Chemical Reactions: Chemical ChangesChemical Changes involve a re- arrangement of atoms producing new substances with new properties. A chemical change cannot easily be reversed.

physical changeA physical change does not produce a new substance and can be easily reversed –Examples of physical changes include boiling, melting, freezing, dissolving….

The Equation: Original Substances → New Substances (Reactants)(Products) A (s) + B (l) → C (g) + D (aq) Where: +Reads “plus” or “and” or “reacted with” → Reads “yields” or “produces” (s) Solid (l) Liquid (g) Gas (aq) aqueous (dissolved in water)

Word Equation: Carbon Dioxide Water Vinegar Baking Soda Salt

Skeleton Equation: CO 2 H2OH2OH2OH2O CH 3 COOH NaHCO 3 NaC 2 H 3 O 2

Balanced Equation: CO 2 H2OH2OH2OH2O CH 3 COOH NaHCO 3 NaC 2 H 3 O 2 Balance this equation for bonus marks

Balancing equations: The number of atoms in the reactants and number of the atoms in products must balance. Place the correct coefficients in front of each formula (you do not need to write 1’s) to balance the reactants and products ___K + ___O 2 → ___K 2 OK=O=

Balancing equations You can also balance from left to right Remember you cannot change the subscripts in the formulas of the compounds. ___Fe 2 O 3 → ___Fe + ___O 2

Other hints: Save balancing the hydrogen and oxygen until the end for very large equations ___Al(OH) 3 + ___H 2 CO 3 → ___Al 2 (CO 3 ) 3 + ___H 2 O

Other hints: You can reduce coefficients, but it is an all or nothing process! __Mg(OH) 2 + __ HCl → __ MgCl 2 + __ H 2 0

Assignment: Workbook: –Read p –Questions P77 Q1-20, p78 Q1-12 –Be careful of diatomic molecules (H 2, O 2 …) –Use Pencil…or things will get messy!

Classifying chemical reactions: Intro: Compound: when two or more different elements are combined ex: H 2 O, CaCO 3, Al 2 (SO 4 ) 3 Free element: when an element is not combined with another (Al, Fe, Zn) –Sometimes a free element can be combined with itself Cl 2, O 2, H 2 (diatomic molecules) even P 4 and S 8

1) Synthesis: When free elements combine into a compound Free + Free → Compound A + B → AB 2Al + 3Cl 2 → 2AlCl 3 4K + O 2 → 2K 2 O

2) Decomposition: The opposite of synthesis When a compound breaks up into free elements. Compound → Free + Free + … AB → A + B 2NaCl → 2 Na + Cl 2 8CaSO 4 → 8Ca + S O 2

3) Single Replacement: When a free element and a compound react. A + BC → Free + Compound → Na + MgCl 2 → CaI 2 + O 2 →

4) Double Replacement When two compounds react AB + XY → BaBr 2 + K 2 O → Na 2 CO 3 + MgCl 2 → Compound + Compound → 2 new compounds

5) Neutralization: ACIDBASEA special double replacement reaction between an ACID and a BASE Acid and Base → Salt and Water HCl + NaOH → NaCl + H 2 O

Assignment: p 123 quick check P 131 Q# 1-3