Chemical Reactions A process in which one or more substances are converted into new substances with different chemical and physical properties Examples? Substances that enters into a chemical reaction are the reactants Substances that are produced from chemical reactions are the products Reactants  Products

Reasons for chemical reactions What accounts for the ability of different substances to undergo chemical reactions The arrangement of electrons in an atom determines whether it will bond with other atoms and with which atoms it will bond with. During a chemical reaction, bonds are broken, atoms are rearranged, and new bonds are created as new substances are created.

Chemical Equations Chemical Reactions are represented by sentences known as chemical equations A chemical equation describes what happens in a chemical reaction Identifies the reactants and the products

Word Equations Simplest type of equation Give only the names of the reactants and products Write the following word reactions: Hydrogen gas is burned in oxygen to yield water Sodium metal is combined with chlorine gas to yield sodium chloride.

Formula Equations Chemical equations are more commonly written with chemical symbols Write the chemical formulas for the above two reactions The key to writing formula equations is to be very careful to use the correct chemical symbols and formulas for the reactants and products.

Balancing Equations The total mass of the reactants must be equal to the total mass of the products. For mass to remain constant before and after a chemical reaction, the number of atoms of each element must be the same before and after a chemical reaction. Why can’t we merely change the subscripts of the chemical formula so they match on each side of arrow?

Steps for balancing equations Write the word equation that describes the reaction Replace the words in the equation with symbols and formulas Count the number of atoms of each element on both sides of the equation To balance the equation, it is usually best to begin with those elements that occur in only one substance on each side of the equation.

Examples Manganese metal reacts with sulfuric acid to produce manganese (II) sulfate and hydrogen gas. Silver chlorate is decomposed with heat to give silver chloride and oxygen gas. Chromium metal is heated in oxygen to produce chromium(III) oxide Copper(II) hydroxide and potassium sulfate are produced when potassium hydroxide reacts with copper(II) sulfate

Examples Sodium hydroxide reacts with phosphoric acid to produce trisodium phosphate and water Potassium reacts with water to produce hydrogen and potassium hydroxide. Aluminum reacts with iron(II) nitrate to form aluminum nitrate and iron Magnesium hydroxide decomposes to form magnesium oxide and water

Examples When solid copper reacts with aqueous silver nitrate, the products are aqueous copper(II) nitrate and solid silver. The reaction between solid iron(III) oxide and carbon monoxide gas produces solid iron and carbon dioxide gas. The reaction between solid zinc sulfide and oxygen gas produces solid zinc oxide and sulfur dioxide gas.