Search found 30 matches

by Andres Reynoso 1J
Sun Mar 18, 2018 1:54 am
Forum: Administrative Questions and Class Announcements
Topic: Lavelle: Professor by day, wizard by night
Replies: 6
Views: 734

Re: Lavelle: Professor by day, wizard by night

Well... this is definitely what I needed to lighten up before the final lol
by Andres Reynoso 1J
Sat Mar 17, 2018 8:53 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Inert Electrodes
Replies: 1
Views: 82

Re: Inert Electrodes

You need to add an inert electrode, such as platinum (Pt), when there are no other conducive metals in a half reaction in order to allow current to flow through the cell. You'd just need to add the electrode to the side that doesn't have a solid metal e.g. Zn(s) | Zn 2+ (aq) || Sn 4+ (aq),Sn 2+ (aq)...
by Andres Reynoso 1J
Sat Mar 17, 2018 8:42 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: Practice Midterm W18 #3A
Replies: 1
Views: 208

Re: Practice Midterm W18 #3A

Essentially, you would solve for the entropy at each individual step then add the totals up; this can be done because entropy is a state function. Your first step would to be to calculate the change in entropy due to the change in volume of helium gas. Step two would be to calculate the entropy chan...
by Andres Reynoso 1J
Sat Mar 17, 2018 6:03 pm
Forum: Administrative Questions and Class Announcements
Topic: Organic Chem
Replies: 2
Views: 231

Re: Organic Chem

I'm pretty sure Professor Lavelle said that we will need to know the functional groups we went over in lecture. We also talked about SN2 substitution reactions and went over those on the practice final, so I don't think it would hurt to review that as well.
by Andres Reynoso 1J
Sat Mar 17, 2018 5:57 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Cp & Cv?
Replies: 3
Views: 259

Re: Cp & Cv?

No, does not have to equal zero in a bomb calorimeter, meaning pressure is not a constant.
by Andres Reynoso 1J
Sat Mar 17, 2018 1:21 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Slow Step Determining Overall Rate
Replies: 3
Views: 130

Slow Step Determining Overall Rate

Under what conditions does the rate law of the slow step determine the overall rate law of the reaction in a reaction mechanism? Is it when the slow step is the first step of the reaction mechanism?
by Andres Reynoso 1J
Mon Mar 12, 2018 7:38 pm
Forum: Student Social/Study Group
Topic: Post All Chemistry Jokes Here
Replies: 7348
Views: 887822

Re: Post All Chemistry Jokes Here

Q: What is the name of 007's Eskimo cousin?
A: Polar Bond.
by Andres Reynoso 1J
Mon Mar 12, 2018 12:23 pm
Forum: Calculating Work of Expansion
Topic: Practice Problem
Replies: 1
Views: 90

Re: Practice Problem

I think you're correct Michelle and agree with your conclusion; the value should be positive because of \Delta U=q+w . Additionally, part b should be work done on the system. Perhaps a typo in the question? Typo could make sense given the 982 kJ - 492 kJ = +490 kJ, not 491... I think you're correct,...
by Andres Reynoso 1J
Mon Mar 12, 2018 12:10 pm
Forum: Arrhenius Equation, Activation Energies, Catalysts
Topic: Catalyst Example from lecture 3/12
Replies: 3
Views: 127

Re: Catalyst Example from lecture 3/12

I'm pretty sure the catalyst was NO (g).
by Andres Reynoso 1J
Sat Mar 03, 2018 6:39 pm
Forum: Kinetics vs. Thermodynamics Controlling a Reaction
Topic: Rate Constant Units
Replies: 9
Views: 415

Re: Rate Constant Units

You can use the rate law rate=k[A]^{n} and plug in the units for each variable and simplify. For example, for zero order reactions: \frac{mol A}{L\cdot s} = k[A]^{0} \frac{mol A}{L\cdot s} = k For first order: \frac{mol A}{L\cdot s} = k[A]^{1} \frac{mol A}{L\cdot s} = k(\frac{mol A}{L}) \fra...
by Andres Reynoso 1J
Sat Mar 03, 2018 5:58 pm
Forum: Student Social/Study Group
Topic: Post All Chemistry Jokes Here
Replies: 7348
Views: 887822

Re: Post All Chemistry Jokes Here

Q: Anyone know any jokes about sodium?
A: Na
by Andres Reynoso 1J
Sat Mar 03, 2018 5:33 pm
Forum: General Rate Laws
Topic: 15.27
Replies: 2
Views: 101

Re: 15.27

Using the given half-life, we can use the formula to calculate the k value. From there, we can use the formula to calculate time. [A]t is the concentration remaining after time t.
by Andres Reynoso 1J
Sat Feb 24, 2018 8:37 pm
Forum: Balancing Redox Reactions
Topic: Oxidation state
Replies: 5
Views: 199

Re: Oxidation state

In short, yes. The oxidation number represents the number of electrons that an element can lose (if negative) or gain (if positive), relative to the electronegativity of any other element is in combination with. Because O 2 and H 2 have the same electronegativity, respectively, their oxidation numbe...
by Andres Reynoso 1J
Sat Feb 24, 2018 8:25 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: When do you need to include Pt? [ENDORSED]
Replies: 5
Views: 179

Re: When do you need to include Pt? [ENDORSED]

No you do not always need to include Pt in your cell diagram. Platinum is used when there are no other inert metals in the reaction in order to allow current to flow through the cell. Most the time, you see Pt(s) being used when you are dealing with a cell that has a half-reaction that does not have...
by Andres Reynoso 1J
Sat Feb 24, 2018 8:20 pm
Forum: Method of Initial Rates (To Determine n and k)
Topic: n
Replies: 8
Views: 245

Re: n

I believe in lecture Friday, Professor Lavelle also used 'n' to represent the order of the reactant in the "rate law" ( ) if that is what you are referring to when you say kinetics.
by Andres Reynoso 1J
Sat Feb 10, 2018 7:36 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Arithmetic in 11.19c
Replies: 2
Views: 133

Re: Arithmetic in 11.19c

http://i1380.photobucket.com/albums/ah165/andresreynoso/chemcomm_zps6ilqogyd.jpg
Hopefully this helps!

*Edit: Photobucket doesn't allow third party hosting, so I just submitted the direct link.
by Andres Reynoso 1J
Sat Feb 10, 2018 6:54 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: 11.111
Replies: 2
Views: 134

Re: 11.111

Because the question asks for the standard Gibbs free energy of the second reaction, we assume that the temperature the reaction occurred at is 25°C since that is the accepted temperature for standard conditions.
by Andres Reynoso 1J
Sat Feb 10, 2018 6:34 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Explain Figure 9.25...
Replies: 1
Views: 87

Re: Explain Figure 9.25...

The graph is essentially showing us the relationship between temperature and the (molar) Gibbs free energy of a substance at a given pressure and how they both correlate to what phase a certain substance in in. It shows us that at low temperatures, the Gibbs free energy is lowest for solids. Because...
by Andres Reynoso 1J
Sat Feb 03, 2018 8:09 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: G at minimum
Replies: 6
Views: 163

Re: G at minimum

Gibbs free energy is essentially a measure of how much energy we can get from a system. So if the free energy is at a minimum, then the reaction is at equilibrium and no more change in energy can be done in the system. If anyone would like to add, please feel free.
by Andres Reynoso 1J
Sat Feb 03, 2018 7:47 pm
Forum: Calculating Work of Expansion
Topic: Confused about work formulas and specific heats
Replies: 2
Views: 148

Re: Confused about work formulas and specific heats

I'm pretty sure Cv and Cp are only to be used when the conditions dictate that the system is under constant volume or pressure, respectively, which is why it is often used when temperature is changing. For example, using Cp for a system where pressure is changing wouldn't work since pressure must be...
by Andres Reynoso 1J
Sat Feb 03, 2018 7:34 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Example from Wednesday's Lecture
Replies: 3
Views: 93

Example from Wednesday's Lecture

Professor Lavelle did an example on Wednesday where he asked at what temperature is Br(l)\rightarrow Br(g) spontaneous at 1 atm given \Delta H^{o}= 31.0 kJ/mol and \Delta S^{o}= 93.0 J/Kmol . He said that we were looking to find the temperature when \Delta G^{o}= 0 and said that neit...
by Andres Reynoso 1J
Sat Jan 27, 2018 5:32 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: 9.7 and 9.11 formula differences
Replies: 4
Views: 186

Re: 9.7 and 9.11 formula differences

The difference lies in what the question is asking. For 9.7 part a, the question asks for the entropy change at a constant pressure with a change in temperature. For this we use the known equation \Delta S=nC_{p}ln\frac{T_{2}}{T_{1}} where C p is the specific heat of a gas at constant pressure. For ...
by Andres Reynoso 1J
Sat Jan 27, 2018 5:04 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Bondy Enthalpy Accuracy
Replies: 3
Views: 168

Re: Bondy Enthalpy Accuracy

Using bond enthalpies is the least accurate method to calculate standard reaction enthalpies because bond enthalpies are averages of the dissociation enthalpies of bonds from several different molecules. Essentially, they are the least accurate because it is an average, where other methods are more ...
by Andres Reynoso 1J
Sat Jan 27, 2018 4:41 pm
Forum: Thermodynamic Definitions (isochoric/isometric, isothermal, isobaric)
Topic: isothermal system
Replies: 4
Views: 172

Re: isothermal system

Yes, when a system is isothermal it means that there is no temperature change in the system and thus the temperature would be constant. Only for ideal gases does this mean that the change in internal energy is 0 because, for ideal gases, \Delta U = \frac{3}{2}nR\Delta T and \Delta T = 0 (Anything mu...
by Andres Reynoso 1J
Sat Jan 20, 2018 4:26 pm
Forum: Phase Changes & Related Calculations
Topic: HW #1 PART E
Replies: 3
Views: 150

Re: HW #1 PART E

Mercury in a thermometer is a closed system because only energy can be exchanged with its surroundings. Matter cannot be exchanged within the system. Here is a more detailed example for the thermometer's case: A thermometer is placed under someone's tongue. The heat (energy) from their body (surroun...
by Andres Reynoso 1J
Sat Jan 20, 2018 4:22 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Specific Heat Capacity
Replies: 3
Views: 118

Re: Specific Heat Capacity

Yes it does stand for Kelvin. It is equivalent to degrees Celsius because specific heat equations usually involve temperature change . The magnitude for temperature change is the same for Kelvin and Celsius; so both units are interchangeable for specific heat capacity problems depending on which tem...
by Andres Reynoso 1J
Sat Jan 20, 2018 4:03 pm
Forum: Phase Changes & Related Calculations
Topic: Temperature [ENDORSED]
Replies: 2
Views: 98

Re: Temperature [ENDORSED]

For temperature changes , it doesn't matter if it is degrees Celsius or degrees Kelvin because the value of the difference would be the same (e.g. 1 C heats to 5 C = +4 C; 274.15 K heats to 278.15 K = +4 K). When using a formula that doesn't involve temperature change, where the other units indicate...
by Andres Reynoso 1J
Sat Jan 13, 2018 5:42 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Bond Enthalpy vs. Bond Dissociation Enthalpy
Replies: 3
Views: 118

Bond Enthalpy vs. Bond Dissociation Enthalpy

What is the difference between these two terms? I do not think bond dissociation enthalpy has not been discussed in class but I came across the term reading online and am curious.
by Andres Reynoso 1J
Sat Jan 13, 2018 5:26 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Question 8.41
Replies: 2
Views: 80

Re: Question 8.41

There is a negative sign in front of the value for heat (water) because it is the heat lost from the initial sample of water that is being gained by the water of the ice cube. The negative sign indicates the loss of that heat.

Edit: I agree with Jessica above.
by Andres Reynoso 1J
Sat Jan 13, 2018 11:07 am
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Heat Capacity
Replies: 3
Views: 139

Re: Heat Capacity

I think that, for the scope of this class, the specific heat capacity of a substance will always be provided, given that the specific heat of a substance is determined through experimentation.

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