Chapter 7: Chemical Reactions

Introduction Reactions involve chemical changes in matter resulting in new substances

Reactions involve rearrangement and exchange of atoms to produce new molecules

Elements are not changed during a reaction

Evidence of Chemical Reactions visual clues (permanent) such as…color change, precipitate formation, gas bubbles,

flames, heat release, cooling, light

other clues- new odor, permanent new state

Chemical Equations Shorthand way of describing a reaction

Provides information about the reaction such as… o Formulas of reactants and products o States of reactants and products o Relative numbers of reactant and product molecules that are required o Can be used to determine weights of reactants used and of products that can be

made

Conservation of Mass Matter cannot be created or destroyed

In a chemical reaction, all the atoms present at the beginning are still present at the end therefore the total mass cannot change

Therefore the total mass of the reactants will be the same as the total mass of the products

Writing Equations

Use proper formulas for each reactant and product

A proper equation should be balanced and must… o obey the Law of Conservation of Mass o all elements on reactants side also on product side o equal numbers of atoms of each element on reactant side as on product side

Balanced equation shows the relationship between the relative numbers of molecules of reactants and products

Can be used to determine mass relationships

Symbols Used in Equations Symbols used after chemical formula to indicate state

(g) = gas; (l) = liquid; (s) = solid: (aq) = aqueous, dissolved in water