## Search found 102 matches

Sat Mar 14, 2020 12:42 pm
Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
Topic: n in NFE
Replies: 19
Views: 204

### Re: n in NFE

n is the number of electrons transferred in the final equation
Sat Mar 14, 2020 12:30 pm
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Replies: 6
Views: 123

They don't affect the equilibrium constant, it only affects the forward and reverse rates by increasing them. At equilibrium these rates are also equal to each other.
Sat Mar 14, 2020 12:28 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Equilibrium Constants
Replies: 8
Views: 106

### Re: Equilibrium Constants

Yes, the equation must be balanced before you can calculate K
Sat Mar 14, 2020 12:27 pm
Forum: First Order Reactions
Topic: First order rxns
Replies: 6
Views: 81

### Re: First order rxns

You can either look at the rate law to see if there's only one concentration in it or look at a graph that graphs time as the x axis and 1/ln(concentration). If this graph makes a line with a negative slope, it is first order.
Sat Mar 14, 2020 12:26 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Half/Rxn & Balanced Equations for galvanic cells.
Replies: 8
Views: 82

### Re: Half/Rxn & Balanced Equations for galvanic cells.

Cells typically need some solid electrode for it to work. So if your equation does not have a solid in it, we have to add Pt(s) at the ends of the cell diagram to show that it is the electrode that passes electrons from the anode to the cathode.
Fri Mar 06, 2020 12:56 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Signs of Enaught
Replies: 7
Views: 80

### Re: Signs of Enaught

When E naught is negative, it means that the reaction is not favorable. If the E cell is negative, then the cell is electrolytic.
Fri Mar 06, 2020 12:52 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: acidic solution
Replies: 5
Views: 112

### Re: acidic solution

You would still have to do the half reaction steps to balance out the redox reactions. The cell diagram procedure would be exactly the same as you would include the aqueous H+ and leave out the H2O since it is a liquid and cell diagrams do not include liquids.
Fri Mar 06, 2020 12:49 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Purpose of Electrode
Replies: 9
Views: 157

### Re: Purpose of Electrode

The electrode allows the movement of electrons from the anode to the cathode. Since is usually a metal which is conductive, it can allow the passage of electrons to allow the half reactions to occur.
Fri Mar 06, 2020 12:49 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Purpose of Electrode
Replies: 9
Views: 157

### Re: Purpose of Electrode

The electrode allows the movement of electrons from the anode to the cathode. Since is usually a metal which is conductive, it can allow the passage of electrons to allow the half reactions to occur.
Fri Mar 06, 2020 12:47 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Adding Pt(s) to a Cell Diagram
Replies: 14
Views: 142

### Re: Adding Pt(s) to a Cell Diagram

When there isn't a solid in your reaction or cell diagram, you need to add Pt(s) so it can act was an electrode, which allows the electrons to flow from one end to the other.
Fri Mar 06, 2020 12:45 pm
Forum: First Order Reactions
Topic: order of reaction equations
Replies: 6
Views: 84

### Re: order of reaction equations

You will need to know both which are on your equations sheet, but I highly doubt he would ask you to derive the integrated rate law.
Thu Feb 27, 2020 3:17 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: 6L.5 part b
Replies: 2
Views: 24

### Re: 6L.5 part b

All of the cell diagrams need to have a solid at the end for the most part. So in a reaction if you do not have a solid at the ends of the cell diagram, add Pt(s) at the ends since the cell diagrams need some sort of solid anode or cathode to transfer the electrons.
Thu Feb 27, 2020 3:15 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: How to tell which is anode/cathode based on standard reduction potentials E
Replies: 5
Views: 26

### Re: How to tell which is anode/cathode based on standard reduction potentials E

You can if they tell you what kind of cell it is. For example, for a galvanic cell the overall cell potential has to be positive so you know that you can deduce which half reaction is the anode or cathode since the equation is cathode minus anode. However, for a electrolytic cell, the overall cell p...
Thu Feb 27, 2020 3:12 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Drawing Cell Diagram
Replies: 7
Views: 94

### Re: Drawing Cell Diagram

No we do not need to put in coefficients in the cell diagram nor do we need to include H2O since it is the solvent and we only focus on the gas,solid, and aqueous substances.
Thu Feb 27, 2020 3:10 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Coefficients in Calculating Cell Potential?
Replies: 3
Views: 28

### Re: Coefficients in Calculating Cell Potential?

You still have to balance equations when they ask you to but these coefficients do not change the standard cell potentials that are on the chart that they will give us. This is because in the reaction it doesn't matter how much of each reactant you have it will still have the same standard cell pote...
Thu Feb 27, 2020 3:08 pm
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: log and ln in Nernst
Replies: 8
Views: 77

### Re: log and ln in Nernst

Doesn't really matter. Lavelle only mentioned it since ph is calculated using log so it could be more helpful when you use log in the equation.
Sun Feb 23, 2020 9:19 pm
Forum: Balancing Redox Reactions
Topic: Oxidation States
Replies: 7
Views: 58

### Re: Oxidation States

When looking at oxidation numbers, you really only care about the metal group because that's what is usually oxidized or reduced. First look at oxygen. Oxygen will always be -2 UNLESS it is in peroxide which then it will be -1. Hydrogen for the most part will be +1 unless it is with a cation metal t...
Sun Feb 23, 2020 9:16 pm
Forum: Balancing Redox Reactions
Topic: Hydroxide and H+
Replies: 6
Views: 63

### Re: Hydroxide and H+

The problems should only tell you specifically whether the solution is acidic or basic. That's why you're able to add H+ or OH- freely.
Sun Feb 23, 2020 9:14 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Cathode vs Anode
Replies: 11
Views: 110

### Re: Cathode vs Anode

Cathode is the half reaction that is being reduced while the anode is the half reaction that is being oxidized. I like to use the acronym a RED CAT and AN OX to tell which is which. The cathode also goes on the right side of the diagrams by convention.
Sun Feb 23, 2020 9:11 pm
Forum: Balancing Redox Reactions
Topic: Alkaline
Replies: 3
Views: 39

### Re: Alkaline

For alkaline solutions, at the end of the calculations you add equal amounts of OH- groups to both sides of the equation in order to cancel out the H+ ions. This will create water so you cancel out the waters on each side of the equation and should be left with no H+ on either side. This is just one...
Sun Feb 23, 2020 9:08 pm
Forum: Balancing Redox Reactions
Topic: Balancing Redox Equations
Replies: 7
Views: 66

### Re: Balancing Redox Equations

There's three ways you can tell. One way is to assign oxidation numbers which is really easy and you can find the steps online and see which element's oxidation number is lowered, which is the element being reduced or the number that is raised which is the element that is oxidized. Another short way...
Fri Feb 14, 2020 11:28 am
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: Pizza Rolls 3E
Replies: 4
Views: 73

### Re: Pizza Rolls 3E

If you look at the heating curve, we see that at phase changes the curve is a straight line. At these sections we see that as heat is being added on the x-axis, the temperature of y axis remains the same.
Fri Feb 14, 2020 11:24 am
Forum: Gibbs Free Energy Concepts and Calculations
Topic: K and Q and G
Replies: 6
Views: 99

### Re: K and Q and G

When the reaction is not at equilibrium, deltaG = deltaG(naught) + RTlnQ. There is a difference between deltaG and deltaG(naught). When the system is at equilibrium then delta G would equal 0 and the equation would be deltaG(naught)=-RTlnK. So depending on what state the system is, depends on what e...
Fri Feb 14, 2020 11:21 am
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Gibbs Free energy concept
Replies: 16
Views: 198

### Re: Gibbs Free energy concept

It basically represents the amount of energy available to do work. It also tells you if a reaction is favorable (spontaneous) or unfavorable(not spontaneous). If G is negative then it will be favorable.
Fri Feb 14, 2020 11:19 am
Forum: Thermodynamic Systems (Open, Closed, Isolated)
Topic: Intensive and Extensive Properties
Replies: 7
Views: 145

### Re: Intensive and Extensive Properties

Extensive properties depend on the amount while intensive properties do not. Typically anything that has the word Specific (like specific heat capacity, specific entropy etc) is intensive while extensive would be things like entropy, enthalpy.
Fri Feb 14, 2020 11:12 am
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: Cv vs Cp
Replies: 17
Views: 278

### Re: Cv vs Cp

Cv is at constant volume and Cp is at constant pressure. For most problems, we use Cv so when in doubt use Cv.
Sat Feb 08, 2020 12:44 pm
Forum: Calculating Work of Expansion
Topic: Units for -PV
Replies: 5
Views: 46

### Re: Units for -PV

Try to use L and atm since 101.325J = 1L*1atm which can be used to convert the pressure and volume into energy.
Sat Feb 08, 2020 12:43 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: What the calorimeter allows you to calculate according to conditions
Replies: 5
Views: 121

### Re: What the calorimeter allows you to calculate according to conditions

Since deltaU = deltaH + -p*deltaV we can see that at deltaH = deltaU + p*deltaV. At constant volume, there is no change in volume so deltaV would equal 0 and at constant pressure, the equation still stands since the p value is just a constant anyways.
Sat Feb 08, 2020 12:38 pm
Forum: Ideal Gases
Topic: Compressing a gas
Replies: 5
Views: 73

### Re: Compressing a gas

When a reaction is compressed, you would be lowering the volume therefore increasing the concentration of each reactant and product. Let's say that the reactants have less mols of gas. Since K is products over reactants, the concentration of products would increase a lot more than the increase in re...
Sat Feb 08, 2020 12:32 pm
Forum: Calculating Work of Expansion
Topic: Constant Volume and Pressure Values
Replies: 8
Views: 83

### Re: Constant Volume and Pressure Values

I think we do need to know them, but it's easy to memorize since Cp=Cv+R and you only need to know three values of Cv which are 3/2R, 5/2R and 3R.
Sat Feb 08, 2020 12:26 pm
Forum: Phase Changes & Related Calculations
Topic: General Phase Change Calculations
Replies: 6
Views: 50

### Re: General Phase Change Calculations

For water the most important temperatures you have to remember is 0 and 100 degrees Celsius. When doing calculations and you pass either one of these numbers you have to take into account of a phase change with either Hvap or Hfus. For example if you're going from -20 degrees C to 106 degrees C you'...
Fri Jan 31, 2020 1:33 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: 5% Rule
Replies: 9
Views: 78

### Re: 5% Rule

No only when it is more than 5% then you have to do quadratic
Fri Jan 31, 2020 1:33 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: hess's law
Replies: 13
Views: 87

### Re: hess's law

Yes they need to be on opposite sides to cancel out with one another. It usually works out since most of the times it's obvious what product and reactant you want.
Fri Jan 31, 2020 1:32 pm
Forum: Administrative Questions and Class Announcements
Topic: Midterm
Replies: 8
Views: 119

### Re: Midterm

The midterm will include equilibrium, Acids and Bases, thermochemistry, and thermodynamics. So I'm pretty sure material up until next friday.
Fri Jan 31, 2020 1:30 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: Calculating microstates
Replies: 3
Views: 50

### Re: Calculating microstates

Calculating the number of microstates is just the number of states to the power of how many molecule. For example, if we had 2 states aka the left and the right and 2 molecules you can have 4 possible outcomes. Molecule A and B in left and right together, or the two molecules on opposite sides which...
Fri Jan 31, 2020 1:27 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Test 1 # 4
Replies: 10
Views: 111

### Re: Test 1 # 4

You'd have to use the equation PV=nRT since we have pressure, temperature, gas constant R, and the volume. Solve for n which is the amounts of mols of xenon and convert to grams. Make sure your units cancel out and temperature is in kelvin
Wed Jan 22, 2020 1:59 am
Forum: Equilibrium Constants & Calculating Concentrations
Topic: If [H3O+] < 10^-7
Replies: 2
Views: 40

### Re: If [H3O+] < 10^-7

That note referred to when you do a calculation where there's a weak acid and your answer for the concentration of H3O+ is less than 10^-7 which would make the solution basic. But this doesn't make sense since you added a weak acid which should give you an acidic solution. So when you add a weak aci...
Wed Jan 22, 2020 1:54 am
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Solids and Liquids
Replies: 6
Views: 49

### Re: Solids and Liquids

Yes only aq and gases are included in the equilibrium constant.
Wed Jan 22, 2020 1:53 am
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: 5J.13
Replies: 5
Views: 140

### Re: 5J.13

There will be less NH3 formed since the K value at 700k is a lot smaller than the K value at 600k. this means that at 700 K even when the temperature increases, K is small so the reactants are more favored.
Wed Jan 22, 2020 1:35 am
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: effects on pH
Replies: 7
Views: 67

### Re: effects on pH

Conjugate acids or conjugate bases of strong acids are very weak. This is due to the fact that Kw=Ka*Kb. Since Kw is a constant, when one of the K increases the other must decrease. So take for example HCl, it will have a very high Ka value since it dissociates completely which means the Kb will be ...
Wed Jan 22, 2020 1:33 am
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Changes in K
Replies: 2
Views: 32

### Re: Changes in K

When the reaction is multiplied by a constant, the new K value will be K to the power of that constant.
Wed Jan 15, 2020 2:19 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: cubic equations
Replies: 2
Views: 27

### Re: cubic equations

When K is less than 10^-3. You can also check at the end of the calculation to see if the change is less than 5% to see if the approximation works out.
Wed Jan 15, 2020 2:16 pm
Forum: Ideal Gases
Topic: equilibrium constant
Replies: 5
Views: 51

### Re: equilibrium constant

K is an equilibrium constant that represents the ratio of products to reactants. There's different types of K like Kp, Kc, Ka, Kb, but they all function the same and represent the ratio of products over reactants. The subscripts specify what kind of equilibrium it is. For example, Kp is equilibrium ...
Wed Jan 15, 2020 2:13 pm
Forum: Non-Equilibrium Conditions & The Reaction Quotient
Topic: Calculating Q
Replies: 16
Views: 169

### Re: Calculating Q

Q is calculated the same way as K so you include aqueous and gas in the calculation for Q
Wed Jan 15, 2020 2:11 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: strong vs weak
Replies: 4
Views: 40

### Re: strong vs weak

Yes you can use Kw=pOH+pH and Kw=pKa+pKb
Wed Jan 15, 2020 2:11 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: strong vs weak
Replies: 4
Views: 40

### Re: strong vs weak

Yes you can use Kw=pOH+pH and Kw=pKa+pKb
Wed Jan 15, 2020 2:09 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: x is small approximation
Replies: 6
Views: 72

### Re: x is small approximation

When K is smaller than 10^-3 you can approximate x
Fri Jan 10, 2020 11:13 am
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Units for K
Replies: 10
Views: 84

### Re: Units for K

Because it is a constant and is just a value used to look at the equilibrium of the reaction
Fri Jan 10, 2020 11:12 am
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Kp vs Kc
Replies: 6
Views: 38

### Re: Kp vs Kc

Use Kp for gases and Kc for aqueous reactants and products.
Fri Jan 10, 2020 11:12 am
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Calculating K
Replies: 6
Views: 58

### Re: Calculating K

It would be the inverse of the concentration since K is products over reactants
Fri Jan 10, 2020 11:10 am
Forum: Administrative Questions and Class Announcements
Topic: Required number of responses for chem community
Replies: 7
Views: 58

### Re: Required number of responses for chem community

Yes it is 5 a week.
Fri Jan 10, 2020 11:10 am
Forum: Ideal Gases
Topic: Difference between K and Q
Replies: 9
Views: 76

### Re: Difference between K and Q

K is the equilibrium constant with the equilibrium values of the product and reactants. Q is used when the reaction is not at equilibrium and is used to predict what's favored as the reaction proceeds.
Wed Dec 04, 2019 12:19 pm
Forum: Identifying Acidic & Basic Salts
Topic: pH of salt solutions
Replies: 2
Views: 35

### Re: pH of salt solutions

If the ion came from a strong acid or strong base, it will not affect the ph since the conjugates of these acids and bases are weak. Conjugates of weak acids and bases will affect the ph since they'll be strong acid and bases.
Wed Dec 04, 2019 12:14 pm
Forum: Hybridization
Topic: Hybridization of terminal atoms
Replies: 2
Views: 46

### Re: Hybridization of terminal atoms

No you only need to know the hybridization of the central atoms.
Wed Dec 04, 2019 12:10 pm
Forum: Lewis Acids & Bases
Topic: HCl and HI
Replies: 10
Views: 111

### Re: HCl and HI

HI, since I has a larger atom radius than Cl, HI has a weaker bond than HCl which makes HI dissociate completely very easily.
Wed Dec 04, 2019 12:05 pm
Forum: Amphoteric Compounds
Topic: H2O
Replies: 8
Views: 53

### Re: H2O

Yes, water can act as a base or an acid
Wed Dec 04, 2019 12:02 pm
Forum: Amphoteric Compounds
Topic: amphoteric oxides
Replies: 3
Views: 48

### Re: amphoteric oxides

Know which metal oxides are amphoteric. (BeO, Al2O3, Ga2O3, SnO2, Sb2O5, PbO2)
Sun Dec 01, 2019 8:06 pm
Forum: Calculating pH or pOH for Strong & Weak Acids & Bases
Topic: Strong Acids
Replies: 3
Views: 38

### Re: Strong Acids

Strong acids are acids that completely dissociate to completion (100%). These acids include HCl, HBr, HI, HNO3, H2SO4, and HClO4. They are strong acids because the have weak bonds and are able to dissociate completely which allows them to donate a proton.
Sun Dec 01, 2019 8:04 pm
Forum: Amphoteric Compounds
Topic: Amphoteric Compound
Replies: 5
Views: 58

### Re: Amphoteric Compound

Amphoteric compounds are compounds that can act as both an acid and a base. In class he showed examples of acid and base reactions that involved water. Water can act as both an acid and a base as it can accept H+ to become H3O+ and donate H+ to become OH-. There are also a couple of nonmetal and met...
Sun Dec 01, 2019 8:01 pm
Forum: Interionic and Intermolecular Forces (Ion-Ion, Ion-Dipole, Dipole-Dipole, Dipole-Induced Dipole, Dispersion/Induced Dipole-Induced Dipole/London Forces, Hydrogen Bonding)
Replies: 6
Views: 96

The TA's will update it later most likely. If not then for sure by the end of the quarter when everything is finalized.
Sun Dec 01, 2019 8:00 pm
Forum: Bronsted Acids & Bases
Topic: Bronsted Acid and Base
Replies: 5
Views: 80

### Re: Bronsted Acid and Base

Yes. acids donate a proton while bases accept protons for bronsted definitions
Sun Dec 01, 2019 7:59 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Sigma Bond
Replies: 10
Views: 115

### Re: Sigma Bond

Yes they are. Sigma bonds are also in double and triple bonds.
Sun Nov 24, 2019 9:16 pm
Forum: Hybridization
Topic: hybridization
Replies: 5
Views: 160

### Re: hybridization

Hybridization is the concept of combing orbitals so that an atom has space in their orbitals to hold bonding electrons.
Sun Nov 24, 2019 9:14 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: H3O+
Replies: 11
Views: 6439

### Re: H3O+

H30+ is tetrahedral since the O is bonded to 3 hydrogens and has a lone pair which makes the molecule have 4 electron densities. Since there's one lone pair the shape would be trigonal pyramidal.
Sun Nov 24, 2019 9:12 pm
Forum: Naming
Topic: Order in Naming
Replies: 12
Views: 136

### Re: Order in Naming

Place the ligand names in alphabetical order and determine if the complex has a positive or negative charge to determine if you place it before or after a cation or an anion.
Sun Nov 24, 2019 9:10 pm
Forum: Shape, Structure, Coordination Number, Ligands
Topic: Transition Metals
Replies: 2
Views: 30

### Re: Transition Metals

Transition metals have empty valance-shell orbitals that can accept pairs of electrons from ligands.
Sun Nov 24, 2019 9:08 pm
Forum: Hybridization
Topic: Shapes
Replies: 3
Views: 46

### Re: Shapes

The shapes tell you how many bonds the central atom has with other atoms including lone pairs. With this knowledge, you can determine the hybridization of the central atom by making sure there are enough empty orbitals to make bonds with other atoms. For example NH3 has 4 electron density regions an...
Sat Nov 16, 2019 10:04 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Polar vs. Nonpolar
Replies: 12
Views: 198

### Re: Polar vs. Nonpolar

First look at the molecular geometry that is 3D and draw dipole moments to see if they cancel out. You have to keep in mind that the geometry is 3 dimensional and take it into account when seeing if the dipoles cancel out.
Sat Nov 16, 2019 7:47 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: 2E.7 hw prob
Replies: 1
Views: 28

### Re: 2E.7 hw prob

Since the shape of the molecule is a trigonal pyramidal, there's no difference in the bond angles between S-O-Cl. There's only one bond angle.
Sat Nov 16, 2019 7:45 pm
Forum: Dipole Moments
Topic: 2E. 25a
Replies: 2
Views: 37

### Re: 2E. 25a

CH2CL2 has the molecular shape of a tetrahedral. Due to the nature of a tetrahedral, the Cl atoms will be right next to each other. You can imagine a tripod with another leg above it. No matter how you rotate this shape, Cl will be right next to another Cl. Since the dipole moments move towards both...
Sat Nov 16, 2019 7:41 pm
Forum: Bronsted Acids & Bases
Topic: Test2
Replies: 7
Views: 97

### Re: Test2

Should mostly be VSEPR and Monday's topics. It will ask questions revolving around molecular shapes.
Fri Nov 08, 2019 12:26 pm
Forum: Quantum Numbers and The H-Atom
Topic: Quantum Numbers
Replies: 6
Views: 176

### Re: Quantum Numbers

ms can only have the value of +/- 1/2. When drawing the electron configurations with arrows pointing up and down, you can see that each orbital can only have 2 arrows, one pointing up and one pointing down. This represents ms. One electron can have the value of 1/2 while the other electron has the v...
Fri Nov 08, 2019 12:22 pm
Forum: Lewis Structures
Topic: Exceptions to Octet Rule
Replies: 7
Views: 88

### Re: Exceptions to Octet Rule

With an n value of 3, the value of l can be 2 which is the d subshell. Since they have access to d orbitals, they are able to hold extra electrons in this orbital.
Fri Nov 08, 2019 12:21 pm
Forum: Quantum Numbers and The H-Atom
Topic: Formal names for each letter
Replies: 5
Views: 172

### Re: Formal names for each letter

N is principal quantum number (shell), l is angular momentum quantum number (subshell), ml is the magnetic quantum number (orbital), and ms is the spin.
Fri Nov 08, 2019 12:16 pm
Forum: Dipole Moments
Topic: Drawing Unpaired Electrons
Replies: 7
Views: 77

### Re: Drawing Unpaired Electrons

Yes always draw lone pairs in the lewis structures.
Fri Nov 08, 2019 12:15 pm
Forum: Quantum Numbers and The H-Atom
Topic: n, l ,ml, ms
Replies: 13
Views: 514

### Re: n, l ,ml, ms

ms can only equal +/- 1/2. Each electron in the orbital can only take one of the values. For example, in a Pz orbital, two electrons can be in this orbital. These electrons can't have the same ms values so one must be +1/2 and one must be -1/2.
Sat Nov 02, 2019 3:58 pm
Forum: Formal Charge and Oxidation Numbers
Topic: Formal Charges
Replies: 3
Views: 43

### Re: Formal Charges

Probably not when the question doesn't ask you to, but it doesn't hurt to especially when you're dealing with ions or weird structures.
Sat Nov 02, 2019 3:56 pm
Forum: Formal Charge and Oxidation Numbers
Topic: formal charge
Replies: 5
Views: 83

### Re: formal charge

You should keep in mind formal charges when drawing lewis structures since they give you the most stable structure of the molecule. To calculate it you can just take the valance electrons the element has and subtract the number of lone pair electrons (dots) and the number of bonds the element forms ...
Sat Nov 02, 2019 3:52 pm
Forum: Resonance Structures
Topic: resonance hybrid vs resonance structure
Replies: 2
Views: 38

### Re: resonance hybrid vs resonance structure

Resonance structure is when there is more than one way to draw a lewis structure (double or triple bonds). A resonance hybrid structure is basically a combination of all the resonance structure which is more a more accurate depiction of the structure.
Sat Nov 02, 2019 3:49 pm
Forum: Resonance Structures
Topic: Delocalization
Replies: 4
Views: 70

### Re: Delocalization

Yup! Resonance structures basically mean that the electrons are shared between the entire molecule not just within the covalent bonds. It will be more clear when we learn about pi and sigma bonds.
Sat Nov 02, 2019 3:47 pm
Forum: General Science Questions
Topic: Can We Take The Final In Pencil?
Replies: 14
Views: 762

### Re: Can We Take The Final In Pencil?

No the final has to be taken in pen. But I feel the same way. Usually I would just roughly do the work in pencil and then go over with pen. It takes a lot of time so I just use pencil on the questions that are more difficult.
Sun Oct 27, 2019 2:01 pm
Forum: Properties of Light
Topic: Value for C
Replies: 8
Views: 99

### Re: Value for C

You can use either one. I like using 3x10^8 since its easier on my calculator. Either way .002 wouldn’t make a difference in your final answer.
Sat Oct 26, 2019 6:26 pm
Forum: Ionic & Covalent Bonds
Topic: Resonance (all bonds are a hybrid of different bonds)
Replies: 10
Views: 146

### Re: Resonance (all bonds are a hybrid of different bonds)

You have to draw every combination of the molecule with a double headed arrow between each lewis structure. This shows that the structures can really be any of the combinations you drew. That's the most accurate way to draw it using lewis structures.
Sat Oct 26, 2019 6:24 pm
Forum: Ionic & Covalent Bonds
Topic: Expanded Valence Shells
Replies: 4
Views: 57

### Re: Expanded Valence Shells

These elements are in the third period of the periodic table. This means that since n=3, ml can also be equal to 2 which is the d-orbital. These elements have access to the d-orbital and can hold some electrons in these orbitals.
Sat Oct 26, 2019 6:20 pm
Forum: Ionic & Covalent Bonds
Topic: "Delocalized" Electrons
Replies: 5
Views: 76

### Re: "Delocalized" Electrons

For electrons to be delocalized, it means that the electrons are shared within the entire molecule. In the other examples we have seen,it has always been about electrons being shared between two atoms. For example, the electrons in CH4 are shared between each of the carbon and hydrogen bonds. Howeve...
Sat Oct 26, 2019 6:17 pm
Forum: Ionic & Covalent Bonds
Topic: Ionic and Covalent Bonds
Replies: 4
Views: 44

### Re: Ionic and Covalent Bonds

Ionic bonds occur within a metal and a nonmetal (Na and Cl in NaCl). The electrons have to be taken and transferred from one atom to another. Covalent bonds form between two nonmetals. (C and H in CH4) The atoms in this bond share their electrons.
Sun Oct 20, 2019 3:36 pm
Forum: Heisenberg Indeterminacy (Uncertainty) Equation
Topic: What does the H mean?
Replies: 9
Views: 89

### Re: What does the H mean?

No, the h-bar is just h(Planck's constant) divided by 2*pi
Sun Oct 20, 2019 3:30 pm
Forum: Bohr Frequency Condition, H-Atom , Atomic Spectroscopy
Topic: 1D. 25
Replies: 4
Views: 51

### Re: 1D. 25

1D.25 Which of the following subshells cannot exist in an atom: (a) 2d; (b) 4d; (c) 4g; (d) 6f? Can someone please explain this problem to me? Sub-shells refer to the quantum number l. Since the rule for l is l=0,1,...,n-1 you can look at the n and l values and determine if the following subshells e...
Sun Oct 20, 2019 3:26 pm
Forum: Electron Configurations for Multi-Electron Atoms
Topic: Valence electrons
Replies: 4
Views: 34

### Re: Valence electrons

You would have to include both the 4s orbital and 3d orbital in your count for valance electrons. Valance electrons determine the amount of bonds that is possible for the atom so since you have empty orbitals, they count towards your valance electron count.
Sun Oct 20, 2019 3:21 pm
Forum: Wave Functions and s-, p-, d-, f- Orbitals
Topic: Nodal Plane
Replies: 3
Views: 37

### Re: Nodal Plane

It all boils down to the wave function. Nodal planes are planes that divide lobes of electrons. It's the area where the probability of an electron is also zero. Since the s orbital is just one lobe, there's no nodal plane.
Sat Oct 19, 2019 4:35 pm
Forum: Electron Configurations for Multi-Electron Atoms
Topic: Cr and Cu
Replies: 5
Views: 60

### Re: Cr and Cu

Cr and Cu are considered exceptions to the Aufbau principle. Since having half-filled and full electron orbitals is more stable than a other electron configurations, the 4s electron moves down to the 3d orbital.
Sat Oct 19, 2019 4:16 pm
Forum: Quantum Numbers and The H-Atom
Topic: Correlation Between n and l
Replies: 6
Views: 87

### Re: Correlation Between n and l

l gives the shape of the orbital and it's also called the sub-shell.
l=0: S orbital
l=1: P orbital
l=2: D orbital
l=3: F orbital
Fri Oct 11, 2019 1:12 pm
Forum: Balancing Chemical Reactions
Topic: Fractions
Replies: 34
Views: 521

### Re: Fractions

It should always be expressed as a whole number. However, during the thermodynamics units, it would be beneficial to leave it as a fraction, but for now just express them as whole numbers.
Fri Oct 11, 2019 1:10 pm
Forum: SI Units, Unit Conversions
Topic: Showing work/ rearranging equations
Replies: 8
Views: 238

### Re: Showing work/ rearranging equations

You can really do it anyway you prefer. It's just that when you rearrange the variables first and plug into your calculator all at once, you will get a more accurate answer and avoid rounding off at intermediate steps.
Fri Oct 11, 2019 12:34 pm
Forum: Accuracy, Precision, Mole, Other Definitions
Topic: Accuracy and Precision
Replies: 8
Views: 234

### Re: Accuracy and Precision

It will become more relevant in a lab setting. If multiple trials of an experiment doesn't produce precise values, it will let you know that there is a systematic error (errors that can be eliminated). If your data is not accurate it could be due to random error (error you cannot control).
Fri Oct 11, 2019 12:27 pm
Forum: Empirical & Molecular Formulas
Topic: Decimals to Whole Numbers
Replies: 6
Views: 272

### Re: Decimals to Whole Numbers

It also helps if you don't round at each intermediate step. Just plug it all into your calculator at once. If you do come across a number like 3.1, + or - .2 should be sufficient enough to round down or up.
Fri Oct 11, 2019 12:20 pm
Forum: Photoelectric Effect
Topic: Photoelectric Effect Clarification
Replies: 3
Views: 37

### Re: Photoelectric Effect Clarification

Light sources with short wavelengths would have a larger frequency since there is an inverse relationship between wavelength and frequency. Using the equation E=hv, since a higher frequency correlates to a higher energy level, the light is able to overcome the threshold energy (work function) needed...
Wed Oct 02, 2019 7:20 pm
Forum: Empirical & Molecular Formulas
Topic: Homework question M.17
Replies: 2
Views: 104

### Re: Homework question M.17

The 1 came from the molar mass of H and the 17 came from the molar mass of OH. Knowing that the molar mass of X plus the molar mass of O plus the molar mass of H equals the total molar mass of XOH, you can subtract 17 from 125 to find the molar mass of X. You can do the same for HA and subtract 1 fr...
Wed Oct 02, 2019 1:59 pm
Forum: Empirical & Molecular Formulas
Topic: Rounding for Formulas
Replies: 8
Views: 145

### Re: Rounding for Formulas

There really isn't any cutoff for rounding. It's best if you don't round in your intermediate steps and calculations. That way you have exact values which would make it more clear how many moles of each atom there are. I would say that rounding up from .9 is okay, but anything below that should be r...
Tue Oct 01, 2019 11:56 pm
Forum: Accuracy, Precision, Mole, Other Definitions
Topic: Homework Problem E.15
Replies: 4
Views: 100

### Re: Homework Problem E.15

For this problem, you're given the molar mass of a hydroxide. To find the molar mass of the missing metal, subtract the molar masses of the Oxygen and Hydrogen from 74.10 (remember that there are two of each). Now with the molar mass we can find on the periodic table that the mystery element is Ca. ...