## Search found 50 matches

Sat Mar 17, 2018 10:07 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: I-/I3-
Replies: 3
Views: 974

### Re: I-/I3-

To find whether it is oxidation or reduction you need to have another reaction to compare it to. Then you would look up both of those reactions in the chart with all the half reactions. Whichever has a more negative value that should be the oxidation, and the more positive value should be reduction.
Sat Mar 17, 2018 10:03 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Electrodes
Replies: 3
Views: 311

### Re: Electrodes

You add it to the end of the galvanic cell, so you can have solids at the end if there aren't any present. They are inert.
Sat Mar 17, 2018 9:57 pm
Forum: Thermodynamic Systems (Open, Closed, Isolated)
Topic: Isolated systems
Replies: 3
Views: 387

### Re: Isolated systems

The bomb calorimeter has a constant volume, so it doesn't change. You would have the reaction giving off heat or gaining heat from the calorimeter.
Sun Mar 11, 2018 7:38 pm
Forum: Zero Order Reactions
Topic: Half-Life of Zero Order
Replies: 3
Views: 364

### Re: Half-Life of Zero Order

Yes you should assume it is fair game. It says not used, because those order reactions most likely do not occur often in the real world. However, we will still need to know how to use the formulas when asked about those specific orders.
Sun Mar 11, 2018 7:30 pm
Forum: Arrhenius Equation, Activation Energies, Catalysts
Topic: Arrhenius eq use
Replies: 2
Views: 164

### Re: Arrhenius eq use

The Arrhenius equation can be used when you want to show the effect of change of temperature and activation energy on the rate of a reaction.
Sun Mar 11, 2018 7:26 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: SN2
Replies: 3
Views: 232

### Re: SN2

It is important because it can be used in the situations where the first step is not always the slow step.
Sun Mar 04, 2018 6:49 pm
Forum: Second Order Reactions
Topic: 15.39a
Replies: 2
Views: 202

### Re: 15.39a

Since the problem already gives the initial concentration, final concentration, and the rate constant you can just plug them into the second order reactions formula. You do not need to use the coefficient in this case. With this chapter you mostly do not need to use the coefficients unless you are t...
Sun Mar 04, 2018 6:37 pm
Forum: Second Order Reactions
Topic: Half life constant and Rate reaction constant
Replies: 4
Views: 298

### Re: Half life constant and Rate reaction constant

If you use the second order half life formula then you can use that k in the second order reaction to find the concentration. There are different half life formulas depending on if its zero, first, or second order.
Sun Mar 04, 2018 6:34 pm
Forum: First Order Reactions
Replies: 4
Views: 252

Radioactive decay is a first order reaction because the decay rate is proportional to the first power of radioactive atoms present. Therefore, this matches with first order kinetics.
Sun Feb 25, 2018 8:14 pm
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: NERNST
Replies: 4
Views: 282

### Re: NERNST

Yes because to get that number we use 298K, which is 25 degrees Celsius.
Sun Feb 25, 2018 8:06 pm
Forum: First Order Reactions
Topic: Negative Rates
Replies: 4
Views: 330

### Re: Negative Rates

You sound like you have the correct idea, I would also like to know if it is possible to have a negative rate. I know we can't have negative time or energy, but I am not sure if the same idea applies to rates as well.
Sun Feb 25, 2018 8:03 pm
Forum: Balancing Redox Reactions
Topic: Balancing number of electrons
Replies: 10
Views: 543

### Re: Balancing number of electrons

I don't think it matters until the end. You can just divide all of them to make them as simple as possible.
Sun Feb 18, 2018 8:25 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Cell Diagrams
Replies: 3
Views: 212

### Re: Cell Diagrams

I believe the order doesn't matter when they are separated with commas, which means they are interchangeable. This is when they are both in the same state such as gas, aqueous, etc.
Sun Feb 18, 2018 8:14 pm
Forum: Balancing Redox Reactions
Topic: Basic conditions
Replies: 3
Views: 250

### Re: Basic conditions

If you add OH- on the products or the reactants you have to add it to the other side as well. I believe you would add the same amount of H+ as OH-, in most situations.
Sun Feb 18, 2018 7:55 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Cell Diagram [ENDORSED]
Replies: 5
Views: 313

### Re: Cell Diagram[ENDORSED]

When you look at the cell diagram whichever comes first from the left is the reactant and as you go to the right they are the products. If you see Pt(s) or C(graphite) those are not a part of the reaction.
Sun Feb 11, 2018 6:34 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: H2(g) --> H2(g)
Replies: 2
Views: 234

### Re: H2(g) --> H2(g)

The answer to your first question would be yes, the enthalpy of formation for H2 would be 0, because it is diatomic.
Sun Feb 11, 2018 6:30 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: Vibrational Energy State
Replies: 4
Views: 258

### Re: Vibrational Energy State

Vibrational energy contributes to the increase in molar entropy, because when the molecules vibrate they are moving and causing disorder. Entropy can be thought of as the disorder in a system.
Sun Feb 11, 2018 6:23 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: delta Stotal
Replies: 1
Views: 164

### Re: delta Stotal

The second law of thermodynamics states that in a reversible process, the entropy of the system plus its surroundings is unchanged. Thus, deltaSuniv=0.
Sun Feb 04, 2018 7:24 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: 9.25
Replies: 2
Views: 191

### Re: 9.25

For simple ones, you don't really have to draw them out because you can just imagine them. However, when it gets more complex drawing them out will help you see all the possible orientations. I can't think of any other way to count the orientations without thinking visually or drawing them. If anyon...
Sun Feb 04, 2018 7:19 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: Heat transfer
Replies: 7
Views: 374

### Re: Heat transfer

I had this question on my test. My answer was that heat is being transferred, because the volume and pressure are changing. This means the energy is being altered.
Sun Feb 04, 2018 7:15 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: ΔS of vaporization
Replies: 2
Views: 171

### Re: ΔS of vaporization

The delta S of vaporization might being similar for most compounds because, vaporization occurs at 100 degrees Celsius. This is coming from the chart we have seen in class that shows the graph that includes solids, liquids, vaporization, and sublimation. Thus, when you do the calculations you are go...
Sun Jan 28, 2018 7:33 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: Example 9.2
Replies: 2
Views: 173

### Re: Example 9.2

Since there is a Cv,m does the m stand for constant MOLAR heat capacity?
Sun Jan 28, 2018 7:27 pm
Forum: Calculating Work of Expansion
Topic: Thermodynamics for W
Replies: 3
Views: 346

### Re: Thermodynamics for W

To add onto the previous post, I believe you utilize this equation only when you have an isothermal reversible expansion.
Sun Jan 28, 2018 7:23 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: Reversible vs. Irreversible
Replies: 3
Views: 182

### Re: Reversible vs. Irreversible

One difference in terms of solving a problem is that you use two different equations for Reversible (w=-nrtln(Vf/Vi) and Irreversible (w=-PextdeltaV) expansion.
Sun Jan 21, 2018 7:51 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: 8.77
Replies: 2
Views: 152

### Re: 8.77

If you do not let the wording confuse, you you have to do the same as 8.67 (c) and (d). This means you have to calculate the enthalpy of benzene with and without resonance. You do this with the mean bond enthalpies that can be found in a chart. It is one of the methods that our professor explained t...
Sun Jan 21, 2018 7:18 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: 8.53b - kJ/mol
Replies: 1
Views: 178

### Re: 8.53b - kJ/mol

There is a range in the temperature so you would have to use qcal=CcaldeltaT. After this you would use deltaH=deltaU+PdeltaV and substitute with w=-PextdeltaV. Now you would use the information from the bomb calorimeter, so work=0. Therefore, deltaU=-q.
Sun Jan 21, 2018 7:01 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: 8.41
Replies: 1
Views: 98

### Re: 8.41

You have to set it equal to the change, because it asks for the final temperature of the system, so you need to take in account all the types of heat. Therefore, for the ice, you need the heat of the ice melting (q=mCsdeltaT) + heat of the ice at 0 degrees Celsius (q=ndeltaHf). Next, you need the he...
Sat Jan 13, 2018 4:57 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Closed System
Replies: 7
Views: 410

### Re: Closed System

An example can be found in number 8.1 from the homework, part (c). It asks what type of system is a bomb calorimeter in which benzene is burned, and the answer is an isolated system.
Sat Jan 13, 2018 4:39 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Sig Figs for Question 8.45 (a)
Replies: 5
Views: 302

### Re: Sig Figs for Question 8.45 (a)

My guess would be that it is because of something in your calculations. I would say it might be a rounding error. My advice would be to complete all the steps of the problems and round at the end. Rounding in the middle may give you slightly different numbers.
Sat Jan 13, 2018 4:25 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Are there any periodic trends for enthalpy?
Replies: 4
Views: 207

### Re: Are there any periodic trends for enthalpy?

To add on to the previous posts, professor Lavelle said we do not need to memorize bond enthalpies, so we most likely do not need to know them if there are any. I do think that it may correspond to bond strength, because bond enthalpy is the energy needed to break a bond.
Sun Dec 10, 2017 9:25 pm
Forum: Bronsted Acids & Bases
Topic: Strong Acids and Bases [ENDORSED]
Replies: 3
Views: 612

### Re: Strong Acids and Bases[ENDORSED]

From what we have learned in class strong acids and bases are supposed to completely ionize. In the scenario where they do not dissociate completely they are automatically considered a weak acid or base.
Sun Dec 10, 2017 9:17 pm
Forum: Administrative Questions and Class Announcements
Topic: Final [ENDORSED]
Replies: 4
Views: 1041

### Re: Final[ENDORSED]

Yes, Dr. Lavelle said that salts were not supposed to be on the final. I don't exactly remember the problem, but maybe you could have solved this problem by finding the molarities and then doing -log of the concentration. What I'm drawing from is pH=-log[concentration]. In this case we would disrega...
Sun Dec 03, 2017 6:33 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Bond Angle
Replies: 1
Views: 160

### Re: Bond Angle

The angles to the bonds are shown in the textbook. You can draw out the VSEPR model to see approximately what the angles are. Other than that you may need to memorize them. The angles will be the maximum space apart that the atoms can move to. This is due to the repulsion of the lone pairs.
Sun Dec 03, 2017 6:27 pm
Forum: Lewis Acids & Bases
Topic: Bronsted vs Lewis
Replies: 6
Views: 449

### Re: Bronsted vs Lewis

To add to the previous posts, the Lewis Acids/Bases are referring to electrons, while the Bronsted Acids/Bases are referring to protons. That is the main difference between them. Also if you compare them, Bronsted is opposite to Lewis in terms of accepting or donating.
Sun Nov 26, 2017 7:00 pm
Forum: Dipole Moments
Topic: Polarity based on number of lone pairs
Replies: 2
Views: 234

### Re: Polarity based on number of lone pairs

When the central atom has a lone pair the molecule will be polar. In general if we look at the dipoles of two atoms, they may cancel, however, if a lone pair is present then the atoms will not have the same equal and opposite dipoles. Therefore, the lone pair will interfere and the dipoles will chan...
Sun Nov 26, 2017 6:50 pm
Forum: Ideal Gases
Topic: Units of Partial Pressure
Replies: 7
Views: 613

### Re: Units of Partial Pressure

To add on to the previous posts, professor Lavelle has been repeating that the units should be atmosphere for pressure. However, when you do specific problems it will probably be specified. As long as you remember to use the same units when doing the calculations, you should be fine.
Sat Nov 18, 2017 5:34 pm
Forum: Bond Lengths & Energies
Topic: Regions of Electron Density
Replies: 4
Views: 389

### Re: Regions of Electron Density

To add on to this question, is it only important to know the electron density around the central atom, or does the electron density matter around the other elements as well?
Sat Nov 18, 2017 5:24 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Bent or linear?
Replies: 11
Views: 957

### Re: Bent or linear?

If the central atom does not have lone pairs then it would be linear. Since there is a lack of lone pairs the other elements would not be pushed down. However, if there was a lone pair on the central atom, it would repel the other two elements. In this case they, would be pushed down and bent. Anoth...
Sun Nov 12, 2017 5:49 pm
Forum: Formal Charge and Oxidation Numbers
Topic: Formal Charge
Replies: 8
Views: 612

### Re: Formal Charge

To add on to the previous posts, the formal charge should also be the most favorable when the central atom has a formal charge of zero. This is due to the least electronegative atom being in the center. Thus, the central atom shouldn't have charges. It is better for the atoms around the central atom...
Sun Nov 12, 2017 5:42 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Bond Angles
Replies: 3
Views: 262

### Re: Bond Angles

To add on to the previous posts, some bond angles are not an exact number, because they are based on experimental values. The angles form from electron repulsion (lone pairs). The electrons need to have the maximum space apart. Thus, the shapes are formed.
Sun Nov 05, 2017 7:20 pm
Forum: Lewis Structures
Topic: Formal charge [ENDORSED]
Replies: 3
Views: 294

### Re: Formal charge[ENDORSED]

Yes you are correct! First, we draw the different resonances of the Lewis structures. Then you take each element separately from the structure and calculate its formal charge. Remember that you need a greater number of the individual elements to have a formal charge of zero. Don't let it confuse you...
Sun Nov 05, 2017 7:09 pm
Forum: Electron Configurations for Multi-Electron Atoms
Topic: Electrostatic Potential Energy
Replies: 1
Views: 163

### Re: Electrostatic Potential Energy

You are correct that electrostatic potential energy proves that outer electrons have a nuclear charge. However, I believe that it is also important to know what happens when the distance between them increases or decreases. For example, this formula may help you see the relationship between two elem...
Sun Oct 29, 2017 4:17 pm
Forum: Electron Configurations for Multi-Electron Atoms
Topic: Electron Subshells [ENDORSED]
Replies: 2
Views: 351

### Re: Electron Subshells[ENDORSED]

To add to the previous reply, while you move across the period from left to right, Z effective increases. This is due to high electron density within the same shells, which causes electron repulsion to increase. This then allows the nucleus-electron attraction to be strong, and the nucleus can reach...
Sun Oct 29, 2017 4:11 pm
Forum: Trends in The Periodic Table
Topic: Two Special Elements in Periodic Table
Replies: 3
Views: 308

### Re: Two Special Elements in Periodic Table

The two elements that have exceptions are Cr and Cu, but those aren't the only ones. Some of the elements below them in the column may also have the same exception. Writing out the electron configuration will help.
Sun Oct 22, 2017 1:29 pm
Forum: Wave Functions and s-, p-, d-, f- Orbitals
Topic: Quantum Numbers - Magnetic Quantum Number
Replies: 2
Views: 235

### Re: Quantum Numbers - Magnetic Quantum Number

I also don't exactly know why we have negative numbers and would like to know why. However, I feel that when thinking about the Magnetic Quantum Number, we should pay more attention to how many values there are. For example, in the previous reply it is stated that when m=2, ml= -2,-1,0,+1,+2. In tot...
Sun Oct 22, 2017 1:10 pm
Forum: Wave Functions and s-, p-, d-, f- Orbitals
Topic: Magnetic Quantum numbers vs. Spin Magnetic
Replies: 2
Views: 182

### Re: Magnetic Quantum numbers vs. Spin Magnetic

First you begin with the Principle Quantum Number, which can be found from the periodic table of elements. This determines how many energy levels there are and size. Next, the Angular Momentum Quantum Number describes the "shape". It lets you know if the orbital is s-, p-,d-, or f-. You ob...
Fri Oct 13, 2017 3:21 pm
Forum: Properties of Electrons
Topic: Energy Levels
Replies: 6
Views: 485

### Re: Energy Levels

Question: can an energy level be negative? The energy can be negative when we are discussing the change in energy for atomic spectra. After the electron gets excited, it goes back down to its ground state and emits energy. Therefore, it is losing energy and can be written as a negative value. Howev...
Fri Oct 13, 2017 3:16 pm
Forum: Properties of Electrons
Topic: 1/2mv^2
Replies: 2
Views: 253

### Re: 1/2mv^2

1/2mv^2 is utilized to find the Kinetic Energy. In the Photoelectric Effect, the energy required to remove the electron is subtracted from the energy of the photon. The difference gives you the excess energy which is equal to the Kinetic Energy of the electron. So, E(Photon)-E(Energy to remove e-)=E...
Fri Oct 06, 2017 9:42 am
Forum: Limiting Reactant Calculations
Topic: Limiting Reactants - Neither?
Replies: 2
Views: 243

### Re: Limiting Reactants - Neither?

When there is no limiting reactant in a chemical equation, that means the reaction goes to completion. All of the reactants are used. Also, there is no excess. However, this is very unlikely to occur. I would also like to see an example of this, because I am not sure how to determine how much of a s...
Fri Oct 06, 2017 9:37 am
Forum: SI Units, Unit Conversions
Topic: SI units [ENDORSED]
Replies: 6
Views: 535

### Re: SI units[ENDORSED]

The most important SI units that we should know for Chem 14 A would be mass(kg), length(m), and time(s). Also it would be great to understand how to convert from the SI units. For example, 1000g would equal 1 kg.