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Chemical Reactions
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Chemical Equations A chemical equation is a representation of a chemical reaction; the formulas of the reactants (on the left) are connected by an arrow with the formulas of the products (on the right). Fe + O 2 Fe 2 O 3 A Chemical formula is a combination of symbols that represent the elements in a compound. (add this note to your reading guide )
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All chemical reactions have two parts Reactants - the substances you start with (the ones reacting) Products- the substances you end up with (the ones produced) The reactants turn into the products. Reactants Products
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A chemical reaction rearranges the atoms of the reactants to form new compounds of the products. No new atoms are created, they have only been rearranged.
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4 types of Chemical Reactions: 1.Synthesis Reaction: two or more elements or compounds combine to make one more complex substance (A + B → AB) 1.Decomposition Reaction: a compound is broken down into simpler products (AB → A + B) 2.Single Replacement Reactions: replace one element from a compound with another element. (A + BC B + AC) 4. Double Replacement Reactions: swaps elements between 2 compounds that react together to form two new compounds. (AB + CD AD + CB)
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The Law of Conservation of Mass states that: The mass of the reactants equals the mass of the products. OR - Matter can never be created nor destroyed OR - you can’t get somethin’ outta nothin’(hahaha)
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Word Equations Example Methane + Oxygen Carbon dioxide + Water The arrow means yields, gives, or reacts to produce.
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Rules for balancing Write the correct formulas for all the reactants and products Count the number of atoms of each type appearing on both sides Balance the elements one at a time by adding coefficients (the numbers in front) Check to make sure it is balanced.
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Never Change a subscript to balance an equation. If you change the formula you are describing a different reaction. H 2 O is a different compound than H 2 O 2 Never put a coefficient in the middle of a formula 2 NaCl is okay, Na2Cl is not.
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What is a coefficient? A number that indicates how many atoms of an element are in one molecule What is a subscript? Numbers telling how many molecules are involved in a chemical reaction
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