Search found 54 matches

by Cassandra Mullen 1E
Sun Mar 18, 2018 9:12 am
Forum: Thermodynamic Definitions (isochoric/isometric, isothermal, isobaric)
Topic: Work when pressure is constant
Replies: 6
Views: 381

Re: Work when pressure is constant

If external pressure is given in the problem, then it is irreversible so use w=-P(delta)V
by Cassandra Mullen 1E
Sat Mar 17, 2018 4:59 pm
Forum: Van't Hoff Equation
Topic: Van't Hoff
Replies: 9
Views: 444

Re: Van't Hoff

KayleeMcCord1F wrote:Do we have to know the van't Hoff equation for the final?

I think you should be able to derive the Van't Hoff equation with what's given on the equations sheet.
by Cassandra Mullen 1E
Fri Mar 16, 2018 9:01 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Slow Step in Reaction Mechanisms
Replies: 7
Views: 261

Re: Slow Step in Reaction Mechanisms

Your overall rate law for the reaction will be based on the slow step, since the slow step is the rate-determining step. If the slow step is not the first step in the mechanism, then you'll have intermediates that you'll need to get rid of through substitution.
by Cassandra Mullen 1E
Fri Mar 16, 2018 8:40 pm
Forum: *Electrophilic Addition
Topic: nucleophile and electrophile reactions
Replies: 6
Views: 884

Re: nucleophile and electrophile reactions

Michael Cheng 1C wrote:do we need to know nucleophiles and electrophiles for the final? What is the difference between them?

The nucleophile is the molecule/ion that donates electrons and the electrophile is the molecule/ion that accepts the electrons.
by Cassandra Mullen 1E
Sat Mar 10, 2018 8:05 pm
Forum: Arrhenius Equation, Activation Energies, Catalysts
Topic: Catalyst [ENDORSED]
Replies: 2
Views: 277

Re: Catalyst [ENDORSED]

A catalyst is neither a reactant nor a product, so that's why it's not written in the overall chemical reaction.
by Cassandra Mullen 1E
Sat Mar 10, 2018 7:59 pm
Forum: Experimental Details
Topic: Experimental Techniques
Replies: 3
Views: 300

Re: Experimental Techniques

Reaction rates can be measured through a spectrometric method, where a spectrophotometer measures light absorbance. A conductometric titration can also be used, which measures the voltage change over time as reactant is added. Titrations work well for slow reactions.
by Cassandra Mullen 1E
Sat Mar 10, 2018 7:53 pm
Forum: Experimental Details
Topic: Homework Problem 15.3 Part C
Replies: 5
Views: 335

Re: Homework Problem 15.3 Part C

The unique reaction rate occurs per one mole of the reactant. In this case, you divide by 2 since the stoichiometric coefficient of NO2 is 2.
by Cassandra Mullen 1E
Sun Mar 04, 2018 10:10 pm
Forum: Van't Hoff Equation
Topic: Van't Hoff equation
Replies: 4
Views: 382

Re: Van't Hoff equation

You can derive the equation by substituting ∆G˚=-RTlnk into ∆G˚=∆H˚-T∆S˚ to get -RTlnk =∆H˚-T∆S and then dividing both sides by -RT.
by Cassandra Mullen 1E
Sun Mar 04, 2018 10:02 pm
Forum: Biological Examples (*DNA Structural Transitions, etc.)
Topic: 9.69
Replies: 2
Views: 487

Re: 9.69

Yes, you are trying to cancel out the electrons to balance out the overall reaction of oxidizing 3 mol of NADH. Since the 2nd and 3rd equations are already balanced, you can also add the ∆Gs, which would correspond to 1 mol of NADH, and then multiply by 3 to get the ∆G value for 3.00 mol of NADH.
by Cassandra Mullen 1E
Sun Mar 04, 2018 8:36 pm
Forum: Method of Initial Rates (To Determine n and k)
Topic: When forming rate laws do we include solids and liquids?
Replies: 3
Views: 346

Re: When forming rate laws do we include solids and liquids?

Just like when writing equilibrium constant expressions, the concentration of solids and liquids are essentially constant so they can be omitted in the rate law expression.
by Cassandra Mullen 1E
Sat Feb 24, 2018 10:06 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Galvanic Cells
Replies: 5
Views: 184

Re: Galvanic Cells

A galvanic cell occurs spontaneously due to the positive voltage. The cell potential is positive since the cathode electrode potential is greater than the anode electrode potential. The negatively charged electrons flow in the cell since they are attracted to the more positive end.
by Cassandra Mullen 1E
Sat Feb 24, 2018 9:44 pm
Forum: Balancing Redox Reactions
Topic: Oxidation state
Replies: 5
Views: 199

Re: Oxidation state

The uncombined diatomic elements have an oxidation state of 0. You can also observe that there is no superscript indicating a charge on the molecule.
by Cassandra Mullen 1E
Tue Feb 20, 2018 10:33 am
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: Q for Nernst Equation
Replies: 1
Views: 95

Re: Q for Nernst Equation

Remember when writing equilibrium constant expressions, the concentrations of solids and liquids are excluded, since they essentially have constant concentration throughout the reaction. For cell potential, we are concerned with the voltage related to the concentration of aqueous solutions, since th...
by Cassandra Mullen 1E
Sun Feb 18, 2018 8:14 pm
Forum: Balancing Redox Reactions
Topic: Half Reaction
Replies: 3
Views: 128

Re: Half Reaction

When writing half reactions, I think you only disregard the spectator ions since they don't participate in the actual redox reaction.
by Cassandra Mullen 1E
Sun Feb 18, 2018 8:08 pm
Forum: Balancing Redox Reactions
Topic: oxidation
Replies: 4
Views: 149

Re: oxidation

Most of the halogens have a -1 oxidation number, but there are exceptions if the atom is bonded to a more electronegative element. Oxygen usually has an oxidation number of -2, unless it's in oxygen difluoride, where the oxidation number is +2. In peroxides, oxygen has a oxidation state of +1.
by Cassandra Mullen 1E
Sun Feb 18, 2018 7:52 pm
Forum: Balancing Redox Reactions
Topic: Helpful Videos
Replies: 4
Views: 173

Re: Helpful Videos

This one's pretty good for understanding how the galvanic cell is set up:
https://www.youtube.com/watch?v=a2v7ph3kLXo
by Cassandra Mullen 1E
Sun Feb 11, 2018 8:09 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: Gibbs free
Replies: 5
Views: 196

Re: Gibbs free

In the G=H-TS, you can think of Gibbs Free Energy as the free energy left in the system after subtracting energy lost to heat and entropy (-TS term) from H (enthalpy, the total heat content of a system).
by Cassandra Mullen 1E
Sun Feb 11, 2018 8:05 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: Entropy Equation
Replies: 4
Views: 110

Re: Entropy Equation

You would use delta s=nRlnV2/V1 to calculate the entropy change of an ideal gas in a reversible isothermal expansion.
by Cassandra Mullen 1E
Thu Feb 08, 2018 2:34 pm
Forum: Biological Examples (*DNA Structural Transitions, etc.)
Topic: problem 9.75
Replies: 2
Views: 298

Re: problem 9.75

Just to add on, the 12 orientations/3 orientations come from the octahedral shape (6 directions for the ligands), which is the same for both the cis and trans isomers. In the trans isomer, the ligands are across from each other, and in the cis isomer, the ligands are next to each other. Rotating the...
by Cassandra Mullen 1E
Sun Feb 04, 2018 6:48 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: Heat transfer
Replies: 7
Views: 234

Re: Heat transfer

This is an example of an isothermal process (no heat change) where the energy lost by the system is supplemented by the energy gained in the surroundings.
by Cassandra Mullen 1E
Sat Feb 03, 2018 2:25 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Gibbs free energy question
Replies: 3
Views: 306

Re: Gibbs free energy question

Gibb's free energy accounts for the enthalpy and entropy of the system. You can think of the H term as all of the the energy in the system and TΔS as the energy lost to heat and entropy.
by Cassandra Mullen 1E
Sat Feb 03, 2018 2:15 pm
Forum: Thermodynamic Systems (Open, Closed, Isolated)
Topic: Thermodynamic vocabulary
Replies: 3
Views: 395

Re: Thermodynamic vocabulary

The prefix "iso" means equal, so "isothermal" means equal heat, or maintaining the same heat throughout the process.
by Cassandra Mullen 1E
Fri Jan 26, 2018 8:06 am
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: 8.65
Replies: 3
Views: 223

Re: 8.65

To write the formation equation for dinitrogen pentoxide, you want 1 mol of N2O5 to form from its elements in standard state. After writing down the proper elements, don't forget to balance! :)
by Cassandra Mullen 1E
Fri Jan 26, 2018 7:58 am
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: 8.63
Replies: 4
Views: 160

Re: 8.63

There is a mistake in the solution manual as Dr. Lavelle pointed out on his website: the enthalpy of formation of K2S is actually -471.5 kJ/mol but it says -417.5 kJ/mol in the manual. The correct answer is then -38.72 kJ.
by Cassandra Mullen 1E
Fri Jan 26, 2018 7:50 am
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Heat capacity question
Replies: 5
Views: 287

Re: Heat capacity question

You would use these equations in HW problem 8.31, since you are dealing with ideal gases at constant pressures/constant volumes. The gas constant R is 8.314 J/Kmol.
by Cassandra Mullen 1E
Sat Jan 20, 2018 12:06 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: What does R stand for?
Replies: 13
Views: 657

Re: What does R stand for?

Heat constant. When do you use 8.314 and when do you use 0.00821? Looking at the units helps you to determine which R to use. If you're using the ideal gas equation and pressure is in atm and volume is in L, then you would use 0.00821 Latm/molK. Homework problem 8.49 is an example of using the othe...
by Cassandra Mullen 1E
Sat Jan 20, 2018 11:55 am
Forum: Phase Changes & Related Calculations
Topic: question 8.41
Replies: 5
Views: 248

Re: question 8.41

I'd also like to ask if someone could tell us how many steps will have to be calculated and how they come together to get the final temperature. (Claire Woolson Dis 1K) The overall goal of the problem is to solve for the final temp. just like in an algebra equation. You'll set up the heat of the wa...
by Cassandra Mullen 1E
Sat Jan 20, 2018 11:26 am
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: CH8 HW#99
Replies: 3
Views: 376

Re: CH8 HW#99

You'll also have to base your calculations off of the limiting reactant. Since there are 0.130 mol of Zn (8.5 g Zn= 0.130 mol Zn), and twice as many moles of HCl is required, zinc metal is the limiting reactant.
by Cassandra Mullen 1E
Sun Jan 14, 2018 4:37 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: 8.73.b
Replies: 3
Views: 132

Re: 8.73.b

When determining the bond enthalpy, it helps to draw the molecules or at least visualize the individual bonds within each molecule. The bond enthalpies themselves are defined as the amount of energy to break one mole of the molecule. In this problem, there are four C-H bonds being broken and 4 H-Cl ...
by Cassandra Mullen 1E
Sun Jan 14, 2018 3:57 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: 8.103
Replies: 2
Views: 87

Re: 8.103

To start, check out the box on Section 8.7 pg 277. It says that the molar internal energy of a monatomic ideal gas at temp. T= 3/2RT. The average kinetic energy can be found using this expression.
by Cassandra Mullen 1E
Sat Jan 13, 2018 9:13 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Hess' Law
Replies: 3
Views: 136

Re: Hess' Law

Conceptually, you can sum all the changes using Hess's Law because enthalpy is a state function. Think of these problems as puzzles where you manipulate the steps and cancel out compounds on opposite sides of the reaction to get to the desired equation.
by Cassandra Mullen 1E
Sat Dec 09, 2017 5:33 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Chemical Equilibrium in Test 4 #6
Replies: 3
Views: 314

Re: Chemical Equilibrium in Test 4 #6

If you compare the initial concentrations to the equilibrium concentrations: you will see that on the reactants side, A went from 1.00 M to 2.54 M and B went from 2.00 M to 2.54 M. This means that the reactants increased. C goes from 7.00 M to 5.46 M and D goes from 4.00 to 2.46, so the products dec...
by Cassandra Mullen 1E
Sat Dec 09, 2017 4:13 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Chemical Equilibrium in Test 4 #6
Replies: 3
Views: 314

Re: Chemical Equilibrium in Test 4 #6

This reaction goes in the reverse reaction, which is why the x value you calculated is negative. When you plug this value into your equilibrium values in the ice table, you should get the right answer.
by Cassandra Mullen 1E
Sat Dec 09, 2017 3:55 pm
Forum: Electronegativity
Topic: Kr
Replies: 3
Views: 235

Re: Kr

Yes, Kr is stable since it has a filled valence shell, so it holds onto its electrons much more strongly than Mg does. Even though Mg is smaller, it only has 2 valence electrons, and prefers to lose those valence electrons and form a cation that resembles the fully stable octet of neon. Since it's h...
by Cassandra Mullen 1E
Fri Dec 08, 2017 9:55 am
Forum: Properties & Structures of Inorganic & Organic Acids
Topic: HF Acid Vs HBr Acid
Replies: 2
Views: 281

Re: HF Acid Vs HBr Acid

Fluorine is the most electronegative element and it is tiny compared to bromine. This means that fluorine has a stronger bond with hydrogen than bromine does. Strong acids dissociate completely, and a stronger acid will dissociate more easily. In other words, HF doesn't dissociate as easily HBr does...
by Cassandra Mullen 1E
Thu Dec 07, 2017 10:30 pm
Forum: Non-Equilibrium Conditions & The Reaction Quotient
Topic: Equilibrium Composition
Replies: 4
Views: 308

Re: Equilibrium Composition

When you make x negligible under the small x assumption, you should check to make sure that you can use this assumption. To do this, calculate that the x value you get is less than 5% of the original concentration.
by Cassandra Mullen 1E
Sun Dec 03, 2017 8:13 am
Forum: Ideal Gases
Topic: I deal gas law formula
Replies: 3
Views: 362

Re: I deal gas law formula

As volume increases, pressure decreases. Conversely, if volume decreases, pressure increases. Pressure and volume are on the same side of the equation to show this inverse relationship.
by Cassandra Mullen 1E
Sun Dec 03, 2017 8:07 am
Forum: Ideal Gases
Topic: Bar
Replies: 3
Views: 334

Re: Bar

When converting your pressure units, remember that 1 bar=1 atm. Most of the time we have been using atm as our unit of pressure, especially for the ideal gas law, but it's good to remember the conversion. :)
by Cassandra Mullen 1E
Sun Dec 03, 2017 8:02 am
Forum: Ideal Gases
Topic: Temperature in PV=nRT
Replies: 9
Views: 509

Re: Temperature in PV=nRT

If you're given the temperature in celsius, you can easily convert it to Kelvin by adding 273.15
by Cassandra Mullen 1E
Sat Nov 25, 2017 7:25 pm
Forum: Naming
Topic: HW 17.29 about the metal ion [ENDORSED]
Replies: 2
Views: 161

Re: HW 17.29 about the metal ion [ENDORSED]

When the complex has an overall negative charge, you add the suffix -ate to the metal's name. This is the case for part b, since the anion has an -2 charge. Hope this helps! :)
by Cassandra Mullen 1E
Sat Nov 25, 2017 7:15 pm
Forum: Naming
Topic: Table 17.4 [ENDORSED]
Replies: 2
Views: 175

Re: Table 17.4 [ENDORSED]

The k is kappa and the chemical symbol written next to it denotes which atom is linked to the metal atom, just to avoid ambiguity. If you do choose to use this method, you can also underline the element.
by Cassandra Mullen 1E
Sun Nov 19, 2017 10:22 am
Forum: Air Pollution & Acid Rain
Topic: Acid Rain Damage [ENDORSED]
Replies: 5
Views: 690

Re: Acid Rain Damage [ENDORSED]

Acid rain also affects the biodiversity of certain lands and their ecosystems. Some plants are sensitive to acidic environments and may die as the soil/water becomes more acidic. A certain plant species could perish and be replaced by another species. This impacts the entire food web, since plants a...
by Cassandra Mullen 1E
Sun Nov 19, 2017 10:07 am
Forum: Determining Molecular Shape (VSEPR)
Topic: Bent or linear?
Replies: 11
Views: 624

Re: Bent or linear?

An example of a linear shape with a triple bond on one side and a single bond on the other side is hydrogen cyanide (HCN). A triple bond connects C to N and a single bond connects H to C. It has no lone pairs and 2 VSEPR regions, so the molecular shape is linear.
by Cassandra Mullen 1E
Sun Nov 12, 2017 10:33 am
Forum: Determining Molecular Shape (VSEPR)
Topic: Book Exercises
Replies: 3
Views: 86

Re: Book Exercises

^ Just to add on, a molecule composed of two of the same atom has a nonpolar bond, since the electronegativities are the same (electronegativity difference is 0) and the electrons are shared equally.
by Cassandra Mullen 1E
Wed Nov 08, 2017 8:41 am
Forum: Lewis Structures
Topic: Exceptions to octet rule?
Replies: 6
Views: 286

Re: Exceptions to octet rule?

With access to the 3d orbital (10 extra electrons), the third energy level can technically hold 18 electrons max.
by Cassandra Mullen 1E
Sun Nov 05, 2017 11:05 am
Forum: Heisenberg Indeterminacy (Uncertainty) Equation
Topic: Position: Radius vs. Diameter
Replies: 2
Views: 162

Re: Position: Radius vs. Diameter

Remember that the possibility of finding the electron would be in the space of the atom (electron is confined to within the diameter of the atom), so you use the diameter.
by Cassandra Mullen 1E
Fri Nov 03, 2017 8:58 am
Forum: Electronegativity
Topic: "Higher" Electron Affinity
Replies: 4
Views: 521

Re: "Higher" Electron Affinity

How would you know which electron has a higher electron affinity than the other? You can examine the trends in the periodic table... electron affinity increases across a period and decreases down a group. Also, an atom with less valence electrons is less likely to gain electrons, so it has a lower ...
by Cassandra Mullen 1E
Fri Oct 27, 2017 4:34 pm
Forum: Resonance Structures
Topic: Bond lengths in resonance structures
Replies: 1
Views: 169

Re: Bond lengths in resonance structures

Hi, Dr. Lavelle mentioned that he looked up the bond lengths that were in the powerpoint. The bond lengths were experimentally determined, so we will most likely be given a table with all the bond lengths/bond energies and then be asked to do calculations using these given values.
by Cassandra Mullen 1E
Fri Oct 27, 2017 4:25 pm
Forum: Lewis Structures
Topic: Coulomb Potential Energy
Replies: 2
Views: 105

Re: Coulomb Potential Energy

Coulomb's law can then be related to ionization energy since the inner shell electrons are closer to the nucleus and harder to remove. The inner shell electrons have a higher attractive force (greater numerator) and the distance is less (smaller denominator), which means IE is higher.
by Cassandra Mullen 1E
Mon Oct 23, 2017 8:30 am
Forum: Bohr Frequency Condition, H-Atom , Atomic Spectroscopy
Topic: Atomic Spectra Post-Module Assessment Q. 20 [ENDORSED]
Replies: 2
Views: 250

Re: Atomic Spectra Post-Module Assessment Q. 20 [ENDORSED]

Remember that this process happens at a 1:1 ratio, where one photon excites/interacts with one electron.
by Cassandra Mullen 1E
Tue Oct 17, 2017 1:29 pm
Forum: Photoelectric Effect
Topic: Photoelectric Post Assessment Module 30C
Replies: 4
Views: 271

Re: Photoelectric Post Assessment Module 30C

For Part C, you need to combine several equations to find the frequency. By combining KE= E-threshold, E=hv, and KE=1/2mv^2, you get frequency= (1/2mv^2 + threshold)/ h (Planck's constant) Remember to use the mass of an electron: 9.11 x 10^-31 kg for the mass and to square velocity when plugging in...
by Cassandra Mullen 1E
Sun Oct 15, 2017 1:40 pm
Forum: Photoelectric Effect
Topic: Post-assessment problem
Replies: 3
Views: 187

Re: Post-assessment problem

For Part C, you need to combine several equations to find the frequency. By combining KE= E-threshold, E=hv, and KE=1/2mv^2, you get frequency= (1/2mv^2 + threshold)/ h (Planck's constant) Remember to use the mass of an electron: 9.11 x 10^-31 kg for the mass and to square velocity when plugging int...
by Cassandra Mullen 1E
Sun Oct 15, 2017 1:39 pm
Forum: Photoelectric Effect
Topic: Photoelectric Post Assessment Module 30C
Replies: 4
Views: 271

Re: Photoelectric Post Assessment Module 30C

For Part C, you need to combine several equations to find the frequency. By combining KE= E-threshold, E=hv, and KE=1/2mv^2, you get frequency= (1/2mv^2 + threshold)/ h (Planck's constant) Remember to use the mass of an electron: 9.11 x 10^-31 kg for the mass and to square velocity when plugging int...
by Cassandra Mullen 1E
Sat Oct 14, 2017 7:24 pm
Forum: Properties of Light
Topic: Color at the Quantum Level [ENDORSED]
Replies: 2
Views: 178

Color at the Quantum Level [ENDORSED]

What exactly is happening at the quantum level when we see color? Does this have to do with the "excess" energy leftover when an electron moves up an energy level?

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