## Search found 45 matches

Sun Mar 17, 2019 11:21 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: delta h and q
Replies: 3
Views: 583

### Re: delta h and q

If there is no non-expansion work on the system and the pressure is still constant, then the change in enthalpy (delta h) will equal the heat consumed or released by the system (q).
Sun Mar 17, 2019 11:11 pm
Forum: Calculating Work of Expansion
Topic: Work in a System
Replies: 4
Views: 363

### Re: Work in a System

Work is equal to zero when the system does not undergo any change in volume. In this case, Delta U is simply equal to q since w (work) is equal to zero.
Sun Mar 17, 2019 11:06 pm
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: Le Chatlier Principle
Replies: 10
Views: 1438

### Re: Le Chatlier Principle

The catalyst does not interfere with the reaction at equilibrium. It merely speeds up the rate of the forward and reverse reactions.
Sun Mar 10, 2019 11:47 pm
Forum: General Rate Laws
Topic: Slow step of reactions
Replies: 3
Views: 154

### Re: Slow step of reactions

In kinetics, the rate of a reaction with several steps is determined by the slowest step, which is known as the rate-determining, or rate-limiting, step. Thus, the rate determining step determines the rate law
Sun Mar 10, 2019 11:39 pm
Forum: Zero Order Reactions
Topic: Zero order reactions
Replies: 4
Views: 173

### Re: Zero order reactions

Zero order reactions are more common because the rates of these reactions are independent of the concentration of reactants. Increasing order reactions are less common because they require they require molecules to collide at specific moments in time. P
Sun Mar 10, 2019 7:36 pm
Forum: Second Order Reactions
Topic: Second order reactions
Replies: 2
Views: 183

### Re: Second order reactions

2 NO2→ 2 NO + O2 is also an example of a 2nd order reaction.
Sun Mar 03, 2019 11:57 pm
Forum: Interesting Applications: Rechargeable Batteries (Cell Phones, Notebooks, Cars), Fuel Cells (Space Shuttle), Photovoltaic Cells (Solar Panels), Electrolysis, Rust
Topic: electrolytic cell
Replies: 4
Views: 523

### Re: electrolytic cell

In an electrolytic cell, electrons are forced via a voltage to be reduced at the cathode. In this case the the cathode is negative as a force is required to push the electrons.
Sun Mar 03, 2019 11:50 pm
Forum: Balancing Redox Reactions
Topic: Ecell
Replies: 4
Views: 219

### Re: Ecell

Compare the standard reduction potentials for the half reactions. Flip the reaction that will give you the greatest positive cell potential.
Sun Mar 03, 2019 11:43 pm
Forum: General Rate Laws
Topic: The value of K
Replies: 5
Views: 211

### Re: The value of K

K is dependent upon the temperature. So as long as the reactions occur at different temperatures, the k values will be different.
Sun Feb 24, 2019 11:56 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: inert conductor besides Pt
Replies: 3
Views: 179

### Re: inert conductor besides Pt

In addition to Platinum, Professor Lavelle mentioned Graphite (Carbon), Gold, and Mercury as possible inert conductors.
Sun Feb 24, 2019 11:53 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Salt Bridges
Replies: 3
Views: 191

### Re: Salt Bridges

They are made of an inert electrolyte because these electrolytes are chemically inactive. This ensures that the intended redox reaction goes on unaltered. Salt bridges are commonly made up of sodium chloride or potassium chloride.
Sun Feb 24, 2019 11:49 pm
Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
Topic: n in -nFE
Replies: 14
Views: 274

### Re: n in -nFE

n is equal to the number of electrons transferred. A negative value of n is impossible, thus n is either equal to 0 or a positive integer.
Sun Feb 17, 2019 11:56 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: Negative Temperature
Replies: 5
Views: 238

### Negative Temperature

Systems with a positive temperature will increase in entropy as one adds energy to the system, while systems with a negative temperature will decrease in entropy as one adds energy to the system. Do negative temperature systems violate the 2nd Law of Thermodynamics?
Sun Feb 17, 2019 11:50 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: Residual Entropy
Replies: 2
Views: 166

### Re: Residual Entropy

As I understand it, for the purposes of this course, S = k ln W should suffice. From the homework problems that I’ve seen, I haven’t used the second equation you mentioned.
Sun Feb 17, 2019 11:47 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Intensive vs extensive
Replies: 4
Views: 207

### Re: Intensive vs extensive

Gibbs free energy is an extensive property. Intensive properties are independent of the size of a thermodynamic system.
Sun Feb 10, 2019 11:57 pm
Forum: Phase Changes & Related Calculations
Topic: Combustion/form of water produced
Replies: 2
Views: 152

### Re: Combustion/form of water produced

Combustion produces carbon dioxide and water vapor. However, most of the time we write water in its liquid form in the reaction.
Sun Feb 10, 2019 11:54 pm
Forum: Phase Changes & Related Calculations
Topic: Heat vs Q
Replies: 5
Views: 248

### Re: Heat vs Q

Q is the amount of heat transferred to a system. Delta H on the other hand is a thermodynamic potential. It is essentially the measure of potential energy within a system.
Sun Feb 10, 2019 10:40 pm
Forum: Thermodynamic Definitions (isochoric/isometric, isothermal, isobaric)
Topic: Isochoric
Replies: 3
Views: 225

### Re: Isochoric

Yes, an isochoric system is one where the volume is held constant. Thus, work is equal to 0.
Sun Feb 03, 2019 11:57 pm
Forum: Thermodynamic Systems (Open, Closed, Isolated)
Topic: Examples of Open Closed Isolated
Replies: 5
Views: 287

### Re: Examples of Open Closed Isolated

Open System: Boiling water without a lid.
Closed System: A pressure cooker.
Isolated System: A thermoflask.
Sun Feb 03, 2019 11:46 pm
Forum: Thermodynamic Systems (Open, Closed, Isolated)
Topic: implications of open vs closed beakers
Replies: 2
Views: 152

### Re: implications of open vs closed beakers

An open beaker can remain at a constant pressure with its surroundings because it can exchange energy and matter to come to an equilibrium pressure state. A closed beaker implies that there is no exchange of matter between the beaker and its surroundings. However, there is an exchange of energy.
Sun Feb 03, 2019 11:40 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Enthalpies
Replies: 2
Views: 156

### Re: Enthalpies

ΔH° is the symbol for standard enthalpy change. ΔH°r represents the standard enthalpy change of reaction. ΔH°f is the standard enthalpy change of formation. Finally, ΔH°c symbolizes the standard enthalpy change of combustion.
Sun Jan 27, 2019 11:57 pm
Forum: Phase Changes & Related Calculations
Topic: Steam
Replies: 11
Views: 511

### Re: Steam

When boiling water comes into contact with your skin, it will transfer the difference in heat to your skin which results in a burn. However, when steam touches your skin it not only transfers the difference in heat similar to boiling water, but it also transfers the energy from the latent heat of va...
Sun Jan 27, 2019 11:49 pm
Forum: Non-Equilibrium Conditions & The Reaction Quotient
Topic: Units of Kp
Replies: 9
Views: 1605

### Re: Units of Kp

Partial pressure can be measured in any normal pressure units. Most commonly this will be in atm or pascals.
Sun Jan 27, 2019 11:45 pm
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: Injecting noble gasses
Replies: 7
Views: 363

### Re: Injecting noble gasses

It changes the pressure but does not change the volume of the solution. Thus, the molar concentration will not change and it will not affect the equilibrium.
Sun Jan 20, 2019 11:57 pm
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: The Conjugate Seesaw
Replies: 13
Views: 477

### Re: The Conjugate Seesaw

The conjugate seesaw describes the relationship between conjugate acids and bases. A strong acid has a weak conjugate base. Similarly, a strong base has a weak conjugate acid.
Sun Jan 20, 2019 11:52 pm
Forum: Ideal Gases
Topic: kc vs kp
Replies: 19
Views: 1048

### Re: kc vs kp

Kc and Kp are different. Kc is defined by molar concentrations, whereas Kp is defined by the partial pressure of the gasses inside a closed system. However, you can convert between the two with the following equation: Kp = Kc(RT)^Δn.
Sun Jan 20, 2019 11:21 pm
Forum: Ideal Gases
Topic: Calculating the Equilibrium Constant by Approximation
Replies: 2
Views: 176

### Re: Calculating the Equilibrium Constant by Approximation

Using the balanced equation you can make an ICE Table to describe how the partial pressures change when the reaction reaches equilibrium. Use the stoichiometric coefficients to know how much each product x increases by. Assuming you know the total increase in pressure,you can add up the individual p...
Sun Jan 13, 2019 11:55 pm
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: Types of Chemical Reactions
Replies: 3
Views: 121

### Types of Chemical Reactions

As we learned, if a reaction requires heat while forming a product, then heating will favor product formation. If a reaction gives off heat while forming a product then heating will favor reactant formation. However, is it possible for a reaction to be neither exothermic nor endothermic? If it is po...
Sun Jan 13, 2019 11:48 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Actual Yield of Products
Replies: 2
Views: 121

### Actual Yield of Products

Is it only possible to make a reaction go to completion if you keep adding reactants to the reaction? Is there any other way to make a reaction go to completion without external forces aiding it? Is the P/R ratio the reason why reactions don't go to absolute completion?
Sun Jan 13, 2019 11:44 pm
Forum: Non-Equilibrium Conditions & The Reaction Quotient
Topic: Reaction Quotient Value
Replies: 5
Views: 140

### Reaction Quotient Value

As we learned, if at some time during a reaction, the reaction quotient, Q, is less than K then the forward reaction is favored. If Q is greater than K then the reverse reaction is favored. However, what happens if Q is equal to K? Does that just mean that the same amount of reactants and products a...
Sun Dec 02, 2018 11:59 pm
Forum: Properties & Structures of Inorganic & Organic Acids
Topic: Bronsted vs Lewis
Replies: 2
Views: 109

### Bronsted vs Lewis

Which is the more accurate way to identify a molecule as an acid or a base? Does the Bronsted definition encompass a wider range or application or does the Lewis definition? Are both definitions needed to properly perform experiments with acids and bases?
Sun Dec 02, 2018 11:57 pm
Forum: Properties & Structures of Inorganic & Organic Acids
Topic: DNA
Replies: 1
Views: 81

### DNA

The full name for DNA is deoxyribonucleic acid. Is DNA actually acidic in nature? If so, wouldn't that comprise the functionality of the organelles in a cell? Are cells slightly basic overall to counteract this acidity?
Sun Dec 02, 2018 11:50 pm
Forum: Properties & Structures of Inorganic & Organic Acids
Topic: Acid dissociation
Replies: 5
Views: 248

### Acid dissociation

Is it possible for 100% of an acid to dissociate with absolutely no atoms left un-ionized? If a strong acid can achieve complete dissociation, where is the cutoff point where some atoms are left un-ionized? I have the same question in regards to bases.
Sun Nov 18, 2018 11:54 pm
Forum: Electronegativity
Topic: Question about what makes something ionic
Replies: 5
Views: 216

### Re: Question about what makes something ionic

Ionic bonds form when the electro negativity difference between the bonding elements is roughly 1.8 or higher. Less than a 1.8 difference results in the creation of either a non-polar or a polar covalent bond. Thus, HBr does not form an ionic bond as their electronegativity difference is not greater...
Sun Nov 18, 2018 11:47 pm
Forum: Resonance Structures
Topic: Bond Length
Replies: 4
Views: 522

### Re: Bond Length

We discuss resonance when discussing the distribution of electron densities in bonds. For example, in benzene, there is resonance, meaning that all of the C-C bonds are the same length and the electrons are delocalized meaning that they are all shared equally among the carbon atoms. Thus, not one C-...
Sun Nov 18, 2018 11:42 pm
Forum: Dipole Moments
Topic: London Force Times
Replies: 3
Views: 204

### Re: London Force Times

London dispersion forces form continuously and temporarily. The temporary dipoles are formed when the electrons of a neutral molecule by chance gather on one side of the molecule. This produces a ‘flickering’ type effect and lasts as long as the electrons gather and produce a dipole.
Mon Oct 29, 2018 12:01 am
Forum: Wave Functions and s-, p-, d-, f- Orbitals
Topic: Orbitals and Energy Levels
Replies: 1
Views: 187

### Orbitals and Energy Levels

Aren't orbitals the "decimal places" in energy levels? We learned that energy levels are quantized. However, in each energy level there are orbitals at different distances from the nucleus. Aren't these technically continuous states?
Sun Oct 28, 2018 11:59 pm
Forum: Properties of Light
Topic: Speed of Light
Replies: 1
Views: 100

### Speed of Light

We know that the speed of light in a vacuum is 3 x 10^8 m/s. However, why does light slow down when travelling through a medium? Is there an equation or formula available that can be used to calculate light's speed when travelling through specific materials?
Sun Oct 28, 2018 11:56 pm
Forum: Heisenberg Indeterminacy (Uncertainty) Equation
Topic: Heisenberg Uncertainty Experiment
Replies: 1
Views: 173

### Heisenberg Uncertainty Experiment

As we learned, we cannot know both the position and momentum of an electron. However, we also learned that in experimentation, the electron's trajectories are skewed off course due to influence from the photons hitting it. Doesn't this imply that photons have some degree of mass or force to them?
Sun Oct 21, 2018 11:56 pm
Forum: Photoelectric Effect
Topic: Visible Light Spectrum
Replies: 6
Views: 259

### Re: Visible Light Spectrum

Yes, the typical human eye will respond to wavelengths from about 390 to 700 nanometers with violent having the shortest wavelength and red having the longest in the visible spectrum. However, this is just the part of the electromagnetic spectrum that we can see. Light also refers to all the other w...
Fri Oct 19, 2018 7:10 pm
Forum: Properties of Light
Topic: Wave-Particle Duality [ENDORSED]
Replies: 1
Views: 109

### Wave-Particle Duality[ENDORSED]

What experiments display the particle-like qualities of light? Through the double-slit experiment we observe how light behaves as a wave by the interference patterns that light produces. I know that Einstein proposed that light is made up of small "packets" of energy, but what experiments ...
Fri Oct 19, 2018 6:56 pm
Forum: Photoelectric Effect
Topic: Oil Drop Experiment
Replies: 2
Views: 168

### Oil Drop Experiment

In Robert Millikan's oil drop experiment, a fine mist of oil droplets are sprayed into a container with an electrically charged gas. The oil droplet's location is monitored by using a microscope as it passes between two charged plates. However, in the experiment, the oil droplets are also charged. T...
Thu Oct 11, 2018 6:47 pm
Forum: Photoelectric Effect
Topic: Photoelectric Effect
Replies: 2
Views: 147

### Photoelectric Effect

As we learned, very specific frequencies are needed in order to get the surface of a metal to ionize and release electrons. Does this mean that everyday, when the sun is out, everyday objects are experiencing the photoelectric effect and releasing electrons? Furthermore, does the photoelectric effec...
Thu Oct 11, 2018 6:05 pm
Forum: Properties of Electrons
Topic: Mass of Electrons and Photons
Replies: 2
Views: 160

### Mass of Electrons and Photons

Do photons have mass? We know that light feels the effects of gravity similarly to matter. We also know that when an excited electron drops down an energy level, the electron emits energy in the form of light. If photons have mass, then wouldn't that mean that when an excited electron drops to lower...
Thu Oct 11, 2018 5:36 pm
Forum: Photoelectric Effect
Topic: Photoelectric Effect
Replies: 3
Views: 76

### Photoelectric Effect

We learned that energy levels are quantized and that n can only equal whole numbers. So when an excited electron begins to "relax" and starts descending energy levels back to the ground state, does the electron jump immediately from a level (let's say n=4) back to the ground state? Or does...

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