Download 1) COMBINATION REACTION

Out of my mind
BACK IN 5 MINUTES
A CHEMICAL REACTION IS A REARRANGMENT
OF ATOMS IN WHICH SOME OF THE
ORIGINAL CHEMICAL BONDS ARE BROKEN AND
NEW BONDS AFE FORMED TO GIVE DIFFERENT
CHEMICAL STRUCTURES.
A + B  C + D
reactants
products
REACTANTS ARE THE THINGS YOU START
OUT WITH, AND PRODUCTS ARE THE THINGS
YOU END UP WITH.
HOW DO YOU KNOW A CHEMICAL
REACTIION OCCURRED?
1) THE REACTANTS DISAPPEAR OR ARE
REDUCED IN QUANTITY.
2) THE NEW SUBSTANCES THAT APPEAR
(PRODUCTS) HAVE DIFFERENT
PROPERTIES THAN THE REACTANTS.
3) ENERGY (HEAT, LIGHT, SOUND,
ELECTRICITY) IS RELEASED OR
ABSORBED.
CHEMICAL REACTIONS CAN BE DIVIDED
INTO SEVERAL DIFFERENT TYPES:
1) COMBINATION REACTION (SYNTHESIS).
HERE, TWO REACTANTS COMBINE TO GIVE
A PRODUCT.
A + B  AB
AN EXAMPLE WOULD BE MAGNESIUM METAL
REACTING WITH OXYGEN TO FORM MgO,
MAGNESIUM OXIDE.
2Mg + O2  2 MgO
2) DECOMPOSITION REACTION – JUST THE
REVERSE OF A COMBINATION REACTION. A
SUBSTANCE IS BROKEN DOWN INTO TWO OR
MORE SIMPLER SUBSTANCES.
AB  A + B
AN EXAMPLE WOULD BE WATER
DECOMPOSING INTO HYDROGEN AND
OXYGEN.
2 H2O  2 H2 + O2
3) SINGLE REPLACEMENT REACTION – ONE
ELEMENT REPLACES ANOTHER IN A
COMPOUND.
A + BC  B + AC
AN EXAMPLE WOULD BE ALUMINUM IN THE
THERMITE REACTION:
Al + Fe2O3  2Fe + Al2O3 + lots of heat
4) DOUBLE REPLACEMENT REACTION – TWO
SUBSTANCES CHANGE PLACES WITH EACH
OTHER IN COMPOUNDS – TYPICAL IN
PRECIPITATION REACTIONS.
AB + CD  AD + BC
AN EXAMPLE WOULD BE POTASSIUM IODIDE
REACTING WITH LEAD (II) NITRATE TO
FORM LEAD (II) IODIDE AND POTASSIUM
NITRATE:
2 KI + Pb(NO3)2  2 KNO3
+ PbI2 (yellow)
5) COMBUSTION REACTIONS – COMMON
WITH HYDROCARBONS.
A HYDROCARBON REACTS WITH OXYGEN
TO FORM CARBON DIOXIDE AND WATER.
CH4 + O2  CO2 + 2 H2O
REACTIONS CAN EITHER GIVE OFF HEAT
OR ABSORB HEAT DEPENDING ON
WHETHER THE REACTANTS HAVE MORE
ENERGY IN THEIR CHEMICAL BONDS THAN
THE PRODUCTS.
EXOTHERMIC REACTION – HEAT RELEASED
A PRACTICAL APPLICATION OF
EXOTHERMIC REACTIONS IS IN THE
HEATER PACKS USED IN “MRE’S” – MEALS
READY TO EAT. THESE USE THE
OXIDATION OF MAGNESIUM:
Mg + 2H2O  Mg(OH)2 + H2 + heat
AN ALLOY OF MAGNESIUM AND IRON IS
USED, AND THESE CAN PRODUCE ENOUGH
HEAT TO BOIL WATER.
ENDOTHERMIC REACTION – HEAT ABSORBED
A GOOD EXAMPLE OF AN ENDOTHERMIC
REACTION IS THE REACTION OF BAKING
SODA AND CITRIC ACID.
ANOTHER WOULD BE DISSOLVING
AMMONIUM CHLORIDE IN WATER.
ALL CHEMICAL REACTIONS REQUIRE A
CERTAIN AMOUNT OF ENERGY TO GET
THEM STARTED.
THIS MINIMUM AMOUNT OF ENERGY IS
CALLED THE ACTIVATION ENERGY.