Pre-AP Chemistry Introduction to Chemical Reactions

Chemical reactions  Processes that change one or more substances into different substances.  Described by chemical equations.  Represented by chemical symbols and formulas to show amounts of reactants (starting materials) and products (end materials)  Ex) 2 H 2 O (l) ---> 2 H 2 (g) + O 2 (g)

Chemical Reaction

Energy and reactions  Energy must be added to form chemical bonds. Breaking bonds releases energy.  Energy is conserved in chemical reactions.  Reactions that release energy are exothermic.  Reactions that absorb energy from the surroundings are endothermic.

Evidence of a chemical reaction  Substance produced different than reactants  Heat and/or light is released  Production of a gas  Color change  Precipitate is formed

Reaction Types  Synthesis- a reaction of at least two substances that forms a new, more complex compound Ex) A + B ---> AB Na + Cl---> NaCl  Decomposition- a single compound undergoes a reaction that produces two or more simpler substances. Ex) AB ---> A + B 2H 2 O 2 ---> 2H 2 O + O 2

Reaction types, cont.  Single-displacement- one element replaces a similar element in a compound. Ex) XA + B ---> AB + X 3Mg + Fe 2 O 3 ---> 2Fe + 3MgO

Single-Displacement Reaction

Types of Reactions, cont.  Double-displacement- the ions of two compounds exchange places in an aqueous solution to form two new compounds. Acid-base neutralization is an example Ex) AX + BY ---> AY + BX HCl + NaOH ---> NaCl + H 2 O

Types of Reactions, cont.  Combustion- a substance combines with oxygen, releasing a large amount of energy in the form of light and heat.  Burning of propane and gasoline are examples. C 3 H O 2 ---> 3 CO H 2 O