## Search found 31 matches

Sat Mar 16, 2019 9:13 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Rules for delta U
Replies: 2
Views: 286

### Re: Rules for delta U

deltaU = q when there is no work being done on the system (no change in volume)
Sat Mar 16, 2019 6:16 pm
Forum: Method of Initial Rates (To Determine n and k)
Topic: Molecularity
Replies: 3
Views: 318

### Re: Molecularity

For example, the reaction: [A]---->[P] would be unimolecular because there is only one molecule on the reactants side [A] + [B]----->[P] AND [A]^2----->[P] would be bimolecular since in each case there are 2 molecules on the reactant side [A] + [B] + [C]----->[P] AND [A]^2+[B]----->[P] would be term...
Sat Mar 16, 2019 6:12 pm
Forum: *Enzyme Kinetics
Topic: graphing intermediates
Replies: 2
Views: 265

### Re: graphing intermediates

Like the above answer stated, catalysts are not needed in the graph. The intermediates can be found right after the first transition state is achieved, and before the activation energy for the second transition state.
Sat Mar 16, 2019 6:08 pm
Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
Topic: Reduction Potentials
Replies: 2
Views: 253

### Reduction Potentials

Is it true that when given 2 E* values, the larger one is always going to be the E* value of the reduction reaction, and we must reverse the smaller one to get the E* of the oxidation reaction?
Thu Mar 07, 2019 10:46 pm
Forum: General Rate Laws
Topic: Ratios and Rate laws
Replies: 2
Views: 122

### Re: Ratios and Rate laws

for example let's take the reaction: N2 + 3H2 ---> 2NH3 (the balanced equation for the synthesis of ammonia) using the rate equations (or just by observing the reaction) we can see that the rate of degradation of H2 is -1 mol/(L*s), the rate of degradation of N2 is -1/3 mol/(L*s) and the rate of for...
Thu Mar 07, 2019 10:36 pm
Forum: Second Order Reactions
Topic: Half Lives
Replies: 1
Views: 117

### Half Lives

I understand the equations that allow us to calculate the half life in 0,1 and 2 order reactions. But in general, is there a specific order of a reaction that corresponds to a longer or shorter half life? I'm just confused as to the conceptual basis of this observation.
Thu Mar 07, 2019 10:32 pm
Forum: Method of Initial Rates (To Determine n and k)
Topic: Units of k
Replies: 4
Views: 183

### Re: Units of k

Since we know that in the end we must have a rate in mol/(L*s) and the units of molarity are fixed at mol/L we must adjust the units of k to end up with the correct units at the end.
Sat Mar 02, 2019 1:16 pm
Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
Topic: Which Molar Ratio?
Replies: 2
Views: 116

### Re: Which Molar Ratio?

As the above comment stated, you must first balance the equations to find the number of electrons (n) to put into the deltaG equation. If the reduction reaction gained 4 electrons and the oxidation reaction only lost 2 electrons you would have to multiple the oxidation reaction by 2 to get and equal...
Sat Mar 02, 2019 1:13 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: H+, OH-, water
Replies: 9
Views: 290

### Re: H+, OH-, water

Would we be penalized for including the presence of water in the cell diagram? If it doesn't contribute to a charge difference I don't see why we would, but I just want to make sure.
Sat Mar 02, 2019 1:09 pm
Forum: Balancing Redox Reactions
Topic: Creating a cell diagram
Replies: 8
Views: 280

### Creating a cell diagram

When writing the cell diagram, do you include the presence of H20 and H+ when they are part of the original solution?
Fri Feb 22, 2019 4:34 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Gibs Free Energy and Enthalpy
Replies: 2
Views: 144

### Re: Gibs Free Energy and Enthalpy

As mentioned above, knowing that the deltaH value is negative makes the possibility of deltaG being negative possible. Though, in order for this to occur we must also know that T*deltaS is either some positive number OR a negative number that is LESS than deltaH (meaning deltaH>T*deltaS). In any oth...
Fri Feb 22, 2019 4:24 pm
Forum: Interesting Applications: Rechargeable Batteries (Cell Phones, Notebooks, Cars), Fuel Cells (Space Shuttle), Photovoltaic Cells (Solar Panels), Electrolysis, Rust
Topic: Recharging Batteries [ENDORSED]
Replies: 10
Views: 631

### Re: Recharging Batteries[ENDORSED]

In a favorable reaction, the system is doing work. By charging a battery, you are doing work to a system. While possible, it is just simply not ideal.
Fri Feb 22, 2019 4:23 pm
Forum: Balancing Redox Reactions
Topic: oxidation state of MnO4-
Replies: 3
Views: 140

### Re: oxidation state of MnO4-

In general, we take what we know and use it to find the missing piece, in this case the oxidation state of Mn. Since we know that the oxidation state of O2 is always going to be 2- and the other oxidation states are given as superscripts, we can deduce that the charge of Mn must be +7. This method c...
Fri Feb 15, 2019 11:07 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: delta(S) total
Replies: 2
Views: 108

### Re: delta(S) total

As mentioned above, change in entropy = 0 occurs at equilibrium and also when the degeneracy state (W) value = 1 meaning each particle only has one possible state. No matter how many particles there are in the system, if they can only occupy one position the entropy = 0. An example of this would be ...
Fri Feb 15, 2019 11:01 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: 3 Step Entropy Change Calculations
Replies: 2
Views: 112

### 3 Step Entropy Change Calculations

I was wondering if someone could explain to me how to calculate the overall change in entropy in equations like the one on Lyndon’s worksheet where you go from T1 to T2, have a delta H value, then go back to T1. I understand the rise and drop in temperature equations, I just don’t understand that mi...
Fri Feb 15, 2019 10:58 pm
Forum: Calculating Standard Reaction Entropies (e.g. , Using Standard Molar Entropies)
Topic: Monatomic VS Diatomic Gases and their C
Replies: 3
Views: 318

### Monatomic VS Diatomic Gases and their C

I was wondering if someone could explain to me how to calculate the different Cv & Cp values for monatomic and diatomic gases. Also, why are they different? I would like to understand it on a conceptual basis. Thank you!
Sat Feb 09, 2019 11:43 pm
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: gas expansion when delta U is zero
Replies: 1
Views: 73

### Re: gas expansion when delta U is zero

This relates to the relationship between entropy and degeneracy. Gas molecules have higher entropy because they have higher degeneracy (they can occupy a larger selection of positions due to their kinetic energy, size, and motion). So when delta U is zero and volume increases, we can say that the ga...
Sat Feb 09, 2019 11:28 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: Work Done
Replies: 2
Views: 122

### Work Done

How do we know whether work is being done on the system by the surroundings, or if the surroundings are doing work on the system? How does this change the sign of w?
Sat Feb 09, 2019 11:22 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: Entropy Change in reversible reaction
Replies: 3
Views: 141

### Re: Entropy Change in reversible reaction

I’m not sure this is correctly interpreted. In reversible reactions entropy change does not = 0. The change in internal energy (deltaU) = 0 but this still constitutes a spontaneous process (in the gas phase) because there is still the factor of degeneracy, multiple potential states for the gas molec...
Fri Feb 01, 2019 6:21 pm
Forum: Thermodynamic Definitions (isochoric/isometric, isothermal, isobaric)
Topic: Heating Curve
Replies: 2
Views: 143

### Heating Curve

In the heating curve diagram, in general is the amount of heat released during exothermic phase changes (melting and vaporization) EXACTLY equal to the heat used to break the bonds? I just noticed that the lines in the heating curve depicted in phase changes had no slope which indicates that the pos...
Fri Feb 01, 2019 6:11 pm
Forum: Calculating Work of Expansion
Topic: formula for work with integral
Replies: 3
Views: 124

### Re: formula for work with integral

I believe he was trying to show us the relationship between the area under the curve of a work function and the first equation we derived for work. w=force x distance (which ultimately becomes -P x deltaV) since both equations give us an answer in this format I assume he was just showing us another ...
Fri Feb 01, 2019 6:04 pm
Forum: Thermodynamic Definitions (isochoric/isometric, isothermal, isobaric)
Topic: Delta U
Replies: 3
Views: 437

### Re: Delta U

It is helpful to think of delta U in the sense of a graph mapping the change in reactants and products during a reaction. If you remember, Dr. Lavelle drew us an example of this to represent delta U as a state function. If a reaction takes place and ends up back at the exact same point it started in...
Thu Jan 24, 2019 11:26 am
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Enthalpy Definition Clarification
Replies: 2
Views: 95

### Enthalpy Definition Clarification

I noticed that the definition of enthalpy involves the reaction occurring at a constant pressure. I was wondering if other parameters such as volume must also remain constant?
Thu Jan 24, 2019 11:20 am
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: pKa and pKb
Replies: 2
Views: 106

### Re: pKa and pKb

You can however use pKb and pKa to find pH and pOH. If you take 10^(pKa) this will give you Ka. The equation for Ka=[products]/[reactants] so if one of those molar concentrations is unknown you can use this Ka value to find the missing concentration.
Thu Jan 24, 2019 11:16 am
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Replies: 2
Views: 104

In cases such as a change in pressure you must consider the overall effect of the system. In the equation PV=nRT we can see that pressure and number of moles have a direct relationship. Thus an increase in pressure would increase the number of moles, the system would compensate by directing toward t...
Tue Jan 15, 2019 8:31 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Relationship between pKa, pKb, and pH
Replies: 1
Views: 39

### Relationship between pKa, pKb, and pH

Given a pK value how do we calculate pH? The relationship is a little difficult to interpret from the text.
Tue Jan 15, 2019 8:27 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Polyprotic Acids
Replies: 2
Views: 68

### Polyprotic Acids

When an acid is able to donate more than one proton, how will we know when this is to occur? Will it be specified the question specifically the number of protonations in the initial reaction?
Tue Jan 15, 2019 8:23 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Cations as acids
Replies: 2
Views: 78

### Cations as acids

How do we know when a cation will act as an acid in a reaction and predict their relative strength?
Tue Jan 08, 2019 11:05 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Leaning to the left/right
Replies: 4
Views: 175

### Re: Leaning to the left/right

When K is large (usually =>10000) equilibrium will favor the products (on the right side of the double arrow) so this is called 'leaning to the right'. When K is small (usually <= .0010) equilibrium will favor the reactants (on the left side of the double arrow) so this is called 'leaning to the lef...
Tue Jan 08, 2019 10:59 pm
Forum: Ideal Gases
Topic: Audio Visual Test Question
Replies: 1
Views: 61

### Audio Visual Test Question

One of the audio visual test questions mentioned that only a certain percentage of a compound reacted (18% or something?) if anyone had a question similar to this could you briefly explain how you did the problem? Thanks!
Tue Jan 08, 2019 10:56 pm
Forum: Ideal Gases
Topic: Q and Spontaneity
Replies: 1
Views: 78

### Q and Spontaneity

I'm having trouble grasping the concept of the change in Q with respect to the spontaneous reaction. I understand the relationship between Q and K but I don't see how this applies to "spontaneity" in forming products. Thanks!