Chemical Reactions
Exothermic Reactions
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reactions that release heat – gives off energy in the form of heat… therefore feel hot
happens when you burn an object in the presence of oxygen
when your body metabolizes food it gives off heat… this is an exothermic reaction
Endothermic Reactions
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reactions that absorb heat – take up energy in the form of heat… therefore feel cold
Chemical Reactions Involving Oxygen
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the most common type of chemical reactions involve oxygen
Combustion:
 a chemical reaction that occurs when oxygen reacts with a substance to form a new
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substance and give off energy (heat)
this is a highly EXOTHERMIC reaction
combustion required FUEL, OXYGEN and FUEL – combustion triangle – if one is
missing there is no reaction
fire is the most common example of a combustion reaction
wood + oxygen → heat + light + carbon dioxide + water
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fire is perhaps the first chemical reaction used by humans
combustion also occur in the engine of a car or in your barbeque
gasoline or propane + oxygen → energy + water + carbon dioxide
Corrosion:
 a slow chemical reaction that occurs when oxygen in the air reacts with a metal
 the reaction is enhanced when there is moisture in the air
 this is called oxidation of metals (or rocks)
 a common example is rust such as what we see on a car
iron
4 Fe (s)
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+
+
oxygen
3O2 (g)
→
→
iron oxide
2Fe2O3 (s)
once corrosion starts it can accelerate… because there is more and more surface area for
the reaction to occur on
one way to protect metal from corrosion is to apply a thin coat of paint which eliminates or
slows down the contact between the iron and the oxygen
some metals are coated with zinc, which is more resistant to corrosion … this is called
galvanizing
sometimes harder metals like chromium are used as a coating to protect softer metals like
iron … the process of coating one metal with another is called electroplating
Cellular Respiration:
 a chemical reaction that takes place in the cells of our body
food (glucose) + oxygen → energy + water + carbon dioxide
C6H12O6 (s)
+ O2 → energy + H2O +
CO2