Search found 31 matches

by Sarah Maraach 2K
Sun Mar 18, 2018 9:21 am
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Stoichiometric coefficients
Replies: 4
Views: 381

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.
by Sarah Maraach 2K
Sun Mar 18, 2018 9:12 am
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Elementary steps
Replies: 2
Views: 274

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.
by Sarah Maraach 2K
Sun Mar 18, 2018 9:04 am
Forum: *Nucleophiles
Topic: SN2 Reactions
Replies: 4
Views: 1045

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...
by Sarah Maraach 2K
Sun Mar 18, 2018 8:57 am
Forum: *Electrophiles
Topic: How do you categorize Electrophiles?
Replies: 2
Views: 714

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.
by Sarah Maraach 2K
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: 214

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.
by Sarah Maraach 2K
Sun Mar 11, 2018 5:21 pm
Forum: First Order Reactions
Topic: Integrated Rate Laws
Replies: 4
Views: 310

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.
by Sarah Maraach 2K
Mon Mar 05, 2018 9:49 pm
Forum: Second Order Reactions
Topic: 2nd order rxn integration
Replies: 2
Views: 115

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.
by Sarah Maraach 2K
Sun Mar 04, 2018 5:40 pm
Forum: First Order Reactions
Topic: Integrated rate law for first order reaction
Replies: 3
Views: 170

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.
by Sarah Maraach 2K
Sun Mar 04, 2018 2:39 pm
Forum: General Rate Laws
Topic: Multiple Reactants
Replies: 2
Views: 140

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...
by Sarah Maraach 2K
Sun Mar 04, 2018 2:16 pm
Forum: General Rate Laws
Topic: How to know when to use which formula?
Replies: 2
Views: 133

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...
by Sarah Maraach 2K
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: 139

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.
by Sarah Maraach 2K
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: 173

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.
by Sarah Maraach 2K
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: 171

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.
by Sarah Maraach 2K
Sun Feb 18, 2018 1:26 pm
Forum: Balancing Redox Reactions
Topic: process to balance redox reactions
Replies: 2
Views: 162

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.
by Sarah Maraach 2K
Sun Feb 18, 2018 1:23 pm
Forum: Balancing Redox Reactions
Topic: Acidic vs. Basic Solutions
Replies: 3
Views: 170

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.
by Sarah Maraach 2K
Sun Feb 18, 2018 1:20 pm
Forum: Balancing Redox Reactions
Topic: Sign of E when anode rxn reverses
Replies: 2
Views: 145

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...
by Sarah Maraach 2K
Sun Feb 11, 2018 10:20 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Oxidation
Replies: 4
Views: 115

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.
by Sarah Maraach 2K
Sun Feb 11, 2018 10:16 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Cell Potential
Replies: 2
Views: 96

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.
by Sarah Maraach 2K
Sun Feb 11, 2018 10:13 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: E and G
Replies: 2
Views: 121

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.
by Sarah Maraach 2K
Sun Feb 04, 2018 11:27 am
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Gibbs Free Energy: State Function?
Replies: 3
Views: 135

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...
by Sarah Maraach 2K
Sun Feb 04, 2018 10:58 am
Forum: Gibbs Free Energy Concepts and Calculations
Topic: deltaG at equilibrium
Replies: 5
Views: 135

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.
by Sarah Maraach 2K
Sun Feb 04, 2018 10:52 am
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Spontaneity
Replies: 4
Views: 151

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
by Sarah Maraach 2K
Sun Jan 28, 2018 1:18 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: isothermal system
Replies: 3
Views: 187

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...
by Sarah Maraach 2K
Sun Jan 28, 2018 1:12 pm
Forum: Thermodynamic Definitions (isochoric/isometric, isothermal, isobaric)
Topic: isothermal system
Replies: 4
Views: 185

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.
by Sarah Maraach 2K
Sun Jan 28, 2018 1:07 pm
Forum: Thermodynamic Systems (Open, Closed, Isolated)
Topic: Systems in practice
Replies: 4
Views: 204

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.
by Sarah Maraach 2K
Sun Jan 21, 2018 3:10 pm
Forum: Thermodynamic Systems (Open, Closed, Isolated)
Topic: Internal Energy
Replies: 3
Views: 220

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.
by Sarah Maraach 2K
Sun Jan 21, 2018 3:06 pm
Forum: Calculating Work of Expansion
Topic: Lecture notes , work eqn
Replies: 3
Views: 141

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.
by Sarah Maraach 2K
Sun Jan 21, 2018 12:10 pm
Forum: Calculating Work of Expansion
Topic: Irreversible vs Reversible
Replies: 2
Views: 168

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.
by Sarah Maraach 2K
Sun Jan 14, 2018 1:25 pm
Forum: Phase Changes & Related Calculations
Topic: Temperature during Phase Change
Replies: 6
Views: 223

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...
by Sarah Maraach 2K
Sun Jan 14, 2018 1:08 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Specific heat capacity vs molar heat capacity
Replies: 5
Views: 169

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...
by Sarah Maraach 2K
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: 373

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...

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