Search found 29 matches

by marinah
Sat Mar 05, 2016 6:01 pm
Forum: *Alkanes
Topic: Dichlorodiflouromethane line structure
Replies: 1
Views: 311

Dichlorodiflouromethane line structure

How do you know which side the flouro and chloro go on when the problem doesn't state cis/trans?
--> dichlorodiflouromethane
by marinah
Tue Mar 01, 2016 9:01 pm
Forum: *Alkenes
Topic: Quiz prep 1 #3
Replies: 1
Views: 440

Quiz prep 1 #3

CH3CH=C(CH3)CH(CH3)2
I named this compound 2,3 dimethyl-2-pentene but the answer is 3,4 dimethyl-2-pentene. Is this because we start counting to the double bond from the left side and so we must use the same side when numbering the substituents?
by marinah
Sun Feb 28, 2016 11:21 am
Forum: *Alkanes
Topic: Carbons
Replies: 2
Views: 415

Carbons

CH3CH(CH3)CH(CH2CH3)C(CH3)3 how do you decide which carbons are part of the parent chain while the others are substituents? I'm just confused because don't the parenthesis go around the substituents?
(this is #2 in the first quiz 3 prep)
by marinah
Tue Feb 16, 2016 11:51 am
Forum: First Order Reactions
Topic: Units
Replies: 1
Views: 354

Units

if given the half life of a rxn in minutes and we are trying to find k should we convert to seconds? and should we also convert the given t to seconds as well (t used in the integrated rate law)?
by marinah
Wed Feb 10, 2016 8:30 pm
Forum: Student Social/Study Group
Topic: Post All Chemistry Jokes Here
Replies: 8223
Views: 1435292

Re: Chemistry Jokes

What did the chemistry student say when they asked her why she was crying?

"just too much pressure atm"
by marinah
Tue Feb 09, 2016 10:07 am
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Midterm 2011 Q5C
Replies: 1
Views: 379

Midterm 2011 Q5C

Where does the (1mol glucose/2,885 kJ) come from? is it calculated or given?
question asks for the mass of glucose would need to be metabolized in order to produce the energy necessary for the formation of myoglobin assuming it is made up of 153 peptide bonds (16kJ free energy per peptide bond)
by marinah
Mon Feb 08, 2016 11:17 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Midterm 2011 Q4
Replies: 1
Views: 338

Re: Midterm 2011 Q4

so first you want to find what deltaG of the reaction equals so you can plug that value into the deltaG=-RTlnK and solve for K. The question does not ask for the value of K however, so you know K=Partial Pressure of Products/Partial Pressure of Reactants. therefore, K=P(PCl5)/(P(PCl3)*P(Cl2)) which ...
by marinah
Sun Feb 07, 2016 12:34 am
Forum: Gibbs Free Energy Concepts and Calculations
Topic: 2014 Midterm Q6
Replies: 2
Views: 458

Re: 2014 Midterm Q6

Yes okay so I converted entropy and the constant R to kJ and I got lnK=13.2... (just like the solution manual) then I used the exact answer my calc gave me and calculated e^13.2.... so I got 550760.4866 (which I'm guessing is the exact answer because the solution manual rounded lnK to exactly 13.2 a...
by marinah
Sat Feb 06, 2016 6:27 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: 2014 Midterm Q6
Replies: 2
Views: 458

2014 Midterm Q6

For Q6, asking to calculate the equilibrium constant at 37C of O2+Mb-->MbO2 with given entropy=-133 J/molK and enthalpy=-75.3 kJ/mol, the solution show K=540365 however I calculated K by converting enthalpy from kJ to J and got K=550760.4866. Are these answers close enough to be correct?
by marinah
Tue Jan 26, 2016 9:42 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Isothermal Processes
Replies: 4
Views: 651

Re: Isothermal Processes

how about for an isolated system? ex) If an isolated system contained +5 kJ of energy, after 100 years deltaU=?
why will deltaU eventually reach 0. is it because the system uses those +5kJ of energy for work within the system itself?
by marinah
Wed Jan 20, 2016 12:45 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Calculating Reaction enthalpy
Replies: 1
Views: 364

Calculating Reaction enthalpy

Can someone please explain how to estimate the reaction enthalpy using bond enthalpies. I've done some problems correctly but there are others that are a little confusing. Ex: #3 in the first quiz from the workbook asks to estimate the reaction enthalpy for burning 1 mol of Butane. C4H10(g) + O2(g) ...
by marinah
Mon Jan 18, 2016 3:34 pm
Forum: Calculating Standard Reaction Entropies (e.g. , Using Standard Molar Entropies)
Topic: Something wrong in HW 8.63
Replies: 3
Views: 663

Re: Something wrong in HW 8.63

Is there also a mistake with 8.61 answer. I did the problem and I ended up getting reaction enthalpy=-195.76 kJ/mol since I multiplied N2+3H2--> 2NH3 by 1/3 therefore multiplying -92.22 by 1/3 as well. The solution manual answer is -72.80 kJ/mol. Am I missing something?
by marinah
Sat Jan 16, 2016 1:08 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: Question 8.19 units and equation
Replies: 6
Views: 1448

Question 8.19 units and equation

For number 19, it asks to calculate the required heat that must be supplied to a 500.0-g stainless steel vessel containing 400.0g of water to raise its temp from 22.0 C to 100.0 C. I started out by using the equation q= gCpΔT I'm just confused on why we have to add (400g)(4.184)(100-22) + (500g)(0.3...
by marinah
Wed Jan 13, 2016 11:19 pm
Forum: Calculating Work of Expansion
Topic: Calculating required heat
Replies: 4
Views: 4822

Calculating required heat

How should a question like 8.19 be approached when asking you to calculate the heat that must be supplied (required heat) to raise temperatire of the system? is there a specific equation for finding required heat? 8.19: (a) Calculate the heat that must be supplied to a 500.0-g copper kettle containi...
by marinah
Wed Jan 13, 2016 10:20 pm
Forum: Phase Changes & Related Calculations
Topic: delta U
Replies: 2
Views: 870

Re: delta U

Delta U is the change in internal energy of a system. Internal energy is the energy within the system itself and not the surroundings. For example, the human body is a system and we function within our surroundings. The body contains internal energy in which we can use to carry out work (just do wor...
by marinah
Mon Jan 11, 2016 6:11 pm
Forum: Phase Changes & Related Calculations
Topic: Why does steam cause severe burns?
Replies: 1
Views: 283

Why does steam cause severe burns?

This question, Why does steam cause severe burns, is on page 2 of the thermochemistry section of the course reader. I was just wondering if the answer to this question has anything to do with the process of pressurized, high in temperature steam hitting your skin and undergoing a phase change from g...
by marinah
Sun Jan 10, 2016 9:15 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: Problem 8.13
Replies: 2
Views: 321

Re: Problem 8.13

I agree with the answer given above. Make sure you use delta U (meaning the change in internal energy) instead of delta W (the change in work). The course reader also states on page 10 of the first unit: "Change in internal energy = energy transferred by heating (+q) + energy transferred by com...
by marinah
Sun Jan 10, 2016 8:45 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: System Confusion
Replies: 2
Views: 393

Re: System Confusion

In addition, the definition of a coolant is a liquid or gas that is used to remove heat from something. This shows us that this coolant will remove heat from the surroundings. With this information, we can confidently select the closed system option as the coolant in the fridge will only exchange en...
by marinah
Sat Jan 09, 2016 11:16 pm
Forum: Phase Changes & Related Calculations
Topic: Why does a phase change graph have mutiple plateaus?
Replies: 2
Views: 3643

Re: Why does a phase change graph have mutiple plateaus?

That is correct. Multiple plateaus represent the different phase changes. Looking at page 12 of the first section of the course reader, the first plateau indicates solid state (ice) melting to enter the liquid state (water). The graph slopes up again as the liquid heats and reaches a second plateau,...
by marinah
Sat Dec 05, 2015 11:55 pm
Forum: Non-Equilibrium Conditions & The Reaction Quotient
Topic: Endo/Exothermic
Replies: 3
Views: 860

Re: Endo/Exothermic

You take in energy to break bonds, and release energy to to form bonds (in the form of heat).
by marinah
Sat Nov 28, 2015 12:20 am
Forum: Photoelectric Effect
Topic: Video- The Photoelectric Effect
Replies: 3
Views: 787

Re: Video- The Photoelectric Effect

Attached, please find our video on the photoelectric effect (in ".mov" format). It contains an explanation along with detailed examples of the topic. Thanks for watching!
by marinah
Fri Nov 20, 2015 11:30 pm
Forum: Ideal Gases
Topic: Exothermic and Endothermic Reactions
Replies: 3
Views: 868

Re: Exothermic and Endothermic Reactions

Another helpful component of these endo/exo-thermic reactions is with the addition of heat, what occurs to the reaction shift. Endothermic reactions: (+enthalpy) 1) increasing temperature, shifts reaction to the right. 2) decreasing temperature, shifts reaction to the left. Exothermic reactions: (-e...
by marinah
Fri Nov 13, 2015 11:19 pm
Forum: Hybridization
Topic: Writing sp3d2 in the correct order
Replies: 1
Views: 423

Re: Writing sp3d2 in the correct order

I think you might be referring to the workbook problem (quiz 2 prep, #1) My answer was sp3d2, I believe you must show the filling in of the p orbital before moving on to higher orbitals like d. Showing the order sp3d2 allows for understanding of how you obtained this hybridization based on the numbe...
by marinah
Fri Nov 06, 2015 4:53 pm
Forum: *Molecular Orbital Theory (Bond Order, Diamagnetism, Paramagnetism)
Topic: Molecular Orbital Theory
Replies: 2
Views: 394

Re: Molecular Orbital Theory

Yes, if at least one of the elements has Z less than 8, then you use that mo diagram, only changing the center of the diagram (sigma2pz, pi2px, pi2py)
by marinah
Sat Oct 31, 2015 10:00 am
Forum: Determining Molecular Shape (VSEPR)
Topic: Lone Pair Repulsion in Bent Molecules
Replies: 5
Views: 1171

Re: Lone Pair Repulsion in Bent Molecules

For this linear molecular shape, the AX2E3, the lone pairs pull in different directions somewhat canceling each other out, therefore being non polar. Because this is a linear shape still, the bond angles are slightly less than 180 due to those lone pairs pulling.
by marinah
Fri Oct 23, 2015 8:40 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Sigma bonds and Pi Bonds
Replies: 8
Views: 1015

Re: Sigma bonds and Pi Bonds

that is correct, as taught, single bond corresponds to one sigma bond, double bond to one sigma and one pi, and triple bond to one sigma and two pi. There cannot be two sigma bonds because of the overlap end to end versus side to side discussed above.
by marinah
Fri Oct 16, 2015 6:29 pm
Forum: Lewis Structures
Topic: Drawing & Determining Correct Lewis Structure
Replies: 4
Views: 638

Re: Drawing & Determining Correct Lewis Structure

Resonance structures are the multiple structures you are referring to. I believe the structure that has reached an octet is the most stable. The lone pairs will later determine the shape of that specific structure so single and double bonds are important to keep in mind as they will affect this shap...
by marinah
Fri Oct 09, 2015 7:42 pm
Forum: Trends in The Periodic Table
Topic: shielding
Replies: 2
Views: 514

Re: shielding

On the periodic table, there is a trend for shielding. Shielding increases as you go to the lower left. The elements as you go to the lower left of the periodic table are more shielded than others. This corresponds to element size as well. Size increases as you go to the lower left of the pt.
by marinah
Fri Oct 02, 2015 6:03 pm
Forum: Empirical & Molecular Formulas
Topic: Finding molecular formula
Replies: 2
Views: 450

Re: Finding molecular formula

Yes, that is correct since you are trying to find the empirical formula, you have to divide by the smallest number to find the ratio and then write the empirical formula (which is itself the ratio of each molecule in the formula). After that, if the question asks for the molecular formula, you do (m...

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