## Search found 60 matches

Sat Mar 16, 2019 9:35 pm
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: Positive or Negative Ecell Values
Replies: 4
Views: 397

### Positive or Negative Ecell Values

How do you know if the Ecell should be positive or negative? For example, in galvanic cells, Ecell should be positive, but in other cells it is negative. What part of the question gives you this information?
Sat Mar 16, 2019 9:29 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Galvanic Cells
Replies: 4
Views: 130

### Galvanic Cells

How do you know which reaction is the cathode and which is the anode in a galvanic cell?
Sat Mar 16, 2019 1:43 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: C(gr) vs Pt(s)
Replies: 1
Views: 77

### C(gr) vs Pt(s)

When writing out cell diagrams, when do we use C(gr) as a solid as opposed to Pt(s)?
Fri Mar 15, 2019 9:12 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Order of States of Matter
Replies: 1
Views: 86

### Order of States of Matter

In what order do we put solid, liquid, gas, and aqueous elements in a cell diagram?
Fri Mar 08, 2019 10:21 am
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: E˚ vs E
Replies: 13
Views: 1676

### Re: E˚ vs E

E˚ is standard conditions, and will be given to you on a formula sheet or in the question for many reactions. E is nonstandard and has to be calculated using data.
Fri Mar 08, 2019 10:15 am
Forum: Second Order Reactions
Topic: Final
Replies: 30
Views: 794

### Re: Final

Final will be cumulative, and all topics will be more or less equally represented.
Tue Mar 05, 2019 9:04 am
Forum: First Order Reactions
Topic: Units
Replies: 3
Views: 145

### Units

How do you figure out the units for k in different ordered reactions?
Tue Feb 26, 2019 1:36 am
Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
Topic: Problem 6N.1 Redox Reaction
Replies: 1
Views: 80

### Problem 6N.1 Redox Reaction

In Problem 6N.1, the reaction is written as follows:

(b) In3+(aq) + U3+(aq)⇌In2+(aq) + U4+(aq)

The answer key shows one of the redox reactions to be:

In3+(aq) + 2e- --> In2+(aq)

Why is it 2e- and not 1e-?
Tue Feb 26, 2019 1:05 am
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Cell Diagrams
Replies: 2
Views: 90

### Cell Diagrams

In the cell diagram

C(gr)|Sn4+(aq),Sn2+(aq)||Pb4+(aq),Pb2+(aq)|Pt(s),

Why are the Sn separated by a comma (as well as the Pb) and not a | ?
Tue Feb 26, 2019 12:35 am
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Anode reaction
Replies: 3
Views: 111

### Anode reaction

When writing out the half-reaction for anodes, do we have to have the electrons on the reactant side of the equation or is it correct to write it in its "reverse form" with the electrons on the right side of the equation?
Tue Feb 26, 2019 12:12 am
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Problem 6L.3
Replies: 1
Views: 67

### Problem 6L.3

In Problem 6L.3 b,

Write the half-reactions and the balanced equation for the cell reaction for each of the following galvanic cells:
(b) C(gr)|H2(g)|H+(aq)∥Cl−(aq)|Cl2(g)|Pt(s),

The half reaction for Chlorine is written as Cl2(g) + 2e- --> 2Cl-. Why is it not written in reverse order?
Mon Feb 25, 2019 4:47 pm
Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
Topic: Problem 6L.1
Replies: 4
Views: 242

### Problem 6L.1

In the problem 6L.1 (7th Edition),

Calculate the standard reaction Gibbs free energy for the following cell reactions:

(a) 2 Ce4+(aq) + 3 I−(aq) →2 Ce3+(aq) + I3−(aq), Ecell°=+1.08V,

What value n do I use for Ecell = -nFE?
Fri Feb 15, 2019 10:10 am
Forum: Calculating Work of Expansion
Topic: Reversible vs Irreversible
Replies: 4
Views: 171

### Reversible vs Irreversible

What is the best way to tell if a system is reversible or irreversible?
Fri Feb 15, 2019 10:06 am
Forum: Biological Examples (*DNA Structural Transitions, etc.)
Topic: Structures of the Human Body and Systems
Replies: 5
Views: 499

### Re: Structures of the Human Body and Systems

Organs would be considered open systems. This is because they exchange heat with their surroundings, as well as matter. All our organs are constantly taking up and expelling molecules, as well as heat energy, to maintain homeostasis.
Fri Feb 15, 2019 10:04 am
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Delta G
Replies: 2
Views: 115

### Re: Delta G

The formula for Gibbs free energy is deltaG = deltaH - TdeltaS

If deltaG is negative, the reaction is spontaneous. If it is positive, the reaction is not spontaneous.

Thus, the higher the temperature, the lower the Gibbs free energy, making it more spontaneous, and thus less stable.
Mon Feb 11, 2019 5:03 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: Equation for temperature change, 4F.11
Replies: 4
Views: 214

### Re: Equation for temperature change, 4F.11

I, as well as many other posters on chemistry community, have faced the same problem. I believe it to be a solutions manual error, as we have never encountered that equation in lecture and it is not on the formula sheet.
Mon Feb 11, 2019 4:59 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: 7th edition 4F.11
Replies: 3
Views: 181

### Re: 7th edition 4F.11

The full question is, "During the test of an internal combustion engine, 3.00 L of nitrogen gas at 18.5°C was compressed suddenly (and irreversibly) to 0.500 L by driving in a piston. In the process, the temperature of the gas increased to 28.1°C. Assume ideal behavior. What is the change in en...
Mon Feb 11, 2019 4:42 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: 7th edition 4F.11
Replies: 4
Views: 488

### Re: 7th edition 4F.11

The question is, "During the test of an internal combustion engine, 3.00 L of nitrogen gas at 18.5°C was compressed suddenly (and irreversibly) to 0.500 L by driving in a piston. In the process, the temperature of the gas increased to 28.1°C. Assume ideal behavior. What is the change in entropy...
Sun Jan 27, 2019 1:42 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: The 3 methods
Replies: 5
Views: 188

### Re: The 3 methods

If you have all the necessary information than yes, but usually you will only be given enough information for one of the methods.
Sun Jan 27, 2019 1:40 pm
Forum: Phase Changes & Related Calculations
Topic: Sublimation
Replies: 6
Views: 212

### Re: Sublimation

It will bypass the liquid state if there is not enough pressure for the compound to form a liquid state, and thus will skip directly to the gas phase. For there to be a liquid state, the pressure would have to be very high.
Sun Jan 27, 2019 1:20 pm
Forum: Phase Changes & Related Calculations
Topic: Modules
Replies: 17
Views: 431

### Re: Modules

Not required, though I recommend just taking the post-assessment sections. These will be the most efficient practice for tests, and will help you figure out what you don't really know.
Sat Jan 26, 2019 9:48 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Cancelling Out with Hess's Method
Replies: 3
Views: 429

### Re: Cancelling Out with Hess's Method

The 2NOs cancel out because one is a reactant and the other is a product. The O2s do not cancel out since they are both reactants, and thus they are added together.
Sat Jan 26, 2019 9:46 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Enthalpy
Replies: 2
Views: 68

### Re: Enthalpy

Enthalpy is a state function because the only values that matter when calculating ΔH are the final and initial values; any intermediate steps are not used in the calculation.
Sat Jan 26, 2019 9:43 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Sign changes
Replies: 3
Views: 106

### Re: Sign changes

Yes they can, and if the enthalpy is negative it is an exothermic reaction, while if the enthalpy is positive it is an endothermic reaction.
Thu Jan 17, 2019 8:43 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Sig Figs
Replies: 3
Views: 143

### Re: Sig Figs

Yes, you are correct. If you are ever unclear, Dr. Lavelle has a very helpful page on his class site.
Thu Jan 17, 2019 8:39 pm
Forum: Non-Equilibrium Conditions & The Reaction Quotient
Topic: Hydronium Concentration
Replies: 3
Views: 137

### Re: Hydronium Concentration

This is because when you plug in a value where [H3O+]<10^-7 into the formula for pH, you get a value greater than 7. However, this does not make sense, since acids have a pH of less than 7. Thus, we say the solution is neutral.
Thu Jan 17, 2019 8:36 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: [H3O+] =[OH-]
Replies: 2
Views: 130

### Re: [H3O+] =[OH-]

Those values are equal when a substance is "neutral".
Thu Jan 10, 2019 12:18 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Why Would Equilibrium cause death in humans?
Replies: 3
Views: 754

### Re: Why Would Equilibrium cause death in humans?

Many human processes require gradients in order to function (gradients are a form of potential energy). If our bodies were at equilibrium, many reactions would not proceed past enough for our bodies to function.
Thu Jan 10, 2019 12:15 pm
Forum: Non-Equilibrium Conditions & The Reaction Quotient
Topic: Finding K in 5I.7
Replies: 3
Views: 111

### Re: Finding K in 5I.7

The only method we need to know for now is the method we were taught in lecture (note how 5I.7 is not included in this unit's homework problems).
Thu Jan 10, 2019 12:13 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: 7th Edition 5H.3
Replies: 1
Views: 45

### Re: 7th Edition 5H.3

When combining K values, you have to make sure that the products in both equations are balanced (have the same coefficients). If you look at the example problem in section 5H.2 of the textbook, note how they balance one of the equations to make the products match, and then factor this in when combin...
Sat Dec 08, 2018 10:23 am
Forum: Interionic and Intermolecular Forces (Ion-Ion, Ion-Dipole, Dipole-Dipole, Dipole-Induced Dipole, Dispersion/Induced Dipole-Induced Dipole/London Forces, Hydrogen Bonding)
Topic: 6th edition q6.1
Replies: 2
Views: 335

### Re: 6th edition q6.1

Since the electronegativity of Oxygen is much higher than that of Selenium, it will have a greater pull on the electrons. This greater pull creates a dipole interaction, which allows it to form dipole-dipole forces with other H2SeO4.
Sat Dec 08, 2018 10:16 am
Forum: Shape, Structure, Coordination Number, Ligands
Topic: dantate and angle
Replies: 1
Views: 113

### Re: dantate and angle

Two lone pairs have to be more than 90 degrees to be polydentate because of repulsion between the lone pairs. Repulsion between the lone pairs binding to the same central atom prevents them from being closer than 90 degrees.
Sat Dec 08, 2018 10:10 am
Forum: Properties of Light
Replies: 3
Views: 376

Since we did naming in class and it was on the homework, there is a good chance that naming will be on the final, so I would study for it.
Sat Dec 08, 2018 10:08 am
Forum: Einstein Equation
Replies: 5
Views: 4196

Lavelle looks at all the grades and then he decides what is a fair A, B, C, etc. However, no one's grade will go down, only up. For example, he might decide a solid B is an 80%, and thus he would scale everyone's grade up 5%. However, he will not scale the grades down in any situation.
Thu Dec 06, 2018 5:24 pm
Forum: Bronsted Acids & Bases
Topic: J.9
Replies: 2
Views: 181

### Re: J.9

The best way to approach this problem is to write out a balanced equation. Then, the compound formed from the cation and the anion of the products should be your salt.
Thu Dec 06, 2018 5:20 pm
Forum: Bronsted Acids & Bases
Topic: Zinc Nitrate
Replies: 2
Views: 160

### Re: Zinc Nitrate

The base you would use is Zn(OH)2(aq).
Thu Dec 06, 2018 5:03 pm
Forum: Air Pollution & Acid Rain
Topic: acid rain
Replies: 4
Views: 335

### Re: acid rain

It is a multistep equation:

2NO2 + H2O → HNO3 + HNO2
2HNO2 + O2 → 2HNO3
Thu Nov 29, 2018 2:36 pm
Forum: Naming
Topic: Cyano vs. Cyanido
Replies: 2
Views: 306

### Re: Cyano vs. Cyanido

Since they are the same ligand, you can use either interchangeably.
Thu Nov 29, 2018 2:33 pm
Forum: Naming
Topic: 17.31 6th ed
Replies: 1
Views: 77

### Re: 17.31 6th ed

When writing out the formula, write the central atom first, then the ligands in alphabetical order (unless there is a neutral ligand and an anion, then write the neutral ligand first), then put the charge of the compound outside of brackets, or the proper number of cations/anions. Let's do part A as...
Thu Nov 29, 2018 2:21 pm
Forum: Naming
Topic: 9C.3 part D 7h edition
Replies: 1
Views: 86

### 9C.3 part D 7h edition

On part d of 9C.3, the question asks to write the chemical formula for sodium bisoxalato(diaqua)ferrate (III). I got the answer correct, but why is bisoxalato written before diaqua in the question? Shouldn't they be in alphabetical order regardless of Greek prefixes?
Thu Nov 15, 2018 12:41 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: AX and AXE
Replies: 2
Views: 132

### Re: AX and AXE

When writing out the VSEPR formula, A represents the central atom, X represents the attached atoms, and E represents the lone pairs. When writing out the formula, always put A first, then put Xn where n is the number of attached atoms, and Em where m is the number of lone pairs on the central atom. ...
Thu Nov 15, 2018 12:32 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: HW 2E3 PART B (7TH EDITION)
Replies: 4
Views: 179

### Re: HW 2E3 PART B (7TH EDITION)

No, the lone pairs around the non-central atoms do not affect shape. So in the case of CH2F2, the shape will be tetrahedral; the bond angles will not be affected by Fluorine's lone pairs.
Thu Nov 15, 2018 12:23 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Homework #4.13 part a (6th edition)
Replies: 1
Views: 107

### Re: Homework #4.13 part a (6th edition)

When looking at the Lewis structure, notice how there are 5 electron densities around the central Iodine: two iodines and 3 lone pairs. This gives a trigonal bipyramidal shape. The three electron pairs will want to maximize their distance from one another, so they will take up positions 120 degrees ...
Thu Nov 08, 2018 2:53 pm
Forum: Ionic & Covalent Bonds
Topic: Bond Length
Replies: 8
Views: 291

### Re: Bond Length

You do not need to know how to calculate bond lengths unless the covalent radii are given for each atom (then the bond length is the sum of these radii). It is helpful to know that triple bonds are the shortest, then double bonds, then single bonds, and that triple bonds are the strongest, then doub...
Thu Nov 08, 2018 2:49 pm
Forum: Ionic & Covalent Bonds
Topic: Covalent Bond Exception?
Replies: 2
Views: 167

### Re: Covalent Bond Exception?

They will not form covalent bonds in the traditional sense, but some metals and nonmetals might form ionic bonds with strong covalent characteristics depending on the electronegativity of the atoms.
Thu Nov 08, 2018 2:44 pm
Forum: Ionic & Covalent Bonds
Topic: Electron Distortion definition
Replies: 2
Views: 141

### Re: Electron Distortion definition

Simply, electron distortion is when the electrons of an anion are drawn to the positive charge of an anion, slightly distorting the electron density. This can give ionic bonds covalent characteristics.
Thu Nov 01, 2018 2:31 pm
Forum: Formal Charge and Oxidation Numbers
Topic: Formal Charge and the Octet Rule
Replies: 6
Views: 321

### Re: Formal Charge and the Octet Rule

When determining Lewis structures, start off by following the octet rule, and then determine any alternate depictions. Keep in mind that not all atoms require 8 valence electrons. Then compare between the different Lewis structures for the lowest FC of each atom/overall FC of the molecule or compound.
Thu Nov 01, 2018 2:24 pm
Forum: Ionic & Covalent Bonds
Topic: 2A.19 7th edition
Replies: 3
Views: 158

### Re: 2A.19 7th edition

The electrons are removed from the 4s orbital before 3d when forming ions. This is because electrons are always removed from the outermost orbital first, in this case 4s. This is why it is [Ar]3d8 and not [Ar]3d64s2.
Thu Nov 01, 2018 2:18 pm
Forum: Formal Charge and Oxidation Numbers
Topic: Lowest Energy Lewis Structure: N2O
Replies: 2
Views: 808

### Re: Lowest Energy Lewis Structure: N2O

The structure with -1 for O, +1 for N, and 0 for N would be the most stable, as the overall formal charge is 0, while the overall FC for the other is +2.
Thu Oct 25, 2018 3:14 pm
Forum: *Shrodinger Equation
Topic: Schrodinger's wave function
Replies: 2
Views: 425

### Re: Schrodinger's wave function

A wave function is used as it can model the wavelike properties of an electron as well as the possible momentum and position of an electron given their uncertainty.
Thu Oct 25, 2018 3:07 pm
Forum: Heisenberg Indeterminacy (Uncertainty) Equation
Topic: Calculating Uncertainty in Momentum
Replies: 3
Views: 268

### Calculating Uncertainty in Momentum

If you are asked to calculate the uncertainty in momentum, would you normally use the diameter or radius of the atom for the uncertainty in position?

Furthermore, if it is stated that the uncertainty is 1% of the radius 0.05 nm, would the uncertainty in position value equal 0.01*0.05*10^-9?
Thu Oct 18, 2018 3:14 pm
Forum: Wave Functions and s-, p-, d-, f- Orbitals
Topic: Problem 1D 23
Replies: 2
Views: 151

### Re: Problem 1D 23

The number of possible orbitals can be found by either n, l or ml. Always look to ml first if it's given, and if not, then to l, then to n. If ml is given, this describes the orientation of the orbital, and thus only the one orbital is allowed. So in part b, since ml= -2, this tells us the orientati...
Thu Oct 18, 2018 2:57 pm
Forum: Wave Functions and s-, p-, d-, f- Orbitals
Topic: 1D.21 7th edition pg-41
Replies: 1
Views: 103

### Re: 1D.21 7th edition pg-41

An orbital is a region where you are most likely to find an electron and is represented by a wave function. A subshell is essentially a group of orbitals that are a similar distance from the nucleus. An energy level contains one or more subshells. The subshell notation can be inferred by the princip...
Thu Oct 18, 2018 2:34 pm
Forum: Wave Functions and s-, p-, d-, f- Orbitals
Topic: Homework Question 1D.15 7th Edition
Replies: 1
Views: 64

### Re: Homework Question 1D.15 7th Edition

The angular momentum quantum number can be known by looking at the orbital letters:

If it is an s orbital, then l = 0

If p, l = 1

If d, l = 2

If f, l = 3.
Fri Oct 12, 2018 6:51 pm
Forum: Bohr Frequency Condition, H-Atom , Atomic Spectroscopy
Topic: Audio Visual Question 28
Replies: 1
Views: 59

### Re: Audio Visual Question 28

To solve this problem, divide 1 meter by 1,650,763.73. This will give you the wavelength of krypton-86 (approx. 606 nm).
Fri Oct 12, 2018 6:46 pm
Forum: DeBroglie Equation
Topic: Negative Energy?
Replies: 2
Views: 89

### Re: Negative Energy?

The energy is not negative. The negative is there because it represents the energy lost by the electron. Think of it as the electron decreasing in energy, rather than giving off negative energy. When this energy is lost, it is released as a photon, and thus the photon has that energy (and is positiv...
Fri Oct 12, 2018 6:43 pm
Forum: Properties of Light
Topic: Photon energy
Replies: 2
Views: 83

### Re: Photon energy

Photons are given off when an electron loses energy. So when change in energy is negative, that energy lost is the energy of the photon, which is positive. So the electron loses energy, but that energy is given to the photon, and thus is positive.
Thu Oct 04, 2018 9:42 pm
Forum: Limiting Reactant Calculations
Topic: Calculating reactant moles [ENDORSED]
Replies: 4
Views: 148

### Re: Calculating reactant moles[ENDORSED]

Let's say you have 2kg of hamburger patties and 1kg of hamburger buns. How many hamburgers can you make? As you can see, we would need to know the amount of hamburger patties and buns you have in order to make this calculation. This is why we convert from grams into moles, so that we know the amount...
Thu Oct 04, 2018 9:27 pm
Forum: SI Units, Unit Conversions
Topic: L35 Tons Conversion Rate
Replies: 4
Views: 168

### Re: L35 Tons Conversion Rate

You will need to convert tonnes into grams. For the conversion rate, 1 tonne = 1000 kg.
Thu Oct 04, 2018 9:19 pm
Forum: Balancing Chemical Reactions
Topic: Problem H1 (7th EDITION) Part A
Replies: 4
Views: 166

### Re: Problem H1 (7th EDITION) Part A

Adding an O to the product side would imply that free Oxygen atoms would be formed from the reaction, however this does not happen.