Chapter 8 Chemical Equations and Reactions 1
Section 8.1 Objectives: List 3 observations that suggest that a chemical reaction has taken place. List 3 requirements for a correctly written chemical reaction. Balance a formula equation by inspection. 2
Chemical vs Physical Change Physical change a change in substance that does not change its chemical composition; ex: phase changes, size changes Chemical change a change in substance that results in entirely new substance with different chemical composition and properties; ex: burning, tarnishing, rusting, baking 4
Chemical Reactions A chemical reaction is a process by which substances are changed into different substances (chemical change). Chemical reactions DO NOT destroy or change actual atoms, but they do break and rearrange bonds between atoms often combining them into different compounds or freeing atoms to be in a pure state. 5
Indicators of a Chemical Reaction 1. Evolution of heat and/or light 2. Evolution of a gas (bubbles) 3. Formation of a precipitate Precipitate = a solid that is formed as a result of a chemical reaction in a solution Sometimes, Colors change (not a positive indication of a chemical reaction) 6
Indicators of a Chemical Reaction 1. Change in temperature (drop in temperatureor evolution of heat) and/or production of light 2. Evolution of a gas (bubbles) 3. Formation of a precipitate Precipitate = a solid that is formed as a result of a chemical reaction in a solution Elephant toothpaste Sometimes, Colors change indicates a reaction but not always. Be careful what is actually changing color. If acid/base indicator, may not be a chemical reaction. 7
Cold and Hot Packs - Chemical Reactions 8
Chemical reactions are described by chemical equations - a written representation of a chemical reaction. 6H 2 O + 6CO 2 C 6 H 12 O 6 + 6O 2 The original substances are called reactants. The resulting substances are called products. Reactants Products 9
Symbols used in chemical equations + means and or reacts with means yields or produces or breaks down into or decomposes 10
More Symbols used in chemical equations: (s) solid (l) liquid (g) gas (aq) aqueous = dissolved in water Heat or Δ 11
Requirements for chemical equation: 1. Must include all reactants and products 2. Must contain correct formulas AND.. 12
3. Must satisfy Law of Conservation of Mass mass (atoms) cannot be created or destroyed in ordinary chemical and physical changes - same number of atoms of each element must be on each side of equation Equation must be balanced done with coefficients, whole numbers in front of formulas. 6CO 2 + 6H 2 O C 6 H 12 O 6 + 6O 2 Coefficients represent the relative number of MOLES of that substance. If there is no coefficient - it is assumed to be 1. 13
How do you balance a chemical equation? Na 2 O + H 2 O NaOH Only by adding coefficients. 14
NEVER CHANGE A FORMULA! H 2 O H 2 O 2 15
Assignment Using coefficients, balance the assigned equations on handout page 61. 16
Writing correct equations from sentences. 1 st identify reactants and products 2 nd write correct formulas for each reactant and product 3 rd add symbols for physical states, + and yield, catalysts, etc. 4 th balance with coefficients 17
Remember diatomic elements! 7 diatomic elements Always found as diatomic if alone in an equation. H 2, N 2, O 2, F 2, Cl 2, Br 2, I 2 Sulfur should be written as S 8 Phosphorus should be written as P 4 When pure do not include prefixes in name!!! 18
Iron reacts with water and oxygen in air to yield iron III oxide. 1 st identify reactants and products and write word equation with symbols for + and 2 nd write formula equation with correct formulas 3 rd add symbols for physical states, catalysts, etc. 4 th balance with coefficients 19
Write formula equation Solid sulfur reacts with oxygen gas to produce gaseous sulfur trioxide. 1 st identify reactants and products and write word equation with symbols for + and 2 nd write formula equation with correct formulas 3 rd add symbols for physical states, catalysts, etc. 4 th balance with coefficients 20
Dicarbon hexoxide reacts with oxygen to produce carbon dioxide and water. 1 st identify reactants and products and write word equation with symbols for + and 2 nd write formula equation with correct formulas 3 rd add symbols for physical states, catalysts, etc. 4 th balance with coefficients 21
Potassium chloride and phosphoric acid are produced when potassium phosphate reacts with hydrochloric acid. 1 st identify reactants and products and write word equation with symbols for + and 2 nd write formula equation with correct formulas 3 rd add symbols for physical states, catalysts, etc. 4 th balance with coefficients 22
Assignment Complete Handout page 62 Word Equations. 23
Section 8.2 Objectives: Define synthesis, decomposition, single-replacement, and double-replacement reactions. Classify a reaction as synthesis, decomposition, singlereplacement, and double-replacement, or combustion. Predict the products of simple reactions given the reactants. 24
Types of Chemical Reactions 1. Synthesis A + X AX 2. Decomposition AX A + X 3. Single-Replacement A + BX AX + B 4. Double-Replacement AX + BY AY + BX 5. Combustion CH 4 + O 2 CO 2 + H 2 O 25
Synthesis A + X AX Produces one product Examples: 2Fe + O 2 2FeO S 8 + 8O 2 8SO 2 26
Decomposition AX A + X One compound in the reactant side of equation. Examples: 2H 2 O 2H 2 + O 2 CaCO 3 CaO + CO 2 Ca(OH) 2 CaO + H 2 O 2KClO 3 2KCl + 3O 2 H 2 SO 4 SO 3 + H 2 O 27
Single-Replacement A + BX AX + B Also called a single-displacement Elements replace like elements (+ + - -) A + BX AX + B or Y + BX BY + X Remember if hydrogen in water is being replaced that water is HOH. 2Na + 2H 2 O 2NaOH + H 2 2Na + 2HOH 2NaOH + H 2 28
Double-Replacement AX + BY AY + BX Also called a double-displacement compound + compound compound + compound HCl + NaOH NaCl + HOH Mg(NO 3 ) + K 3 PO 4 Mg 3 (PO 4 ) 2 + KNO 3 29
Combustion When a substance combines with oxygen and burns to produce carbon dioxide and water. Hydrocarbons C 3 H 8 + 5O 2 3CO 2 + 4H 2 O 30
On handout, write the type of reaction and, where indicated, write the balanced equation. 31
Knowing the type of reaction, you can predict products. 32
Predict product(s) and write the balanced chemical equation. Single replacement reaction between magnesium bromide and chlorine 33
Predict product(s) and write the balanced chemical equation. Single replacement reaction between aluminum and iron (III) oxide 34
Predict product(s) and write the balanced chemical equation. Double replacement reaction between silver I nitrate and zinc I chloride 35
Predict product(s) and write the balanced chemical equation. Double replacement reaction between sulfuric acid and sodium hydroxide 36
Predict product(s) and write the balanced chemical equation. Decomposition of HgO into mercury and oxygen 37
Predict product(s) and write the balanced chemical equation. Synthesis of carbon dioxide from carbon monoxide and oxygen. 38
Activity Series Silently read page 271-272 Write yourself an explanation of how to use the activity series chart. 39
What will be the products? NaCl + F 2 FeCl 3 + NaOH Ag 2 O AlBr 3 + K 2 SO 4 C 8 H 18 + O 2 40
Use the Activity Series to predict the products of these possible reactions Ni + AgNO 3 Ca + HCl Ag + HCl Br 2 + NaI I 2 + NaBr 41