Search found 113 matches

by Rachel Yu 1G
Mon Mar 09, 2020 5:52 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: 7.11 part b
Replies: 2
Views: 26

Re: 7.11 part b

From part A you know what the rate-determining step. This is the step that is the slowest, meaning it has the largest activation energy needed to go through the reaction. Between the second reactants and second products, there will be the biggest bump to account for it being the slow step. I believe...
by Rachel Yu 1G
Mon Mar 09, 2020 5:47 pm
Forum: Second Order Reactions
Topic: 7.21 part H
Replies: 2
Views: 67

7.21 part H

Which of the following plots will be linear?
Part H. half-life against [A] for a reaction that is second order in A.

The answer is that the plot is not linear but I'm not quite understanding why. Is it because you have to account for [A]^2? Can someone explain? Thanks!
by Rachel Yu 1G
Mon Mar 09, 2020 2:40 pm
Forum: General Rate Laws
Topic: Textbook question 7A.17
Replies: 3
Views: 63

Re: Textbook question 7A.17

I actually got 2.85 x 10^12 mol/Ls for the rate constant. The only difference is that in the problem, the initial concentration and initial rate are given in mmol/Ls rather than mol/Ls. I think you can get the right answer for part D because the units match up (mmol for both k and concentrations).
by Rachel Yu 1G
Mon Mar 09, 2020 2:23 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: calculating delta H for an expansion
Replies: 3
Views: 99

Re: calculating delta H for an expansion

You can find the enthalpy by using the standard enthalpies of formation in the back of the textbook. Use equation deltaH = sum of deltaH products - sum of deltaH reactants to find the delta H value.
by Rachel Yu 1G
Mon Mar 09, 2020 12:35 pm
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: Concentration Cells
Replies: 3
Views: 27

Re: Concentration Cells

One equation that is commonly used in concentration cells is the Nernst equation: Ecell = Eºcell - (RT/nF) lnQ. The differing concentrations can be plugged into Q to find Ecell or Eºcell. It is also important to note that in concentration cells the reactants is the cell with the higher concentration...
by Rachel Yu 1G
Wed Mar 04, 2020 1:20 pm
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: calculate largest E cell
Replies: 1
Views: 59

Re: calculate largest E cell

To find the largest possible E°cell you would want the strongest reduction half-reaction and strongest oxidation half-reaction. The strongest reduction half-reaction will have the largest E°cell potential while the strongest oxidation reaction will have the smallest E°cell potential since a weaker r...
by Rachel Yu 1G
Wed Mar 04, 2020 1:13 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: 6L 5 part d)
Replies: 1
Views: 34

Re: 6L 5 part d)

I used Au+ as the reactant for both half-reactions.
by Rachel Yu 1G
Wed Mar 04, 2020 1:11 pm
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: Writing reaction equations for concentration cells
Replies: 3
Views: 40

Re: Writing reaction equations for concentration cells

In a concentration cell, the reactions are the same and will cancel out. I believe there would not be an overall reaction.
by Rachel Yu 1G
Mon Mar 02, 2020 8:39 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Cell Diagrams and Metal Solids
Replies: 2
Views: 27

Cell Diagrams and Metal Solids

For cell diagrams, I know that there must be a solid metal (whether it's from the redox reaction or it's Pt(s)). Would alkaline metals also count as a solid metal for cell diagrams or would Pt(s) be necessary?
by Rachel Yu 1G
Mon Mar 02, 2020 6:26 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: 6.45
Replies: 1
Views: 34

6.45

Volta discovered that when he used different metals in his “pile,” some combinations had a stronger effect than others. From that information he constructed an electrochemical series. How would Volta have ordered the following metals, if he put the most strongly reducing metal first: Fe, Ag, Au, Zn,...
by Rachel Yu 1G
Sun Mar 01, 2020 9:52 pm
Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
Topic: n value
Replies: 4
Views: 80

n value

Since n = number of electrons exchanged in the reaction, does this value change for the Nernst equation if the reactions were halved or doubled? I was just a bit confused since cell potential is an intensive property.
by Rachel Yu 1G
Sun Mar 01, 2020 3:23 pm
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: 6N. 3b)
Replies: 3
Views: 63

Re: 6N. 3b)

If the solution manual is using the formula Ecathode - Eanode to calculate the cell potential then you leave the E value its reducing form, since subtraction will account for switching the signs of the anode/oxidation reaction. I think in lecture Dr. Lavelle told us to be careful about this because ...
by Rachel Yu 1G
Sun Mar 01, 2020 3:15 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Calculating cell potential
Replies: 2
Views: 28

Re: Calculating cell potential

Yes. You would treat it the same as the reverse reactions for other state functions like delta H.
by Rachel Yu 1G
Thu Feb 27, 2020 8:08 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Cell Diagram Aqueous Solutions Order
Replies: 1
Views: 23

Cell Diagram Aqueous Solutions Order

Let's say we are given a cell diagram |Pt(s)|I-(aq)|I2(s)||Ce4+, Ce3+|Pt(s)

In any cell diagram that has something like Ce4+ and Ce3+ in the same section, does it have to be in that specific order? Would it be accurate if I wrote Ce3+, Ce4+ instead?
by Rachel Yu 1G
Thu Feb 27, 2020 12:35 am
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: 6L5 part D
Replies: 1
Views: 51

6L5 part D

6L5. Write the half-reactions, the balanced equation for the cell reaction, and the cell diagram for each of the following skeletal equations.
(d) Au+(aq) -> Au(s) + Au3+ (aq)

How do we approach finding the half-reaction given this skeletal equation since there are only three molecules involved?
by Rachel Yu 1G
Thu Feb 27, 2020 12:30 am
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: When to use anode/cathode not in the reaction
Replies: 3
Views: 28

When to use anode/cathode not in the reaction

In general, how do we know when the cathode/anode that is not in a redox reaction?

For example, in homework problem 6L5 part b, the redox reaction is 2Ce4+ + 2I- -> I2 + 2Ce3+. However, the cell diagram is Pt(s)|2I-|I2||Ce4+, Ce3+|Pt(s). How do we know that the anode/cathode is made up of Pt(s)?
by Rachel Yu 1G
Thu Feb 20, 2020 12:38 am
Forum: Balancing Redox Reactions
Topic: 6K.5 partA
Replies: 2
Views: 30

Re: 6K.5 partA

I believe since Br- is oxidized we can assume that O3 -> O2 is the reduced half-reaction.
by Rachel Yu 1G
Thu Feb 20, 2020 12:37 am
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Charge Buildup
Replies: 3
Views: 36

Re: Charge Buildup

In a galvanic cell, electrons flow from the anode to the cathode. In the cathode solution, the electrons bond with the cations. However, this leaves cations in the anode that will gradually increase the charge of the anode solution. A "charge buildup" occurs when the anode solution is so p...
by Rachel Yu 1G
Thu Feb 20, 2020 12:29 am
Forum: Balancing Redox Reactions
Topic: 6K.3 Part c
Replies: 1
Views: 31

Re: 6K.3 Part c

For each half-reaction, Cl2 will the reactant. You can compare the oxidation numbers between Cl2(the reactant) and the product to find the reaction that is reduced and oxidized. In this case, Cl2 technically serves as both the oxidizing and reducing reactant. You will get the half-reactions: oxidati...
by Rachel Yu 1G
Tue Feb 18, 2020 3:21 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: delta vs. delta naught
Replies: 3
Views: 53

delta vs. delta naught

What is the difference between delta G, H, and S versus delta G naught, H naught, and S naught?
by Rachel Yu 1G
Mon Feb 17, 2020 8:32 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: delta G vs. delta G naught
Replies: 6
Views: 75

delta G vs. delta G naught

Just to clarify, would the reaction Gibb's free energy be delta G and the standard Gibb's free energy be delta G naught. Conceptually, what is the difference?
by Rachel Yu 1G
Wed Feb 12, 2020 3:01 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: units for heat capacity
Replies: 2
Views: 116

Re: units for heat capacity

Heat capacity is most commonly given in Joules/Celcius. Specific heat capacity is most commonly given in Joules/(Celcius x grams). Unless the problem specifies that the final answer has to given in joules, using kilojoules is ok.
by Rachel Yu 1G
Wed Feb 12, 2020 2:58 pm
Forum: Ideal Gases
Topic: Ideal gases, Cp and Cv
Replies: 2
Views: 101

Re: Ideal gases, Cp and Cv

Cp and Cv are the heat capacities for monatomic ideal gases at constant pressure and constant volume respectively. It would get plugged in when you need heat capacity (i.e. q=nCpdeltaT or q=nCvdeltaT). On the other hand, Cp or Cv does not replace R in PV=nRT.
by Rachel Yu 1G
Wed Feb 12, 2020 2:54 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: 4F. 11
Replies: 3
Views: 44

Re: 4F. 11

Use PdeltaV=nRdeltaT to find the moles. You know every value in this equation except n.
by Rachel Yu 1G
Wed Feb 12, 2020 2:52 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: Isochoric = Irreversible?
Replies: 2
Views: 60

Re: Isochoric = Irreversible?

Isochoric would technically use the equation w=PdeltaV, however since isochoric implies a constant volume, then deltaV = 0 and work = 0. I believe most isochoric reactions are irreversible unless stated otherwise.
by Rachel Yu 1G
Wed Feb 12, 2020 2:46 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: Pizza Rolls #5
Replies: 5
Views: 104

Re: Pizza Rolls #5

For Part A, you have to add up three different delta S values to find the total change of entropy in the system. This includes deltaS for H2 container expansion, deltaS of Krypton gas for container expansion, and deltaS based on temperature change. Since entropy is a state function, this allows us t...
by Rachel Yu 1G
Wed Feb 12, 2020 2:42 pm
Forum: Calculating Work of Expansion
Topic: substitution
Replies: 3
Views: 96

Re: substitution

If you are talking about substituting it for w=nRdeltaT, it really depends on what values are given in the prompt.
by Rachel Yu 1G
Wed Feb 12, 2020 2:40 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: Pizza Rolls 3E
Replies: 4
Views: 73

Re: Pizza Rolls 3E

This is false because in phase changes heat can be removed but the temperature will not change. If you look at a heating curve, you'll see that temperature stays constant during a phase change despite the change in heat. i.e. When ice is in the process of melting into water (phase change), heat can ...
by Rachel Yu 1G
Wed Feb 12, 2020 2:37 pm
Forum: Calculating Work of Expansion
Topic: Pizza Rolls review number 6
Replies: 2
Views: 118

Re: Pizza Rolls review number 6

Because the whole reaction results in the substance back in its initial state. Both internal energy and entropy are state functions meaning that the intermediate steps in this reaction do not matter, only the initial and ending conditions. Since the initial and final states are the same, entropy and...
by Rachel Yu 1G
Mon Feb 10, 2020 10:38 am
Forum: Calculating Standard Reaction Entropies (e.g. , Using Standard Molar Entropies)
Topic: Self-test 4D.4A
Replies: 1
Views: 20

Re: Self-test 4D.4A

Incomplete combustion is when a reaction of an organic molecule and O2 result in products carbon monoxide, carbon, and water. This is different from complete combustion that has products of CO2 and water. This will be important to the problem since you have to apply Hess' Law.
by Rachel Yu 1G
Mon Feb 10, 2020 10:28 am
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: Entropy Equations
Replies: 3
Views: 66

Entropy Equations

When do we use ΔS=qrev/T versus ΔS=nRln(V2/V1) or ΔS=nRln(P1/P2)? In the lecture these equations were derived from an isothermal reversible expansion so does that mean it can only be used for those types of reactions? Also just to clarify, which entropy equations are used for irreversible reactions?...
by Rachel Yu 1G
Mon Feb 10, 2020 10:24 am
Forum: Thermodynamic Definitions (isochoric/isometric, isothermal, isobaric)
Topic: Reversible and Isothermal
Replies: 4
Views: 61

Reversible and Isothermal

I am pretty sure isothermal reactions are not always reversible. However, can we assume that reversible reactions are always isothermal? Thanks!
by Rachel Yu 1G
Mon Feb 10, 2020 10:20 am
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Is heat capacity/specific heat capacity a state function?
Replies: 2
Views: 29

Is heat capacity/specific heat capacity a state function?

I understand that heat capacity is an extensive property whereas specific heat capacity is an intensive property. But I'm not sure if this relates to heat capacity/specific heat capacity being a state function or not. Thanks!
by Rachel Yu 1G
Mon Feb 10, 2020 10:17 am
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: Spontaneity and Entropy
Replies: 3
Views: 40

Spontaneity and Entropy

What is the relationship between entropy and spontaneous reactions? Does it always depend on the Gibbs free energy equation?
by Rachel Yu 1G
Thu Feb 06, 2020 8:41 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: Boltzmann Constant
Replies: 2
Views: 22

Boltzmann Constant

I know the numerical value and units for the Boltzmann constant, but what does it conceptually represent/why is it included in the equation S = kb ln(W)? Thanks!
by Rachel Yu 1G
Thu Feb 06, 2020 8:37 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: reversible vs irreversible work
Replies: 4
Views: 47

Re: reversible vs irreversible work

A system is reversible if the reactants can form the products AND the products can form the reactants. I think usually it will be given whether in the prompt if a reaction is reversible or not. However, there are some cases where you know if the reaction was reversible. An example of a reversible re...
by Rachel Yu 1G
Thu Feb 06, 2020 8:31 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: Homework Problem 4F.9
Replies: 3
Views: 41

Re: Homework Problem 4F.9

The equation is similar to the volume version. You can use the equation ΔS = nRln(P1/P2) to find entropy change with pressure changes.
by Rachel Yu 1G
Thu Feb 06, 2020 8:28 pm
Forum: Calculating Work of Expansion
Topic: Isothermal
Replies: 17
Views: 164

Re: Isothermal

The expansion of a gas is isothermal when the volume of a system changes with a constant temperature. It is best to use equations where volume and pressure change rather than temperature change.
by Rachel Yu 1G
Thu Feb 06, 2020 8:24 pm
Forum: Calculating Work of Expansion
Topic: Constant Pressure
Replies: 3
Views: 30

Re: Constant Pressure

Do you mean no expansion work done when the volume is constant? Since w= -PdeltaV, no change in volume makes deltaV (and therefore w) equal to 0.
by Rachel Yu 1G
Wed Jan 29, 2020 1:07 pm
Forum: Calculating Work of Expansion
Topic: Systems of Equilibrium Practice
Replies: 2
Views: 44

Systems of Equilibrium Practice

Are there any problems in the homework that uses the equation for work in a system of equilibrium (the integral equation that Dr. Lavelle went over in the lecture today)? Thanks!
by Rachel Yu 1G
Wed Jan 29, 2020 12:59 pm
Forum: Calculating Work of Expansion
Topic: Irreversible vs. Reversible Reactions
Replies: 6
Views: 63

Irreversible vs. Reversible Reactions

What is the difference between reversible and irreversible reactions besides that different equations are used to solve for w?
by Rachel Yu 1G
Wed Jan 29, 2020 12:45 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Why can't qv equal delta H?
Replies: 3
Views: 60

Re: Why can't qv equal delta H?

qv actually equals delta U. Since deltaU = q + work or deltaU = q - PdeltaV. Since qv means that there is a constant volume, then deltaV = 0 and work = 0, leaving deltaU = qv. On the other hand, qp=delta H because enthalpy (H) is defined as the amount of heat released/absorbed at a constant pressure...
by Rachel Yu 1G
Wed Jan 29, 2020 12:39 pm
Forum: Calculating Work of Expansion
Topic: How does compression/expansion change the energy in a system?
Replies: 2
Views: 34

Re: How does compression/expansion change the energy in a system?

Compression is when work is done to a system, like a piston pushing down on the system. Expansion decreases the energy of a system because it takes work (therefore energy) from the system to push the piston against the pressure of the surroundings.
by Rachel Yu 1G
Wed Jan 29, 2020 12:31 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: Work
Replies: 6
Views: 69

Work

When is work positive or negative and why?
by Rachel Yu 1G
Mon Jan 20, 2020 10:19 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Percent Ionization
Replies: 4
Views: 30

Percent Ionization

HA + H2O <--> A- + H3O+ Is the equation for % ionization %=[A-]/[HA] x 100% or % = [H3O+]/[HA]? Most of the time I found that [A-] and [H3O+] tend to have the same concentration because they have the same stoichiometric coefficients. However, if there is a reaction where this isn't the case, which c...
by Rachel Yu 1G
Mon Jan 20, 2020 10:13 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Ignoring the -X
Replies: 1
Views: 34

Re: Ignoring the -X

What I heard from my TA is that if the K value is < 10^-3 we can ASSUME that approximation is allowed. However, we can ACCEPT the approximation when the (x/[initial]) is less than or equal to 5%. You will definitely be allowed to approximate on the test.
by Rachel Yu 1G
Mon Jan 20, 2020 10:09 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Buffer Practice Problems
Replies: 1
Views: 54

Re: Buffer Practice Problems

I think 6D17 is an example where they ask you to calculate the pH of salts in water. Part A asks for the pH of 0.63 M NaCH2CO2 and Part B asks for 0.65 M KCN. Dr. Lavelle said everything we covered up to Friday will be on the test and buffer problems were the last thing covered so I think it is some...
by Rachel Yu 1G
Mon Jan 20, 2020 10:03 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Kw change
Replies: 1
Views: 22

Kw change

When and why does Kw stay constant even with different substances involved? In what conditions does the Kw value change?
by Rachel Yu 1G
Mon Jan 20, 2020 10:01 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: 6E3
Replies: 1
Views: 33

6E3

Calculate the pH of each of the following solutions of diprotic acids at 25C, ignoring second deprotonations only when the approximation is justified.

Can someone clarify what does it mean to ignore the second deprotonations and why can we ignore it when the approximation is justified?
by Rachel Yu 1G
Mon Jan 20, 2020 9:56 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Homework 6c.1
Replies: 1
Views: 31

Re: Homework 6c.1

(a) This means to write the reaction for how the proton on an acid would transfer to form hydronium in the products. (HA + H2O <--> H3O+ A-). Because the problem says in correspondence to Ka, we know they are referring to the acid rather than base reaction. (b) This means to write out the equation f...
by Rachel Yu 1G
Mon Jan 13, 2020 3:14 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Autoprotolysis
Replies: 6
Views: 32

Re: Autoprotolysis

Yes, autoprotolysis occurs in any molecule that can make proton transfers amongst itself.
by Rachel Yu 1G
Mon Jan 13, 2020 3:11 pm
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: 5J.9
Replies: 3
Views: 21

Re: 5J.9

Remember in lecture Dr. Lavelle said that increasing/decreasing pressure changes the concentration IF pressure is changed by volume. I think in this problem we assume that pressure is changed by volume. This means that an increase in the partial pressure of NO results in an increase in the concentra...
by Rachel Yu 1G
Mon Jan 13, 2020 3:06 pm
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: 5J.1
Replies: 3
Views: 29

Re: 5J.1

This is because if the concentration of CO is increased, the reaction will return to equilibrium concentrations by becoming more product favored, increasing the concentration of H2.
by Rachel Yu 1G
Mon Jan 13, 2020 2:44 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Textbook question 5.35
Replies: 2
Views: 32

Re: Textbook question 5.35

For part a you can find the balanced equation by looking at the graph. Substance A decreases from 28 P/kPa to 18 making a difference of 10. Substance B increases from 0 to 5 while Substance C increases from 0 to 10. This means that 10 P/kPa of A was lost -> 10 P/kPa of C and 5 P/kPa was created. If ...
by Rachel Yu 1G
Mon Jan 13, 2020 2:25 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Kp and Kc
Replies: 4
Views: 37

Kp and Kc

When do we use Kp vs Kc? I understand that Kp is for pressure and Kc is for concentration but for gases do we use Kp or Kc? Also, just to clarify, do we use PV=nRT to convert between equilibrium concentrations of Kp and Kc?
by Rachel Yu 1G
Wed Jan 08, 2020 2:02 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Module: Chemical Equilibrium Part 3
Replies: 2
Views: 29

Re: Module: Chemical Equilibrium Part 3

You can simplify the equations when K < 10^-4. This is because a small Kc value means not much product is formed and that the "x" value is small and negligible when trying to approximate equilibrium concentrations.
by Rachel Yu 1G
Wed Jan 08, 2020 1:56 pm
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: Le Chatelier's Principle
Replies: 3
Views: 49

Re: Le Chatelier's Principle

Le Chatelier's Principle is the idea that "chemical reactions adjust to minimize the effect of any changes". Some effects that can cause changes includes adding/removing a substance of the reaction, changing pressure, and changing the temperature. Le Chatelier's Principle shows that when t...
by Rachel Yu 1G
Wed Jan 08, 2020 1:52 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Chem Equilibrium Part 2 Post-Assessment, #30
Replies: 1
Views: 24

Re: Chem Equilibrium Part 2 Post-Assessment, #30

Pure liquids and solids are not included in the K expression so you don't have to find the molarity for C(s). Try finding the K value without C(s) and you should get the right answer.
by Rachel Yu 1G
Wed Jan 08, 2020 1:45 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Chem Equilibrium Part 2 Post-Assessment, #29
Replies: 2
Views: 31

Re: Chem Equilibrium Part 2 Post-Assessment, #29

First, an ICE table with 2BrCl, Br2, and Cl2. With the given information, you can fill out the "Initial" section of 2BrCl. Since you known 18.3% of BrCl remains at equilibrium, you can find the equilibrium concentration of BrCl to be 1.84 x 10-4 M x 0.183. Since now we know the Initial and...
by Rachel Yu 1G
Wed Jan 08, 2020 1:38 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Small K value and Large K value
Replies: 10
Views: 107

Re: Small K value and Large K value

K >10^3 means that the reaction strongly favors the formation of products.
K < 10^-3 means that the reaction strongly favors the formation of reactants
10^-3 < K < 10^3 means that the reaction is not reactant or product favored.
by Rachel Yu 1G
Sat Dec 07, 2019 6:48 pm
Forum: Calculating pH or pOH for Strong & Weak Acids & Bases
Topic: pH sig figs
Replies: 11
Views: 126

Re: pH sig figs

Yes, the sig fig is equal to the # of numbers after the decimal for pH.
by Rachel Yu 1G
Mon Dec 02, 2019 12:50 pm
Forum: Amphoteric Compounds
Topic: 6A17
Replies: 2
Views: 39

6A17

Decide whether oxides are acidic, basic or amphoteric
a. BaO
b. SO2
c. AsO3
d. Bi2O3

Can someone explain how to determine the property of these molecules?
by Rachel Yu 1G
Mon Dec 02, 2019 12:45 pm
Forum: Calculating pH or pOH for Strong & Weak Acids & Bases
Topic: 6D11 part c and d
Replies: 1
Views: 25

6D11 part c and d

6D11 asks to decide if salts are equal, greater, or less than pH 7.

c. KF
d. KBr

Can someone explain why KF has a pH of more than 7 while KBr is neutral?
by Rachel Yu 1G
Mon Dec 02, 2019 12:41 pm
Forum: Naming
Topic: 9C 1 part D
Replies: 2
Views: 50

Re: 9C 1 part D

If you draw out the Lewis structure, you can see that the formal charges on oxygen result in a 2- charge. In the context of the question, there is a table in the book listing charges of various molecules like SO4 2- or NH4+. I think it is something we need to memorize.
by Rachel Yu 1G
Mon Dec 02, 2019 12:25 pm
Forum: Bronsted Acids & Bases
Topic: 6.5
Replies: 1
Views: 50

Re: 6.5

SO3 is the Lewis acid while H2O2 is the Lewis base. In this question, think of H202 as 2 OH, where one has a lone pair. When forming H2SO5, SO3 breaks one of its double bonds with oxygen and finds to an OH pair with lone pairs. Therefore, SO3 is accepting the OH lone pairs and serves as the Lewis ac...
by Rachel Yu 1G
Mon Dec 02, 2019 12:15 pm
Forum: Conjugate Acids & Bases
Topic: Self-test 6A.1B
Replies: 2
Views: 38

Re: Self-test 6A.1B

a. H3O
b. NH2
by Rachel Yu 1G
Tue Nov 26, 2019 2:26 pm
Forum: Bronsted Acids & Bases
Topic: J.7
Replies: 8
Views: 109

Re: J.7

Neutralizations are reactions where acids and base react to form water and another compound. Most likely, the H+ and OH- of the reactants will form H2O and the other atoms will form the substance asked for in each part.
by Rachel Yu 1G
Tue Nov 26, 2019 2:18 pm
Forum: Shape, Structure, Coordination Number, Ligands
Topic: Oxidation Number vs. Coordination Number
Replies: 8
Views: 139

Oxidation Number vs. Coordination Number

What is the difference between oxidation numbers and coordination numbers?
by Rachel Yu 1G
Tue Nov 26, 2019 2:13 pm
Forum: Naming
Topic: 9C7
Replies: 2
Views: 49

Re: 9C7

Chelates are ligands that can bind to the same metal center atoms at two or more points. B is the only isomer that can for chelating complexes because the two amino groups are close enough to bind to the same metal center atom. In a and c, the amino groups can bind to two different metal centers, bu...
by Rachel Yu 1G
Tue Nov 26, 2019 2:05 pm
Forum: Shape, Structure, Coordination Number, Ligands
Topic: HW Question 9C.5
Replies: 4
Views: 42

Re: HW Question 9C.5

I would suggest drawing out the Lewis structures first because at least for me it helped visual where the lone pairs on the ligand are. a. tridentate because there are three nitrogens with lone pairs, meaning there are three spots that can bind to the center metal. b. bidentate, there are two oxygen...
by Rachel Yu 1G
Tue Nov 26, 2019 1:43 pm
Forum: Shape, Structure, Coordination Number, Ligands
Topic: 9C.9
Replies: 2
Views: 38

9C.9

9C.9. With the help of Table 9C.1 determine the coordination number of the metal ion in each of the following complexes.

a. [NiCl4]2-
b. [Ag(NH3)2]+
c. [PtCl(en)2]2+
d. [Cr(edta)]-

Can someone explain how to get the right coordination numbers for part c and d?
by Rachel Yu 1G
Mon Nov 18, 2019 12:13 pm
Forum: Bond Lengths & Energies
Topic: Curve
Replies: 4
Views: 184

Re: Curve

Dr. Lavelle adjusts the total grade in the class at the end of the quarter. I'm not sure how much but it depends on what the class average is.
by Rachel Yu 1G
Mon Nov 18, 2019 12:02 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: VSEPR, Molecular Geometry, and Molecular Shape
Replies: 4
Views: 85

VSEPR, Molecular Geometry, and Molecular Shape

What is the difference between VSEPR, molecular geometry, and molecular shape?
by Rachel Yu 1G
Mon Nov 18, 2019 11:57 am
Forum: Resonance Structures
Topic: Bond length
Replies: 5
Views: 172

Re: Bond length

There are all the same! The bond length for a resonance structure is the average of all the possible resonance structures.
by Rachel Yu 1G
Mon Nov 18, 2019 11:52 am
Forum: Hybridization
Topic: Hybridization
Replies: 3
Views: 32

Re: Hybridization

There can only be three 2sp2 orbitals because there are three electron density regions for each C atom. However, there are four valence electrons to account for in the C atom so one valence electron will be in the 2p orbital.
by Rachel Yu 1G
Mon Nov 18, 2019 11:49 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: 3F.19
Replies: 2
Views: 35

Re: 3F.19

For part B, vapor pressure increases with weaker intermolecular forces. Diethyl ether has weaker intermolecular forces than water because it has dipole-dipole interactions while water has hydrogen bonding, Also, diethyl ether is a larger molecule and is, therefore, more polarizable and can form more...
by Rachel Yu 1G
Mon Nov 11, 2019 2:22 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: H2O and Ionic Compounds
Replies: 3
Views: 38

Re: H2O and Ionic Compounds

The large electronegativity difference between hydrogen and oxygen make water a polar molecule, resulting in partial positive and negative charges on the hydrogen and oxygen respectively. These partial charges bond with cations and anions, splitting ionic compounds. Other known solvents are organic ...
by Rachel Yu 1G
Mon Nov 11, 2019 2:08 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: 3F.15
Replies: 3
Views: 40

3F.15

Explain the difference between boiling points of AsF3 (63 C) and AsF5 (-53 C) The Lewis structure for AsF3 has three As-F bonds and a lone pair whereas AsF5 had five As-F bonds. Is AsF3 a polar molecule because the As-F bonds create an unequal electron distribution with the presence of the lone pair...
by Rachel Yu 1G
Mon Nov 11, 2019 1:59 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: 2E.11
Replies: 1
Views: 24

Re: 2E.11

Noble gases like Xe have very low ionization energy/high polarizability so it can be ionized by some of the most electronegative atoms (like oxygen). Xe also has empty d-block and I think this allows these bonds to exist.
by Rachel Yu 1G
Mon Nov 11, 2019 1:57 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: shape of molecule/intermolecular forces
Replies: 3
Views: 37

Re: shape of molecule/intermolecular forces

Part of the molecules in parentheses aren't part of the main carbon chain. With this information, you can tell that pentane has a longer, flatter molecular shape compared to 2,2-dimethylpropane, which doesn't form a carbon chain, but rather four C-C bonds around the main carbon atom.
by Rachel Yu 1G
Mon Nov 11, 2019 1:51 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: 3F5C
Replies: 3
Views: 85

3F5C

The question asks if CHI3 or CHF3 has a higher normal melting point. The solution manual says the answer is CHI3 because is has greater London dispersion forces but I thought CHF3 was polar/had dipole interactions. Why does CHI3 have stronger intermolecular interactions?
by Rachel Yu 1G
Sun Nov 10, 2019 9:57 pm
Forum: Electronegativity
Topic: Atom size
Replies: 16
Views: 648

Re: Atom size

I believe it's the other way around, in which atom size affects electronegativity. Atom size decreases across a period because the atomic number of an atom increases, meaning the positive charge of the nucleus pulls in electrons more strongly, leading to a stronger electronegativity. Overall, smalle...
by Rachel Yu 1G
Sun Nov 10, 2019 9:55 pm
Forum: Dipole Moments
Topic: Dipole moments
Replies: 3
Views: 40

Re: Dipole moments

Dipole moments is the measure of polarity between two atoms through a chemical bond. Polarity is measured through the difference of electronegativities
by Rachel Yu 1G
Mon Nov 04, 2019 7:46 pm
Forum: Octet Exceptions
Topic: noble gas bonding
Replies: 3
Views: 53

Re: noble gas bonding

Noble gases like Xe have very low ionization energy so it can be ionized by the most electronegative atoms (fluorine). Xe also has empty d-block and I think this allows these bonds to exist, though it is rare.
by Rachel Yu 1G
Mon Nov 04, 2019 7:42 pm
Forum: Electron Configurations for Multi-Electron Atoms
Topic: Atoms after f-block
Replies: 2
Views: 66

Re: Atoms after f-block

No, Lavelle said in lecture that we wouldn't need to know electron configuration for elements after the fourth period/first d block. He updated the homework to omit part E also.
by Rachel Yu 1G
Mon Nov 04, 2019 7:40 pm
Forum: Electron Configurations for Multi-Electron Atoms
Topic: Electrostatic Potential Energy
Replies: 1
Views: 51

Electrostatic Potential Energy

What does the equation for electrostatic potential energy we went over in lecture represent?
by Rachel Yu 1G
Mon Nov 04, 2019 5:44 pm
Forum: Dipole Moments
Topic: Interactions between Ions and Molecules
Replies: 5
Views: 61

Re: Interactions between Ions and Molecules

I think it represents the energy that is released if the intermolecular force is broken. The value is negative because energy is being released rather than stored up as potential energy. The largest negative value is in the ion-ion interaction because a cation and anion will have a large attraction ...
by Rachel Yu 1G
Mon Nov 04, 2019 11:12 am
Forum: Electron Configurations for Multi-Electron Atoms
Topic: Electron Configuration vs. Ground-state Electron Configuration
Replies: 2
Views: 71

Electron Configuration vs. Ground-state Electron Configuration

Is there a difference between electron configuration and ground-state electron configuration? I thought ground-state referred to neutral atoms but the past-exam question in lecture today asked for the ground-state e- configuration of ions.
by Rachel Yu 1G
Mon Oct 28, 2019 9:41 pm
Forum: Heisenberg Indeterminacy (Uncertainty) Equation
Topic: Example 1B.5 in textbook
Replies: 1
Views: 50

Re: Example 1B.5 in textbook

The two comes from the given equation ΔpΔx = 1/2h which is converted into Δx = h/2mΔv. The textbook then plugs in the given values to the latter equation, which is where the 2 comes from. While the mass (m) and uncertainty in speed (Δv) values are converted within the equation, the 2 value remains t...
by Rachel Yu 1G
Mon Oct 28, 2019 9:31 pm
Forum: Ionic & Covalent Bonds
Topic: Homework 2A23 Help
Replies: 2
Views: 45

Re: Homework 2A23 Help

Indium(III) Sulfide results from indium and sulfur ions, which are In3+ and S2-. However, you want the charges to equal 0 to satisfy the octet rule. By having 2 In3+ and 3 S2-, the 6+ and 6- charge results in a neutral charge, giving us In2S3 as the chemical formula.
by Rachel Yu 1G
Mon Oct 28, 2019 9:27 pm
Forum: Ionic & Covalent Bonds
Topic: 2A23 Part E
Replies: 4
Views: 56

2A23 Part E

2A23 asks for the chemical formula of bismuth (III) fluoride which ends up being BiF3, an ionic bond between Bi 3+ and 3F-. Why does Bismuth (III) have a charge of 3+ when it is a Group 5 element? I though Group 5 ions would have a charge of 3-.
by Rachel Yu 1G
Mon Oct 28, 2019 3:12 pm
Forum: Ionic & Covalent Bonds
Topic: 2A.1
Replies: 2
Views: 39

Re: 2A.1

Valence electrons refer to the electron on the outer n shell. So for part A (Sb), the outer shell is the fifth shell, consisting of orbitals s and p. The s orbital has 2 valence electrons and the p orbital (up to 5p3) has three valence electrons, adding up to five valence electrons for antimony. I u...
by Rachel Yu 1G
Mon Oct 28, 2019 3:04 pm
Forum: Photoelectric Effect
Topic: Problem 1.31a
Replies: 1
Views: 78

Problem 1.31a

1.31) In a suspense film, two secret agents must penetrate a criminal’s stronghold monitored by a lithium photomultiplier cell that is continually bathed in light from a laser. If the beam of light is broken, an alarm sounds. The agents want to use a handled laser to illuminate the cell while they p...
by Rachel Yu 1G
Wed Oct 23, 2019 6:32 pm
Forum: Electron Configurations for Multi-Electron Atoms
Topic: Homework Question 1E.9
Replies: 3
Views: 53

Re: Homework Question 1E.9

Remember that ml values are dependent on l value. ml = -l to +l. Since l=0, the only possible value for ml is 0. This means that the ml value of -1 is not possible.
by Rachel Yu 1G
Wed Oct 23, 2019 6:29 pm
Forum: Electron Configurations for Multi-Electron Atoms
Topic: 1E25 b
Replies: 2
Views: 28

1E25 b

Give the notation for the valence-shell configuration of:
b. Group 15 elements

I get how the answer comes out to be ns^2 np^3 but in the lower periods wouldn't we have to consider the d-block and/or f-block in the notation? Or do we not have to consider it for the problem?
by Rachel Yu 1G
Wed Oct 23, 2019 6:22 pm
Forum: Electron Configurations for Multi-Electron Atoms
Topic: General Terminology for Electron Configuration
Replies: 2
Views: 17

General Terminology for Electron Configuration

I've been having a bit of trouble with some chemistry vocabulary. What's the difference between energy shells, orbitals, and subshells? Or are the terms used interchangeably?
by Rachel Yu 1G
Wed Oct 23, 2019 6:13 pm
Forum: Electron Configurations for Multi-Electron Atoms
Topic: Electron Configuration Exceptions:
Replies: 3
Views: 42

Re: Electron Configuration Exceptions:

d^5 and d^10 are two states where the element is stable because the electrons fill up half the orbital or the full orbital. Atoms want to achieve this state, so d^4 and d^5 use an electron from the s orbital to get to the half/full d orbitals, resulting in s^1 instead of s^2
by Rachel Yu 1G
Wed Oct 23, 2019 6:10 pm
Forum: Lewis Structures
Topic: Number of valence electrons
Replies: 3
Views: 49

Re: Number of valence electrons

There are some instances where an atom can hold more than eight valence electrons, it is called an expanded valence shell/expanded octet. One example of this would be PCL5. I don't think we need to know about this for the basics of Lewis structures though.
by Rachel Yu 1G
Tue Oct 15, 2019 2:55 pm
Forum: Einstein Equation
Topic: kJ/mol
Replies: 4
Views: 106

Re: kJ/mol

The conversion is 1 kJ = 1000 J since kilo is 1000. If that's the conversion you used then you might have made a calculation error elsewhere.
by Rachel Yu 1G
Tue Oct 15, 2019 2:43 pm
Forum: DeBroglie Equation
Topic: 1B.5
Replies: 3
Views: 74

Re: 1B.5

I don't think we would have to memorize the conversion. If we needed it for a test it would either be given or on the formula sheet.

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