Search found 31 matches

by Amanda Wu 2C
Mon Mar 12, 2018 2:33 pm
Forum: *Enzyme Kinetics
Topic: Catalysts
Replies: 11
Views: 554

Re: Catalysts

Yes, catalysts increase the rates of the forward and reverse reactions. In turn, both the forward and reverse rate constants, k and k', increase but their ratio, k/k' which equals the equilibrium constant K, remains the same.
by Amanda Wu 2C
Mon Mar 12, 2018 2:31 pm
Forum: *Enzyme Kinetics
Topic: Adsorption
Replies: 11
Views: 480

Re: Adsorption

As Lavelle mentioned in class, I think the main difference between absorption and adsorption is that in absorption, a substance goes inside another substance (as in water into a sponge) whereas in adsorption, the reactants just sit on the surface of the catalyst.
by Amanda Wu 2C
Mon Mar 12, 2018 2:27 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Intermediate
Replies: 6
Views: 229

Re: Intermediate

Both intermediates and catalysts don't show up in the overall net reaction. What distinguishes a catalyst from an intermediate is that a catalyst is there to begin with and becomes consumed (reactants side) in an elementary step only to be reformed again (products side) whereas an intermediate is fo...
by Amanda Wu 2C
Wed Mar 07, 2018 4:22 pm
Forum: Kinetics vs. Thermodynamics Controlling a Reaction
Topic: Diamond/Graphite
Replies: 4
Views: 688

Re: Diamond/Graphite

Although diamond is thermodynamically unstable because delta G is negative (the reaction is spontaneous) and diamond has a higher energy than graphite, diamond is considered kinetically stable because the pathway in which diamond becomes graphite has a large activation energy barrier that prevents i...
by Amanda Wu 2C
Wed Mar 07, 2018 4:15 pm
Forum: Administrative Questions and Class Announcements
Topic: Formulas on test?
Replies: 3
Views: 178

Re: Formulas on test?

The equations sheet including the integrated rate laws and half lives were given on the test. However, the equations are not indicated as 0th, 1st, or 2nd order so you'd still have to be able to identify them on the sheet.
by Amanda Wu 2C
Wed Mar 07, 2018 4:13 pm
Forum: General Rate Laws
Topic: Coefficients
Replies: 6
Views: 227

Re: Coefficients

As others have mentioned, coefficients affect the unique reaction rate or the rate law for elementary steps of a reaction. In the case of the unique reaction rate, the stoichiometric coefficients are in the denominator of the rate of consumption/formation of a reactant/product to get the unique rate...
by Amanda Wu 2C
Wed Feb 28, 2018 9:24 pm
Forum: Kinetics vs. Thermodynamics Controlling a Reaction
Topic: Half-life
Replies: 4
Views: 198

Re: Half-life

The half life is the time it takes for the concentration of a species to decrease to half its initial concentration. It can be 1/2 (whatever time units is used in a particular case) but the half life itself is not always 1/2. It just means the time it takes for a species' concentration to become 1/2...
by Amanda Wu 2C
Wed Feb 28, 2018 9:21 pm
Forum: General Rate Laws
Topic: Negative Signs [ENDORSED]
Replies: 6
Views: 288

Re: Negative Signs [ENDORSED]

It is customary that the unique reaction rate is positive, because you're describing the rate at which the reaction proceeds as time progresses. Thus, you negate the reactant rate (d[R]/dt) (and if needed, divide by the stoichiometric coefficient of R) to get the positive unique reaction rate.
by Amanda Wu 2C
Wed Feb 28, 2018 9:17 pm
Forum: Method of Initial Rates (To Determine n and k)
Topic: units of K
Replies: 5
Views: 227

Re: units of K

The units of K, the rate constant, change depending on the order of the overall reaction. This is because the unique reaction rate always has units of M/s or mol(L^-1)(s^-1). Thus, the units of K have to be adjusted to account for its multiplication with zero, one, or more reactant concentrations in...
by Amanda Wu 2C
Tue Feb 20, 2018 9:49 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Cell Diagram
Replies: 3
Views: 124

Re: Cell Diagram

The single line (|) indicates the interface of two different states of matter (within each respective electrode) whereas commas in the cell diagram are used to separate species (within each respective electrode) with the same states of matter; often times, these species are dissolved as ions in an a...
by Amanda Wu 2C
Tue Feb 20, 2018 9:45 pm
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: metals dissolving
Replies: 1
Views: 121

Re: metals dissolving

Lavelle went over an example of whether a metal dissolves (the gold ring in nitric acid example) in lecture. In looking at his example, I think he calculated the standard cell potential for the reaction occurring and then plugged that value into to the delta G naught = -nFE naught equation to find t...
by Amanda Wu 2C
Tue Feb 20, 2018 9:37 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Pt in Cell diagrams
Replies: 4
Views: 204

Re: Pt in Cell diagrams

There are also cases in which a Pt electrode is necessary even if one of the species is not in solution. Such an example includes I2 (s). Because it isn't a metal and is a poor conductor of electricity, it is necessary to have a Pt electrode in this case even if the species is a solid. On the opposi...
by Amanda Wu 2C
Thu Feb 15, 2018 8:31 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Standard Gibbs Free Energy
Replies: 3
Views: 131

Re: Standard Gibbs Free Energy

Standard Gibbs Free Energy (delta G naught) is given under standard conditions where temperature is 25 degrees Celsius. Given for other temperatures, it would just be Gibbs Free Energy (delta G).
by Amanda Wu 2C
Thu Feb 15, 2018 8:27 pm
Forum: Thermodynamic Definitions (isochoric/isometric, isothermal, isobaric)
Topic: Isothermal
Replies: 2
Views: 165

Re: Isothermal

In the case of an ideal gas, the change in internal energy is given by delta U = (3/2)*R*delta T. If a reaction involving an ideal gas is isothermal, the temperature remains constant, meaning delta T=0. Hence, plugging delta T=0 in the aforementioned delta U equation gives delta U=0.
by Amanda Wu 2C
Thu Feb 15, 2018 8:23 pm
Forum: Thermodynamic Definitions (isochoric/isometric, isothermal, isobaric)
Topic: isothermal and deltaU=0
Replies: 3
Views: 200

Re: isothermal and deltaU=0

For an ideal gas, delta U = (3/2)*R*delta T. If a system with an ideal gas is isothermal, then temperature remains constant, meaning delta T=0. Hence, if you calculate delta U with the aforementioned formula, delta U is also 0.
by Amanda Wu 2C
Thu Feb 08, 2018 1:34 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: Extensive Property?
Replies: 3
Views: 155

Re: Extensive Property?

As others have mentioned, an intensive property is a property that is not dependent on the size of a system or the amount of material present within the system. Intensive properties include density (which is the ratio of mass over volume) and the standard reduction potential, which remains the same ...
by Amanda Wu 2C
Thu Feb 08, 2018 1:30 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Half Reactions
Replies: 6
Views: 216

Re: Half Reactions

If you use the second method Lavelle spoke about in class to calculate the standard reduction potential of the cell, you first identify the half reactions and look up the standard reduction potentials of these respective half reactions. Thus, I believe, in the tables, you'll notice that the half rea...
by Amanda Wu 2C
Thu Feb 08, 2018 1:22 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Spontaneity
Replies: 9
Views: 419

Re: Spontaneity

A negative delta G indicates that a reaction/process is spontaneous or favorable. This is due to the fact that a negative delta G indicates a loss of free energy (going from a higher free energy of the reactants to a lower free energy of the products), which is a favorable process.
by Amanda Wu 2C
Wed Jan 31, 2018 3:59 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: sign of entropy
Replies: 11
Views: 281

Re: sign of entropy

The sign of entropy is indicative of the heat flow in or out of the system. A system in which heat flows out to the surroundings will have a negative entropy whereas a system in which heat flows in from the surroundings will have a positive entropy.
by Amanda Wu 2C
Wed Jan 31, 2018 3:43 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: A spontaneous reaction
Replies: 7
Views: 216

Re: A spontaneous reaction

A spontaneous reaction is one that is favorable to proceed given the current conditions without an external input of energy or intervention. In a spontaneous reaction, delta G is negative because the free energy of the products is lower than that of the reactants, much like the picture Lavelle illus...
by Amanda Wu 2C
Wed Jan 31, 2018 3:39 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Class Example
Replies: 6
Views: 181

Re: Class Example

Setting delta G to 0 merely gives the boiling point, in this case T=333 K. At this temperature, both the gas and liquid phases exist; therefore, the forward reaction isn't favored until T>333 K, causing delta G to be negative. If finding the boiling point by setting delta G to 0 complicates the calc...
by Amanda Wu 2C
Wed Jan 24, 2018 8:13 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Adding reactions
Replies: 2
Views: 123

Re: Adding reactions

Yes, it's because the 2NO produced as a product in the 1st reaction is used up as a reactant in the 2nd reaction (aka the NO serves as an intermediate between the two reactions). Therefore, the 2NO does not appear in the total net reaction.
by Amanda Wu 2C
Wed Jan 24, 2018 8:07 pm
Forum: Thermodynamic Definitions (isochoric/isometric, isothermal, isobaric)
Topic: Why is internal energy independent of volume for an ideal gas?
Replies: 1
Views: 240

Re: Why is internal energy independent of volume for an ideal gas?

I think the reasoning behind why the internal energy of an ideal gas is independent of volume is best understood through Gay-Lussac's Joule experiment: Simply put, the experiment consisted of two containers, one of which contained an ideal gas and one of which was completely evacuated, connected to ...
by Amanda Wu 2C
Wed Jan 24, 2018 7:50 pm
Forum: Calculating Work of Expansion
Topic: Reversible expansion and work in a vacuum
Replies: 2
Views: 129

Re: Reversible expansion and work in a vacuum

As I recall from the book, a system does no expansion work when it expands into a vacuum because there is not an opposing force (pressure is 0). However, in Lavelle's lecture today, I believe he included a mass that was outside the vacuum chamber attached to the piston by a string. Because the expan...
by Amanda Wu 2C
Tue Jan 16, 2018 10:11 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Work function
Replies: 4
Views: 146

Re: Work function

When work is done on a system, the value of w is positive (w > 0) while when work is done by the system, the value of w is negative. (w < 0).
by Amanda Wu 2C
Tue Jan 16, 2018 10:08 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: K vs C
Replies: 6
Views: 209

Re: K vs C

In calculating temperature change, K and C can be used interchangeably because the temperature change will have the same magnitude in both units due to the conversion relation (linear translation - 273 is added to every Celsius temperature to get its Kelvin equivalent) between Kelvin and Celsius. In...
by Amanda Wu 2C
Tue Jan 16, 2018 9:57 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: internal energy
Replies: 5
Views: 178

Re: internal energy

The change in internal energy of a system (Delta U) is the sum of the heat (q) added (q > 0) to or
removed (q < 0) from the system and the work (w) done on (w > 0) or by (w < 0) the system. In short, delta U = q + w.
by Amanda Wu 2C
Thu Jan 11, 2018 10:28 am
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: Celsius the same as Kelvin? [ENDORSED]
Replies: 9
Views: 1195

Re: Celsius the same as Kelvin? [ENDORSED]

As others have mentioned, whether your units are in Celsius or Kelvin, the change in the temperature, delta T would still equate to 7.32. This is because, even if you were to add 273.15 to the initial and final temperatures given in Celsius to convert them to Kelvin, both of the magnitudes of the te...
by Amanda Wu 2C
Wed Jan 10, 2018 9:14 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Systems
Replies: 3
Views: 156

Re: Systems

The classification of systems as open, closed, or isolated depend on whether they are able to permit exchanges of energy and/or matter between the system itself and its surroundings. For example, in an open system such as a lidless pot of boiling water set on a stovetop burner, there is both an exch...
by Amanda Wu 2C
Wed Jan 10, 2018 12:36 am
Forum: Phase Changes & Related Calculations
Topic: Endothermic Reaction
Replies: 10
Views: 1008

Re: Endothermic Reaction

The characterization of exothermic and endothermic reactions is with respect to energy going in or out of a system. In this case, the ice cube would be considered the system while the hand holding the ice cube is the surroundings. As such, the heat energy from your hand is transferred to the ice cub...
by Amanda Wu 2C
Tue Jan 09, 2018 11:04 pm
Forum: Calculating Work of Expansion
Topic: Potential to do work in Irreversible vs. Reversible Expansion
Replies: 1
Views: 242

Potential to do work in Irreversible vs. Reversible Expansion

From reading the textbook and from the calculus (integral) point of view, I understand that work done by a system in irreversible expansion is less than that of the system in reversible expansion, which the book attributes to a less than maximal possible opposing pressure at each stage of expansion ...

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