Search found 30 matches

by Luke Bricca 1H
Tue Mar 13, 2018 10:26 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: 15.85
Replies: 2
Views: 116

Re: 15.85

Awesome, thank you. I just looked back at my notes and it was in there, so I guess I must've missed it.
by Luke Bricca 1H
Tue Mar 13, 2018 7:49 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: 15.85
Replies: 2
Views: 116

15.85

In this question it asks us to draw a proposed structure for the activated complex of a chemical reaction. What is this and was it covered in class?
by Luke Bricca 1H
Mon Mar 12, 2018 4:38 pm
Forum: Arrhenius Equation, Activation Energies, Catalysts
Topic: 15.63
Replies: 3
Views: 186

15.63

In the solutions manual, the answer has a -0.59 added to the right side of the Arrhenius equation, and I was wondering where that came from?
by Luke Bricca 1H
Mon Mar 05, 2018 8:35 pm
Forum: Second Order Reactions
Topic: Differential vs Integrated
Replies: 4
Views: 356

Re: Differential vs Integrated

Usually the question tells you if a reaction is first, second, or zero order, but if you need to calculate it you can by comparing the rates of separate equations and how reactant concentrations change with them. You use the differential rate law when determining a rate of an equation (either a gene...
by Luke Bricca 1H
Mon Mar 05, 2018 8:32 pm
Forum: First Order Reactions
Topic: 15.23C
Replies: 6
Views: 329

Re: 15.23C

The coefficient being 2 doesn't necessarily mean that A is second order. Order is determined by how the rate reacts to changes in reactant concentration, and the coefficient isn't used in determining that. A coefficient could be helpful if [B] or [C] was given and you needed to convert a final conce...
by Luke Bricca 1H
Mon Mar 05, 2018 6:54 pm
Forum: General Rate Laws
Topic: Temperature Signifcance
Replies: 4
Views: 183

Re: Temperature Signifcance

Temperature is used to find k on the tables listed, but since in the problem you're already given k, the temperature given is not used in the problem.
by Luke Bricca 1H
Sat Mar 03, 2018 5:36 pm
Forum: Balancing Redox Reactions
Topic: Inert Conductors [ENDORSED]
Replies: 2
Views: 146

Re: Inert Conductors [ENDORSED]

A secondary inert conductor that shows up in the HW for ch 14 fairly often is graphite, or C(s), which would also be good to familiarize yourself with.
by Luke Bricca 1H
Sat Mar 03, 2018 5:32 pm
Forum: Second Order Reactions
Topic: Non-integer orders [ENDORSED]
Replies: 3
Views: 164

Re: Non-integer orders [ENDORSED]

My TA also said these types of problems most likely won't be on any test since they're not in the homework and not in the class notes.
by Luke Bricca 1H
Sat Mar 03, 2018 5:27 pm
Forum: General Rate Laws
Topic: 15.27
Replies: 2
Views: 123

Re: 15.27

You can assume that the initial concentration equals 1 and the final concentration you're looking for equals 0.15 when solving the half-life equation for time.
by Luke Bricca 1H
Wed Feb 21, 2018 8:50 pm
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: 14.31
Replies: 6
Views: 239

Re: 14.31

Furthermore, you could also solve the Nernst equation for K which would show its sign. This would be more work and is inefficient but guarantees a correct answer.
by Luke Bricca 1H
Wed Feb 21, 2018 8:38 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: When to include Pt in cell diagram
Replies: 2
Views: 135

When to include Pt in cell diagram

When is it appropriate to use Pt(s) or another metal like C(s) to border a cell diagram?
by Luke Bricca 1H
Thu Feb 15, 2018 8:09 am
Forum: Balancing Redox Reactions
Topic: Nature
Replies: 5
Views: 177

Re: Nature

Specifically, the concept of "reaction coupling" is found often in nature where processes such as the oxidation of ATP drive other processes that require reduction within the body. In these cases, the oxidation reaction provides the energy required for the reduction reaction.
by Luke Bricca 1H
Thu Feb 15, 2018 7:52 am
Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
Topic: Units for Gibbs Free Energy
Replies: 4
Views: 338

Re: Units for Gibbs Free Energy

Usually Gibbs Free Energy is given in kJ/mol, but you can multiply out the moles and just have kJ. By multiplying the Gibbs Free Energy by the number of moles, you're cancelling them in the denominator.
by Luke Bricca 1H
Thu Feb 15, 2018 7:47 am
Forum: Balancing Redox Reactions
Topic: Balancing Redox Reactions
Replies: 2
Views: 84

Re: Balancing Redox Reactions

In a redox reaction, a transfer of electrons is shown, which often requires H+ ions to show. In redox reactions containing acids and bases, H2O is a likely product.
by Luke Bricca 1H
Sat Feb 10, 2018 3:15 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: isothermal expansion
Replies: 2
Views: 122

Re: isothermal expansion

In an isothermal process, the internal temperature remains constant and the internal energy of an ideal gas is independent of its volume and pressure. Therefore, the internal energy of an ideal gas is wholly reliant on its temperature which is unchanging, so the delta U is unchanging as well, equall...
by Luke Bricca 1H
Sat Feb 10, 2018 3:10 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: Isothermal and Isovolumetric Calculations [ENDORSED]
Replies: 1
Views: 125

Re: Isothermal and Isovolumetric Calculations [ENDORSED]

Entropy is a state function and therefore changes in entropy can be calculated separately and then added together. For your question, a question would state that there was a change in temperature as well as a change in volume and ask for the final entropy of the system. To calculate this, you can us...
by Luke Bricca 1H
Sat Feb 10, 2018 3:01 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: Standard State
Replies: 2
Views: 98

Re: Standard State

Standard state refers to the standard temperature and pressure of a substance, and altering either affects both entropy and enthalpy if you look at the equations used to calculate both.
by Luke Bricca 1H
Sun Feb 04, 2018 9:36 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: Residual Entropy
Replies: 4
Views: 180

Re: Residual Entropy

To add to this, residual entropy is the difference in entropy between a non-equilibrium state system and a system near absolute zero (where the entropy should theoretically be zero.)
by Luke Bricca 1H
Sun Feb 04, 2018 9:34 am
Forum: Calculating Standard Reaction Entropies (e.g. , Using Standard Molar Entropies)
Topic: Absolute and statistical entropy
Replies: 2
Views: 147

Re: Absolute and statistical entropy

Furthermore, absolute entropy is measured on an absolute scale and relates to the third law of thermodynamics.
by Luke Bricca 1H
Sun Feb 04, 2018 9:29 am
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: sign of entropy
Replies: 11
Views: 282

Re: sign of entropy

Additionally, in connection with Gibbs free energy, if the sign of the delta G is negative, the reaction is spontaneous and favorable.
by Luke Bricca 1H
Sat Jan 27, 2018 4:10 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: Reversible isothermal expansion
Replies: 4
Views: 113

Re: Reversible isothermal expansion

It's probably best to understand the reasons behind the derivations we learned in class as the logic used when deriving each equation could be helpful on a conceptual question on a future test or midterm, but I agree with the post above in that I think it's super unlikely we'll need to derive any eq...
by Luke Bricca 1H
Sat Jan 27, 2018 4:06 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: Pressure Internal vs. External
Replies: 2
Views: 249

Re: Pressure Internal vs. External

To add onto this using gasses as an example, P external must be used because work is achieved through expansion or compression against a constant external pressure or force, not against the internal pressure of the system.
by Luke Bricca 1H
Sat Jan 27, 2018 3:51 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: Adiabatic system
Replies: 6
Views: 218

Re: Adiabatic system

An adiabatic system is also an insulated system where there is no heat flow, so q=0.
by Luke Bricca 1H
Sat Jan 20, 2018 9:34 am
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Enthalpy
Replies: 4
Views: 103

Re: Enthalpy

Bond enthalpies are the specific quantities of energy needed to break or form a bond between two atoms (ex: C--C or C--H). Bond enthalpies can be summed (since enthalpy is a state property) to find the total enthalpy of a reaction. Enthalpies of formation are the standard reaction enthalpies require...
by Luke Bricca 1H
Sat Jan 20, 2018 9:27 am
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: 8.37
Replies: 3
Views: 156

Re: 8.37

Both of your answers are right, and I'm sure on the test it'll specify which units we're supposed to use. Usually enthalpy is given in kJ/mol, but not always.
by Luke Bricca 1H
Sat Jan 20, 2018 9:19 am
Forum: Phase Changes & Related Calculations
Topic: 8.39
Replies: 2
Views: 123

Re: 8.39

In addition, if the problem instead wanted the final phase to be steam, another phase change would be required, adding a third step to your calculations. For any phase change problem, the work can be chunked into sections: energy required to raise temp to 0 deg C, energy for fusion phase change, ene...
by Luke Bricca 1H
Sat Jan 13, 2018 11:14 am
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: HW 8.45 (b)
Replies: 1
Views: 98

HW 8.45 (b)

For question 8.45 part b, why is the enthalpy value found divided by the 4 moles of CS2? I know that the standard enthalpy of formation is per one mole formed of the product, but in the reaction there are 4 moles of carbon used to form 4 moles of CS2, so shouldn't the ratio be 1:1 and therefore the ...
by Luke Bricca 1H
Sat Jan 13, 2018 10:05 am
Forum: Phase Changes & Related Calculations
Topic: Sublimation
Replies: 4
Views: 244

Re: Sublimation

Follow up question: what is the triple point on a phase change diagram? In its definition it says that it's when all three phases of a substance "coexist in thermodynamic equilibrium," but what does that mean?
by Luke Bricca 1H
Sat Jan 13, 2018 9:43 am
Forum: Phase Changes & Related Calculations
Topic: Heat Curve of Water
Replies: 3
Views: 179

Re: Heat Curve of Water

It takes far more energy to excite liquid water molecules and break the bonds between them to cause vaporization than to break the crystalline-structured bonds between water molecules found in ice so the heating curve is much longer for vaporization.

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