## Search found 58 matches

Fri Mar 15, 2019 9:59 am
Forum: Second Order Reactions
Topic: 6th edition 15.39 part b
Replies: 2
Views: 304

### Re: 6th edition 15.39 part b

You subtract instead of add because A is the reactant and it's getting used up. The B concentration that they give us is the concentration of B formed after the time we need to solve for. The concentration of B formed correlates to the concentration of A used up to produce B. Thus, you subtract the ...
Fri Mar 15, 2019 9:56 am
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: ordering reduction potential powers
Replies: 3
Views: 113

### Re: ordering reduction potential powers

When you think of the cell potentials that are listed in the back of the book, think of them as specifically reduction potentials / as how likely a species is to be reduced. If you are ordering the species in terms of increasing oxidizing power, you would order them from lower reduction potential to...
Tue Mar 12, 2019 8:14 pm
Forum: Kinetics vs. Thermodynamics Controlling a Reaction
Topic: 15.39
Replies: 2
Views: 243

### Re: 15.39

The molarity of B is given in the problem as 0.19.
Sun Mar 10, 2019 8:29 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Microscopic reversibility
Replies: 2
Views: 125

### Re: Microscopic reversibility

I think microscopic reversibility means that for the forward and reverse directions of a reaction, there are the same intermediates involved, so the forward and reverse reactions go on the same, single pathway.
Sun Mar 10, 2019 8:26 pm
Forum: General Rate Laws
Topic: rate of reaction formula
Replies: 1
Views: 89

### Re: rate of reaction formula

I believe there is a negative sign because they are asking for the rate of the overall reaction of NO2, which needs to be positive so they add the negative sign to make the value become positive. If they were asking for the rate of consumption of NO2, I think there would not be a negative sign in fr...
Sun Mar 10, 2019 8:20 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: What does K say about stability?
Replies: 5
Views: 602

### Re: What does K say about stability?

For this question, since K >10^3, at equilibrium and K = concentration of products / concentration of reactants, then there are more products than reactants and the reaction lies to the right. Therefore, there is more SO3 (the product) at equilibrium, which then refers to its stability. Since there ...
Sun Mar 03, 2019 11:29 pm
Forum: General Rate Laws
Topic: The value of K
Replies: 5
Views: 162

### Re: The value of K

K changes with temperature, so for each reaction, when the reaction occurs at different temperatures, K is different.
Sun Mar 03, 2019 11:25 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Edition 6 14.25
Replies: 3
Views: 176

### Re: Edition 6 14.25

Reducing agents refer to substances that are being oxidized, which then in turn causes another substance to become reduced. Stronger reducing agents are lower in cell potential, so for this problem, you would want to rank the metals in order of highest cell potential to lowest cell potential as list...
Sun Feb 24, 2019 7:27 pm
Forum: Student Social/Study Group
Topic: Final
Replies: 24
Views: 1038

### Re: Final

Lavelle will post on his website when the final review sessions start, but usually it is during week 10 that they do.
Sat Feb 23, 2019 4:49 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Salt Bridge
Replies: 2
Views: 96

### Re: Salt Bridge

Since the electrons are moving from the anode to the cathode, there is a charge difference between the two and the resulting charge buildup would cause the electrode reaction to stop. To prevent the reaction from stopping, the salt bridge allows ions to cross over and prevent the cathode from being ...
Sat Feb 23, 2019 4:39 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Cell Diagram
Replies: 2
Views: 88

### Re: Cell Diagram

We separate them with a comma because they are both in the same phase. The solid line is for when they are in two different phases, such as liquid and solid. I think it's just the rule.
Mon Feb 18, 2019 10:57 am
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Polyprotic Acids
Replies: 5
Views: 195

### Re: Polyprotic Acids

For polyprotic acids, the K for the reactions are different for each time, so you would only write the conjugate acid in the specific reaction you are looking at to find the equilibrium constant.
Tue Feb 12, 2019 11:02 pm
Forum: Calculating Work of Expansion
Topic: Reversible Expansions and delta H
Replies: 1
Views: 117

### Reversible Expansions and delta H

For reversible expansion problems, since pressure isn't constant anymore, does that mean we cannot say that q=delta H? If we were asked to find q, would we have to use q=mCdeltaT?
Tue Feb 12, 2019 10:47 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: clarification
Replies: 1
Views: 123

### Re: clarification

Yes I think so because reversible means the process is at equilibrium so there is no change in entropy.
Sat Feb 09, 2019 4:26 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: What is kB in the equation deltaS=kB lnW?
Replies: 1
Views: 82

### Re: What is kB in the equation deltaS=kB lnW?

kb is Boltzmann's constant and it's 1.38 x 10-23 J/K. It's given on the constants and equations sheet online so I don't think we have to memorize it.
Fri Feb 08, 2019 11:06 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: 6th edition 8.57
Replies: 1
Views: 86

### Re: 6th edition 8.57

The main reason in figuring out that the reaction is a combustion reaction is that for delta H that are listed, there is a subscript "c" that represents combustion. You then have to set up the combustion equations and use Hess' method to get the equation that is originally given and the ov...
Sun Feb 03, 2019 6:12 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: Delta U
Replies: 7
Views: 296

### Re: Delta U

A positive delta U means the internal energy of the system you are looking at has increased while a negative delta U means internal energy of the system has decreased.
Sat Feb 02, 2019 7:05 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Bond enthalpies
Replies: 3
Views: 175

### Re: Bond enthalpies

For this problem, I think you just have to know (by drawing its lewis structure) that benzene has resonance structures. That means all of its bonds are the same length, which is between the length of a single and double bond between carbons. So since benzene has 6 carbon-carbon bonds of the same len...
Thu Jan 31, 2019 10:06 am
Forum: Calculating Work of Expansion
Topic: Units
Replies: 1
Views: 102

### Re: Units

The unit for pressure is kg/(ms^2). The unit for volume is m^3. Since work = external pressure multiplied by change in volume, the units for work are (kg/(ms^2))m^3. When you simplify that, you get (kgm^2)/s^2 = Joules.
Sat Jan 26, 2019 2:15 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Standard enthalpy of formation
Replies: 2
Views: 80

### Re: Standard enthalpy of formation

The standard enthalpy of formation specifically refers to the amount of enthalpy for the formation of 1 mole of a substance, so that's why the units for it is kJ/mol. The standard reaction enthalpy has no mention of mols (hence no mols in the units, just kJ as the standard unit) and refers to the wh...
Fri Jan 25, 2019 12:34 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: First row question
Replies: 3
Views: 203

### Re: First row question

These cations from group 1 and 2 are very weak Lewis acids, and they're so weak to the point that they don't have an effect on the water molecules around them. Therefore, you don't account for them when calculating pH.
Sat Jan 19, 2019 1:53 pm
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: exothermic/endothermic
Replies: 3
Views: 250

### Re: exothermic/endothermic

If you are given delta H of the equation, you can identify if the reaction is endothermic or exothermic. If delta H (which represents the change in enthalpy) is positive, then it is an endothermic reaction. If delta H is negative, then it is an exothermic reaction since energy is being released, not...
Fri Jan 18, 2019 12:39 pm
Forum: Non-Equilibrium Conditions & The Reaction Quotient
Topic: Kw
Replies: 6
Views: 244

### Re: Kw

Yes, in pure water the concentrations of hydronium and hydroxide are equal. When an acid or base is added though, these concentrations can change.
Tue Jan 15, 2019 1:24 pm
Forum: General Science Questions
Topic: SIG FIGS
Replies: 5
Views: 496

### Re: SIG FIGS

For doing sig figs with pH, you start counting the sigfigs after the decimal point. For example, a pH of 1.11 has 2 sig figs or a pH of 10.000 has 3 sig figs.
Sun Jan 13, 2019 10:28 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Question 5I 19
Replies: 2
Views: 105

### Re: Question 5I 19

For this question, the HI and I2 are not really left over but have equilibrium concentrations that you need to solve for in order to get K. To get their equilibrium concentrations, you set up an ICE table. The 60% of H2 used up refers to the change in H2, "x", which you can get by multiply...
Sun Jan 13, 2019 10:16 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Equilibrium composition, estimation method vs quadratic method
Replies: 1
Views: 45

### Re: Equilibrium composition, estimation method vs quadratic method

I think Dr. Lavelle will address it in class but in the module he did say to use the estimation method when dealing with the concentrations with a power of 3.
Sat Jan 12, 2019 4:57 pm
Forum: Ideal Gases
Topic: A bit of confusion
Replies: 3
Views: 121

### Re: A bit of confusion

For the problem you mentioned in the textbook, the equation they gave us is actually a combination of 2 separate equations that you can find on the 11.2 table. The rule is that when there are 2 or more equations combined together, the overall equilibrium constant (K) is the product of the separate e...
Sat Dec 08, 2018 12:02 am
Forum: Biological Examples
Topic: Cisplatin
Replies: 3
Views: 344

### Re: Cisplatin

Cisplatin is used in chemotherapy for the treatment of cancer cells, which are characterized by rapid cell growth, because it can bind to DNA and prevent cell replication and thus stop cancer cells from growing. More specifically, cisplatin binds to the DNA base guanine. The nitrogens in guanine ess...
Thu Dec 06, 2018 11:55 pm
Forum: Naming
Topic: Naming
Replies: 2
Views: 145

### Re: Naming

It is bis when naming the complex because there are 2 molecules of oxalate in the complex. Since oxalate is polydentate, different prefixes must be used so you use bis- for when there's 2 of them.
Thu Dec 06, 2018 9:10 pm
Forum: DeBroglie Equation
Topic: Test 2 confusion
Replies: 1
Views: 377

### Re: Test 2 confusion

For #2, I think you got all the calculations right, but you might have gotten points off because of units. You needed to put meters after your calculation for the minimum delta x. But I'm not sure if that's just 1 point off or 2!
Fri Nov 30, 2018 10:48 pm
Forum: Sigma & Pi Bonds
Topic: Rotating Bond?
Replies: 4
Views: 436

### Re: Rotating Bond?

Sigma bonds are able to rotate but pi bonds are not.
Thu Nov 29, 2018 8:58 pm
Forum: Trends in The Periodic Table
Topic: Ionization Energy
Replies: 2
Views: 513

### Re: Ionization Energy

Oxygen's ionization energy is lower than Nitrogen's despite the fact that ionization energy typically increases as you go across a period because of their electron configurations. Oxygen's electron configuration is 1s 2 2s 2 2p 4 . Nitrogen's electron configuration is 1s 2 2s 2 2p 3 . Because of Nit...
Wed Nov 28, 2018 3:48 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Changing shared electrons to lone pairs
Replies: 1
Views: 201

### Re: Changing shared electrons to lone pairs

It depends on the VSEPR shape. For a molecule with 5 bonded atoms and no lone pair around a central atom aka AX5 (trigonal bipyramidal), for the shape to become seesaw (AX4E), you remove the equatorial electrons first. As you keep removing the equatorial electrons from the trigonal bipyramidal shape...
Sun Nov 25, 2018 11:34 am
Forum: Formal Charge and Oxidation Numbers
Topic: Formal charge on atom w/ expanded valence shell
Replies: 1
Views: 402

### Re: Formal charge on atom w/ expanded valence shell

Usually, I think that the purpose of the expanded valence shell is to get the formal charge of the central atom to be neutral. But I'm not sure if it's necessarily that all atoms with an expanded octet when bonded to other atoms will have a formal charge of 0. When you're looking at XeF4 particularl...
Sat Nov 24, 2018 3:27 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: 4.25 6th edition: Polarity of SF4
Replies: 4
Views: 222

### Re: 4.25 6th edition: Polarity of SF4

But wouldn’t the polarity between Sulfur and Fluorine overall “cancel out” to result in an overall nonpolar molecule? The dipole moments are all equal and pointing in opposite directions so won’t they “cancel out”? Does it have anything to do with the fact that Sulfur has a lone pair in the molecule?
Sat Nov 24, 2018 12:30 pm
Forum: *Molecular Orbital Theory (Bond Order, Diamagnetism, Paramagnetism)
Topic: Pi Bond
Replies: 1
Views: 64

### Re: Pi Bond

If 2 carbons that are in a pi bond do rotate, the bond will break. So for instance, in C2H4 (ethene), in the double bond between the 2 carbons, one of the bonds is a pi bond which restricts the molecule from rotating and makes it so that the whole molecule is on 1 plane. If one of the carbons were t...
Sat Nov 24, 2018 12:26 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: 4.25 6th edition: Polarity of SF4
Replies: 4
Views: 222

### 4.25 6th edition: Polarity of SF4

For question 4.25 in the 6th edition of the textbook, why is SF4 polar? I thought since the dipole moments pointing towards F cancel out, the molecule would be nonpolar.
Sun Nov 18, 2018 6:33 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: lone pairs and bond angle
Replies: 6
Views: 206

### Re: lone pairs and bond angle

In addition, lone pairs, because of electron repulsion, "push" down onto the other bond angles to make them smaller.
Sat Nov 17, 2018 5:09 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: Energy of Intermolecular Forces
Replies: 6
Views: 266

### Energy of Intermolecular Forces

Why are the energies of the different interactions Dr. Lavelle talked about in class negative?
For example, the energy of an ion-ion interaction is -250 kJ/mol. I am a little confused why it's a negative number and not a positive one.
Sat Nov 17, 2018 4:55 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Molecular shape
Replies: 2
Views: 118

### Re: Molecular shape

The shape of a molecule contributes to strength of interaction because when the shape of the molecules makes it so that the distance between the 2 molecules is shorter and that there is more surface area interacting with each other, the strength of the interaction between the two will be stronger. F...
Mon Nov 12, 2018 10:52 am
Forum: Electronegativity
Topic: ChemistryHow are electronegativity values for elements determined?
Replies: 3
Views: 162

### Re: ChemistryHow are electronegativity values for elements determined?

I'm not sure how the values for electronegativity are calculated, but they are based on the element's electron affinity and ionization energy. I believe we don't need to know how to calculate it, we just need to know the definition and how it relates to covalent bonds and other topics.
Mon Nov 12, 2018 10:48 am
Forum: Bond Lengths & Energies
Topic: High Boiling Points and Bond Strengths [ENDORSED]
Replies: 4
Views: 236

### Re: High Boiling Points and Bond Strengths[ENDORSED]

The rod shaped molecules have stronger bonds than the spherical ones because in the rod shaped molecules, there is more contact between the molecules and more surface area interacting with each other. As a result, the bond is shorter between the two molecules and stronger. As a result of the stronge...
Mon Nov 12, 2018 10:42 am
Forum: Dipole Moments
Topic: Polarizability vs Polarizing Power
Replies: 4
Views: 156

### Re: Polarizability vs Polarizing Power

They can be seen as opposites. Polarizability refers to how an atom's electrons can get distorted or in other words feel the pull towards the positive nucleus of another atom. For example, the iodide ion has higher polarizability than a chloride ion because the electrons in the larger iodide ion are...
Sat Nov 03, 2018 10:03 pm
Forum: Trends in The Periodic Table
Topic: Cation and Anion Ionic Radius
Replies: 3
Views: 76

### Re: Cation and Anion Ionic Radius

Anions are larger than their parent atoms because an anion has more electrons than its parent electron. The increase in electrons leads to more electron repulsion, so electrons are more spread out from each other which causes the ionic radius to increase. Cations are smaller than their parent atoms ...
Fri Nov 02, 2018 12:55 pm
Forum: Molarity, Solutions, Dilutions
Topic: Dilution Units
Replies: 1
Views: 328

### Re: Dilution Units

For dilutions or calculating the molarity, the unit is always mol/liters. So if you were given the grams of the solute and you need to calculate the molarity, you would need to use the molar mass to change that to mols. Generally, I don't think we would be asked what the concentration of the solvent...
Fri Nov 02, 2018 12:45 pm
Forum: Trends in The Periodic Table
Topic: Electron Affinity
Replies: 1
Views: 71

### Re: Electron Affinity

When a gas-phase atom gains an electron, it gets closer to completing an octet or having a noble gas electron configuration. Having a noble gas electron configuration provides more stability for the atom, and thus with more stability the electron is now at a lower energy state. The change of the ele...
Sun Oct 28, 2018 1:25 pm
Forum: Ionic & Covalent Bonds
Topic: Determining the number of electrons in a compound [ENDORSED]
Replies: 2
Views: 136

### Re: Determining the number of electrons in a compound[ENDORSED]

With SO4^2-, you need to first look at the periodic table to determine how many valence electrons sulfur and oxygen have. Both of them are in Group 16, so they both have 6 valence electrons. Since the ionic compound has 4 oxygens, you do 4 x 6 = 24 to get the total number of electrons from oxygen in...
Sun Oct 28, 2018 1:20 pm
Forum: Ionic & Covalent Bonds
Topic: ionization energy
Replies: 7
Views: 333

### Re: ionization energy

The 2nd ionization energy is always higher than the first ionization energy because when removing the second electron, you are removing it from the cation of the element. It takes more energy to remove an electron from a cation than a neutral atom because the cation is holding onto the electrons mor...
Sat Oct 27, 2018 10:15 pm
Forum: Trends in The Periodic Table
Topic: effective nuclear charge
Replies: 1
Views: 99

### Re: effective nuclear charge

The effective nuclear charge refers to the net charge or attraction that an electron in an atom feels towards the positively charged nucleus. In multielectron atoms, the nuclear charge coming from the nucleus is called "effective" because other electrons that are closer to the nucleus shie...
Sat Oct 20, 2018 11:45 am
Forum: Heisenberg Indeterminacy (Uncertainty) Equation
Topic: Heisenberg Indeterminacy Equation
Replies: 1
Views: 76

### Re: Heisenberg Indeterminacy Equation

The Heisenberg Indeterminacy Equation basically tells us that we can't know 100% what both the momentum and position of a particle, such as an electron, is at one point in time, aka there is a limit on the accuracy to which the momentum and position of a particle can be known simultaneously. The act...
Sat Oct 20, 2018 11:35 am
Forum: Heisenberg Indeterminacy (Uncertainty) Equation
Topic: Kinetic Energy based on uncertainty
Replies: 1
Views: 160

### Re: Kinetic Energy based on uncertainty

The formula for kinetic energy is KE=(mv^2)/2. With this post-assessment problem, you can plug in the uncertainty of the velocity and the mass of an electron, which is 9.1 x 10^-31 kg (I just searched it up on Google), into the KE equation and get the uncertainty in kinetic energy. Keep in mind that...
Sat Oct 20, 2018 11:23 am
Forum: *Shrodinger Equation
Topic: Double Derivative and Shrodinger Equation
Replies: 1
Views: 152

### Double Derivative and Shrodinger Equation

In lecture, Dr. Lavelle briefly mentioned a double derivative within the Shrodinger equation, but I was confused on that part. What/how does a double derivative relate to the equation?
Sat Oct 13, 2018 5:36 pm
Forum: Properties of Electrons
Topic: Diffraction patterns
Replies: 9
Views: 437

### Re: Diffraction patterns

A wave does not necessarily "go" from constructive to destructive interferences. These types of interferences describe what happen when waves meet up with each other, or interact with each other.
Sat Oct 13, 2018 5:30 pm
Forum: Properties of Light
Topic: The PhotoElectric Effect
Replies: 2
Views: 60

### Re: The PhotoElectric Effect

The photoelectric effect shows how in order for an electron to be removed from a metal, the wave of light needs to have a higher frequency/shorter wavelength. The level of intensity does not matter in this case. Thus, in the photoelectric effect, light is not acting as a classical wave and instead, ...
Sat Oct 13, 2018 11:00 am
Forum: Properties of Light
Topic: Diffraction Pattern with Constructive Interference
Replies: 2
Views: 70

### Re: Diffraction Pattern with Constructive Interference

The resulting marks from the experiment show the existence of a diffraction pattern from light waves. When the waves constructively interfere with each other, waves with bigger amplitudes are produced. The result of this is that the light that hits the wall is brighter. Ultimately, the existence of ...
Sun Oct 07, 2018 3:49 pm
Forum: Limiting Reactant Calculations
Topic: L7
Replies: 2
Views: 76

### Re: L7

In L7 part B, when it's asking what mass of oxygen is needed to oxidize the tristearin, it's asking how much oxygen will be used up along with the 454 grams of tristearin in the combustion/oxidation reaction. It's the same method you used in part A, so you'll need to convert the 454 grams of tristea...
Sun Oct 07, 2018 12:38 am
Forum: Molarity, Solutions, Dilutions
Topic: hw problem F17
Replies: 1
Views: 62

### Re: hw problem F17

Mass spectrum refers to the technique of mass spectrometry, which is a method that scientists use to measure the molar mass of elements or a sample.

In F17, the problem mentions "mass spectrum" to explain how the molar mass of the molecule was discovered.
Tue Oct 02, 2018 11:00 pm
Forum: Empirical & Molecular Formulas
Topic: Using the Mass Spectrum in F17(b)
Replies: 2
Views: 366

### Re: Using the Mass Spectrum in F17(b)

You need to divide the given molar mass by the empirical formula mass because the empirical formula is still just a ratio of the number of atoms in each element of the molecule or compound. It’s like the reduced version of the actual molecular formula, so when you divide the molar mass by the empiri...