4.1 Introduction to Chemical Reactions

All chemical reactions: have two parts Reactants - the substances you start with Products- the substances you end up with The reactants turn into the products. Reactants  Products

Describing chemical reaction The way atoms are joined is changed Atoms aren’t created or destroyed. Can be described several ways In a sentence : Copper reacts with chlorine to form copper (II) chloride. In a word equation: Copper + chlorine  copper (II) chloride In a chemical equation: Cu (s) + Cl 2 (g)  CuCl 2 (aq)

Symbols used in equations (s) after the formula –solid Cu (s) (g) after the formula –gas H 2 (g) (l) after the formula -liquid H 2 O (l) (aq) after the formula - dissolved in water, an aqueous solution. CaCl 2 (aq)

Symbols used in equations indicates a reversible reaction. shows that heat is supplied to the reaction., or is used to indicate a catalyst used supplied, in this case, platinum., indicates a pressure other than STP

Indicators of chemical reactions Formation of a gas Emission of light or heat Formation of a precipitate Color change Emission of odor

There are five types of chemical reactions that we will learn in this course:

Copyright © 2010 McGraw-Hill Ryerson Ltd. Writing Chemical Equations A chemical equation is a representation of what happens to the reactants and products during a chemical change. There are three forms of chemical equations. 1. Word Equations show the names of the reactants and products, with an arrow dividing reactants on the left from products on the right. 2. Skeleton Equations replace the names of the reactants and products with their chemical formulas. 3. Balanced Chemical Equations add coefficients in front of the skeleton reactants and products to balance the equations.

Balancing Equations

Copyright © 2010 McGraw-Hill Ryerson Ltd. Tips for Balancing Chemical Equations The following tips can help you avoid errors when balancing equations.

Aluminum metal reacts with liquid bromine to form solid aluminum bromide Translate Equation

1.calcium fluoride and sulfuric acid make calcium sulfate and hydrofluoric acid 2. calcium carbonate will come apart when you heat it to leave calcium oxide and carbon dioxide. 3. aluminum sulfate and calcium hydroxide become aluminum hydroxide and calcium sulfate. 4. copper metal and silver nitrate react to form silver metal and copper (II) nitrate. Translate some equations!