the product of pressure and volume, so internal energy is included in the enthalpy calculation. Also, internal energy has to do with the kinetic and potential energies of molecules in ...
by Cooper1C
Fri Jan 12, 2018 10:09 am
Forum: Thermodynamic Systems (Open, Closed, Isolated)
Topic: 8.1 part c [ENDORSED]
Replies: 8
Views: 451

Re: 8.1 part c [ENDORSED]

IMG_4781.JPG
Here is a diagram of a bomb calorimeter from the textbook (page 271)
by Cooper1C
Thu Dec 07, 2017 6:53 pm
Forum: Amphoteric Compounds
Topic: Amphiprotic [ENDORSED]
Replies: 5
Views: 474

Re: Amphiprotic [ENDORSED]

Amphiprotic is the ability of a molecule to both accept and donate protons.

Amphoteric is the ability of a molecule to react with both acids and bases.

See page 469 in the textbook.
by Cooper1C
Thu Dec 07, 2017 6:43 pm
Forum: Calculating pH or pOH for Strong & Weak Acids & Bases
Topic: 12.25
Replies: 1
Views: 160

Re: 12.25

I believe the acid/base will not dissociate unless it is in some sort of solvent. In this case, the problem states Ba(OH)2 is in an aqueous solution. Ba(OH)2 is a strong acid, so you do not need to set up an ice box, and you are not given Kb. Because Ba(OH)2 is a strong base, we assume it is 100% io...
by Cooper1C
Wed Dec 06, 2017 11:43 am
Forum: Acidity & Basicity Constants and The Conjugate Seesaw
Topic: 12.49
Replies: 5
Views: 403

Re: 12.49

Is there any way to figure out this problem by looking at the Lewis structures?
by Cooper1C
Tue Nov 28, 2017 6:51 pm
Forum: Naming
Topic: (EDTA) and (en) Q17.37
Replies: 1
Views: 143

Re: (EDTA) and (en) Q17.37

If you look at table 4, the full name of the ligand is given and the abbreviation is in parentheses: ethylenediamine (en) enthylenediaminetetraacetato (edta) After the parentheses is a symbol that corresponds to one of the footnotes telling you whether the ligand is bidentrate, tridentate, or hexade...
by Cooper1C
Tue Nov 28, 2017 6:36 pm
Forum: Naming
Topic: 17.33 (a)
Replies: 1
Views: 128

Re: 17.33 (a)

The carbons and nitrogens form a long chain, with the hydrogens bonded to each atom. The order in which the atoms are written gives the order of the chain, and because there are two identical segments, the molecule can be drawn as symmetrical. If you count the number of available valence electrons, ...
by Cooper1C
Tue Nov 28, 2017 6:13 pm
Forum: Naming
Topic: naming with anions
Replies: 2
Views: 171

Re: naming with anions

This makes sense because in order for it to be a neutral compound, there must be three chlorine atoms. The chromium atom has a +3 charge, so there must be three chlorine atoms, each with a -1 charge. "Trichloride would be redundant."
by Cooper1C
Mon Nov 13, 2017 7:47 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: AXE
Replies: 3
Views: 170

Re: AXE

The subscript of E is the number of lone pairs around the central atom. You would have to draw the Lewis structure.
by Cooper1C
Mon Nov 13, 2017 4:45 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: lone pairs in trigonal bipyramidal shape
Replies: 2
Views: 134

Re: lone pairs in trigonal bipyramidal shape

See figure 4.5 in the textbook (page 115): "If the lone pairs had taken the axial positions, they would have been at 90 degree angles from the equatorial positions, resulting in greater repulsion."
by Cooper1C
Mon Nov 13, 2017 4:39 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Question 4.25
Replies: 2
Views: 256

Re: Question 4.25

You also have to think about the shape of the molecule. For example, in part (a) (CH2Cl2), the molecule has a tetrahedral shape, so the dipole moments do not cancel, even though they look they could in the Lewis structure -> The molecule is polar.
by Cooper1C
Mon Nov 13, 2017 4:10 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Book Questions 4.1&4.2
Replies: 4
Views: 156

Re: Book Questions 4.1&4.2

Page 118 of the textbook provides good graphics for this concept. For the linear model, the molecule can either have the formula AX2 or AX2E3, so it could have lone pairs around the central atom.
by Cooper1C
Mon Nov 13, 2017 3:41 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Question 4.13 a
Replies: 2
Views: 124

Re: Question 4.13 a

If you look on page 118 in the textbook, there are really good diagrams that show the shapes. If you think about a molecule with 5 regions of electron density and no lone pairs, the shape is trigonal bipyramidal. Then if you replace the 3 atoms in the plane with 3 lone pairs, the shape is linear.
by Cooper1C
Mon Nov 13, 2017 11:24 am
Forum: Determining Molecular Shape (VSEPR)
Topic: 4.1
Replies: 5
Views: 175

Re: 4.1

It is possible for (b) to have lone pairs if it has 3 lone pairs around the central atom. It will still be a linear shape. See page 118 of the book for a graphic.
by Cooper1C
Mon Nov 13, 2017 10:20 am
Forum: Determining Molecular Shape (VSEPR)
Topic: Organic vs inorganic molecules
Replies: 3
Views: 170

Re: Organic vs inorganic molecules

I also believe that organic molecules are usually chains or rings.
by Cooper1C
Mon Nov 13, 2017 10:11 am
Forum: Lewis Structures
Topic: Bond Lengths [ENDORSED]
Replies: 3
Views: 209

Re: Bond Lengths [ENDORSED]

This could be because of resonance. The molecule is an average of the resonance structures, so the bond length is an average as well.
by Cooper1C
Tue Oct 24, 2017 2:45 pm
Forum: Wave Functions and s-, p-, d-, f- Orbitals
Topic: Question 51
Replies: 1
Views: 139

Re: Question 51

I looked at the last block the electrons occupy. For example, Bi has 3 electrons in the 6p-block, and because of Hund's Rule and the Pauli Exclusion Principle, each electron will occupy a separate subshell (px, py, pz), so there are three unpaired electrons.
by Cooper1C
Tue Oct 24, 2017 2:39 pm
Forum: Wave Functions and s-, p-, d-, f- Orbitals
Topic: Ground State naming of elements
Replies: 1
Views: 122

Re: Ground State naming of elements

I believe we are expected to know the s-block, p-block, and first row of the transition metals.
by Cooper1C
Wed Oct 18, 2017 11:06 pm
Forum: Properties of Light
Topic: Angstrom
Replies: 3
Views: 317

Re: Angstrom

1 Ångström is 10^-10 meters. Bond lengths are about 1 Ångström.
by Cooper1C
Sun Oct 15, 2017 6:15 pm
Forum: Photoelectric Effect
Topic: Wavelike properties [ENDORSED]
Replies: 4
Views: 236

Re: Wavelike properties [ENDORSED]

If it creates a diffraction pattern (like the electrons did in the slit experiment), it must have wavelike properties.

Or, based on De Broglie's relation, any moving particle with momentum has wavelike properties, but sometimes the wavelength is so small there are no measurable wavelike properties.
by Cooper1C
Tue Oct 10, 2017 2:58 pm
Forum: SI Units, Unit Conversions
Topic: Significant Figures [ENDORSED]
Replies: 2
Views: 212

Re: Significant Figures [ENDORSED]

I believe this rule is to eliminate rounding errors in a multi-step problem (50% is rounded up and 50% is rounded down). However, in order to be as precise as possible you should not round your answer until the very end of the problem.
by Cooper1C
Tue Oct 10, 2017 2:49 pm
Forum: Properties of Light
Topic: Converting to Different Units
Replies: 3
Views: 177

Re: Converting to Different Units

In case you do not have them on hand, the prefixes are: centi 10^-2 mili 10^-3 micro 10^-6 nano 10^-9 An easy way to remember the prefixes is that they decrease by three powers every "step," with the exclusion of centi (which you can remember by centipede or centimeter, although I do not b...

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