CHEMICAL Equations

Chemical Changes vs. Physical Changes Physical changes are changes in the physical appearance, state or size of a substance. Chemical changes are changes in the arrangements and connections between ions and atoms, and a change in chemical properties.

Example of a physical change: Melting Ice

Example of a chemical change: “Burning” Magnesium Ribbon

Chemical Equations Is a representation (in words or symbols) of a chemical reaction Provides information about: The reactants (the starting materials) The products (the materials produced )

WORD EQUATION Not much information other than the elements/compounds involved Potassium metal + oxygen gas  potassium oxide Products are on the right-hand side of the equation Reactants are on the left-hand side of the equation + sign means “reacts with” Arrow means produces/yields/ makes

Components of a Chemical Equation 6 CO2(g) + 6 H2O(g)  C6H12O6(s) + 6 O2(g) Coefficients- numbers in front of the formulae that show the ratio of the reactant(s) and product(s) States of matter- indicate the state of the substance reacting or being produced ; (g)= gas, (l)= liquid, (aq)= aqueous, and (s) = solid

States of matter: A small piece of sodium which lived in a test tube fell in love with the Bunsen burner: "Oh Bunsen, my flame. I melt whenever I see you . . .", the sodium pined. "It's just a phase you're going through", replied the Bunsen burner.

Counting Atoms in Equations In order to determine how many atoms of each element are involved in a chemical equation you must always watch two things: The subscripts in the formula The coefficient in front of the formula CuCl2 Means 2 chlorine atoms/ ions in the molecule Means two water molecules, each of which has 2 H atoms and 1 oxygen atom 2H2O

Examples of counting atoms How many oxygen atoms are indicated by each formula: CO C6H12O6 2 SO2 Mg(OH)2 3Sn(Cr2O7)2 1 6 4 2 42

ASIDE! THE “FANCY SEVEN”  When these atoms are elements (i.e. they are all on their own) they are DIATOMIC (they are in pairs) e.g. N2 O2 F2 Cl2 Br2 I2 H2

Law of Conservation of Mass This LAW states that the total mass of all products always equals the total mass of all reactants