EXOTHERMIC AND ENDOTHERMIC

Jim McCulloch (jim@emptysea.co.uk) wrote:
>Please, what does exothermic mean?

     All chemical reactions take energy to start them, and all chemical
reactions release energy in the process of completing.

     A chemical reaction consists of two or more elements or molecules
coming together and forming a bond, or splitting apart and breaking a
bond.

     It takes energy to make two chemicals come together, and it takes
energy to make two chemicals split apart.

     When two chemicals come together they also release energy of their
own and when chemicals split apart they release energy of their own.
 
     Strike a match, you put energy into the chemicals with your hand
strike, then the match lights and releases energy of its own.

     Exothermic reactions release more energy than it took to start
them.  They tend to be self sustaining such as the burning of paper.
Once you get it burning, it generates enough heat to start the next
section of paper burning plus some.  Thus more energy is released than
needed to start the reaction.

     Endothermic reactions release less energy than is need to start
them.  They tend to be STORAGE reactions, the energy is pumped into the
chemical reaction, which releases less than is pumped in, and thus
energy is stored in the chemical bonding or separation as the case may
be.

     The classic case of endothermia is the splitting of CO2 into Carbon
and Oxygen.  It takes great energy to split them, and only a little is
released in the splitting, so more is stored than released in the end.

     The classic case of exothermia is when Carbon and Oxygen get back
together again and form CO2, this is a burning fire as you know it, wood
fire etc.  It only takes a little bit of energy to get them together,
and they release all the energy stored in them when they were taken
apart.

     The basic plant animal food cycle takes place as follows:

     1.) Plants take energy from the sun and CO2 from the air, and use
the energy to split the CO2 into Carbon and Oxygen.  Oxygen is released
into the atmosphere and Carbon becomes part of the plant, wood,
cellulose etc.  This is an endothermic reaction, more energy is absorbed
in the splitting of CO2 into C and O than is released, and thus the
plant is acting as a storage battery during its recharge cycle.

     2.) Animals take the carbon from the plant and the oxygen from the
atmosphere, and burn it in their digestive systems, which turns C and O
back into CO2 again, and releases all the energy that was stored by the
plant when it split the CO2 into C and O in the first place.  The CO2 is
released by the animal into the atmosphere making it available to be
split again by plants during the next phase of the cycle.

     Animals are a slow fire to the plant kingdom.

     When a farmer plants a single seed of corn, this process takes
energy from the sun, and CO2 from the air, and turns it into a whole
corn stalk with 500 or more corn seeds in the cob.

     This reaction is endothermic because more energy is being absorbed
into the corn than is being released during its growth, the corn stalk
is a charging battery.

     However once the farmer harvests the corn and eats it, he gets back
all that stored energy, either as food energy, or as 500 seeds to plant
500 more corn stalks, thus from his point of view the whole sow and reap
cycle is exothermic, it produces a positive return on his investment.
He puts in one seed of corn and gets back 500.

     It is actually endothermic in the growth of the corn, and
exothermic in the consumption or use (replanting) of the corn.

     Homer