Chemical Reactions: The dance of the atoms

Chemistry basics Chemical reactions are the rearrangement of atoms The reactants are the molecules & atoms that start the reaction. The products are the molecules & atoms that are formed by the reaction. Energy is either released or absorbed during a reaction

Energy & Chemical reactions Energy must be added to break chemical bonds Forming bonds releases energy Exothermic reactions release energy (often as heat) Endothermic Reaction require energy (often colder after reaction)

Reaction Types Synthesis Decomposition Single displacement Double Displacement Combustion

Synthesis At least two reactants make a product A + B = AB Photosynthesis is an example of a Synthesis Reaction. 6CO H 2 O  C 6 H 12 O 6 + O 2

Decomposition Larger molecules are broken into smaller ones. A B  A + B Respiration is an example of a Decomposition Reaction. C 6 H 12 O 6 + O 2  6CO H 2 O

Single Displacement elements trade places AX + B  A + BX Example of a Single Displacement Reaction: 3CuCl 2 + 2Al  2AlCl 3 + 3Cu The more reactive element replaces the less reactive one in Single Displacement Reactions.

Double Displacement Two Compounds Exchange Ions AX + BY  AY + BX An example of Double Displacement Reaction: Pb(NO 3 ) 2 + K 2 CrO 4  PbCrO 4 + 2KNO 3

Combustion Oxygen gas is a reactant Examples of Combustion Reactions: 2CH 4 + 4O 2  2CO 2 + 4H 2 O 2CH 4 + 3O 2  2CO + 4H 2 O 2CH 4 + 2O 2  2C + 4H 2 O When there is not enough oxygen for this Combustion Reactions carbon monoxide or soot will be produced instead of carbon dioxide.

Reaction Review Two substances are combined to make one Oxygen gas is a reactant Two compounds trade places One element trades places with another Substances are broken apart

Review 1.What kind of reaction releases heat? 2.What kind of reaction requires oxygen gas? 3.What kind of reactions is the break down of large molecules into smaller ones?