1. Chemical Reactions The process in which one or more substances are converted into new substances with different chemical and physical properties.

2. Chemical Reactions Atoms & Compounds undergo chemical reactions to achieve stability. During a chemical reaction: ● chemical bonds form ● chemical bonds break ● atoms rearrange Reactants → Products (substances that enter rxn) (substances produced by rxn)

3. Evidence of Chemical Reactions Energy changes in the form of heat and light Production of a gas Formation of a precipitate Color change

4. Representing Chemical Reactions Word Equations: Magnesium + Oxygen → Magnesium Oxide Dihydrogen monoxide → Hydrogen + Oxygen Formula Equations: 2Mg + O 2 → 2MgO 2H 2 O → 2H 2 + O 2

5. Law of Conservation of Mass In an ordinary chemical reaction or physical change, mass cannot be created nor destroyed. mass of reactants = mass of products # atoms of each element of reactants = # atoms of each element of products

6. Balancing Chemical Equations Mg+O 2 → MgOunbalanced 1Mg1 2O1 To balance an equation, COEFFICIENTS are placed in front of formulas in the chemical equation: 2Mg+O 2 → 2MgObalanced 2Mg2 2O2

7. Balancing Chemical Equations Coefficient  a small whole number that appears in front of a chemical formula & specifies the relative number of moles of a substance 2Mg+O 2 → 2MgO means 2 moles of Mg + 1 mole of O2  2 moles of MgO *When 2 moles of magnesium reacts with 1 mole of oxygen, 2 moles of magnesium oxide are produced.

8. How to Balance Chemical Reactions:

9. Balancing Equation Practice Try these individually … the solutions are on the next slide. Mg +N 2 → Mg 3 N 2 O 2 +CS 2 → CO 2 +SO 2 KNO 3 → KNO 2 +O 2 Al(NO 3 ) 3 + NaOH → Al(OH) 3 +NaNO 3 Fe+H 2 SO 4 → Fe 2 (SO 4 ) 3 + H 2

10. Balancing Equation - Solutions 3Mg +N 2 → Mg 3 N 2 3O 2 +CS 2 → CO 2 +2SO 2 2KNO 3 → 2KNO 2 +O 2 Al(NO 3 ) 3 + 3NaOH → Al(OH) 3 +3NaNO 3 2Fe+3H 2 SO 4 → Fe 2 (SO 4 ) 3 + 3 H 2