Search found 32 matches

by Melissa Per 2J
Sat Mar 17, 2018 2:25 pm
Forum: Phase Changes & Related Calculations
Topic: Test 1, Q7
Replies: 3
Views: 374

Re: Test 1, Q7

Was the answer 18.06 degrees C? Thank you so much!!
by Melissa Per 2J
Sat Mar 17, 2018 1:44 pm
Forum: Phase Changes & Related Calculations
Topic: Test 1, Q7
Replies: 3
Views: 374

Test 1, Q7

In order to make iced tea, a 50.0 g ice cube at 0.0 degrees C is added to 250 mL of tea at 20.0 degrees C. What is the final temp of the iced tea once it has reached thermal equilibrium? Assume that no hear is transferred to or from the surroundings. The density of water (and iced tea) is 1.00 g/mL ...
by Melissa Per 2J
Sat Mar 17, 2018 12:36 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Enthalpy of RXN using standard enthalpy of formation
Replies: 2
Views: 319

Enthalpy of RXN using standard enthalpy of formation

In question one of the first test, we are given the standard enthalpies of formation for C2H2 (+226.73) and C2H2Cl2 (-.50). C2H2 is a reactant and C2H2Cl2 is a product. Do we change the signs if we know the bonds are being broken vs. formed before we put these numbers into the equation to find the s...
by Melissa Per 2J
Sun Mar 11, 2018 11:02 pm
Forum: Method of Initial Rates (To Determine n and k)
Topic: rate law
Replies: 5
Views: 556

Re: rate law

What would a proposed rate law look like versus a verified one? Is the experiment just for the order or does the rate constant come from there too?
by Melissa Per 2J
Sun Mar 11, 2018 10:54 pm
Forum: Calculating Work of Expansion
Topic: Midterm 4a
Replies: 5
Views: 521

Re: Midterm 4a

Could you post the question from the midterm here please?
by Melissa Per 2J
Fri Mar 09, 2018 3:06 am
Forum: First Order Reactions
Topic: 15.27
Replies: 2
Views: 239

15.27

The question is asking us to use the half life derivation of the first order rate law to find the time it takes for a reaction to reach certain concentrations. The solutions manual is saying that the formula we use to do this is: t=(ln [A]0/ln[A]t)/k. Typically the equation we use is t=-(ln [A]t/ln[...
by Melissa Per 2J
Sun Mar 04, 2018 9:11 pm
Forum: Experimental Details
Topic: spectroscopy
Replies: 2
Views: 474

spectroscopy

Is a spectrometer able to record data during a reaction? Or does it only record the amount of light absorbed at the end of a reaction? If it records during how specific would the data be for those reactions that happen in a second? I am in awe of our awareness of these reactions that happen so quick...
by Melissa Per 2J
Sun Mar 04, 2018 8:15 pm
Forum: First Order Reactions
Topic: 15.23 c
Replies: 2
Views: 224

15.23 c

Determine the rate constant for 2A ----> B+C given that [A]0 = 0.153 molxL^-1 and that after 115 s the concentration of B rises to 0.034 molxL^-1.
I keep getting it wrong. Please help.
by Melissa Per 2J
Sun Mar 04, 2018 7:48 pm
Forum: Balancing Redox Reactions
Topic: Test 2, Q5
Replies: 4
Views: 321

Test 2, Q5

We are told to rank the following in order of increasing reducing power: Zn, Mn, Cr and Al, Br2, and I2.

Are these rankings based off the placement of the elements on the periodic table?
by Melissa Per 2J
Sun Feb 25, 2018 11:26 pm
Forum: General Rate Laws
Topic: rate of reaction vs rate law
Replies: 2
Views: 217

rate of reaction vs rate law

What is the difference between rate of reaction and rate law?
by Melissa Per 2J
Sun Feb 25, 2018 11:23 pm
Forum: Interesting Applications: Rechargeable Batteries (Cell Phones, Notebooks, Cars), Fuel Cells (Space Shuttle), Photovoltaic Cells (Solar Panels), Electrolysis, Rust
Topic: The Chromium example
Replies: 2
Views: 380

The Chromium example

Does anyone remember the chromium example that Dr. Lavelle explained in class the last day we went over electochemistry? I recall being confused and would like to go over it again.
by Melissa Per 2J
Sun Feb 25, 2018 11:21 pm
Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
Topic: standard conditions [ENDORSED]
Replies: 4
Views: 309

standard conditions [ENDORSED]

Do standard conditions have anything to do with equilibrium?
by Melissa Per 2J
Sun Feb 11, 2018 11:59 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: higher molar entropy
Replies: 2
Views: 240

higher molar entropy

Lead has a higher molar entropy than carbon because it is heavier?
by Melissa Per 2J
Sun Feb 11, 2018 11:53 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: heat capacity sign
Replies: 2
Views: 284

heat capacity sign

In the practice exam (1F), it was said that heat capacities can NOT be negative for simple molecules. Is this specific to simple molecules or can heat capacities never be negative?
by Melissa Per 2J
Sun Feb 11, 2018 11:48 pm
Forum: Balancing Redox Reactions
Topic: redox reactions and salts
Replies: 2
Views: 367

redox reactions and salts

Do all REDOX reaction need to have a salt product? And does producing a salt have something to do with making a reaction nuetral?
by Melissa Per 2J
Sun Feb 04, 2018 11:40 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: test question 7 [ENDORSED]
Replies: 6
Views: 448

test question 7 [ENDORSED]

The question from the test is: In order to make iced tea a 50.0 g ice cube at 0.0 degrees Celcius is added to 250 mL of tea at 20.0 degrees Celcius. What is the final temp. of the iced tea once it has reached themal equilibrium? Assume no heat is transferred to or from the surroundings. Density of [...
by Melissa Per 2J
Sun Feb 04, 2018 11:31 pm
Forum: Thermodynamic Systems (Open, Closed, Isolated)
Topic: test question 5
Replies: 5
Views: 399

test question 5

Why are the CONTENTS of an ideal cooler at 3 degrees Celcius an isolated system?
by Melissa Per 2J
Sun Feb 04, 2018 11:20 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: requirements for reversible reactions
Replies: 1
Views: 87

requirements for reversible reactions

Do delta G and delta S total both have to be equal to zero for a reaction to be reversible? Why or why not?
by Melissa Per 2J
Sun Jan 28, 2018 9:08 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: Examlpe 9.6
Replies: 2
Views: 189

Re: Examlpe 9.6

And because I didn't say it in the last post, Acetone has the formula C3H6O which is most definitely nonlinear.
by Melissa Per 2J
Sun Jan 28, 2018 8:55 pm
Forum: Thermodynamic Systems (Open, Closed, Isolated)
Topic: Question from test?
Replies: 4
Views: 338

Re: Question from test?

An easy way to differentiate between the systems: when N is the number of atoms and q is heat, In open systems, dN \neq 0 and dq \neq 0 In closed systems, dN=0 and dq \neq 0 In isolated systems, dN=0 and dq=0 In adiabatic systems, dN \neq 0and dq=0 Just remember that determining what kind of system ...
by Melissa Per 2J
Sun Jan 28, 2018 8:45 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: Examlpe 9.6
Replies: 2
Views: 189

Re: Examlpe 9.6

On page 281 of the textbook there is a table with the methods of finding R based on the type of molecule we are looking at. So the Cv,m for atoms is (3/2) R, for linear molecules is (5/2)R, and for nonlinear molecules is 3R. Cp,m for atoms is (5/2) R, for linear molecules is (7/2)R, and for nonlinea...
by Melissa Per 2J
Sun Jan 21, 2018 11:36 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: closed sysytem
Replies: 3
Views: 239

closed sysytem

I'm not sure if this question belongs under this category, but I was wanting to see in another person's words, why a thermometer with mercury is a closed system. Thank you.
by Melissa Per 2J
Sun Jan 21, 2018 11:24 pm
Forum: Phase Changes & Related Calculations
Topic: time in equilibrium thermodynamics
Replies: 1
Views: 188

time in equilibrium thermodynamics

I have written in the margins of my notes that there is no such thing as time in equilibrium thermodynamics. I am now confused as to why it is not taken into account in any of the calculations we do. And is it only in calculations for systems in equilibrium that time is completely irrelevant?

Thanks.
by Melissa Per 2J
Sun Jan 21, 2018 11:13 pm
Forum: Phase Changes & Related Calculations
Topic: enthalpy vs. heat
Replies: 2
Views: 201

enthalpy vs. heat

How is enthalpy a state function, but heat a path function?
by Melissa Per 2J
Sun Dec 10, 2017 9:10 am
Forum: Determining Molecular Shape (VSEPR)
Topic: 180 bond angles
Replies: 1
Views: 265

180 bond angles

On Lyndon's practice final exam, one of the options for a possible bond angle was slightly less than 180 degrees. Is this possible? How and in what circumstances?
by Melissa Per 2J
Sun Dec 03, 2017 11:47 pm
Forum: Air Pollution & Acid Rain
Topic: compounds for acid rain
Replies: 3
Views: 655

compounds for acid rain

Are CO2 and NO the only molecules that increase acidity in rain? There have to be others... but what are they?
by Melissa Per 2J
Sun Dec 03, 2017 10:42 pm
Forum: Calculating pH or pOH for Strong & Weak Acids & Bases
Topic: Very acidic and Very basic
Replies: 1
Views: 146

Very acidic and Very basic

How are 1 M H3O+ and 10^-14 M OH- both very acidic and with the same pH of 0? Similarly, how are 1 M of OH- and 10^-14 M H3O+ both very basic and with a pH of 14?
by Melissa Per 2J
Sun Nov 26, 2017 10:17 pm
Forum: Non-Equilibrium Conditions & The Reaction Quotient
Topic: units for pressure
Replies: 5
Views: 278

units for pressure

Do we prefer a unit for pressure? Bar vs. atm? Is there one that we need to convert to the other for the sake of units canceling with the units of R?
by Melissa Per 2J
Sun Nov 26, 2017 10:07 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: 11.7
Replies: 5
Views: 407

11.7

In this question, we have four flasks demonstrating the disassociation of a molecule till it reaches equilibrium in flask 3. In part c it asks us to: Assuming that the initial pressure of X2 was 0.10 bar, calculate the value of K for the decomposition. With no other information aside from the pictur...
by Melissa Per 2J
Sun Nov 19, 2017 9:23 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Why lone pairs occupy equatorial plane
Replies: 2
Views: 861

Re: Why lone pairs occupy equatorial plane

If we look at the bond angles of a trigonal bipyramidal structure, the atoms in the axial plane have a 90 degree bond angle with the three atoms in the equatorial plane. And these atoms in the equatorial plane have a 120 degree bond angle with each other. It is better for the lone pair to be in the ...
by Melissa Per 2J
Sun Nov 19, 2017 9:03 pm
Forum: Hybridization
Topic: bent molecular structure [ENDORSED]
Replies: 4
Views: 427

bent molecular structure [ENDORSED]

Why does having two sets of lone pairs and two paired electrons create a bent molecular structure?
by Melissa Per 2J
Wed Nov 08, 2017 1:06 am
Forum: Hybridization
Topic: Electron configuration of elements with f orbitals [ENDORSED]
Replies: 1
Views: 188

Electron configuration of elements with f orbitals [ENDORSED]

In the problem 3.5 from the textbook, we are asked to find the ground state electron configuration of Bi^3+. I originally wrote the configuration as [Xe] 5d^10 6s^2. Where does the 10th electron in the d orbital come from and how should I denote the f orbital? Please help. Thank you!

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