Search found 33 matches

by Ashley Garcia 2L
Mon Mar 12, 2018 10:50 am
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Intermediates in Rate law
Replies: 3
Views: 182

Re: Intermediates in Rate law

For the overall rate law you should not include intermediates (because they are produced and then used up by the reaction). The rate law should only include reactants. Example: Step 1: A + B → C Step 2: C → D Overall: A + B → D (C is the intermediate) rate law = k[A][B] (do not include [C] in the ra...
by Ashley Garcia 2L
Mon Mar 12, 2018 10:46 am
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Rate-determining slowest step
Replies: 5
Views: 186

Re: Rate-determining slowest step

The rate determining step is the slowest step in the reaction mechanism. You can determine which of the elementary steps is the slow step by comparing their activation energies. The step with the largest activation energy is the rate determining/slow step because it requires the largest input of ene...
by Ashley Garcia 2L
Mon Mar 12, 2018 10:41 am
Forum: Arrhenius Equation, Activation Energies, Catalysts
Topic: What is A?
Replies: 4
Views: 144

Re: What is A?

Frequency factor (A) represents the frequency of collisions between reactant molecules with the correct orientation. Therefore, increasing A increases k (the rate constant), which increases the rate of the reaction.
by Ashley Garcia 2L
Mon Mar 05, 2018 4:25 pm
Forum: Second Order Reactions
Topic: Limiting Step
Replies: 7
Views: 434

Re: Limiting Step

The reaction rate is always dependent on the slow step, which is the limiting step. The slow step has the highest activation energy out of all the steps, and therefore has the slowest reaction rate because more energy is needed to overcome the activation energy barrier.
by Ashley Garcia 2L
Mon Mar 05, 2018 4:19 pm
Forum: Zero Order Reactions
Topic: Half life and rate order
Replies: 4
Views: 165

Re: Half life and rate order

Each rate order has different corresponding half-life equation.

Zero order reaction: half-life= [A]o/2k
*1st order reaction: half-life=ln2/k
2nd order reaction: half-life=1/k[A]o

*Note that the 1st order half-life does not depend on the initial concentration of the reactant.
by Ashley Garcia 2L
Mon Mar 05, 2018 4:17 pm
Forum: Zero Order Reactions
Topic: slope
Replies: 9
Views: 341

Re: slope

Using A → B Zero order reaction: graph [A] vs. time, this plot will produce a negative slope. Therefore, slope=-k because the rate constant k must be a positive value. 1st order reaction: graph ln[A] vs. time, this plot will produce a negative slope. Therefore, slope=-k because the rate constant k m...
by Ashley Garcia 2L
Mon Feb 26, 2018 2:45 pm
Forum: Kinetics vs. Thermodynamics Controlling a Reaction
Topic: units of the rate of reaction
Replies: 7
Views: 387

Re: units of the rate of reaction

The units of the rate of the reaction (k) depends on the order of the reaction and the corresponding rate law.

0 order: rate=k, units (1/s)
1st order: rate=k[R], units (L/mol x s)
2nd order: rate=k[R]^2, units (L^2/mol^2 x s)
by Ashley Garcia 2L
Mon Feb 26, 2018 2:41 pm
Forum: Kinetics vs. Thermodynamics Controlling a Reaction
Topic: Diamond and graphite
Replies: 8
Views: 600

Re: Diamond and graphite

The reaction of diamond --> graphite is spontaneous. Spontaneous does not imply that the reaction is fast, it means the reaction will eventually occur (because energy of the reactants > energy of the products). Therefore, a diamond is kinetically stable with respect to graphite because there is a la...
by Ashley Garcia 2L
Mon Feb 26, 2018 2:33 pm
Forum: First Order Reactions
Topic: Calculating slope
Replies: 4
Views: 180

Calculating slope

For a first order reaction, why does the slope = -k? Why do we need a negative sign in front of k?
by Ashley Garcia 2L
Mon Feb 19, 2018 2:51 pm
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: Concentration cell vs. Galvanic and Electrolytic cells [ENDORSED]
Replies: 1
Views: 1021

Concentration cell vs. Galvanic and Electrolytic cells [ENDORSED]

What is the difference between a concentration cell, galvanic cell, and electrolytic cell? Would a concentration cell be considered a galvanic or electrolytic cell?
by Ashley Garcia 2L
Mon Feb 19, 2018 2:48 pm
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: Concentration Cells
Replies: 5
Views: 187

Re: Concentration Cells

A concentration cell consists of two half-cells with the same electrodes but with different concentrations. This difference in ion concentration drives the flow of electrons from the more concentrated solution to the lower concentrated solution, which creates a voltage as the cell reaches equilibriu...
by Ashley Garcia 2L
Mon Feb 19, 2018 2:43 pm
Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
Topic: 14.51
Replies: 1
Views: 96

14.51

Question 14.51 asks us to consider a cell Ag(s) / Ag+(aq, 5.0mmolxL-1)// Ag+(aq, 0.15molxL-1) / Ag(s) and asks if this cell can do work. Why can we assume that the cell can do work because [Ag+] anode < [Ag+] cathode and the ratio is less than 1 and E>0 (as stated in the solutions manual)?
by Ashley Garcia 2L
Fri Feb 16, 2018 4:46 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Anode/ Cathode
Replies: 6
Views: 209

Re: Anode/ Cathode

Generally, the anode is on the left and the cathode is on the right. If this is not the case, however, you can identify which electrode is the anode and which is the cathode by looking at the half reactions. The oxidation half reaction takes place at the anode (electrons are lost), the reduction hal...
by Ashley Garcia 2L
Fri Feb 16, 2018 4:44 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Standard cell reduction potential
Replies: 1
Views: 75

Standard cell reduction potential

Why don't we flip the sign of the anode or multiply the standard cell reduction potential by any coefficients (ex. in a case where we multiply the entire half oxidation reaction by 3 to cancel out the 3 electrons gained the he half reduction reaction)? Does this have to do with cell potential being ...
by Ashley Garcia 2L
Fri Feb 16, 2018 4:37 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: 14.5 part a
Replies: 1
Views: 104

14.5 part a

We are asked to write the cell diagram for the reaction: AgBr(s) <--> Ag+(aq) + Br-(aq). I am confused about the order in which the ions and molecules are written for the anode portion of the cell diagram: Ag(s) | AgBr(s) | Br-(aq) || Ag+(aq) | Ag(s) The half-reaction for the anode is Ag+(aq) + Br-(...
by Ashley Garcia 2L
Fri Feb 09, 2018 9:46 pm
Forum: Thermodynamic Systems (Open, Closed, Isolated)
Topic: Open, closed, or isolated test 1 question
Replies: 10
Views: 550

Re: Open, closed, or isolated test 1 question

A 20mL vial with an organic solvent is an open system. An open system can exchange both energy and matter with the surroundings. Solvent (matter) can be taken out of the vial, the key word is that the vial is "open." The solvent can be heated up or cooled down, in which energy is exchange ...
by Ashley Garcia 2L
Fri Feb 09, 2018 9:43 pm
Forum: Calculating Standard Reaction Entropies (e.g. , Using Standard Molar Entropies)
Topic: How to calculate W [ENDORSED]
Replies: 6
Views: 298

How to calculate W [ENDORSED]

How do you calculate W in the equation S = kBlnW? What does W represent?
by Ashley Garcia 2L
Fri Feb 09, 2018 9:38 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: ΔG=0
Replies: 2
Views: 119

ΔG=0

What does it mean when ΔG=0? Why does ΔG=0 at the boiling point of a substance?
by Ashley Garcia 2L
Sat Feb 03, 2018 3:44 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Spontaneous
Replies: 14
Views: 385

Re: Spontaneous

When △G is negative, the reaction is spontaneous. A spontaneous reaction is one occurs on its own without being driven by an outside force. The products are favored over the formation of the reactants in a spontaneous reaction. Using the equation △G=△H-T△S: Positive △S and negative △H = spontaneous ...
by Ashley Garcia 2L
Sat Feb 03, 2018 3:37 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: When to use Q versus K [ENDORSED]
Replies: 6
Views: 471

Re: When to use Q versus K [ENDORSED]

Q is the reaction quotient and expresses the relative ratio of products to reactants at a given instant. Whereas, K is the equilibrium constant and expresses the ratio of products to reactants at equilibrium (when delta G=0). Use ΔG= ∆G°+ RTlnQ when the system is not at equilibrium. Use ΔG= ∆G°+ RTl...
by Ashley Garcia 2L
Sat Feb 03, 2018 3:32 pm
Forum: Van't Hoff Equation
Topic: How to calculate K [ENDORSED]
Replies: 3
Views: 297

How to calculate K [ENDORSED]

How would you calculate K if you are given ΔG°? I used the equation ΔG°=-RTlnK and isolated lnK so that lnK=ΔG°/-RT. How do you isolate the K term from lnK?
by Ashley Garcia 2L
Sat Jan 27, 2018 4:54 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Bondy Enthalpy Accuracy
Replies: 3
Views: 168

Bondy Enthalpy Accuracy

When calculating standard reaction enthalpies, why is using bond enthalpies the least accurate method?
by Ashley Garcia 2L
Sat Jan 27, 2018 4:50 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: Adiabatic system
Replies: 6
Views: 192

Re: Adiabatic system

Adiabatic systems are isolated systems, in which both energy/heat and matter are not transferred to the surroundings. Therefore q=0 and delta U=w (using the equation delta U = q + w) adiabatic process is one that occurs without transfer of heat or matter between a thermodynamic system and its surrou...
by Ashley Garcia 2L
Sat Jan 27, 2018 4:45 pm
Forum: Thermodynamic Systems (Open, Closed, Isolated)
Topic: Formation of Snow in Clouds [ENDORSED]
Replies: 5
Views: 969

Re: Formation of Snow in Clouds [ENDORSED]

Formation of snow in clouds is an exothermic process because heat is being transferred from the system (liquid water in the sky) to the surroundings, and the surroundings therefore heat up. In order for liquid water to be condensed into a solid form as snow, heat must be removed from the liquid wate...
by Ashley Garcia 2L
Mon Jan 22, 2018 3:58 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: Heat versus work
Replies: 6
Views: 189

Re: Heat versus work

Heat and work are both forms of energy. Heat is the energy associated with the random motion of particles, while work is the energy of ordered motion in a specific direction. First Law: Heat and work contribute to the total energy of the system. ΔU = q + w Second Law: Work can be transformed into he...
by Ashley Garcia 2L
Mon Jan 22, 2018 3:51 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: the sign of q
Replies: 5
Views: 130

Re: the sign of q

If the system loses/releases heat and warms the surroundings then q is negative (exothermic), if the system gains/absorbs heat and cools the surroundings then q is positive (endothermic). Therefore, in your example if an reaction " required 5.5 kJ of heat. How would we know if that value was po...
by Ashley Garcia 2L
Mon Jan 22, 2018 3:47 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: ΔU = ΔH for biological reactions
Replies: 2
Views: 98

ΔU = ΔH for biological reactions

Why does ΔU = ΔH in most biological reactions if ΔU = q + w? Why don't we account for work when calculating the change internal energy (ΔU).
by Ashley Garcia 2L
Mon Jan 15, 2018 9:56 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Hess's Law
Replies: 3
Views: 132

Re: Hess's Law

Hess's law states that the overall reaction enthalpy change is the sum of all the reaction enthalpies, regardless of the multiple steps into which the reaction can be divided. We are able to add the reaction enthalpies because enthalpy is a state function, in which the overall reaction enthalpy chan...
by Ashley Garcia 2L
Mon Jan 15, 2018 9:48 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: Expansion Work vs. Nonexpansion Work
Replies: 2
Views: 142

Expansion Work vs. Nonexpansion Work

What is the difference between expansion work and nonexpansion work? Why does the equation for expansion work have a negative sign in front of the external pressure? What is the equation for nonexpansion work?

Equation for expansion work: w = -Pex ΔV
by Ashley Garcia 2L
Mon Jan 15, 2018 9:37 pm
Forum: Thermodynamic Systems (Open, Closed, Isolated)
Topic: Type of Systems
Replies: 2
Views: 151

Re: Type of Systems

There are three types of systems (the region in which we are interested): open, closed, or isolated. Open system : can exchange matter and energy with the surroundings (everything else besides the system). An example of an open system is boiling soup in an open saucepan. The saucepan is an open syst...
by Ashley Garcia 2L
Fri Jan 12, 2018 5:43 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: 8.61
Replies: 4
Views: 156

Re: 8.61

Reverse the first equation and multiply it by 2 to get HBr on the product side with a coefficient of 2. Reverse the second equation to get the 2 NH3's to cancel out. Leave the last equation as is. You must also reverse the sign and multiply the first equations ΔH° by 2 and reverse the sign of the se...
by Ashley Garcia 2L
Fri Jan 12, 2018 5:33 pm
Forum: Phase Changes & Related Calculations
Topic: Heat Capacity vs. Specific Heat Capacity
Replies: 3
Views: 225

Heat Capacity vs. Specific Heat Capacity

Why is heat capacity considered an extensive property and specific heat capacity considered an intensive property? Why is specific heat capacity more useful in calculations than heat capacity, does this have to do with the fact that one is intensive and the other is extensive, respectfully?
by Ashley Garcia 2L
Fri Jan 12, 2018 5:26 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Standard Enthalpies of Formation of Diatomic Molecules
Replies: 6
Views: 1024

Re: Standard Enthalpies of Formation of Diatomic Molecules

The standard enthalpy of formation for diatomic molecules such as O2 (g) equals 0 because no change occurs in the reaction O2 (g) --> O2 (g). The definition of the standard enthalpy of formation is that the standard enthalpy of formation of an element in its most stable form equals 0. O2 (g) is the ...

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