Search found 32 matches

by RyanS2J
Mon Mar 12, 2018 11:28 am
Forum: Biological Examples
Topic: Nitric Oxide Catalyses
Replies: 6
Views: 288

Re: Nitric Oxide Catalyses

You can determine NO is a catalyst from the fact that it is a species that appears as a reactant in an early step and as a product in a later step, indicating that the species is not consumed in the reaction, a fundamental property of catalysts.
by RyanS2J
Mon Mar 12, 2018 5:49 am
Forum: Arrhenius Equation, Activation Energies, Catalysts
Topic: 65.b
Replies: 2
Views: 78

Re: 65.b

You could also determine the reaction is endothermic from the fact that the activation energy of the forward reaction is greater than that of the reverse reaction. Were it the opposite, the reaction would be exothermic.
by RyanS2J
Mon Mar 12, 2018 4:20 am
Forum: Arrhenius Equation, Activation Energies, Catalysts
Topic: 15.71
Replies: 1
Views: 73

Re: 15.71

Catalysts typically appear as a reactant in an early elementary step and again as a product in a later step; they are not consumed in the course of a reaction. OH- is a catalyst because it meets these criteria.
by RyanS2J
Mon Mar 05, 2018 8:52 am
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Slow Steps
Replies: 1
Views: 52

Re: Slow Steps

Yes; the overall rate law is governed by the slowest elementary step, since the overall reaction can only go as fast as the slowest step permits. The slowest elementary step is thus also known as the rate-determining step.
by RyanS2J
Mon Mar 05, 2018 5:56 am
Forum: Second Order Reactions
Topic: Half-life of second order reactions
Replies: 2
Views: 78

Re: Half-life of second order reactions

The half-life of a second order reaction is dependent on reactant concentration. The second order half-life is the time it takes for [A]t in 1/[A]t = 1/[A]o + kt to become half of [A]o. Substituting in [A]o/2 for [A]t yields that the half-life is 1/k[A]o. That is, the half life is inversely proporti...
by RyanS2J
Mon Mar 05, 2018 5:46 am
Forum: Second Order Reactions
Topic: 15.35
Replies: 2
Views: 95

Re: 15.35

Since it's a second order reaction, you would use 1/[A]t = 1/[A]o + kt for the final step rather than ln[A]t = ln[A]o - kt, which only applies for first order reactions.
by RyanS2J
Mon Feb 26, 2018 7:12 am
Forum: Zero Order Reactions
Topic: Homework question
Replies: 2
Views: 101

Re: Homework question

For a zero order reaction, since rate = k, the units of k would simply be moles per liter per second, or mol•L^-1•s^-1.
by RyanS2J
Mon Feb 26, 2018 6:01 am
Forum: First Order Reactions
Topic: 15.27
Replies: 6
Views: 223

Re: 15.27

Since the reaction is first order, I used ln[A]t = ln[A]o - kt, where [A]t is the concentration of A after some time and [A]o is the initial concentration of A, and plugged in the fraction of A remaining after some time for [A]t and 1 for [A]o.
by RyanS2J
Mon Feb 26, 2018 5:53 am
Forum: General Rate Laws
Topic: Unique Rate of Reactions
Replies: 3
Views: 88

Re: Unique Rate of Reactions

The unique rate of a reaction is the rate a particular species is consumed or formed divided by its coefficient in the chemical reaction.
by RyanS2J
Tue Feb 20, 2018 7:29 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Cell Potential and Spontanaeity
Replies: 2
Views: 74

Re: Cell Potential and Spontanaeity

If the overall cell potential E is negative, by deltaG = -nFE, deltaG would be positive, indicating a non-spontaneous reaction.
by RyanS2J
Mon Feb 19, 2018 10:45 am
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Electrolytes in Galvanic Cells
Replies: 1
Views: 40

Re: Electrolytes in Galvanic Cells

In a Galvanic cell, electrons flow from anode to cathode. The ions (such as SO4 2- in this case) are simply present to complete the electric circuit.
by RyanS2J
Mon Feb 19, 2018 9:22 am
Forum: Balancing Redox Reactions
Topic: Standard Reduction Potential
Replies: 3
Views: 102

Re: Standard Reduction Potential

From a mathematical standpoint, if you take a look at the equation deltaG = -nFE, and rearrange it into E = -deltaG/nF, you will see that if we multiply the chemical reaction by a factor, both deltaG and n change by that factor, so the net result is no change to the value of E.
by RyanS2J
Mon Feb 19, 2018 12:19 am
Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
Topic: G=-nFE
Replies: 3
Views: 151

Re: G=-nFE

n is simply referring to the number of moles of electrons transferred. If it were delta n, then a negative change in moles would result in a negative value for delta n.
by RyanS2J
Mon Feb 12, 2018 9:24 am
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Gibbs and Stability
Replies: 1
Views: 54

Re: Gibbs and Stability

Molecules in nature tend to proceed toward their most stable state. A chemical reaction with a positive Gibbs free energy is nonspontaneous, which means energy is required to move the molecule from its current state to a less stable state (for were the reaction spontaneous, no energy input would be ...
by RyanS2J
Mon Feb 12, 2018 5:59 am
Forum: Gibbs Free Energy Concepts and Calculations
Topic: 9.103
Replies: 2
Views: 177

Re: 9.103

That formula still applies. It's just that CH3CH2OH is the only noteworthy product (H2 has a standard Gibbs free energy of 0), so you'd be subtracting the reactant Gibbs free energy values from that of CH3CH2OH. But regardless, the formula should still give you the correct value.
by RyanS2J
Mon Feb 12, 2018 5:23 am
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: Self Test 9.2
Replies: 1
Views: 78

Re: Self Test 9.2

Since they're asking for molar entropy (by definition the entropy at one mole of substance), n would simply be 1.
by RyanS2J
Mon Feb 05, 2018 3:35 pm
Forum: Balancing Redox Reactions
Topic: 14.3
Replies: 3
Views: 74

Re: 14.3

Also, to clarify, the question is asking for the oxidizing and reducing agents. The oxidizing agent oxidizes another element or molecule by taking the electron(s) from this other element or molecule (which then loses the electron(s)), and by taking the electron(s), the oxidizing agent itself is redu...
by RyanS2J
Mon Feb 05, 2018 2:14 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: 9.85
Replies: 2
Views: 104

Re: 9.85

b) The entropy generally increases for a reaction wherein a salt (a highly stable and structured compound) is dissolved into its component ions. Thus, for the dissolving of potassium nitrate in aqueous solution, the entropy increases, yielding a positive deltaS.
by RyanS2J
Mon Feb 05, 2018 1:59 pm
Forum: Balancing Redox Reactions
Topic: 14.3
Replies: 3
Views: 74

Re: 14.3

Since sulfur S is going from a state of +2 in the reactants to +6 in the products, it looks to me like sulfur is the one losing the electrons and being oxidized.
by RyanS2J
Mon Feb 05, 2018 9:48 am
Forum: Gibbs Free Energy Concepts and Calculations
Topic: DG = 0 [ENDORSED]
Replies: 3
Views: 135

Re: DG = 0 [ENDORSED]

DeltaG is 0 at equilibrium because neither the forward nor the reverse reactions are favored. They occur at equal rates. If deltaG were to be negative and spontaneous for one reaction (either forward or reverse), that would mean the opposite reaction (either reverse or forward, respectively), would ...
by RyanS2J
Mon Jan 29, 2018 10:51 am
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: 9.15a [ENDORSED]
Replies: 2
Views: 68

Re: 9.15a [ENDORSED]

Since freezing is an exothermic process (heat is released from the system), the deltaH in the equation would take a negative sign. Also, as in Table 8.3, the standard enthalpy of melting is +6.01 kJ/mol, so since you are concerned with the reverse reaction (freezing), you would flip the sign and mak...
by RyanS2J
Mon Jan 29, 2018 10:47 am
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: Temperature units for Entropy [ENDORSED]
Replies: 2
Views: 95

Re: Temperature units for Entropy [ENDORSED]

It matters, since calculating in Kelvin versus in Celsius gives you different values for the natural log. Entropy should be calculated using Kelvin.
by RyanS2J
Mon Jan 29, 2018 10:42 am
Forum: Thermodynamic Systems (Open, Closed, Isolated)
Topic: Second Law of Thermodynamics [ENDORSED]
Replies: 5
Views: 234

Re: Second Law of Thermodynamics [ENDORSED]

Though organisms such as humans have grown and do grow more ordered over time, they only do so at the expense of other reactions that generate more entropy to compensate for and override the entropy decrease that accompanies the building of complex molecules and structures. Cellular respiration to g...
by RyanS2J
Tue Jan 23, 2018 3:12 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: H2O as a liquid or vapor
Replies: 2
Views: 66

Re: H2O as a liquid or vapor

Combustion can produce either liquid or vapor water, but in the case of the standard enthalpy of combustion (calculated under standard conditions), water is taken to be in liquid form.
by RyanS2J
Tue Jan 23, 2018 3:00 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Standard state
Replies: 2
Views: 75

Re: Standard state

Some examples that might be helpful are that carbon in its standard state is graphite, and certain elements (H, N, O, F, Cl, Br, I) exist in their diatomic forms at standard state (H2, N2, O2, F2, etc.).
by RyanS2J
Tue Jan 23, 2018 12:47 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Hess's Law
Replies: 5
Views: 156

Re: Hess's Law

When adding two chemical equations using Hess' Law, identities such as CO2 that appear on both sides can indeed be crossed out, provided they are in equal quantities.
by RyanS2J
Tue Jan 16, 2018 9:05 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: reaction enthalpies
Replies: 1
Views: 67

Re: reaction enthalpies

You would first find, through given information or through Appendix 2A, the value of the standard reaction enthalpy, or delta H, for your reaction. You would then convert however many moles you are reacting or producing to however much heat the reaction is absorbing or releasing by treating heat as ...
by RyanS2J
Tue Jan 16, 2018 3:37 pm
Forum: Phase Changes & Related Calculations
Topic: question 8.41
Replies: 5
Views: 223

Re: question 8.41

Since you are melting the ice cube in water when you place it in the glass, make sure you don't forget to include the enthalpy of fusion term needed to transform an ice cube at 0 degrees into liquid water at 0 degrees. Also make sure that units are consistent (ex. convert J to kJ, or vice versa).
by RyanS2J
Tue Jan 16, 2018 3:20 pm
Forum: Calculating Standard Reaction Entropies (e.g. , Using Standard Molar Entropies)
Topic: standard state of substances
Replies: 4
Views: 146

Re: standard state of substances

Some common ones are that H2, N2, O2, F2, Cl2, Br2, and I2 are the standard states of their respective elements. These standard states are often used in the calculation of standard reaction enthalpy.
by RyanS2J
Wed Jan 10, 2018 6:57 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Enthalpy and Entropy
Replies: 2
Views: 79

Re: Enthalpy and Entropy

Enthalpy is the measurement of the sum of the internal energy and the product of the pressure and volume of a system. Entropy, on the other hand, is simply a measurement of disorder in the universe. Although we haven't covered it yet, the equation G = H - TS partially relates enthalpy H and entropy ...
by RyanS2J
Wed Jan 10, 2018 3:20 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Change in Enthalpy of the Reverse Reaction
Replies: 5
Views: 148

Re: Change in Enthalpy of the Reverse Reaction

With melting and vaporization (think melting an ice cube in your hand or boiling water on a stove), an input of heat is required to transform solid to liquid, and liquid to gas, respectively. Because heat is added to the system in order for these reactions to occur, the reaction is endothermic, with...
by RyanS2J
Tue Jan 09, 2018 5:09 pm
Forum: Phase Changes & Related Calculations
Topic: Endothermic Reaction
Replies: 10
Views: 434

Re: Endothermic Reaction

If you think of placing an ice cube on your hand, the ice cube melts because the heat of your hand is transferred to the ice cube. In other words, your hand provides the input of heat needed to melt the ice cube, and since heat must be put in in order for this melting reaction to proceed, this react...

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