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CHEMICAL REACTIONS

CHEMICAL REACTIONS. Fall 2013. CHEMICAL REACTIONS. 1. A chemical reaction is a process that changes one or more substances into one or more new substances. 2 . Five observations that indicate a chemical reaction has occurred are:

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CHEMICAL REACTIONS

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  1. CHEMICAL REACTIONS Fall 2013

  2. CHEMICAL REACTIONS • 1. A chemical reaction is a process that changes one or more substances into one or more new substances. • 2. Five observations that indicate a chemical reaction has occurred are: • a) permanent color changeb) formation of a precipitatec) gas is producedd) endergonicor exergonic(energy)e) production of light • 3. A chemical equation is a shorthand method used by scientist to show the changes that take place in a chemical reaction.

  3. CHEMICAL REACTIONS • 4. A chemical reaction can be shown by writing a word equation. • magnesium plus sulfur yields magnesium sulfide • More often symbols and chemical formulas are used in place of words. This is called a formula equation. • Mg + S ----> MgS

  4. CHEMICAL REACTIONS • 5.The starting substances in a chemical reaction are called reactants. The new substances that are formed in a reaction are called products. • In a chemical equation reactants are written to the left of the arrow and products are written to the right. • reactants -----> products

  5. CHEMICAL REACTIONS • 6.A balanced chemical equation has the same number and type of atoms on both the reactant and product side of the equation. • A coefficient is a whole number placed in front of a symbol or formula to show the number of atoms or molecules involved. • When balancing an unbalanced equation, only coeffientscan be changed. The subscripts are not changed.

  6. CHEMICAL REACTIONS • 7.A diatomic molecule is made up of two atoms of a single element. The seven diatomic molecules are Bromine, Iodine, Nitrogen, Chlorine, Hydrogen, Oxygen and Fluorine. • These elements are so reactive, they are never found alone. They will always be with another element, OR they travel in pairs. • Br2I2 N2 Cl2H2 O2F2

  7. CHEMICAL REACTIONS • 8.The Law of Conservation of Mass states: In a chemical reaction the total mass of the reactants equals the total mass of the products. • The number of atoms of each element on each side of the equation stays the same. • A balanced equation satisfies the Law of Conservation of Mass.

  8. CHEMICAL REACTIONS • 9. Types of Reactions • A synthesis reaction is a reaction in which two or more substances combine to form only one product. General equation: • A + B ------> AB Ex. Mg + S ------> MgS

  9. CHEMICAL REACTIONS • 9. Types of Reactions • A decomposition reaction is a reaction in which a compound breaks down into two or more products.General equation: • AX ------> A + X • BaS ------> Ba + S

  10. CHEMICAL REACTIONS • 9. Types of Reactions • A single displacement reaction takes place when one element replaces another element in a compound. This forms a new compound and leaves the weaker element by itself.When the free element is a metal: General equation: • A + BC ------> B + AC [only if A is stronger than B] • ZnS+ Mg -------> MgS + Zn

  11. CHEMICAL REACTIONS • 9. Types of Reactions • A double displacement reaction takes place when the compounds in a reaction exchange ions. General equation: • AB + CD ---> AD + CB • BaS+ CaO ------> BaO + CaS

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