## Search found 42 matches

Fri Mar 16, 2018 11:07 am
Forum: Reaction Mechanisms, Reaction Profiles
Topic: 15.67
Replies: 3
Views: 222

### Re: 15.67

Then using that ratio, you compare the rates by showing Kcat/Kuncat is different by a factor of 1000 (set equal to 1000). Next, using the exponential equation you divide the two formulas (replacing Ea(cat) with .6Ea(uncat)). Algebraic manipulation leads you to the expnential: e^(.4(125)/(298x8.314))...
Fri Mar 16, 2018 10:59 am
Forum: Kinetics vs. Thermodynamics Controlling a Reaction
Topic: Test 3
Replies: 1
Views: 249

### Re: Test 3

Could you clarify what you mean here? Thanks!
Mon Mar 12, 2018 8:03 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: reaction profile
Replies: 3
Views: 227

### reaction profile

are the activation energies for the forward and reverse reactions ever equivalent?
Sun Mar 11, 2018 1:01 pm
Forum: Arrhenius Equation, Activation Energies, Catalysts
Topic: catalyst vs intermediate
Replies: 2
Views: 209

### catalyst vs intermediate

how do we determine the difference between the two since they are on both sides of the equation when given the steps to a reaction mechanism and we have to write the overall reaction? Thanks!
Sun Mar 11, 2018 11:58 am
Forum: Arrhenius Equation, Activation Energies, Catalysts
Topic: 15.63
Replies: 2
Views: 201

### 15.63

Why does ln (k1/k2)=0.59? On my calculator I keep getting -0.59 because when I use the Arrhenius equation isn't the activation energy variable negative? Thanks!
Mon Mar 05, 2018 11:27 pm
Forum: First Order Reactions
Topic: Half-Lives for First Order Reactions
Replies: 2
Views: 272

### Re: Half-Lives for First Order Reactions

For the half life formula for first order reactions, the initial condition is in the equation but they are canceled to simplify! For [A] at its half life it is equivalent to 1/2[A]o (half of initial concentration) So in the integrated rate law, ln 1/2[A]o = -kt1/2 + ln [A]o simplifying... ln ((1/2[A...
Mon Mar 05, 2018 11:06 pm
Forum: Zero Order Reactions
Topic: slope
Replies: 3
Views: 368

### slope

for the plot of concentration vs time for the integrated rate law of a zero reaction, I understand how the slope is negative k from a mathematical viewpoint, but what does that mean in real life?
Sun Mar 04, 2018 6:25 pm
Forum: First Order Reactions
Replies: 4
Views: 248

Is radioactive decay a first order reaction? If so, why?
Sun Mar 04, 2018 6:18 pm
Forum: Method of Initial Rates (To Determine n and k)
Topic: order of reactant importance
Replies: 2
Views: 210

### order of reactant importance

How does the order of the reactant (n) give insight into the reaction mechanism?
Tue Feb 27, 2018 2:28 pm
Forum: First Order Reactions
Topic: 15.23 (c)
Replies: 1
Views: 136

### Re: 15.23 (c)

Because the overall reaction is different (2A -> B + C vs the previous A -> B), you have to calculate [A]t. Since [A]t is concentration of A, you incorporate the coefficient here to 'cancel' mol B. [A]t = [A]0 - [(2 mol A/1 mol B)(.034 mol B/L)] You can see, the mol B cancel so the calculation for [...
Sun Feb 25, 2018 10:04 pm
Forum: General Rate Laws
Topic: Reaction rates
Replies: 3
Views: 227

### Re: Reaction rates

because in a reaction initially, all we know are the reactant concentration (since products are forming during the reaction)
Tue Feb 20, 2018 4:40 pm
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: 14.47 a
Replies: 6
Views: 428

### 14.47 a

Hi I understand how ln Q = (about) 15, but how does that mean Q = 10^6?
Mon Feb 19, 2018 1:43 pm
Forum: Interesting Applications: Rechargeable Batteries (Cell Phones, Notebooks, Cars), Fuel Cells (Space Shuttle), Photovoltaic Cells (Solar Panels), Electrolysis, Rust
Topic: calculating potentials with electrolysis
Replies: 1
Views: 324

### calculating potentials with electrolysis

Did Lavelle say we must understand electrolysis and be able to do calculations/problems related to it for the test? My notes only seem to be the concepts of electrolysis, but in his list of chapter problems there are some that ask for calculating minimum potential for an onset of electrolysis. Thanks!
Wed Feb 14, 2018 12:35 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: stability vs spontaneity [ENDORSED]
Replies: 1
Views: 446

### stability vs spontaneity[ENDORSED]

what is the relationship between entropy, stability, and spontaneity? is it if entropy is greater than 0, which means the rxn is spontaneous, the stability is low?
Mon Feb 12, 2018 8:51 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: work and free energy
Replies: 2
Views: 121

### work and free energy

what is the relationship between free energy and work?
Fri Feb 09, 2018 9:43 am
Forum: Gibbs Free Energy Concepts and Calculations
Topic: oxygen has 0 Gibbs free energy of formation
Replies: 2
Views: 2444

### Re: oxygen has 0 Gibbs free energy of formation

Yes, and the enthalpy of formation of elements in their standard state, like H2, O2 and I2, are all 0. So when you calculate delta G formation, the numerator is 0 so the delta G is 0. Hope this helps!
Fri Feb 09, 2018 9:39 am
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: 9.7
Replies: 2
Views: 196

### Re: 9.7

For this problem it requires two steps, and the final answer should be in J/K. A) First, using the C of an ideal gas at a constant pressure = 5/2(R). Next, using that C value, you use the equation delta S = n x C x ln (T2/T1). Don't forget to convert the temperature into Kelvin from Celsius. B) The ...
Fri Feb 09, 2018 9:32 am
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: Entropy Phase Change
Replies: 2
Views: 170

### Re: Entropy Phase Change

Entropy is often associated as the amount of disorder in a system. By looking at the pictures, you can see there is an increase in disorder as the particles shift from a rigid solid, to a little more broken up liquid phase, to random movement of particles in the gaseous stage. That is why there is a...
Fri Feb 09, 2018 9:17 am
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Problem 9.81
Replies: 1
Views: 140

### Re: Problem 9.81

If this problem was on a test I believe we would be given the equation clearly stating the products and reactants, but we would possibly have to balance the equation. Using the equation you can calculate delta G by subtracting the delta G of the reactants from the delta G of the products and the app...
Fri Feb 09, 2018 9:08 am
Forum: Third Law of Thermodynamics (For a Unique Ground State (W=1): S -> 0 as T -> 0) and Calculations Using Boltzmann Equation for Entropy
Topic: Statistical entropy
Replies: 1
Views: 123

### Re: Statistical entropy

I think the textbook said this because Boltzmann equation is the number of possible microstates, and statistical analysis looks at the relationship between possibility and actual.
Mon Feb 05, 2018 2:20 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: 9.85 part e
Replies: 1
Views: 140

### 9.85 part e

How do we determine the driving force of a reaction?
Mon Feb 05, 2018 9:53 am
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: DS= q/T for surroundings or system?
Replies: 2
Views: 189

### Re: DS= q/T for surroundings or system?

Yes, I believe we can use that equation for calculating both ∆S for a system or its surroundings, but you would have to make sure the sign of q on the numerator matches the situation correctly.
Mon Feb 05, 2018 9:33 am
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: 8.67c
Replies: 1
Views: 129

### Re: 8.67c

The molecule is actually C6H6, not C6H8. Therefore the equation is 6C(s) + 3H2(g) -> C6H6(l)
Mon Feb 05, 2018 9:30 am
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: Heat Capacity Value
Replies: 2
Views: 203

### Re: Heat Capacity Value

I think that equation is averaged by the real values for heat capacity of monatomic ideal gases (ex: Helium, Argon, Neon, etc).
Wed Jan 31, 2018 9:36 am
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: 9.11
Replies: 2
Views: 151

### 9.11

In this problem the equation we are using delta S = n R ln p1/p2 since volume and pressure are inversely related, but for the value of R why are we using 8.314 J/Kmol and not 0.08206 Latm/Kmol since the unit within the natural log part of the equation is atm?
Sun Jan 28, 2018 11:27 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: 8.41
Replies: 3
Views: 207

### Re: 8.41

the most important fact of this problem is q(system)=-q(surroundings) so whatever heat the ice lost the water gained. When calculating you can't forget the negative sign! One side of the equation you multiply the moles of ice (must convert) times the heat of fusion then add that to the equation of q...
Sun Jan 28, 2018 11:22 pm
Forum: Thermodynamic Systems (Open, Closed, Isolated)
Topic: Can a system exchange matter but not energy?
Replies: 4
Views: 223

### Re: Can a system exchange matter but not energy?

I do not think this is possible because transferring matter even if there is no change in temperature is still exchanging energy. The opposite, exchanging energy but not matter is a closed system.
Sun Jan 28, 2018 11:14 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: entropy property? [ENDORSED]
Replies: 2
Views: 157

### entropy property?[ENDORSED]

Is entropy an intensive or extensive property?
Sun Jan 21, 2018 10:26 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: 8.93 part a
Replies: 1
Views: 133

### 8.93 part a

Why does the change in moles of only gas matter versus the overall difference in moles on each side of the reaction?
Sun Jan 21, 2018 9:13 pm
Forum: Thermodynamic Definitions (isochoric/isometric, isothermal, isobaric)
Topic: work definition
Replies: 5
Views: 295

### Re: work definition

work is the energy transferred by compression or expansion while heat is the energy transferred by heating or cooling. hope this helps!
Sun Jan 21, 2018 4:39 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Enthalpy equation
Replies: 2
Views: 189

### Re: Enthalpy equation

It comes from the equation for calculating internal heat when changing the energy of a closed system at a constant pressure. That equation is U = H - PV, so when rearranged you can get H = U + PV

hope this helps!
Sat Dec 09, 2017 9:51 pm
Forum: Photoelectric Effect
Topic: Number of photons and intensity
Replies: 2
Views: 174

### Re: Number of photons and intensity

yes, increasing the number of photons does increase the intensity of the light, but in the photoelectric effect since we are talking about light as particles (photons), increasing intensity has no effect on removing an electron from the metal surface. to do that you must increase the frequency at wh...
Sat Dec 09, 2017 9:47 pm
Forum: Calculating pH or pOH for Strong & Weak Acids & Bases
Topic: titration
Replies: 3
Views: 211

### Re: titration

no!
Sat Dec 09, 2017 4:54 pm
Forum: Wave Functions and s-, p-, d-, f- Orbitals
Topic: Lobes [ENDORSED]
Replies: 4
Views: 312

### Re: Lobes[ENDORSED]

When it comes to lobes I think we just need to understand their shape when it comes to bonding (i.e. pi bonds).
Sun Dec 03, 2017 6:04 pm
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: 11.73 Concept Question
Replies: 3
Views: 218

### 11.73 Concept Question

I know that an increase in pressure means a decrease in volume due to PV=nRT, but how does this apply to the direction of the reaction?
Sun Dec 03, 2017 5:54 pm
Forum: Lewis Acids & Bases
Topic: Weak Bases
Replies: 2
Views: 227

### Re: Weak Bases

Weak bases do not completely ionize because they do not protonate fully, which means they do not transfer protons as well as strong bases. Strong bases, however, do completely ionize since they can remove hydrogen ions from any acid, even weak ones, to form conjugate acids.

I hope this helps!
Sun Nov 19, 2017 1:12 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: All bond angles
Replies: 3
Views: 257

### Re: All bond angles

I believe so because knowing the bond angles makes it easier to understand the shape of the molecule. Also within the molecule most of the bond angles are repeated in the structure so it's not too complicated.
Tue Nov 07, 2017 9:21 pm
Forum: Octet Exceptions
Replies: 4
Views: 1271

a radical lewis structure is a lewis structure with an unpaired electron due to an odd number of valence electrons. they are highly unstable and rare, therefore unfavored in nature. when drawing a radical i believe you leave it as an unpaired electron, so one dot, next to the atom in corresponds to....
Mon Oct 30, 2017 9:41 pm
Forum: Electronegativity
Topic: ELECTRON AFFINITY
Replies: 7
Views: 782

### Re: ELECTRON AFFINITY

Electron affinity decreases down a group because as the atom radius increases, the valence electrons are further from the nucleus so those outer electrons feel a reduced electrostatic attraction (due to shielding of inner electrons), therefore the outer electrons are easier to remove or add. That is...
Fri Oct 27, 2017 2:33 pm
Forum: Trends in The Periodic Table
Topic: 2.67 part B
Replies: 4
Views: 314

### Re: 2.67 part B

does this rule of half-filled being more stable and therefore lower electron affinities apply to the entirety of Group 15 or just nitrogen?
Thu Oct 26, 2017 1:18 pm
Forum: *Shrodinger Equation
Topic: Using Shrodinger's Equation
Replies: 4
Views: 581

### Re: Using Shrodinger's Equation

I am also confused on how to apply this equation in mathematical problems, but because he did not include any in the assigned problems for The Quantum World I don't think we need to know how to use it. We should understand how the equation describes an electron as a wave since it has duality as a pa...
Sun Oct 15, 2017 10:42 pm
Forum: DeBroglie Equation
Topic: DeBroglie Equation & Units [ENDORSED]
Replies: 2
Views: 272

### Re: DeBroglie Equation & Units[ENDORSED]

yes, only for this equation (so far) we have to remember to convert the mass if it is given in grams to kilograms before calculating the wavelength.