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Day 10: What is a Reaction? (Chemical Rxn (breathing & blood), Formulating, Carbon dioxide, Fire);
Fire occurs naturally as a result of volcanic activity,
meteorites, and lightning strikes. People understand that
an igniter was needed for fire since the stone age. Even
though they did not understand friction, one can imagine
picking up a flint rock and hitting it on a stone near leather
and wood. The spark heated up the fuel to a temperature
causing autoiginition. Later, and oxidizing agent was aided
to the fuel. Once the process began, oxygen could take over
as the oxidizer or oxidant. The flame would have different
cones. In special cases, the fuel and the oxidant may be
combined within the same chemical molecule, and this is
the case in some propellants and explosives. The chemical
reaction between the fuel and oxidant is called
“Combustion;” it is accompanied by the release of heat and
usually by the emission of light in the visible region of the
spectrum. The flames temperature depends upon the fuel
to air ratio and the degree of combustion in the reaction.
Researchers are also interested in the colors of the flame.
The flow rate of fuel is usually low for everyday flames, but
can be higher in rockets. In general, all hydrocarbon
flames, whether rich or lean, go through such a stage with
CO and H2 being formed in the first main reaction zone,
and the second stage combustion of the CO and H2 initially
formed is characterized by the emission of blue light; this
blue emission being a key feature of the combustion of all
carbon (and hydrocarbon) containing fuels. This process is
more pronounced in slightly fuel-rich flames and is
termed afterburning. A premixed flame of a particular fuel-
air combination is characterized by three main
parameters, the burning velocity, flame
temperature and flammability limit, which are also
determined by the pressure, temperature and, of course,
mixture ratio. (http://thermopedia.com/content/766/)
The match was invented in 1827. It is a mixture like
gunpowder. The igniter is red phosphorus, the fuel is
sulfur, and the oxidizer is potassium chloride. Powered
glass is included in the head to help the material to light
up and burn evenly. Animal glue helps the material burn
and keeps everything together. Hot paraffin wax is used on
the matchstick wood to keep the flame burning, and for
extra safety, the matchstick wood needs ammonium
phosphate to stifle the afterglow when the flame goes
away. [http://www.discovery.com/tvshows/mythbusters/about-this-show/how-matcheswork/]. However, the story of fire and phosphorus did not
start with the match. People thought about the oracle early
1670- The scientific revolution continues as French-born
British physicist Denis Papin proves that water’s boiling point
depends on pressure
Ionic compounds are compounds composed of ions, charged
particles that form when an atom (or group of atoms, in the case
of polyatomic ions) gains or loses electrons.
A cation is a positively charged ion
An anion is a negatively charged ion.
Covalent or molecular compounds form when elements share
electrons in a covalent bond to form molecules. Molecular
compounds are electrically neutral.
Ionic compounds are (usually) formed when a metal reacts with a nonmetal (or a
polyatomic ion). Covalent compounds are formed when two nonmetals react with
each other. Since hydrogen is a nonmetal, binary compounds containing hydrogen are
also usually covalent compounds.
Metal + Nonmetal —> ionic compound (usually)
Metal + Polyatomic ion —> ionic compound (usually)
Nonmetal + Nonmetal —> covalent compound (usually)
Hydrogen + Nonmetal —> covalent compound (usually)
Writing Formulas of Ionic Compounds
The cation is written first, followed by the monatomic or
The subscripts in the formula must produce an electrically
neutral formula unit. (That is, the total amount of positive charge
must equal the total amount of negative charge.)
The subscripts should be the smallest set of whole numbers
If there is only one of a polyatomic ion in the formula, do not place parentheses
around it; e.g., NaNO3, not Na(NO3). If there is more than one of a polyatomic ion in
the formula, put the ion in parentheses, and place the subscript after the parentheses;
e.g., Ca(OH)2, Ba3(PO4)2, etc.
Binary Covalent Compounds Between Two Nonmetals.
Two nonmetals combine to form a covalent or molecular
compound (i.e., one that is held together by covalent bonds
which result from the sharing of electrons).
In many cases, two elements can combine in several different ways to make
completely different compounds. (This cannot happen with ionic compounds, except
in the cases of metals that can form more than one charge.) For instance, carbon can
share electrons with one oxygen to make CO (carbon monoxide), or with two oxygens
to make CO2 (carbon dioxide). For this reason, it is necessary to specify how many of
each element is present within the compound.
The formula is written with the more electropositive element
(the one further to the left on the periodic table) placed first,
then the more electronegative element (the one further to the
right on the periodic table).
[Important exception: when the compound contains oxygen and
a halogen, the halogen is placed first. If both elements are in the
same group, the one with the higher period number is named
The first element in the formula is given the neutral element
name, and the second one is named by replacing the ending of
the neutral element name with -ide. A prefix is used in front of
each element name to indicate how many atoms of that element
If there is only one of the first element in the formula, the monoprefix is dropped.
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