## Search found 60 matches

Fri Mar 16, 2018 9:17 pm
Forum: Arrhenius Equation, Activation Energies, Catalysts
Topic: 15.63
Replies: 2
Views: 172

### 15.63

I'm looking at the answer for this question and I understand how to do everything, except for the value '-0.59'
I'm assuming that's the lnA from the Arrhenius Equation, however, how do we calculate that with the values given?
Fri Mar 16, 2018 9:09 pm
Forum: Arrhenius Equation, Activation Energies, Catalysts
Topic: 15.61
Replies: 2
Views: 178

### 15.61

How is the equation listed in the answers derived?
I understand it's from lnk=-Ea/RT with changes in T, but my question is where did lnA go?
Thanks!
Fri Mar 16, 2018 7:31 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Homework 11.111
Replies: 1
Views: 450

### Re: Homework 11.111

you would use the equation dG = - RT lnK for this question rearrange and substitute in the values you have lnK=- -200000/(8.314*298) = 80.7 solve for K K=1.14*10^35 the question says the equilibrium constant of the first step is 10 times greater than that of the second step so you simply divide the ...
Fri Mar 16, 2018 7:25 pm
Forum: Balancing Redox Reactions
Topic: Ranking elements
Replies: 2
Views: 192

### Re: Ranking elements

Ti < Mn < Ag
Al < Pb < Cu
Fri Mar 16, 2018 7:17 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: 14.15.a
Replies: 1
Views: 158

### Re: 14.15.a

Im not sure but maybe it has to do with the states each compound is in. AgBr is a solid while Br- is aqueous. And just to keep things neat the solids (Ag and AgBr) are placed next to each other.
I've seen this done in other examples
Fri Mar 16, 2018 7:06 pm
Forum: Arrhenius Equation, Activation Energies, Catalysts
Topic: A?
Replies: 6
Views: 619

### Re: A?

yes, it is a constant
Wed Mar 07, 2018 9:27 pm
Forum: General Rate Laws
Topic: 15.23 b
Replies: 3
Views: 248

### 15.23 b

Why is the formula used for this question ln[A]0 / [A]t , instead of ln [A]t/[A]0?
Wed Feb 14, 2018 3:12 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Problem 11.111
Replies: 2
Views: 199

### Re: Problem 11.111

use the equation deltaG = -RTlnK
and rearrange
lnK= - 200000/(8.314*298)
= 80.7
K = 1.14*10^35
divide by 10 so K2 = 1.14*10^34
and then use it in the same equation as above
deltaG2 = -8.314*298*ln1.14*10^34
= -194 kJ
Tue Feb 13, 2018 10:20 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: Heat Transfer with no temperature given
Replies: 2
Views: 213

### Re: Heat Transfer with no temperature given

I don't know what the question is exactly?
But maybe if the question also suggests/says the change in internal energy is 0, you could use q=-w
and just substitute the given values into w=-PdeltaV ?
Just a thought
Tue Feb 13, 2018 10:15 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: Trouton's rule
Replies: 1
Views: 149

### Re: Trouton's rule

nope. because none of the questions pertaining to trouton's rule are on the syllabus/homework problem list
Tue Feb 13, 2018 10:12 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Specific Heat capacity
Replies: 1
Views: 416

### Re: Specific Heat capacity

so use q=mCdelta T to calculate the heat produced by the water when the temperature is raised from 22.6 to 34.6 so it would look something like this: 115.43*4.184*(34.6-22.6) = 5795.51 J and then for the metal because Qsys=-Qsurr 245.7*C*(34.6-75.2)= -5795.51 J C=-9975.42/-5795.51 =0.580979 =0.581 J...
Tue Feb 13, 2018 10:05 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: Ex 9.10 pg. 342
Replies: 1
Views: 129

### Re: Ex 9.10 pg. 342

they are the same thing you just have to inverse the sign
Tue Feb 13, 2018 3:59 pm
Forum: Calculating Standard Reaction Entropies (e.g. , Using Standard Molar Entropies)
Topic: why entropy for aqueous ions are negative
Replies: 1
Views: 504

### why entropy for aqueous ions are negative

Will we have to know what the entropy for aqueous ions are mostly negative
(like in question 9.89)?
Tue Feb 13, 2018 1:29 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: 9.53
Replies: 1
Views: 145

### 9.53

I understand how we need to use deltaG = deltaH - TdeltaS for this question, and how we need to use the tables in the textbook to find the values for deltaH and deltaS, however, why is the value of delta S listed in the solutions "97.6J/K/mol" ?
Where does that value come from?
Tue Jan 23, 2018 11:56 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Mean Bond Enthalpy
Replies: 2
Views: 184

### Re: Mean Bond Enthalpy

I think they would give nearly the same result as the average bond enthalpy values are averages of that said bond in a bunch of different molecular structures.
But i'm not 100% sure
Tue Jan 23, 2018 11:46 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: 8.113
Replies: 3
Views: 249

### Re: 8.113

what does the state (gr) mean?
Tue Jan 23, 2018 11:44 pm
Forum: Administrative Questions and Class Announcements
Topic: Equations and constants sheet 14B
Replies: 2
Views: 268

### Re: Equations and constants sheet 14B

yep it's decimeter
where 1 decimeter^3 = 1 Liter
Mon Jan 22, 2018 11:32 pm
Forum: Calculating Standard Reaction Entropies (e.g. , Using Standard Molar Entropies)
Topic: HW 8.99
Replies: 2
Views: 229

### Re: HW 8.99

because we need the amount of mol of product, which would depend on the limiting reagent of the reaction
Mon Jan 22, 2018 10:50 pm
Forum: Phase Changes & Related Calculations
Topic: Heat capacities
Replies: 5
Views: 326

### Re: Heat capacities

if it's calculating temperature change, then the difference will be the same whether it's in kelvin or celcius
Mon Jan 22, 2018 10:45 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Average Kinetic Energy
Replies: 2
Views: 165

### Average Kinetic Energy

Will there be questions involving average kinetic energy (like question 8.103) in the upcoming test?
I don't recall Dr Lavelle going over it in lecture, nor do I see it on his outline 1...
Mon Jan 22, 2018 10:12 pm
Forum: Phase Changes & Related Calculations
Topic: 8.9 torr conversion
Replies: 1
Views: 116

### Re: 8.9 torr conversion

torr is another way to express pressure, but thermodynamics answers are usually always in atm so the conversion from torr to atm is on the formula sheet where 1 atm=760 torr!
and for the 1000ml, it's because work is calculated with liters
Mon Jan 22, 2018 9:55 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: 8.61
Replies: 1
Views: 166

### Re: 8.61

reaction enthalpies may not just be indicating 1 mol of substance so it's only kJ. If it were enthalpy of formation or enthalpy of combustion, then it would be kJ/mol as it's the reaction enthalpy of the formation/combustion of 1 mole of a substance
Sun Jan 21, 2018 11:56 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Question 85
Replies: 1
Views: 134

### Question 85

specifically part b, why is the final step in the answer book shown as the mole (from after calculating it with PV=nRT) being multiplied by 180.6kJ? I would've thought it would be multiplied by 90.3kJ which is reaction enthalpy that produces 1 mole of NO.
Sun Jan 21, 2018 11:49 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: 8.25
Replies: 3
Views: 314

### Re: 8.25

oh yea, I completely forgot about that.
Thanks so much!
Sun Jan 21, 2018 11:48 pm
Forum: Thermodynamic Definitions (isochoric/isometric, isothermal, isobaric)
Topic: Heat and systems
Replies: 3
Views: 264

### Re: Heat and systems

if you have deltaH/Q, you can look at the sign it has -deltaH means that energy is released by the system (exothermic; the system is losing energy, thus the minus sign) and so energy is being transfered from the system to the surroundings. eg combustion reactions +deltaH means that energy is gained ...
Sun Jan 21, 2018 11:44 pm
Forum: Calculating Work of Expansion
Topic: When to use equation [ENDORSED]
Replies: 3
Views: 223

### Re: When to use equation[ENDORSED]

for the first equation, usually the question says "isothermic" (as in the assigned text book questions)
but it's not going to be on this coming test! :)
Sun Jan 21, 2018 11:43 pm
Forum: Thermodynamic Systems (Open, Closed, Isolated)
Topic: System Types
Replies: 7
Views: 405

### Re: System Types

the example Dr lavelle gave in class was just to think of 3 test tubes - Open system: both matter and energy can travel out, which would be an open test tube with no insulation - Closed system: only energy can travel out, not matter, which would be a closed test tube - Isolated system: neither matte...
Sun Jan 21, 2018 10:21 pm
Forum: Calculating Work of Expansion
Topic: Types of Work [ENDORSED]
Replies: 3
Views: 227

### Re: Types of Work[ENDORSED]

Im pretty sure this is the only type of work because a) Dr Lavelle didn't talk about the rest in lecture and b) the practice questions he set aren't about any other types of work (to the extent of my knowledge)
Sun Jan 21, 2018 5:38 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: 8.25
Replies: 3
Views: 314

### 8.25

for question 8.25, I understand everything up until the point where the answer key says Qreaction + Qcalorimeter =0, which then leads to the final answer. Can someone explain why the heat from the reaction + the heat of the calorimeter equals to 0?

Thanks :)
Sun Jan 21, 2018 4:48 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: Standard Enthalpies of Formation
Replies: 3
Views: 211

### Re: Standard Enthalpies of Formation

the two are different but that's how you would do a calculation of the enthalpy of reaction through bond enthalpies
Sat Dec 09, 2017 4:05 pm
Forum: Naming
Topic: Ligand Prefixes: Di- vs. Bis-
Replies: 1
Views: 271

### Re: Ligand Prefixes: Di- vs. Bis-

the most common example would be diethylenetriammine where if it was (dien)2 then it would be didiethylenetriammine, so instead of having "didi-" you switch the first 'di' out and replace it with 'bis' so it's clearer
--> bisdiethylenetriammine
Sat Dec 09, 2017 12:27 am
Forum: Calculating pH or pOH for Strong & Weak Acids & Bases
Topic: Percentage deprotonation
Replies: 2
Views: 259

### Re: Percentage deprotonation

because a representative equation for acid reactions is HA --> H3O+ + A- where Kc=[H3O+][A-]/[HA] if you were to use an ice table to calculate molarities, Kc would become: Kc= x^2 / [HA]-x as both have the same amount of moles and because the concentration of [H3O+] and [A-] are the same, it can be ...
Sat Dec 09, 2017 12:20 am
Forum: Determining Molecular Shape (VSEPR)
Topic: Bond Angles
Replies: 3
Views: 290

### Re: Bond Angles

I think as far as what was taught in class, yes. molecules might have angles of <109.5 if there are lone pairs present (eg in bent/angular shapes) as they have greater repulsion than normal bonds. molecules with angles of >109.5.. I would assume there's only molecules with 120 degrees (as far as wha...
Thu Dec 07, 2017 9:29 pm
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: 11.79
Replies: 1
Views: 187

### Re: 11.79

you add the change in N2 to the original value so now PN2=4.68 and the rest of the initial values are the values they give you.
and from here you just solve for x as you would any other ICE table.
Thu Dec 07, 2017 9:25 pm
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: Reaction shift
Replies: 3
Views: 176

### Re: Reaction shift

the reaction will favor the reactants and thus shift left as K must remain constant
and K=[P]/[R] so if P increases, R will increase to keep K remain the same
Tue Nov 28, 2017 12:11 am
Forum: Naming
Topic: Di, Tri, Tetra vs. Bis, Tris, Tetrakis
Replies: 1
Views: 803

### Re: Di, Tri, Tetra vs. Bis, Tris, Tetrakis

so you would use di, tri, tetra on ligands that don't have said prefixes in their names already, eg dichlorido while if you were to write (dien)2, instead of it being didiethlynetriamine which would be confusing, it's bisdiethylenetriamine, same with (en)2 for example, it would be bisethylenediamine...
Tue Nov 28, 2017 12:08 am
Forum: Naming
Topic: Question 17.31c and d
Replies: 1
Views: 175

### Re: Question 17.31c and d

I think either one is ok, the (OH2) just makes the fact that it is O that's bonded to the metal clearer
Tue Nov 28, 2017 12:07 am
Forum: Ideal Gases
Topic: Partial pressures
Replies: 4
Views: 489

### Re: Partial pressures

use the equation PV=nRT and substitute the values in
Mon Nov 27, 2017 9:54 pm
Forum: Shape, Structure, Coordination Number, Ligands
Topic: Polydentate Ligands(17.33)
Replies: 1
Views: 163

### Re: Polydentate Ligands(17.33)

Mon Nov 27, 2017 9:52 pm
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: Compressing a Reaction Mixture
Replies: 1
Views: 316

### Re: Compressing a Reaction Mixture

adding inert gas doesn't change the concentration of the reactants/products as the moles and the volume of R and P remain constant while increasing the pressure, and thus decreasing the volume does - C=n/V so because the number of moles of the reactants/products remain the same but the volume decrea...
Mon Nov 27, 2017 9:48 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Homework 11.1d
Replies: 1
Views: 142

### Re: Homework 11.1d

change in concentration doesn't affect K, and the only way this is possible is that if the concentration of reactants are increased, the concentration of products will increase as well to keep the P/R ratio the same
Mon Nov 27, 2017 9:45 pm
Forum: Shape, Structure, Coordination Number, Ligands
Topic: Diethylenediamine
Replies: 2
Views: 225

### Re: Diethylenediamine

If you're talking about (en)2, it would be called bisethylenediamine and yes; while diethylenetriamine (dien) would have 3 bonding sites each
Mon Nov 27, 2017 9:44 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Equilibrium constants
Replies: 1
Views: 116

### Re: Equilibrium constants

K can either indicate Kc (equilibrium constant with concentrations) or Kp (equilibrium constant using partial pressure)
Sun Nov 26, 2017 10:24 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: 11.7
Replies: 5
Views: 391

### Re: 11.7

use the method of how you would find the equilibrium constant
K=[X]^2 / [X2]
=[(12/17)*0.1]^2 / [(5/17)*0.1]
=0.17

the 12/17 and 5/17 are the number of molecules that have/ haven't dissociated, as given in the diagrams of the 4 containers
Sun Nov 26, 2017 10:21 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Lone Pairs [ENDORSED]
Replies: 3
Views: 274

### Re: Lone Pairs[ENDORSED]

no
Sun Nov 26, 2017 10:21 pm
Forum: Hybridization
Topic: 4.41
Replies: 4
Views: 751

### Re: 4.41

So first, draw out the Lewis Structure - use valence electrons of each atom to determine the bonding (eg every carbon makes 4 bonds), then once you have the structure drawn out it'll be more straightforward to determine the hybridization - basically the number of electron densities of each carbon, a...
Sun Nov 05, 2017 8:07 pm
Forum: Formal Charge and Oxidation Numbers
Topic: Formal Charge
Replies: 8
Views: 611

### Re: Formal Charge

when the formal charge = 0
Sun Oct 29, 2017 10:14 pm
Forum: Ionic & Covalent Bonds
Topic: Homework 3.5 part c [ENDORSED]
Replies: 3
Views: 353

### Re: Homework 3.5 part c[ENDORSED]

[Ar] 3d10

basically Ga Z=31
but it's Ga3+ so 31-3=28
Thu Oct 26, 2017 9:09 pm
Forum: Trends in The Periodic Table
Topic: Exceptions to Ionization Energy Trend
Replies: 1
Views: 196

### Re: Exceptions to Ionization Energy Trend

Maybe the ones where we're able to work out from the periodic table? Like the electron configuration of nitrogen is 1s2 2s2 2p3 (stable, half filled) while Oxygen has an electron configuration of 1s2 2s2 2p4 (one extra electron from being stably half filled), so taking an electron from the oxygen is...
Thu Oct 26, 2017 9:02 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Periodic Trends
Replies: 2
Views: 127

### Re: Periodic Trends

Ionisation Energy for atoms would be different when they're in the gaseous state than in other states - which is the easiest way to compare the energy required between different atoms as there is very little attraction with other atoms. In liquids/solids, the intermolecular forces will distort the v...
Sun Oct 15, 2017 9:19 pm
Forum: Properties of Light
Topic: Lyman vs Balmer Series
Replies: 4
Views: 279

### Re: Lyman vs Balmer Series

electrons in the Lyman series emit light in the UV region, while electrons in the Balmer series emit light in the visible light region.
So you would look at the wavelength of the light emitted and deduce it from that.

(Im not sure if I answered what you were asking, but yeah)
Sun Oct 15, 2017 9:16 pm
Forum: Properties of Electrons
Topic: Atomic Spectra [ENDORSED]
Replies: 4
Views: 363

### Re: Atomic Spectra[ENDORSED]

I think in the case of ~Atomic Spectra~, it's not so much the attraction of electrons to protons, but instead the absorption and emission of energy.

n=1 is the ground state/ energy level for electrons, which is the furthest "way down" an electron can go after emitting energy.
Sun Oct 15, 2017 9:13 pm
Forum: Properties of Electrons
Topic: Hydrogen series
Replies: 5
Views: 458

### Re: Hydrogen series

there is also a "Brackett series" which is n=4 but i'm 99.9% sure we don't need to know this
Sun Oct 15, 2017 9:11 pm
Forum: Photoelectric Effect
Topic: Photoelectric effect [ENDORSED]
Replies: 4
Views: 328

### Re: Photoelectric effect[ENDORSED]

An experiment showed that if a light beam had high enough frequency it could make a surface eject an electron. The emphasis is on frequency here as the intensity of the light had no effect on the electron, which showed that the light was not acting like a classic wave. --> this boils down to the ide...
Sun Oct 15, 2017 9:00 pm
Forum: Properties of Light
Topic: Planck's Constant
Replies: 10
Views: 675

### Re: Planck's Constant

whenever you need to use an equation with the constant "h" in it.
eg E=hv

good thing is, the value is on the formula sheet so we don't have to memorize it :)
Sun Oct 15, 2017 8:59 pm
Forum: Properties of Light
Topic: Question 1.15
Replies: 2
Views: 327

### Re: Question 1.15

1. convert the wavelength given to m 102.6x10^-9m 2. figure out the frequency by rearranging c=wavelength*frequency v=c/wavelength = 2.998*10^8 / 102.6*10^-9 = 2.922x10^15 3. as the question says "in the ultraviolet spectrum", one can concur that the final energy level is n=1 4. put known ...
Sun Oct 08, 2017 8:25 pm
Forum: Administrative Questions and Class Announcements
Topic: Chapter 1 Test this week [ENDORSED]
Replies: 2
Views: 233

### Chapter 1 Test this week[ENDORSED]

So it's posted on the website that there's going to be a test on Chapter 1 up to 1.5 in the textbook this week during the discussion section you're enrolled in. I'm in discussion 1B on Tuesday mornings so I was just wondering if the test was going to be on this week's discussion section (October 10)...
Tue Oct 03, 2017 10:32 pm
Forum: Limiting Reactant Calculations
Topic: m11
Replies: 7
Views: 659

### Re: m11

my bad i only did half the question, but yes what @Ivy Lu 1C said
Tue Oct 03, 2017 10:30 pm
Forum: Student Social/Study Group
Topic: Fundamental M.25
Replies: 3
Views: 936

### Re: Fundamental M.25

@Hyein Cha 1K

I do it the same way
Tue Oct 03, 2017 10:21 pm
Forum: Limiting Reactant Calculations
Topic: m11
Replies: 7
Views: 659

### Re: m11

I'm assuming this is the white phosphorus to phosphorus oxide question. P4 + 3O2 --> P4O6 masses for both the reactants = 5.77g get the molar mass of the elements from a periodic table and divide the mass with it to get the number of moles of each particle n (P4) = 5.77/(30.97*4) = 0.0466 n (O2) = 5...