Search found 31 matches
- Sun Mar 18, 2018 9:21 am
- Forum: Reaction Mechanisms, Reaction Profiles
- Topic: Stoichiometric coefficients
- Replies: 4
- Views: 916
Re: Stoichiometric coefficients
Yes, stoichiometric coefficients are used in the elementary steps' rate laws, but you can't use it for the overall rate law as the coefficients may not align with the order.
- Sun Mar 18, 2018 9:12 am
- Forum: Reaction Mechanisms, Reaction Profiles
- Topic: Elementary steps
- Replies: 2
- Views: 570
Re: Elementary steps
Yes, for problems in which we are finding the overall rate law using elementary steps, you would use the coefficients as the order of each individual step's rate law. For an overall rate law, you can't.
- Sun Mar 18, 2018 9:04 am
- Forum: *Nucleophiles
- Topic: SN2 Reactions
- Replies: 4
- Views: 3633
Re: SN2 Reactions
Yes, this is the only type of reaction we are supposed to know, I believe. An SN2 reaction consists of an electrophile and a nucleophile, which are both just molecules like CH3I and OH- for example. The reaction that takes place is that the nucleophile (OH-) 'attacks' the electrophile at the same ti...
- Sun Mar 18, 2018 8:57 am
- Forum: *Electrophiles
- Topic: How do you categorize Electrophiles?
- Replies: 2
- Views: 1510
Re: How do you categorize Electrophiles?
An electrophile will generally have a + charge on the entire molecule or it will not have any lone pairs on the central atom.
- Sun Mar 11, 2018 8:00 pm
- Forum: Method of Initial Rates (To Determine n and k)
- Topic: Overall Order with Negative Suborders
- Replies: 2
- Views: 514
Re: Overall Order with Negative Suborders
Yes, the general rule for figuring out the order of a reaction is to just sum up all the individual reactant orders.
- Sun Mar 11, 2018 5:21 pm
- Forum: First Order Reactions
- Topic: Integrated Rate Laws
- Replies: 4
- Views: 715
Re: Integrated Rate Laws
Yes most of the time you will probably only encounter second order reactions with only one reactant counted in the rate equation.
- Mon Mar 05, 2018 9:49 pm
- Forum: Second Order Reactions
- Topic: 2nd order rxn integration
- Replies: 2
- Views: 356
Re: 2nd order rxn integration
The equation ends up being 1/[A] = 1/[A]0 + kt. So the negative would end up getting multiplied by another negative to form a positive kt.
- Sun Mar 04, 2018 5:40 pm
- Forum: First Order Reactions
- Topic: Integrated rate law for first order reaction
- Replies: 3
- Views: 487
Re: Integrated rate law for first order reaction
I think you may be referring to the half life equation, which is used only in the case or first order reactions. This would’ve used if you are looking for the half life of the reaction or you know the half-life and are just looking for k.
- Sun Mar 04, 2018 2:39 pm
- Forum: General Rate Laws
- Topic: Multiple Reactants
- Replies: 2
- Views: 363
Re: Multiple Reactants
A good way to decide is to determine the type of relationship present in an equation. For example, if tripling the concentration causes a triple in rate, then you have a first order reaction because (3x)^1 = 3x. If this change causes an increase in rate by a factor of 9, then it’s a second order rea...
- Sun Mar 04, 2018 2:16 pm
- Forum: General Rate Laws
- Topic: How to know when to use which formula?
- Replies: 2
- Views: 414
Re: How to know when to use which formula?
Your formula depends on the order of the reaction. So, if you’re given k and asked to solve for [A] at either initial or final or for t, then you’d look at the units of k to determine what order the reaction is. If you’re solving for k, you will most likely be given the order of the reaction as ther...
- Sun Feb 25, 2018 10:54 pm
- Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
- Topic: Standard E values and inverse values
- Replies: 2
- Views: 404
Re: Standard E values and inverse values
E is the reduction potential of an atom, so if A --> B is reduction and B --> A is the same atom but getting oxidized, then E would be negative. But if A --> B is a reaction, then E shouldn't change since it is not a state property such as enthalpy.
- Sun Feb 25, 2018 10:46 pm
- Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
- Topic: Metals in Cell Diagrams
- Replies: 3
- Views: 502
Re: Metals in Cell Diagrams
Also, the reason for needing an inert metal electrode is so that it may not partake in the reaction taking place.
- Sun Feb 25, 2018 10:37 pm
- Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
- Topic: Order of Same State Molecules
- Replies: 4
- Views: 565
Re: Order of Same State Molecules
Generally you list the anode on the left side and cathode on the right. So the anode is the oxidized and the cathode is the reduced.
- Sun Feb 18, 2018 1:26 pm
- Forum: Balancing Redox Reactions
- Topic: process to balance redox reactions
- Replies: 2
- Views: 452
Re: process to balance redox reactions
Generally speaking, you'll want to use H+ when balancing acidic reactions and OH- for basic reactions. H2O can be used in either as needed to balance, however it's likely you'll always need H20 in balancing reactions.
- Sun Feb 18, 2018 1:23 pm
- Forum: Balancing Redox Reactions
- Topic: Acidic vs. Basic Solutions
- Replies: 3
- Views: 524
Re: Acidic vs. Basic Solutions
Technically, you could use H30+ for acidic solutions and balancing from there, but you'll end up with a mess balancing things out. It's much easier to just use H+ since you only have to worry about balancing the H's.
- Sun Feb 18, 2018 1:20 pm
- Forum: Balancing Redox Reactions
- Topic: Sign of E when anode rxn reverses
- Replies: 2
- Views: 348
Re: Sign of E when anode rxn reverses
Since the table explicitly shows reduction potential values, you just need to make sure that you place them in the proper equations. As said above, using the Ecathode - Eanode will always give you the correct answer, but using the Ecathode +Eanode would require some sign-changing for the original va...
- Sun Feb 11, 2018 10:20 pm
- Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
- Topic: Oxidation
- Replies: 4
- Views: 397
Re: Oxidation
A good way to remember this is to associate the anode side with being your negative end of a battery wherein its charge comes from electrons, which are negatively charged.
- Sun Feb 11, 2018 10:16 pm
- Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
- Topic: Cell Potential
- Replies: 2
- Views: 310
Re: Cell Potential
Furthermore, unlike free energy, a reaction will not be favored in the current direction if the E is negative. The reaction (in terms of electrons and ions) flows in the forward direction if the E is positive.
- Sun Feb 11, 2018 10:13 pm
- Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
- Topic: E and G
- Replies: 2
- Views: 371
Re: E and G
In other words, there is a direct relationship where if E increases so will the DeltaG, and if E decreases DeltaG will as well.
- Sun Feb 04, 2018 11:27 am
- Forum: Gibbs Free Energy Concepts and Calculations
- Topic: Gibbs Free Energy: State Function?
- Replies: 3
- Views: 473
Re: Gibbs Free Energy: State Function?
Generally, anything with a delta in front of it will be a state function, because the delta means 'change in'. So, to calculate the change, you must subtract the initial value from the final value, therefore the only relevant values are your initial and final, fitting the definition of a state funct...
- Sun Feb 04, 2018 10:58 am
- Forum: Gibbs Free Energy Concepts and Calculations
- Topic: deltaG at equilibrium
- Replies: 5
- Views: 577
Re: deltaG at equilibrium
Calculating a negative deltaG means that the reaction is favorable in the forward direction. However, if you get a positive deltaG, this means the current direction is unfavorable, so it would proceed in the reverse direction.
- Sun Feb 04, 2018 10:52 am
- Forum: Gibbs Free Energy Concepts and Calculations
- Topic: Spontaneity
- Replies: 4
- Views: 479
Re: Spontaneity
Yes, all you would need is deltaG to determine spontaneity. However, in the absence of it, you would need enthalpy, temperature, and entropy in order to then determine deltaG
- Sun Jan 28, 2018 1:18 pm
- Forum: Concepts & Calculations Using First Law of Thermodynamics
- Topic: isothermal system
- Replies: 3
- Views: 462
Re: isothermal system
As far as isothermal systems go, I don't believe we can have a problem in which number of moles change since matter is neither created nor destroyed. However, the important part of an isothermal system is that temperature doesn't change. In this case, deltaU would be zero since our equation is depen...
- Sun Jan 28, 2018 1:12 pm
- Forum: Thermodynamic Definitions (isochoric/isometric, isothermal, isobaric)
- Topic: isothermal system
- Replies: 4
- Views: 438
Re: isothermal system
A good way to remember the types of systems is to break apart the word, so iso: same and thermal: temperature-related. Since the temperature is the same throughout the reaction, it would follow that Tf - Ti would equal 0. Then, in calculation, your change in internal energy would also be 0.
- Sun Jan 28, 2018 1:07 pm
- Forum: Thermodynamic Systems (Open, Closed, Isolated)
- Topic: Systems in practice
- Replies: 4
- Views: 524
Re: Systems in practice
Very true that real-world systems aren't ever truly isolated. However, devices such as the bomb calorimeter are close enough to be considered isolated since the amount of energy exchanged in an environment is very small. Thus, it can be practical to assume it's isolated.
- Sun Jan 21, 2018 3:10 pm
- Forum: Thermodynamic Systems (Open, Closed, Isolated)
- Topic: Internal Energy
- Replies: 3
- Views: 562
Re: Internal Energy
If you look at it mathematically, delta V is final V minus initial V, therefore your change would equate to the amount displaced. But, overall, we really are using the values of the entire system’s volume, just using the actual change between the two volumes.
- Sun Jan 21, 2018 3:06 pm
- Forum: Calculating Work of Expansion
- Topic: Lecture notes , work eqn
- Replies: 3
- Views: 280
Re: Lecture notes , work eqn
Yes exactly. Also, an irreversible reaction would be at equilibrium only after it has reacted, therefore it would not be able to react further.
- Sun Jan 21, 2018 12:10 pm
- Forum: Calculating Work of Expansion
- Topic: Irreversible vs Reversible
- Replies: 2
- Views: 298
Re: Irreversible vs Reversible
Additionally, because of the mechanisms of the irreversible reaction, you should always end up with a larger energy value than for a reversible reaction.
- Sun Jan 14, 2018 1:25 pm
- Forum: Phase Changes & Related Calculations
- Topic: Temperature during Phase Change
- Replies: 6
- Views: 443
Re: Temperature during Phase Change
In changing the temperature of a substance, heat can play a role as long as we aren't at the points of phase change for that substance. For example, water at 50 C can increase or decrease in temperature since it remains in its liquid state; however, as it hits 100 C, it stops changing temperature, b...
- Sun Jan 14, 2018 1:08 pm
- Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
- Topic: Specific heat capacity vs molar heat capacity
- Replies: 5
- Views: 620
Re: Specific heat capacity vs molar heat capacity
Not necessarily; Specific heat is particularly per a unit of mass, rather than just an amount of something. Molar heat capacity falls under an 'amount' since it is per one mole. So, I wouldn't associate them as one type of the other, but just two similar measures of heat capacity useful in their own...
- Sun Jan 14, 2018 1:00 pm
- Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
- Topic: Hess's Law
- Replies: 8
- Views: 1437
Re: Hess's Law
The only situation in which you wouldn't be able to cancel out intermediate compounds is if you haven't fixed the coefficients at all or there was a mathematical mistake in doing so. Otherwise, you can be confident in knowing that a Hess's Law problem is solvable. Be sure to double check coefficient...