Search found 30 matches

by Sarah Kiamanesh 1D
Tue Mar 12, 2019 5:48 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Units
Replies: 3
Views: 56

Re: Units

Zero order reactions: concentration over time (M/s)
First order reactions: s^-1
Second order reactions: 1/(M*s)
by Sarah Kiamanesh 1D
Tue Mar 12, 2019 5:45 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: molecularity
Replies: 3
Views: 69

Re: molecularity

Molecularity is determined from each step in the mechanism. You can count up the moles of reactants in each to find this. If the molecularity of the overall reaction is being determined, simply add up the elementary steps and cancel any intermediate terms, then add the moles of reactants to find this.
by Sarah Kiamanesh 1D
Tue Mar 12, 2019 5:41 pm
Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
Topic: Largest E°cell question test #2
Replies: 4
Views: 120

Re: Largest E°cell question test #2

The way to determine which species is the best reducing agent is by looking at the reduction potentials. Good reducing agents have low reduction potentials, meaning that they get oxidized and give up their electrons. On the other hand, good oxidizing agents have high reduction potentials, meaning th...
by Sarah Kiamanesh 1D
Tue Mar 05, 2019 11:24 am
Forum: First Order Reactions
Topic: order
Replies: 5
Views: 97

Re: order

using experimental data, as shown in lecture, we isolate changing concentrations of reactants by keeping the others constant and divide the rate and concentrations to obtain the order for that particular reactant. After doing so for each, we sum all of these orders to attain the overall reaction ord...
by Sarah Kiamanesh 1D
Tue Mar 05, 2019 11:21 am
Forum: General Rate Laws
Topic: Overall Order
Replies: 3
Views: 64

Re: Overall Order

Rate order helps us gauge how fast a reaction will occur. Reactant exponents are related to the concentrations, so depending on how much reactant we start with, rate order can tell us how long it will take for reactants to decrease and products to form
by Sarah Kiamanesh 1D
Tue Mar 05, 2019 11:20 am
Forum: General Rate Laws
Topic: Order of Reaction
Replies: 6
Views: 110

Re: Order of Reaction

The number of reactants do play a role in the overall order, as each contributes a certain exponent to the total that is added to derive this number. I believe that Professor Lavelle said that reactions become less common as their rate orders increase, so we should expect reactions to be of orders: ...
by Sarah Kiamanesh 1D
Mon Feb 25, 2019 10:22 am
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: 6L.5d
Replies: 1
Views: 40

Re: 6L.5d

Whatever phase you start with, you maintain it in the half reaction. Solids can oxidize too
by Sarah Kiamanesh 1D
Mon Feb 25, 2019 10:16 am
Forum: Gibbs Free Energy Concepts and Calculations
Topic: 9.63
Replies: 1
Views: 56

Re: 9.63

Positive values denote instability because it means that the reverse reaction is spontaneous. the reactants are produced more than the products are.
Negative values denote stability because the forward reaction is stable. the products are spontaneously produced.
by Sarah Kiamanesh 1D
Mon Feb 25, 2019 10:05 am
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: When to use Platinum
Replies: 5
Views: 89

Re: When to use Platinum

Take this reaction, for example:
Cu(s)+2Fe3+(aq)→Cu2+(aq)+2Fe2+(aq)

The cell diagram becomes
Cu∣Cu2+∥Fe2+,Fe3+∣Pt

Since both Fe2+ and Fe3+ are in solution, a Pt electrode is used
by Sarah Kiamanesh 1D
Wed Feb 20, 2019 7:16 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Delta H
Replies: 5
Views: 95

Re: Delta H

delta G = delta H - Tdelta S
spontaneity (denoted by either a positive or negative gibbs value) depends on both the change in enthalpy of the reaction as well as the temperature and change in entropy. Enthalpy alone is not enough to determine spontaneity
by Sarah Kiamanesh 1D
Wed Feb 20, 2019 7:14 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: stoichiometric coefficients for calculating Gibbs free energy
Replies: 2
Views: 53

stoichiometric coefficients for calculating Gibbs free energy

I understand that in some equations like the formation of NH3 (N2 + 3H2 --> 2NH3), the coefficients are all divided by two to produce 1/2N2 + 3/2H2 --> NH3, while other equations keep their original coefficients. what's the procedure for this? when do we need to do this? does it make a difference?
by Sarah Kiamanesh 1D
Wed Feb 20, 2019 7:09 pm
Forum: Balancing Redox Reactions
Topic: Reducing agents and oxidizing agents
Replies: 6
Views: 100

Re: Reducing agents and oxidizing agents

reducing agents bring about reduction by becoming oxidized and giving up their electrons
oxidizing agents bring about oxidation by becoming reduced and accepting electrons
by Sarah Kiamanesh 1D
Thu Feb 14, 2019 10:16 am
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: Changes in Pressure
Replies: 5
Views: 95

Re: Changes in Pressure

as given by Boyle's law, P1V1=P2V2. If you divide the P2 over to the left and the V1 over to the right, the relation becomes
P1/P2 = V2/V1. The left side of the equation is therefore interchangeable with the ratio on the right
by Sarah Kiamanesh 1D
Thu Feb 14, 2019 10:15 am
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Stability
Replies: 2
Views: 72

Re: Stability

the equilibrium constant is a ratio between concentration of products and reactants. if this value is greater than one, that means the numerator (products) are more prevalent, indicating that they are more stable. On the other hand, if this value is less than one, then the denominator (reactants) ar...
by Sarah Kiamanesh 1D
Thu Feb 14, 2019 10:13 am
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: Statistical and residual entropy
Replies: 3
Views: 79

Re: Statistical and residual entropy

Statistical entropy is what is deduced after using Boltzmann's Formula: S = klnW
Residual entropy, however, is the entropy of a system after it has been cooled to 0K. In a perfect crystal structure, there would be no residual entropy, but distortions in structure contributes to this.
by Sarah Kiamanesh 1D
Tue Feb 05, 2019 3:38 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Standard formation deltaH
Replies: 2
Views: 46

Re: Standard formation deltaH

delta H of formation is the change in enthalpy during the formation of one mole of the substance from its constituent elements. It's used in calculating the change in enthalpy of a reaction, where we calculate the delta formation of the products and subtract that of the reactants from it.
by Sarah Kiamanesh 1D
Tue Feb 05, 2019 2:59 pm
Forum: Calculating Work of Expansion
Topic: Reversible and Irreversible Reactions
Replies: 2
Views: 54

Re: Reversible and Irreversible Reactions

More work is performed if the process is completed slowly rather than quickly, which loses less heat to the surroundings. Reversible processes are infinitely slow and perform the maximum work. This is a reversible process because a very small increase in the external pressure would cause the gas to ...
by Sarah Kiamanesh 1D
Tue Feb 05, 2019 2:55 pm
Forum: Calculating Standard Reaction Entropies (e.g. , Using Standard Molar Entropies)
Topic: 4I.3
Replies: 3
Views: 305

Re: 4I.3

Entropy (S) of vaporization = delta H (vaporization) / Boiling Point in Kelvin Using this equation and plugging in the values we already know: 85 = delta H (vap) / (80 + 273) which results in: Delta H (vap) = 30.0KJ/mol Now for part B: we know that for 1 mole of benzene, delta S (system) = 85 J/mole...
by Sarah Kiamanesh 1D
Wed Jan 30, 2019 10:20 am
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Most stable form enthalpy
Replies: 3
Views: 87

Re: Most stable form enthalpy

Elements in their most stable form have standard enthalpy of formation equal to zero because that is how they exist naturally in nature. During reactions, these bonds aren't formed, they exist like that prior to the reaction. Because there is no formation, the value is zero.
by Sarah Kiamanesh 1D
Wed Jan 30, 2019 10:17 am
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: 4D.23 7th Ed.
Replies: 1
Views: 45

Re: 4D.23 7th Ed.

For this problem, we want to cancel out NO2 using Hess's Law because that's the only component for which we don't know the standard enthalpy of formation for. To cancel this, we multiply the second equation by 1/2 and add the two equations. Remember to adjust the standard enthalpies of the reactions...
by Sarah Kiamanesh 1D
Wed Jan 30, 2019 10:06 am
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: Standard enthalpy of formation vs. enthalpy of formation
Replies: 3
Views: 58

Re: Standard enthalpy of formation vs. enthalpy of formation

Standard enthalpy of formation uses the enthalpy values for reactants and products in their standard states, yes. The textbook uses contradictory units, but if the problem gives you energy in KJ/mole, keep that consistent.
by Sarah Kiamanesh 1D
Wed Jan 23, 2019 9:37 pm
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: Increase in Volume Effect on Equilibrium
Replies: 6
Views: 149

Re: Increase in Volume Effect on Equilibrium

Volume and pressure are inversely related. When volume increases, pressure decreases, which is also an altered state of the system that needs to be corrected by Le Chatelier's principle. The system increases pressure back to its original amount by favoring the side of the reaction with more moles, s...
by Sarah Kiamanesh 1D
Wed Jan 23, 2019 9:35 pm
Forum: Phase Changes & Related Calculations
Topic: ∆Hsub=∆Hfus+∆Hvap
Replies: 3
Views: 61

Re: ∆Hsub=∆Hfus+∆Hvap

Sublimation is the phase change from solid to vapor. Fusion is the transition from solid to liquid, and vaporization is the transition from liquid to gas. Because these transitions are state properties, their enthalpies can be added together. The enthalpy of fusion added to the enthalpy of vaporizat...
by Sarah Kiamanesh 1D
Tue Jan 22, 2019 8:44 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: concentration of H3O and OH-
Replies: 1
Views: 58

Re: concentration of H3O and OH-

Basically, because hydroiodic acid is a strong acid, it dissociates completely in an aqueous solution. This means that the hydronium concentration is equivalent to the initial molarity of the acid. The back of the book represented this value in micromoles, so instead of just writing it as 6.0x10^-5,...
by Sarah Kiamanesh 1D
Mon Jan 14, 2019 8:33 pm
Forum: Non-Equilibrium Conditions & The Reaction Quotient
Topic: Maintaining relation between [H3O+] and [OH-]
Replies: 2
Views: 64

Maintaining relation between [H3O+] and [OH-]

The textbook emphasizes that because Kw is an equilibrium constant, the product of the concentrations of H3O+ and OH- ions in any aqueous solution is always equal to Kw and that when the concentration of one increases, the other decreases, and vice versa, to maintain this proportion. What is the pro...
by Sarah Kiamanesh 1D
Mon Jan 14, 2019 8:05 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: the value of equilibrium constant
Replies: 3
Views: 63

Re: the value of equilibrium constant

It's crucial you pay attention to whether the problem specifies molecular quantities in molar concentration or partial pressures, because the constant's value is dependent on this. To convert between these two constants, use the formula:
K = (RT)^(delta nr)(Kc)
by Sarah Kiamanesh 1D
Mon Jan 14, 2019 7:56 pm
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: Changes in pressure
Replies: 2
Views: 63

Re: Changes in pressure

By Le Chatelier's Principle, the system works to minimize any changes in pressure. If the pressure of the system increases by way of decreasing volume, it responds by shifting in the direction of the least separate molecules so as to reduce particle collisions and decrease pressure. If pressure is i...
by Sarah Kiamanesh 1D
Wed Jan 09, 2019 10:29 am
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: Exothermic Reactions
Replies: 9
Views: 145

Re: Exothermic Reactions

You basically need to know the enthalpies of all the products and reactants. These are set values provided in tables. If the sum of the enthalpies of the reactants is greater than those of the products, the reaction will be exothermic. It releases energy into the system. If the sum of the enthalpies...
by Sarah Kiamanesh 1D
Wed Jan 09, 2019 10:20 am
Forum: Ideal Gases
Topic: Units
Replies: 5
Views: 74

Re: Units

For the Ideal Gas Law:
P (pressure) is measured in pascals
V (volume) is measured in cubic meters
n is the number of moles
T (temperature) is measured in kelvins
R (the constant) has value 8.314 J/(K. mol)
by Sarah Kiamanesh 1D
Wed Jan 09, 2019 10:15 am
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: Applying Le Chatelier's principle
Replies: 2
Views: 49

Re: Applying Le Chatelier's principle

For exothermic reactions, when the temperature of the system is increased, reactants are favored and the equilibrium constant (K) decreases. This results in less heat being released, which offsets the increase in temperature. For endothermic reactions, when the temperature of the system is increased...

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