Wednesday, Sept. 4 th : A Day Thursday, Sept. 5 th : B Day Agenda Homework questions/collect (pg. 274: 1-6 & WS) Quiz Sec. 8.2: Balancing Chemical Equations Sec. 8.3, Day 1: Classifying Chemical Reactions Combustion, synthesis, decomposition Homework: 1. Sec. 8.3 review, pg. 285: #1-4, 8b,c,f, 10a,b,e,f, 12 2. Practice pg. 279: #1-4 3. Concept Review: Classifying Chemical Reactions 1-3, 6-9 only
Homework Questions Pg. 274: #1-6 Chemical Formulas and Equations Worksheet Writing Chemical Formulas Worksheet
Section 8.2 Quiz Balancing Chemical Equations As always, you may use your guided notes and book on the quiz May the FORCE be with you!
Diatomic Elements Before we begin this section, remember that the following elements are diatomic and exist as molecules H 2, O 2, N 2, F 2, Cl 2, Br 2, I 2
Sec. 8.3 Classifying Chemical Reactions By classifying chemical reactions into several types, the products that are likely to form are more easily predicted. Also, reactions of each type follow certain patterns, which will make balancing them easier. The 5 types of reactions that are covered in this section are.
5 Types of Chemical Reactions 1.Combustion 2.Synthesis (sometimes called combination) 3.Decomposition 4.Single Displacement 5.Double Displacement
Combustion Reactions Combustion reaction: the oxidation reaction of an organic compound, in which heat is released. The reaction of a carbon-based compound with oxygen. Products are always carbon dioxide, CO 2, and water vapor, H 2 O. C 3 H 8 + 5 O 2 3 CO 2 + 4 H 2 O (Complete combustion of propane, C 3 H 8 )
Combustion Reactions If theres not enough oxygen present, the combustion reaction is INCOMPLETE. Carbon monoxide, CO, and unburned carbon (soot) are produced along with CO 2 and H 2 O. 2 C 3 H 8 + 7 O 2 2 C + 2 CO + 2 CO 2 + 8 H 2 O (Incomplete combustion of propane, C 3 H 8 ) **Combustion reactions can be tricky to balance**
Synthesis Reaction Synthesis Reaction: a reaction in which two or more substances combine to form a new compound. (Occasionally more than 1 product) A single compound forms from 2 or more reactants. If the reaction only has 1 product, its a synthesis reaction. Many times, the reactants are 2 elements or 2 small compounds. Sometimes called combination reactions
Synthesis Reactions Two Elements Form a Binary Compound If the reactants are 2 elements, the only way they can react is to form a binary compound, which is composed of 2 elements. When a metal reacts with a non-metal, an ionic compound forms and the charges on the ions can be used to predict the formula for the compound that will be formed. 2 Na + Cl 2 2 NaCl (synthesis of sodium chloride)
Synthesis Reactions Two Elements Form a Binary Compound When 2 non-metals react, often more than one compound could form, so predicting the products of these reactions is not always easy. C + O 2 CO 2 2 C + O 2 2 CO You will probably need more information to predict the products of these reactions and to balance them correctly.
Synthesis Reactions 2 Compounds Form a Ternary Compound Two compounds can combine to form a ternary compound, a compound composed of 3 elements. CaO(s) + H 2 O(l) Ca(OH) 2 (s) **(Group 1 or 2 metal oxides react w/water to form a metal hydroxide)** CO 2 (g) + H 2 O(l) H 2 CO 3 (aq) (Some oxides of non-metals can combine w/water to produce acids)
Decomposition Reactions Decomposition Reaction: a reaction in which a single compound breaks down to form two or more simpler substances. Decomposition reactions are the OPPOSITE of synthesis reactions - only 1 reactant A single compound breaks down, often with the input of energy, into 2 or more elements or simpler compounds
Decomposition Reactions If your reactant is a binary compound, then the products will most likely be the 2 elements that make up the compound. 2 H 2 O(l) electricity O 2 (g) + 2 H 2 (g) (decomposition of water)
Decomposition Reactions Compounds made up of 3 or more elements usually dont decompose into those elements. CaCO 3 (s) heat CaO(s) + CO 2 (g) **(A metal carbonate decomposes to form a metal oxide and carbon dioxide)** **A compound with a polyatomic ion, like CO 3, will likely break down to a simpler substance, like CO 2 **
Sample Problem D, Pg. 279 Predicting Products Predict the product(s) and write a balanced equation for the reaction of potassium with chlorine. Reactants: Potassium, K, and chlorine, Cl 2 Because the reactants are 2 elements, the reaction is most likely a synthesis reaction. K will LOSE 1 electron to form K + and Cl will GAIN an electron to form Cl - so the formula for the product will be KCl. K + Cl 2 KCl Lastly, balance the equation: 2 K + Cl 2 2 KCl
Additional Example Predict the product(s) and write a balanced equation for the reaction of pentane, C 5 H 12, with oxygen. Reactants: pentane, C 5 H 12, and oxygen, O 2 Because the reactants are a hydrocarbon and oxygen, we have a combustion reaction. Products: CO 2 and H 2 O C 5 H 12 + O 2 CO 2 + H 2 O Lastly, balance the equation: C 5 H 12 + 8 O 2 5 CO 2 + 6 H 2 O
Additional Example Predict the product(s) and write a balanced equation for the decomposition of sodium chloride, NaCl. Reactant: Sodium chloride, NaCl Because we have 1 reactant, the reaction is a decomposition reaction. NaCl Na + Cl 2 Lastly, balance the equation: 2 NaCl 2 Na + Cl 2
Homework Sec. 8.3 review, pg 285: 1-4, 8b,c,f, 10a,b,e,f, 12 Practice box, pg. 279: #1-4 Concept Review, Classifying Chemical Reactions: 1-3, 6-9 We will finish section 8.3 next time High School Open House: Tonight, 6:30 -8:00 pm