## Search found 63 matches

Sun Mar 10, 2019 10:12 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Pre-equilibrium reaction mechanisms
Replies: 1
Views: 121

### Pre-equilibrium reaction mechanisms

What is meant by approximated concentrations for pre-equilibrium reaction mechanisms? How does this differ from the steady state? How are intermediates involved?
Sun Mar 10, 2019 10:09 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Rate and equilibrium constant
Replies: 1
Views: 88

### Rate and equilibrium constant

What is the relationship between rate constant and equilibrium constant?
Thu Mar 07, 2019 9:31 pm
Forum: Balancing Redox Reactions
Topic: Balancing Redox Reactions
Replies: 4
Views: 252

### Re: Balancing Redox Reactions

Balance the same as an acidic solution, just add an OH- to balance out every H+. If there are H+ and OH- on the same side, add them to form H20.
Thu Mar 07, 2019 9:20 pm
Forum: General Rate Laws
Topic: Average rate
Replies: 2
Views: 131

### Re: Average rate

The average rate is obtained by taking the slope of the line connecting any two points on the curve during that period. Ie amount of change/time taken. The instantaneous rate is obtained by taking the slope of the line tangent to the curve at a given time (t). The instantaneous rate is essentially t...
Thu Mar 07, 2019 8:50 pm
Forum: Zero Order Reactions
Topic: Zero Order Reaction- how to identify
Replies: 2
Views: 145

### Re: Zero Order Reaction- how to identify

A reaction is zero-order if concentration data is plotted versus time and the result is a straight line.
Sat Mar 02, 2019 7:19 pm
Forum: Second Order Reactions
Topic: Pseudo-first-order reaction
Replies: 4
Views: 186

### Re: Pseudo-first-order reaction

A reaction which is made first order by increasing or decreasing the concentration of a reactant is a pseudo first order reaction.
Sat Mar 02, 2019 7:15 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: H+ in cell diagrams
Replies: 5
Views: 279

### Re: H+ in cell diagrams

Include H+ in cell diagrams when it is used to balance out the H2O on the opposite side of reaction
Sat Mar 02, 2019 7:14 pm
Forum: General Rate Laws
Topic: Kinetics
Replies: 3
Views: 157

### Re: Kinetics

The average rate is obtained by taking the slope of the line connecting any two points on the curve during that period. Ie amount of change/time taken. The instantaneous rate is obtained by taking the slope of the line tangent to the curve at a given time (t). The instantaneous rate is essentially t...
Tue Feb 26, 2019 9:14 am
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Finding K using standard potential
Replies: 1
Views: 58

### Finding K using standard potential

Is there a way to use cell potential to calculate Ka without using Nernst? Can you go about this by finding Ecell, using that to find dG and then solving for K usuing -RTlnK?
Tue Feb 26, 2019 9:09 am
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Changes in cell potential
Replies: 1
Views: 98

### Changes in cell potential

How would you predict the effect of changes in concentration of reactants and products on the cell potential?
Mon Feb 25, 2019 5:05 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Anode and Cathode
Replies: 6
Views: 249

### Re: Anode and Cathode

In a galvanic (voltaic) cell are the cathode and anode the same as in an electrolytic cell?
Mon Feb 25, 2019 4:44 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Anode and Cathode
Replies: 6
Views: 249

### Re: Anode and Cathode

Cations (positively charged molecules) gain electrons from the cathode, which is where reduction takes place. Contrarily, anions (negatively charged molecules) lose electrons at the anode, which is where oxidation takes place. Remember OIL RIG. Electrons always flow from the anode to the cathode or ...
Mon Feb 25, 2019 2:04 pm
Forum: Balancing Redox Reactions
Topic: Adding H+, OH- and H20
Replies: 4
Views: 354

### Re: Adding H+, OH- and H20

H2O and H+ are used to balance out the numbers of oxygen and hydrogen atoms in the reaction, look at 14.1 in textbook for an example
Mon Feb 25, 2019 1:46 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Test topics
Replies: 1
Views: 76

### Test topics

Wondering how much the second test will cover, up to where in the textbook/homework problems and how far into electrochemistry
Mon Feb 18, 2019 8:46 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Delta G
Replies: 3
Views: 140

### Re: Delta G

Exergonic processes release energy. The change in Gibbs free energy (ΔG) is a negative value because energy is lost,
whereas an endergonic processes absorbs energy and their products are of greater free energy than the reactants.
Mon Feb 18, 2019 8:20 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: standard Gibbs Free Energy
Replies: 4
Views: 158

### Re: standard Gibbs Free Energy

Standard state being 1atm and at 25°C. The standard Gibbs free energy of formation of a compound is the change of Gibbs free energy that occurs when 1 mole of a substance in its standard state is formed from its constituent elements which are also in their standard states
Mon Feb 18, 2019 8:13 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Positive vs Negative E value
Replies: 5
Views: 2970

### Re: Positive vs Negative E value

The Ecell value is obtained from the two half reactions or the balanced chemical equation. Ecell is E(cathode) minus E(anode). For deltaG to be negative, which indicates that the reaction is a spontaneous one, E cell must be positive.
Mon Feb 11, 2019 11:48 am
Forum: Thermodynamic Definitions (isochoric/isometric, isothermal, isobaric)
Topic: delta U [ENDORSED]
Replies: 10
Views: 671

### Re: delta U[ENDORSED]

Recall that dU=q+w. For an isothermal expansion q=-w. Also, temperature does not change (hence isothermal), therefore q=0. If q=0 then w=0. Thus, dU=0+0=0.
Mon Feb 11, 2019 11:39 am
Forum: Calculating Work of Expansion
Topic: Reversible vs Irreversible
Replies: 10
Views: 408

### Re: Reversible vs Irreversible

W for reversible isothermal expansion of an ideal gas W=-nRTln(V2/V1)
Mon Feb 11, 2019 11:37 am
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: deltaS=nCvln(t2/t1) what is Cv?
Replies: 7
Views: 484

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

If a gas is compressed suddenly and irreversibly, treat it as a two step process where the dS from dT and dS from dV need to be accounted for. In this case, you would do dS=nCvln(T2/T1) if v was constant + deltaS=nRln(V2/V1).
Mon Feb 11, 2019 11:29 am
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: 4G. 2B 7th edition
Replies: 2
Views: 124

### Re: 4G. 2B 7th edition

T=0 ie absolute zero does not necessarily mean that there is zero entropy. It does, however, mean that entropy and enthalpy will be at their minimum values.The Third Law of Thermodynamics states that as the temperature of a system approaches absolute zero, its entropy approaches a constant- for pure...
Thu Jan 31, 2019 11:19 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Enthalpy
Replies: 6
Views: 174

### Re: Enthalpy

Bond breaking is an endothermic process ie a process that requires energy. For endothermic reactions, the products of the reaction have a greater enthalpy than the reactants, and heat is absorbed by the system from its surroundings. Therefore, the delta H b must be positive because the energy is bei...
Thu Jan 31, 2019 11:14 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: U:Internal Energy
Replies: 4
Views: 180

### Re: U:Internal Energy

They are essentially the same. It just depends which values you are given in the question, and which you can plug into the equation.
Thu Jan 31, 2019 11:10 pm
Forum: Thermodynamic Systems (Open, Closed, Isolated)
Topic: q=-q
Replies: 4
Views: 202

### Re: q=-q

no heat is transferred between two objects in thermal equilibrium
Thu Jan 31, 2019 11:04 pm
Forum: Phase Changes & Related Calculations
Topic: Phase change and temperature
Replies: 3
Views: 145

### Re: Phase change and temperature

Temperature of a substance does not change during a phase change. If heat is coming into a substance during a phase change, then this energy is used to break the bonds between the molecules of the substance.
Thu Jan 31, 2019 10:59 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Bonds and energy release
Replies: 2
Views: 155

### Re: Bonds and energy release

To break the bond, you have to fight against the bond, so energy is required in bon breaking. Potential energy is stored in molecules and this energy is released when bonds forms. Things tend to go to the lowest energy state possible
Sun Jan 20, 2019 7:40 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Concentrations Effect on K
Replies: 8
Views: 214

### Re: Concentrations Effect on K

Out of the various stresses, only temperature changes Kc
Sun Jan 20, 2019 7:37 pm
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: Temperature's effect on Kc
Replies: 2
Views: 104

### Temperature's effect on Kc

According to Le Chatelier's Principles, how and why does temperature impact Kc?
Sun Jan 20, 2019 7:31 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: ICE calculation sig figs
Replies: 5
Views: 162

### Re: ICE calculation sig figs

You should always refer to the question, and go by the number of sig figs used there.
Wed Jan 09, 2019 10:04 am
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Kc vs. Kp
Replies: 7
Views: 314

### Re: Kc vs. Kp

for Kc, you use the square brackets to denote concentration
Wed Jan 09, 2019 10:02 am
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: Catalysts
Replies: 3
Views: 153

### Catalysts

Do catalysts act as a stressor in a reaction? Do catalysts favor a particular direction ie the forward or the reverse?
Wed Jan 09, 2019 10:00 am
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: Applying Le Chatelier's principle
Replies: 2
Views: 101

### Applying Le Chatelier's principle

What would happen if one were to increase the temperature of a reaction, and why?
Wed Jan 09, 2019 9:58 am
Forum: Ideal Gases
Topic: Units
Replies: 5
Views: 159

### Units

What are the units for P=(nRT)/V? And what is the ideal gas constant?
Thu Jun 07, 2018 8:23 pm
Forum: Calculating the pH of Salt Solutions
Topic: How temperature affects pH
Replies: 3
Views: 821

### Re: How temperature affects pH

Technically temperature should have no real effect on pH, however, since water undergoes deconstruction of some sort from H2O -> OH- + H,
and there are 2x H. Since pH quantifies the quantity of H+ in a solution, the pH would be slighlty lower/more acidic in higher temperatures.
Thu Jun 07, 2018 8:17 pm
Forum: Amphoteric Compounds
Topic: Identifying an amphoteric compound
Replies: 3
Views: 1458

### Re: Identifying an amphoteric compound

If something has the ability to act as BOTH an acid and a base then it is amphoteric, so when looking at a reaction/equation, test if the compound has the ability to be a proton donor AND an hydroxide donor. One of the most common amphoteric substances out there is water as it behaves in this way.
Thu Jun 07, 2018 8:05 pm
Forum: Calculating pH or pOH for Strong & Weak Acids & Bases
Topic: Calculating the difference between two pH values
Replies: 2
Views: 273

### Calculating the difference between two pH values

How do you calculate the difference between two pH values of the same acid, just diluted. 12.9 is an example of a question that asks you to do this.

Thanks
Wed May 30, 2018 4:50 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Resonance structure effect on molecular shape
Replies: 3
Views: 232

### Resonance structure effect on molecular shape

ClO2+ has 4 different resonance structures so I am wondering if each structure would warrant a different molecular shape.

Thanks
Wed May 30, 2018 4:37 pm
Forum: Lewis Structures
Topic: Electrons in Valence Shell
Replies: 4
Views: 393

### Re: Electrons in Valence Shell

You can also use the principle quantum numbers of the element to determine how many electrons it can hold. Typically, the highest number of electrons that can fit in any given shell = 2n².
Thu May 24, 2018 3:34 pm
Forum: Resonance Structures
Topic: 3.47
Replies: 3
Views: 352

### Re: 3.47

Hydrocarbons often form structures like this, with carbon as the central atom and hydrogens branching off- for example benzene rings. So just predict such structures for molecules with multiple carbons and hydrogens.
Thu May 24, 2018 3:29 pm
Forum: Bond Lengths & Energies
Topic: Dissociation Energy
Replies: 3
Views: 329

### Re: Dissociation Energy

Dissociation energy is a measure of the strength of a bond. Therefore, it can be measured by breaking bonds, and recording how much energy was required to do so.
Thu May 24, 2018 3:25 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Regions of electron density
Replies: 7
Views: 365

### Re: Regions of electron density

electron density counts for both bonding and unshared electron pairs around the central atom
Tue May 15, 2018 1:56 pm
Forum: Lewis Structures
Topic: Lewis Structures
Replies: 4
Views: 314

### Re: Lewis Structures

The central atom is the atom that has the lowest electronegativity or the highest valence. You expand from there.
Mon May 14, 2018 11:17 pm
Forum: Lewis Structures
Topic: Identifying elements in Lewis structures [ENDORSED]
Replies: 2
Views: 272

### Identifying elements in Lewis structures[ENDORSED]

For question 3.37, why would the answer be phosphorus specifically and not, say nitrogen, or any of the other period 3 elements. Would they not all work due to having 5 valence electrons. In general, how does one figure out an unknown element from a lewis structure?
Mon May 14, 2018 10:32 pm
Forum: Formal Charge and Oxidation Numbers
Topic: Oxidation Number & Bonds
Replies: 6
Views: 338

### Re: Oxidation Number & Bonds

Seeing as the question asks for a maximum and a minimum oxidation number, can there be an intermediary oxidation number or must the answer be +7 and/or -1?
Wed May 09, 2018 12:50 am
Forum: Photoelectric Effect
Topic: Work function and kinetic energy
Replies: 1
Views: 195

### Work function and kinetic energy

If the work function of A is 6x10^-19 J per atom and the work function of B were let's say 7x10^-19, wouldn't you expect A to eject a slower electron than B if the same light source shines on both. Why is this NOT the case??
Tue May 08, 2018 10:50 pm
Forum: Properties of Electrons
Topic: Wave-like properties
Replies: 1
Views: 205

### Re: Wave-like properties

Yes, all matter has both wave-like and particle properties- including protons and neutrons. The concept is just typically used with quantum mechanics due to the small scale because large scale matter has a wavelength that is far too short to be detected.
Tue May 08, 2018 10:45 pm
Forum: Trends in The Periodic Table
Topic: Ionization exceptions [ENDORSED]
Replies: 8
Views: 1049

### Re: Ionization exceptions[ENDORSED]

Yes and we should know how to explain why the exceptions occur, for example because a full shell OR half full shell are most stable. Nitrogen's half full shell is what makes it more stable than oxygen, resulting in a higher ionization energy.
Tue May 08, 2018 9:46 pm
Forum: Heisenberg Indeterminacy (Uncertainty) Equation
Topic: Uncertainty calculation
Replies: 1
Views: 182

### Uncertainty calculation

If a proton is accelerated in a cyclotron to a very high speed that is known to within 3.0x10^2km*s^-1. So you know the speed, you can find out the momentum, but how do you find out the minimum uncertainty in the position.
Sun May 06, 2018 11:45 pm
Forum: Quantum Numbers and The H-Atom
Topic: Difference between the quantum number for particle and electron
Replies: 3
Views: 268

### Re: Difference between the quantum number for particle and electron

when we talk about the principle quantum number for a particle, we are referring to electrons
Sun May 06, 2018 11:16 pm
Forum: Wave Functions and s-, p-, d-, f- Orbitals
Topic: Energy difference between 4s and 3d
Replies: 3
Views: 422

### Re: Energy difference between 4s and 3d

The 4s shell is only lower in energy if there than 3d when there aren't electrons in 3d, which is why atoms lose the 4s electrons before they lose the 3d electrons. Those in the 3d shell would be the highest energy electrons due to the repulsive forces of electrons already in the 3d shell.
Sun May 06, 2018 10:59 pm
Forum: Trends in The Periodic Table
Topic: Electron Affinity
Replies: 3
Views: 262

### Re: Electron Affinity

electron affinity is the energy released when an atom acquires an electron (ie these would be negative values). So yes, a high electron affinity would mean the energy released when an electron is added would technically be very low.
Sun Apr 29, 2018 10:32 pm
Forum: Quantum Numbers and The H-Atom
Topic: Orientation of Lobes
Replies: 3
Views: 292

### Re: Orientation of Lobes

You would describe the magnetic quantum number (m) which labels different orbitals of a subshell including nodal planes ie symmetric density distribution or not
Sun Apr 29, 2018 10:28 pm
Forum: Wave Functions and s-, p-, d-, f- Orbitals
Topic: orbitals/lobes
Replies: 3
Views: 220

### Re: orbitals/lobes

I believe we should be able to identify and draw different orbital according to information given about the planes and quantum values (n,l and m)
Sun Apr 29, 2018 10:26 pm
Forum: Wave Functions and s-, p-, d-, f- Orbitals
Topic: PROBLEM 2.1
Replies: 4
Views: 243

### Re: PROBLEM 2.1

The orbital that hydrogen's electron is in is the 1s orbital, the 1 meaning that the electron is in the energy level closest (1st energy level) to the nucleus. If an electron is in a 2 orbital (2nd energy level) it just means that there is a greater chance that the electron will be further away from...
Thu Apr 26, 2018 5:22 pm
Forum: Photoelectric Effect
Topic: Question 1.33, part b
Replies: 1
Views: 120

### Question 1.33, part b

The velocity of an electron that is emitted from a metallic surface by a photon is 3.6x10^3 km/s. No electrons are emitted from the surface of the metal until the frequency of the radiation reaches 2.50x10^16Hz. How much energy is required to remove the electron from the metal? I know you eventually...
Thu Apr 26, 2018 4:03 pm
Forum: DeBroglie Equation
Topic: Calculating wavelength of an electron
Replies: 4
Views: 279

### Calculating wavelength of an electron

When you know the velocity of an electron, how do you then calculate the wavelength?
Thanks
Wed Apr 25, 2018 7:32 pm
Forum: Photoelectric Effect
Topic: Calculating kinetic energy of an emitted electron [ENDORSED]
Replies: 3
Views: 424

### Calculating kinetic energy of an emitted electron[ENDORSED]

I'm wondering how you go about calculating the kinetic energy of an ejected electron when you are only given the speed at which it is ejected. What would you would put for mass of electron in the KE equation.

Thanks
Thu Apr 12, 2018 2:44 pm
Forum: SI Units, Unit Conversions
Topic: Correct Units?? [ENDORSED]
Replies: 8
Views: 508

### Re: Correct Units??[ENDORSED]

you would normally use grams unless the question uses or states otherwise or if the calculated number is very large, making it more convenient or logical to use kg. Typically, you'll be able to tell what is appropriate.
Thu Apr 12, 2018 2:11 pm
Forum: Photoelectric Effect
Topic: Original Photoelectric Experiment
Replies: 3
Views: 206

### Re: Original Photoelectric Experiment

I believe the aim was to observe how the transfer of energy from light to an electron in the metal results in the emission of said electron from the metal
Tue Apr 10, 2018 4:46 pm
Forum: Balancing Chemical Reactions
Topic: Fastest way to balance chemical equation
Replies: 9
Views: 3781

### Re: Fastest way to balance chemical equation

start by balancing the atoms with the highest number of atoms in the reaction. Typically you leave balancing oxygen and/or hydrogen until last
Tue Apr 10, 2018 4:41 pm
Forum: Accuracy, Precision, Mole, Other Definitions
Topic: rounding [ENDORSED]
Replies: 10
Views: 553

### Re: rounding[ENDORSED]

you should always use the number of sig figs of the number with the lowest number of sig figs in the question and subsequent calculations
Tue Apr 10, 2018 4:37 pm
Forum: Molarity, Solutions, Dilutions
Topic: Mixtures and Solutions
Replies: 2
Views: 192

### Re: Mixtures and Solutions

Hi so n is moles, m is mass and M is molar mass. Thus, moles is equal to mass divided by molar mass. You would get the molar mass from the periodic table. Also, c is concentration, n (again) is moles and V is volume.Thus, concentration is equal to moles divided by volume of solution. In each equatio...
Tue Apr 10, 2018 4:30 pm
Forum: Molarity, Solutions, Dilutions
Topic: G.11 / Volumes for Solutions
Replies: 2
Views: 200

### Re: G.11 / Volumes for Solutions

Volume is equal to moles/concentration, so you would do 4.5x10^-3 mols divided by 0.278M.
Hope this helps