14.1 Chemical Reactions ANNE - 1: start at 7; 2: done; 3: start at 6; 4: done

Chemical Reactions Chemical reaction: the process of breaking chemical bonds and reforming new bonds to make new substances

Evidence of Chemical Change Four indicators of a chemical change: 1. Formation of new gas 2. Formation of new solid 3. Release energy (heat or light) 4. Color change Coke and Chlorine Iodine Clock Reaction Chameleon Reaction

Reactants and Products Reactant: starting substance(s) Product: new substance(s) formed

Reaction Symbols arrow = “to produce” The small symbols in the parentheses (s, l, g, aq) indicate the phase of each substance in the reaction. Symbol Meaning (s) solid (l) liquid (g) gas (aq) aqueous - dissolved in solution

Law of Conservation of Mass Mass cannot be created or destroyed, only rearranged.

Law of Conservation of Mass Mass of reactants = mass of products

Example 5.0 g of magnesium (Mg) burns in 1.0 g of oxygen (O2). How many grams of magnesium oxide (MgO) should be produced? Mg + O2  MgO 6 g

Check-In 10.2 g of Lithium Fluoride (LiF) and an unknown amount of sodium chloride (NaCl) react to form 13.5 g of Lithium chloride (LiCl) and 21.2 g of Sodium fluoride (NaF). How many grams of sodium chloride reacted? LiF + NaCl  LiCl + NaF 24.5 g

A Reminder: Numbers in Chemical Formulas

Balancing Chemical Equations The law of conservation of mass tells us that atoms and molecules must be balanced on both sides of a chemical equation.

Balancing Chemical Equations coefficient subscript Rules: Subscripts (small numbers) CANNOT be changed. Coefficients (big numbers) placed in front of the chemical formula. A coefficient applies to ALL atoms in the chemical formula. Multiply coefficients by subscripts to get the total atoms.

Balancing Chemical Equations coefficient subscript Write in pencil So you can Erase!! Balancing Steps: Draw a line to separate reactants from products Make a list! – each element on each side --Write in the same order Add coefficients if needed (change your list!)

Balancing Chemical Equations ___Li2S + ___ Cl2 → ___ LiCl + ___S

Balancing Chemical Equations ___Mg + ___ O2 → ___ MgO

Balancing Chemical Equations Example #1 ___Cu2S + ___ O2 → ___ Cu2O + ___ SO2

Balancing Chemical Equations Example #2 ___ Al + ___ O2 → ___ Al2O3

Balancing Chemical Equations EXIT SLIP ___ CO2 + ___ H2 → ___ CH4 + ___ H2O

Hints for balancing: Save single elements (Al, Cu, Na) and diatomic molecules (I2, Cl2, O2) for last. C2H4 + O2 → CO2 + H2O

Hints for balancing: Find Common Multiples KClO3 → KCl + O2

Hints for balancing: Keep polyatomic ions together H2SO4 + Ca3(PO4)2 → Ca(H2PO4)2 + CaSO4