Blog post #4 -- Last Gen Chem 112post

 

1. Most valuable lesson?

I learned that chemistry and science in general tend to be selfish, they usually require a lot of time and effort; but then after all the efforts you get to see what you were able to accomplish. However, I enjoyed it because it is challenging and a very complete course.

 

2. Most challenging concept?

 For me the more challenging part of this course is using succesive approximations to find the concentraton of ions, and to work with ice equations.

 

3.  Advice: Do read the chapters and work the "For Practice Problems" that are in the book. 





Blog Post #3 --- Thoughtful question

Here is my question: If the heat from burning 7.800 g of C6H6 is added to 2.387 kg of water that is initially at a temperature of 21 degrees C, what is the final temperature of the water? The specific heat of liquid is 4.184 J/g*Degrees C.

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Data:                                                                                Find:  Tf: ? of the water
   Benzene (C6H6) : 7.800 g
   H2O : 2.387 Kg
   Ti : 21.0 *C
   Specific heat of water : 4.184 J/g . C


1) First we have to find the amount of heat released by the burning of  7.800 g of benzene. To find the it, we need to first write down the balanced equation for the combustion of benzene. Then use the ∆hf* of the reactants and products  to find the ΔH°_{rxn using Hess' Law:}

ΔH°_rxn = Σ ΔH°_f (products) - Σ ΔH°_f (reactants)

  2 C6H6(l) + 15 O2(g) ----> 12CO2(g) + 6H2O(g)      ΔH°_rxn = - 6271 K

ΔH°_rxn =  12(CO₂) + 6( H₂O) – 2(C₆H₆) + 15(O₂)

ΔH°_rxn = 12(-393.5 KJ/mol) + 6 ( -241.8 KJ/ mol) – 2(49.1 KJ/ mol) + 15 (0 KJ/ mol) = -6271 KJ

2) Once we have the ΔH°_{rxn  for the balanced equation of the combustion process, we can find the amount of heat released by the burning of 7.800 g of C6H6 by simply converting from grams to moles of benzene and calculating the heat produced by the burning of that many moles of reactant.} 

7.800 g C₆H₆ x (1 mol C₆H₆ / 78.108 g) = 0.09986173 mol C₆H₆

(-6271 KJ / 2 mol C₆H₆ ) x 0.09986173 mol C₆H₆ = - 313.1165 KJ 

3) Now that we know the amount of heat produced by the  combustion of 7.800g of benzene, we are ready to plug in the values we were given and the heat we just found to solve for the ∆T  of the water using the formula q = m x C_s x ∆T; where q is the amount of heat in J, m is the mass of the substance (water) in g, C_{s is the specific heat capacity, and} ∆T is the change in temperature in °C (Nivaldo J. Tro 241). Notice that q is positive because the heat is being absorbed by the water, therefore is an endothermic process. 

q = m x C_s x ∆T

313116.5 J = (2387 g) x (4.184 J/ g . °C) x ∆T

313116.5 J/ (2387 g) x (4.184 J/ g . °C)  = ∆T

 ∆T = 31.35 °C

∆T = T_f - T_i 

∆T + T_i = T_f

T_f =  31.35 °C + 21.0 °C = 52.35 °C 

• http://www.mychemistrytutor.com/questions/calculating-delta-hrxn-combustion-benzene-using-enthalpy-formation-values
• http://www.saplinglearning.com/ibiscms/mod/ibis/view.php?id=492792
• https://sites.google.com/site/chempendix/thermo
• http://www.chemteam.info/Thermochem/HessLawIntro2.html
• Tro, Nivaldo J. “Chemistry A Molecular Approach.”Pearson. 2^nd Ed. pp. 612-655.Print.2008.

ENZYMES : Ribulose-1,5- bisphosphate carboxylase/ oxygenase

Ribulose-1,5- bisphosphate carboxylase/ oxygenase

Active site/ reactions carried out

2D structure 

                         

Ribulose-1,5- bisphosphate molecule structure

Ribulose-1,5- bisphosphate carboxylase oxylase

•  chemical formula:  CH2OHCO(CHOH) 2CH2OH    
•  molar mass: 310.09 g/mol
• ligands: Mg+2 ion 

This enzyme is commonly known by the shorter name RuBisCO,  and is an enzyme involved in the Calvin cycle that catalyzes the first major step of carbon fixation, which is the process by which the atoms of atmospheric carbon dioxide are made available to organisms in the form of energy-rich molecules such as glucose. RuBisCO is very important in terms of biological impact because it catalyzes the primary chemical reaction by which inorganic carbon permanently enters the biosphere.

 RuBisCO catalyzes either the carboxylation or the oxygenation of ribulose-1,5-bisphosphate (also known as RuBP) with carbon dioxide or oxygen.

.

Carboxylation reaction

Oxygenation reaction

The rate of reaction for this enzyme is really slow compared to most enzymes. RuBisCO fixes only about three carbon dioxide molecules per second while most enzymes can process thousands of molecules per second. However plants compensate this slow rate by building lots of it. This enzyme also shows an unfortunate lack of specificity, since molecules of oxygen and carbon dioxide are similar in shape and properties, RuBisCO enzymes occasionally fix oxigen molecules to the sugar chain, forming faulty oxigenated  products.

references:
http://en.wikipedia.org/wiki/Ribulose-1,5-bisphosphate
http://guweb2.gonzaga.edu/faculty/cronk/biochem/R-index.cfm?definition=rubisco
http://guweb2.gonzaga.edu/faculty/cronk/biochem/R-index.cfm?definition=rubisco (3D ribbon structure)
http://www.climatewiki.org/wiki/Rubisco
http://www.rcsb.org/pdb/101/motm.do?momID=11

Epinephrine - Adrenaline

Epinephrine, commonly known as Adrenaline, is a hormone and a neurotransmitter secreted by the adrenal medulla in response to a physical or metal stress

. -Chemical Formula:  C₉H₁₃NO₃  

-molecular weight: 183.204 gr/mol.

-IUPAC name: (R)-4-(1-hydroxil)-2-(methylamino)ethyl)benzene-1,2-diol

Physical Properties: 

• meltings point 211 *C
• Water Insoluble. Slightly soluble in salutions of inorganis acids. Aquous solutions are slightly alkaline
• Odorless

Polar or Non-polar..?

http://www.youtube.com/watch?v=P79WCZIZXwk&list=PLFD3F0A2FD73A4E63

Spring semester 2013

http://www.youtube.com/watch?v=IKQXZhO2rH8&list=PLFD3F0A2FD73A4E63