## Search found 62 matches

Mon Mar 11, 2019 12:20 pm
Forum: First Order Reactions
Topic: concept
Replies: 2
Views: 139

### Re: concept

A second order reaction means that the reaction rate is proportional to either the square of the concentration of one reactant, or to the concentrations of two reactants multiplied together; so two molecules have to collide for the reaction.
Mon Mar 11, 2019 12:14 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Rate-determining step
Replies: 1
Views: 106

### Rate-determining step

Given the elementary steps of a reaction mechanism, how are you supposed to figure out which one is the rate-determining/slow step? What kind of information would have to be given to be able to know?
Mon Mar 11, 2019 12:12 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Born-Haber Cycles
Replies: 1
Views: 100

### Re: Born-Haber Cycles

Since it isn't in the syllabus, I don't think we need to know it.
Mon Mar 11, 2019 12:08 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Frequency factor
Replies: 3
Views: 144

### Re: Frequency factor

The frequency factor represents how often molecules collide in the correct orientation for a reaction to occur.
Mon Mar 04, 2019 8:33 pm
Forum: Interesting Applications: Rechargeable Batteries (Cell Phones, Notebooks, Cars), Fuel Cells (Space Shuttle), Photovoltaic Cells (Solar Panels), Electrolysis, Rust
Topic: Corrosion
Replies: 2
Views: 356

### Re: Corrosion

A metal is corroded when it loses electrons (it's oxidized). These electrons are conducted to a cathode, which is then reduced, and gets plated.
Mon Mar 04, 2019 12:42 pm
Forum: Administrative Questions and Class Announcements
Topic: Week 9 HW
Replies: 6
Views: 282

### Re: Week 9 HW

I think this week's homework should be mainly kinetics problems since we started covering kinetics last week.
Mon Mar 04, 2019 12:40 pm
Forum: First Order Reactions
Topic: First Order Reactions
Replies: 6
Views: 219

### Re: First Order Reactions

Yes, I believe first order reaction graphs will always be straight lines when they are graphed as ln[R] vs time.
Mon Feb 25, 2019 8:53 am
Forum: Calculating Standard Reaction Entropies (e.g. , Using Standard Molar Entropies)
Topic: 6th edition 9.65
Replies: 2
Views: 317

### Re: 6th edition 9.65

I think they probably want us to use the elements in their most stable form, which for carbon is C (s), graphite.
Mon Feb 25, 2019 8:48 am
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Gibbs Free Energy and equilibrium concentration
Replies: 2
Views: 123

### Re: Gibbs Free Energy and equilibrium concentration

Since K is equal to concentration of products over concentration reactants, if one of the reactant's concentration is quadrupled, then the the original K is divided by 4.
Mon Feb 25, 2019 8:44 am
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Gibbs Free Energy
Replies: 1
Views: 128

### Re: Gibbs Free Energy

This is similar to the Hess's Law approach we used for calculating reaction enthalpy. Basically, you want to make sure that the substances you are not interested in cancel each other out. In this case, you are trying to find the Gibbs Free Energy of ATP hydrolysis, and therefore want to cancel out t...
Tue Feb 19, 2019 10:32 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Spontaneous vs Not Spontaneous
Replies: 7
Views: 265

### Re: Spontaneous vs Not Spontaneous

Yes, if delta G is positive, the reaction is always not spontaneous.
Tue Feb 19, 2019 10:30 pm
Forum: Calculating Standard Reaction Entropies (e.g. , Using Standard Molar Entropies)
Topic: Test 2
Replies: 4
Views: 379

### Re: Test 2

The lecture in which we started Gibbs free energy was on 2/8, right after we finished entropy, so I would start from there excluding the entropy material.
Tue Feb 19, 2019 10:19 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: 9.83
Replies: 1
Views: 119

### Re: 9.83

It might be because the 1 mL = 1 gram is only applicable for water, not for other substances.
Tue Feb 12, 2019 7:31 pm
Forum: Administrative Questions and Class Announcements
Topic: Lyndon's HOTDOG MIDTERM REVIEW SESSION!! FINALLY!
Replies: 49
Views: 4025

### Re: Lyndon's HOTDOG MIDTERM REVIEW SESSION!! FINALLY!

005199302 wrote:for #6, how do we know that change in entropy is zero?

Since the system starts and ends at the same state, the entropy doesn't change.
Mon Feb 11, 2019 10:08 am
Forum: Thermodynamic Definitions (isochoric/isometric, isothermal, isobaric)
Topic: Degeneracy
Replies: 8
Views: 323

### Re: Degeneracy

I am still confused as to what exactly the difference between degeneracy and entropy? Don't both of these concepts relate to disorder in a system? While both of them relate to disorder, degeneracy is just the number of states a system has that are the same energy level. Entropy, however, is the deg...
Mon Feb 11, 2019 9:54 am
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: cooling a system
Replies: 3
Views: 185

### Re: cooling a system

If the reaction is endothermic, then cooling will favor reactant formation; if the reactant is exothermic, then cooling will favor product formation. This occurs according to Le Châtelier's Principle, since the systems will adjust to minimize the temperature change.
Mon Feb 04, 2019 3:16 pm
Forum: Thermodynamic Definitions (isochoric/isometric, isothermal, isobaric)
Topic: Degeneracy
Replies: 8
Views: 323

### Re: Degeneracy

Basically, degeneracy is the number of states in which energy can be at a given level. If a given particle can only be at a certain energy level in one particular state (i.e. if it moves, its energy level changes), then it has a degeneracy of 1. Going back to the example Professor Lavelle gave in cl...
Mon Feb 04, 2019 2:55 pm
Forum: Administrative Questions and Class Announcements
Topic: Final from 14A
Replies: 2
Views: 234

### Re: Final from 14A

They're available to pick up in Young 3034! You just have to show your bruin card and then you can get your final.
Mon Feb 04, 2019 2:54 pm
Forum: Thermodynamic Definitions (isochoric/isometric, isothermal, isobaric)
Topic: Isothermal reversible expansion
Replies: 2
Views: 140

### Isothermal reversible expansion

Could someone please explain why reversible expansion must be isothermic?
Mon Jan 28, 2019 7:40 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Extensive Vs Intensive Properties
Replies: 1
Views: 92

### Re: Extensive Vs Intensive Properties

An extensive property is something that depends on how much of something is being measured, like mass, which changes depending on how much of a substance you weigh. An intensive property doesn't depend on the amount of substance; for example, density remains the same throughout some substance no mat...
Mon Jan 28, 2019 7:22 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Calorimetry
Replies: 5
Views: 252

### Re: Calorimetry

In a bomb calorimeter, volume is kept constant, so pressure changes; in the other type of calorimeter, pressure is kept constant, so volume can change.
Mon Jan 28, 2019 5:50 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Enthalpy and Heat Capacity
Replies: 2
Views: 109

### Re: Enthalpy and Heat Capacity

Enthalpy is the amount of heat released or absorbed in some reaction at a constant pressure, whereas heat capacity is the heat required to raise the temperature of some substance by 1 degree Celsius. In both cases, the units to use are Celsius or Kelvin.
Mon Jan 21, 2019 7:19 pm
Forum: Non-Equilibrium Conditions & The Reaction Quotient
Topic: Percent Protonation
Replies: 6
Views: 240

### Re: Percent Protonation

I believe it is the concentration of the conjugate acid over the initial concentration of the base multiplied by 100.
Mon Jan 21, 2019 6:52 pm
Forum: Acidity & Basicity Constants and The Conjugate Seesaw
Topic: weak acids/bases
Replies: 2
Views: 319

### Re: weak acids/bases

Yes, since strong acids and bases are 100% ionized.
Mon Jan 21, 2019 5:08 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Salt on Test 1
Replies: 5
Views: 211

### Re: Salt on Test 1

Yes, salts will be included on the test (everything up to last Friday will be on the test).
Tue Jan 15, 2019 3:03 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Ionization Constant
Replies: 2
Views: 120

### Ionization Constant

In lecture, Dr. Lavelle stated that the ionization constant of water is Kw = [H3O+][OH-] = 10^-14. What exactly does ionization constant mean? Is it the same thing as equilibrium constant?
Tue Jan 15, 2019 2:38 pm
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: Test Next Week
Replies: 2
Views: 129

### Re: Test Next Week

I would recommend doing as many practice problems from the textbook from different topics as you feel necessary for your own understanding. There are also weekly review worksheets on Chemistry Community (if you search "Session Worksheets" you should be able to find them). If you feel like ...
Mon Jan 14, 2019 2:20 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Kp
Replies: 7
Views: 297

### Re: Kp

As long as you keep the units consistent throughout a single problem, you can use both bars and atm to calculate Kp, depending on which one is given in a problem.
Tue Jan 08, 2019 3:19 pm
Forum: Non-Equilibrium Conditions & The Reaction Quotient
Topic: Spontaneous reaction
Replies: 4
Views: 169

### Re: Spontaneous reaction

A spontaneous reaction is a reaction that takes place without any external interference; a spontaneous reaction is exothermic (there is a decrease of energy in the system).
Tue Jan 08, 2019 1:44 pm
Forum: Ideal Gases
Topic: Pressure units
Replies: 4
Views: 247

### Pressure units

For units of partial pressure, should we use bars or atmospheres? What is the difference between the two?
Tue Jan 08, 2019 10:26 am
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Kc vs Kp
Replies: 4
Views: 66

### Re: Kc vs Kp

I believe it depends on what you are given: if you are given the concentrations of the molecules in the chemical reaction, then it's Kc, and if you are given the partial pressures, you have to find Kp.
Mon Dec 03, 2018 4:48 pm
Forum: Calculating pH or pOH for Strong & Weak Acids & Bases
Topic: Resonance
Replies: 1
Views: 96

### Re: Resonance

When a compound has resonance structures, its negative charge/electrons are delocalized. This makes it more stable, so if that compound has a bond with H, it is more likely to lose H+ since the resulting anion will be stabilized by delocalization. In other words, the more stable the anion is, the mo...
Mon Dec 03, 2018 4:36 pm
Forum: Shape, Structure, Coordination Number, Ligands
Topic: Coordination Number
Replies: 2
Views: 158

### Re: Coordination Number

Drawing the most stable Lewis structure is probably the best way to go about it, because it will give you the correct answer every time if it is drawn correctly.
Mon Dec 03, 2018 1:43 pm
Forum: Amphoteric Compounds
Topic: Definition
Replies: 5
Views: 207

### Re: Definition

Amphoteric refers to a compound, especially metal oxides/hydroxides, that can act as either a base or an acid.
Mon Nov 26, 2018 3:48 pm
Forum: Shape, Structure, Coordination Number, Ligands
Topic: Coordinate covalent bond
Replies: 2
Views: 119

### Re: Coordinate covalent bond

A coordinate covalent bond is a covalent bond in which two of the electrons come from a single atom. Hope this helps!
Mon Nov 26, 2018 3:35 pm
Forum: General Science Questions
Topic: Test 3
Replies: 4
Views: 277

### Re: Test 3

The end of outline 3, which is chemical bonds, and all of outline 4 (molecular shape and structure).
Mon Nov 26, 2018 3:24 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Determining Shape
Replies: 4
Views: 208

### Re: Determining Shape

CLO2+ has three regions of electron density (one lone pair and two double bonds), but since the name of the shape of a compound is only based on bonds and excludes lone pairs, its shape is angular/bent. In terms of electron density regions, however, it is trigonal planar.
Mon Nov 19, 2018 1:27 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Bond angles of H3O+
Replies: 2
Views: 74

### Re: Bond angles of H3O+

Since H3O+ has a lone pair and three bonds, I think the bond angles would be <109.5 degrees, since the electron densities are tetrahedral, but a lone pair is more diffuse than a bond so it pushes the covalent bonds closer together.
Mon Nov 19, 2018 1:13 pm
Forum: Hybridization
Topic: Electron Density Shape
Replies: 2
Views: 80

### Re: Electron Density Shape

Basically, we name molecule shapes based on the number of bonds they have, not based on the number of regions of electron density. So in terms of regions of electron density, ammonia is tetrahedral because there is one lone pair and three bonds (so four areas of electron density), but since we only ...
Mon Nov 19, 2018 9:45 am
Forum: Determining Molecular Shape (VSEPR)
Topic: Bent vs. Angular
Replies: 3
Views: 170

### Re: Bent vs. Angular

Yes, bent and angular both describe the same molecular shape!
Tue Nov 13, 2018 3:11 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Biological Activity
Replies: 3
Views: 196

### Re: Biological Activity

Enzymes and proteins have active sites which other molecules bind to; they are then converted into some product and released. The shape of an enzyme's active site, which is influenced by electronic structure, determines what kind of molecules can attach to it, and therefore what the function of that...
Tue Nov 13, 2018 3:09 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: Induced Dipole
Replies: 2
Views: 156

### Re: Induced Dipole

It results in momentary areas of relatively high or low electron density, causing nearby atoms to be attracted to the positive area, which is how Van Der Waals forces are created.
Mon Nov 12, 2018 10:25 pm
Forum: Ionic & Covalent Bonds
Topic: What is Distortion?
Replies: 3
Views: 87

### Re: What is Distortion?

Distortion is when the shape of the electron cloud of an atom is changed due to attraction from another atom. If an atom is highly polarizable, that means that its electron cloud can be distorted easily by a polarizing atom.
Tue Nov 06, 2018 2:18 pm
Forum: Empirical & Molecular Formulas
Topic: Assumption of 100g
Replies: 2
Views: 538

### Re: Assumption of 100g

Multiplying the percentage by the molar mass is more accurate and faster than assuming 100g and converting that into moles, and then dividing by the smallest number. You can then use the grams found by multiplying percentage by molar mass to convert into moles, which gives you the molecular formula,...
Tue Nov 06, 2018 10:12 am
Forum: Lewis Structures
Topic: Lewis Structures for Ionic Compunds
Replies: 1
Views: 145

### Re: Lewis Structures for Ionic Compunds

Since MgCl2 is a salt, I believe you would draw it similar to NH4Cl, by putting Mg in the middle with full octet in brackets and one Cl- on either side without any dots for electrons.
Mon Nov 05, 2018 3:50 pm
Forum: Lewis Structures
Topic: Double Bonds
Replies: 7
Views: 304

### Re: Double Bonds

You should add a double bond if it lowers the formal charges, since the most stable Lewis structure for a molecule is the one with the smallest formal charges on each atom. The number of bonds depends on which specific Lewis structure you're drawing, but in general you should never have more than th...
Tue Oct 30, 2018 2:47 pm
Forum: Resonance Structures
Topic: Lengths of bonds
Replies: 3
Views: 131

### Re: Lengths of bonds

Double bonds are shorter because they share more electrons, attracting the nuclei of two atoms closer together than a single bond does.
Tue Oct 30, 2018 11:12 am
Forum: Resonance Structures
Topic: Resonance
Replies: 8
Views: 415

### Re: Resonance

None of the resonance structures we draw as Lewis symbols actually exist in real life, because in an actual molecule that has resonance structures, the double bond is divided up in between the atoms equally. For example, for a nitrate ion, NO3-, we draw the Lewis structure as nitrogen having a doubl...
Mon Oct 29, 2018 8:35 pm
Forum: DeBroglie Equation
Topic: Uncertainty
Replies: 4
Views: 309

### Re: Uncertainty

Yes, I believe when an object is large its uncertainty is so small in comparison that it's basically irrelevant to calculations done
Mon Oct 22, 2018 9:21 am
Forum: Bohr Frequency Condition, H-Atom , Atomic Spectroscopy
Topic: Explaining Rydberg Equation
Replies: 1
Views: 95

### Re: Explaining Rydberg Equation

I think it's a convention, because when an electron's energy is zero, it's on the verge of escaping from the atom. If the electron is closer to the negative, it has less potential energy, so it becomes negative. The negative sign lets us differentiate between attached electrons and free electrons; t...
Mon Oct 22, 2018 9:10 am
Replies: 4
Views: 545

A black body is a theoretical object that absorbs all wavelengths of radiation. When an object is heated up, it emits light, so black-body radiation is the wavelengths of light a black body emits when heated up. Observation of black-body radiation has shown that the intensity of the radiation emitte...
Mon Oct 22, 2018 8:56 am
Forum: Heisenberg Indeterminacy (Uncertainty) Equation
Topic: Value of Delta X
Replies: 9
Views: 554

### Re: Value of Delta X

When we're given ∆x, it's usually the diameter of an atom, but one of the problems in the book uses diameter of a nanoparticle. I think in general we will be given some sort of diameter.
Tue Oct 16, 2018 8:08 pm
Forum: Photoelectric Effect
Topic: Photoelectric Effect Module
Replies: 3
Views: 1207

### Re: Photoelectric Effect Module

Light hits a sodium metal surface and the velocity of the ejected electron is 6.61 x 105 m.s-1. The work function for sodium is 150.6 kJ.mol-1. Answer the following three questions. A. What is the kinetic energy of the ejected electron? How would one go about to solve this problem? What equation wo...
Tue Oct 16, 2018 8:05 pm
Forum: Properties of Light
Topic: 7th Edition 1A.3
Replies: 4
Views: 110

### Re: 7th Edition 1A.3

The answer is C, the extent of the change in the electrical field at a given point decreases, because since E =hv, when frequency decreases, so does energy. Less energy means less of a change in the electrical field. Hope this helps!
Tue Oct 16, 2018 8:03 pm
Forum: *Shrodinger Equation
Topic: Schrodinger Equation
Replies: 3
Views: 303

### Re: Schrodinger Equation

natalieg4e wrote:Will this equation be provided on the test?

Yes, it's on the constants and equations sheet that we're provided for tests.
Tue Oct 09, 2018 8:09 pm
Forum: SI Units, Unit Conversions
Topic: Preferred Units for Tests and Homework
Replies: 3
Views: 229

### Re: Preferred Units for Tests and Homework

I don't think it should matter, since it's just different notation forms of writing them, and g/mol makes dimensional analysis easier
Tue Oct 09, 2018 7:50 pm
Forum: Properties of Light
Topic: Balmer series vs Lyman series
Replies: 4
Views: 144

### Re: Balmer series vs Lyman series

I think you use the Balmer series when n = 2, so electrons are in the second energy level, and the Lyman series when n = 1, so electrons are in ground state.
Tue Oct 09, 2018 10:24 am
Forum: Significant Figures
Topic: Sig Fig zero rules
Replies: 7
Views: 856

### Re: Sig Fig zero rules

Hi! The rules of sig figs are: 1. All non-zero digits are significant 2. Any zeros in between two non-zero numbers are significant 3. A zero at the end of a number without a decimal point is not significant 4. Any zeros at the beginning of a number are not significant 5. Final/trailing zeros in a nu...
Wed Oct 03, 2018 6:49 pm
Forum: Empirical & Molecular Formulas
Topic: Question 22 on the post assessment for Empirical Formulas
Replies: 2
Views: 117

### Re: Question 22 on the post assessment for Empirical Formulas

The molar mass of the molecular formula Xylitol is given as 152.15, and when you add up all the molar masses of C5H12O5, you get the same number, which means that it's the molecular formula. In this case the molecular formula is also the empirical formula, since the amounts of each element are alrea...
Wed Oct 03, 2018 5:08 pm
Forum: Limiting Reactant Calculations
Topic: Finding the Limiting Reactant
Replies: 2
Views: 144

### Re: Finding the Limiting Reactant

If there is no excess of either reactant, that means that all reactants are present in exactly the right molar ratio. This means calculating the moles of product with any reactant would give you the same answer. This works even if they don't have the same number of moles; as long as the ratio is rig...
Tue Oct 02, 2018 12:11 pm
Forum: Molarity, Solutions, Dilutions
Topic: Molarity and Dilution of a Solution:Post-Module Assessment Question 19
Replies: 2
Views: 104

### Re: Molarity and Dilution of a Solution:Post-Module Assessment Question 19

Hi! When I solve for V using the formula M = n/V, I get V = n/M, so I think you might have accidentally inverted molarity and moles. Then when I do the problem, I get
V = 0.03/0.06, which gives me 0.5 Liters.
I hope this helps!
Fri Sep 28, 2018 5:03 pm
Forum: Accuracy, Precision, Mole, Other Definitions
Topic: Precision of One Point [ENDORSED]
Replies: 2
Views: 97

### Re: Precision of One Point[ENDORSED]

I think only multiple points can be precise, since precision is defined as a series of measurements being close to each other, and a single point can't do that.