Search found 54 matches

by peteryim
Thu Mar 12, 2020 11:02 pm
Forum: Administrative Questions and Class Announcements
Topic: Final
Replies: 2
Views: 54

Re: Final

Professor Lavelle will release more information on the final shortly. Please stay calm and do not worry too much about it.
by peteryim
Thu Mar 12, 2020 11:00 pm
Forum: Balancing Redox Reactions
Topic: Determing balanced rxns for a basic solution
Replies: 5
Views: 105

Re: Determing balanced rxns for a basic solution

I think the method you're describing works. Basically, if you need to balance hydrogens on one side of the reaction, you add water to the side that needs hydrogens and an equal amount of hydroxide to the other side of the reaction. The hydroxide will cancel out everything in the water molecule excep...
by peteryim
Thu Mar 12, 2020 10:56 pm
Forum: Arrhenius Equation, Activation Energies, Catalysts
Topic: Activation Energy vs Free Energy of Activation
Replies: 6
Views: 76

Re: Activation Energy vs Free Energy of Activation

Activation energy is specific to a reaction. molecules will need to overcome an energy threshold to undergo the reaction. Free energy of activation refers to how much energy is available to cause a reaction to take place.
by peteryim
Thu Mar 12, 2020 10:55 pm
Forum: Arrhenius Equation, Activation Energies, Catalysts
Topic: Homework question 7.1
Replies: 2
Views: 62

Re: Homework question 7.1

Kinetic control v thermodynamic control refers to what process is dominating the reaction process, kinetics or thermodynamics. Kinetic control infers that the fastest reaction will be taking place, whereas thermodynamic control means the reaction that is the most energy conserving, I think.
by peteryim
Thu Mar 12, 2020 10:50 pm
Forum: Student Social/Study Group
Topic: final?
Replies: 7
Views: 203

Re: final?

I think Prof. Lavelle will give more details in days to come. I wouldn't worry about it too much though.
by peteryim
Sun Mar 08, 2020 10:48 pm
Forum: First Order Reactions
Topic: How does a first order reaction "collide" with itself? [ENDORSED]
Replies: 2
Views: 54

How does a first order reaction "collide" with itself? [ENDORSED]

Professor Lavelle said that the order of the reaction indicates how many molecules are colliding in the reaction. How does a first order reaction work, since one molecule cannot collide with itself?
by peteryim
Sun Mar 08, 2020 10:45 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: 6L.3
Replies: 4
Views: 59

Re: 6L.3

The right side of the diagram will be the cathode; it will be a reduction half reaction. Take whatever ions or substances are given, and make a reduction half reaction from them. The left side will be an anode; it will be an oxidation half reaction. Take whatever ions or substances are given, and ma...
by peteryim
Sun Mar 08, 2020 10:42 pm
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: Purpose of Nernst Equation
Replies: 5
Views: 35

Re: Purpose of Nernst Equation

The Nernst equation is used to find the cell potential of an electrochemical reaction that is not in equilibrium, but is in transit. Since you can plug in reaction quotient Q, you can determine the "weaker" cell potential, since the reaction has been going on for some time.
by peteryim
Sun Mar 08, 2020 10:40 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Speed of a reaction
Replies: 2
Views: 33

Re: Speed of a reaction

Is there a specific problem you are asking about?

The size of the rate law will generally tell you how fast the rate is relative to other rates.
by peteryim
Sun Mar 08, 2020 10:38 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: test 1
Replies: 2
Views: 35

Re: test 1

Use the pH to find concentration of H+ ions. That equals the concentration of conjugate base. You divide this concentration by the total concentration to get the percent ionized. To get Ka, use the formula [A-][H+]/[HA].
by peteryim
Mon Mar 02, 2020 12:31 am
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Electrolysis (6.O.1)
Replies: 3
Views: 51

Re: Electrolysis (6.O.1)

You can always look it up on google.
by peteryim
Mon Mar 02, 2020 12:30 am
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: concentration cell
Replies: 3
Views: 46

Re: concentration cell

Concentration cell is a different type of cell from the galvanic cell, since the same ion is on both side. However, the due to the concentration difference, which creates a different cell potential on each side, there is a flow of electrons, a current.
by peteryim
Mon Mar 02, 2020 12:29 am
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: cell diagrams
Replies: 1
Views: 17

Re: cell diagrams

In a cell diagram, you always put the cathode on the right side of the double lines, and the anode on the left side of the double lines. any phase change is separated by a single line. If there is no phase change, use commas.
by peteryim
Mon Mar 02, 2020 12:27 am
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: Nernst Equation Use
Replies: 3
Views: 56

Re: Nernst Equation Use

Use the Nernst equation to calculate cell potential in nonstandard conditions. Also, while the redox reaction is taking place.
by peteryim
Mon Mar 02, 2020 12:26 am
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: Nernst
Replies: 10
Views: 107

Re: Nernst

Remember that Q is the reaction quotient. (quo-tee-ent)
by peteryim
Mon Feb 24, 2020 12:00 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: surroundings
Replies: 4
Views: 117

Re: surroundings

When the reaction is reversible expansion, delta S total is zero. Thus, delta S surroundings = negative delta S system.
When reaction is irreversible free expansion, delta S total equals delta S of system, and delta S of surroundings is zero.
by peteryim
Sun Feb 23, 2020 11:58 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Electron Transfer
Replies: 3
Views: 38

Re: Electron Transfer

Electrons are too small and fast moving to be quantified, so they cannot be directly counted.
by peteryim
Sun Feb 23, 2020 11:57 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: gibbs free energy
Replies: 15
Views: 130

Re: gibbs free energy

You can think of Gibbs free energy as the energy level of reactants/products. If you think of a reaction curve where the reactants sit at a certain G and the products sit at another G, the difference between those energies will be delta G. If the reactants G are lower than products G then it will re...
by peteryim
Sun Feb 23, 2020 11:55 pm
Forum: Balancing Redox Reactions
Topic: Tips for Balancing Reactions
Replies: 3
Views: 45

Re: Tips for Balancing Reactions

Also, just adding onto the above point, if the solution is basic, then you can add OH- to the reactants. If acidic, you can add H+. It's really just trial and error until you make it work.
by peteryim
Sun Feb 23, 2020 11:49 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: cell potential
Replies: 3
Views: 37

Re: cell potential

Concentration tells you what direction the reaction will go in. If it is not going forward, then the cell will not be going forward.
by peteryim
Sun Feb 23, 2020 11:46 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: salt bridge
Replies: 9
Views: 82

Re: salt bridge

Adding on, the salt bridge consists of salts that will balance out the building charge of the anion and cation.
by peteryim
Sun Feb 23, 2020 11:45 pm
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: conducting solids
Replies: 5
Views: 57

Re: conducting solids

Examples of conducting solids are all transition metals and some metalloids. Non conducting solids are everything that is not in those two categories.
by peteryim
Sun Feb 16, 2020 1:47 pm
Forum: Balancing Redox Reactions
Topic: Number of electrons
Replies: 5
Views: 39

Re: Number of electrons

Just adding on, for the overall redox reaction, you usually wouldn't write the electrons, but in the reduction and oxidation half reactions you would.
by peteryim
Sun Feb 16, 2020 1:36 pm
Forum: Administrative Questions and Class Announcements
Topic: about the Midterm...
Replies: 8
Views: 158

Re: about the Midterm...

Hi Janet, I'm sorry you felt that way about the midterm. Honestly, sometimes tests are more about test taking than knowing the material. I know you probably did a lot of practice tests, but the only advice I can give is to do practice test. Finding previous midterms can be difficult, but is possible...
by peteryim
Sun Feb 16, 2020 1:32 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: relationship between delta G and K
Replies: 2
Views: 32

Re: relationship between delta G and K

at equilibrium, delta G = -RTlnK
by peteryim
Sun Feb 16, 2020 1:31 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: signs of G with different values of K
Replies: 3
Views: 33

Re: signs of G with different values of K

For the delta G equation at equilibrium, you take the natural log of K. If K is less than 1 but greater than 0 (so a fraction) then the value of the natural log will be a negative number. That's why it will be negative.
by peteryim
Sun Feb 16, 2020 1:29 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: maximum work
Replies: 5
Views: 86

Re: maximum work

That's my understanding of it. Max work only occurs in a theoretical scenario, as does most of thermodynamics and chemistry, because real life situations are too complicated.
by peteryim
Sun Feb 09, 2020 9:16 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Heat capacity
Replies: 2
Views: 26

Re: Heat capacity

Basically, you don't have to worry about the process of determining the heat capacity. Just worry about the heat capacity itself, which usually functions as a constant.
by peteryim
Sun Feb 09, 2020 9:14 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: constant p
Replies: 4
Views: 43

Re: constant p

This is the equation for change in enthalpy at constant pressure. At constant pressure, delta H is equal to the heat.
by peteryim
Sun Feb 09, 2020 9:14 pm
Forum: Ideal Gases
Topic: Gas constant
Replies: 10
Views: 115

Re: Gas constant

It depends on the units of the other measurements given.
by peteryim
Sun Feb 09, 2020 9:13 pm
Forum: Thermodynamic Systems (Open, Closed, Isolated)
Topic: problem 4A9
Replies: 2
Views: 44

Re: problem 4A9

So the q of the copper is equal to the - q of the water. Just set them equal to each other, then plug in all the variables you know. Since you don't know the final temperature, plug that in as a variable. Since the final temperature will be the same for both materials, you use -q(cu) = q(h2o) to sol...
by peteryim
Sun Feb 09, 2020 9:11 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Is heat capacity an extensive or intensive property?
Replies: 2
Views: 24

Re: Is heat capacity an extensive or intensive property?

Heat capacity is intensive. It does not matter what quantity is there, the heat capacity stays the same.
by peteryim
Sun Feb 02, 2020 10:13 pm
Forum: Calculating Work of Expansion
Topic: Integral Calculations
Replies: 3
Views: 52

Re: Integral Calculations

You're right, integrals are used to quickly find the sum of an infinite number of sums. I don't think Lavelle has given us any problems that require us to use it yet...
by peteryim
Sun Feb 02, 2020 10:12 pm
Forum: Phase Changes & Related Calculations
Topic: Pressure in an Open Beaker
Replies: 10
Views: 84

Re: Pressure in an Open Beaker

If it says the surroundings are at standard temp and pressure it would be 1atm. If it's not specified, then you probably don't need the specific pressure to solve the problem.
by peteryim
Sun Feb 02, 2020 10:08 pm
Forum: Calculating Work of Expansion
Topic: Enthalpy
Replies: 5
Views: 29

Re: Enthalpy

State functions can be contrasted with path functions, where the pathway to the current state does matter. Compared to those, state functions do not rely on the pathway, so yes, can be added or subtracted simply.
by peteryim
Sun Feb 02, 2020 9:59 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: Degeneracy
Replies: 4
Views: 31

Re: Degeneracy

Degenerate describes states that have the same energy level, but different positions/configurations. For example, the three p-orbitals of a given energy level are degenerate. Calculating it is complicated because it depends on the number of particles and the types of particles in the system.
by peteryim
Sun Feb 02, 2020 9:55 pm
Forum: Phase Changes & Related Calculations
Topic: Pressure in an Open Beaker
Replies: 10
Views: 84

Re: Pressure in an Open Beaker

An open beaker has constant pressure because you are assuming the only pressure acting upon it is air pressure, which will be uniform on the contents of the beaker.
by peteryim
Sun Jan 26, 2020 5:21 pm
Forum: Phase Changes & Related Calculations
Topic: State Properties
Replies: 3
Views: 29

Re: State Properties

It's any quantity that is independent of how the substance was prepared.
by peteryim
Sun Jan 26, 2020 5:20 pm
Forum: Phase Changes & Related Calculations
Topic: State Properties
Replies: 3
Views: 29

Re: State Properties

Pressure, volume, temperature, enthalpy.
by peteryim
Sun Jan 26, 2020 5:19 pm
Forum: Non-Equilibrium Conditions & The Reaction Quotient
Topic: Kw Equations
Replies: 10
Views: 152

Re: Kw Equations

Also, keep in mind that although:

[Ka][Kb] = Kw and [H3O+][OH-] = Kw

[Ka] != [H3O+] and [Kb] != [OH-]
by peteryim
Sun Jan 26, 2020 5:15 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Bond Enthalpies
Replies: 2
Views: 18

Re: Bond Enthalpies

Yes, if 2 bonds of C-H were formed, multiply by 2. Coefficients do matter, a lot. Make sure the equation is balanced.
by peteryim
Sun Jan 26, 2020 5:14 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Bond Enthalpies
Replies: 2
Views: 18

Re: Bond Enthalpies

Enthalpies should be given. It is hard to determine them on your own. And you will need to know number of bonds broken and formed for the second method that Dr. Lavelle mentioned in class.
by peteryim
Sun Jan 26, 2020 5:13 pm
Forum: Phase Changes & Related Calculations
Topic: Combustion vs. Cellular Respiration
Replies: 5
Views: 67

Re: Combustion vs. Cellular Respiration

Technically, since energy is conserved, the change in overall free energy would be the same. However, there are many other factors that come into play, such as entropy.
by peteryim
Sun Jan 26, 2020 5:05 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Standard enthalpy of solids and liquids
Replies: 2
Views: 22

Re: Standard enthalpy of solids and liquids

Enthalpy of formation will depend on the substance you are working with. But yes, it is standard for each substance.
by peteryim
Sun Jan 19, 2020 11:06 pm
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: Conjugates
Replies: 2
Views: 32

Re: Conjugates

Conjugates are also good to know for weak acids and bases; the conjugates tell you which reactant/products are related in the equation.
by peteryim
Sat Jan 18, 2020 5:27 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Acids and Bases Ice Box
Replies: 5
Views: 55

Re: Acids and Bases Ice Box

In summary of the above comments, using Ka or Kb is situational. However, many times the question will give you the constant that you need to answer the question.
by peteryim
Sat Jan 18, 2020 5:25 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: 6B. 9 Solutions Typo
Replies: 1
Views: 27

Re: 6B. 9 Solutions Typo

The solution manual is correct for these. Make sure you are using the equation 1.0 x 10^-14 = [H3O+][OH-]
by peteryim
Sat Jan 18, 2020 5:20 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: 6D. 7
Replies: 3
Views: 42

Re: 6D. 7

I'm not really sure what this question is asking, but I don't think you need Ka or Kb. It looks like the questions just wants you to convert pH into concentration of [H3O+].
by peteryim
Thu Jan 16, 2020 3:09 am
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: Endothermic/Exothermic Rxns and Delta H
Replies: 3
Views: 117

Re: Endothermic/Exothermic Rxns and Delta H

As for the first part of the question, photosynthesis is not an exothermic reaction in the forward direction, because exothermic implies that the reaction is spontaneous, and the products have a lower free energy than the reactants. However, CO2 and H2O have less free energy than a large molecule li...
by peteryim
Sun Jan 12, 2020 5:28 pm
Forum: Non-Equilibrium Conditions & The Reaction Quotient
Topic: Reaction Q
Replies: 7
Views: 74

Re: Reaction Q

To clarify further upon Anna's comment, when the forward reaction is favored, more products will be created, and the concentration of products will grow. If the reverse reaction is favored, more reactants will be created, and the concentration of reactants will increase. Q is relevant because it com...
by peteryim
Sun Jan 12, 2020 5:24 pm
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: Le Chatelier's Principle
Replies: 5
Views: 69

Re: Le Chatelier's Principle

Le Chatelier's Principle applies fundamentally to changes in temperature, pressure, or concentration. Changing other physical parameters will matter when they affect these three factors. For example, changing the volume of the container in which the reaction takes place effects the concentration of ...
by peteryim
Wed Jan 08, 2020 11:47 am
Forum: Non-Equilibrium Conditions & The Reaction Quotient
Topic: N2O4 <--> 2NO2, color?
Replies: 3
Views: 50

N2O4 <--> 2NO2, color?

Professor Lavelle mentioned this reaction in class. Apparently, nitrogen dioxide is the gas that gives smog its yellowish color, because as a gas it appears yellow to brown. Interesting!
by peteryim
Tue Jan 07, 2020 4:38 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: 5G.11
Replies: 3
Views: 57

Re: 5G.11

For substances that are aqueous (aq), simply plug the concentration (n/V) of that substance at equilibrium into the equation for K.
by peteryim
Mon Jan 06, 2020 7:13 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Equilibrium constant v. Reaction quotient
Replies: 3
Views: 55

Equilibrium constant v. Reaction quotient

What exactly is the difference between an equilibrium constant and a reaction quotient? The textbook said that the reaction quotient can be used for any stage of the reaction, and it accounts for free energy, but I am confused as to how exactly it does this.

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