Search found 27 matches

by Julianna Thrasher 1B
Sun Mar 11, 2018 8:53 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: 15.51? Molecularity?
Replies: 3
Views: 123

Re: 15.51? Molecularity?

I agree with Sabrina. To elaborate, if the slow step is the first step (not the second), then it is the only step that matters for the overall reaction order. The second step (fast) occurs too quickly to modify the rate law and also because it occurs after the slow step. The slow step will always be...
by Julianna Thrasher 1B
Sun Mar 11, 2018 8:46 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: intermediates in forward and reverse rxn
Replies: 1
Views: 85

Re: intermediates in forward and reverse rxn

Do you mean one reaction that is written out in one direction (forward) and written in the opposite direction below (reverse)? There would not be a reaction because the intermediate would have to be a substance that stays the same throughout the reaction, in the same phase, and appears on both sides...
by Julianna Thrasher 1B
Sun Mar 11, 2018 8:43 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Steps
Replies: 3
Views: 128

Re: Steps

We will always have to be told by the problem which step is slow and which step is fast. These terms can be in parentheses next to the steps, or they can be determined by the k values. A lower k value means a slower reaction rate, means that step is the slow step.
by Julianna Thrasher 1B
Sun Mar 04, 2018 7:30 pm
Forum: General Rate Laws
Topic: Self Test 15.6B
Replies: 1
Views: 91

Re: Self Test 15.6B

This is how you can express rate before you separate the variables and integrate them to find the 1st order integrated rate law.
For the reaction: A --> P
Rate = -d[A]/[A] = k[A]'
I am assuming the textbook means [A]' = P.
by Julianna Thrasher 1B
Sun Mar 04, 2018 7:21 pm
Forum: Method of Initial Rates (To Determine n and k)
Topic: order of reactant importance
Replies: 2
Views: 129

Re: order of reactant importance

Kinetics studies the rate of reactions and measuring those rates. The order of the reaction is important to help determine how reaction rate of the concentration changes over time. The greater the exponent, n, of the reaction, then the more molecules of that reactant there are to react, thus a great...
by Julianna Thrasher 1B
Sun Mar 04, 2018 6:53 pm
Forum: First Order Reactions
Topic: K constant
Replies: 3
Views: 145

Re: K constant

For a first order reaction, the integrated rate law is: ln[A] = -kt + ln[A]0. If you set ln[A]=y and -k=m you can get a typical slope equation in the form of y=mx+c. Since -k=m then the slope of the curve is negative so a negative k implies a negative slope. A 1st order reaction of ln[A] vs time mea...
by Julianna Thrasher 1B
Sun Feb 25, 2018 8:59 pm
Forum: General Rate Laws
Topic: 15.3
Replies: 2
Views: 147

Re: 15.3

Unique -average- rate of reaction just means applying the rate law to the given reaction with the stoichiometric coefficients of the substances. All substances can react at different rates so the unique average rate of reaction means choosing one of these rates and diving it by the stoichiometric co...
by Julianna Thrasher 1B
Sun Feb 25, 2018 8:54 pm
Forum: Kinetics vs. Thermodynamics Controlling a Reaction
Topic: The rate of a reaction
Replies: 5
Views: 209

Re: The rate of a reaction

K is dependent on temperature because the molecules in the substances in the given reactions will change due to the change in temperature. A higher temperature will cause molecules to vibrate more and move more rapidly, which could then increase or decrease the rate of the reaction, thus the value o...
by Julianna Thrasher 1B
Sun Feb 25, 2018 8:49 pm
Forum: Kinetics vs. Thermodynamics Controlling a Reaction
Topic: Chapter 15 related videos
Replies: 6
Views: 219

Re: Chapter 15 related videos

I like Crash Course by John Green! Very basic review just to remind you of topics in the chapter. https://www.youtube.com/watch?v=7qOFtL3VEBc
by Julianna Thrasher 1B
Sun Feb 18, 2018 9:45 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Galvanic Cell
Replies: 3
Views: 135

Re: Galvanic Cell

It is both useful for you and the grader to indicate the direction or flow of the charge. It wouldn't hurt you to include it, also because Na+ and Cl- would split and flow in different directions and not stay as NaCl if I understand correctly.
by Julianna Thrasher 1B
Sun Feb 18, 2018 9:41 pm
Forum: Balancing Redox Reactions
Topic: H+ vs H2
Replies: 3
Views: 107

Re: H+ vs H2

H+ is used when the system is under acidic conditions. With H2 molecules in the system, then it would not be acidic, due to their neutral charge. The problem tells you when it is in acidic conditions.
by Julianna Thrasher 1B
Sun Feb 18, 2018 9:37 pm
Forum: Interesting Applications: Rechargeable Batteries (Cell Phones, Notebooks, Cars), Fuel Cells (Space Shuttle), Photovoltaic Cells (Solar Panels), Electrolysis, Rust
Topic: Iron Reduction
Replies: 1
Views: 214

Re: Iron Reduction

It is because the reaction 2Ag+ + Fe(s) --> 2Ag(s) + Fe2+ (aq) is spontaneous, Ecell > 0. In the half reactions, Ag+ + e- --> Ag (s) and Fe(s) --> Fe2+ + 2e-, Silver is being reduced and gaining electrons while Iron is being oxidized and giving off electrons
by Julianna Thrasher 1B
Sun Feb 11, 2018 8:37 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: Vibrational Energy State
Replies: 4
Views: 151

Re: Vibrational Energy State

This is in section 9.7 of the textbook. Vibrational energy levels are due to how close the atoms are since the closer the atoms are, the closer the allowed energies of the atoms are. You can think of vibrational energy levels as rotational energy levels as we learned in Chem 14B when we learned abou...
by Julianna Thrasher 1B
Sun Feb 11, 2018 8:29 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: entropy sign
Replies: 5
Views: 177

Re: entropy sign

You can look at the phases of all substances in the chemical reaction. Entropy increases from solid --> liquid --> gas since entropy is a measure of disorder and disorder increases with with less rigidity of a substance. If the reactants are mainly liquids and solids and the products are all gases, ...
by Julianna Thrasher 1B
Sun Feb 11, 2018 8:26 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: free expansion
Replies: 2
Views: 146

Re: free expansion

Free expansion is a irreversible process of a gas expanding in a system. There is no work done because the gas can expand freely without any external pressures on the system.
by Julianna Thrasher 1B
Sun Feb 04, 2018 9:18 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: state functions
Replies: 3
Views: 94

Re: state functions

Yes, I agree. Free energy is a state function because it does not depend on the path taken by the system to go from reactants to products. Refer to Lecture 9.
by Julianna Thrasher 1B
Sun Feb 04, 2018 9:16 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Delta G°
Replies: 5
Views: 142

Re: Delta G°

When ΔG=0 then the system is at equilibrium, not when ΔG° is 0. G° is standard free energy of a gas at 1atm. If G°=0 I believe it means there is no free energy due to change in pressures.
by Julianna Thrasher 1B
Sun Feb 04, 2018 9:12 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: thermodynamically favored
Replies: 6
Views: 701

Re: thermodynamically favored

A reaction that is thermodynamically favored has a negative ΔG, so the products are at a lower energy than the reactants so that reaction will spontaneously occur. For ΔG to be negative, ΔH has to be small in the equation ΔG=ΔH−TΔS.
by Julianna Thrasher 1B
Sun Jan 28, 2018 10:25 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: Boltzmann equation: positional entropy or thermal entropy?
Replies: 3
Views: 90

Re: Boltzmann equation: positional entropy or thermal entropy?

For Miranda, quantifying simply means putting a number to the amount of energy. If you quantify entropy you add the units Joules per degree Kelvin. For any entropy, both positional and thermal you can quantify it. When you quantify the amount of energy you can evaluate how it was used in reactions.
by Julianna Thrasher 1B
Sun Jan 28, 2018 10:14 pm
Forum: Thermodynamic Systems (Open, Closed, Isolated)
Topic: Difference between systems? [ENDORSED]
Replies: 8
Views: 308

Re: Difference between systems? [ENDORSED]

Kennedy is correct about the thermos. It is isolated until it is opened for a drink then it becomes an open system. When the drink is taken and done and the bottle is closed again, the system is re-isolated. The system will go to equilibrium at a new temperature/heat that may not be the same as it w...
by Julianna Thrasher 1B
Sun Jan 28, 2018 9:40 pm
Forum: Phase Changes & Related Calculations
Topic: Endothermic or Exothermic
Replies: 20
Views: 502

Re: Endothermic or Exothermic

Condensation is exothermic. This is because heat is released when a substance changes from gas to a liquid and it is condensing.
by Julianna Thrasher 1B
Sun Jan 21, 2018 5:19 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: Heat versus work
Replies: 6
Views: 189

Re: Heat versus work

Heat is a form of energy that is transferred due to a temperature difference. Heat flows from a high temperature region to a lower temperature region. Temperature measures the flow of heat energy, or the speed of the random moving particles. Work is "the process of achieving motion against an o...
by Julianna Thrasher 1B
Sun Jan 21, 2018 5:14 pm
Forum: Thermodynamic Systems (Open, Closed, Isolated)
Topic: Sublimation
Replies: 4
Views: 217

Re: Sublimation

Sublimation is an endothermic reaction. This means that when a solid transforms into vapor, the enthalpy is positive and heat is required for the transformation. For dry ice, the most obvious example of sublimation, the dry ice feels cool because the ice is taking the heat from the surroundings in o...
by Julianna Thrasher 1B
Sun Jan 21, 2018 5:05 pm
Forum: Calculating Work of Expansion
Topic: w=-P*deltaV
Replies: 3
Views: 135

Re: w=-P*deltaV

We use this equation when the system is at equilibrium (and is therefore reversible) in order to calculate work done by expansion against constant pressure and slight changes in volume. The negative sign shows the system is losing energy.
by Julianna Thrasher 1B
Fri Jan 12, 2018 12:44 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: What is bond enthalpy and can someone explain to me what Lavelle was doing with the Lewis Structures in today's lecture?
Replies: 3
Views: 130

Re: What is bond enthalpy and can someone explain to me what Lavelle was doing with the Lewis Structures in today's lect

When Professor Lavelle drew out the Lewis structures he was just visually explaining which bonds will be broken in the reactants in order to form new bonds for the products. You only use the bond energies of the bonds broken and formed in order to calculate bond enthalpy, and it may be tricky someti...
by Julianna Thrasher 1B
Fri Jan 12, 2018 12:40 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Hess's Law
Replies: 8
Views: 327

Re: Hess's Law

In regards to multiplying by 1.5 to cancel out the reactants, you can do this because enthalpy is a state function, which means it is additive. By multiplying the coefficients in the equation you must also multiply the delta H by the same equation. Doing this makes the equation still the same, just ...
by Julianna Thrasher 1B
Fri Jan 12, 2018 12:29 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Differences in the delta Hs
Replies: 2
Views: 141

Re: Differences in the delta Hs

h is used in chemistry to symbolize enthalpy so I do not think you can have a delta H with a subscript of h because delta H is the change in enthalpy so h can not be enthalpy as well. Delta H can have subscripts of final, initial, products, reactants, vapor, fusion, sublimation, solid, liquid, etc.

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