## Search found 35 matches

Sun Mar 17, 2019 11:00 am
Forum: Zero Order Reactions
Topic: Zero order reaction
Replies: 8
Views: 413

### Re: Zero order reaction

You can derive the integrated rate law from -d[A]/dt= k bc and see that the rate is independent of concentration.
Sun Mar 17, 2019 10:58 am
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: OH-(aq) in cell diagram
Replies: 3
Views: 270

### Re: OH-(aq) in cell diagram

You include whatever compounds are in your overall balanced cell rxn in your cell diagram.
Sun Mar 17, 2019 10:57 am
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Inert Electrodes
Replies: 3
Views: 286

### Re: Inert Electrodes

Use Platinum as an inert conductor even if an electrolyte is solid because you have to make sure it's a metal because metals are good conductors.
Sat Mar 09, 2019 3:02 pm
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: 14.97
Replies: 2
Views: 103

### 14.97

The two standard potentials are +2.87V and +3.03V so wouldn't the latter be the cathode, making the total cell potential positive?
The solutions manual makes +2.87V potential the cathode potential.
Also, why do you get Ka when you take the square root of K?
Fri Mar 08, 2019 3:15 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Reaction Mechanism
Replies: 2
Views: 112

### Reaction Mechanism

Can someone explain what exactly is meant by the term "reaction mechanism"?
Fri Mar 08, 2019 2:58 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Water in a cell diagram
Replies: 5
Views: 148

### Re: Water in a cell diagram

If water is liquid, you don't include it in the cell diagram if you have another aqueous solution.
Fri Mar 08, 2019 2:52 pm
Forum: Zero Order Reactions
Topic: Enzymatic Reactions
Replies: 2
Views: 96

### Re: Enzymatic Reactions

A zero order rxn usually occurs when a catalyst or enzyme is saturated by the reactants (substrate).
Wed Mar 06, 2019 4:50 pm
Forum: First Order Reactions
Topic: How to do 15.11 6th edition?
Replies: 4
Views: 168

### Re: How to do 15.11 6th edition?

I assume that because you're only looking for the initial rate of decomposition, the problem doesn't consider "being heated to 65*C" as factoring into the rate because it happens after the N2O5 is added.
Wed Mar 06, 2019 4:45 pm
Forum: General Rate Laws
Topic: Difference between instantaneous and unique rate
Replies: 3
Views: 96

### Re: Difference between instantaneous and unique rate

As everyone said, the instantaneous rate refers to the rate of change in the concentration of reactants and products at ONE moment, given by -d(R)/dt. The unique rate of the reaction is the one average rate of the reaction taking into consideration that the reactant/product concentrations are all ch...
Wed Mar 06, 2019 4:33 pm
Forum: Zero Order Reactions
Topic: Example of a zero order rxn
Replies: 4
Views: 156

### Re: Example of a zero order rxn

The reverse Haber process, 2NH3(g) -> N2 (g) + 3H2 (g), is an example of a zero order reaction because the rxn's rate is completely independent on the concentration of ammonia.
Tue Mar 05, 2019 6:25 pm
Forum: Kinetics vs. Thermodynamics Controlling a Reaction
Topic: Purpose of Kinetics
Replies: 6
Views: 337

### Re: Purpose of Kinetics

Kinetics is the study of the rate of reactions which can be useful in studying enzymes, drugs, and so many other types of chemical reactions. Kinetics are especially applicable to biology because the infinite number of chemical reactions that happen in biological systems are all in an effort to main...
Tue Mar 05, 2019 5:47 pm
Forum: First Order Reactions
Topic: Exponential Curve
Replies: 6
Views: 158

### Re: Exponential Curve

The integrated rate law can be expressed in exponential form as [A]=[A].e−kt First order reactions show an exponential decay of reactants as a function of time. Because natural log (ln) was introduced into the integration, we had to use "e" to make calculations easier. In doing that, the r...
Tue Mar 05, 2019 5:32 pm
Forum: Zero Order Reactions
Topic: Initial reactions rates
Replies: 3
Views: 152

### Re: Initial reactions rates

By focusing on only reactants, you are also somewhat tracking the rate of product formation because molecules in your solution are either reactants or products, nothing else. The rate of the reaction is also defined by the rate at which reactants form products, so looking at the concentration of rea...
Tue Feb 19, 2019 11:39 am
Forum: Thermodynamic Systems (Open, Closed, Isolated)
Topic: System vs Surroundings
Replies: 14
Views: 521

### Re: System vs Surroundings

System vs. surrounding should be evident depending on the question that is given. It usually just determines whether a certain value is positive or negative in relation to the system at hand. For example, if the question states the surroundings gained x amount of energy, then energy left the system,...
Tue Feb 19, 2019 10:34 am
Forum: Thermodynamic Definitions (isochoric/isometric, isothermal, isobaric)
Topic: Microstates
Replies: 7
Views: 477

### Re: Microstates

Microstates are the possible number of same energy configurations of a set of molecules. Because it is a statistical calculation of entropy, you put it to the power of the number of molecules you are handling in a certain problem.
Tue Feb 19, 2019 10:33 am
Forum: Thermodynamic Definitions (isochoric/isometric, isothermal, isobaric)
Topic: Microstates
Replies: 7
Views: 477

### Re: Microstates

Microstates are the possible number of same energy configurations of a set of molecules. Because it is a statistical calculation of entropy, you put it to the power of the number of molecules you are handling in a certain problem.
Tue Feb 19, 2019 10:21 am
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Negative Delta G
Replies: 7
Views: 538

### Re: Negative Delta G

Reactions with a negative delta G are very spontaneous, and therefore highly favorable! The more favorable a reaction is, the more it will proceed towards the products. That means that K is rather large at equilibrium because the ratio of products is high compared to reactants.
Mon Feb 18, 2019 8:42 am
Forum: Thermodynamic Definitions (isochoric/isometric, isothermal, isobaric)
Topic: Reversible vs. Irreversible
Replies: 5
Views: 518

### Re: Reversible vs. Irreversible

Just remember that more work is done in an isothermal reversible system than an irreversible system. Think of the work as the integral of the graphs we were shown in class when the irreversible system is basically held at constant P.
Mon Feb 18, 2019 8:36 am
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: Negative Temperature
Replies: 5
Views: 143

### Re: Negative Temperature

I am not sure there exists such a thing as a negative temperature system because basically all movement stops at 0 K.
Sat Feb 09, 2019 10:41 am
Forum: Thermodynamic Definitions (isochoric/isometric, isothermal, isobaric)
Topic: Work Equations
Replies: 2
Views: 120

### Re: Work Equations

As Alexa said, the first is for the irreversible reaction (the graph shown in class with the box-shaped integral). The second and third are under reversible conditions and are ultimately integrals of V and P in respect to one another (think about the area under the curve shaped graph that Lavelle sh...
Sat Feb 09, 2019 10:35 am
Forum: Calculating Work of Expansion
Topic: when to use each equation
Replies: 2
Views: 90

### Re: when to use each equation

An easy way to remember it is that whatever variable is constant is included in the equation.
CONSTANT P: w = -Pex(deltaV)
CONSTANT T: w = -nRTln(V2/V1)?
Sat Feb 09, 2019 10:32 am
Forum: Calculating Work of Expansion
Topic: Temperature in Work Equations
Replies: 3
Views: 122

### Re: Temperature in Work Equations

I think you have to include T in the first equation because when you derive it you have to use the integral of P in respect to volume, but you ultimately replace P with the other side of the ideal gas equation (nRT/V). When you take the integral, you can pull out the "-nRT" because it's te...
Fri Feb 01, 2019 3:09 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Heat Capactiy
Replies: 5
Views: 149

### Re: Heat Capactiy

Heat capacity refers to raising the "temperature of a body" by one degree whereas specific heat capacity is more SPECIFIC and refers to how much energy you have to put in to raise a single gram of said "substance/body" by one degree.
Fri Feb 01, 2019 2:58 pm
Forum: Thermodynamic Systems (Open, Closed, Isolated)
Topic: Isolated Systems
Replies: 6
Views: 181

### Re: Isolated Systems

There are no actually isolated systems other than the universe, but I think for the sake of this class we just assume an isolated system is merely one that does not exchange energy or matter with its surroundings. ex: soup in a closed thermos, bomb calorimeter, etc.
Fri Feb 01, 2019 2:55 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: Finding Heat
Replies: 4
Views: 125

### Re: Finding Heat

You can use either because you can convert between Celsius and Kelvin like this: Kelvin = Celsius + 273.15.
The conversion only adds, so the differences temperature (whether K or C) are the same values.
Fri Feb 01, 2019 2:49 pm
Forum: Thermodynamic Systems (Open, Closed, Isolated)
Topic: Analogy of Boulder
Replies: 5
Views: 208

### Re: Analogy of Boulder

I think Lavelle was also referring to the idea of doing work on surroundings vs. on a system. If the boulder rolls down the hill, it does work on the surroundings because it releases energy (work is positive- exergonic). When the boulder is pushed up the hill, it's an endergonic process because work...
Fri Feb 01, 2019 2:44 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Phase changes and enthaplies
Replies: 3
Views: 96

### Re: Phase changes and enthaplies

Remember that Lavelle said that enthalpy is a state function, meaning its value depends on the phase of the substance which you are referring to. However, enthalpy change is a two-state function so wouldn't even be considered a state function.
Wed Jan 23, 2019 5:47 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: 6th Ed. 11.57
Replies: 1
Views: 53

### 6th Ed. 11.57

In 11.57, the solution manual includes the conc. of water in the ICE table. I thought we didn't include the concentrations of water in ICE tables and especially when calculating Kc. Can someone please clarify?
Fri Jan 18, 2019 5:59 pm
Forum: Non-Equilibrium Conditions & The Reaction Quotient
Topic: Kw
Replies: 6
Views: 223

### Re: Kw

Kw=[H3O+][OH-]
Kw= constant 1.0x10^-14
In neutral water with pH=7, the H3O+ and OH- concentrations are equal so
1.0x10^-14=[H3O+][OH-] with both of them being 1.0 x 10^-7.
Fri Jan 18, 2019 4:43 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: ICE table
Replies: 2
Views: 74

### Re: ICE table

You have to keep in mind molar ratio when doing your ice tables. If the product of a reaction was "3HCl" you would subtract "3x" from the initial concentration. Then it just carries over to your quadratic as a coefficient and when everything is foiled out, you will end up with a,...
Fri Jan 18, 2019 4:33 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: When is X negligible.
Replies: 6
Views: 150

### Re: When is X negligible.

My TA also said today it is not mandatory to do the shortcut and that the quadratic works fine. But, if you have to do the shortcut because of time constraints you have to check that x is less than 5% of the initial concentration to get credit for that step.
Fri Jan 11, 2019 6:28 pm
Forum: Ideal Gases
Topic: Definition of Ideal Gases?
Replies: 3
Views: 100

### Re: Definition of Ideal Gases?

Ideal gases are all theoretical. They are made up of point-sized randomly moving particles whose interactions are perfectly elastic collisions, meaning no energy loss or gain occurs when the particles hit each other. Ideal gases also don't take into account intramolecular forces and volume created b...
Fri Jan 11, 2019 6:16 pm
Forum: Ideal Gases
Topic: Units
Replies: 19
Views: 370

### Re: Units

Yes, as people said before you should always use Kelvin. It is also important to note that you must match pressure units for whatever R constant you are using or else your answer will be incorrect. You can also convert to whatever units the question asks before plugging in your values to PV=nRT.
Fri Jan 11, 2019 6:12 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Kp vs Kc
Replies: 6
Views: 174

### Re: Kp vs Kc

Yes, Kc or Kp totally depends on the question you're asked. If the formula uses gases, use Kp for partial pressure instead of concentration. If you want to find Kc after, you have to a derivation of Kc in terms of Kp using PV=nRT.
Thu Jan 10, 2019 10:19 am
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Effects on Equilibrium
Replies: 2
Views: 101

### Re: Effects on Equilibrium

I believe that a temperature change can have the greatest effect on K. Also, the concentration of reactants and products and the pressure of the system can also affect K.