## Search found 60 matches

Mon Mar 11, 2019 9:33 am
Forum: Zero Order Reactions
Topic: Graphs
Replies: 6
Views: 384

### Re: Graphs

Knowing the graphs can be helpful since the slope (ln[A] vs. T graph) can tell you the value of k for each order reaction. In addition, the graph can help you identify what order the reaction is.
Mon Mar 11, 2019 9:27 am
Forum: Administrative Questions and Class Announcements
Topic: Homework week 9
Replies: 3
Views: 188

### Re: Homework week 9

For week 10 we only have to turn in 7 problems since it would be the last discussion. You don't have to turn anything in finals week.
Mon Mar 11, 2019 9:26 am
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: Test 2 Question
Replies: 1
Views: 111

### Re: Test 2 Question

To solve this problem try using the van't Hoff equation and solve for K2 (make sure the temperature is in Kelvin). Using that value, you can solve for the concentration of H+ and then the pH.
Mon Mar 04, 2019 10:12 am
Forum: Kinetics vs. Thermodynamics Controlling a Reaction
Replies: 73
Views: 3786

### Re: Study Advice

If you need to improve your problem solving skills, I think the step up and workshop sessions are great for that. If you are unable to make it to some of the sessions, you can also find some of the worksheets with practice problems and solutions on chemistry community. Also, some TAs post their powe...
Mon Mar 04, 2019 10:06 am
Forum: Van't Hoff Equation
Topic: Sample problem
Replies: 2
Views: 323

### Re: Sample problem

Also you can use the equation to calculate the equilibrium constant at a different temperature (T2).
Mon Mar 04, 2019 10:01 am
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: Class on 2/27 and 3/1
Replies: 2
Views: 99

### Re: Class on 2/27 and 3/1

The topics that were discussed in lecture were the applications of electron transfer reactions, ion-selective electrodes, electrolysis, and the introduction to kinetics.
Mon Feb 25, 2019 6:00 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Negative Delta G
Replies: 2
Views: 99

### Re: Negative Delta G

Spontaneous reactions release free energy, thus the sign of ΔG must be negative. Looking at the Gibbs free energy equation, when ΔH is negative and ΔS is positive, the sign of ΔG will always be negative and therefore the reaction will be spontaneous at all temperatures.
Mon Feb 25, 2019 5:55 pm
Forum: Administrative Questions and Class Announcements
Topic: test 2
Replies: 2
Views: 147

### Re: test 2

According to the course website, Test 2 covers Gibbs free energy and electrochemistry (mostly the stuff in Chapter 14.1-14.11). Nernst equation, which was taught in lecture this Monday, will not be on the test.
Mon Feb 25, 2019 5:45 pm
Forum: General Science Questions
Topic: Test #2
Replies: 2
Views: 353

### Re: Test #2

The test will be on Gibbs free energy and electrochemistry but not including the Nernst equation, which Professor Lavelle taught in lecture this Monday.
Tue Feb 19, 2019 1:40 pm
Forum: General Rate Laws
Topic: test 3
Replies: 6
Views: 225

### Re: test 3

Test 2 will be on Gibbs free energy and electrochemistry, which Professor Lavelle will cover in lecture on Wednesday and Friday.
Tue Feb 19, 2019 1:38 pm
Forum: Calculating Standard Reaction Entropies (e.g. , Using Standard Molar Entropies)
Replies: 35
Views: 1127

### Re: Midterm Grades

According to my TA, midterms are being passed out after Wednesday's lecture (2/20) and your TA will be handing them out
Tue Feb 19, 2019 1:36 pm
Forum: Administrative Questions and Class Announcements
Topic: Midterms
Replies: 4
Views: 176

### Re: Midterms

Midterms will be passed out after Wednesday's lecture and your TA will be passing them outside the lecture room
Sun Feb 10, 2019 11:52 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Conversions
Replies: 4
Views: 200

### Re: Conversions

Most conversions that we will need to know on the midterm are provided on the equation sheet. The equation sheet can be found on the course website so you can see which ones are or are not provided.
Sun Feb 10, 2019 11:48 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: deltaS=nCvln(t2/t1) what is Cv?
Replies: 7
Views: 405

### Re: deltaS=nCvln(t2/t1) what is Cv?

If the problem gives you temperature and the system is not isothermal, deltaS=nCvln(t2/t1) is used to determine the change in entropy. To calculate the change in entropy of an ideal gas in a reversible isothermal expansion, use deltaS=nRln(V2/V1).
Sun Feb 10, 2019 11:34 pm
Forum: Thermodynamic Systems (Open, Closed, Isolated)
Topic: Mondays class
Replies: 3
Views: 160

### Re: Mondays class

I believe we will be going over past exam problems during lecture on Monday to prepare for the midterm.
Mon Feb 04, 2019 3:03 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: Degeneracy
Replies: 5
Views: 198

### Re: Degeneracy

Degeneracy is the number of ways of achieving a specific energy state. In other words, there are different positions and these configurations determine the energy state. W=(number of possible positions of an atom)^(number of particles). Gases have a higher degeneracy because they occupy larger volum...
Mon Feb 04, 2019 2:43 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: W=2^NA
Replies: 3
Views: 151

### Re: W=2^NA

NA is the number of particles per mole. For example, if the problem gives us mols to work with, we know that the degeneracy W=(number of possible positions of an atom)^(number of moles x Avogadro's number). However, if you are given particles to work with, W=(number of possible positions of an atom)...
Mon Feb 04, 2019 2:27 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Units
Replies: 2
Views: 118

### Re: Units

I believe by definition that the standard enthalpy of formation (Hf) represents the standard reaction's enthalpy per mole for the formation of a substance from its elements in their most stable form. Hf therefore is represented in units of kJ/mol. In addition, bond dissociation energies (aka bond en...
Mon Jan 28, 2019 7:27 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Standard Rxn Enthalpies for liquids and solids
Replies: 2
Views: 100

### Re: Standard Rxn Enthalpies for liquids and solids

To add on, the standard state basically is the physical state (solid, liquid, or gas) that a substance would be in under standard conditions (1.00 atm and 25 degrees Celsius). So, the standard state for carbon is solid and for water is liquid.
Mon Jan 28, 2019 7:21 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Standard Enthalpies
Replies: 2
Views: 105

### Re: Standard Enthalpies

The standard enthalpy of formation for an element in its standard state is zero. Standard state is like the physical state ( can be either solid, liquid, or gas) that a substance would be in under standard conditions (1.00 atm and 25 °C). Therefore, in standard conditions, the standard state for car...
Mon Jan 28, 2019 7:07 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Enthalpy and Heat Capacity
Replies: 2
Views: 84

### Re: Enthalpy and Heat Capacity

Also, a change in enthalpy means the change in heat of a system. Enthalpy is expressed usually in units such as J or kJ/mol. Heat capacity is calculated by dividing the total energy by the change in temperature. Heat capacity is expressed in J/K or J/degree Celsius.
Thu Jan 24, 2019 6:39 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: pH
Replies: 9
Views: 415

### Re: pH

pH is a logarithmic scale (from 0 to 14) that determines how acidic or basic an aqueous solution is based on the concentration of hydronium ions.
pH= -log [H3O+}
Thu Jan 24, 2019 6:36 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Equilibrium Composition
Replies: 2
Views: 100

### Re: Equilibrium Composition

Percent ionization is equal to : concentration of weak acid ionized (H+ concentration) / initial concentration of the weak acid x 100%. For strong acids, ionization is around 100% but for weak acids, the percent ionization changes depending on the concentration. The more diluted an acid is, the grea...
Thu Jan 24, 2019 6:29 pm
Forum: Phase Changes & Related Calculations
Topic: Why steam causes severe burns
Replies: 9
Views: 536

### Re: Why steam causes severe burns

Essentially 100 degrees Celsius steam burns skin more than 100 degrees Celsius water because the enthalpy of steam is greater. More heat energy is needed to be supplied in order to vaporize water compared to boiling water. Therefore, when steam comes into contact with skin, the amount of heat energy...
Mon Jan 14, 2019 2:33 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Kp
Replies: 7
Views: 263

### Re: Kp

You can convert between atm and bars when dealing with partial pressures depending on the question/problem. 1atm is approximately equivalent to 1.01325 bars
Mon Jan 14, 2019 2:28 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: solids on the reactant side
Replies: 3
Views: 2348

### Re: solids on the reactant side

Solvents and solids are not included when calculating the equilibrium constant K, so they dont change the value of the equilibrium constant. If a compound is stated to be aqueous, you can assume there is water. However, you can not assume there is water if there is only a solid compound stated and n...
Mon Jan 14, 2019 2:18 pm
Forum: Non-Equilibrium Conditions & The Reaction Quotient
Topic: Converting Kc to Kp
Replies: 3
Views: 238

### Re: Converting Kc to Kp

To clarify using the formula above, delta n is calculated via (c+d) - (a+b), where a and b are the coefficients of the gaseous reactants, and c and d are the coefficients of the gaseous products.
Tue Jan 08, 2019 4:56 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Help on 11.9: b and c
Replies: 4
Views: 141

### Re: Help on 11.9: b and c

That equation from the book is used when you want to write Kp in terms of Kc. For this problem you can just use the formula given in lecture to find the equilibrium constant.
Tue Jan 08, 2019 4:42 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: 11.37 6th Edition
Replies: 3
Views: 122

### Re: 11.37 6th Edition

In other words for part A, you are looking for the equilibrium constant of the reverse reaction. Since we know that K=41 for the forward reaction, K for the reverse reaction would be the inverse of that of the forward reaction. Thus, the equilibrium constant of the reverse reaction would be K^{-1} a...
Tue Jan 08, 2019 4:28 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: K'
Replies: 3
Views: 141

### Re: K'

As said above, K' usually is written to refer to the equilibrium constant of the reverse reaction whereas K represents the equilibrium constant of the forward reaction. You don't have to take any derivatives, it is just a way of notation.
Wed Dec 05, 2018 1:59 pm
Forum: Naming
Topic: Naming
Replies: 2
Views: 150

### Re: Naming

For naming, if a ligand is polydentate or already has a prefix, then you would use bis, tris, tetrakis, etc.
Wed Dec 05, 2018 1:57 pm
Forum: Electronegativity
Topic: Electronegativity
Replies: 6
Views: 418

### Re: Electronegativity

Going down a group has more impact on the electronegativity of an atom than going across a period. As you go down a group, there will be another valence shell added. This means that the outermost electrons feel less pull from the positive nuclear charge. Because of this, chlorine is less electronega...
Wed Dec 05, 2018 1:28 pm
Forum: Lewis Acids & Bases
Topic: Difference between Bronsted and Lewis Acids
Replies: 2
Views: 5595

### Re: Difference between Bronsted and Lewis Acids

A Bronsted acid is a proton (H+) donor and a Bronsted base is a proton acceptor. A Lewis acid is an electron acceptor while a Lewis base is an electron donor. Because the Bronsted definitions restricts acids to be H+ donors, ions like Al 3+ (which are Lewis acids since they can accept electrons) are...
Mon Nov 26, 2018 2:34 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Less than Angles
Replies: 2
Views: 175

### Re: Less than Angles

The bond angles depend on the existence of lone pairs because the lone pairs repel each other and other atoms in molecules. Bond angles decrease as the number of lone pairs increase. For example, in a tetrahedral shape, the bond angle would be 109.5 given that there are 4 atoms. If one of the atoms ...
Mon Nov 26, 2018 2:17 pm
Forum: Polarisability of Anions, The Polarizing Power of Cations
Topic: Polarizability
Replies: 5
Views: 176

### Re: Polarizability

In general on the periodic table, polarizability decreases across a period (due to increasing effective nuclear charge) and increases down on a group (due to atomic size increasing which allows for electron clouds to distort more easily).
Mon Nov 26, 2018 2:12 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: Polar vs Non-polar
Replies: 2
Views: 106

### Re: Polar vs Non-polar

To determine if a molecule is polar, find the electronegativities of each atom in a molecule and denote if the molecule is slightly negative or positive. From there draw the dipole moments going from the slightly positive atom to the slightly negative atom. If the dipole moments cancel out, then the...
Mon Nov 19, 2018 3:58 pm
Forum: Lewis Structures
Topic: Lewis Structure of BrO3-
Replies: 3
Views: 4833

### Re: Lewis Structure of BrO3-

BrO3- has a total of 26 valence electrons. In the Lewis structure, Br is placed in the center since it is lower in electronegativity. With all single bonds connecting the atoms, the formal charge of the O atoms are each -1 while the Br is 2. However, it is best to reduce the formal charges as much a...
Mon Nov 19, 2018 3:47 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: Polar Molecules
Replies: 2
Views: 124

### Re: Polar Molecules

Another way to determine if a molecule is polar is to look at the dipole moments between the atoms. If the dipole moments cancel each other out, the molecule would be nonpolar. On the other hand, if the dipole moments produce a net dipole moment, the molecule is polar.
Mon Nov 19, 2018 3:40 pm
Forum: Dipole Moments
Topic: Identifying whether there is a dipole moment
Replies: 4
Views: 183

### Re: Identifying whether there is a dipole moment

I'm sure that you just have to only know the periodic trend of electronegativity (increases across a period and decreases down a group)
Wed Nov 14, 2018 11:31 pm
Forum: Lewis Structures
Topic: 7th Edition #2E.5(a)
Replies: 2
Views: 126

### Re: 7th Edition #2E.5(a)

Yes chlorine can have more than an octet because it can hold electrons in its d-orbital. Usually elements in period 3 or higher (e.g P, S, Cl, etc.) can have an expanded octet.
Wed Nov 14, 2018 11:15 pm
Forum: Sigma & Pi Bonds
Topic: Sigma v. Pi
Replies: 6
Views: 386

### Re: Sigma v. Pi

In addition it is also good to know that a sigma bond can exist without a pi bond, but a pi bond cannot exist without a sigma bond.
Wed Nov 14, 2018 11:04 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: homework 2E #11 part b
Replies: 2
Views: 146

### Re: homework 2E #11 part b

Another way to put it is that the molecule has 2 lone electron pairs and a Steric number of 5 (number of atoms bonded to a central atom of a molecule + the number of lone pairs attached to the central atom). Therefore, in terms of the VSEPR model it would be T-shaped.
Tue Nov 06, 2018 7:34 pm
Forum: Bond Lengths & Energies
Topic: Bond Lengths
Replies: 6
Views: 240

### Re: Bond Lengths

I believe bond lengths usually are given in the problem and when they are given, they are usually in the units pm (picometer) or A (angstroms).
Tue Nov 06, 2018 7:19 pm
Forum: Lewis Structures
Topic: Lewis Structure for N2O
Replies: 7
Views: 357

### Re: Lewis Structure for N2O

Oxygen is more electronegative than nitrogen because oxygen has a greater nuclear charge (more protons). Electronegativity in a sense measures how tightly an atoms holds its electrons, where atoms with high electronegativity are more likely to gain/share electrons rather than lose them. Nitrogen is ...
Tue Nov 06, 2018 7:05 pm
Forum: Ionic & Covalent Bonds
Topic: Covalent bonds
Replies: 3
Views: 158

### Re: Covalent bonds

Yes, usually when a diatomic molecule (e.g H2) is formed a nonpolar covalent bond (electrons are equally shared) is made. Usually this type of bond results when the atoms have similar or the same electron affinity.
Thu Nov 01, 2018 4:05 pm
Forum: DeBroglie Equation
Topic: De Broglie vs. speed of light/Einstein equation
Replies: 3
Views: 336

### Re: De Broglie vs. speed of light/Einstein equation

λ=h/p (Broglie wavelength) is used when you need to find the wavelength of a particle (e.g. an electron) with a certain speed. On the other hand, E=hc/λ is used to find the wavelength of a photon of a certain energy
Thu Nov 01, 2018 4:01 pm
Forum: Administrative Questions and Class Announcements
Topic: Diagonal Relationships
Replies: 1
Views: 65

### Re: Diagonal Relationships

I believe that since it was not covered in lecture, diagonal relationships of elements will not be asked on the exam. However, it wouldn't be bad to have a general idea of the concept and knowing that elements have similar properties.
Thu Nov 01, 2018 3:55 pm
Forum: Lewis Structures
Topic: Lewis Structure NO3-
Replies: 3
Views: 123

### Re: Lewis Structure NO3-

In NO3- the total number of valence electrons is 24 (N has 5 valence electrons, 3 O have 18 electrons, plus 1 more electron due to the ion's charge). When doing Lewis dot structures, the atom with the lowest ionization energy is placed in the center (in this case N) and the total number of valence e...
Thu Oct 25, 2018 6:51 pm
Forum: Quantum Numbers and The H-Atom
Topic: Quantum numbers
Replies: 3
Views: 223

### Re: Quantum numbers

The principal quantum number, n, determines the size of the orbital (or how far the electrons extend from the nucleus) and its energy. The magnetic quantum number, ml, divides the subshells into individual orbitals. The number denotes the orientation of the orbitals (for example px, py, pz) and is c...
Thu Oct 25, 2018 6:14 pm
Forum: Properties of Electrons
Topic: mass of electron
Replies: 5
Views: 287

### Re: mass of electron

Most constants and equations are provided during the exam so you don't have to memorize them all.
Tue Oct 23, 2018 12:51 am
Forum: Properties of Light
Topic: worksheet3 question11
Replies: 3
Views: 198

### Re: worksheet3 question11

I assume that for part d, a higher frequency doesn't always imply that the emitted electrons have higher kinetic energies because the frequency has to be within a certain threshold (thus the wavelength has to also be within a certain threshold) in order for electrons to even be emitted.
Fri Oct 19, 2018 3:46 pm
Forum: Electron Configurations for Multi-Electron Atoms
Topic: energy in shells closer to the nucleus
Replies: 4
Views: 185

### Re: energy in shells closer to the nucleus

Another way to think of it is that a greater amount of energy is required to free an electron from the inner shell rather than an electron from the outer shell. Because of this, electrons in the outer shell have a higher (potential) energy compared to those in the inner shell.
Fri Oct 19, 2018 3:38 pm
Forum: Properties of Light
Topic: Intensity vs. Amplitude
Replies: 5
Views: 115

### Re: Intensity vs. Amplitude

In the wave model of electromagnetic radiation, intensity is proportional to the square of the amplitude. However, in the particle model, intensity is proportional to the number of photons present at an instant.
Fri Oct 19, 2018 3:34 pm
Forum: Photoelectric Effect
Topic: Test 2
Replies: 16
Views: 529

### Re: Test 2

Check out outline 2 on the class website and you'll see the list of concepts that should be known for the exam!
Thu Oct 11, 2018 11:02 pm
Forum: *Black Body Radiation
Topic: The Importance of Black Body Radiation (?)
Replies: 5
Views: 512

### Re: The Importance of Black Body Radiation (?)

During lecture it was said that black body radiation will not be discussed much during the course. However it would be good to be familiar of what it is regardless
Thu Oct 11, 2018 10:41 pm
Forum: Properties of Light
Topic: Intensity
Replies: 2
Views: 64

### Re: Intensity

It's also good to keep in mind that in the wave model of electromagnetic radiation, intensity is proportional to the square of the amplitude. However, in the particle model, intensity is proportional to the number of photons present at an instant.
Thu Oct 11, 2018 10:36 pm
Forum: Accuracy, Precision, Mole, Other Definitions
Topic: Formula M1V1=M2V2 [ENDORSED]
Replies: 5
Views: 3245

### Re: Formula M1V1=M2V2[ENDORSED]

Yes this equation can be used to solve problems like dilutions. Just be sure that your units always are converted to liters and mols/L (M) so that they cancel out during calculations.
Wed Oct 03, 2018 3:03 pm
Forum: Balancing Chemical Reactions
Topic: Combustion Reactions.
Replies: 8
Views: 910

### Re: Combustion Reactions.

As said in the previous posts, the products of a complete combustion are always CO2 and H2O. However it's also good to keep in mind that during an incomplete combustion (not enough oxygen is provided for the reactant to completely burn) other products, such as C and CO (carbon monoxide), can also be...
Wed Oct 03, 2018 2:41 pm
Forum: Accuracy, Precision, Mole, Other Definitions
Topic: Formula Units [ENDORSED]
Replies: 3
Views: 1187

### Re: Formula Units[ENDORSED]

Correct. 2NaCl would mean that there are 2 formula units of NaCl. You usually first calculate the number of moles (divide the mass of the sample by the molar mass) and then multiply it by Avogadro's number (6.022 x 10^23) to calculate the number of formula units. This procedure is the same as if you...
Wed Oct 03, 2018 2:27 pm
Forum: Significant Figures
Topic: Rules For Significant Figures
Replies: 6
Views: 393

### Re: Rules For Significant Figures

The number 705.0090 would have 7 significant figures based on the rules listed above.

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