Changing Matter Matter can be changed two ways: Physically Chemically October 10, 2006 Changing Matter Matter can be changed two ways: Physically Physical reaction Physical change Chemically Chemical reaction Chemical change

Physical Changes Do NOT CHANGE THE TYPE OF MATTER Nothing new or different is formed Could be a change in: Mass Volume Density Change in state Color Shape Size

Examples of Physical Changes Boiling Freezing Dissolving Breaking Making a mixture 2 or more types of matter (substances) mixed together Not in specific amounts Can be separated physically

Chemical Changes Atoms have electrons arranged in energy levels or energy shells Electrons in the last (outermost) shell are called valence electrons Valence electrons let atoms bond with other atoms Ionic bonding Gaining or losing electrons Covalent bonding Sharing electrons

Chemical Changes Atoms that bond form molecules May be the same type of atom or, Different types of atoms Different types  compounds

Chemical Changes Molecules can bond and “unbond” Atoms can re-arranged in different combinations For example: CaCO3 (1 atom Ca, 1 atom C, 3 atoms O) Add heat to re-arranged the atoms: CaO CO2

Chemical Changes Evidence of a chemical reaction Formation of gas Formation of precipitate Change in color Change in energy Endothermic Absorbs heat energy (gets cold) Exothermic Releases heat energy (gets hot)

Chemical Changes Chemical reactions can be represented by equations CaCO3  CaO + CO2 Reactants Products

Chemical Changes Atoms are re-arranged, NOT created or destroyed Law of Conservation of Matter Law of Conservation of Mass

Chemical Changes Matter is conserved  type of atoms does not change Nothing is created or destroyed Mass is conserved  amount of atoms cannot change

Chemical Changes To show conservation of mass  Balance equations Make sure there are the same number of each type of atom in the products and in the reactants

The equation for the burning of methane gas in oxygen is: Balancing Equations The equation for the burning of methane gas in oxygen is: CH4 + 2 O2 → CO2 + 2 H2O Subscript Shows # of atoms Coefficient Shows # of molecules

Balancing Equations 1 C  1 C 4 H  4 H 4 O  4 O No subscript or coefficient is understood to be 1 CH4 + 2 O2 → CO2 + 2 H2O = C1H4 + 2 O2 → C1O2 + 2 H2O1 1 C  1 C 4 H  4 H 4 O  4 O

Types of Chemical Reactions Synthesis Reaction 2 or more simple substances combine to form a more complex substance. A+B  AB Decomposition Reaction A more complex substance breaks down into its more simple parts AB  A + B

Types of Chemical Reactions Replacement Reactions AB + CD  AD + CD