Search found 27 matches

by Nathaniel 2E
Wed Mar 13, 2019 10:41 pm
Forum: General Rate Laws
Topic: Deriving integrated rate laws
Replies: 1
Views: 31

Re: Deriving integrated rate laws

My TA stressed we need to know how to derive them, but another TA in their review session said we wouldn't, so I'm not sure... I would know how to just to be safe. Dr. Lavelle has a link on his website to a sheet outlining the derivations : https://lavelle.chem.ucla.edu/wp-content/supporting-files/C...
by Nathaniel 2E
Wed Mar 13, 2019 10:35 pm
Forum: Arrhenius Equation, Activation Energies, Catalysts
Topic: NO as a catalyst for O2 to O3
Replies: 1
Views: 40

Re: NO as a catalyst for O2 to O3

NO does not *need* to be present for the reaction to occur, but, realistically, you will only find oxygen gas becoming ozone with the presence of a catalyst. The activation energy barrier to go from oxygen gas to ozone is too high for that reaction to occur with any frequency, but it is still possib...
by Nathaniel 2E
Wed Mar 13, 2019 10:23 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Test 2, Question 6 part a
Replies: 4
Views: 79

Re: Test 2, Question 6 part a

Yeah... the whole reducing power/oxidizing power and reducing agent/oxidizing agent is a bit counterintuitive. Reducing power is how well the reaction oxidizes. We know that in an oxidation reaction we flip the reduction reaction and reduction potential, so our reduction potentials become the opposi...
by Nathaniel 2E
Sat Mar 09, 2019 6:25 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Test #2 Question 5 (ph acidic or basic)
Replies: 1
Views: 46

Test #2 Question 5 (ph acidic or basic)

This question from Test #2 baffled me, I still don't know what was the correct way to approach it: The ionic dissociation of water is given by the following reaction: The deltaHo for the reaction is 58 kJ/mol. The Kw for the reaction at 25 degrees C is 10^-14. Is a pH of 7 acidic or basic at 10 degr...
by Nathaniel 2E
Sat Mar 09, 2019 6:14 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Determining the slow step
Replies: 2
Views: 39

Re: Determining the slow step

The central idea of the slow step is that it is the rate determining step, i.e., that the reaction's overall rate law is determined by the rate law of the slow step. If we know the experimentally determined rate law of a reaction, which we will most probably always receive when dealing with reaction...
by Nathaniel 2E
Sat Mar 09, 2019 6:10 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Slow step
Replies: 2
Views: 31

Re: Slow step

I believe you are referring to the example where we had NO2(g)+CO(g) --> NO(g)+CO(g), with the elementary steps of: 1. NO2(g)+NO2(g) --> NO3(g)+NO(g) 2. NO3(g)+CO(g) --> NO2(g)+CO2(g) We were given that the experimentally determined rate law was rate=k[NO2]^2. Since the slow step is the rate determi...
by Nathaniel 2E
Mon Feb 25, 2019 1:58 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: inert metals
Replies: 2
Views: 32

Re: inert metals

Inert electrodes, like the platinum electrode, do not participate in the oxidation-reduction reaction and are present so that current can flow through the cell. Platinum or gold generally make good inert electrodes because they are chemically unreactive. It is necessary to use an inert electrode, su...
by Nathaniel 2E
Mon Feb 25, 2019 1:56 pm
Forum: Balancing Redox Reactions
Topic: Adding H+, OH- and H20
Replies: 4
Views: 78

Re: Adding H+, OH- and H20

For acidic solutions, first balance O by adding H2O, then balance H by adding H+.

For basic solutions, first balance O by adding H2O, then balance H by adding H2O to the side of each half reaction that needs H and adding OH- to the other side.
by Nathaniel 2E
Mon Feb 25, 2019 1:54 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Anode and Cathode
Replies: 6
Views: 66

Re: Anode and Cathode

I use the mneumonic "An Ox" (Anode, Oxidation) and "Red Cat" (Reduction, Cathode) to keep them straight
by Nathaniel 2E
Sun Feb 17, 2019 2:40 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: S=qrev/ T
Replies: 3
Views: 151

Re: S=qrev/ T

Yes, for this class, isothermal and reversible mean the same thing- if the problem tells you it is an isothermal reaction, we know it is a reversible process. We also will always be told in a question if it is reversible by either the problem calling to reversible or calling it isothermal.
by Nathaniel 2E
Sun Feb 17, 2019 2:35 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Gibbs Free Energy vs Internal Energy
Replies: 3
Views: 59

Re: Gibbs Free Energy vs Internal Energy

Gibbs Free Energy is the maximum amount of non-expansion work that can be extracted from a thermodynamically closed system, a maximum that can be attained only in a completely reversible process. "Free energy" refers to energy available to do non-expansion work.
by Nathaniel 2E
Sun Feb 17, 2019 2:22 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Meaning of Spontaneity
Replies: 3
Views: 62

Re: Meaning of Spontaneity

The equation of the change in Gibbs Free Energy can be of help: delta G = delta H - T*delta S The change in the free energy of the system measures the balance between the two driving forces that determine whether a reaction is spontaneous, enthalpy and entropy. The change in enthalpy is favorable fo...
by Nathaniel 2E
Sun Feb 10, 2019 11:01 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: conversions
Replies: 3
Views: 56

Re: conversions

No, since that conversion is on constants and equations sheet
by Nathaniel 2E
Sun Feb 10, 2019 10:59 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: Reversible vs. Irreversible
Replies: 6
Views: 79

Re: Reversible vs. Irreversible

Think about them in terms of the "area under the curve" in a graph of Pressure x Volume. Because the reversible reaction depends logarithmically on volume, while the irreversible reaction depends linearly on volume. Therefore, the area under the curve (work) is larger for reversible, as th...
by Nathaniel 2E
Sun Feb 10, 2019 10:46 pm
Forum: Calculating Work of Expansion
Topic: Volume and Entropy
Replies: 2
Views: 44

Re: Volume and Entropy

Greater volume allows for more micro sates to be available, hence increasing the degeneracy, and therefore entropy of the system. This means then that decreasing volume would decrease entropy
by Nathaniel 2E
Sun Feb 03, 2019 4:44 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Reversible vs Irreversible Expansion
Replies: 1
Views: 35

Reversible vs Irreversible Expansion

I'm not exactly sure on the meaning of reversible and irreversible reactions- how are they different and how can you tell if the problem doesn't specify? In question 8.11 from the 6th edition, irreversible expansion work is modeled by -P(deltaV) and reversible -nRTln(V2/V1) why do we use different e...
by Nathaniel 2E
Sun Feb 03, 2019 4:35 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Molar Heat Capacities of Ideal Gases
Replies: 1
Views: 59

Molar Heat Capacities of Ideal Gases

In question 8.31 from the 6th addition, the solutions manual explains that for monatomic ideal gases at constant pressure, the molar heat capacity is (5/2)R, and for a monatomic ideal gases at constant volume, the molar heat capacity is (3/2)R. Why can we assume these two claims to be true?
by Nathaniel 2E
Sun Feb 03, 2019 1:12 pm
Forum: Phase Changes & Related Calculations
Topic: State Function
Replies: 10
Views: 102

Re: State Function

A state function is a property whose value does not depend on the path taken to reach that specific value. Temperature is a state function because the path of temperature changes doesn't change the final temperature (Heating water by 5 degrees vs heating water by 7 degrees and then cooling it by 2 d...
by Nathaniel 2E
Sun Jan 27, 2019 10:06 pm
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: Ph and Pka
Replies: 5
Views: 64

Re: Ph and Pka

Going from pH to pKa, take 10^-(pH) to get the hydronium ion concentration. Use that in your ICE table (it will end up being x) and solve for Ka. Take the negative log of Ka, and you have your pKa
by Nathaniel 2E
Sun Jan 27, 2019 10:01 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Order of Hess's Law
Replies: 1
Views: 27

Re: Order of Hess's Law

I believe that the process being modeled is simultaneous, and that if the reaction is exothermic, say, it will remain exothermic and not become endothermic when another reactant is added
by Nathaniel 2E
Sun Jan 27, 2019 9:52 pm
Forum: Phase Changes & Related Calculations
Topic: State functions
Replies: 2
Views: 48

Re: State functions

Work can't be a state function because it is proportional to the distance an object is moved, which depends on the path used to go from the initial to the final state. Like Prof. Lavelle showed us in class with the mountain example, the hikers taking the different paths arrived at the same end point...
by Nathaniel 2E
Sun Jan 20, 2019 6:38 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: ICE box
Replies: 1
Views: 33

Re: ICE box

We use ICE tables when we're calculating equilibrium concentrations for reactions and for reactions with weak acids or bases. Good rule of thumb is if you're given a K value or asked for a K value, you'll use an ICE table General steps are to fill out your initial concentrations for all aqueous or g...
by Nathaniel 2E
Sun Jan 20, 2019 6:14 pm
Forum: Calculating pH or pOH for Strong & Weak Acids & Bases
Topic: Number 71 Chapter 12 Homework
Replies: 2
Views: 150

Re: Number 71 Chapter 12 Homework

It's because NaCH3CO2 is a salt, and when dissolved in water, the sodium ion dissociates from the CH3CO2-. In full, the reaction is : Na+ + CH3CO2- + H2O <---> HCH3CO2 + OH- + Na+ But, since the sodium ion is on both sides of the reaction, we can cancel them out and don't need to factor them into th...
by Nathaniel 2E
Sat Jan 19, 2019 2:01 pm
Forum: Non-Equilibrium Conditions & The Reaction Quotient
Topic: Acid and Base Salt Equation
Replies: 1
Views: 63

Acid and Base Salt Equation

A problem calls for writing out the equilibrium equation for AlCl3. The solution writes it out as:

Al(H2O)6 3+ (aq) + H2O (l) <---> H3O+ (aq) + Al(H2O)5OH 2+ (aq)

What does the H2O in parentheses attached to the aluminum ions mean? Why do we assume they exist and write the equation like that?
by Nathaniel 2E
Sat Jan 12, 2019 2:53 pm
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: Effect of Partial Pressure on Concentration
Replies: 2
Views: 50

Effect of Partial Pressure on Concentration

The photosynthesis reaction, 6 CO2(g) + 6 H2O(l) ⇌ C6H12O6(aq) + 6 O2(g), is endothermic. What effect will decreasing the partial pressure of CO2 have on the concentration of O2? Was having a hard time visualizing this... would decreasing the partial pressure of a reactant mean that the reactant sid...
by Nathaniel 2E
Thu Jan 10, 2019 2:47 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Calculating Equilibrium Constant from Percent of Reactant
Replies: 2
Views: 36

Calculating Equilibrium Constant from Percent of Reactant

A researcher fills a 1.00 L reaction vessel with 1.84 x 10-4 mol of BrCl gas and heats it to 500 K. At equilibrium, only 18.3 % of the BrCl gas remains. Calculate the equilibrium constant, assuming the following reaction is taking place. 2BrCl(g) ⇌ Br2 (g) + Cl2(g) Was stumped on this question, felt...
by Nathaniel 2E
Wed Jan 09, 2019 9:14 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Calculating the Reaction Quotient
Replies: 3
Views: 41

Calculating the Reaction Quotient

Calculate the reaction quotient, QC, from the following equilibrium data collected in a 3.00 L sealed reaction vessel for the reaction: AsH3 (g) ⇌ As (s) + H2 (g) AsH3 = 5.55 x 10-4 mol, As = 3.31 x 10-3 mol, H2 = 1.23 x 10-3 mol. This is from the second module, I keep messing up and not arriving at...

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