Chemical Changes

Chemical Reactions

A change in which one or more substances are changed into new substances

Chemical equations have two parts Reactants – substances that react Products – new substances that are formed or

produced Reactants Products

Symbols of Chemical Reactions

Symbol Meaning

Produce or forms

+ Plus

(s) Solid

(l) Liquid

(g) Gas

(aq) Aqeuous

Heat/Light/Electricity

The reactants re heated/lighted/ or given electrocoty

Law of Conservation of Mass

The total mass of the products always equals the total mass of the reactants

Mass is neither created or destroyed, only transferred

Chemical Equations

Shorthand way to describe a chemical reaction using chemical formulas and other symbols

Example: Hydrogen gas plus oxygen gas produces liquid

dihydrogen monoxide H2 (g) + O2 (g) H2O (l)

Balancing Chemical Equations

Coefficients represent the number of units of each substance taking part in a reaction

Allow chemists to add the correct amounts of reactants to a reaction and tells them exactly how much product will form

Balancing an equation does not change what happens in a reaction, only changes the way the reaction is represented

Balancing Chemical Equations

A balanced chemical equation is an equation in which the same number of atoms each element on both sides of the equation

Trial and error

Balancing Chemical Equations

1. Write a chemical equation for the reaction using formulas and symbols.

2. Count the atoms in reactants and products.

3. Choose coefficients that balance the equation. Never change subscripts of a correct formula to balance an equation.

4. Recheck the numbers of each atom on each side of the equation and fix coefficients again if necessary.