## Search found 50 matches

Sun Mar 11, 2018 12:06 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Elements Acting as Electrodes
Replies: 2
Views: 207

### Re: Elements Acting as Electrodes

Solids are not the only forms elements can be in to have an oxidation state of zero. For example, H2(g) has an oxidation state of zero.
Sun Mar 11, 2018 11:58 am
Forum: Kinetics vs. Thermodynamics Controlling a Reaction
Topic: units
Replies: 4
Views: 452

### Re: units

It might be useful to know, but on the equation sheet he does give us the conversation between kPa and atm (1 atm = 101.325 kPa), so this is not something you would have to memorize.
Sun Mar 11, 2018 11:55 am
Forum: General Rate Laws
Topic: graphs
Replies: 8
Views: 457

### Re: graphs

If you understand what parts of the equations represent y=mx+b the graphs should make sense!
Tue Mar 06, 2018 11:29 pm
Forum: General Rate Laws
Topic: Isolation Method
Replies: 2
Views: 150

### Re: Isolation Method

Keep in mind that the k you get using the isolation method is the pseudo rate constant (k') not the actual k since you are making assumptions that one reactant will be in such large excess.
Tue Mar 06, 2018 11:15 pm
Forum: First Order Reactions
Topic: Negative Order RXN?
Replies: 2
Views: 383

### Re: Negative Order RXN?

I'm not sure, but would it be if the concentration of the reactant doubled, but the rate halved? Would this be an example of a -1 order reaction?
Tue Mar 06, 2018 11:05 pm
Forum: General Rate Laws
Topic: Writing rate laws
Replies: 4
Views: 274

### Re: Writing rate laws

If a reaction is zero order it should not be included in the rate law. If it was there, it would falsely report that concentration of the reactant influences the rate of reaction. It does not, so it should not be included.
Tue Mar 06, 2018 11:03 pm
Forum: Method of Initial Rates (To Determine n and k)
Topic: 15.17
Replies: 1
Views: 201

### Re: 15.17

The mmol G means the amount of moles of product G. The L^-1 s^-1 is per liter second. Mol/L s is a typical unit for rate. The only difference is that this is millimol instead of mol, and it is specifying that it is millimol of G, as opposed to product F.
Tue Mar 06, 2018 11:00 pm
Forum: Method of Initial Rates (To Determine n and k)
Topic: 15.19 (a)
Replies: 3
Views: 390

### Re: 15.19 (a)

If the number that you get does not easily come out to a number that can easily round to whole number, it is likely that you have made an error in calculations. If you get an answer like that, make sure you go back and check your work.
Tue Mar 06, 2018 10:55 pm
Forum: General Rate Laws
Topic: Coefficients
Replies: 6
Views: 376

### Re: Coefficients

The only time coefficients can be used in order to determine the order of a reaction is when it is an elementary reaction.
Wed Feb 21, 2018 10:11 am
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Electrode
Replies: 2
Views: 115

### Re: Electrode

An electrode is a metal that is used conduct electricity.
Wed Feb 21, 2018 10:11 am
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: platinum in cell diagram
Replies: 3
Views: 138

### Re: platinum in cell diagram

You use platinum when the products and reactants of a half-reaction are in the same state (ex. aqueous).
Wed Feb 21, 2018 10:07 am
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Galvanic Cells
Replies: 2
Views: 192

### Re: Galvanic Cells

Yes, this is the definition of a galvanic cell. They convert things from chemical energy to electrical energy. The cell potential needs to be positive. An example of a cell that has a negative cell potential is an electrolytic cell.
Wed Feb 21, 2018 10:05 am
Forum: Balancing Redox Reactions
Topic: redox agent
Replies: 5
Views: 328

### Re: redox agent

If something is being oxidized it is losing e-. It if is the oxidizing agent, it is causing something else to be oxidized. The only way to cause something to lose electrons (be oxidized) it to accept them (and thereby being reduced). So, being an oxidizing agent is the same as being reduced.
Wed Feb 21, 2018 10:03 am
Forum: Balancing Redox Reactions
Topic: HW #14.3 d
Replies: 3
Views: 261

### Re: HW #14.3 d

There are still 2 half reactions present.
Wed Feb 21, 2018 10:02 am
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Galvanic Cell model [ENDORSED]
Replies: 3
Views: 217

### Re: Galvanic Cell model[ENDORSED]

Since Cu is on the right side of the cell it is the cathode. That means this is where reduction occurs. Therefore, there will be an accumulation of Cu(s) on the right side on the electrode, as it is reduced from Cu+2(aq). On the left side of the cell with Zn, it is the anode, so oxidation is occurri...
Tue Feb 06, 2018 11:43 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: 9.31
Replies: 2
Views: 194

### Re: 9.31

Sometimes the book expects you to know info that we are not always required to know for tests. I believe Professor Lavelle would give us this information, since it is needed for the problem, if a problem like this were to appear on the midterm.
Tue Feb 06, 2018 11:41 pm
Forum: Phase Changes & Related Calculations
Topic: Environmental impact?
Replies: 6
Views: 586

### Re: Environmental impact?

Since he has not covered it in lecture, I would be very surprised if this was tested on the midterm. The only way I could see it being tested is perhaps in the background in a conceptual question.
Tue Feb 06, 2018 11:39 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: W
Replies: 3
Views: 214

### Re: W

I just remember that W= (# of possible states) raised to the power of (# of particles).
Wed Jan 31, 2018 12:31 am
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: 9.11
Replies: 4
Views: 300

### Re: 9.11

You are correct in thinking that the initial pressure (P1) is 15 and the final pressure (P2) is .5. However, you are using an incorrect equation, which resulted in the wrong answer. The equation is change in entropy= nRln(P1/P2). The equations for change in volume and temperature have ln(V2/V1) and ...
Wed Jan 31, 2018 12:23 am
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: Comparing 9.1 and 9.3
Replies: 3
Views: 235

### Re: Comparing 9.1 and 9.3

It is important to remember that q(sys)= -q(surroundings).
Wed Jan 31, 2018 12:18 am
Forum: Gibbs Free Energy Concepts and Calculations
Topic: G=H-TS
Replies: 4
Views: 446

### Re: G=H-TS

You are correct. When H is positive and S is negative, having a high temperature will increase G. In fact, since this equation is uses temperature in K, there can't be a negative temperature, so in these conditions, the G will always be positive. The book must have been referring to a case in which ...
Mon Jan 29, 2018 8:55 am
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Hess's Law [ENDORSED]
Replies: 7
Views: 437

### Re: Hess's Law[ENDORSED]

I think either type of question can be asked. He can either give us the equation, or lets say there is a problem on the change in enthalpy of combustion, we would be expected to know how to write and balance the equations of combustion that correspond to the enthalpy of combustion data we are given.
Mon Jan 29, 2018 8:53 am
Forum: Thermodynamic Systems (Open, Closed, Isolated)
Topic: Open, closed, or isolated [ENDORSED]
Replies: 3
Views: 391

### Re: Open, closed, or isolated[ENDORSED]

The universe is isolated because neither matter or energy can be exchanged with it. This is because the universe encompasses everything, so it does not have surroundings it could exchange matter or energy with.
Mon Jan 29, 2018 8:49 am
Forum: Thermodynamic Definitions (isochoric/isometric, isothermal, isobaric)
Topic: Reversible an Irreversible [ENDORSED]
Replies: 4
Views: 415

### Re: Reversible an Irreversible[ENDORSED]

Also, more work is done in a reversible reaction. Looking at the graph of volume vs pressure for brother reversible and irreversible reactions, the area under the curve (aka the integral) is work. It makes sense that more work is done in a reversible reaction because the area under the curve is visi...
Tue Jan 16, 2018 9:26 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Heat Capacities
Replies: 6
Views: 213

### Re: Heat Capacities

It is important that you understand both, because different problems will give you different units to work with. For example, if the problem gives you mass of iron in grams, use the specific heat (since that is in terms of grams). If you only have access to the molar heat capacity and are given iron...
Tue Jan 16, 2018 9:22 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Enthalpy of formation vs reaction enthalpy
Replies: 2
Views: 108

### Re: Enthalpy of formation vs reaction enthalpy

I believe that the enthalpy of formation is a type of reaction enthalpy. Every formation reaction is a reaction, but not every reaction is a formation reaction. Therefore, enthalpy of formation is just one example of reaction enthalpy.
Tue Jan 16, 2018 9:13 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: First Law
Replies: 2
Views: 200

### Re: First Law

The first law of thermodynamics states that energy can't be created or destroyed. This means that throughout a calculation, the amount of energy at the beginning of the problem is the same at the end. Knowing this, you know that energy does not disappear, but instead can change forms (for example in...
Sun Jan 14, 2018 6:00 pm
Forum: Phase Changes & Related Calculations
Topic: phase changes
Replies: 1
Views: 113

### Re: phase changes

For ice changing to steam you have to do several calculations. First you have to calculate energy needed to bring the ice to 0 degrees Celsius. Then calculate energy needed to phase change from ice to liquid. Then you have to calculate the energy needed to bring the water from 0 degrees Celsius to 1...
Sun Jan 14, 2018 5:57 pm
Forum: Phase Changes & Related Calculations
Topic: Temperature during Phase Change
Replies: 6
Views: 304

### Re: Temperature during Phase Change

Also another way to think about it is that at 100 degrees Celsius, that is when boiling begins, not when all of it is 100% boiled. So more energy needs to be added to get it to be boiled 100%.
Sun Jan 14, 2018 1:57 pm
Forum: Thermodynamic Systems (Open, Closed, Isolated)
Topic: Systems
Replies: 7
Views: 510

### Re: Systems

Another example is the earth. We are an open system because we get to both matter (meteors) and energy (sunlight) from outside of the earth itself.
Thu Dec 07, 2017 12:11 am
Forum: Properties & Structures of Inorganic & Organic Acids
Topic: Types and strength of Acids/Bases
Replies: 3
Views: 469

### Re: Types and strength of Acids/Bases

In high school, I learned that these were the strong acids, and then you could assume that the rest are weak acids, since it is much more common for something to be a weak acid than a strong one.

Strong acids:
HClO4
HClO3
HCl
HBr
HI
HNO3
H2SO4
Thu Dec 07, 2017 12:03 am
Forum: Calculating pH or pOH for Strong & Weak Acids & Bases
Topic: When to use Equilibrium arrow vs. reaction arrow [ENDORSED]
Replies: 1
Views: 279

### Re: When to use Equilibrium arrow vs. reaction arrow[ENDORSED]

Yes, I think it would be better to use a double arrow to indicate that you know that weak acids are not completely dissociated in H2O, so there is an equilibrium present.
Sun Dec 03, 2017 8:52 pm
Forum: Lewis Acids & Bases
Topic: Writing equations with acids and bases
Replies: 5
Views: 337

### Re: Writing equations with acids and bases

I agree, I think by omitting the double arrows and instead just having one forward arrow better shows your understanding of the reaction that is occurring. It shows that you have recognized that this is a strong acid/base.
Sun Dec 03, 2017 8:49 pm
Forum: Properties & Structures of Inorganic & Organic Acids
Topic: K values
Replies: 2
Views: 243

### Re: K values

For a strong acid, for example, HCl, that means nearly 100% of the acid dissociates into H+ and Cl- ions. This would mean there is a high K value for the dissociation of a strong acid.
Tue Nov 21, 2017 7:19 pm
Forum: Lewis Structures
Topic: Best way to start Lewis Structures
Replies: 12
Views: 761

### Re: Best way to start Lewis Structures

First I count all of the valence electrons involved in the bonding. If you do not get this step right, your structure will be off. Then I figure out what is the central atom and place the other atoms around it. Then I put a single bond between each, because you know that there will at least be a sin...
Tue Nov 21, 2017 7:07 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: K and Q
Replies: 2
Views: 200

### Re: K and Q

K and Q are calculated the same way. If the reaction is aA + bB --> cC + dD, then K= [C]^c x [D}^d / [A]^a x [B]^b . K is when the equation is at equilibrium, Q is when the reaction is not at equilibrium. Based upon the values of K and Q, you can determine if a reaction is at equilibrium or how the ...
Thu Nov 16, 2017 12:21 am
Forum: Determining Molecular Shape (VSEPR)
Topic: Determing Molecular Shape
Replies: 2
Views: 240

### Re: Determing Molecular Shape

Since many of the homework problems in chapter 4 ask for the bond angle of familiar shapes, it will be necessary to know these for test #4 and the final.
Thu Nov 16, 2017 12:20 am
Forum: Determining Molecular Shape (VSEPR)
Topic: 4.1 Lone pairs
Replies: 6
Views: 524

### Re: 4.1 Lone pairs

Yes, Gianna's diagram is really helpful. There are two instances where the shape is linear:
1. 2 areas of electron density where none of which are lone pairs
or
2. 5 regions of electron density where three of which are lone pairs
Wed Nov 08, 2017 1:45 pm
Forum: Heisenberg Indeterminacy (Uncertainty) Equation
Topic: Uncertainty in position
Replies: 2
Views: 266

### Re: Uncertainty in position

Yes, you should use the diameter not the radius to find the uncertainty in position. So make sure if the question gives you the radius, double it to get the diameter. This is a small little detail, but it is important that you remember to do that so that you receive full credit for the problem.
Wed Nov 08, 2017 1:38 pm
Forum: Electron Configurations for Multi-Electron Atoms
Topic: Electron config of elements in 5d and 6d
Replies: 4
Views: 630

### Re: Electron config of elements in 5d and 6d

You do not count the f-block square, and it is 5d6.
Thu Nov 02, 2017 9:49 am
Forum: Lewis Structures
Topic: electron configuration
Replies: 6
Views: 477

### Re: electron configuration

Yes this is correct. The 3d will be written before the 4s and 4p because principal quantum number n=3 is lower energy than principal quantum number n=4, and it is standard to write it in order of increasing energy.
Thu Nov 02, 2017 9:42 am
Forum: Heisenberg Indeterminacy (Uncertainty) Equation
Topic: Reasonable Model
Replies: 2
Views: 210

### Re: Reasonable Model

Yes, it does not make sense/is not a reasonable model when the speed of the electron is faster than the speed of light.
Thu Oct 26, 2017 12:50 am
Forum: Lewis Structures
Topic: Chemical Bonds Lewis Structures
Replies: 1
Views: 259

### Re: Chemical Bonds Lewis Structures

The trend in ionization energies is that ionization energy increases from left to right and from bottom to top. You are correct in that the rule is to use the element with the lowest ionization energy as the central atom. Therefore, Cl has a higher ionization energy than C, so C should be the centra...
Thu Oct 26, 2017 12:35 am
Forum: Electron Configurations for Multi-Electron Atoms
Topic: s and d valence electrons
Replies: 1
Views: 185

### Re: s and d valence electrons

If you have a transition metal, the number of valence electrons you have will come from the s and d blocks depending upon how many electrons are lost. The 4s orbital has slightly lower energy than the 3d block. In iron, the 3d6 has higher energy than the 4s2. In Iron, the 4s2 electrons will be lost ...
Wed Oct 18, 2017 9:39 pm
Forum: Properties of Electrons
Topic: Hydrogen series
Replies: 5
Views: 472

### Re: Hydrogen series

I agree, I think that for this test we only need to know the two that he mentioned in lecture and that are mentioned in the book. My TA went over two others, but I think it is best to spend your time studying the two that we are most familiar with.
Wed Oct 18, 2017 9:36 pm
Forum: Properties of Light
Topic: EM spectrum
Replies: 6
Views: 491

### Re: EM spectrum

My TA told me that in terms of visible light, we should know the top and bottom of the range of wavelengths for visible light, and know which end corresponds to red and which corresponds to violet, but that we do not need to know, for example, exactly what is the wavelength for green and what is ora...
Thu Oct 12, 2017 12:04 am
Forum: Properties of Light
Topic: How to Find Wavelength Given only the velocity? [ENDORSED]
Replies: 2
Views: 304

### Re: How to Find Wavelength Given only the velocity?[ENDORSED]

To do this problem you use the equation wavelength=h/(mv). You must look up the mass of an electron (in kg) to put in the equation for m. For v you put in the velocity, and h is a constant. Then you are able to solve for wavelength.
Thu Oct 12, 2017 12:00 am
Forum: Photoelectric Effect
Topic: Photoelectric Effect
Replies: 8
Views: 499

### Re: Photoelectric Effect

You say that you have memorized " long wavelengths cannot and short wavelengths can" in terms of wavelengths of light that can eject electrons from metal. From my understanding, it is not that all short wavelenghts can, it is just that having a shorter wavelength makes it so the frequency ...
Wed Oct 04, 2017 6:09 pm
Forum: Empirical & Molecular Formulas
Topic: Trouble in finding the Molecular Formula
Replies: 6
Views: 1140

### Re: Trouble in finding the Molecular Formula

Once you have the ratio in decimal form such as 1:1:1.333, in some instances it could be helpful to convert the decimals to fractions. Then the ratio is 1:1:4/3. Written like this, it is easier to see that multiplying by three would get rid of all the denominators and turn into a ratio of whole numb...
Wed Oct 04, 2017 6:05 pm
Forum: Limiting Reactant Calculations
Topic: Net Ionic Equation
Replies: 4
Views: 2109

### Re: Net Ionic Equation

Yes I completely agree. The response above was stated very well. When thinking about net ionic equations, an important part is to remember the solubility rules. If you know your solubility rules (outlined within the fundamentals), then you will be able to determine which of the compounds in the prod...