Search found 31 matches

Sat Mar 17, 2018 6:30 pm
Forum: Balancing Redox Reactions
Topic: Homework Problem 14.1
Replies: 2
Views: 269

Re: Homework Problem 14.1

The two H atoms add a net +2 charge to the product side, so you need to add two e- to balance that out.
Sat Mar 17, 2018 6:27 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: Second Law application
Replies: 3
Views: 380

Re: Second Law application

Gibbs Free Energy is heavily dominated by the enthalpy term. Even though entropy can be negative in terms of the system, the reaction overall can still be spontaneous as stated above by its relation to the entropy of surroundings.
Sat Mar 17, 2018 6:25 pm
Forum: Balancing Redox Reactions
Replies: 6
Views: 469

You only add OH when the redox reaction is in a basic solution
Sat Mar 17, 2018 6:24 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Reaction Graphs
Replies: 3
Views: 337

Re: Reaction Graphs

Higher peaks should indicate a slower rate since it takes more energy to overcome the higher activation energy. Lower peaks are easier to overcome thus indicating a lower activation energy.
Sat Mar 17, 2018 4:42 pm
Forum: Arrhenius Equation, Activation Energies, Catalysts
Topic: Activation Energy
Replies: 5
Views: 410

Re: Activation Energy

The highest peak should be the slowest step which is the rate determining step
Sat Mar 17, 2018 4:38 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: Internal Energy of Isolated Systems
Replies: 6
Views: 1290

Re: Internal Energy of Isolated Systems

Yeah of course! As Dr. Lavelle discussed in class, the internal energy of an isolated system is constant. Since the universe is defined as an isolated system, the summation of all the work and heat transferred in the universe is constant. Therefore the change in internal energy (delta U) of the univ...
Sat Mar 17, 2018 4:34 pm
Forum: Student Social/Study Group
Topic: Final Review Time Tips
Replies: 5
Views: 523

Re: Final Review Time Tips

I think that old tests and homework problems are the way to go!
Sat Mar 17, 2018 4:32 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: Internal Energy of Isolated Systems
Replies: 6
Views: 1290

Re: Internal Energy of Isolated Systems

Yes, because I think that this is the first law of thermodynamics where energy is neither created nor destroyed :)
Sat Mar 17, 2018 4:27 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Steady State Approximation Vs Pre Equilibrium
Replies: 2
Views: 446

Re: Steady State Approximation Vs Pre Equilibrium

I think if we are given which steps are slow or fast, the pre-equilibrium approach is the most preferred. The steady state approximation is used when we are not given the slow and fast steps and need to assume that the concentration of intermediate(s) is constant (or at a steady state) to be able to...
Sat Mar 17, 2018 4:14 pm
Forum: Arrhenius Equation, Activation Energies, Catalysts
Topic: catalyst
Replies: 4
Views: 372

Re: catalyst

The catalyst provides a different path for reactants to end up at the same products. Increased collisions allow it to proceed with less energy.
Sat Mar 17, 2018 4:08 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Fast or Slow
Replies: 8
Views: 476

Re: Fast or Slow

The pre-equilibrium method is essentially writing the rate law for the slow step and substituting any intermediate terms with equivalents derived from previous or consequent steps' equilibrium constants.
Sat Feb 17, 2018 9:06 pm
Forum: Calculating Work of Expansion
Topic: -w vs +w
Replies: 2
Views: 206

Re: -w vs +w

If work is negative, the system is losing energy as it uses it to expand.

If work is positive, the system is gaining energy as it gains it from the compressing force.
Sat Feb 17, 2018 9:03 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Relationship between free energy and work
Replies: 2
Views: 198

Re: Relationship between free energy and work

Gibbs Free Energy is essentially the amount of energy available for work so deltaG is also equal to max work possible.
Sat Feb 17, 2018 9:02 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: 8.49
Replies: 3
Views: 224

Re: 8.49

Yes, usually for these problemes, if it isn't stated, we should probably assume standard conditions.
Sat Feb 10, 2018 8:23 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: Self-Test 9.10A [ENDORSED]
Replies: 1
Views: 263

Self-Test 9.10A[ENDORSED]

Calculate the entropy of a sample of a solid in which the molecules may be found in any one of three orientations with the same energy. Suppose there are 30 molecules in the sample.

Using Boltzmann's formula, the value for W would be 30^3? How would you arrive to the answer of 4.5 x 10^-22 J/K?
Sat Feb 10, 2018 8:18 am
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Entropy
Replies: 7
Views: 367

Re: Entropy

Dylan Mai 1D wrote:is there an entropy of fusion?

I don't think it is a tabulated value in any of the tables or appendixes in the textbook, but you can definitely calculate it similarly to calculating the entropy of vaporization.
entropy of fusion = enthalpy of fusion/melting point (Tb)
Sat Feb 10, 2018 8:14 am
Forum: Balancing Redox Reactions
Topic: Midterm Topics [ENDORSED]
Replies: 2
Views: 167

Re: Midterm Topics[ENDORSED]

No, electrochemistry should not be on the midterm. Dr. Lavelle said in class that the midterm would only cover material from Ch. 8,9, and 11.
Tue Jan 30, 2018 7:34 am
Forum: Gibbs Free Energy Concepts and Calculations
Topic: A spontaneous reaction
Replies: 7
Views: 351

Re: A spontaneous reaction

Spontaneous reactions are the likely paths reactions or processes will take without an input of energy (ice melting for instance).
Tue Jan 30, 2018 7:31 am
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Heat Capacity
Replies: 8
Views: 562

Re: Heat Capacity

A steeper slope would indicate a lower heat capacity since it heats up faster with less energy; conversely, a flatter slope would indicate a higher heat capacity because the same amount of heat is heating the substance in question slower.
Tue Jan 30, 2018 7:27 am
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: Test question [ENDORSED]
Replies: 16
Views: 863

Re: Test question[ENDORSED]

Along with the equation, I also just stated that energy can neither be created nor destroyed, just transferred in various forms.
Thu Jan 25, 2018 2:03 am
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: 8.113
Replies: 1
Views: 209

8.113

Water gas is an inexpensive, low-grade fuel that can be made from coal. (a) Is the production of water gas exothermic or endothermic? In the reaction given in the problem, the reactants are carbon (s) and water vapor (g) and the products are carbon monoxide (g) and hydrogen (g). Why is the reaction ...
Mon Jan 22, 2018 3:32 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: work
Replies: 2
Views: 165

Re: work

In general with the problems we've had, a gas doing expansion work is doing work on the surroundings (negative work in terms of the whole system). When a gas compresses, work is being done on it (so positive work since energy is being put into the system to compress the gas).
Mon Jan 22, 2018 2:59 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Concepts for Chapter 8 [ENDORSED]
Replies: 5
Views: 369

Re: Concepts for Chapter 8[ENDORSED]

I think reading the textbook might be a good start (it seems to be helping conceptually) :)
Mon Jan 22, 2018 2:57 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: First Law Concept
Replies: 4
Views: 246

Re: First Law Concept

The first law is basically conservation of energy (energy is neither created nor destroyed). The more practical application of the law that we have been using is delta U = q+w
Thu Jan 18, 2018 8:57 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: 8.23
Replies: 5
Views: 335

Re: 8.23

Both units of answer seem to be appropriate, but the kJ variation would only make it neater in terms of truncating the number.
Thu Jan 18, 2018 8:53 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: 8.31
Replies: 5
Views: 348

Re: 8.31

As the response stated above iterates, since you know that Krypton is assumed to behave as an ideal gas, you must refer to the molar heat capacity constants for ideal gases under constant pressure and volume (in this case, 5/2R and 3/2R respectively. Using those values in q= n(molar heat capacity un...
Thu Jan 18, 2018 8:47 pm
Forum: Phase Changes & Related Calculations
Topic: 8.37
Replies: 3
Views: 182

Re: 8.37

For this problem, I found it easier to consider the units of the enthalpy of vaporization. In the table of enthalpy of vaporization values, we are given values with units of kJ/mol. In other words, each value tells us the number of kJ it takes to vaporize 1 mol of said substance. In both parts a and...
Tue Jan 09, 2018 11:56 pm
Forum: Calculating Work of Expansion
Topic: Potential to do work in Irreversible vs. Reversible Expansion
Replies: 1
Views: 321

Re: Potential to do work in Irreversible vs. Reversible Expansion

So in irreversible processes, the tendency is for the reaction to go toward completion as quickly as possible. In the image from an older response in the link below that I found, you can see that it abruptly changes to a lower than optimal constant pressure being used in the irreversible reaction (i...
Mon Jan 08, 2018 6:07 pm
Forum: Phase Changes & Related Calculations
Topic: Endothermic Reaction
Replies: 10
Views: 3874

Re: Endothermic Reaction

The ice cube needs energy in the form of heat to melt it further and further. By adding energy to the ice cube via the heat of your hand if you hold it, the reaction is endothermic. The ice cube absorbs the heat energy in order to melt it. An endothermic reaction is defined as a process that absorbs...
Mon Jan 08, 2018 5:27 pm
Forum: Phase Changes & Related Calculations
Topic: Question 8.11
Replies: 1
Views: 136

Re: Question 8.11

https://lavelle.chem.ucla.edu/forum/viewtopic.php?t=5062
Found this post from a while back in the forum. Hope it helps!
Mon Jan 08, 2018 5:21 pm
Forum: Phase Changes & Related Calculations
Topic: Temperature and Exothermic Reaction [ENDORSED]
Replies: 4
Views: 271

Re: Temperature and Exothermic Reaction[ENDORSED]

I think he was specifically referencing the example/problem he gave in class with the fishbowl and test tube where an exothermic reaction occurred at a constant temperature with that device in the fishbowl. There was a system where an exothermic reaction occurred inside the test tube (which is sligh...