Q: How could you chemically describe this reaction? A: Scientists use a standard method to represent a chemical reaction, called a chemical equation. Chemical equations are used to represent CHEMICAL REACTIONS General equation for reaction I which iron rusts: General equation for reaction I which iron rusts: Fe + O 2 Fe 2 O 3 Iron + Oxygen Iron Oxide (RUST) 2Al + 3I 2 Al 2 I 6 VIDEO: Aluminum and Iodine Reaction Q: What are the reactants and products? 2Al + 3I 2 Al 2 I 6 Reactant(s) Product(s) The atoms/compounds you have BEFORE the reaction occurs. The atoms/compounds you have AFTER the reaction occurs. When is an equation balanced? When there is the same the number of each type of atom on both sides When there is the same the number of each type of atom on both sides BEFORE: 4 White (H) 1 Black (C) 4 Red (O) AFTER: 4 White (H) 1 Black (C) 4 Red (O) Chemical Equations Coefficient : numbers in front of the letters, represents how many molecules you have coefficients 4 Al (s) + 3 O 2 (g) 2 Al 2 O 3 (s) Chemical Equations Subscript: numbers behind the letters, represent how many atoms are in that molecule subscripts Chemical Equations 4 Al (s) + 3 O 2 (g) 2 Al 2 O 3 (s) The letters (s), (g), and (l) are the physical states (aq) means aqueous (aq) means aqueous The arrow means : yield/create/produce/form Learning Check 2Li (s) + 2H 2 O (l) 2LiOH (aq) + H 2 (g) What does 2 mean in front of LiOH? What does 2 to the right of H 2 mean? What does (aq) to the right of LiOH mean? Number of molecules Number of atoms of H Aqueous solution What does mean? Yield, form, produce Q: What is the chemical equation for this reaction? A: The chemical equation is: C + O 2 CO 2 Q: How have the atoms of the reactants been rearranged in the products of the reaction? C + O 2 CO 2 A: Carbon atom chemically bonds with two oxygen atoms. What bonds are broken and what new bonds have formed? A: Bonds between the Oxygen atoms have broken New bonds have formed between Carbon and the 2 Oxygens C + O=O C + O 2 CO 2 O=C=OO=C=O Bonds Break New Bonds Form Q: What type of bond has formed between the Carbon and 2 Oxygens? C + O=O C + O 2 CO 2 O=C=OO=C=O Bonds Break New Bonds Form A: COVALENT Bond (Nonmetal to nonmetal) The charcoal used in a grill is basically carbon. The carbon reacts with oxygen to yield carbon dioxide. The chemical equation for this reaction, C + O 2 CO 2, Is this a balanced equation? YES RP Count the number of atoms of each element found in the reaction. 1 C 2 O Learning Check Q: What needs to happen for a chemical reaction (change) to take place? A: Bonds between atoms of the reactants break and NEW bonds form to create the products Learning Check Q: Is this chemical reaction correct? Explain why. A: No. The numbers of each type of square on both sides are not equal + + Learning Check Why is this reaction correct? The numbers of each type of atom on both sides are equal. (so the atoms rearranged) + + NEW PRODUCTS To Balance and equation, you are only allowed to add Coefficients (the numbers in front of chemical formulas in the equation) You CANNOT add or change the subscripts because this would change the identity of the molecules The order of the Coefficients in the Chemical Equation is important because this is how you write the COEFFICIENT RATIO. For example: O 2 is Oxygen but O 3 is Ozone Balancing using shapes ____H 2 + ____O 2 ____H 2 O Is this reaction balanced? Now fix the H on the left. BALANCED ! 221 Balancing Equations using T-chart ___ H 2 (g) + ___ O 2 (g) ___ H 2 O(l) This equation is NOT balanced! 1. Count the number of atoms of each element found in the reaction. RP H - 2 O - 2O - 1 R P H - 2 H - 2 O - 2 O - 1 Balancing Equations using T-chart ___ H 2 (g) + ___ O 2 (g) ---> ___ H 2 O(l) Don t forget to recount. 2. Add coefficients to balance the atoms Now fix the H on the left. Don t forget there is a 1 in front of O 2. Now it is balanced! _____Fe + ____O 2 ____Fe 2 O 3 Now You Try! Coefficient ratio: 4:3:2 432 Find the common denominator: 6 6/3 = 2 Now fix the Fe atoms 2 x 2 = 4 6/2 = 3 Now You Try Again! Al + O 2 Al 2 O 3 3 RP 1 Al 2 Al 2 O3 O x 2 = 6 2:3 find a common multiple 2 2 x 2 = x 3 = 6 Coefficient ratio: 4:3:2 RULE: Balance O and H Last!