Search found 63 matches

by Samantha Hoegl Roy 2C
Sun Feb 17, 2019 5:36 pm
Forum: Calculating Work of Expansion
Topic: 4.7
Replies: 2
Views: 22

Re: 4.7

So can I always assume that if the combustion happens at below 100° Celsius that water will be liquid? And if it is above 100° that water vapor will be released instead?
by Samantha Hoegl Roy 2C
Tue Feb 12, 2019 6:53 pm
Forum: Calculating Work of Expansion
Topic: 4.7
Replies: 2
Views: 22

4.7

how do we know that for the combustion of C6H6(l), H2O will be created in liquid form? Is this always the case?
by Samantha Hoegl Roy 2C
Mon Feb 11, 2019 7:53 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: H and S relationship
Replies: 1
Views: 14

H and S relationship

"how ∆S is related to ∆H for a change at constant temperature and pressure and explain
the relationship"
Is this the proof we did in class where we divided H by -T? If yes can someone quickly explain it
by Samantha Hoegl Roy 2C
Sat Feb 09, 2019 3:07 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: formulas given on midterm
Replies: 4
Views: 26

formulas given on midterm

Does anyone have an idea which formulas will be given to us? I was looking at the formulas that were given to us for the first test, but, if I remember correctly, Dr. Lavelle uses a different formula booklet. Are there any we need to know by heart?
by Samantha Hoegl Roy 2C
Sat Feb 09, 2019 1:41 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: entropy midterm
Replies: 2
Views: 28

entropy midterm

Dr.Lavelle stated that we have to know everything up to entropy. I was wondering which sections of the book he wants us to cover. Is it 4F to 4I?
by Samantha Hoegl Roy 2C
Thu Feb 07, 2019 4:54 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: 4D7
Replies: 2
Views: 11

4D7

OF2 + H20 -> O2 + 2HF
ΔH = - 318kJ

what is the change in internal energy for the reaction of 1.00 mol OF2?
why is -PΔV = -ΔnRT used? isnt the change is ΔU = q + w; where does -ΔnRT come from?
by Samantha Hoegl Roy 2C
Fri Feb 01, 2019 10:35 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: 4A3
Replies: 1
Views: 14

4A3

for 4A3) the equation given in the solution manual is w = - (2.00 atm)(-0.14L)(101.325J/Latm) what does the 101,325 J mean? it's not part of the equation w = -PΔV
by Samantha Hoegl Roy 2C
Fri Feb 01, 2019 10:05 pm
Forum: Phase Changes & Related Calculations
Topic: w = -nRTln(v2/v1)
Replies: 2
Views: 28

w = -nRTln(v2/v1)

what does w = -nRTln(v2/v1) mean? I don't think it was discussed in class, but since it is in the assigned reading we probably have to know it. Can anyone explain the ln(v2/v1) part? thanks!!
by Samantha Hoegl Roy 2C
Fri Feb 01, 2019 4:36 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: 4A11
Replies: 2
Views: 23

4A11

A calorimeter was calibrated with an electric heater, which supplied 22.5 KJ of energy as heat to the calorimeter and increased the temperature from 22.45 to 23.97. what is the heat capacity of the calorimeter? I don't really understand how to tackle this problem; how would you go about it (the step...
by Samantha Hoegl Roy 2C
Sun Jan 27, 2019 12:32 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Accuracy of Enthalpy Calculation
Replies: 3
Views: 15

Re: Accuracy of Enthalpy Calculation

the bond enthalpy of a diatomic molecule is the exact enthalpy needed to break the bond. For other bonds, the bond enthalpy is the average enthalpy of breaking this bond in several different molecules. This makes the number rather incorrect since it is just the average and not the exact enthalpy for...
by Samantha Hoegl Roy 2C
Sun Jan 27, 2019 12:29 pm
Forum: Phase Changes & Related Calculations
Topic: closed vs isolated system
Replies: 3
Views: 19

closed vs isolated system

can someone quickly remind me what the difference is? I have a hard time remembering the difference!
by Samantha Hoegl Roy 2C
Fri Jan 25, 2019 10:31 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: methods
Replies: 2
Views: 19

methods

Do we have to know all 3 methods or can we focus on the one we prefer?
by Samantha Hoegl Roy 2C
Sun Jan 20, 2019 1:34 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: buffer questions on test
Replies: 7
Views: 48

buffer questions on test

On Friday we covered buffer questions, yet, on the acid and bases outline, buffers are never mentioned. Are we supposed to know what to do with buffer questions although it not written on the outline for the test next week?
by Samantha Hoegl Roy 2C
Sun Jan 20, 2019 12:46 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: 6D 19
Replies: 1
Views: 17

6D 19

A sample of CH3NH3CL of mass 15.5g is dissolved in water to make 450ml of solution. what is the pH of the solution?
I was wondering where they found the Ka value because I can't find it in any of the tables.
by Samantha Hoegl Roy 2C
Sat Jan 19, 2019 8:21 pm
Forum: Identifying Acidic & Basic Salts
Topic: cations and anions that can be ignored
Replies: 2
Views: 23

cations and anions that can be ignored

Dr. Lavelle started to list the anions and cations that can be ignored in a solution as they do not affect the pH.
cations: Group 1 and 2 do not affect pH
anions: Cl, Br, I do not affect pH

are there any other elements that do not affect the pH?
by Samantha Hoegl Roy 2C
Sat Jan 19, 2019 8:18 pm
Forum: Acidity & Basicity Constants and The Conjugate Seesaw
Topic: 6B.9 (7th edition)
Replies: 1
Views: 39

Re: 6B.9 (7th edition)

For ii) I just calculated the pOH: -log(1.5) = 0.176
14 - pOH = pH thus the pH is 13.824. to find the H3o+ concentration i did 10^-13.824, which gives you 1.499 x 10^-14
by Samantha Hoegl Roy 2C
Wed Jan 16, 2019 11:50 pm
Forum: Acidity & Basicity Constants and The Conjugate Seesaw
Topic: difficulties recognizing weak acids and bases
Replies: 8
Views: 74

difficulties recognizing weak acids and bases

I still have difficulties figuring out if a substance is a weak acid or base; for example, NH3. Does anyone have any advice and tips to make it easier?
by Samantha Hoegl Roy 2C
Thu Jan 10, 2019 12:42 pm
Forum: Ideal Gases
Topic: alternative forms of the equilibrium constant
Replies: 3
Views: 21

Re: alternative forms of the equilibrium constant

Chem_Mod wrote:Hi,
Could you show where you get this?

page 412 in the 7th edition, topic 5H.3
by Samantha Hoegl Roy 2C
Thu Jan 10, 2019 12:23 pm
Forum: Ideal Gases
Topic: alternative forms of the equilibrium constant
Replies: 3
Views: 21

alternative forms of the equilibrium constant

do we need to know/understand K = (cRT/P)^nr(Kc)? If yes, can someone explain it?
by Samantha Hoegl Roy 2C
Wed Jan 09, 2019 5:39 pm
Forum: Ideal Gases
Topic: units for PV=nRT
Replies: 5
Views: 65

Re: units for PV=nRT

P: I think is bar or atm
V: Liter
n: mole
r: constant
T: kelvin
by Samantha Hoegl Roy 2C
Wed Jan 09, 2019 5:37 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: 5G.9c, d, e
Replies: 2
Views: 20

Re: 5G.9c, d, e

the ratio of [O2]/[O3] is not the same because it is not balanced. It is therefore not K and just represents the concentration of both O2 and O3 present. since both samples have different concentrations, [O2]/[O3] cannot be the same
by Samantha Hoegl Roy 2C
Wed Jan 09, 2019 12:25 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: "lie to the right" vs "shifted to the right"
Replies: 6
Views: 34

Re: "lie to the right" vs "shifted to the right"

Both essentially mean there are more products than reactants, but I'm assuming "lie to the right" refers to when the reaction has not yet reached equilibrium yet, while "equilibrium shifted to the right" has the equation already at equilibrium. that makes sense! But what does it...
by Samantha Hoegl Roy 2C
Wed Jan 09, 2019 11:50 am
Forum: Equilibrium Constants & Calculating Concentrations
Topic: "lie to the right" vs "shifted to the right"
Replies: 6
Views: 34

"lie to the right" vs "shifted to the right"

In the first auto visual focus-topic, some questions ask about the meaning of "Lie to the right" and "shifted to the right": With respect to equilibrium constants, what does it mean when a reaction is said to “lie to the right”? With respect to equilibrium constants, what does it...
by Samantha Hoegl Roy 2C
Thu Dec 06, 2018 10:01 pm
Forum: Calculating the pH of Salt Solutions
Topic: 6D 11 e) and f)
Replies: 2
Views: 71

Re: 6D 11 e) and f)

Chem_Mod wrote:Could you provide more information? What exactly are the reactants?

"Decide whether an aqueous solution of each of the following salts has a pH equal to, greater than, or less than 7. write a chemical equation to justify your answer.
by Samantha Hoegl Roy 2C
Thu Dec 06, 2018 5:30 pm
Forum: Lewis Acids & Bases
Topic: 6.5
Replies: 1
Views: 25

6.5

why is H2O2 a lewis base and SO3 a lewis acid? doesn't SO3 have more lone pairs to donate?
by Samantha Hoegl Roy 2C
Thu Dec 06, 2018 4:56 pm
Forum: Calculating the pH of Salt Solutions
Topic: 6D 11 e) and f)
Replies: 2
Views: 71

6D 11 e) and f)

for e) AlCl3 and f) Cu(NO3)2 how would you know how to write the chemical equation?
by Samantha Hoegl Roy 2C
Tue Dec 04, 2018 10:55 pm
Forum: Calculating the pH of Salt Solutions
Topic: The pH of Solutions of Weak Acids and Bases 12.65
Replies: 5
Views: 65

Re: The pH of Solutions of Weak Acids and Bases 12.65

hi can you clarify why Na, K and Br "do nothing"? What do you mean by that and how did you know<?
by Samantha Hoegl Roy 2C
Tue Dec 04, 2018 10:10 pm
Forum: Calculating pH or pOH for Strong & Weak Acids & Bases
Topic: HW 7th edition 6B.9
Replies: 3
Views: 39

Re: HW 7th edition 6B.9

For part i) why is the OH- concentration 1.5 x 10^-14? I thought the equation for was a concentration of H3o+ multiplied by the concentration of OH- = 10 x 10^-14
thus OH- conc = 10 x 10^-14 / 1.5 but that seems to be wrong
by Samantha Hoegl Roy 2C
Mon Dec 03, 2018 2:19 pm
Forum: Properties & Structures of Inorganic & Organic Acids
Topic: Fundamentals J7
Replies: 5
Views: 92

Re: Fundamentals J7

oh, that makes sense! What about J9) b). no water is produced, so how can I make the equation?
by Samantha Hoegl Roy 2C
Sun Dec 02, 2018 4:50 pm
Forum: Properties & Structures of Inorganic & Organic Acids
Topic: Fundamentals J7
Replies: 5
Views: 92

Fundamentals J7

select an acid and a base for a neutralization reaction that results in the formation of a) potassium bromide b) zinc nitrate
how would you go about answering this question? how do you chose the bases and acids; is the a rule to follow?
by Samantha Hoegl Roy 2C
Sat Dec 01, 2018 12:57 pm
Forum: Shape, Structure, Coordination Number, Ligands
Topic: Coordination number
Replies: 1
Views: 20

Re: Coordination number

coordination number is the number of points at which ligands are attached to the central atom 4 in Ni(CO)4 and 6 in (Fe(CN)6)4- thus, for a polydentate ligand, I would assume you just multiply the number of ligands present with the number of bonds it can form to find the coordination number. For exa...
by Samantha Hoegl Roy 2C
Sat Dec 01, 2018 12:46 pm
Forum: Naming
Topic: For the Final
Replies: 1
Views: 25

For the Final

Do we now have to know what all the names stand for? like ammonium nitrate and stuff like that?
by Samantha Hoegl Roy 2C
Sat Nov 24, 2018 6:17 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: Intermolecular energy
Replies: 3
Views: 39

Intermolecular energy

Dr. Lavelle gave us the equation E is proportional to (alpha 1 * alpha2)/ r^6. Can someone explain me this formula again?
by Samantha Hoegl Roy 2C
Sat Nov 24, 2018 3:34 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: 2E 13a)
Replies: 2
Views: 26

2E 13a)

How come I3- is linear? There are three lone pair, will this not make the shape of the molecule angular?
by Samantha Hoegl Roy 2C
Sat Nov 24, 2018 1:25 pm
Forum: Electronegativity
Topic: Arrows showing charge
Replies: 4
Views: 60

Arrows showing charge

In Dr. lavelles class, do we draw the arrows towards the negative charge of a molecule or towards the negative charge? The book says both way exists, so I just want to make sure I use the correct one.
by Samantha Hoegl Roy 2C
Sat Nov 24, 2018 1:01 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Bond length
Replies: 2
Views: 25

Re: Bond length

I think the only calculations we could be asked is to “guess” the bond length in a resonance structure by knowing the double bond and signle bond length. Dr. Lavelle said several times that we would not have to calculate anything with bond length
by Samantha Hoegl Roy 2C
Sun Nov 18, 2018 5:50 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: lone pairs and bond angle
Replies: 6
Views: 53

Re: lone pairs and bond angle

because lone pairs repel the other atoms more as they are more electronegative (2 e- are much more strongly negative than a bond)
by Samantha Hoegl Roy 2C
Sat Nov 17, 2018 12:37 pm
Forum: Sigma & Pi Bonds
Topic: Double bond question
Replies: 1
Views: 45

Double bond question

How come that when there is a double bond, there is one sigma bond and one pi bond? Why are not both pi bonds? Didn’t dr. Lavelle say something about bound atoms no longer being able to rotate?
by Samantha Hoegl Roy 2C
Sat Nov 17, 2018 12:34 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Seesaw Shape
Replies: 2
Views: 25

Re: Seesaw Shape

I am pretty sure the angles are less than 180 and 90 degrees
by Samantha Hoegl Roy 2C
Sun Nov 11, 2018 2:14 pm
Forum: Resonance Structures
Topic: Drawing resonance
Replies: 17
Views: 175

Re: Drawing resonance

if there is resonance, yes. You have to show that you know there are 3 different structures for the same molecule. if you only draw one, one could assume you believe one bond is shorter than the others
by Samantha Hoegl Roy 2C
Sat Nov 10, 2018 8:53 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: how to know which shape it is
Replies: 6
Views: 88

how to know which shape it is

trigonal planar, trigonal pyramidal and p shaped all have three atoms; how do you tell them apart?
by Samantha Hoegl Roy 2C
Sat Nov 10, 2018 8:51 pm
Forum: Bond Lengths & Energies
Topic: 2D 15)
Replies: 3
Views: 52

2D 15)

Which do you predict to have the strongest CX bond, where X is a halogen? a)CF4 b) CCl4 c) CBr4

how would you figure out the solution, I am not sure where to start
by Samantha Hoegl Roy 2C
Fri Nov 02, 2018 8:20 pm
Forum: Resonance Structures
Topic: 2B.19 (7th ed)
Replies: 2
Views: 42

Re: 2B.19 (7th ed)

For CN- you have 4e- + 5e- + 1e- = 10 e-

You can not violate the octate rule with these specific elements. If you give them five bonds, this goes against the octate rule. Thus, the triple bond with the two lone pairs in the only solution that works
by Samantha Hoegl Roy 2C
Wed Oct 31, 2018 6:24 pm
Forum: Resonance Structures
Topic: 1B 13)
Replies: 1
Views: 82

1B 13)

hi guys, I am struggling with this question. Why are there only 4 possible resonances structures? how do you know where to put the double bonds? I had like 6 models
by Samantha Hoegl Roy 2C
Wed Oct 31, 2018 5:56 pm
Forum: Lewis Structures
Topic: 2B 3 c)
Replies: 1
Views: 23

2B 3 c)

In the solution, Br has 10 valence electrons. Is this an exception to the octet rule? I thought it only applied to elements in the third period (P, Cl, S)?
by Samantha Hoegl Roy 2C
Sun Oct 28, 2018 6:20 pm
Forum: Ionic & Covalent Bonds
Topic: elements with low ionization energies
Replies: 3
Views: 31

Re: elements with low ionization energies

if they have low ionization energy it means that it does not take a lot of energy to take out an electron. Thus, it is easier for it to lose an electron, becoming a cation.
by Samantha Hoegl Roy 2C
Sun Oct 28, 2018 6:19 pm
Forum: Trends in The Periodic Table
Topic: Electron affinity trend
Replies: 2
Views: 33

Electron affinity trend

Hi! I am a little bit confused why Helium has the highest electron affinity. And what does the number stand for (He <0)? The trend is also not clear to me as there is no pattern.
by Samantha Hoegl Roy 2C
Sun Oct 28, 2018 6:15 pm
Forum: Electron Configurations for Multi-Electron Atoms
Topic: 1E 25)
Replies: 2
Views: 40

1E 25)

Do we need to know what the alkali metals are and if yes, are there any other specific names for a group of metals I am supposed to know?
by Samantha Hoegl Roy 2C
Sat Oct 20, 2018 10:53 pm
Forum: Bohr Frequency Condition, H-Atom , Atomic Spectroscopy
Topic: Q 42 on post assessment
Replies: 5
Views: 42

Re: Q 42 on post assessment

can you explain it in more detail i still don't understand because i can figure out E(n=4), E of everything, and the wavelengths of E(n=4) and E(everything - n=4)
by Samantha Hoegl Roy 2C
Sat Oct 20, 2018 9:16 pm
Forum: Bohr Frequency Condition, H-Atom , Atomic Spectroscopy
Topic: Q 42 on post assessment
Replies: 5
Views: 42

Q 42 on post assessment

An excited hydrogen atom emits light with a frequency of 1.14 x 1014 Hz to reach the energy level n = 4. In what principle quantum level did the electron begin?

how would you solve this question?
by Samantha Hoegl Roy 2C
Thu Oct 18, 2018 4:08 pm
Forum: Wave Functions and s-, p-, d-, f- Orbitals
Topic: 1D 15
Replies: 2
Views: 26

Re: 1D 15

also magnetic quantum number
by Samantha Hoegl Roy 2C
Thu Oct 18, 2018 4:02 pm
Forum: Wave Functions and s-, p-, d-, f- Orbitals
Topic: 1D 15
Replies: 2
Views: 26

1D 15

what does principal and orbital angular momentum stand for? is n principal momentum and l orbital angular momentum?
by Samantha Hoegl Roy 2C
Wed Oct 17, 2018 3:06 pm
Forum: DeBroglie Equation
Topic: 1B.15
Replies: 4
Views: 44

Re: 1B.15

the mass of an electron is given to you m(e) = 9.1095 x 10^-31 kg
by Samantha Hoegl Roy 2C
Tue Oct 16, 2018 5:08 pm
Forum: Bohr Frequency Condition, H-Atom , Atomic Spectroscopy
Topic: when to use which formula
Replies: 1
Views: 51

when to use which formula

when would you use En = - hR / n^2 or En = h^2n^2/8mL^2?
by Samantha Hoegl Roy 2C
Sun Oct 14, 2018 10:35 pm
Forum: DeBroglie Equation
Topic: 1B.15
Replies: 4
Views: 44

Re: 1B.15

1/2mV^2=hv (because you V (velocity), mass of the electron, and H (which is a constant) then you know the frequency --> c = (v)(wavelength)
by Samantha Hoegl Roy 2C
Sun Oct 14, 2018 10:32 pm
Forum: Properties of Light
Topic: Experiments and Equations
Replies: 3
Views: 22

Re: Experiments and Equations

i don't think we have to know that
by Samantha Hoegl Roy 2C
Sun Oct 14, 2018 10:24 pm
Forum: DeBroglie Equation
Topic: detectability of waves
Replies: 4
Views: 43

detectability of waves

to which size did Professor Lavelle say that the waves are detectable? Was it 10^-18 or 16?
by Samantha Hoegl Roy 2C
Sun Oct 14, 2018 10:22 pm
Forum: Quantum Numbers and The H-Atom
Topic: Hydrogen
Replies: 2
Views: 24

Hydrogen

what are the principal quantum levels of the H-atom? I know they exist and that electrons go from one level to another, but why do these levels exist? and what are they? I am a little confused! :)
by Samantha Hoegl Roy 2C
Sun Oct 07, 2018 3:27 pm
Forum: Empirical & Molecular Formulas
Topic: Steps to calculating Molecular Formulas
Replies: 3
Views: 87

Re: Steps to calculating Molecular Formulas

Our TA said to just go with "your feeling"; like 3.9 is close enough, but 3.8 logically not. I would just always do the step, where you divide the numbers by the smallest one to be sure
by Samantha Hoegl Roy 2C
Sun Oct 07, 2018 3:24 pm
Forum: Limiting Reactant Calculations
Topic: Calculating Molar Mass in Limiting Reactant Problem
Replies: 3
Views: 47

Re: Calculating Molar Mass in Limiting Reactant Problem

can you be more specific? are you talking about the CaC2 + 2H2O --> Ca(OH)2 + C2H2 example? :)
by Samantha Hoegl Roy 2C
Sat Oct 06, 2018 1:26 pm
Forum: Balancing Chemical Reactions
Topic: Combustion Question on Modules
Replies: 3
Views: 37

Re: Combustion Question on Modules

you should probably remember that for combustion of butane (or something else) it's always: x mole of Butane (or methane..) + x mole of O2 --> x mole of CO2 + x mole of H2O

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