## Search found 66 matches

Sat Mar 09, 2019 7:15 pm
Forum: Kinetics vs. Thermodynamics Controlling a Reaction
Topic: Instantaneous vs Average
Replies: 11
Views: 405

### Re: Instantaneous vs Average

Instantaneous rate is the rate of the reaction at a particular time.
Average rate is the rate of the reaction over the time taken to the reaction's completion
Sat Mar 09, 2019 7:10 pm
Forum: General Rate Laws
Topic: Unique Reaction Rates [ENDORSED]
Replies: 33
Views: 77904

### Re: Unique Reaction Rates[ENDORSED]

The unique reaction rate is defined as the rate of the increase in product concentration or the rate in decrease of product concentration divided by the stoichiometric coefficient.
Sat Mar 09, 2019 7:08 pm
Forum: Zero Order Reactions
Topic: Half Life and k
Replies: 11
Views: 617

### Re: Half Life and k

This is because k is associated with how fast a reaction runs. If the reaction runs faster then the amount of time needed for the substance to fall to half its original decreases. Hence, K is inversely proportional to Half life.
Mon Mar 04, 2019 12:02 am
Forum: Balancing Redox Reactions
Topic: oxidizing agent and reducing agent
Replies: 15
Views: 508

### Re: oxidizing agent and reducing agent

The oxidizing agent always oxidizes the other substance and gets reduced.
The reducing agent always reduces the other substance and gets oxidized.
Sun Mar 03, 2019 11:59 pm
Forum: Balancing Redox Reactions
Topic: Ecell
Replies: 4
Views: 168

### Re: Ecell

You always flip the anode reaction. You can usually determine the anode reaction by choosing the reaction which has the lowest reduction potential (more negative and less positive)
Sun Mar 03, 2019 11:58 pm
Forum: Balancing Redox Reactions
Topic: Order in Cell diagrams
Replies: 3
Views: 172

### Re: Order in Cell diagrams

it is always anode then cathode. According to Dr Lavelle, we have to also put states in the following manner- solids on the outside and aqueous in the middle.
Fri Feb 15, 2019 2:19 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Gibbs free energy idea
Replies: 2
Views: 95

### Gibbs free energy idea

What exactly is Gibbs free energy? (conceptually speaking)
Fri Feb 15, 2019 2:18 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: using gas constant R
Replies: 4
Views: 169

### Re: using gas constant R

5/2 R= C when the pressure is constant
3/2 R= C when the volume is constant
Fri Feb 15, 2019 2:17 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: ΔS=q/t
Replies: 8
Views: 376

### Re: ΔS=q/t

This can only be said when pressure is constant since q(at constant pressure)= delta H
Fri Feb 15, 2019 2:17 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Gibbs free energy
Replies: 5
Views: 181

### Re: Gibbs free energy

It tells us about spontaneity of a reaction, work and can be used to calculate the equilibrium constant.
Fri Feb 08, 2019 2:17 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Delta G units
Replies: 3
Views: 1868

### Re: Delta G units

G is always in terms of Joules. But the equation G=nFE is molarly dependent. Thus, the units are slightly different. But essentially, the conceptual idea is the same.
Fri Feb 08, 2019 2:15 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Predicting Spontaneity
Replies: 4
Views: 328

### Re: Predicting Spontaneity

Yes. We will have to know how to predict spontaneity based on the values. Sign of the enthalpy change Sign of the entropy change Spontaneity positive (+) positive (+) The reaction is spontaneous at high temperature positive (+) negative (-) The reaction is never spontaneous negative (-) negative (-)...
Fri Feb 08, 2019 2:11 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Spontaneity of Exo and Endo reactions
Replies: 4
Views: 234

### Re: Spontaneity of Exo and Endo reactions

Yes. But spontaneity is largely dependent on the 3 factors: enthalpy change, entropy change and temperature. Based on the values of each, the gibbs free energy is either positive or negative. Usually, however, exothermic reactions are more likely to be spontaneous because is H is less than 0, and si...
Sat Feb 02, 2019 10:46 pm
Forum: Phase Changes & Related Calculations
Topic: PΔV for solids and liquids
Replies: 5
Views: 184

### Re: PΔV for solids and liquids

This equation does apply to every system. However, when we consider solids and liquids, change in volume is essentially 0 (Dr. Lavelle described this in lecture). Hence P(V final- V initial) is 0 and does not affect systems with solid and liquids.
Sat Feb 02, 2019 10:43 pm
Forum: Phase Changes & Related Calculations
Topic: Steam vs Boiling Water
Replies: 10
Views: 1602

### Re: Steam vs Boiling Water

Essentially, boiling water at 100 degrees celcius, becomes steam at 100 degrees celcius when it overcomes the latent heat of vaporization. Hence, when skin is exposed to steam, it absorbs more heat from steam as it fist needs to lose the heat of vaporization and convert back to water at 100 degrees....
Sat Feb 02, 2019 10:40 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Bond Angles
Replies: 5
Views: 164

### Re: Bond Angles

Bond formation is exothermic while bond breaking is exothermic. Hence, when bonds are formed, since they release energy, we put a negative sign before the values.
Sun Jan 27, 2019 3:22 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Enthalpy Units
Replies: 7
Views: 303

### Re: Enthalpy Units

It depends on the situation. When considering a free reaction, we consider kJ since that is the exact amount of energy being released or absorbed. But, when we consider the situation where in we are considering a standard reaction (ex: Haber's process for 1 mol of ammonia), then we write kJ mol-1 to...
Wed Jan 23, 2019 1:11 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Polyprotic acids
Replies: 1
Views: 99

### Polyprotic acids

How do we calculate the pH of polyprotic acids with very small second or third Ka values? And how small should they be?
Wed Jan 23, 2019 1:10 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Strong acids and bases
Replies: 6
Views: 261

### Re: Strong acids and bases

Yes. Dr. Lavelle gave us a couple in 7a. We should remember those.
Wed Jan 23, 2019 1:09 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Acidity & Basicity Constants
Replies: 3
Views: 98

### Re: Acidity & Basicity Constants

No. The values will be given on the test.
Wed Jan 23, 2019 1:08 pm
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: autoprotolysis
Replies: 5
Views: 269

### Re: autoprotolysis

No, because 10^-4= Kw at 298K is an experimentally determined value.
Wed Jan 16, 2019 1:09 pm
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: Negative pH
Replies: 12
Views: 691

### Re: Negative pH

True. Professor Lavelle referred to these acids as super acids.
Wed Jan 16, 2019 1:08 pm
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: Le Chatelier's Principle
Replies: 7
Views: 150

### Re: Le Chatelier's Principle

Le Chatelier's principle states that a system will respond to change in a means to minimize the effect of the change. That means that the system tries to reverse the effect to return to what it was (essentially). For example, increases the concentration of products causes the Q value to increase. To...
Wed Jan 16, 2019 1:03 pm
Forum: Ideal Gases
Topic: K value
Replies: 8
Views: 299

### Re: K value

Because that would indicate that the products and reactants are in the same ratio. Essentially, in the real world, that would be rare.
Wed Jan 16, 2019 1:02 pm
Forum: Ideal Gases
Topic: Pressure and Temperature [ENDORSED]
Replies: 2
Views: 152

### Re: Pressure and Temperature[ENDORSED]

As temperature increases, the molecules of gas have more energy and begin striking the walls of a container with higher frequency. Essentially, the molecules exhibit a higher pressure on the container since they attempt to further themselves from each other.
Wed Jan 16, 2019 1:00 pm
Forum: Ideal Gases
Topic: R in PV=nRT
Replies: 34
Views: 683

### Re: R in PV=nRT

R is the ideal gas constant 8.314 J/(K mol)
Wed Jan 16, 2019 12:59 pm
Forum: Ideal Gases
Topic: bar or atm
Replies: 8
Views: 274

### Re: bar or atm

Bar and atm are the same. They can be interchanged.
Wed Jan 16, 2019 12:58 pm
Forum: Ideal Gases
Topic: Using Kc or Kp
Replies: 13
Views: 421

### Re: Using Kc or Kp

Kp is used when the substances are gaseous. But Kc can be used when the substances are gaseous or aqueous.
Wed Jan 09, 2019 1:00 pm
Forum: Ideal Gases
Topic: Q and K [ENDORSED]
Replies: 35
Views: 1677

### Re: Q and K[ENDORSED]

No difference. It's the same but K is when equilibrium is achieved. Q is at any point of the reaction.
Fri Nov 30, 2018 11:12 pm
Forum: Lewis Acids & Bases
Topic: solution of weak acids with higher pH
Replies: 4
Views: 390

### Re: solution of weak acids with higher pH

Weak acids do not completely dissociate and thus the proton yield is lower. Consequently, the pH is higher than for a strong acid which almost always dissociate completely and yields higher proton concentration.
Fri Nov 30, 2018 11:10 pm
Forum: Lewis Acids & Bases
Topic: Strong Acid
Replies: 8
Views: 571

### Re: Strong Acid

Strong acids almost always dissociate completely to yield hydronium ions.
Fri Nov 30, 2018 11:09 pm
Forum: Lewis Acids & Bases
Topic: Determine Lewis Acid
Replies: 13
Views: 819

### Re: Determine Lewis Acid

Lewis acids are electron pair acceptors.
Fri Nov 30, 2018 3:01 am
Forum: Shape, Structure, Coordination Number, Ligands
Topic: Polydentate
Replies: 3
Views: 189

### Re: Polydentate

It refers to one ligand that can form multiple coordinate bonds with the central metal ion. Ex: EDTA
Wed Nov 21, 2018 5:07 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Test 3
Replies: 10
Views: 430

### Re: Test 3

Test 3 covers: End of Bonding from 3.12 (6 Ed.) and from 2D (7 Ed.); and all of Molecular Shape and Structure
Wed Nov 21, 2018 5:06 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Ethylene bond angle
Replies: 2
Views: 147

### Re: Ethylene bond angle

Ethylene is formed from a sp2 hybridization of carbon and the arrangement on the orbitals are in the triangular planar. The angles are thus all 120 degrees.
Wed Nov 21, 2018 5:02 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Sigma/Pi bonds
Replies: 7
Views: 288

### Re: Sigma/Pi bonds

Sigma bonds are formed when orbitals overlap head on, along the bond axis. Pi bonds are formed when the ortibals overlap above and below the bond axis.
Wed Nov 14, 2018 10:57 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Bond Strengths
Replies: 5
Views: 227

### Re: Bond Strengths

Ionic bonds are stronger since they are the electrostatic force of attraction between positively and negatively charged ions. Hydrogen bonds are weaker since they are between dipoles (partially charged regions of a molecule).
Wed Nov 14, 2018 10:55 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Angular Shape
Replies: 4
Views: 196

### Re: Angular Shape

Angular shape can exist in two forms: 1) 3 regions of electron density (1 lone pair and 2 bonded pairs- Sulfur dioxide)- it has a bond angle of less than 120 (around 117) 2) 4 regions of electron density (2 lone pairs and 2 bonded pairs- dihydrogen monoxide)- it has a bond angle of less than 109.5 (...
Wed Nov 14, 2018 10:52 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Molecular Shape
Replies: 4
Views: 189

### Re: Molecular Shape

Molecular shape is dependent on the areas of electron density around the central atom. It can be divided into two categories: 1. Bonded pairs (single, double and triple) 2. Lone pairs The repulsion affects the shape further: lone-lone> lone-bonded> bonded-bonded These are the main features that affe...
Wed Nov 14, 2018 10:50 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Bond Angles
Replies: 3
Views: 84

### Re: Bond Angles

Bond angles are dependent on the number of lone pairs and bonding pairs around the central atom. Bonding pairs are less repelled by one another than from lone pairs. When we take Methane for example, there are 4 bonding pairs around the carbon and to space themselves out maximally, they form a tetra...
Sat Nov 10, 2018 8:18 pm
Forum: Bond Lengths & Energies
Topic: bond lengths and strengths
Replies: 9
Views: 341

### Re: bond lengths and strengths

Single bonds are the weakest since only one electron pair is being shared. Thus, the force of attraction between the nucleus and the shared pair is low. However, with double bonds, the area of electron density is much more dense/strong since more number of electrons are being shared and thus the for...
Sat Nov 10, 2018 8:16 pm
Forum: Dipole Moments
Topic: Melting points
Replies: 5
Views: 221

### Re: Melting points

Hydrogen bonds by definition only form when hydrogen is directly bonded to N, F and O. The electronegativity difference in sulphur and hydrogen is much lower than that of hydrogen and oxygen. Hydrogen sulphide, thus, is less polar and the dipole formed are weaker than in water. Thus, a hydrogen bond...
Sat Nov 10, 2018 8:13 pm
Forum: Bond Lengths & Energies
Topic: Bond Lengths
Replies: 6
Views: 205

### Re: Bond Lengths

They can only be determined experimentally. However, the relative bond lengths can be determined by the electronegativity differences between the elements participating in the bond (carbon-fluorine bonds have a shorter bond length than carbon-bromine bonds)
Sat Nov 10, 2018 8:11 pm
Forum: Electronegativity
Topic: Electronegativity relationship with Polarizability
Replies: 3
Views: 272

### Re: Electronegativity relationship with Polarizability

Electronegativity is the tendency of an atom of an element to attract electrons towards itself when bonded. Polarizability is the tendency to be polarized (electrons can be 'distorted' by other atoms) Generally substances with high electronegativity has a tendency to be less polarized (since the ele...
Sun Nov 04, 2018 7:31 pm
Forum: Dipole Moments
Topic: london forces
Replies: 7
Views: 439

### Re: london forces

Yes, every atom can exhibit london dispersion forces because it is due to the essentially random movement of electrons in an atom resulting in the formation of a temporary dipole.
Sun Nov 04, 2018 7:30 pm
Forum: Electronegativity
Topic: electronegativity vs electron affinity
Replies: 4
Views: 147

### Re: electronegativity vs electron affinity

Electron affinity is calculated for gaseous atoms (the energy change when an electron is added to the gaseous atom) and its unit is kJ/mol. This is experimentally derived. Electronegativity is the tendency of an atom to attract electrons towards in a bonded state and is for bonded atoms only. It is ...
Sun Nov 04, 2018 7:28 pm
Forum: Formal Charge and Oxidation Numbers
Topic: Why does PCl5 break the Octet Rule?
Replies: 8
Views: 832

### Re: Why does PCl5 break the Octet Rule?

This is because phosphorous can utilize the d orbitals and, thus, has an expanded octet.
Sun Nov 04, 2018 7:27 pm
Forum: Ionic & Covalent Bonds
Topic: Naming Ionic Compounds
Replies: 5
Views: 198

### Re: Naming Ionic Compounds

Naming works pretty easily. The name of the cation always comes before the name of the anion. Most cations would be the name of the metal (sodium, lithium, calcium, etc.) The name of the anion is variable: Halogens would end in "ide" (fluoride, chloride, bromide, etc) The same applies for ...
Tue Oct 30, 2018 12:16 pm
Forum: Significant Figures
Topic: Exam
Replies: 6
Views: 750

### Exam

How do we determine the number of significant figures to use in the exam?
Tue Oct 30, 2018 12:16 pm
Forum: Octet Exceptions
Topic: Structure of HClO3
Replies: 1
Views: 1415

### Structure of HClO3

How do we draw the lewis structure of HClO3?
Tue Oct 30, 2018 12:15 pm
Forum: Octet Exceptions
Topic: Octet exception chlorine and xenon
Replies: 1
Views: 96

### Octet exception chlorine and xenon

Why can xenon extend to more number of electrons through expanded octet than chlorine?
Tue Oct 30, 2018 12:14 pm
Forum: Sigma & Pi Bonds
Topic: Strength of bonds
Replies: 1
Views: 247

### Strength of bonds

Why are sigma bonds stronger than pi bonds?
Tue Oct 30, 2018 11:06 am
Forum: Ionic & Covalent Bonds
Topic: ionization energy
Replies: 7
Views: 337

### Re: ionization energy

Because the second ionization energy is the removal of the electron from a cation which has a stronger pull on the electron than the neutral atom.
Sun Oct 21, 2018 11:44 pm
Forum: Heisenberg Indeterminacy (Uncertainty) Equation
Topic: h with a line through it?
Replies: 8
Views: 329

### Re: h with a line through it?

h bar is h/2pi
Sun Oct 21, 2018 11:44 pm
Forum: Electron Configurations for Multi-Electron Atoms
Topic: Shielding
Replies: 5
Views: 230

### Re: Shielding

Shielding is when electrons in lower energy levels "shielding" or preventing the nuclear charge from reaching electrons in outer shells. Thus, when there are more number of orbitals, there is more shielding on the outer electrons.
Sun Oct 21, 2018 11:39 pm
Forum: Properties of Electrons
Topic: Electron Spin
Replies: 7
Views: 523

### Re: Electron Spin

There is not much to be known for this course. In each orbital, 2 electrons can exist and they take up opposite spins. They take the values 1/2 and -1/2 since there's 50% chance of up spin and 50% chance of down spin.
Sun Oct 21, 2018 11:37 pm
Forum: Wave Functions and s-, p-, d-, f- Orbitals
Topic: Wave functions
Replies: 4
Views: 204

### Wave functions

Do we have to know how to solve the wave functions for the orbitals?
Sun Oct 14, 2018 11:24 pm
Topic: What exactly is Black Body Radiation?
Replies: 1
Views: 295

### Re: What exactly is Black Body Radiation?

The black body radiation refers to the idea that a body which absorbs all frequencies of light of the electromagnetic spectrum. It also happens to not only be the ideal absorber of light but the ideal emitter (ex: a star) - emitting light of all frequencies.
Sun Oct 14, 2018 11:20 pm
Forum: Heisenberg Indeterminacy (Uncertainty) Equation
Topic: Uncertainty Principle
Replies: 5
Views: 210

### Re: Uncertainty Principle

The uncertainty principle works on the idea that both the momentum and the location of an electron cannot be known at once. When one is known, the other can be calculated but not known in that point of time. Thus, when we calculate anything regarding the uncertainty, its a range of possibilities (he...
Sun Oct 14, 2018 11:18 pm
Forum: Photoelectric Effect
Topic: SI Unit for Work Function
Replies: 4
Views: 808

### Re: SI Unit for Work Function

It would be preferred to stick to Joules since the entire equation focuses on generating the amount of energy needed to for the photoelectric effect.
Thu Oct 11, 2018 9:36 am
Forum: Properties of Light
Topic: Light acts as a wave or not?
Replies: 10
Views: 253

### Re: Light acts as a wave or not?

Light acts like both a wave and a particle. Depending on the situation, for questions in class, we tend to adopt the wave or particle model which fits a particular explanation.
Thu Oct 11, 2018 9:34 am
Forum: Properties of Light
Topic: Do I need to memorize the Light Spectrum? [ENDORSED]
Replies: 13
Views: 349

### Re: Do I need to memorize the Light Spectrum?[ENDORSED]

I think it would be advisable to have a general idea, like Dr. Lavelle said, about where a particular wavelength falls.
100-400 nm: UV light
400-700 nm: Visible light
700 nm- 1 mm: Infrared radiation
Thu Oct 11, 2018 9:31 am
Forum: Properties of Light
Topic: Photoelectric effect
Replies: 4
Views: 90

### Re: Photoelectric effect

Yes. The photon of the incident light must have sufficient energy such that it exceeds or equals the work function. Only then, will the electron have sufficient energy to be ionized and get released to be detected and produce the photoelectric effect.
Thu Oct 04, 2018 8:54 pm
Forum: Accuracy, Precision, Mole, Other Definitions
Topic: Isotopes [ENDORSED]
Replies: 12
Views: 803

### Re: Isotopes[ENDORSED]

Isotopes are atoms of the same elements but have different mass numbers or different number of protons!
Thu Oct 04, 2018 8:52 pm
Forum: Empirical & Molecular Formulas
Topic: How many atoms, how many moles are in epsom salts?
Replies: 2
Views: 851

### Re: How many atoms, how many moles are in epsom salts?

Epsom salts consist of magnesium sulfate heptahydrate. Write its formula. a) How many atoms of oxygen are in 5.15g of Epsom salts? b) How many formula units of the compound are present in 5.15g? c) How many moles of water molecules are in 5.15 g of Epsom salts? Answers: a) no. of moles of magnesium ...
Sun Sep 30, 2018 12:45 pm
Forum: Accuracy, Precision, Mole, Other Definitions
Topic: Accuracy vs Precision
Replies: 23
Views: 1348

### Re: Accuracy vs Precision

From an experimental chemistry standpoint, an example of accuracy vs. precision would be: If we conducted an experiment to test the volumes of carbon dioxide released when different concentrations of acid were added to metal carbonates, the study would have- 1. Low accuracy and Low precision if the ...