Biology Forums - Study Force

Anybody out there... I really need some help with this discussion board!!

As evidenced by the Introductions you did in the first week, you all have a varied and unique background. Some of us like to workout, some of us are involved in explosive abatement, some of us have medical backgrounds, etc. Please think about your own background and interests when considering your reply to this Lesson's Discussion Forum topic.
 
 Chemical reactions are happening around us all the time; the CO2 in a can of soda is at equilibrium, batteries, fuel cells, acid rain, decaffeination of coffee (why bother?), reaction of sunscreen with skin, and on and on and on. There are also a number of household chemicals that when mixed can create an explosion or other hazardous situation. Try to think of a way chemicals are reacting around you and post the following:
 
(A). Identify the chemical reaction. (chemical formulas and arrows)
(B). Is this a reaction that could happen accidently?
(C). What is/are the consequence(s) of this reaction? How can you tell a reaction has taken place?
(D). Is this reaction endo or exo thermic / endo or exergonic?
(E). Is this reaction reversible?
(F). Can you classify this reaction? Is this a synthesis, decomposition, single displacement or double displacement reaction? Acid Base? Redox?

Please remember to list your references

Content hidden

An example of synthesis is the formation of kidney stones. It has been shown that when you don't consume enough calcium, there is a high chance that the calcium that you do get will bond with oxalate in your gastrointestinal tract. The bonding of these two liquids forms the solid calcium oxalate. This is what the majority of kidney stones are made of. The chemical equation for this is Ca + C204 --> CAC2O4.

Synthesis

4Fe + 3O2 --> 2Fe2O3

Iron(III) rusts when in contact with air because synthesis reaction occurs with the reactants being iron(III) and oxygen and product being iron(III) oxide/hydroxide.

Decomposition

2H2O2 --> H2O + O2

Hydrogen peroxide gradually decomposes into water and oxygen gas.

Double Replacement

2MnO2 + H2O => Mn2O3 + 2OH

In an alkaline battery, Magnesium oxide reacts with water to form a different magnesium oxide and hydroxide. This is half of the pair of reactions that give batteries their electrical charges.

Single Replacement

2AgNO3 + Cu --> Cu(NO3)2 + 2Ag

This isn't exactly a reaction you see when you're walking down the street. A solution of silver nitrate will turn blue when copper is submerged in it. Also, the copper will change into a cool, silvery color.

Thanx so much everybody. They are all great examples. Since I'm a girl that loves to bake, I think I'm gonna go with the baking example. :D

Thanx again!

Ha ha, all right whatever works.

Haha! :-)  I can apply this more to my life.
I am having trouble now trying to figure out if its endo or exo thermic / endo or exergonic? I think a cake absorbs energy, but I am thinking it also releases energy..?
And this isn't reversible is it?

Thanx in advance for any help!

Not reversible... and

There is no set rule on double displacement and/or single displacement being exothermic or endothermic. Exothermic vs. endothermic depends on the individual molecules and the transformation taking place in each individual reaction.

To figure out if a reaction is exothermic or endothermic, you have to evaluate the heat of the reaction. This is done by factoring the heat of formation of the products and the heat of breaking apart the reactants into your calculation.

The quantity you will evaluate for each reaction is dHrxn (the d stands for delta).
If dHrxn < 0, the reaction is exothermic
If dHrxn > 0, the reaction is endothermic

dHrxn = sum dHf(products) - sum dHf(reactants)
Hf is the heat of formation of a substance and can be found in a table, there should be one in your chemistry text or they may be found from a reliable source online. The quantities are usually given in a per mole basis, so you multiply by the number of moles in your given reaction to the quantity you need.

Example: Is the following reaction endothermic or exothermic?
8 Al(s) + 3 Fe3O4(s) --> 4 Al2O3(s) + 9 Fe(s)
Step 1: Find dHf(products)
from a table
Hf Al203 = -1669.8 kJ
Hf Fe = 0 because it is in its natural state
so dHf(products) = 4 x (-1669.8) = -6679.2

Step 2: Find dHf (reactants)
Hf Fe3O4 = -1120.9 kJ
Hf Al = 0 because it is in its natural state
dHf (reactants) = 3(-1120.9) = -3362.7

dHrxn = dHf (products) - dHf (reactants)
= -6679.2 - -3362.7
= -3316.5 kJ

dHrxn < 0, so the reaction is exothermic (it gave off heat to the environment)