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Chemical Reactions
• a change of one or more substances converted into new substances
• Ex. Iron mixed w/the oxygen in theair to form rust
Chemical Reactions
1. Reactants – substances that combine or change
2. Products – new substances that are produced
Reactants Products
• Butt of the arrow are the reactants and point of the arrow is the products
Reactants ProductsProduce
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
Writing equations
• chemical equation – uses chemical formulas and symbols to describe a chemical reaction and the product(s) it produces
Chemical Equations
1. Chemical formula express the relationship between the elements in the compounds and molecule they make up
2. Coefficients – numbers which represent the number of units of each substance in a reaction
3. Knowing coefficients of chemical reactions allows chemists to use the correct amounts of reactants to predict the amounts of products
4. Subscripts – numbers which represent the number of atoms in a molecule of a particular element
Symbols used in chemical equations
Symbol 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
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