Search found 98 matches

by Valerie Doan 3I
Fri Feb 26, 2021 1:51 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Redox prob given no reaction [ENDORSED]
Replies: 2
Views: 58

Redox prob given no reaction [ENDORSED]

Hi! We did this problem in Colin's discussion, but I'm not sure how we determine which species is getting oxidized or reduced and how many electrons it gains or loses. (a) Write balanced half-reactions for the redox reaction of an acidified solution of potassium permanganate and iron(II) chloride. (...
by Valerie Doan 3I
Fri Feb 26, 2021 1:48 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Order of cell diagrams
Replies: 4
Views: 16

Re: Order of cell diagrams

The UAs and Sapling said to put the aqueous solutions in the middle (closest to the salt bridge) and the solids on the outside (furthest from salt bridge).
by Valerie Doan 3I
Fri Feb 26, 2021 1:43 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Cathode vs. Anode
Replies: 8
Views: 45

Re: Cathode vs. Anode

Definitely look at the setup, especially the electron flow. Another way you can look at it is by looking at the standard reduction potentials to determine which side is the anode and which is the cathode. Larger standard reduction potential means that it has a higher tendency to get reduced (has a s...
by Valerie Doan 3I
Fri Feb 26, 2021 1:35 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Electrochemical series
Replies: 3
Views: 15

Re: Electrochemical series

The electrochemical series arranges various redox equilibria in order of their standard electrode potentials. The most negative E° values are at the top of the electrochemical series, and the most positive at the bottom. Negative (or lower) E° values indicate stronger reducing power and more positiv...
by Valerie Doan 3I
Fri Feb 26, 2021 1:27 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: H+ in cell diagrams
Replies: 3
Views: 17

Re: H+ in cell diagrams

H+ is included in the cell diagram to indicate that the reaction is in acidic conditions.
by Valerie Doan 3I
Sat Feb 20, 2021 9:11 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Textbook 4A.13
Replies: 3
Views: 20

Re: Textbook 4A.13

The question is a bit confusing and wordy, but actually is very simple if you shift your perspective and focus on the surroundings (calorimeter) instead of the system. We know that in an insulated system such as a calorimeter there is no exchanging of matter or energy from the system to surrounding....
by Valerie Doan 3I
Sat Feb 20, 2021 9:05 pm
Forum: Van't Hoff Equation
Topic: Application of Van't Hoff Equation
Replies: 11
Views: 44

Re: Application of Van't Hoff Equation

In the chemical equilibrium unit, we learned that equilibrium constants change with temperature (increase or decrease) due to the endothermic and exothermic nature of chemical reactions. The Van't Hoff equation takes this idea into account and is used to find the equilibrium constant of a reaction g...
by Valerie Doan 3I
Sat Feb 20, 2021 8:59 pm
Forum: Calculating Work of Expansion
Topic: Isobaric
Replies: 4
Views: 27

Re: Isobaric

Here are a list of equations that you can use for isobaric processes:
- with
-
- because enthalpy is the heat absorbed/released by the system at constant pressure.
by Valerie Doan 3I
Sat Feb 20, 2021 8:55 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: Delta S for Isothermal
Replies: 8
Views: 30

Re: Delta S for Isothermal

For both isothermal reversible and isothermal irreversible, the entropy of the system can be calculated using delta S = nRln(V2/V1). Note for isothermal reversible, the entropy of the surroundings is negative of delta S system (which is found by applying the above equation) while in isothermal irrev...
by Valerie Doan 3I
Wed Feb 17, 2021 11:41 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: Textbook 4H.9
Replies: 2
Views: 14

Textbook 4H.9

Container A is filled with 1.0 mol of the atoms of an ideal monatomic gas. Container B has 1.0 mol of atoms bound together as diatomic molecules that are not vibrationally active. Container C has 1.0 mol of atoms bound together as diatomic molecules that are vibrationally active. The containers all ...
by Valerie Doan 3I
Sun Feb 14, 2021 8:22 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: confusion with notation
Replies: 11
Views: 37

Re: confusion with notation

I believe the d represents the change in S and change in q or enthalpy. He uses d instead of when the change is infinitesimal or really small.
by Valerie Doan 3I
Sun Feb 14, 2021 8:19 pm
Forum: Calculating Standard Reaction Entropies (e.g. , Using Standard Molar Entropies)
Topic: Entropy in Complex Molecules
Replies: 5
Views: 22

Re: Entropy in Complex Molecules

More complex molecules have higher standard molar entropies because they have a greater number of vibrational and rotational motions (these arise from bonds and overall shape/structure of the molecule), which means that they an occupy more positions.
by Valerie Doan 3I
Sun Feb 14, 2021 8:14 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Sapling W5-6 Q15
Replies: 6
Views: 21

Re: Sapling W5-6 Q15

Hmmm I would make sure that your units are all the same because the problem gives you enthalpy in kJ while entropy in J/K but the final answer should be in kJ. Also, maybe your forgot to multiply the \Delta S and \Delta H for the second reaction by a factor of -2 in order to cancel out the spectator...
by Valerie Doan 3I
Sun Feb 14, 2021 8:07 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Gibbs, Spontaneity, and Temp Review
Replies: 3
Views: 25

Gibbs, Spontaneity, and Temp Review

I know that we have some homework questions about finding the T that makes the reaction spontaneous ( \Delta G<0 ), so here is a helpful summary of the effect of entropy and enthalpy on Gibbs free energy!! \Delta H<0 and \Delta S>0 --> reaction is spontaneous at all temperatures \Delta H>0 and \Delt...
by Valerie Doan 3I
Sun Feb 14, 2021 7:45 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: Sapling #6 weeks 5 & 6
Replies: 2
Views: 14

Re: Sapling #6 weeks 5 & 6

Eliana is right. With these problems, I usually like to split it up into two steps: one instance when the temperature is constant (V is changing) and the other scenario when volume is constant (T is changing). From there, I use the equations on the equation sheet for entropy and add the two entropie...
by Valerie Doan 3I
Sun Feb 14, 2021 7:41 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: Sapling #7 Week 5/6
Replies: 3
Views: 34

Sapling #7 Week 5/6

For Sapling number 7, I was able to find the and , but I don't understand how to order them based on least ordered and most ordered. Why does a greater increase in disorder indicate a more ordered arrangement of the molecules in the liquid state?
by Valerie Doan 3I
Sat Feb 06, 2021 10:27 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: Entropy and Volume Relationship
Replies: 1
Views: 12

Entropy and Volume Relationship

From week 5 Friday lecture, Dr. Lavelle talked about how if volume doubled in an isothermal reversible expansion of an ideal gas, the number of possible positions is twice that of initial. This means that the degeneracy is doubled. Why is that though? I'm having a hard time understanding how he came...
by Valerie Doan 3I
Sat Feb 06, 2021 10:19 pm
Forum: Thermodynamic Systems (Open, Closed, Isolated)
Topic: Sapling Week 3/4 #19
Replies: 6
Views: 63

Re: Sapling Week 3/4 #19

1. Find the heat capacity of the calorimeter 1.11 kJ / 2.10 C 2. Find q_{cal} by multiplying the heat capacity in step 1 with 6.59 C 3. Because this is a closed system, we know that q_{cal}+q=0 therefore q_{cal}=-q 4. Then, we can use the equation \Delta U=q+w=q-P\Delta V . We know the q from step 2...
by Valerie Doan 3I
Sat Feb 06, 2021 10:11 pm
Forum: Calculating Work of Expansion
Topic: Reversible and Irreversible Expansion
Replies: 3
Views: 20

Re: Reversible and Irreversible Expansion

You can also determine if it is a reversible or irreversible expansion based on the given P internal and P external. For an isothermal reverible expansion, the pressure of the expanding gas is the same as the external pressure resisting the expansion.
by Valerie Doan 3I
Sat Feb 06, 2021 2:11 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: sapling 18
Replies: 1
Views: 15

Re: sapling 18

Because it is constant pressure, we know that q_{p}=\Delta H 1. To find heat, we are given moles and the molar specific heat for CO2. So, we use the equation q=nc\Delta T 2. To find internal energy, we use the equation \Delta U=q+w . We use the heat we found in step 1 for q. The work equation we can...
by Valerie Doan 3I
Sat Feb 06, 2021 2:04 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: Week 3/4 Sapling 10
Replies: 1
Views: 20

Week 3/4 Sapling 10

Could someone help me with #10 on the Sapling for Week 3/4? I understand that the equation is \triangle H_{fus}+q_{ice}=-q_{water} but for some reason when I calculate for the final temperature I get around 4 degrees celsius which is incorrect. An ice cube with a mass of 51.8 g at 0.0 ∘C is added to...
by Valerie Doan 3I
Fri Jan 29, 2021 2:20 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Cubic Equations
Replies: 6
Views: 32

Re: Cubic Equations

I would just know how to solve for cubic equations (can do that on the calculator), but you will rarely have to do that because usually K is less that 10^-4 so we use the approximation and assume that there is negligible change in the initial concentration.
by Valerie Doan 3I
Fri Jan 29, 2021 2:18 pm
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: Textbook problem 6.61
Replies: 7
Views: 24

Re: Textbook problem 6.61

Water or solids and liquids in general do not affect the equilibrium because their concentrations do not change by a specific amount. So, if there's a question asking "how does K change when H2O (l) is added?" the answer would be no effect. Remember only temperature can change the equilibr...
by Valerie Doan 3I
Fri Jan 29, 2021 2:12 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Textbook Focus 4.31
Replies: 8
Views: 29

Re: Textbook Focus 4.31

In this problem, you are given pressure, volume, and temperature. In order to find the moles of H2, you have to use the ideal gas law which is PV=nRT and re-arrange it so that you get n=PV/RT. Make sure you use the appropriate R constant that cancels out the units of pressure, volume, and temperatur...
by Valerie Doan 3I
Fri Jan 29, 2021 2:09 pm
Forum: Phase Changes & Related Calculations
Topic: Polyprotic acid solutions
Replies: 4
Views: 43

Re: Polyprotic acid solutions

The only polyprotic acid that is strong is H2SO4, hence there would be complete ionization. For other polyprotic acids (weak), you would have to do an ICE table for the first dissociation to determine the equilibrium constant and concentrations. You wouldn't have to do another ICE table for the seco...
by Valerie Doan 3I
Tue Jan 26, 2021 3:06 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: kJ vs. kJ/mol Enthalpy units [ENDORSED]
Replies: 3
Views: 69

kJ vs. kJ/mol Enthalpy units [ENDORSED]

I am doing the textbook problems for section 4D right now, and I'm having a hard time determining when to give the enthalpy in kJ or in kJ/mol. What are the units I'm supposed to use? And when do I use kJ and kJ/mol? Thanks in advance!
by Valerie Doan 3I
Sun Jan 24, 2021 11:20 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Textbook 6D.15
Replies: 2
Views: 15

Textbook 6D.15

Could someone help me with part b of the problem 6D.15?

Calculate the pH of (a) 0.19 M NH4Cl(aq); (b) 0.055 M AlCl3(aq).
by Valerie Doan 3I
Sun Jan 24, 2021 8:32 pm
Forum: Phase Changes & Related Calculations
Topic: Steam
Replies: 32
Views: 139

Re: Steam

Basically, water has a higher enthalpy of vaporization (in this case condensation) due to hydrogen bonds. When these bonds re-form, they release heat, causing severe burns.
by Valerie Doan 3I
Sun Jan 24, 2021 8:10 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Bond enthalpies and phase changes
Replies: 6
Views: 29

Bond enthalpies and phase changes

Using the bond enthalpy method, how do we find the net enthalpy change for a compound that undergoes a phase change? For example, in lecture Dr. Lavelle used the example Br2 (l) --> Br2 (g) --> 2Br (g).
by Valerie Doan 3I
Sun Jan 24, 2021 8:05 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: pH of salt/bases
Replies: 4
Views: 30

Re: pH of salt/bases

I would split up the compounds to its respective cations and anions and see the relative strengths using their conjugate acids and bases. In this case, CH3NH3+ is the cation and Cl- is the anion. Cl- is the conjugate base of the strong acid, HCl, so it will not affect the pH because it is a spectato...
by Valerie Doan 3I
Fri Jan 22, 2021 10:42 pm
Forum: Calculating pH or pOH for Strong & Weak Acids & Bases
Topic: Concentration X
Replies: 4
Views: 19

Re: Concentration X

Nayra is correct. We can use the approximation method if K is less than 10 ^-4. Use this method first and then double check with the 5% approximation rule (percent protonation/de-protonation less than 5%) to ensure that the change in x is negligible.
by Valerie Doan 3I
Fri Jan 22, 2021 9:26 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Sapling #5
Replies: 4
Views: 28

Sapling #5

Could someone help me with this problem from this week's Sapling? The Kb for an amine is 2.579×10−5. What percentage of the amine is protonated if the pH of a solution of the amine is 9.821 ? Assume that all OH− came from the reaction of B with H2O. I keep getting 38%, but that isn't the correct ans...
by Valerie Doan 3I
Fri Jan 15, 2021 10:55 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Week 2 Sapling #1
Replies: 2
Views: 19

Re: Week 2 Sapling #1

A concentration change is small compared to its initial concentration if the change is less than 5% of the initial. But, generally the rule of thumb is when K<10^-4 we can approximate the change as close to zero. We really only do the 5% calculation if K is on the cusp of 10^-3 or 10^-4, and we are ...
by Valerie Doan 3I
Fri Jan 15, 2021 10:50 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: ICE Box
Replies: 28
Views: 99

Re: ICE Box

Usually, the ICE box method is only used for weak acids and bases because they don't fully dissociate in water. However, strong acids and bases do completely ionize so we can just directly use the pH, Ka, or Kb formula without having to do an ICE box.
by Valerie Doan 3I
Fri Jan 15, 2021 10:47 pm
Forum: Polyprotic Acids & Bases
Topic: What Does Monoprotic Mean?
Replies: 8
Views: 49

Re: What Does Monoprotic Mean?

A monoprotic acid is an acid that can only donate one proton like HCl. On the other, a polyprotic acid is an acid that can donate multiple protons like H3PO4 because it has 3 hydrogens that can be donated.
by Valerie Doan 3I
Fri Jan 15, 2021 10:44 pm
Forum: Non-Equilibrium Conditions & The Reaction Quotient
Topic: Acid and Bases always Happening in Water?
Replies: 3
Views: 35

Re: Acid and Bases always Happening in Water?

I believe for this course we're only looking at acids and bases reacting with water, which is why we exclude H2O from equilibrium constants. Water is the solvent. However, if the reaction is not occurring in an aqueous solution, I assume that H2O would need to be accounted for in the chemical reacti...
by Valerie Doan 3I
Fri Jan 15, 2021 10:40 pm
Forum: Non-Equilibrium Conditions & The Reaction Quotient
Topic: ka vs kb
Replies: 20
Views: 69

Re: ka vs kb

Adding on, to convert Ka to Kb or vice versa you can use the equation Kw=Ka x Kb with Kw=10^-14.
by Valerie Doan 3I
Sun Jan 10, 2021 6:08 pm
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: Textbook 5J.1
Replies: 2
Views: 30

Textbook 5J.1

I'm confused about how partial pressures of the reactant/products would increase or decrease if there is a change. Could someone explain this textbook problem? Consider the equilibrium CO(g)+H2O(g)-->CO2(g)+H2(g). (a) If the partial pressure of CO2 is increased, what happens to the partial pressure ...
by Valerie Doan 3I
Fri Jan 08, 2021 9:11 pm
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: Change in Amount of Product
Replies: 4
Views: 29

Re: Change in Amount of Product

That's a way of doing it I think! I personally stumbled upon this question as well, and what I did was I took the equilibrium concentrations of all products and reactants and made that the initial concentrations, and then just changed the initial concentration of what you are asking, in this case, ...
by Valerie Doan 3I
Fri Jan 08, 2021 9:05 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: How to Know Solid from Example in Lecture in H2O
Replies: 3
Views: 20

Re: How to Know Solid from Example in Lecture in H2O

In this problem, the H2O is the solvent and dissociation of the solid can only occur in water.
by Valerie Doan 3I
Thu Jan 07, 2021 10:34 pm
Forum: Ideal Gases
Topic: Chemical Equilibrium Part 1A Post-Module Assessment
Replies: 11
Views: 38

Re: Chemical Equilibrium Part 1A Post-Module Assessment

Your answer you chose (B) is wrong because any change in the initial concentration of reactants or products will eventually stabilize and reach equilibrium. A good analogy I can think of is a pendulum or swing. No matter how hard you push the swing or where (how high) you drop it, the swing will eve...
by Valerie Doan 3I
Thu Jan 07, 2021 10:27 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Kc
Replies: 11
Views: 75

Re: Kc

Yes, the units for concentration in Kc are mol/L. Note that if we are not given molarity, we can calculate that by doing n/v= P/RT. The n/v represents the molarity aka concentration of the reactant or product. n is the moles and v is the volume, hence the units are mol/L.
by Valerie Doan 3I
Thu Jan 07, 2021 10:19 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Textbook Problem 5G.11
Replies: 2
Views: 10

Re: Textbook Problem 5G.11

Remember that solids and liquids are not included in the equilibrium constant or the reaction quotient. So, you would basically do the same calculation as K with products divided by reactants, each raised to their stoichiometric coefficients. a) 1/[BCL3]^2 b) [H2S]^10 * [H3PO40^4 c) [BrF3]^2 / [F2]^...
by Valerie Doan 3I
Mon Dec 14, 2020 11:55 pm
Forum: Interionic and Intermolecular Forces (Ion-Ion, Ion-Dipole, Dipole-Dipole, Dipole-Induced Dipole, Dispersion/Induced Dipole-Induced Dipole/London Forces, Hydrogen Bonding)
Topic: Thymine Hydrogen bonding
Replies: 2
Views: 49

Re: Thymine Hydrogen bonding

I'm not sure what the Marshmallow problem is, but I counted 8 possible hydrogen bonds. Lone pairs of electronegative atoms, F, O, N, can act as hydrogen bond acceptors. Hydrogen atoms bonded to a F,O,N are hydrogen bond donors. With this in mind, you can see how many I found in the image. Someone co...
by Valerie Doan 3I
Mon Dec 14, 2020 11:46 pm
Forum: Lewis Acids & Bases
Topic: help with problem 6B
Replies: 3
Views: 44

Re: help with problem 6B

The second method is correct! The reason why the first method you used was wrong was that you solved for moles of H+. However, the pH equation is equal to -log[H+], with [H+] being the molarity or moles/L of hydronium ions. Because you just used moles, your answer was wrong.
by Valerie Doan 3I
Sun Dec 13, 2020 10:42 am
Forum: Determining Molecular Shape (VSEPR)
Topic: Lone Pairs
Replies: 5
Views: 68

Lone Pairs

Where should lone pairs be placed (axial or equatorial) to reduce lone pair-lone pair repulsions? If you could also explain why that would be great!
by Valerie Doan 3I
Sat Dec 12, 2020 6:39 pm
Forum: Octet Exceptions
Topic: 2.61 Radicals
Replies: 1
Views: 27

2.61 Radicals

When drawing the Lewis structure, which atom gets the unpaired electron? For textbook problem 2.61, it asks us to draw the Lewis structure for HOCO. I did it differently and I put C in the middle and the three other atoms around. The O got the unpaired electron. However, the textbook answer shows a ...
by Valerie Doan 3I
Sat Dec 12, 2020 5:55 pm
Forum: Hybridization
Topic: 2F. 15 What does it mean for S-character to increase?
Replies: 5
Views: 103

Re: 2F. 15 What does it mean for S-character to increase?

I understand the quantification, but what does s-character actually mean? How does this relate to molecular shape?
by Valerie Doan 3I
Sun Dec 06, 2020 6:01 pm
Forum: Coordinate Covalent Bonds
Topic: Coordination Compounds vs Ionic Compounds
Replies: 2
Views: 29

Re: Coordination Compounds vs Ionic Compounds

Transition elements tend to form coordination complexes more than s and p block elements because they are small, highly charged ions and they have low energy orbitals that are vacated. This allows transition metals to accept lone pairs of electrons donated by other groups or ligands.
by Valerie Doan 3I
Sun Dec 06, 2020 5:52 pm
Forum: Naming
Topic: Anion Naming
Replies: 7
Views: 79

Re: Anion Naming

A tip that I learned in a step up session is to think of the coordination compounds as ionic compounds when naming them (note: they're not the same lol but use as an analogy). Think of the ionic compound, MgCl2. You wouldn't say magnesium dichloride right? It would just be magnesium chloride. Same w...
by Valerie Doan 3I
Fri Dec 04, 2020 1:19 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: difference
Replies: 4
Views: 37

Re: difference

Trigonal planar molecules have 4 electron pairs, 1 lone PR and 3 bonding pairs (with 3 atoms). T-shaped molecules have 5 electron pairs, 2 lone pairs and 3 bonding pairs (with 3 atoms). Both of these have 3 bonding pairs with 3 separate atoms, but the amount of lone pairs differs.
by Valerie Doan 3I
Fri Dec 04, 2020 1:10 pm
Forum: Lewis Acids & Bases
Topic: lewis vs bronsted
Replies: 8
Views: 99

Re: lewis vs bronsted

I would also like to add that all Bronsted-Lowry acids are Lewis acids, but the reverse is not true. The definition of a Lewis acid is used as a baseline, but for specificity reasons, the definition of a Bronsted acid is better. Also, every Bronsted-Lowry base is also a Lewis base, but the reverse i...
by Valerie Doan 3I
Fri Dec 04, 2020 12:59 pm
Forum: Shape, Structure, Coordination Number, Ligands
Topic: Iron Naming
Replies: 3
Views: 29

Re: Iron Naming

Fe is called ferrate because the complex ion is an anion. If the complex ion is a cation, the metal has the same name as the element. For example, Co in a complex cation is call cobalt and Pt is called platinum. However, if the complex ion is an anion, the name of the metal ends with the suffix ate ...
by Valerie Doan 3I
Sat Nov 28, 2020 6:48 pm
Forum: Sigma & Pi Bonds
Topic: Pi Bonds Being Parallel or Perpendicular
Replies: 2
Views: 37

Re: Pi Bonds Being Parallel or Perpendicular

I'm not really sure what you mean, but a pi bond is formed when two p-orbitals overlap parallel to each other but perpendicular to the sigma bonds and the internuclear axis. Here is a picture that may help you visualize.

Hope this answers your question!
by Valerie Doan 3I
Sat Nov 28, 2020 12:39 pm
Forum: Dipole Moments
Topic: 2E #25a CH2Cl2 Lewis dot Structure
Replies: 3
Views: 58

Re: 2E #25a CH2Cl2 Lewis dot Structure

Isaac is correct. You probably thought that the two Cl atoms were in the axial positions and therefore their dipoles cancelled. However that is not the case. Because there are 4 bonding pairs, VSEPR tells us that it is tetrahedral. So, only one atom is in the axial position and the three other atoms...
by Valerie Doan 3I
Sat Nov 28, 2020 12:08 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Sapling #17
Replies: 5
Views: 63

Sapling #17

Could someone explain how they found the bond angles and hybridizations for C3H4? Thanks
by Valerie Doan 3I
Sat Nov 28, 2020 11:20 am
Forum: Determining Molecular Shape (VSEPR)
Topic: Double/Triple Bonds and Polarity
Replies: 8
Views: 61

Double/Triple Bonds and Polarity

Do double and triple bonds affect polarity? For example in , As has 3 single bonds with oxygen and 1 double bond. Would the double bond make the molecule polar?
by Valerie Doan 3I
Sat Nov 28, 2020 12:44 am
Forum: Determining Molecular Shape (VSEPR)
Topic: Preferential Interactions
Replies: 4
Views: 50

Preferential Interactions

Dr. Lavelle talked about preferential interactions, but I still don't understand what he means. Could someone explain how you know if a molecule is polar based on preferential interactions? Thank you.
by Valerie Doan 3I
Sun Nov 22, 2020 12:06 am
Forum: Determining Molecular Shape (VSEPR)
Topic: Sigma and Pi bonds
Replies: 3
Views: 40

Re: Sigma and Pi bonds

In this case, it doesn't matter if the central atom has an expanded octet; it will not affect how many sigma and pi bonds the molecule has. For example, in PCl5, phosphorous has 10 valence elections, but there are still 5 sigma bonds (P-Cl). You would just count these bonds like you normally would. ...
by Valerie Doan 3I
Sat Nov 21, 2020 11:51 pm
Forum: Lewis Structures
Topic: Sapling Hw #12
Replies: 3
Views: 47

Re: Sapling Hw #12

Yep! Use the mass percentage to find the empirical formula, then use the molar mass to get the molecular formula. After that, you can draw the Lewis structure.
by Valerie Doan 3I
Sat Nov 21, 2020 11:01 pm
Forum: Dipole Moments
Topic: What are dipole moments
Replies: 9
Views: 71

Re: What are dipole moments

There are also two different types of dipole moments: a permanent dipole moment and an induced dipole moment. Molecules with polar bonds have permanent dipole moments and can interact with other polar molecules and create dipole-dipole forces. On the other hand, molecules with induced dipole moments...
by Valerie Doan 3I
Sat Nov 21, 2020 10:56 pm
Forum: Electronegativity
Topic: Textbook problem 2d.5
Replies: 3
Views: 36

Re: Textbook problem 2d.5

Just remember that the most electronegative atoms on the periodic table are F, O, N, and Cl, which is why CF4 would be more ionic. Also, C-H bonds are generally regarded as non-polar because their electronegativity difference is miniscule.
by Valerie Doan 3I
Sat Nov 21, 2020 10:53 pm
Forum: Electronegativity
Topic: Polarizability vs. Polarizing Power
Replies: 6
Views: 64

Re: Polarizability vs. Polarizing Power

Polarizability refers to the behavior of the anions, while polarizing power refers to cations.
by Valerie Doan 3I
Sat Nov 14, 2020 9:39 pm
Forum: Polarisability of Anions, The Polarizing Power of Cations
Topic: Polarisability for Ionic bonds
Replies: 3
Views: 37

Re: Polarisability for Ionic bonds

Polarizability can be used to determine the strength of both intermolecular and intramolecular forces. For intramolecular forces most specifically ionic bonds, polarizability refers to how easily a cation can distort the electron field of the anion and pull the electrons towards the shared region. W...
by Valerie Doan 3I
Sat Nov 14, 2020 9:26 pm
Forum: Polarisability of Anions, The Polarizing Power of Cations
Topic: Consequences of polarizability
Replies: 4
Views: 145

Re: Consequences of polarizability

Polarizing power refers to an atoms ability to pull an electron towards it. Since cations are positive, they are able to attract electrons away from the anions and towards themselves. Anions are negative. Therefore, they do not attract more electrons.
by Valerie Doan 3I
Sat Nov 14, 2020 9:00 pm
Forum: Bond Lengths & Energies
Topic: Effect of size on IMF and intramolecular
Replies: 2
Views: 18

Effect of size on IMF and intramolecular

What is the effect of size on intermolecular forces vs. intramolecular forces(like London dispersion forces)? Do bigger molecules have stronger bonds than smaller molecules?

Thanks!
by Valerie Doan 3I
Sat Nov 14, 2020 8:55 pm
Forum: Electron Configurations for Multi-Electron Atoms
Topic: Electrons and Shielding
Replies: 1
Views: 13

Re: Electrons and Shielding

An electron that is close to the nucleus (say for example in the 1s orbital) will experience a much higher effective nuclear charge from the protons from the nucleus. On the other hand, electrons farther from the nucleus such as those in the 4d orbital will experience a significantly smaller effecti...
by Valerie Doan 3I
Sat Nov 14, 2020 8:49 pm
Forum: Formal Charge and Oxidation Numbers
Topic: Formal Charge Formula
Replies: 4
Views: 40

Re: Formal Charge Formula

In this equation, the lone stands for all of the free/unbonded electrons. Don't think of it as lone pairs as you might count two electrons as one pair and plug 1 in the equation. Think of it as the individual electrons, so in this example it would be 2 electrons and you would use 2 in the FC equation.
by Valerie Doan 3I
Sat Nov 14, 2020 8:46 pm
Forum: Lewis Structures
Topic: Minimizing formal charges
Replies: 3
Views: 33

Re: Minimizing formal charges

The most stable and favorable Lewis structure is one where most of the atoms have a zero formal charge. A -1 and +1 charge is favorable too, but you just want to ensure that the Lewis structure has the least amount of those charges. A good thing to also note is that usually the most electronegative ...
by Valerie Doan 3I
Sun Nov 08, 2020 3:45 pm
Forum: Electronegativity
Topic: Shielding Effect
Replies: 6
Views: 35

Re: Shielding Effect

Thanks for the explanation guys! But, what about the shielding effects of s and p orbitals with different principle quantum numbers? For example, if we compare a 2p orbital and a 3s orbital, is a 2p orbital more effective at shielding? Or is it in general s-orbitals are more effective at shielding n...
by Valerie Doan 3I
Sun Nov 08, 2020 3:40 pm
Forum: Polarisability of Anions, The Polarizing Power of Cations
Topic: Covalent character vs. Ionic character
Replies: 4
Views: 47

Covalent character vs. Ionic character

Could someone explain the difference between a bond having covalent character vs. a bond with ionic character? It seems that all bonds have both ionic and coval. character, so how do we differentiate them? Thanks!
by Valerie Doan 3I
Sun Nov 08, 2020 3:33 pm
Forum: Polarisability of Anions, The Polarizing Power of Cations
Topic: Distortion
Replies: 8
Views: 75

Re: Distortion

Hayden and Rajshree did a really good job at explaining distortion and the polarizability of electrons. Here is an image that can help you visualize the concept: derr - Copy - Copy.png When electrons are highly distorted, they are described as highly polarizable because the outer electrons of the an...
by Valerie Doan 3I
Sun Nov 08, 2020 3:24 pm
Forum: Formal Charge and Oxidation Numbers
Topic: formal charge
Replies: 11
Views: 43

Re: formal charge

Yes, an atom needs to bonded. The formal charge equation includes the shared electrons that the atom has and the nonbonding electrons.
by Valerie Doan 3I
Fri Nov 06, 2020 8:56 pm
Forum: Ionic & Covalent Bonds
Topic: Formal Charge Equation
Replies: 10
Views: 52

Re: Formal Charge Equation

To form a bond, each atom shares one of its valence electrons and "gains" a new electron from another atom. In reality, these atoms are sharing the two electrons. You can think of the S/2 term in the formal charge equation as counting the one valence electron that the atom already had PRIO...
by Valerie Doan 3I
Fri Nov 06, 2020 8:43 pm
Forum: Electronegativity
Topic: Shielding Effect
Replies: 6
Views: 35

Shielding Effect

This is part of a homework question from the textbook that my TA went over, but I still don't understand it.

Why are electrons in an s orbital more effective at shielding from the nuclear charge than p orbitals?
by Valerie Doan 3I
Sun Nov 01, 2020 7:49 pm
Forum: Trends in The Periodic Table
Topic: Stuck on #23 for Sapling Week 4 regarding electron affinity
Replies: 1
Views: 36

Re: Stuck on #23 for Sapling Week 4 regarding electron affinity

Hey! We are given wavelength so we can use \frac{hc}{\lambda } to find E photon. We are given the electron's kinetic energy 0.137eV but it needs to be converted to J by multiplying 1.602\times 10^{-19}J/eV . Once you get the 2 energies subtract them to find the electron affinity. Note that this answ...
by Valerie Doan 3I
Sun Nov 01, 2020 7:36 pm
Forum: SI Units, Unit Conversions
Topic: Sapling WEEK 4 #22
Replies: 5
Views: 56

Re: Sapling WEEK 4 #22

First, you use De Broglie's equation \lambda = \frac{h}{mv} but re-arrange it to find velocity instead. So that would be v=\frac{h}{\lambda m} . Using that velocity, you plug it into the kinetic energy equation E=\frac{1}{2}mv^{^{2}} . Your answer will be in Joules but you need to convert it to elec...
by Valerie Doan 3I
Sat Oct 31, 2020 3:07 pm
Forum: Einstein Equation
Topic: de Broglie and neutrons
Replies: 8
Views: 66

Re: de Broglie and neutrons

Yup! Here is a summary of what equations can be used for certain particles. E=hv --> only for photon c=\lambda v --> only for photon E=\frac{1}{2}mv^{2} --> anything that has a mass and velocity (eg: electrons) so NO PHOTONS \lambda = \frac{h}{mv} --> anything that has a mass and velocity so again N...
by Valerie Doan 3I
Sat Oct 31, 2020 3:01 pm
Forum: DeBroglie Equation
Topic: sapling 2, 3, 4: #25
Replies: 4
Views: 70

Re: sapling 2, 3, 4: #25

Yes, you should use de Broglie's equation! It says it in the problem. Because you are already given wavelength, you re-arrange the de Broglie eq. to get v=h/ \lambda *m. You use that to solve for velocity. After that, you plug the velocity into the kinetic energy equation E=0.5mv^2. This is the ener...
by Valerie Doan 3I
Sat Oct 31, 2020 2:55 pm
Forum: Bohr Frequency Condition, H-Atom , Atomic Spectroscopy
Topic: Sapling spectroscopy problem
Replies: 2
Views: 39

Sapling spectroscopy problem

Hello, I know that multiple people have posted this, but I still don't understand the reasoning. "The electron in a hydrogen atom is excited to the n=6 shell and emits electromagnetic radiation when returning to lower energy levels. Determine the number of spectral lines that could appear when ...
by Valerie Doan 3I
Sun Oct 25, 2020 10:58 pm
Forum: Einstein Equation
Topic: de Broglie and neutrons
Replies: 8
Views: 66

Re: de Broglie and neutrons

Yes, de Broglie's equation can be used for anything that has a mass and velocity, even larger objects like basketballs!
by Valerie Doan 3I
Sun Oct 25, 2020 10:55 pm
Forum: Properties of Electrons
Topic: Kinetic energy for electrons
Replies: 3
Views: 43

Re: Kinetic energy for electrons

In this case, the problem would say that the energy of the incoming photon matches the threshold energy. There is no 'excess energy' because all the energy from the photon is used to eject electrons, therefore the electrons have no kinetic energy.
by Valerie Doan 3I
Sun Oct 25, 2020 10:52 pm
Forum: Properties of Electrons
Topic: Work Function
Replies: 3
Views: 40

Re: Work Function

There is no specific formula to find the work function. However, in certain problems they will say "the minimum frequency or wavelength required to eject an electron is x". In cases like that, you would use E=hv=hc/wavelength to find the threshold energy. Sometimes, you are given E(photon)...
by Valerie Doan 3I
Sun Oct 25, 2020 3:38 pm
Forum: Bohr Frequency Condition, H-Atom , Atomic Spectroscopy
Topic: Rydberg Equation Confusion
Replies: 3
Views: 50

Rydberg Equation Confusion

Hello,

In the Rydberg equation (the one that gives us frequency), there is n1 and n2. Which n is the initial and which is the final?

Thanks
by Valerie Doan 3I
Thu Oct 22, 2020 9:01 pm
Forum: Photoelectric Effect
Topic: 1B.15 Textbook Problem
Replies: 2
Views: 35

Re: 1B.15 Textbook Problem

For part (a), the textbook actually asks for the wavelength of the ejected electron! For this, I used the DeBroglie equation plugging in Planck's constant (h), 9.109 x 10^-31 kg for m, and 3.6 x 10^6 m/s (which is converted from the given value in km/s to m/s) for v. Hope this clears things up! Tha...
by Valerie Doan 3I
Thu Oct 22, 2020 8:49 pm
Forum: Photoelectric Effect
Topic: 1B.15 Textbook Problem
Replies: 2
Views: 35

1B.15 Textbook Problem

Hello, could someone help me solve this prob? I keep getting the wrong answer for part a. The velocity of an electron that is emitted from a metallic surface by a photon is 3.6 3 103 km?s21. (a) What is the wavelength of the ejected electron? (b) No electrons are emitted from the surface of the meta...
by Valerie Doan 3I
Tue Oct 20, 2020 11:52 pm
Forum: Heisenberg Indeterminacy (Uncertainty) Equation
Topic: Question 20 from Heisenberg Module
Replies: 2
Views: 40

Question 20 from Heisenberg Module

Hello, I'm currently doing the Heisenberg module right now and I came across this question that said to "comment on its value." How do I determine if the uncertainty of KE is 'huge' or 'small'. I know that for the uncertainty of velocity you compare it to the speed of light. For kinetic en...
by Valerie Doan 3I
Sat Oct 17, 2020 8:33 pm
Forum: Einstein Equation
Topic: What are the units for E
Replies: 16
Views: 124

Re: What are the units for E

In the equation E(PHOTON) - E(ENERGY REMOVE e-) = E(EXCESS) = Ek(e-), the units for all energies is Joules (J). For E(PHOTON)=hv, the units for h is Joules*second, and the units for v (frequency) is Hertz. For the kinetic energy equation Ek(e-)=0.5mv^2, mass is in kg and v (velocity) is in meters pe...
by Valerie Doan 3I
Fri Oct 16, 2020 11:01 pm
Forum: Quantum Numbers and The H-Atom
Topic: Atomic Spectra Post-Assessment #29
Replies: 4
Views: 35

Re: Atomic Spectra Post-Assessment #29

For this problem, the only numbers you need are the wavelength (1850 nm) and the energy emitted (11J). The 60W is irrelevant information as it's not used in Einstein's equation: E=hv=hc/λ.
by Valerie Doan 3I
Fri Oct 16, 2020 10:53 pm
Forum: Bohr Frequency Condition, H-Atom , Atomic Spectroscopy
Topic: Rydberg Equation
Replies: 7
Views: 44

Re: Rydberg Equation

I'm a little bit confused on this, because in the lecture Professor Lavelle said it was more useful to us to understand the concepts if we used the Bohr frequency condition equation (freq = delta E / h) and Esubn = - hr/n^2 rather than the equation. However, I think I saw in the discussion section ...
by Valerie Doan 3I
Wed Oct 14, 2020 10:09 pm
Forum: Properties of Light
Topic: Amplitude and Energy
Replies: 6
Views: 32

Re: Amplitude and Energy

Amplitude is synonymous with intensity. It's important to note that intensity is proportional to the number of photons. Although increasing intensity leads to an increase in the # of photons, it will not lead to an increase in ENERGY per photon. The energy per photon will not match the energy to rem...
by Valerie Doan 3I
Wed Oct 14, 2020 9:54 pm
Forum: Properties of Electrons
Topic: Atomic Spectra and Exciting Electrons
Replies: 4
Views: 48

Re: Atomic Spectra and Exciting Electrons

I agree with Brian, Mirren, and Isabel. The energy of the incoming light must match the energy difference between the two energy levels in order for the light to be absorbed. You might be confusing the atomic spectra and the photoelectric effect. In the photoelectric effect, the incoming light with ...
by Valerie Doan 3I
Fri Oct 09, 2020 12:08 am
Forum: Empirical & Molecular Formulas
Topic: L.39 Textbook question
Replies: 3
Views: 54

L.39 Textbook question

Could someone help me with L.39 from the textbook hw? I keep getting the wrong answer but I don't know why. A 1.50-g sample of metallic tin was placed in a 26.45-g crucible and heated until all the tin had reacted with the oxygen in air to form an oxide. The crucible and product together were found ...
by Valerie Doan 3I
Fri Oct 09, 2020 12:02 am
Forum: Balancing Chemical Reactions
Topic: Naming compounds
Replies: 21
Views: 204

Re: Naming compounds

I would recommend learning how to name simple inorganic compounds, which includes acids and bases. The nomenclature of some chemical compounds do get complicated, but I think it's best that we know how to name the simpler and most frequently used ones like H2SO4 (sulfuric acid).
by Valerie Doan 3I
Thu Oct 08, 2020 11:51 pm
Forum: Molarity, Solutions, Dilutions
Topic: Fundamental G.27
Replies: 4
Views: 81

Re: Fundamental G.27

Thanks for all the helpful solutions! I am still a bit confused on how the 37.5% concentration is applied in the problem. How does the concentration of the solute (37.5%) impact the mass that you would calculate from the number of moles(~271 g)? Are you trying to find 37.5% of the 271 g? Or is the ...
by Valerie Doan 3I
Wed Oct 07, 2020 6:02 pm
Forum: Limiting Reactant Calculations
Topic: Percentage Yield with Limiting Reactant Calc
Replies: 4
Views: 48

Percentage Yield with Limiting Reactant Calc

Hello, my TA gave us this problem during our discussion and I still don't understand parts c and d. I got a and b already. If someone can help, that would be great! a) C2H5OH burns in O2 to form CO2 and H2O. Write a balanced equation for the reaction. b) Determine the limiting reagent (L.R.) when 14...
by Valerie Doan 3I
Wed Oct 07, 2020 5:52 pm
Forum: Molarity, Solutions, Dilutions
Topic: Fundamental G.27
Replies: 4
Views: 81

Re: Fundamental G.27

I didn't realize that someone had already post the solution minutes before me, but here is a more step-by-step version! The density 1.205 g/cm3 is the same as 1.205 g/mL since 1 cm3 = 1 mL. After that, I basically set up conversion factors to cancel out known units to find the volume of the solution...
by Valerie Doan 3I
Wed Oct 07, 2020 4:58 pm
Forum: General Science Questions
Topic: Nomenclature
Replies: 7
Views: 98

Re: Nomenclature

Hello Jaden, It is important to learn how to name compounds as there will be problems on quizzes that will not provide us will chemical formulas. Yes, many compounds do get very complicated, but I would recommend reviewing how to name simple inorganic molecular compounds including acids and bases. O...

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