Search found 17203 matches

by Chem_Mod
Sun Mar 17, 2019 12:58 am
Forum: Biological Examples
Topic: atp example
Replies: 1
Views: 45

Re: atp example

This is much more biological, but in relatively simple terms, the energy created by breaking the H off of NADH is used to drive the ATP reaction. :)
by Chem_Mod
Sun Mar 17, 2019 12:54 am
Forum: First Order Reactions
Topic: rate law
Replies: 2
Views: 53

Re: rate law

Once you calculate all the orders of the reactants, you would use this along with the rate of the reaction and initial concentrations of those reactants in order to calculate your rate constant, k. :)
by Chem_Mod
Sun Mar 17, 2019 12:49 am
Forum: Calculating Standard Reaction Entropies (e.g. , Using Standard Molar Entropies)
Topic: molar mass
Replies: 2
Views: 74

Re: molar mass

It might be because you may need to use the molar heat capacity in several of the entropy formulas. When using the molar heat capacity for a substance in these equations, you must be able to convert the substance's mass into moles. :)
by Chem_Mod
Sun Mar 17, 2019 12:46 am
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Reversible vs irreversible
Replies: 1
Views: 52

Re: Reversible vs irreversible

During a reversible expansion, typically a force must be applied for a longer period of time since during a slow reversible expansion, at every point in the expansion, the internal pressure of the confined gas must be equal to the external pressure of the surrounding gas(es). During an irreversible ...
by Chem_Mod
Sun Mar 17, 2019 12:41 am
Forum: Kinetics vs. Thermodynamics Controlling a Reaction
Topic: trials
Replies: 2
Views: 57

Re: trials

You set up the rate law expressions for the different experiments and then you divide one rate law expression by another rate law expression in order to cancel out terms and get only one exponent that you can solve for, using logarithms if necessary. These exponents are the orders. :)
by Chem_Mod
Sun Mar 17, 2019 12:34 am
Forum: Ideal Gases
Topic: ideal gases
Replies: 1
Views: 46

Re: ideal gases

For monoatomic ideal gases, a change could be occurring under the conditions of constant pressure or constant volume. Based on the degrees of freedom for the atoms under constant pressure or constant volume, we'll see that the heat capacity values will be different for constant pressure and constant...
by Chem_Mod
Sun Mar 17, 2019 12:31 am
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: specific heat
Replies: 1
Views: 41

Re: specific heat

The specific heat technically changes with temperature; however, you do not need to concern yourself with these changes for the final exam. For all intensive purposes, yes, the specific heat for a given chemical species will be a fixed value. :)
by Chem_Mod
Sun Mar 17, 2019 12:28 am
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: salt bridge
Replies: 4
Views: 95

Re: salt bridge

The main function of the salt bridge is to prevent charge build-up. :)
by Chem_Mod
Sun Mar 17, 2019 12:24 am
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: porous disk
Replies: 2
Views: 67

Re: porous disk

The porous disk serves the same function as the salt bridge (prevent charge build-up). :)
by Chem_Mod
Sun Mar 17, 2019 12:22 am
Forum: Second Order Reactions
Topic: k'
Replies: 1
Views: 46

Re: k'

You can typically use k' for any step in a multi-step mechanism. When you use k1', it is the symbol for the rate constant of the reverse reaction for step 1 of the mechanism. :)
by Chem_Mod
Sun Mar 17, 2019 12:19 am
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Liquids and Solids
Replies: 2
Views: 53

Re: Liquids and Solids

For K and Q, you are typically using the concentrations or partial pressures of the chemical species to write those expressions. But it's very difficult to define or even measure the concentrations or partial pressures of pure solids and pure liquids. It's much clearer how to measure the concentrati...
by Chem_Mod
Sun Mar 17, 2019 12:05 am
Forum: Balancing Redox Reactions
Topic: Balancing reaction in basic medium
Replies: 1
Views: 48

Re: Balancing reaction in basic medium

In this case, the P4 has an oxidation state (charge) of zero. On the right side, the P in H2PO2- will get an oxidation state of +1 and the P in PH3 will get an oxidation state of -3. So, P4 would be used as the reactant in both the oxidation and the reduction half reactions. From there, you will fol...
by Chem_Mod
Sat Mar 16, 2019 11:55 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: bomb calorimeter
Replies: 6
Views: 141

Re: bomb calorimeter

A bomb calorimeter is a closed system since it can't absorb or release energy from/to the surroundings and it also can't gain or lose mass to the surroundings. :)
by Chem_Mod
Sat Mar 16, 2019 11:53 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: K
Replies: 3
Views: 60

Re: K

Capital K is the equilibrium constant. It represents the value you get when you divide concentrations of the product(s) by the concentrations of the reactant(s) once the chemical reaction has reached a state of chemical equilibrium. :)
by Chem_Mod
Sat Mar 16, 2019 11:50 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: Deriving Enthalpy Equations
Replies: 3
Views: 74

Re: Deriving Enthalpy Equations

You probably won't have to worry about deriving equations on the exam. :)
by Chem_Mod
Sat Mar 16, 2019 11:48 pm
Forum: *Enzyme Kinetics
Topic: Elementary Steps
Replies: 1
Views: 42

Re: Elementary Steps

I think what you're referring to is that when you have to calculate the E value for a reaction like this: Ti +4 + 2e- -> Ti +2 , you cannot simply add the E values for the reactions Ti +4 + e- -> Ti +3 and Ti +3 + e- -> Ti +2 . The details about why this happens aren't too important, but this is a g...
by Chem_Mod
Sat Mar 16, 2019 11:34 pm
Forum: Second Order Reactions
Topic: Half Life
Replies: 5
Views: 129

Re: Half Life

While the formula sheets vary from year to year, it's likely that if these half-life equations were on the most recent exam, they will be on the final exam formula sheet. :)
by Chem_Mod
Sat Mar 16, 2019 11:31 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: pseudo rate reactions
Replies: 2
Views: 66

Re: pseudo rate reactions

Not quite, because k1' can represent the rate constant of the reverse reaction for step 1 in a mechanism. But, k' in pseudo rate kinetics often will be equal to k*[some reactant]. :)
by Chem_Mod
Sat Mar 16, 2019 11:27 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: unique rate law and reaction mechanisms?
Replies: 1
Views: 60

Re: unique rate law and reaction mechanisms?

One could set the unique rate of reaction equal to the rate law derived from a mechanism since both are mathematical expressions of the overall rate of the reaction. :)
by Chem_Mod
Sat Mar 16, 2019 11:23 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Elementary Rxns
Replies: 2
Views: 58

Re: Elementary Rxns

If and only if that particular reaction is an elementary reaction (meaning it's a reaction for one step in a mechanism), then yes, the coefficients in the balanced chemical equation will become the orders of those reactants. :)
by Chem_Mod
Sat Mar 16, 2019 11:22 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: standard cell potential and free energy
Replies: 3
Views: 69

Re: standard cell potential and free energy

Turns out that Gibbs free energy is an extensive property. :)
by Chem_Mod
Sat Mar 16, 2019 11:20 pm
Forum: Method of Initial Rates (To Determine n and k)
Topic: Week 9 Worksheet (2E,I,K)
Replies: 13
Views: 753

Re: Week 9 Worksheet (2E,I,K)

I think this may be due to you using log instead of ln? On the equations sheet for the nearest equation they use ln. Which should we use? Hi Elle, You can use both. Please be aware that the difference is 0.0592 for log and 0.0257 for ln. If you plug in the number into two equations (in attachment),...
by Chem_Mod
Sat Mar 16, 2019 11:16 pm
Forum: Arrhenius Equation, Activation Energies, Catalysts
Topic: Arrhenius equation
Replies: 2
Views: 62

Re: Arrhenius equation

Activation energy is the delta G value between a reactant and a transition state. So you could say that the delta G for the overall reaction = delta H of the reaction - T*(delta S of the reaction). But otherwise, there isn't an equation which relates the activation energy and delta H. :)
by Chem_Mod
Sat Mar 16, 2019 11:12 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Porous Disk vs Salt Bridge
Replies: 3
Views: 65

Re: Porous Disk vs Salt Bridge

The reason isn't too important. What's important is that you know that for a galvanic cell, the notation for a porous disk is a single vertical line and the notation for a salt bridge is 2 vertical lines. :)
by Chem_Mod
Sat Mar 16, 2019 11:07 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Enthalpy of Fusion
Replies: 1
Views: 48

Re: Enthalpy of Fusion

Yes, it's definitely good to know about the enthalpies associated with the phase changes (melting, boiling, freezing, etc.). :)
by Chem_Mod
Sat Mar 16, 2019 10:52 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: UNITS
Replies: 2
Views: 63

Re: UNITS

The units for deltaS is units J/K
by Chem_Mod
Sat Mar 16, 2019 10:50 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: units
Replies: 1
Views: 48

Re: units

Delta H is typically in joules or joules/mole
by Chem_Mod
Sat Mar 16, 2019 10:49 pm
Forum: Arrhenius Equation, Activation Energies, Catalysts
Topic: Arrhenius Equation
Replies: 3
Views: 59

Re: Arrhenius Equation

A is the pre-exponential or frequency factor which essentially gives you the proportion of reactants that collide in the correct orientation and with enough energy in order to form products.
by Chem_Mod
Sat Mar 16, 2019 10:48 pm
Forum: Method of Initial Rates (To Determine n and k)
Topic: Units and order
Replies: 1
Views: 44

Re: Units and order

Yes you can solve for the units of the rate constant k because you know that the units for rate is molarity/second and the units for concentration is molarity, therefore the units for the rate constant k changes depending on the exponent of the concentration.
by Chem_Mod
Sat Mar 16, 2019 10:46 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: units
Replies: 1
Views: 50

Re: units

It's either in Joules or Joules/mole
by Chem_Mod
Sat Mar 16, 2019 10:46 pm
Forum: Arrhenius Equation, Activation Energies, Catalysts
Topic: Catalyst in molecularity
Replies: 1
Views: 42

Re: Catalyst in molecularity

Molecularity is calculated by the number of molecules that must react with each other in order to form your products. Important thing to note is to realize that the stoichiometric coefficients must be accounted for in calculating molecularity.
by Chem_Mod
Sat Mar 16, 2019 10:42 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: ln k and 1/t
Replies: 3
Views: 64

Re: ln k and 1/t

What profile are you talking about. Are you referring to the rate law plots?
by Chem_Mod
Sat Mar 16, 2019 10:37 pm
Forum: Thermodynamic Definitions (isochoric/isometric, isothermal, isobaric)
Topic: when is w=0 and when is q=0?
Replies: 1
Views: 59

Re: when is w=0 and when is q=0?

Work is 0 when there is no change in volume (isochoric). Heat is 0 for an adiabatic process, which will usually be explicitly stated.
by Chem_Mod
Sat Mar 16, 2019 10:33 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Bond enthalpy
Replies: 2
Views: 54

Re: Bond enthalpy

Sum of bonds broken - sum of bonds formed because this is essentially the amount of energy you are putting into the system to break bonds - the amount of energy that is released by the formation of new bonds.
by Chem_Mod
Sat Mar 16, 2019 10:29 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Drawing cells
Replies: 3
Views: 77

Re: Drawing cells

In general, you want to include the anode, cathode, ions, salt bridge, and direction the electrons are traveling.
by Chem_Mod
Sat Mar 16, 2019 9:19 pm
Forum: Administrative Questions and Class Announcements
Topic: Saying Thank You to Dr. Lavelle
Replies: 202
Views: 48181

Re: Saying Thank You to Dr. Lavelle

Thank you all your thoughtful and encouraging messages.

Posting that video was great!

A Big Thank You for the Valentine Cappella.
A first and most appreciated.

Great Quarter!
Great Classes!
by Chem_Mod
Sat Mar 16, 2019 9:07 pm
Forum: Student Social/Study Group
Topic: class pictures
Replies: 15
Views: 842

Re: class pictures

WOW.

Many great photos!
:-)

Many Thanks to All!

You Rock!
by Chem_Mod
Sat Mar 16, 2019 7:50 pm
Forum: First Order Reactions
Topic: Clarification
Replies: 2
Views: 51

Re: Clarification

I am not sure what you are referring to.
by Chem_Mod
Sat Mar 16, 2019 7:47 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Standard of Formation
Replies: 1
Views: 45

Re: Standard of Formation

It will be clear what the constants that you are given represent.
by Chem_Mod
Sat Mar 16, 2019 7:45 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: HW 4A.11
Replies: 1
Views: 50

Re: HW 4A.11

Kelvin is the standard unit for temperature. As a good rule of thumb always have your temperature be in Kelvin.
by Chem_Mod
Sat Mar 16, 2019 7:43 pm
Forum: Balancing Redox Reactions
Topic: 6th edition 14.5
Replies: 2
Views: 47

Re: 6th edition 14.5

Please be more specific. Post the problem and part you are stuck on.
by Chem_Mod
Sat Mar 16, 2019 7:42 pm
Forum: Phase Changes & Related Calculations
Topic: heat capacity of an object
Replies: 3
Views: 68

Re: heat capacity of an object

Heat capacity are in those units so that you can multiply it by whatever the mass of your total object is giving you the heat capacity for that object or piece of matter.
by Chem_Mod
Sat Mar 16, 2019 7:41 pm
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: Ka and K
Replies: 1
Views: 36

Re: Ka and K

Ka and K are the same thing. Ka is just the equilibrium constant for an a reaction in which an acid is reacting.
by Chem_Mod
Sat Mar 16, 2019 7:39 pm
Forum: Calculating Standard Reaction Entropies (e.g. , Using Standard Molar Entropies)
Topic: Delta S=0 for elemental molecules?
Replies: 1
Views: 42

Re: Delta S=0 for elemental molecules?

The entropy of formation is 0 because they are elemental molecules, meaning this is how they are found in nature, therefore there is no entropy change associated with them being formed.
by Chem_Mod
Sat Mar 16, 2019 7:36 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Reaction Profiles
Replies: 1
Views: 30

Re: Reaction Profiles

For endergonic reactions the reactant has a lower Gibb's free energy value than the products, which makes sense because when you take the gibb's free energy of the products - reactants you get a positive change in gibb's free energy. For an exergonic reaction, the reactants have a higher gibb's free...
by Chem_Mod
Sat Mar 16, 2019 7:32 pm
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: Changes in Concentration
Replies: 2
Views: 60

Re: Changes in Concentration

Le Chatelier's Principle states that the reaction will lean toward the side that opposes the change that has just occurred. For example, if you increase products then the reaction will lean to the left and products will turn into reactants, decreasing products. If you decrease products, the reaction...
by Chem_Mod
Sat Mar 16, 2019 7:30 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Equilibrium constant from G
Replies: 1
Views: 43

Re: Equilibrium constant from G

It comes from the equation
When the reaction is at equilibrium is equal to 0 and Q turns into K.
by Chem_Mod
Sat Mar 16, 2019 7:25 pm
Forum: Student Social/Study Group
Topic: Final Jitters
Replies: 6
Views: 1403

Re: Final Jitters

These are some great tips! Some things I would add: 1) If you ever run into a question you have no idea how to tackle, think about the concept it's trying to test. Try to note anything that you remember about that concept. Usually that tells yourself that you do know something. It just may take some...
by Chem_Mod
Sat Mar 16, 2019 7:24 pm
Forum: Arrhenius Equation, Activation Energies, Catalysts
Topic: 7E3 7th edition
Replies: 2
Views: 41

Re: 7E3 7th edition

Please be more specific, posting the problem would be very helpful.
by Chem_Mod
Sat Mar 16, 2019 7:22 pm
Forum: Student Social/Study Group
Topic: Midterm
Replies: 2
Views: 73

Re: Midterm

I do not believe Dr. Lavelle stated the average.
by Chem_Mod
Sat Mar 16, 2019 7:21 pm
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: Ka stuff
Replies: 2
Views: 63

Re: Ka stuff

HA and A- are just examples of an acid/base reaction, where HA is any acid and A- is its conjugate base. Know that Ka and Kb are the equilibrium constants for acids and bases respectively and that strong acids/bases do not have Ka/Kb because they dissociate completely.
by Chem_Mod
Sat Mar 16, 2019 7:19 pm
Forum: Calculating Work of Expansion
Topic: 7th Edition, 4.B.13
Replies: 2
Views: 48

Re: 7th Edition, 4.B.13

When the pressure is constant the work does not equal the change in volume. The equation for an irreversible expansion is W=-nRTln(V2/V1).
by Chem_Mod
Sat Mar 16, 2019 7:13 pm
Forum: Arrhenius Equation, Activation Energies, Catalysts
Topic: 7th Edition 7D.5
Replies: 3
Views: 60

Re: 7th Edition 7D.5

Hi Whitney,

You are absolutely correct. That negative should be an equal's sign. Good job!
by Chem_Mod
Sat Mar 16, 2019 5:04 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Intermediates
Replies: 1
Views: 39

Re: Intermediates

In mechanisms, intermediates are chemicals introduced to us as products and then used up as reactants in later mechanism steps. For example:

A + B -> C + D
C + E -> F
D + G -> H

In this scenario, C and D are the only intermediates.

Hope this helps! :)
by Chem_Mod
Sat Mar 16, 2019 5:02 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: Heat and Entropy
Replies: 2
Views: 45

Re: Heat and Entropy

Most likely, that would be true. I'm sure other factors are involved, but if heat is transferred from the surroundings to the system, since S = q rev/T, we'd probably expect an increase in entropy (disorder). :)
by Chem_Mod
Sat Mar 16, 2019 4:52 pm
Forum: Ideal Gases
Topic: Bar for partial pressure [ENDORSED]
Replies: 4
Views: 83

Re: Bar for partial pressure [ENDORSED]

You can treat bar and atm as almost the same thing, but if you want to be super safe, you can use that conversion factor to convert atmospheres into units of bar. :)
by Chem_Mod
Sat Mar 16, 2019 4:47 pm
Forum: General Rate Laws
Topic: H.W. Problem 15.17
Replies: 5
Views: 80

Re: H.W. Problem 15.17

In general, it's a good idea to start with the pairs of experiments where only one reactant's concentration is changing while the other concentrations are held constant. Looking at experiments 1 and 2, we see that both [A] and [C] are changing.

Hope this helps! :)
by Chem_Mod
Sat Mar 16, 2019 4:36 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Rate determining step & overall rate law
Replies: 1
Views: 42

Re: Rate determining step & overall rate law

In the case where the first step of the mechanism is the rate determining step, then yes. But in other cases, that's probably not going to be true because other k terms will be introduced if you have to use the pre-equilibrium approach to get rid of intermediate terms in the overall rate law express...
by Chem_Mod
Sat Mar 16, 2019 4:26 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: Monoatomic Gas
Replies: 3
Views: 65

Re: Monoatomic Gas

A monoatomic ideal gas can be under conditions of constant T, constant P, and/or constant V, depending on the system presented to you. A monoatomic ideal gas is just an ideal gas (obeys PV = nRT) which has only 1 atom (Ne (g), Ar (g), etc.)

Hope this helps! :)
by Chem_Mod
Sat Mar 16, 2019 4:20 pm
Forum: First Order Reactions
Topic: deriving integrated forms
Replies: 1
Views: 48

Re: deriving integrated forms

You most likely won't be asked to derive the integrated rate laws on the final exam.

Cheers! :)
by Chem_Mod
Sat Mar 16, 2019 4:13 pm
Forum: Calculating pH or pOH for Strong & Weak Acids & Bases
Topic: Test 1 problem 5
Replies: 6
Views: 112

Re: Test 1 problem 5

You'd do an ICE table with this reaction C3H5O2-(aq) + H20(l) --> C3H6O2(aq) + OH-(aq) You'd plug in the initial concentration of C3H5O2- to be 0.02 M and you'd solve for the Kb of C3H5O2- using Ka*Kb = 10^-14. Once you solve for x, x will be the [OH-]. Taking the negative log of [OH-] will give you...
by Chem_Mod
Sat Mar 16, 2019 4:06 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Rate Law with Intermediates
Replies: 1
Views: 37

Re: Rate Law with Intermediates

Typically you can create a new rate constant which includes several k terms in it. For example, let's say you get rate = k 1 k 2 [OH-][KCl]/k -1 k -2 [PCl3], you can simplify this equation to being rate = k'[OH-][KCl]/[PCl3] if you write, "k' = k 1 k 2 /k -1 k -2 " Hope this helps! :)
by Chem_Mod
Sat Mar 16, 2019 3:57 pm
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: Vant Hoff equation on formula sheet
Replies: 6
Views: 157

Re: Vant Hoff equation on formula sheet

The formula sheets can vary from exam to exam, so your best bet is to probably do enough problems with the Vant Hoff equation so it's very familiar to you for the next exam.

Cheers! :)
by Chem_Mod
Sat Mar 16, 2019 3:50 pm
Forum: Balancing Redox Reactions
Topic: multiplying half reactions [ENDORSED]
Replies: 4
Views: 57

Re: multiplying half reactions [ENDORSED]

You would not multiply the cell potential by that same factor. So for example, Ag+1 + e- -> Ag has a standard E value of 0.8 V.

If I were to multiply it by 3, giving me 3Ag+1 + 3e- -> 3Ag, this reaction would also have a standard E value of 0.8 V.

Hope this helps! :)
by Chem_Mod
Sat Mar 16, 2019 3:45 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: standard cell potentials
Replies: 5
Views: 56

Re: standard cell potentials

Standard cell potentials do not have to be positive, but when a cell potential is positive, then, the delta G value is going to be negative which results in the cell reaction being spontaneous.

Hope this helps! :)
by Chem_Mod
Sat Mar 16, 2019 3:42 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Porous Disk vs Salt Bridge
Replies: 2
Views: 43

Re: Porous Disk vs Salt Bridge

The porous disk and salt bridge essentially serve the same function. That being said, when using a porous disk, in the cell diagram, you would show the porous disk with one line "|" while you would show a salt bridge using 2 lines "||"

Hope this helps! :)
by Chem_Mod
Sat Mar 16, 2019 3:38 pm
Forum: Balancing Redox Reactions
Topic: cell diagram
Replies: 3
Views: 63

Re: cell diagram

You would add Pt (s) when either the oxidation and/or reduction reaction does not have a pure metal solid in the reaction. So for example, if the oxidation reaction was Fe2+ -> Fe3+ + e-, then you would have to add Pt (s) on the left-most side of the cell diagram.

Hope this helps! :)
by Chem_Mod
Sat Mar 16, 2019 3:33 pm
Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
Topic: e- transfer
Replies: 1
Views: 47

Re: e- transfer

By measuring the E (potential) for the anode and adding it to the E for the cathode, you will get the E for the redox reaction produced. The E for the anode and cathode can be measured by using a reference electrode such as the Standard Hydrogen Electrode (SHE). Typically, the E can be measured usin...
by Chem_Mod
Sat Mar 16, 2019 3:24 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: Midterm Question 6
Replies: 6
Views: 90

Re: Midterm Question 6

Please, provide the full question when possible since we don't have full access to the midterms.

Thanks in advance! :)
by Chem_Mod
Sat Mar 16, 2019 3:18 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Reaction Mechanisms without unknown rate-determining step
Replies: 2
Views: 43

Re: Reaction Mechanisms without unknown rate-determining step

If a mechanism is provided, but there isn't enough information given to figure out which step is slow and which step(s) are fast, then there isn't enough information to be able to solve for the rate law of this reaction mechanism.

Hope this helps! :)
by Chem_Mod
Sat Mar 16, 2019 3:13 pm
Forum: First Order Reactions
Topic: half life
Replies: 3
Views: 62

Re: half life

The half-life equations are derived using the integrated rate law formulas by setting the final concentration equal to half the initial concentration and solving for time (t). When deriving the half-life equation for the 1st order reactions, the initial concentration terms will cancel out. However, ...
by Chem_Mod
Sat Mar 16, 2019 3:06 pm
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: Nernst equation
Replies: 1
Views: 35

Re: Nernst equation

Eo are the standard reduction potential values that are typically given as constants. At equilibrium E is = 0 because there is no net transfer of electrons, which is how you go from the first equation to the second.
by Chem_Mod
Sat Mar 16, 2019 3:05 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: delta s
Replies: 2
Views: 56

Re: delta s

When delta S total is positive, the process is spontaneous. This means that if the delta S total is negative, then the process is not spontaneous. When bonds are formed, the delta S total is typically negative since forming bonds usually decreases the amount of disorder (entropy) overall. This is be...
by Chem_Mod
Sat Mar 16, 2019 2:59 pm
Forum: Arrhenius Equation, Activation Energies, Catalysts
Topic: Question 15.79 (Sixth Edition)
Replies: 1
Views: 37

Re: Question 15.79 (Sixth Edition)

If the product that is formed due to the faster reaction is under kinetic control then that is the reaction with a lower activation energy. We know this because lower activation energy means higher reaction rate. Kinetic control predominates at lower temperature because due to the lack of sufficient...
by Chem_Mod
Sat Mar 16, 2019 2:50 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: 14.3c, 6th edition
Replies: 1
Views: 30

Re: 14.3c, 6th edition

The products are H+1 and Cl-1 because we know that HCl dissolves in an aqueous solution. To answer your second question, you add a solid such as Pt when there is no solid present to facilitation the transfer of electrons.
by Chem_Mod
Sat Mar 16, 2019 2:49 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Week 10 Discussion Notes (2E,2I,2K)
Replies: 6
Views: 263

Re: Week 10 Discussion Notes (2E,2I,2K)

Hi, does anyone know why delta H was 300 and not -300 when calculating the reverse activation energy? Didn't they give it as -300, and it's an exothermic reaction so deltaH should be negative? For the reverse reaction, new delta H = - delta H. The forward reaction is exothermic and delta H = -300, ...
by Chem_Mod
Sat Mar 16, 2019 2:48 pm
Forum: Calculating pH or pOH for Strong & Weak Acids & Bases
Topic: justified approximation
Replies: 1
Views: 49

Re: justified approximation

I am not sure what you are referring to when you say second ionization but if you are referring to the second ionization for a diprotic or polyprotic acid we can, for the most part, ignore it because the amount of hydronium (H +1 ) produced from the first deprotonation is significantly greater than ...
by Chem_Mod
Sat Mar 16, 2019 2:41 pm
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: Reducing Power and Oxidation Power
Replies: 1
Views: 33

Re: Reducing Power and Oxidation Power

Reducing power is the ability of a substance to reduce another substance. Therefore, in order for something to have high reducing power it itself must easily be oxidized. Thus, the relationship is as reducing power increases, reduction potential (desire to gain electrons) decreases. Oxidizing power ...
by Chem_Mod
Sat Mar 16, 2019 2:39 pm
Forum: Arrhenius Equation, Activation Energies, Catalysts
Topic: Homogenous/Heterogeneous Catalysts
Replies: 2
Views: 46

Re: Homogenous/Heterogeneous Catalysts

In terms of the difference between the two, understand that a homogenous catalyst is more effective because it mixes much better with your reactants. This makes sense if you think about liquid reactants mixing with a liquid catalyst as opposed to liquid reactants interacting with a solid catalyst. T...
by Chem_Mod
Sat Mar 16, 2019 2:36 pm
Forum: Arrhenius Equation, Activation Energies, Catalysts
Topic: 7th Edition 7D.5
Replies: 3
Views: 60

Re: 7th Edition 7D.5

Please post the entire problem.
by Chem_Mod
Sat Mar 16, 2019 2:35 pm
Forum: First Order Reactions
Topic: ln
Replies: 1
Views: 42

Re: ln

No, taking the natural log of a number with units will lead to an answer without units.
by Chem_Mod
Sat Mar 16, 2019 2:33 pm
Forum: Arrhenius Equation, Activation Energies, Catalysts
Topic: Homework 7E3
Replies: 1
Views: 33

Re: Homework 7E3

Please post the entire problem
by Chem_Mod
Sat Mar 16, 2019 2:32 pm
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: 6N.3c Cell Potential
Replies: 1
Views: 23

Re: 6N.3c Cell Potential

The left side of this cell notation is the anode and the right side is the cathode. This applies for all cell notations.
by Chem_Mod
Sat Mar 16, 2019 2:30 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: K
Replies: 1
Views: 22

Re: K

K represents the equilibrium constant
by Chem_Mod
Sat Mar 16, 2019 2:18 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: 5.35
Replies: 3
Views: 80

Re: 5.35

So the reason why they divide by 100 is to convert kPa into atm. We do this because atm is the standard unit when calculating Kp, and if we used kPa, it would deviate from the expected answer.
by Chem_Mod
Sat Mar 16, 2019 1:14 pm
Forum: Ideal Gases
Topic: Bar for partial pressure [ENDORSED]
Replies: 4
Views: 83

Re: Bar for partial pressure [ENDORSED]

Yes, bar is the standard unit for partial pressure in K calculation
by Chem_Mod
Sat Mar 16, 2019 12:41 pm
Forum: Administrative Questions and Class Announcements
Topic: LYNDON'S PORK RAMEN REVIEW
Replies: 37
Views: 2254

Re: LYNDON'S PORK RAMEN REVIEW

I do not have an answer key made to be able to post anything. In addition, many of the questions involve drawing or explaining and I unfortunately do not have the time to make an adequate postable key. During my session, I will ask for some neat note-takers to post their notes here though.
by Chem_Mod
Sat Mar 16, 2019 12:17 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Problem 11.27 (sixth edition)
Replies: 1
Views: 25

Re: Problem 11.27 (sixth edition)

The equilibrium constant K which is 25 = Partial Pressure of Products /Partial Pressure of reactants. Therefore,
25 = ( PPCL3 PCl2 )/ PPCl5

You can then plug in the values that you have and solve for the partial pressure of PCl3.
by Chem_Mod
Sat Mar 16, 2019 12:13 pm
Forum: Arrhenius Equation, Activation Energies, Catalysts
Topic: HW problem 15.67
Replies: 1
Views: 32

Re: HW problem 15.67

In order to answer this question you have to set a ratio for the Arrhenius Equations and solve for the ratio of the rate constants. You then realize that by whatever factor the rate constants changed is the factor by which the rates changed because there is a linear relationship between the two give...
by Chem_Mod
Sat Mar 16, 2019 12:08 pm
Forum: Arrhenius Equation, Activation Energies, Catalysts
Topic: HW problem 15.73
Replies: 1
Views: 26

Re: HW problem 15.73

Within the individual steps it may appear that the catalyst is being consumed, however this question is trying to get at the fact that in the course of the overall reaction a catalyst is not consumed, which is true.
by Chem_Mod
Sat Mar 16, 2019 12:06 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Coefficients for the rate of reaction
Replies: 1
Views: 36

Re: Coefficients for the rate of reaction

You can only do this for an elementary reaction because that is the only step that leads to your products. With other reactions, the overall reaction often times contains multi-step mechanisms that are not shown, therefore the rate would be dependent only on the slow step of the mechanism.
by Chem_Mod
Sat Mar 16, 2019 11:59 am
Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
Topic: Combustion
Replies: 1
Views: 35

Re: Combustion

The spontaneity of combustion reactions can be understood by looking at the entropy and enthalpy of the system. Combustion reaction have a negative enthalpy change because heat is released in going from reactants to products. That coupled with the fact that entropy change is almost always positive l...
by Chem_Mod
Sat Mar 16, 2019 11:52 am
Forum: First Order Reactions
Topic: Using Plots to determine order
Replies: 1
Views: 38

Re: Using Plots to determine order

You do not need to worry about something like that, just know that a zeroth order reaction has a negative slope of [A] vs t,
first order has a negative slope of ln[A] vs t, and second order has a positive slope of 1/[A] vs t.
by Chem_Mod
Sat Mar 16, 2019 11:49 am
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Nernst Equation
Replies: 2
Views: 35

Re: Nernst Equation

These are essentially the same thing. The 0.05916 is the constant that you get when you calculate RT/F.
by Chem_Mod
Sat Mar 16, 2019 1:32 am
Forum: Student Social/Study Group
Topic: Studying for the Final
Replies: 25
Views: 439

Re: Studying for the Final

viewtopic.php?f=160&t=44659

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