Search found 29 matches

by Lindsay Kester 2L
Tue Mar 13, 2018 10:30 pm
Forum: Kinetics vs. Thermodynamics Controlling a Reaction
Topic: Increasing Tempt
Replies: 2
Views: 213

Re: Increasing Tempt

Increasing temperature increases the energy of the atoms or molecules that are participating in a reaction, so it makes them collide more frequently and with higher energy. Because they collide more often and with higher energy, they overcome the activation energy barrier more often, so the reaction...
by Lindsay Kester 2L
Tue Mar 13, 2018 10:28 pm
Forum: Kinetics vs. Thermodynamics Controlling a Reaction
Topic: mechanisms
Replies: 3
Views: 241

Re: mechanisms

Mechanisms need to support the orders shown in the rate law- so if the rate law says that something is second order, then there should be two molecules used up in the slow step of its elementary reaction. However, mechanisms can only provide possible answers to the rate law, not prove one, and there...
by Lindsay Kester 2L
Tue Mar 13, 2018 10:26 pm
Forum: Arrhenius Equation, Activation Energies, Catalysts
Topic: Catalysts
Replies: 2
Views: 131

Re: Catalysts

Catalysts don't show up in the rate law because they are usually 0th order. Because they are not used up in a reaction, their concentration doesn't change the rate of a reaction and so it doesn't show up in the rate law.
by Lindsay Kester 2L
Mon Mar 05, 2018 2:43 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Molecularity
Replies: 3
Views: 107

Re: Molecularity

Molecularity affects the order of the reaction as well- bimolecular reactions are second order, unimolecular is first order, etc.
by Lindsay Kester 2L
Mon Mar 05, 2018 2:41 pm
Forum: General Rate Laws
Topic: 3rd order, 4th order, etc.
Replies: 5
Views: 305

Re: 3rd order, 4th order, etc.

You can derive all of the half life reactions, but since third and fourth order reactions aren't likely, we don't need to know them really.
by Lindsay Kester 2L
Mon Mar 05, 2018 2:40 pm
Forum: General Rate Laws
Topic: Order?
Replies: 3
Views: 140

Re: Order?

You could also look at the slow step of a reaction and figure out it's molecularity. If it's A->B, then first order, A+A->B, second order, and so on.
by Lindsay Kester 2L
Mon Mar 05, 2018 2:39 pm
Forum: Kinetics vs. Thermodynamics Controlling a Reaction
Topic: Catalyst in a Equilibria
Replies: 2
Views: 114

Re: Catalyst in a Equilibria

Yes, the catalyst increases the rate of both the forward and the reverse reaction.
by Lindsay Kester 2L
Sun Mar 04, 2018 8:45 pm
Forum: Arrhenius Equation, Activation Energies, Catalysts
Topic: Homogenous vs. Heterogenous Catalyst and Rate Law
Replies: 2
Views: 133

Re: Homogenous vs. Heterogenous Catalyst and Rate Law

I think that since heterogeneous catalysts are usually used in the solid phase, their appearance in the rate law would depend on the phases of the other reactants and products.
by Lindsay Kester 2L
Sun Mar 04, 2018 8:43 pm
Forum: First Order Reactions
Topic: K constant
Replies: 3
Views: 161

Re: K constant

When we graph K, we make it negative, because the reaction is using up reactants (at least initially). K itself is usually positive.
by Lindsay Kester 2L
Sun Mar 04, 2018 8:41 pm
Forum: General Rate Laws
Topic: catalytic reaction
Replies: 5
Views: 178

Re: catalytic reaction

Enzymes are examples of catalytic reactions, where one molecule that isn't used up helps to facilitate the reaction of another set of molecules.
by Lindsay Kester 2L
Fri Feb 23, 2018 6:46 pm
Forum: General Rate Laws
Topic: Rate Constant K [ENDORSED]
Replies: 4
Views: 185

Re: Rate Constant K [ENDORSED]

Essentially, at different temperatures and activation energies, K changes. You calculate it the same way, using concentrations, but you're going to get a different value at different states. We don't have a way to calculate new K's based on old ones yet, but we might learn one.
by Lindsay Kester 2L
Tue Feb 13, 2018 4:22 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: delta G vs. standard Gibbs free energy
Replies: 1
Views: 89

Re: delta G vs. standard Gibbs free energy

They're almost the same thing! ∆G° is just defined in terms of the standard molar Gibbs energies of the reactants and products; it's the difference in energy between the pure products and the pure reactants that won't change as the reaction proceeds.
by Lindsay Kester 2L
Tue Feb 13, 2018 4:17 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: Reversible vs Irreverisble
Replies: 1
Views: 108

Re: Reversible vs Irreverisble

For anything besides entropy (where it doesn't matter if something is reversible or irreversible), you should be told whether or not it's reversible or irreversible. If the problem just says volume changes from 2L to 5L, you assume it's irreversible. If it says something along the lines of "thr...
by Lindsay Kester 2L
Tue Feb 13, 2018 4:12 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: Entropy equation
Replies: 2
Views: 135

Re: Entropy equation

This depends on which C you're using. When you have to multiply C by n, it means that C is the specific heat per mole of substance, and when you don't, it's just specific heat. You can also tell if you look at the units; specific heat per mole will be in J/mol, while specific heat will just be J.
by Lindsay Kester 2L
Tue Feb 06, 2018 3:08 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Spontaneity and the Direction of a Reaction
Replies: 2
Views: 130

Re: Spontaneity and the Direction of a Reaction

When delta G is negative, it means that the products are at a lower energy level than the reactants, and thus the reaction moves toward them. When it's positive, however, the reactants are at a lower energy level than the products, and so the reaction moves toward them.
by Lindsay Kester 2L
Tue Feb 06, 2018 3:06 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: Irreversible Vs. Reversible Expansion
Replies: 2
Views: 129

Re: Irreversible Vs. Reversible Expansion

However, entropy is a state function, so regardless of whether it's irreversible or reversible expansion, it's going to have the same entropy at the end, and you can use the same formulas.
by Lindsay Kester 2L
Tue Feb 06, 2018 3:03 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Calculating deltaG
Replies: 2
Views: 95

Re: Calculating deltaG

You use them based on the information you're given, and depending on what is being changed (Is value constant, pressure, etc.).
by Lindsay Kester 2L
Wed Jan 31, 2018 11:33 am
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: Definition of Entropy
Replies: 10
Views: 312

Re: Definition of Entropy

The more moles of gas there are in the system, the greater the entropy because W=number of possible states^number of molecules, and when you increase the number of moles in a system you also increase the number of molecules.
by Lindsay Kester 2L
Wed Jan 31, 2018 11:28 am
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: 9.5
Replies: 5
Views: 148

Re: 9.5

Whenever heat is leaving something, the amount of possible spaces (W) that the molecules can take up decreases, so entropy does as well.
by Lindsay Kester 2L
Wed Jan 31, 2018 11:27 am
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Relationship between ΔG⁰ AND K
Replies: 2
Views: 118

Re: Relationship between ΔG⁰ AND K

The K here is also a constant for all equations, and doesn't change with each reaction/molecule being used.
by Lindsay Kester 2L
Sun Jan 28, 2018 5:25 pm
Forum: Thermodynamic Definitions (isochoric/isometric, isothermal, isobaric)
Topic: gas with 2x positions
Replies: 2
Views: 146

Re: gas with 2x positions

The equation is the number of possible states (In this case, 2) raised to the number of particles. If there were three possible states, it would be 3^n, and so on.
by Lindsay Kester 2L
Sun Jan 28, 2018 5:23 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: Gas atoms
Replies: 4
Views: 161

Re: Gas atoms

Gas molecules will never go back to a smaller volume because it would decrease the entropy, or amount of states, of that system. In a smaller volume, there are less possible organizations for the molecules. Objects always want to go to a state of greater entropy, and moving to a smaller volume would...
by Lindsay Kester 2L
Sun Jan 28, 2018 5:21 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: Entropy [ENDORSED]
Replies: 4
Views: 166

Re: Entropy [ENDORSED]

Yes, entropy is a state function, because the it describes the equilibrium state of a system, regardless of how it got to that state.
by Lindsay Kester 2L
Thu Jan 18, 2018 10:00 am
Forum: Phase Changes & Related Calculations
Topic: Thermochemistry Sections in Ch 8
Replies: 2
Views: 138

Re: Thermochemistry Sections in Ch 8

In class, I think we started with 8.11, which is the enthalpy of physical change.
by Lindsay Kester 2L
Wed Jan 17, 2018 11:14 pm
Forum: Thermodynamic Systems (Open, Closed, Isolated)
Topic: Heating/Cooling A System
Replies: 4
Views: 225

Re: Heating/Cooling A System

Because an open system is connected to its surroundings, any heat added would be dispersed throughout its surroundings, so the total E of the system would remain the same. Therefore, it wouldn't work as a way to add energy to a system.
by Lindsay Kester 2L
Wed Jan 17, 2018 11:11 pm
Forum: Thermodynamic Systems (Open, Closed, Isolated)
Topic: Radiation vs. Convection
Replies: 3
Views: 178

Re: Radiation vs. Convection

Radiation doesn't require the use of a medium- think of the Sun, for example, which heats us despite there being nothing directly connecting us. Convection requires a medium- when you put something less hot in something hot, the heat moves from the hot thing to the less hot thing.
by Lindsay Kester 2L
Fri Jan 12, 2018 3:21 pm
Forum: Phase Changes & Related Calculations
Topic: Heat Enthalpies We Need to Know
Replies: 3
Views: 160

Heat Enthalpies We Need to Know

In the reading for Chapter 8, it says that we should include table 8.2, which is a list of some the heat enthalpies. Do we need to memorize these for the test, or will they be provided?
by Lindsay Kester 2L
Fri Jan 12, 2018 3:18 pm
Forum: Administrative Questions and Class Announcements
Topic: Homework grading
Replies: 6
Views: 303

Re: Homework grading

I think this depends on your TA- a friend of mine took 14A last quarter and her TA understood that since most people have or have access to the solutions manual, we usually have the right answers, and just graded the homework on completion. Regardless, though, you should probably just check your ans...
by Lindsay Kester 2L
Fri Jan 12, 2018 3:15 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: What type of system is a Bomb Calorimeter?
Replies: 4
Views: 507

Re: What type of system is a Bomb Calorimeter?

To figure out if something is a closed system, you should first try to figure out what the system is. In a bomb calorimeter, the system is what is inside, the inner chamber. Because this system can't exchange heat or energy with its surroundings, it's a closed system.

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