Search found 31 matches
- Sat Mar 17, 2018 1:17 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: S and delta S
- Replies: 4
- Views: 607
Re: S and delta S
You would usually use delta S to find the change in entropy of a reaction (so some change to the system has to happen in order for there to be a delta S). We've only been using S to find the entropy of a molecule as a result of its structure (so there doesn't have to be any change in its state).
- Sat Mar 17, 2018 1:14 pm
- Forum: Thermodynamic Systems (Open, Closed, Isolated)
- Topic: qreaction and qcalorimeter
- Replies: 3
- Views: 1679
Re: qreaction and qcalorimeter
Kind of... the calorimeter is a very specific type of surroundings though.
- Sat Mar 17, 2018 1:13 pm
- Forum: Thermodynamic Systems (Open, Closed, Isolated)
- Topic: Open, closed, or isolated test 1 question
- Replies: 10
- Views: 1655
Re: Open, closed, or isolated test 1 question
Rachel N 1I wrote:Why is the contents of an ideal cooler at 3 deg Celsius considered isolated and not closed?
In an ideal cooler, no energy is exchanged with the surroundings (because ideally its contents will stay cold without absorbing warmth from the outside), so it's isolated.
- Fri Mar 09, 2018 10:29 am
- Forum: Reaction Mechanisms, Reaction Profiles
- Topic: Finding the intermediate(s)
- Replies: 5
- Views: 705
Re: Finding the intermediate(s)
An intermediate is produced in an earlier step and then used in a later step. It isn't an intermediate if it is used in an early step and produced in a later step.
- Fri Mar 09, 2018 10:26 am
- Forum: Reaction Mechanisms, Reaction Profiles
- Topic: What is Molecularity?
- Replies: 9
- Views: 2495
Re: What is Molecularity?
Also, the greater the molecularity, the less likely the reaction is to happen since the probability of that many molecules colliding is less.
- Fri Mar 09, 2018 10:23 am
- Forum: Reaction Mechanisms, Reaction Profiles
- Topic: Pre-Equilibrium Approach Methodology
- Replies: 2
- Views: 348
Re: Pre-Equilibrium Approach Methodology
In the slow step, we find the unique reaction rate according to the formation of products, which is equivalent to the overall rate law. So, we can set them equal.
- Fri Mar 02, 2018 10:57 am
- Forum: First Order Reactions
- Topic: Pseudo First Order Reaction
- Replies: 5
- Views: 1913
Re: Pseudo First Order Reaction
A pseudo first order reaction is actually a higher order reaction in which the concentrations of all the reactants except one is super high. This way, only the change in concentration of one reactant will be significant and you can solve for its concentration as if it was a real first order reaction.
- Fri Mar 02, 2018 10:51 am
- Forum: Method of Initial Rates (To Determine n and k)
- Topic: Order of the Reaction [ENDORSED]
- Replies: 3
- Views: 498
Re: Order of the Reaction [ENDORSED]
You can use the reaction to figure out order only if it is an elementary reaction.
- Fri Mar 02, 2018 10:48 am
- Forum: Kinetics vs. Thermodynamics Controlling a Reaction
- Topic: Average rate [ENDORSED]
- Replies: 6
- Views: 1026
Re: Average rate [ENDORSED]
As long as the forward reaction is progressing faster than the reverse reaction, the rate of the change in concentration of reactants will be negative because they are being consumed.
- Fri Feb 23, 2018 11:06 am
- Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
- Topic: Table 14.1
- Replies: 1
- Views: 319
Re: Table 14.1
The more positive the reduction potential, the greater its ability to be reduced. Since the table is arranged in order of large to small reduction potential, it works out.
- Fri Feb 23, 2018 11:05 am
- Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
- Topic: 14.33b homework
- Replies: 3
- Views: 489
Re: 14.33b homework
For this problem, we know deltaG for Tl3+/Tl. However, for b we want to know the deltaG for Tl3+/Tl+ in order to find whether or not Tl is disproportionate. We use the reaction potential for Tl+/Tl to calculate deltaG for the half-reaction and then combine the deltaG's for Tl3+/Tl and Tl+/Tl in a He...
- Fri Feb 23, 2018 10:52 am
- Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
- Topic: ln vs log [ENDORSED]
- Replies: 5
- Views: 953
Re: ln vs log [ENDORSED]
They yield the same results though!
- Sun Feb 18, 2018 8:48 pm
- Forum: Balancing Redox Reactions
- Topic: Balancing
- Replies: 3
- Views: 405
Re: Balancing
To determine oxidation numbers, remember that the oxidation number of oxygen is always +2 unless you're looking at a peroxide (I think). Then you just determine the oxidation numbers of the rest of the atoms in the molecules based on the charge of the molecule. The oxidation numbers of all the atoms...
- Sun Feb 18, 2018 8:42 pm
- Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
- Topic: "Molar" form/ Pure number
- Replies: 2
- Views: 368
Re: "Molar" form/ Pure number
I'm pretty sure the r stands for "reaction." So rather than this being a standard deltaG, this is the deltaG of the reaction and the number of moles of electrons in the reaction.
- Sun Feb 18, 2018 8:40 pm
- Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
- Topic: 14.9
- Replies: 2
- Views: 392
Re: 14.9
It helps to write out all your units when you're doing a problem so you can see what cancels out for your final answer.
- Fri Feb 09, 2018 10:55 am
- Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
- Topic: Conducting Metal
- Replies: 3
- Views: 410
Re: Conducting Metal
Yes, a conducting metal/solid is necessary for electrons to be transferred between half-reactions.
- Fri Feb 09, 2018 10:54 am
- Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
- Topic: Galvanic Cell
- Replies: 3
- Views: 410
Re: Galvanic Cell
Yes; it uses spontaneous redox reactions to generate electrical energy.
- Fri Feb 09, 2018 10:51 am
- Forum: Balancing Redox Reactions
- Topic: Standard Reduction Potential
- Replies: 3
- Views: 472
Re: Standard Reduction Potential
Just make sure that the number of electrons cancel out and the charges are balanced and you should be good to calculate the standard reaction potential by adding up E for each half reaction
- Fri Feb 02, 2018 10:45 am
- Forum: Gibbs Free Energy Concepts and Calculations
- Topic: entropy to surroundings
- Replies: 3
- Views: 477
Re: entropy to surroundings
Keep in mind that the second law is referring to the total entropy, aka the entropy of the universe. So, the entropy of the system or of the surroundings can increase without violating the second law as long as the total entropy is not negative.
- Fri Feb 02, 2018 10:41 am
- Forum: Gibbs Free Energy Concepts and Calculations
- Topic: Endergonic vs Endothermic
- Replies: 2
- Views: 414
Re: Endergonic vs Endothermic
For the equation deltaG=deltaH-TdeltaS, for a negative deltaH (exothermic), as long as the TdeltaS term is negative and larger in magnitude than deltaH, deltaG will be positive and the process will be endergonic.
- Fri Feb 02, 2018 10:38 am
- Forum: Gibbs Free Energy Concepts and Calculations
- Topic: 9.75
- Replies: 1
- Views: 218
Re: 9.75
I believe that a trans isomer has a smaller W than its corresponding cis crystal. A trans isomer and its mirror across a certain axis are indistinguishable, but you can tell the difference between a cis crystal and its mirror, so the cis crystal has a greater W.
- Fri Feb 02, 2018 10:32 am
- Forum: Gibbs Free Energy Concepts and Calculations
- Topic: 9.73
- Replies: 1
- Views: 225
Re: 9.73
S, G, and H change depending on the conditions. So, S, G, and H indicate spontaneity for whatever conditions they are given for in the problem.
- Fri Jan 26, 2018 10:32 am
- Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
- Topic: Heat and temp difference
- Replies: 2
- Views: 361
Re: Heat and temp difference
Isothermal just means that there's no change in temperature of the system, but there is still an exchange of heat between the system and the surroundings.
- Fri Jan 26, 2018 10:28 am
- Forum: Phase Changes & Related Calculations
- Topic: Names of phase changes
- Replies: 4
- Views: 483
Re: Names of phase changes
Don't forget that when you are solving for enthalpy change for exothermic phase changes, you just use negative delta H for their endothermic counterparts.
- Fri Jan 26, 2018 10:13 am
- Forum: Concepts & Calculations Using First Law of Thermodynamics
- Topic: Internal Energy in a Vacuum [ENDORSED]
- Replies: 5
- Views: 971
Re: Internal Energy in a Vacuum [ENDORSED]
Also, q is zero in free expansion because no heat exchange occurs between the system and surroundings.
- Sat Jan 20, 2018 11:39 pm
- Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
- Topic: PV=nRT
- Replies: 4
- Views: 916
Re: PV=nRT
If the system expands or is compressed, there can only be a change in the number of moles if the system is open.
- Sat Jan 20, 2018 11:30 pm
- Forum: Thermodynamic Systems (Open, Closed, Isolated)
- Topic: Assigning system/surroundings
- Replies: 5
- Views: 582
Re: Assigning system/surroundings
The system will always be wherever the reaction is occurring, and the surroundings are everything else.
- Sat Jan 20, 2018 11:29 pm
- Forum: Calculating Work of Expansion
- Topic: Reversible vs Irreversible
- Replies: 4
- Views: 501
Re: Reversible vs Irreversible
Reversible work is done very slowly and requires the maximum amount of energy.
- Fri Jan 12, 2018 11:30 am
- Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
- Topic: Liquids and Solids
- Replies: 3
- Views: 446
Re: Liquids and Solids
Yes, even for the same substance, its standard enthalpy of formation is different depending on what state it is in. On tests and in the textbook, the standard enthalpies of formation are given and specific to whatever physical state the molecule is in, so we have to pay attention to that.
- Fri Jan 12, 2018 11:23 am
- Forum: Phase Changes & Related Calculations
- Topic: Expansion and change in pressure
- Replies: 4
- Views: 386
Re: Expansion and change in pressure
Since the internal energy of the gas is less, the molecules have less energy and experience fewer collisions with each other and the walls of the container. So, the temperature and pressure are less. I'm not sure, but with your answer, I believe that the flaw is that the pressure could be greater ev...
- Fri Jan 12, 2018 11:14 am
- Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
- Topic: Most Stable Forms
- Replies: 4
- Views: 1070
Re: Most Stable Forms
The standard enthalpy of formation is 0 when the element is in its purest form. So even though water is in liquid form commonly, its standard enthalpy of formation is not 0 because it's not in its purest form.