## Search found 64 matches

Thu Mar 14, 2019 11:09 am
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Equilibrium Partial pressure Units
Replies: 2
Views: 85

### Equilibrium Partial pressure Units

For calculating equilibrium partial pressure, is there any specific unit that is standard?
Wed Mar 13, 2019 3:25 pm
Forum: Arrhenius Equation, Activation Energies, Catalysts
Topic: 7th Ed. 7E.3
Replies: 1
Views: 67

### 7th Ed. 7E.3

How does one go from e^(-0.6Ea/RT)/ e^(-Ea/RT) to e^((-0.6+1)Ea/RT)? Is this just a log/e rule?
Mon Mar 11, 2019 7:43 pm
Forum: First Order Reactions
Topic: Homework question
Replies: 2
Views: 93

### Re: Homework question

This is a different way to display the first order reaction equation. You start with ln[A]=ln[A(initial)] - kt Then you move ln[A(initial)] to the other side and use log rules to get ln([A]/[A(initial)])=-kt. Then divide by -k or -t depending on what you want to find. The textbook just organizes it ...
Sun Mar 10, 2019 9:15 pm
Forum: First Order Reactions
Topic: 7B.9
Replies: 3
Views: 148

### 7B.9

Before you use the first order integrated rate law, to calculate the concentration of A at the time you want to calculate, you have to do
[A]=[A(initial)]-(mol A/mol B)[B]. What equation is this?
Sun Mar 10, 2019 5:53 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Orders
Replies: 2
Views: 112

### Orders

Do we calculate the order of a reaction by looking at its molecularity (or adding the reactants for the overall order)?
Sat Mar 09, 2019 7:51 pm
Forum: Kinetics vs. Thermodynamics Controlling a Reaction
Topic: Bimolecular
Replies: 13
Views: 661

### Re: Bimolecular

A bimolecular reaction is where the rearrangement of two molecules (as reactants) produce one or more molecules of product.
Thu Mar 07, 2019 2:07 pm
Forum: General Rate Laws
Topic: Rate laws
Replies: 2
Views: 131

### Re: Rate laws

A differential rate law has a rate as the function of [R], whereas an integrated rate law has rate as a function of time.
Wed Mar 06, 2019 8:18 pm
Forum: Second Order Reactions
Topic: Zero vs. Second Order slopes
Replies: 1
Views: 97

### Zero vs. Second Order slopes

Can someone explain to me why the second order rxn's slope is k whereas the zero order rxn's slope is -k? What does this signify conceptually?
Wed Mar 06, 2019 11:10 am
Forum: Van't Hoff Equation
Topic: Temp Units
Replies: 11
Views: 544

### Temp Units

What is the unit of temperature we use in the Van’t Hoff equation? K or C?
Sun Mar 03, 2019 2:54 pm
Forum: Balancing Redox Reactions
Topic: balancing redox reactions
Replies: 5
Views: 183

### Re: balancing redox reactions

If there is just Hydrogen to be balanced, you just add H+ to the opposite side to set the mol H+ equal on both sides.
If there is Oxygen that needs to be balanced, add H2O to the side with less oxygen to make the oxygen equal, then add H+ to the other side so that balances the Hydrogen added in H2O.
Sun Mar 03, 2019 2:49 pm
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: van't hoff equation
Replies: 6
Views: 260

### Re: van't hoff equation

You can convert the equation ln(k1/k2)=x to e^x=(k1/k2) where x is the numerical value obtained by the right side of the Van't Hoff Equation.
Tue Feb 26, 2019 11:47 am
Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
Topic: Value of n
Replies: 7
Views: 377

### Value of n

Is n the difference in the number of moles on each side, or the number of electrons on each side of an equation?
Sun Feb 24, 2019 12:57 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Platinum (s)
Replies: 2
Views: 93

### Platinum (s)

How do we know when we are supposed to add Pt(s) to a cell diagram?
Sat Feb 23, 2019 5:33 pm
Forum: Balancing Redox Reactions
Topic: Oxidating/Reducing AGENTS
Replies: 6
Views: 212

### Oxidating/Reducing AGENTS

What does it mean to be an oxidating/reducing AGENT? How do we identify what are these in a reaction?
Sat Feb 23, 2019 4:48 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Stability
Replies: 2
Views: 92

### Stability

What does it mean that if the Gibbs free energy is higher (larger positive number), it is less stable? How does being spontaneous (or a more negative number) equal to more stability?
Sun Feb 17, 2019 1:57 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Meaning of Spontaneity
Replies: 3
Views: 594

### Meaning of Spontaneity

Why is the change in free energy spontaneous when delta G is less than zero, but NOT when it is greater than zero?
Sun Feb 17, 2019 1:53 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Gibbs Free Energy vs Internal Energy
Replies: 3
Views: 104

### Re: Gibbs Free Energy vs Internal Energy

Gibbs free energy is calculated by the enthalpy minus the entropy times absolute temperature of a system. Whereas the change in internal energy is work plus heat.
Wed Feb 13, 2019 4:49 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Enthalpy and qp
Replies: 3
Views: 192

### Re: Enthalpy and qp

Delta H is equal to Qp because this P signifies constant pressure and the very definition of enthalpy is heat under constant pressure.
Tue Feb 12, 2019 5:16 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Ka value
Replies: 3
Views: 124

### Ka value

At what value do we consider Ka to be a strong acid?
Sun Feb 10, 2019 6:59 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: 4I.1
Replies: 1
Views: 120

### Re: 4I.1

Because these reservoirs are at different temperatures and one is gaining and the other is losing enthropy, you have to take the temperature in K into consideration. Using q (the 40 kJ) and the formula q/T, you add together the delta S for reservoir 1 and 2 to find the total enthropy.
Sat Feb 09, 2019 9:33 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Signs for heat capacities for reactants and products
Replies: 1
Views: 104

### Signs for heat capacities for reactants and products

Is the sum of the heat capacities of the products minus that of the reactants always correct for finding the overall heat capacity?

Because for 7th Ed problems 4D.21 this is the case, whereas for 4D.15 it was not.
Mon Feb 04, 2019 5:18 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: Small Error in S vs. Large Error in W
Replies: 1
Views: 96

### Small Error in S vs. Large Error in W

In class we discussed how due to the thermodynamic property there is a 'small' error in S, while there is a statistical 'large' error in W. What does this mean?
Mon Feb 04, 2019 5:10 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: Kb meaning
Replies: 2
Views: 130

### Kb meaning

What does Kb stand for in the Boltzmann equation? When you multiply it by Avogadro's number when given 1 mol of a substance, you get R, the gas constant. However what happens when you don't have Avogadro's number?
Mon Feb 04, 2019 4:47 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Irreversible vs. Reversible Expansion
Replies: 4
Views: 137

### Re: Irreversible vs. Reversible Expansion

In reversible expansion, the system is in equilibrium with its surroundings, whereas irreversible expansion is not. Irreversible expansion increases entropy of the universe.
Mon Feb 04, 2019 3:56 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: Change of Temp. converting from C to K in Entropy Change Problem
Replies: 2
Views: 119

### Change of Temp. converting from C to K in Entropy Change Problem

Why in an entropy change problem when converting to Kelvin does the book give two different values. It should be 37.6 C to 310.6 K and 157.9 C to 430.9 K. However the solutions manual states that its 310.8 K and 431 K respectively. Is this just a mistake on the book's part or is there a reason we ch...
Mon Jan 28, 2019 3:49 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Constant Pressure of Krypton (4c.3 7th Edition)
Replies: 1
Views: 79

### Constant Pressure of Krypton (4c.3 7th Edition)

How are we supposed to calculate the pressure and volume constant of Krypton?
Specifically where does the (5/2) x 8.314 J.mol.K come from for the constant pressure for example?
Sun Jan 20, 2019 4:24 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: 7th Ed 6D.15
Replies: 1
Views: 88

### 7th Ed 6D.15

How does one find the Ka, when the only information given is that you are trying to find the pH of 0.19 M NH4Cl (aq).
The soln manual says that you take the Kw constant and divide by 1.8 x 10^(-5), the Kb. But where does this value even come from?
Sun Jan 20, 2019 4:00 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: 5I.15 7th Ed
Replies: 1
Views: 49

### Re: 5I.15 7th Ed

The number you get from solving for x is 0.0008, which is very close to 0 but not completely. And although this is typically so small it is ignorable, since it is the x value and there is some change, we must take it into consideration for this problem.
Sun Jan 20, 2019 2:57 pm
Forum: Non-Equilibrium Conditions & The Reaction Quotient
Topic: 5D.5 in 7th Ed
Replies: 1
Views: 120

### 5D.5 in 7th Ed

How does one get the Kb from the pKa being 8.21.
The solution manual says it should be 1.8 x 10^(-5), but I continue getting 1.6 x 10^(-6).
What is the process for getting this number?
Mon Jan 14, 2019 2:16 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: 7th edition 5I.13 Part C
Replies: 1
Views: 88

### Re: 7th edition 5I.13 Part C

The answer for Cl2 is smaller than F2. Therefore we know that F2 has a larger equilibrium constant for the dissociation of the F molecules. So, Cl2 must be more stable because it has a smaller equilibrium constant.
Mon Jan 14, 2019 2:14 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: 5I.23 7th Edition
Replies: 1
Views: 104

### 5I.23 7th Edition

Why in the solutions manual is the initial concentration of CO and H2 2.0 and 3.0 rather than 0.2 and 0.3, when it gives the mols and states that there is a 10 L vial. Is this an error in the manual or is there something specific about this reaction that I am missing?
Sun Jan 13, 2019 6:01 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Aqueous Solutions [ENDORSED]
Replies: 2
Views: 111

### Re: Aqueous Solutions[ENDORSED]

Pure solids and liquids aren't used when calculating the equilibrium constant because they don't affect the reactant amount at equilibrium, so it is assumed to be at 1.
Fri Dec 07, 2018 12:04 am
Forum: Identifying Acidic & Basic Salts
Topic: identify base/acid from lewis structure
Replies: 2
Views: 142

### Re: identify base/acid from lewis structure

An acid has the ability to donate a proton, whereas a base has the ability to accept another proton, or H molecule.
Thu Dec 06, 2018 11:20 pm
Forum: Hybridization
Topic: Labeling hybridization in Test 3
Replies: 2
Views: 82

### Re: Labeling hybridization in Test 3

Because of the 3 bonds and one lone pair, although the geometry is tetrahedral, the actual shape would be trigonal pyramidal, because of the lone pair. This would result in angles slightly less than 109.5 degrees.
Thu Dec 06, 2018 12:09 am
Forum: Determining Molecular Shape (VSEPR)
Topic: Net Dipole
Replies: 3
Views: 359

### Re: Net Dipole

F is more electronegative than Cl, therefore, there will be a net dipole towards the F.
Thu Nov 29, 2018 9:56 pm
Forum: Bond Lengths & Energies
Topic: 7th edition 2D.19
Replies: 2
Views: 261

### Re: 7th edition 2D.19

In this problem, you simply use table 2.11 to add the covalent radii of the 2 different elements that make up a molecule.
For example, part a) C= 77pm + F=58pm = 135 pm.
It has nothing to do with Nitrogen for this problem.
Thu Nov 29, 2018 9:43 pm
Forum: Hybridization
Topic: CH2O hybridization
Replies: 9
Views: 7538

### Re: CH2O hybridization

Because of the trigonal planar shape and 3 atomic orbitals as established by the AX3 VSEPR formula, the hybridization of the central C atom is sp2. S + P + P if you'd like to think of it that way.
Thu Nov 29, 2018 9:36 pm
Forum: Hybridization
Topic: Hybridization connection
Replies: 2
Views: 139

### Re: Hybridization connection

Table 2f.1 does a pretty good job of explaining this correlation in 7th edition, but for example.
If electron arrangement is linear, then the number of atomic orbitals=2, thus the hybridization is sp, and there are 2 hybrid orbitals.
Thu Nov 29, 2018 9:31 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: polarity
Replies: 11
Views: 295

### Re: polarity

Molecules that are completely symmetrical are nonpolar, whereas molecules that are uneven (as in when drawn out in a Lewis Structure) are polar.
Thu Nov 29, 2018 8:10 pm
Forum: Hybridization
Topic: 2F.15 question 7th edition
Replies: 3
Views: 127

### Re: 2F.15 question 7th edition

By the s-character increasing, it means the percentage of s in the hybrid. So sp^3, s is 25% or 1/4, whereas sp^2 is 33.3% or 1/3, and sp has s at 50%. These correlate to different angles as well, so that when there is sp^3, s is at 25% or a 109.5 degree angle. And sp^2 has 33% indicating a 120 degr...
Thu Nov 29, 2018 12:28 pm
Forum: Polarisability of Anions, The Polarizing Power of Cations
Topic: 2D.9 vs 2D.11 in 7th edition
Replies: 1
Views: 92

### 2D.9 vs 2D.11 in 7th edition

In 2D.9, the molecules are ordered so that smaller, more highly charged cations have a greater polarizing power. Yet in 2D.11, the molecules are ordered so that polarizability increases as the ion gets larger and less electronegative. How does this make sense? Is there a difference in polarizability...
Thu Nov 15, 2018 2:15 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: 109.5 Degrees
Replies: 4
Views: 361

### 109.5 Degrees

I understand that a linear shape has 180 degrees, and a trigonal planar has 120. However, why does a tetrahedral have 109.5 degrees? Is there a specific mathematical or scientific reason behind this, or is this just a value we need to memorize?
Thu Nov 15, 2018 2:07 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Trigonal Shapes
Replies: 4
Views: 142

### Re: Trigonal Shapes

Trigonal planar is 3 bonds, whereas trigonal pyrimidal is 3 bonds and 1 lone pair.
Thu Nov 15, 2018 2:00 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: 7th Edition 2E.23
Replies: 1
Views: 45

### 7th Edition 2E.23

Why in this question when we do the Lewis Structure for these molecules, before determining the shape, are the Oxygen atoms NOT double bonded to the central atom? Is this not blatantly disregarding the formal charge?
Thu Nov 15, 2018 1:04 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Square Planar
Replies: 5
Views: 254

### Square Planar

I get that when there are 4 bonds and 1 lone pair, the shape is going to be a seesaw. However, in what situation would the shape be square planar?
Thu Nov 08, 2018 11:40 pm
Forum: Bond Lengths & Energies
Topic: Dispersion Force/State of Matter Correlation
Replies: 2
Views: 133

### Dispersion Force/State of Matter Correlation

How does increasing strength of dispersion forces correlate to the state of matter of a molecule/substance?
Such as how F2 and Cl2 are gaseous at room temperature and Br2 is a liquid and I2 is a solid.
Thu Nov 08, 2018 11:30 pm
Forum: Bond Lengths & Energies
Topic: Larger to weaker bond correlation
Replies: 3
Views: 174

### Larger to weaker bond correlation

In lecture, we learned that larger atoms indicates a larger bond/larger distance, which in turn indicates a weaker bond.
What is the reasoning behind the larger bond resulting in a weaker bond?
Thu Nov 08, 2018 11:20 pm
Forum: Dipole Moments
Topic: Dipole Equation- Units
Replies: 1
Views: 99

### Dipole Equation- Units

From lecture, we learned that the dipole moment is charge x distance between atoms. How does this translate units to the dipole moment unit?
Thu Nov 01, 2018 11:22 pm
Forum: Formal Charge and Oxidation Numbers
Topic: Formal Charge
Replies: 8
Views: 306

### Re: Formal Charge

V, as above stated valence electrons, can be calculated by looking at the periodic table for instance.
L, lone electrons, are the dots surrounding an element, made to represent an electron.
S, shared electrons, are the lines connecting two elements, thus "sharing" them.
Thu Nov 01, 2018 11:20 pm
Forum: Lewis Structures
Topic: 7th edition 2B.7
Replies: 1
Views: 34

### 7th edition 2B.7

What is the most effective strategy for solving problems like this, where you are tasked with going backwards per se and identifying a mystery element from a Lewis structure? How would one begin this process?
Thu Nov 01, 2018 9:21 pm
Forum: Octet Exceptions
Topic: H, He, Li, Be Rule
Replies: 3
Views: 208

### H, He, Li, Be Rule

Is there any specific reason that the first four elements on the periodic table DON'T need an octet?
Thu Oct 25, 2018 10:42 pm
Forum: Heisenberg Indeterminacy (Uncertainty) Equation
Topic: Units
Replies: 8
Views: 310

### Units

What units are used in the Heisenberg Equation? Especially for indeterminacy in position?
Thu Oct 25, 2018 10:30 pm
Forum: DeBroglie Equation
Topic: Units of De Broglie's Equation
Replies: 4
Views: 799

### Re: Units of De Broglie's Equation

Lambda=h/mv
Lambda is in meters
h- Planck's constant (6.63x10^(-34))J s or (kg m^2.s^2) s
m-mass in kg
v- velocity in m.s
Everything cancels out so that Lambda, or wavelength, is just in meters.
Thu Oct 25, 2018 10:13 pm
Forum: Quantum Numbers and The H-Atom
Topic: 7th edition 1D.23
Replies: 1
Views: 41

### 7th edition 1D.23

How many ORBITALS can have the following quantum numbers in an atom? Can someone just explain (a) so I can comprehend the rest?
(a)n=2, l=1
Thu Oct 18, 2018 11:56 pm
Forum: Heisenberg Indeterminacy (Uncertainty) Equation
Topic: Light scattered impacting position
Replies: 1
Views: 75

### Light scattered impacting position

At what level is a light able to alter a particle's position? Such as the baseball and electron example. What size is when the light beam per se is able to physically alter the location of an electron?
Thu Oct 18, 2018 11:51 pm
Forum: DeBroglie Equation
Topic: Momentum and Wavelike Properties
Replies: 2
Views: 140

### Momentum and Wavelike Properties

In class, Prof. Lavelle stated that De Broglie's equation referred only to particles with momentum and wavelike properties. I understand how a particle may not have momentum, but is this correlative to wavelike properties? In what scenario would a particle not have wavelike properties?
Thu Oct 18, 2018 11:38 pm
Forum: Einstein Equation
Topic: Units
Replies: 17
Views: 910

### Units

What unit does J.s^(-1) translate into, and how would we use this new unit to calculate the correct unit for finding wavelength, in say, the equation of λ=h (unit of J.s^(-1)/mv?
Thu Oct 11, 2018 4:08 pm
Forum: Properties of Light
Topic: Problem 1.3 6th ed.
Replies: 3
Views: 120

### Re: Problem 1.3 6th ed.

C is the answer, As frequency increases, wavelength will decrease as they are inversely related and energy will increase as they are positively correlated. Also speed is a constant. So C is the only viable answer. In addition, the increased wavelength size, the less variability you will get over tim...
Thu Oct 11, 2018 4:02 pm
Forum: Einstein Equation
Topic: Units for v(frequency)
Replies: 11
Views: 296

### Re: Units for v(frequency)

Yes, Hz and s^(-1) can be used interchangeably. That is why in the formula c=λv for instance, that the unit of m for wavelength and Hz or s^-1 for frequency combine to create c, which is 3.00 x 10^8 m.s^-1
Thu Oct 11, 2018 3:55 pm
Forum: Properties of Light
Topic: Problem 1A.9 (7th edition)
Replies: 5
Views: 76

### Problem 1A.9 (7th edition)

In this problem, we are given one of the following options for four different scenarios: frequency, wavelength, and photon energy, and have to determine which option matches to which scenario, each of which is a different type of radiation. Is it viable to just use the 2 formulas of c=λv and e=hv to...
Fri Oct 05, 2018 9:43 pm
Forum: Limiting Reactant Calculations
Topic: Total Mass
Replies: 2
Views: 88

### Re: Total Mass

Yes. As previously stated, your method does work correctly. Retaining the number of sig figs is important throughout, but you will be able to retain relatively the same answer regardless. But just to be same, check out the Sig Fig directions on the class website.
Thu Oct 04, 2018 5:16 pm
Forum: Limiting Reactant Calculations
Topic: Question 7 on Module 1 Post-Assessment [ENDORSED]
Replies: 2
Views: 280

### Re: Question 7 on Module 1 Post-Assessment[ENDORSED]

If you multiply the percentages (.7403, .8700, and .1727) by 162.23 g/mol and then divide by the molar mass of C, H and N respectively, you will receive 9.98:14.02:1.99 which is essentially 10:14:2 (the molecular formula). However, this can be simplified down to a 5:7:1 ratio, the empirical formula.
Thu Oct 04, 2018 4:53 pm
Forum: Balancing Chemical Reactions
Topic: Hydrates
Replies: 1
Views: 271

### Re: Hydrates

No, you just have to balance it like a normal equation. The number of molecules of water in a hydrate should be a part of the formula, and when manipulating the stoichiometric coefficients, it applies to the entire molecule. Hydrates are considered part of a single molecule.
Thu Oct 04, 2018 2:04 pm
Forum: Balancing Chemical Reactions
Topic: Order of balancing an equation
Replies: 8
Views: 317

### Re: Order of balancing an equation

As others have stated, I would balance the element of the smallest quantity of moles first. Then move up to the ones with several molecules containing them, or with higher stoichiometric coefficients. For example, in the 7th edition book, chapter H problem 5 part A, NaBH4 + H2O ---> NaBO2 + H2 I wou...