Chemical Reactions

A chemical reaction occurs when elements and compounds combine and form a new arrangement of those elements and compounds. Chemical changes occur during a chemical reaction.

Endothermic Reactions Endothermic Reactions ABSORB heat and feel cooler. Cold packs are an example. –The outer pouch contains water. The inner pouch contains ammonium-nitrate. –When you “pop” the inner pouch, the chemical reaction absorbs heat energy from the surroundings. This is an endothermic reaction. –The temperature of the solution falls to about 35 F for 10 to 15 minutes.

Exothermic Reactions Exothermic Reactions release heat when the chemical change occurs. Heat EXITS the system and the surroundings usually feel warmer.

Components of A Chemical Equation Ag + H 2 S Ag 2 S + H 2 REACTANTS PRODUCTS The elements on the left of the arrow combined and rearranged to form the elements and compounds on the right. REACTANTS are ALWAYS on the LEFT and PRODUCTS are ALWAYS on the RIGHT. 2

In an ENDOTHERMIC REACTION… Energy is on the left side with the REACTANTS since it is being absorbed. 2KClO 3 + Energy 2KCl + 3O 2

In an Exothermic Reaction… Energy is on the right side with the PRODUCTS since it is being released. 3H 2 + N 2 2NH 3 + ENERGY