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Chemical Reactions

Chemical Reactions. Chemical Reaction Vocabulary. Chemical Reaction: One or more reactants change into one or more products Reactant: A substance present at the start of a reaction Product: A substance produced in a chemical reaction

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Chemical Reactions

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  1. Chemical Reactions

  2. Chemical ReactionVocabulary • Chemical Reaction: One or more reactants change into one or more products • Reactant: A substance present at the start of a reaction • Product: A substance produced in a chemical reaction • Chemical Equation: An expression representing a chemical reaction; the formulas of the reactants (on the left) are connected by an arrow with the formulas for the products (on the right). • Example: • Reactants Products

  3. Symbols in Chemical Reactions • Many symbols are used when writing a chemical reaction

  4. Writing Chemical Reactions • First we are going to start with what is considered a skeleton equation • Skeleton equation: a chemical equation that does not indicate the relative amounts of the reactants and products. • Example: Rusting • Fe + O2 Fe203

  5. Writing Chemical equations • Next we want to add in what “state” each of the atoms/molecules is in • Solid (s) • Liquid (l) • Gas (g) • Aqueous solution (aq): a solution in which the solvent is water • You also will indicate if you are adding anything usually either heat or a catalyst (substance that speeds up a reaction, but is not used up or part of either the products or reactants) • ∆ or heat • MnO2 • Example: • Fe(s) + O2(g) Fe2O2(s)

  6. Balancing Chemical Equations • A chemical equation in which mass is conserved; each side of the equation has the same number of atoms of each element • Is this equation balanced? • Fe(s) + O2(g) Fe2O2(s) • On the left side: 1 Fe On the right side: 2 Fe • 2 O 2 O • The iron is not balanced to conserve mass. We have 1 on the left and 2 on the right, so we need to at a coefficient (small whole number that are placed in front of the formulas in an equation in order to balance it). So the equation would look like this: • 2Fe(s) + O2(g) Fe2O2(s)

  7. Rules for Writing and Balancing Equations • Step 1: Determine the correct formulas for all the reactants and products • Step 2: Write the skeleton equation by placing the formulas for the reactants on the left and the formulas for the products on the right with an arrow in between. If two or more reactants or products are involved, separate their formulas with plus signs. • Step 3: Determine the number of atoms of each element in the reactants and products. Count a polyatomic ion as a single unit if it appears unchanged on both sides of the equation. • Step 4: Balance the elements one at a time by using coefficients. When no coefficients is written, it is assumed to be 1. Begin by balancing elements that appear only once on each side of the equation. Never balance an equation by changing the subscripts in a chemical formula. Each substance has only one correct formula. • Step 5: Check each atom or polyatomic ion to be sure they are equal on both sides of the equation. • Step 6: Make sure all the coefficients are in the lowest possible ratio.

  8. Types of chemical equations • There are five general types of reaction • Combination • Decomposition • Single-replacement • Double-replacement • Combustion

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