## Search found 36 matches

Sat Mar 17, 2018 11:02 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Friday Section Test 2
Replies: 2
Views: 227

### Re: Friday Section Test 2

You can also think of the reducing agent as the one that is being oxidized.
Sat Mar 17, 2018 10:57 pm
Forum: *Alkanes
Topic: The symbol R
Replies: 4
Views: 677

### Re: The symbol R

When writing more than one R, do we have to denote them differently? For example, would we use R, R', R''...
Sat Mar 17, 2018 10:54 pm
Forum: Arrhenius Equation, Activation Energies, Catalysts
Topic: Arrhenius Graph
Replies: 2
Views: 430

### Re: Arrhenius Graph

Yes, these will be the axes b/c it will result in a straight line with a negative slope. The slope of the line is equal to the activation energy/R. You can think of it as being in the slope-intercept form y=mx+b
Sat Mar 17, 2018 10:52 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Using Appendix 2A
Replies: 2
Views: 258

### Re: Using Appendix 2A

For our test, I think we'll have to reverse the half reaction of the anode (where oxidation occurs) to get a cell potential that will result in a positive value.
Sat Mar 17, 2018 10:49 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: Standard enthalpy change
Replies: 2
Views: 272

### Standard enthalpy change

Can someone explain why the deltaH was multiplied by 2 mols?
Sat Mar 17, 2018 7:55 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Elementary Reaction
Replies: 2
Views: 263

### Re: Elementary Reaction

An elementary step's rate law must agree with the observed rate law of the overall reaction. The step whose rate law agrees is going to be the slowest step.
Sat Mar 17, 2018 7:35 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Test 2 #5a
Replies: 1
Views: 131

### Re: Test 2 #5a

Would you mind posting the question? It'd be easier on us so that we don't have to refer to it
Sat Mar 17, 2018 5:50 pm
Forum: Balancing Redox Reactions
Topic: Notation question
Replies: 2
Views: 276

### Notation question

given the balanced equation: NaN3 --> 3N2+2Na

Can someone explain how N is oxidized? The solution explains it in the screenshot I attached, but uses a notation I'm not familiar with. Explanation?
Sat Mar 17, 2018 2:00 am
Forum: Phase Changes & Related Calculations
Topic: Sign for compression vs expansion
Replies: 4
Views: 364

### Re: Sign for compression vs expansion

Yes, that is correct. You can assume pressure is 1 atm and then plug in values for delta V to check. If you compress something, Vf-Vi will be negative, so the two negative signs will combine to make a positive value. Delta V is positive for expansion, so the value will end up being negative.
Thu Mar 15, 2018 9:11 pm
Forum: Reaction Mechanisms, Reaction Profiles
Replies: 3
Views: 244

When Lavelle started lecturing on reaction mechanisms, he gave the equation A+B+C–>P He said that if the initial concentrations of both B and C were a lot greater than the initial concentration of A, then the rate=k' [A]^{n} since B and C remain essentially constant. I'm confused as to why we are us...
Fri Feb 23, 2018 5:40 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Galvanic Cells
Replies: 5
Views: 310

### Re: Galvanic Cells

If we calculate a standard potential and the value comes out to be negative, does that mean that it's not a galvanic cell? If not, then what type of cell is it?
Fri Feb 23, 2018 5:38 pm
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: Standard State with Nernst Equation
Replies: 4
Views: 282

### Re: Standard State with Nernst Equation

I believe that the simplified equation of E=Enot-RT/nF*lnQ, which is E=Enot-0.00591/n * log Q, is given to us specifically so that we don't have to plug in values for T, since it's simplified for use under STP.
Fri Feb 23, 2018 5:27 pm
Forum: Kinetics vs. Thermodynamics Controlling a Reaction
Topic: signs
Replies: 6
Views: 688

### Re: signs

Wouldn't it depend on what your initial concentrations are? I would think that if you start with more products, they would decrease over time, and your rate for the reverse rxn would be (-) negative. Is this correct?
Fri Feb 23, 2018 5:17 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Cell Diagrams [ENDORSED]
Replies: 7
Views: 424

### Re: Cell Diagrams[ENDORSED]

If you notice, the inert electrodes are usually denoted as solids by (s), as most metals are solid at STP, and they have conductive properties, which is why they're useful as inert electrodes. There are exceptions, though. For ex, mercury is a liquid at STP, so it'd be written as Hg(l) in the cell d...
Fri Feb 23, 2018 5:01 pm
Forum: General Rate Laws
Topic: Rate Constant K [ENDORSED]
Replies: 4
Views: 276

### Re: Rate Constant K[ENDORSED]

You say that k varies depending on activation energy and temperature, but how exactly would we go about calculating the value of k?
Fri Feb 23, 2018 4:53 pm
Forum: Method of Initial Rates (To Determine n and k)
Topic: Initial rates
Replies: 5
Views: 373

### Re: Initial rates

To explain why we compare initial rates, we can refer to the following equation that Lavelle used in class: NH_{4}^{+}(aq)+NO_{2}^{-}(aq)\rightarrow N_{2}(g)+H_{2}O(l)) Since N2 is a gas, it leaves the solution. As a result the reverse reaction is less likely to o...
Tue Feb 13, 2018 5:37 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Criterion for Assessing Spontaneity of a Reaction
Replies: 1
Views: 79

### Re: Criterion for Assessing Spontaneity of a Reaction

Sorry. The fourth letter should have been
d) $\Delta S_{total}$
Tue Feb 13, 2018 5:22 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Criterion for Assessing Spontaneity of a Reaction
Replies: 1
Views: 79

### Criterion for Assessing Spontaneity of a Reaction

How would you go about answering the following question? Under what conditions, if any, does the sign of each of the following quantities provide a criterion for assessing the spontaneity of a reaction? (a) \Delta G^{\circ}< 0 ; (b) \Delta H^{\circ} ; (c) \Delta S^{\circ} ; (d) \Delta S^{\circ}
Fri Feb 02, 2018 2:41 am
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: Bulk Matter
Replies: 1
Views: 142

### Re: Bulk Matter

The book defines bulk matter as "matter composed of large numbers of atoms." It probably means everyday objects like a piece of wood.
Fri Feb 02, 2018 2:37 am
Forum: Phase Changes & Related Calculations
Topic: Enthalpy vs. Entropy
Replies: 4
Views: 246

### Re: Enthalpy vs. Entropy

Would you mind explaining why enthalpy can be measured as an amount altogether but entropy can only be measured by the changes in it?
Fri Feb 02, 2018 2:35 am
Forum: Gibbs Free Energy Concepts and Calculations
Topic: entropy to surroundings
Replies: 3
Views: 207

### Re: entropy to surroundings

Because the entropy lost by the reaction goes to the surroundings, and the surroundings are gaining the entropy, this means that the entropy gained by the surroundings is equal to that lost by the reaction. If the entropy for the reaction decreased by 1 J/K (-1 J/K), for example, then the entropy of...
Fri Feb 02, 2018 2:25 am
Forum: Calculating Standard Reaction Entropies (e.g. , Using Standard Molar Entropies)
Topic: 9.43
Replies: 3
Views: 223

### Re: 9.43

I also don't understand this question. Are we supposed to convert the grams of water to moles and use the molar heat capacity instead? I see that it says constant pressure, and that almost lead me to believe that I needed to use 5/2R for heat capacity. However, given that it's a liquid, doesn't that...
Fri Feb 02, 2018 1:45 am
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Replies: 3
Views: 169

By definition, an ideal gas is a gas made of point particles (zero dimensional/no volume particles). Therefore, treating any real gas as an ideal gas is always an approximation. While the approximation is closer for monatomic gases (He, Ne, etc.), we can apply it to any real gas. The heat capacity t...
Fri Feb 02, 2018 1:24 am
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: bond enthalpy [ENDORSED]
Replies: 4
Views: 271

### Re: bond enthalpy[ENDORSED]

I'm not sure Lavelle has covered this in lecture, but I would say that polarity has nothing to do bond enthalpies.
Fri Feb 02, 2018 1:18 am
Forum: Thermodynamic Definitions (isochoric/isometric, isothermal, isobaric)
Topic: Extensive/Intensive Property [ENDORSED]
Replies: 4
Views: 266

### Re: Extensive/Intensive Property[ENDORSED]

To add to the above response, you can also consider heat capacity vs. specific heat capacity. The heat capacity of a bomb calorimeter, for example, does not depend on the amount of substance because it is a defined object. It has a specified mass for which to measure it's heat capacity, and we canno...
Tue Jan 30, 2018 10:13 am
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Cv vs. R
Replies: 1
Views: 163

### Re: Cv vs. R

When you are measuring the change in heat, or \Delta H , of an ideal gas at constant volume, the specific heat will be equal to 3/2 times the ideal gas constant. Here is the equation: C_{V}=3/2*R Therefore, when measuring \Delta H , you replace C_{V} with 3/2*R in your \Delta H=mC_{V}\Delta T equati...
Sat Jan 20, 2018 2:25 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: J vs. kJ [ENDORSED]
Replies: 4
Views: 204

### Re: J vs. kJ[ENDORSED]

Typically, you will determine if you need to use J or kJ based on the question. The question may give you a value in kJ, but it can still ask for your answer to use J instead, and vice versa, so all you'd need to do is make the conversion.
Sat Jan 20, 2018 2:22 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: standard heat of combustion vs. standard heat of formation
Replies: 2
Views: 181

### Re: standard heat of combustion vs. standard heat of formation

The standard heat of combustion will always be negative since the reaction will be giving off heat as it breaks the chemical bonds. The heat of formation should always be positive since it will be taking in heat in order to produce the chemical bonds. They can be related to one another by using the ...
Sat Jan 20, 2018 2:00 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: ∆H equation
Replies: 3
Views: 218

### Re: ∆H equation

Isn't the equation for finding change in heat as follows: $\Delta H=q=mC\Delta T$
I know that the m accounts for mass instead of moles(which is usually represented as n), so would we simply switch out the m for n if we are presented with molar heat capacity?
Sat Dec 09, 2017 8:43 pm
Forum: Calculating pH or pOH for Strong & Weak Acids & Bases
Topic: X in ICE table
Replies: 3
Views: 1685

### Re: X in ICE table

If you were given the concentrations to both products and reactants, you would first need to find Q, which is given by [P]/[R]. Given a value for Kc, you would need to compare Q to Kc and see if it is greater than or less than. If Q is greater, then that means that the reaction would shift toward th...
Thu Dec 07, 2017 12:53 pm
Forum: Shape, Structure, Coordination Number, Ligands
Topic: Oxidation Numbers
Replies: 2
Views: 196

### Re: Oxidation Numbers

Oxidation numbers are the total sum of ionic charges for a compound. For example, if we were looking at water, H20, we can see that it has two elements that compose it: 1) hydrogen, which is usually found as H+, so it has a positive charge of one and 2)oxygen, which is usually found as O 2- . If you...
Thu Dec 07, 2017 10:21 am
Forum: Amphoteric Compounds
Topic: Amphoteric vs amphiprotic
Replies: 2
Views: 619

### Re: Amphoteric vs amphiprotic

Amphoteric refers to the ability of X, a compound, to act as both a base and an acid. For example, in the chemical equation H_{2}O(l)+H_{2}O(l)\rightarrow H_{3}O^{+}(aq)+OH^{-}(aq) , water acts as both an acid (whose conjugate base is hydroxide, OH-) and as a base (wh...
Thu Oct 26, 2017 11:16 pm
Forum: Lewis Structures
Topic: S and P blocks and Lewis structures [ENDORSED]
Replies: 4
Views: 405

### Re: S and P blocks and Lewis structures[ENDORSED]

Lewis structures are used to model the chemical bonds between two or more elements regardless of what block they are in. Lewis models use the valance electrons(v.e-) of elements to visualize the bonds because the v.e- are in the outermost shell, and it wouldn't make sense for elements to bond with e...
Thu Oct 26, 2017 5:09 pm
Forum: Trends in The Periodic Table
Topic: Transition Metals
Replies: 3
Views: 274

### Re: Transition Metals

Transition metals are those elements in the d-Block that consists entirely of metals. Those metals always form cations (ions with a positive charge) and the charges in the metals will vary. The reason they all form cations is because transition metals have relatively low ionization energies, so an e...
Fri Oct 13, 2017 4:44 pm
Forum: Photoelectric Effect
Topic: Lyman Series v Balmer series
Replies: 2
Views: 261

### Lyman Series v Balmer series

Can someone explain the difference between the Lyman and Blamer series to me? I couldn't really determine the difference when looking at the graphs Lavelle showed us during lecture. Fundamental difference would be great, and further detail would be much appreciated!
Fri Oct 13, 2017 3:53 pm
Forum: Bohr Frequency Condition, H-Atom , Atomic Spectroscopy
Topic: why is Bohr Frequency equation negative
Replies: 4
Views: 870

### Re: why is Bohr Frequency equation negative

Different elements have different characteristics, so the energy at the ground state of an electron (e-) for Hydrogen (H) is going to be different than the energy for the ground state of an e- of Helium (He), for example. The energy for a hydrogen e- at the ground state is 2.178 x 10^-20 Joules (J),...