## Search found 31 matches

Sat Mar 16, 2019 10:43 pm
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: Partial Pressures
Replies: 3
Views: 271

### Re: Partial Pressures

Le Chatelier's principle is generally referring to equilibrium so you should treat it like an amount of a given substance, which is represented by the partial pressure.
Sat Mar 16, 2019 10:41 pm
Forum: Arrhenius Equation, Activation Energies, Catalysts
Topic: exponential vs ln equations
Replies: 1
Views: 270

### Re: exponential vs ln equations

I'm pretty sure they are just different algebraic methods of solving the problems, and will result in nearly the same answer. I've found that they are pretty generous about your answers as long as your work is correct and you are close to the answer key
Sat Mar 16, 2019 10:39 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: elementary steps
Replies: 3
Views: 369

### Re: elementary steps

It essentially tells you the relevance of that particular element to the overall reaction. Do note though that you can only do that if you are looking at the rate limiting step
Sat Mar 16, 2019 10:37 pm
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: change in cell potential
Replies: 1
Views: 253

### Re: change in cell potential

E-E(standard), as it is derived from the nernst equation which has E = E(standard) - (stuff).
Sat Mar 16, 2019 10:36 pm
Forum: Thermodynamic Definitions (isochoric/isometric, isothermal, isobaric)
Replies: 10
Views: 452

It just means that the heat is constant, there will always be some level of heat within a system. Here it just doesnt change.
Sat Mar 16, 2019 10:35 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: w=-PdeltaW
Replies: 5
Views: 352

### Re: w=-PdeltaW

The equation is w=-PdeltaV and you can use this equation when the pressure is constant and you need to find how much work is being done on the system by expansion
Sat Mar 16, 2019 10:34 pm
Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
Topic: n value
Replies: 3
Views: 284

### Re: n value

It is the number of electrons being transferred, however, if you are reacting several moles of the reaction then you need to account for that and multiply that by the number of electrons per mol of reaction
Sun Mar 03, 2019 10:54 pm
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: Ecell and pH
Replies: 3
Views: 166

### Re: Ecell and pH

I believe that is similar to what we did in class with E = E° + RTlnQ, where E° is the standard cell potential (Concentrations of 1M and standard conditions)
Sun Mar 03, 2019 10:52 pm
Forum: Kinetics vs. Thermodynamics Controlling a Reaction
Topic: how is kinetics different?
Replies: 17
Views: 689

### Re: how is kinetics different?

Kinetics is based on the rate of the reaction, and can give information on certain concentrations, whereas Thermodynamics centers on energy and heat and how those relate to the reaction.
Sun Mar 03, 2019 10:48 pm
Forum: General Rate Laws
Topic: General Rate Law Orders
Replies: 3
Views: 126

### Re: General Rate Law Orders

First order reactions have a negative slope when looking at the natural log of concentration versus time. Second order reactions have a positive slope for the inverse of the concentration versus time.
Sun Feb 24, 2019 8:17 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Current, Charge, Potential, Volt
Replies: 1
Views: 67

### Re: Current, Charge, Potential, Volt

Current is the flow of electric charge (moving electrons); charge itself is just like the protons and electrons is has; electric potential is energy available to do work through oxidation/reduction; voltage is the difference in the two electrical potentials.
Sun Feb 24, 2019 8:10 pm
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: Corrosion
Replies: 2
Views: 128

### Re: Corrosion

Nah, we assume that the cathode and anode are isolated from things like oxygen so no oxides or the like would form as a result of corrosion.
Sun Feb 24, 2019 8:05 pm
Forum: Balancing Redox Reactions
Topic: Hydrogen?
Replies: 3
Views: 93

### Re: Hydrogen?

Generally hydrogen is not reduced or oxidized, but has a consistent oxidation state of +1. If it is a complex molecule that involves hydrogen, like H2SO4, it is usually another element within the molecule that is being reduced or oxidized.
Sun Feb 17, 2019 11:08 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: Remembering Equations
Replies: 5
Views: 171

### Re: Remembering Equations

I find that when all else fails, you can often reprove an equation using information Dr. Lavelle has given in lecture. He does an excellent job of explaining the mathematical origins of many equations, even going over their derivations in class. By using what information you have already know, you c...
Sun Feb 17, 2019 11:05 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Graphs
Replies: 2
Views: 148

### Re: Graphs

I would imagine that graphs of change in free energy would be used to describe reactions, asking us to determine if the value of delta G is positive or negative, and maybe use that along with other info to determine the signs on enthalpy or entropy.
Sun Feb 17, 2019 11:03 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Sign of Free Energy
Replies: 2
Views: 99

### Re: Sign of Free Energy

That would depend on the values of those variables. If the value of temperature multiplied by entropy is greater than the value of enthalpy, then your sign for Gibbs Free Energy will be negative and vice versa for a positive value.
Sun Feb 10, 2019 10:38 pm
Forum: Calculating Work of Expansion
Topic: Pv=nrT
Replies: 2
Views: 109

### Re: Pv=nrT

Not quite, as the delta V makes those unequal. You might be thinking of the w = nRT ln(v1/v2) equation used with isothermal, reversible reactions.
Sun Feb 10, 2019 10:35 pm
Forum: Thermodynamic Definitions (isochoric/isometric, isothermal, isobaric)
Topic: Isothermal vs Reversible
Replies: 2
Views: 117

### Re: Isothermal vs Reversible

Isothermal systems are reversible systems. They have a constant temperature and are less efficient with work. Irreversible reactions do not have a constant temperature (it decreases then increases in expansion) and use the W = -PV equation. Just remember that reversible and isothermal are basically ...
Sun Feb 10, 2019 10:30 pm
Forum: Calculating Work of Expansion
Topic: Work Formula Involving Integral
Replies: 3
Views: 91

### Re: Work Formula Involving Integral

Yes, we do not actually integrate in any problems. It is used to derive the 2 formulas (constant pressure vs variable). Lavelle uses it to explain why we use natural logarithms in the w = nRT ln (v1/v2) equation
Mon Feb 04, 2019 12:36 am
Forum: Thermodynamic Systems (Open, Closed, Isolated)
Topic: Thermochemistry // Thermodynamics
Replies: 2
Views: 134

### Re: Thermochemistry // Thermodynamics

Thermochemistry is just applying the cnocepts of thermodynamics to chemical bonds. So basically taking the laws of thermodynamics and seeing how they relate to reactions and bond enthalpies.
Mon Feb 04, 2019 12:35 am
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: Internal Energy of Ideal Gas
Replies: 1
Views: 97

### Re: Internal Energy of Ideal Gas

The value of 3/2nRT is for monoatomic gases, whereas the 5/2nRT is for diatomics. It is due to the additional axes in diatomics. Can read more about it at http://physics.bu.edu/~duffy/py105/Kinetictheory.html if you want.
Mon Feb 04, 2019 12:31 am
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: How to: Hess's Law
Replies: 1
Views: 85

### Re: How to: Hess's Law

When working on a problem using Hess's Law, you first need to make sure you have a balanced equation for the reaction. Then, you want to find the reaction enthalpies of reactions involving the molecules in the original reaction (probably in some table in the book or given on a test). Then, look to s...
Sun Jan 27, 2019 12:57 am
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Replies: 2
Views: 94

### Re: Equations, Adams Disc 1A

It is my understanding that Lavelle provides a pretty thorough formula sheet on tests and midterms. It has the specific heat of water and the like, and I imagine that for specific problems he would provide the necessary info. Don't worry about memorizing those tables :)
Sun Jan 27, 2019 12:55 am
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: energy production
Replies: 4
Views: 225

### Re: energy production

The heart uses ATP which is created in the body through the breakdown of glucose. There's a cool video https://www.youtube.com/watch?v=v_qYy7LiTdc that explains the process and how cardiac metabolism works :)
Sun Jan 27, 2019 12:06 am
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: State Function?
Replies: 3
Views: 150

### Re: State Function?

Basically a state function is something that depends only on its current equilibrium state, not on how it got there. So for chemical reactions, this means that we can just add/subtract the overall enthalphies, and don't have to worry about the intermediate steps that a reaction may have gone through...
Sat Jan 19, 2019 9:53 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Molar Concentration
Replies: 3
Views: 89

### Re: Molar Concentration

No, the molar concentration given in a problem will be exactly what is stated for that single molecule. However, as the stochiometric coefficients are a ratio of moles of different molecules, you would have to take into account the coefficients when trying to find an unknown concentration of a diffe...
Sat Jan 19, 2019 9:51 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Equilibrium constant in different temperatures
Replies: 3
Views: 65

### Re: Equilibrium constant in different temperatures

Some reactions are endothermic (take in energy) and are thus more likely to form more products with an increased temperature, as the raised temp increases the energy of the reaction. Conversely, some reactions are exothermic (release energy) and will favor the reverse reaction, which is inherently e...
Sat Jan 19, 2019 9:47 pm
Forum: Identifying Acidic & Basic Salts
Topic: cations and anions that can be ignored
Replies: 2
Views: 266

### Re: cations and anions that can be ignored

Generally, I believe ions or molecules that have no possibility of reacting with water to form H3O+ or OH- or an acid or base should have no effect on the pH as pH directly correlates to the concentration of H3O+ and OH-
Sat Jan 12, 2019 7:02 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Heterogeneous and homogeneous equilibria [ENDORSED]
Replies: 8
Views: 286

### Re: Heterogeneous and homogeneous equilibria[ENDORSED]

Yes homogeneous equilibrium just means that all of the reactants and products are in the same phase, whereas in heterogeneous equilibrium, they are not. This is usually only relevant when calculating K, as if one of the products or reactants is a solid or liquid, its concentration would not be used.
Sat Jan 12, 2019 6:58 pm
Forum: Ideal Gases
Topic: When to use and NOT use ideal gases?
Replies: 1
Views: 104

### Re: When to use and NOT use ideal gases?

Generally the ideal gas law is universally used, but in cases where you are not assuming that gas molecules have no volume and have no intermolecular forces you can use the van der Waals equation, which you can learn more about at https://www.khanacademy.org/science/chemistry/gases-and-kinetic-molec...
Fri Jan 11, 2019 9:32 am
Forum: Ideal Gases
Topic: What does K represent?
Replies: 9
Views: 327

### Re: What does K represent?

K represents the ratio of products to reactants when the reaction is at equilibrium. Basically, if you were to let the reaction go (till equilibrium), how much of the products do you have compared to the reactants. Note that equilibrium does not mean the products and reactants are equal, but rather ...