1. Chemical Reactions
Chapter 21: Sec 1&2

2. Chemical Reactions
a change of one or more substances converted into new substances
Ex. Iron mixed w/ the oxygen in the air to form rust

3. Chemical Reactions Reactants – substances that combine or change
Products – new substances that are produced
Reactants
Products

4. Butt of the arrow are the reactants and point of the arrow is the products
Reactants Products
Produce

5. Conservation of Mass
A law which states that, in a chemical reaction matter is not created or destroyed; it stays the same
French chemist Antoine Lavoisier
experimented with mercury (II) oxide and heat
found mass of products (liquid mercury and oxygen gas) equaled the mass of reactants
Mass of reactants = mass of products

6. Writing equations
chemical equation – uses chemical formulas and symbols to describe a chemical reaction and the product(s) it produces

7. Chemical Equations
Chemical formula express the relationship between the elements in the compounds and molecule they make up
Coefficients – numbers which represent the number of units of each substance in a reaction
Knowing coefficients of chemical reactions allows chemists to use the correct amounts of reactants to predict the amounts of products
Subscripts – numbers which represent the number of atoms in a molecule of a particular element

8. Symbols used in chemical equations
Meaning
produces or forms +
Plus
(s)
solid
(l)
liquid
(g)
gas
(aq)
aqueous, a substance is dissolved in water
heat
the reactants are heated
light
the reactants are exposed to liqht
elec.
an electric current is applied to the reactants

9. Balanced Equations
both sides of the equation have same number of atoms of each element
(remember law of conservation of mass)
Coefficients used to balance the amount of reactants and products

10. Writing balanced equations
describe the reaction in words
write the equation using formulas and symbols
check for balance
add coefficients where needed for balance