Search found 35 matches

by Ridhi Ravichandran 1E
Sun Mar 18, 2018 6:21 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Catalyst and Intermediate
Replies: 7
Views: 377

Re: Catalyst and Intermediate

A catalyst and intermediate are both species that are consumed in the reaction, but a catalyst is present in the beginning of the reaction and an intermediate is formed at the end of a step.
by Ridhi Ravichandran 1E
Sun Mar 18, 2018 6:19 pm
Forum: Calculating Standard Reaction Entropies (e.g. , Using Standard Molar Entropies)
Topic: complex molecules
Replies: 8
Views: 382

Re: complex molecules

Complex molecules have higher entropies due to the extra bonds and electrons, which increase the overall potential energy and disorder of the system.
by Ridhi Ravichandran 1E
Sun Mar 18, 2018 6:17 pm
Forum: Calculating Work of Expansion
Topic: Final Question W18: Reversible vs. Irreversible External Pressure
Replies: 4
Views: 232

Re: Final Question W18: Reversible vs. Irreversible External Pressure

Additionally, a reversible expansion does more work than a irreversible expansion because it is the sum of many small expansion steps.
by Ridhi Ravichandran 1E
Wed Mar 14, 2018 6:52 pm
Forum: Biological Examples
Topic: SN2 Reactions
Replies: 1
Views: 426

SN2 Reactions

Will we have to know how to work with substitution reactions on the final? I know we covered it in class, but there were no homework problems based on it and I'm pretty sure they weren't covered in chapter 15.

If so, I'm confused about what exactly they are?

Thanks!
by Ridhi Ravichandran 1E
Mon Mar 12, 2018 1:41 am
Forum: Balancing Redox Reactions
Topic: Ranking elements
Replies: 8
Views: 347

Re: Ranking elements

You would look at standard reduction potentials. the key here is the word reduction, however. you MUST look at reduction potentials, not oxidation potentials, because the signs matter. if you're looking at a reduction potential, the more positive, the more oxidizing power, and the more negative, the...
by Ridhi Ravichandran 1E
Mon Mar 12, 2018 1:38 am
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Rate constant
Replies: 6
Views: 179

Re: Rate constant

A rate constant is simply a proportionality constant included in the rate law. A reaction rate is the actual rate of a reaction, so it tells us how long it takes for reactant to be used up and product to be formed. While a reaction rate always includes units of time, the units of a rate constant var...
by Ridhi Ravichandran 1E
Tue Mar 06, 2018 5:59 pm
Forum: Kinetics vs. Thermodynamics Controlling a Reaction
Topic: Diamond/Graphite
Replies: 4
Views: 580

Re: Diamond/Graphite

Because diamond is thermodynamically unstable with respect to graphite, this means that delta G is negative for this process and diamond will spontaneously turn into graphite. However, because this process is also kinetically stable, this means that the process will occur very slowly. The book is ju...
by Ridhi Ravichandran 1E
Sat Mar 03, 2018 5:39 pm
Forum: Zero Order Reactions
Topic: Dependence on concentration
Replies: 2
Views: 113

Re: Dependence on concentration

The rate law for a zero-order reaction is: rate=k[A]^0. However, anything to the power of 0 is just one, so the rate is simply equal to k. k is a constant that doesn't change throughout the reaction, and concentration is not even part of the equation, so zero-order reactions do not depend on the con...
by Ridhi Ravichandran 1E
Sat Mar 03, 2018 5:36 pm
Forum: General Rate Laws
Topic: Differential and Integrated Rate Laws
Replies: 3
Views: 139

Re: Differential and Integrated Rate Laws

You use integrated rate laws when you need to find the time or final/initial concentrations. Most problems involve using the integrated rate law; we deal with the differential rate law when we need to find reaction orders, etc.
by Ridhi Ravichandran 1E
Sat Mar 03, 2018 5:33 pm
Forum: General Rate Laws
Topic: Integrated Rate Law Units
Replies: 4
Views: 178

Re: Integrated Rate Law Units

Yes, you can use any units as long as they match. In fact, for one of the HW problems, the solutions manual encourages you to not change g to mol/l because it is extra work and unnecessary, especially because the final answer asks for g.
by Ridhi Ravichandran 1E
Sun Feb 25, 2018 8:24 pm
Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
Topic: swapping signs of E values
Replies: 8
Views: 425

Re: swapping signs of E values

You usually swap the sign of the equation that needs to be oxidized. Since the back of the book only lists reduction potentials, and a redox reaction has both reduction and oxidation half reactions, we need to flip one of the equations to turn it into an oxidation. Turning a half reaction from a red...
by Ridhi Ravichandran 1E
Sun Feb 25, 2018 8:19 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Galvanic cell set up
Replies: 8
Views: 223

Re: Galvanic cell set up

Yes, in order to make the overall cell potential positive (which is what we want for a galvanic cell), the anode needs to be on the left and cathode needs to be on the right.
by Ridhi Ravichandran 1E
Sun Feb 25, 2018 8:17 pm
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: NERNST
Replies: 4
Views: 168

Re: NERNST

It cannot be used for ln as well. For ln, there is a different constant (it is listed in the book).
by Ridhi Ravichandran 1E
Mon Feb 19, 2018 1:17 am
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Electrolytes in Galvanic Cells
Replies: 1
Views: 50

Electrolytes in Galvanic Cells

Why do we need the electrolytes in a galvanic cell? For example, there will be a copper electrode immersed in a CuSO4 solution, and a zinc electrode immersed in a ZnSO4 solution. Why is it necessary to have these solutions?
by Ridhi Ravichandran 1E
Sun Feb 18, 2018 9:05 pm
Forum: Thermodynamic Definitions (isochoric/isometric, isothermal, isobaric)
Topic: Isothermal, irreversible?
Replies: 4
Views: 318

Re: Isothermal, irreversible?

delta U equals 0 for isothermal reactions that are both reversible and irreversible. Additionally, it does not need to be an isothermal expansion, it can be a compression as well.
by Ridhi Ravichandran 1E
Sun Feb 18, 2018 9:00 pm
Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
Topic: Delta G= Wmax
Replies: 8
Views: 413

Re: Delta G= Wmax

Wmax actually represents the maximum non-expansion work a reaction can do. Basically, an exothermic reaction will release a certain amount of energy, and this energy can be harnessed to do other kinds of work, such as power a non-spontaneous reaction.
by Ridhi Ravichandran 1E
Sun Feb 18, 2018 8:57 pm
Forum: Thermodynamic Definitions (isochoric/isometric, isothermal, isobaric)
Topic: Work when pressure is constant
Replies: 6
Views: 382

Re: Work when pressure is constant

Yes, it can be -nRT. This formula is especially helpful if you don't know the external pressure and only know the net change in the moles of gas.
by Ridhi Ravichandran 1E
Sat Feb 10, 2018 9:13 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: delta U
Replies: 2
Views: 103

Re: delta U

Delta U is zero for an isothermal (temperature constant) expansion/compression. It can either be a reversible, irreversible, or free expansion. The key idea here is that it is isothermal, so the internal energy doesn't change.
by Ridhi Ravichandran 1E
Sat Feb 10, 2018 9:11 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: 9.13 Gibbs free energy of formation
Replies: 1
Views: 81

Re: 9.13 Gibbs free energy of formation

The reaction they are referring to has the compound as the product. For example, the reaction H2 + (1/2)O2 ----> H2O would have a certain Delta G, which would also equal the delta G of formation for H2O. If delta G were negative, the reaction would move in the forward direction and H2O would spontan...
by Ridhi Ravichandran 1E
Sat Feb 10, 2018 9:04 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Bond Enthalpies
Replies: 2
Views: 132

Re: Bond Enthalpies

Yes, bond enthalpies are only valid for compounds in the gas state. If you want to use this method, you must convert all substances to the gas phase first, then solve for the delta H of the reaction.
by Ridhi Ravichandran 1E
Sun Feb 04, 2018 6:22 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: Example 9.5 (page 325)
Replies: 2
Views: 98

Example 9.5 (page 325)

For this problem, they assumed the volume was constant during the temperature increase and thus used the Cv value to find the change in entropy. However, why did they assume volume was constant? Why couldn't you have assumed pressure was constant and used the Cp value?
by Ridhi Ravichandran 1E
Sun Feb 04, 2018 4:56 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: negative entropy [ENDORSED]
Replies: 10
Views: 307

Re: negative entropy [ENDORSED]

There is no such thing as negative entropy, but a negative change in entropy exists. For example, a reaction that condenses from a gas to liquid would have a negative delta S because the liquid would occupy less possible states than the gas due to the decrease in temperature and volume.
by Ridhi Ravichandran 1E
Sun Feb 04, 2018 4:53 pm
Forum: Calculating Standard Reaction Entropies (e.g. , Using Standard Molar Entropies)
Topic: standard states
Replies: 3
Views: 130

Re: standard states

1 bar is usually standard pressure, but 1 atm is sufficient because it is close enough to one bar. 25 degrees celsius is not technically standard temperature, but it is the temperature at which most reactions take place. Another requirement for "standard state" is that the elements must be...
by Ridhi Ravichandran 1E
Sun Feb 04, 2018 4:45 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: q=-w [ENDORSED]
Replies: 5
Views: 206

Re: q=-w [ENDORSED]

The reason q=-w comes down to the fact that in isothermal expansions, delta U is equal to zero. (The temperature is constant, so the molecules have the same kinetic energy and same potential energy. Thus, there is no change in internal energy). We know that delta U equals q+w, so if delta U is zero,...
by Ridhi Ravichandran 1E
Sun Jan 28, 2018 10:23 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Bond Enthalpies
Replies: 7
Views: 257

Re: Bond Enthalpies

If it takes more energy to break the bond, that means the bond is very stronger, and the attraction between the nuclei of the atoms is also very strong. According to Coulomb's law, stronger attractions mean a lower energy arrangement, which means more stability. Thus strong, high energy bonds have a...
by Ridhi Ravichandran 1E
Sun Jan 28, 2018 10:20 pm
Forum: Thermodynamic Definitions (isochoric/isometric, isothermal, isobaric)
Topic: work definition
Replies: 5
Views: 195

Re: work definition

Work is defined as motion against an opposing force. In Chapter 8, we focus on expansion work, such as a gas expanding against a piston. The piston provides an opposing force. If it weren't there (if the gas was expanding into a vacuum, for example), no work would be done because there would be no o...
by Ridhi Ravichandran 1E
Sun Jan 28, 2018 10:12 pm
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: Reversible and Irreversible Pathways
Replies: 4
Views: 163

Re: Reversible and Irreversible Pathways

Basically, a reversible pathway is one that is in equilibrium. The external and internal pressures are equal, so work is only done if the external pressure decreases slightly, causing the gas to expand to decrease the internal pressure, allowing the system to come back to equilibrium. That is why fo...
by Ridhi Ravichandran 1E
Mon Jan 22, 2018 1:49 am
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: 8.67
Replies: 1
Views: 82

8.67

For part b on 8.67, why do you have to include the heat released when methanol changes from a gas to a liquid? Isn't it already in the liquid phase? According to the solutions manual, the equation is C(gr) + 2H2 + (1/2)O2 ----> CH3OH(l). Doesn't this indicate that methanol is already a liquid? Also,...
by Ridhi Ravichandran 1E
Sat Jan 20, 2018 7:20 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Kekule structures, Resonance, and stability
Replies: 1
Views: 58

Re: Kekule structures, Resonance, and stability

Yes, the lower the energy a molecule has, the more stable it is. That is why you see the dip in the potential energy diagram for atoms in a bond- atoms in a bond have lower energy, which account for the dip.
by Ridhi Ravichandran 1E
Sat Jan 20, 2018 7:18 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Heat Capacity for atoms and molecules
Replies: 1
Views: 86

Re: Heat Capacity for atoms and molecules

I believe we do not have to know these equations. But it is basically because the different types of molecules possess different types of energy (such as rotational or vibrational), which is why the equations for each type of molecule are different.
by Ridhi Ravichandran 1E
Sat Jan 20, 2018 7:17 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Heat not being a state property..
Replies: 1
Views: 59

Re: Heat not being a state property..

Heat is not a state property because it is defined as the energy transferred to/from an object due to a temperature change. This can be accomplished in different ways (such as mixing vigorously or actually heating the object through an external source), so the path matters. Thus, it is not a state f...
by Ridhi Ravichandran 1E
Sun Jan 14, 2018 9:36 pm
Forum: Thermodynamic Definitions (isochoric/isometric, isothermal, isobaric)
Topic: Reversible process
Replies: 2
Views: 178

Reversible process

Why does a reversible process do the most work?
by Ridhi Ravichandran 1E
Sat Jan 13, 2018 6:26 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Bonds Formed Exothermic
Replies: 2
Views: 103

Re: Bonds Formed Exothermic

also, we know that bonds (versus independent atoms) are more stable arrangements. Since stability corresponds with lower energy, it makes sense that forming bonds releases energy and thus lowers the energy of the system.
by Ridhi Ravichandran 1E
Sat Jan 13, 2018 6:20 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: q=mCdeltaT
Replies: 2
Views: 632

Re: q=mCdeltaT

To add, while temperature should usually be in kelvin, you can still use celsius with this formula because it is only the change in temperature, not the actual temperature. So, not having to convert to kelvin will save you time.
by Ridhi Ravichandran 1E
Sat Jan 13, 2018 6:09 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Hess' Law
Replies: 3
Views: 136

Re: Hess' Law

Additionally, you can manipulate equations and add them together to get the final desired equation. When you reverse an equation, the delta H changes signs, and when you multiply an equation by a constant, the delta H is multiplied by that constant. Then, you can add all the new enthalpy values toge...

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