Types of Reactions and Balancing

Curriculum Big Idea: Chemical reactions are predictable Concept: Common chemical reactions can be categorized as synthesis, decomposition, single replacement, double replacement, or combustion. PA Standard: 3.2.C.A2 Predict the chemical formulas for simple ionic and molecular compounds.

Today’s Agenda Opener: What is evidence of a chemical reaction? Notes on chemical reactions Practice Determining the Type and Balancing Reactions Closure Question (see the last slide) Take Home Assignment: 11.1 Section Assessment

Word Equations Reactants  products Examples: Methane + oxygen  carbon dioxide + water Hydrogen peroxide  water + oxygen Iron + oxygen  iron(III) oxide To write a word equation, write the names of the reactants to the left of the arrow separated by plus signs; write the names of the products to the right of the arrow, also separated by plus signs.

Chemical Equations Chemical Equation – a representation of a chemical reaction; the formulas of the reactants (on the left) are connected by an arrow with the formulas of the products (on the right). Examples: Fe + O 2  Fe 2 O 3 Fe(s) + O 2 (g)  Fe 2 O 3 (s)

Catalysts Catalyst – a substance that speeds up the reaction but is not used up in the reaction (neither a reactant nor a product) Example: MnO 2 is a catalyst in the following reaction: MnO 2 H 2 O 2 (aq)  H 2 O(l) + O 2 (g)

Chemical Reactions How can we tell a chemical reaction has taken place?  Temperature change  Color change  Odor  Gas bubbles  Appearance of a solid

Chemical Reactions Representing chemical reactions  Reactants: starting substances  Products: substances formed during the reaction  Word equation: indicates the reactants and products of a chemical reaction. Chemical equations: statement that uses chemical formulas to show the identities of substances. Diatomics- H 2, O 2, N 2, F 2, Cl 2, Br 2, I 2

Chemical Reactions Practice Write the word equation for the reaction in which magnesium reacts with chlorine to produce magnesium chloride. Write the word equation for the reaction in which water decomposed into hydrogen and oxygen.

Chemical Reactions Balancing Chemical Equations coefficient: the number written in from of the reactants or products. steps: 1.Write the chemical equation for the reaction. ex. NaOH + CaBr2  Ca(OH)2 + NaBr 2.Count the atoms of the elements in the reactants and the products.

Chemical Reactions 3.Count the atoms of elements in the products. 4.Change the coefficients to make the number of atoms of each element equal on both sides of the equation. 5.Write the coefficients in their lowest possible ratio. 6.Check your work.

Classifying Reactions Combination Reaction – a chemical change in which two or more substances react to form a single new substance. Example: 2Mg(s) + O 2 (g)  2MgO(s)

Classifying Reactions Decomposition Reaction – a chemical change in which a single compound breaks down into two or more simpler products. Example: 2H 2 O(s)  2H 2 (g) + O 2 (g)

Classifying Reactions Single-Replacement Reaction – a chemical change in which one element replaces a second element in a compound Example: 2K(s) + 2H 2 O(l)  2KOH(aq) + H 2 (g)

Activity Series Activity Series (p. 333) – lists metals in order of decreasing reactivity. A reactive metal will replace any metal listed below it in the activity series. Example: Br 2 (aq) + NaI(aq)  NaBr(aq) + I 2 (aq) Br 2 (aq) + NaCl(aq)  No reaction

Classifying Reactions Double Replacement Reaction – a chemical change involving an exchange of positive ions between two compounds Example: Na 2 S(aq) + Cd(NO 3 ) 2 (aq)  CdS(s) + 2NaNO 3 (aq)

Classifying Reactions Combustion Reaction – is a chemical change in which an element or a compound reacts with oxygen, often producing energy in the form of heat and light. Example: 2C 8 H 18 (l) + 25O 2 (g)  16CO 2 (g) + 18H 2 O(l)

Learning Check Classify the following reactions as 1) combination or 2) decomposition: ___A. H 2 + Br 2  2HBr ___B. Al 2 (CO 3 ) 3  Al 2 O 3 + 3CO 2 ___C. 4 Al + 3C  Al 4 C 3

Learning Check Classify the following reactions as 1) single replacement 2) double replacement __ A. 2Al + 3H 2 SO 4  Al 2 (SO 4 ) 3 + 3H 2 __B. Na 2 SO 4 + 2AgNO 3  Ag 2 SO 4 + 2NaNO 3 __C. 3C + Fe 2 O 3  2Fe + 3CO

Predicting the Products of a Chemical Reaction The number of elements and/or compounds reacting is a good indicator of possible reaction type and thus possible products. See pages

Closure Balance the following equation: H 2 + O 2  H 2 O