Chemical Equations & Types of Reactions College Prep- Textbook Chapter 9 Unit 4

How to Balance Chemical Equations __ Al(s) + __ O 2 (g) __Al 2 O 3 (s) stoichiometric coefficients The numbers in the front are called stoichiometric coefficients. These are the numbers we use to balance the equation. The equation is balanced when there is an equal number of each element on both side of the equation. If you can count you can balance equations! Al(s) + O 2 (g) Al 2 O 3 (s) Al O

Hints for Balancing Chemical Equations There is a particular order that you can follow in balancing. It is the MINOH method which is very simple to use by inspection. Balance in the following order: M - Metals. Balance metals such as Fe or Na first. I - Ions. Looks for polyatomic ions (such as PO 4 ¯3 or SO 4 ¯2 that cross from reactant to product unchanged.. Balance them as a group. N - Non-metals. Look for Cl or S, these are common ones. O – Oxygen Remember, oxygen by itself is O 2 H - Hydrogen.Remember, hydrogen by itself is H 2 Additional Hints: Remember, you cannot change a subscript to balance the equation, nor can you add in new compounds. “Me know Chemistry, Tarzan said as he climbed the Stoichiome-tree.” Often, balancing H and O will involve water on one side or the other. In some cases when balancing, you might want to write water as HOH, instead of H 2 O. (Do this when you have H and OH on both sides of the equation!)

Practice! Practice! Practice! Balancing Chemical Equations!

Signs of Chemical Reactions There are five main signs that indicate a chemical reaction has taken place: change in colorchange in odorproduction of new gases or vapor input or release of energy Formation of a solid release input

Chemical Equations reactantsproducts Depict the kind of reactants and products and their relative amounts in a reaction. 4 Al(s) + 3 O 2 (g) 2 Al 2 O 3 (s) The numbers in the front are called stoichiometric coefficients stoichiometric coefficients. The letters (s), (g), and (l) are the physical states of compounds. reactants product aluminum oxide Reactants – the substances that exist before a chemical change (or reaction) takes place. Products – the new substance(s) that are formed during the chemical changes.

Chemical Equations & Conservation of Matter Because the same atoms are present in a reaction at the beginning (reactants) and at the end (products), the amount of matter in a system does not change. Kotz web conservation of matter Because of this principle of the conservation of matter, equation must be balanced An equation must be balanced. It must have the same number of atoms of the same kind on both sides.

Word Equations A WORD EQUATION describes chemical change using the names of the reactants and products. Write the word equation for the reaction of carbon tetrahydride gas with oxygen gas to form carbon dioxide and water. Carbon tetrahydride + oxygen Reactant Product CH 4 O2O2 CO 2 H2OH2O carbon dioxide + water

Types of Reactions Combination/Synthesis: A + B  AB –DATING Decomposition: AB  A + B –BREAKING UP Single Replacement: A + BX  B + AX –GETTING DUMPED Double Replacement: AX + BY  BX + AY –THE OLD SWITCHEROO Combustion: C x H y + O 2  CO 2 + H 2 O –A HYDROCARBON OR CARBOHYDRATE BURNING –Complete – CO 2 Incomplete – CO and C

Types of Reactions Combination/Synthesis: A + B  AB –DATING Decomposition: AB  A + B –BREAKING UP Single Replacement: A + BX  B + AX –GETTING DUMPED Double Replacement: AX + BY  BX + AY –THE OLD SWITCHEROO Combustion: C x H y + O 2  CO 2 + H 2 O –A HYDROCARBON OR CARBOHYDRATE BURNING –Complete – CO 2 Incomplete – CO and C

Combination/Synthesis A + B  AB 2 or more substances react to form a single new substance Usually release energy 2 nonmetals can combine in more than one way so you will be told the product Water + nonmetal oxide  acid Water + metal oxide  metal hydroxide

Decomposition Reactions AB  A + B Single compound broken down into two or more substances Can be difficult to predict the products Most require energy in the form of heat, light, or electricity Metal chlorates decompose into metal chlorides and oxygen gas. Metal carbonates decompose into metal oxides, and carbon dioxide

Single Replacement/Displacement A + BX  B + AX One element replaces another element in a compounds Use the activity series to predict whether a reaction will occur

Ca Activity Series- Predicting Whether A Reaction Will Occur Foiled again – Aluminum loses to Calcium Printable Version of Activity Series Printable Version of Activity Series Metal will be replaced by one that is higher in the series!

Mg + AlCl 3 Al + MgCl 2 Predict if these reactions will occur Al + MgCl 2 Can magnesium replace aluminum? Activity Series YES, magnesium is more reactive than aluminum Can aluminum replace magnesium? Activity Series NO, aluminum is less reactive than magnesium. Therefore, no reaction will occur. No reaction MgCl 2 + Al No reaction The question we must ask is can the single element replace its counterpart? metal replaces metal or nonmetal replaces nonmetal. Order of reactants DOES NOT determine how they react. Li Rb K Ba Ca Na Mg Al Mn Zn Cr Fe Ni Sn Pb H 2 Cu Hg Ag Pt Au

Single-Replacement Reactions FeCl 2 + Cu MgBr 2 + Cl 2 Zinc in nitric acid 2 A + BX AX + B General Form Zn(NO 3 ) 2 + H 2 Can Fe replace Cu? Yes Li Rb K Ba Ca Na Mg Al Mn Zn Cr Fe Ni Sn Pb H 2 Cu Hg Ag Pt Au F 2 Cl 2 Br 2 I 2 Can Zn replace H? Yes Can Br replace Cl? No NO REACTION Fe + CuCl 2 Zn + HNO 3 MgCl 2 + Br 2 Activity Series

Double Replacement/Displacement AX + BY  BX + AY Ions of two compounds exchange places in an aqueous solution to form two new compounds Driving Forces –Production of a precipitate –Production of a gas –Production of a stable molecular compound like water Use solubility rules to identify precipitates formed.

Combustion Reactions C x H y + O 2  CO 2 + H 2 O A substance combines with oxygen, releasing a large amount of energy Complete combustion of hydrocarbons produce carbon dioxide and water Incomplete combustion of hydrocarbons may produce carbon and carbon monoxide