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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.
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