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Chemical Reactions

Chemical Reactions. I. What is a chemical reaction. Chemical reaction - when substances change chemically to form a new substance Forms new bonds between atoms Makes new substances example - 2 hydrogen atoms (gas) + 1 oxygen atom (gas) react to form 1 water molecule (H 2 O).

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Chemical Reactions

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  1. Chemical Reactions

  2. I. What is a chemical reaction • Chemical reaction- when substances change chemically to form a new substance • Forms new bonds between atoms • Makes new substances • example- 2 hydrogen atoms (gas) + 1 oxygen atom (gas) react to form 1 water molecule (H2O)

  3. I. What is a Chemical Reaction? B. How do you know a reaction occurred? • A gas is produced (bubbles) • example- baking soda & vinegar • A change in color • example- iron rusting • A change in temperature a. example- a flame or cool reaction

  4. I. What is a Chemical Reaction? C. What happens in a reaction? • Reactants react to form products • reactants- the materials that exist before the chemical reaction. • Products- substances that are created by the chemical reaction.

  5. 4 hydrogen atoms 2 oxygen atoms 4 hydrogen atoms 2 oxygen atoms I. What is a Chemical Reaction? C. What happens in a reaction? 2. Atoms are only rearranged (no new atoms are created) a. 2 H2 + O2 2 H2O

  6. II. Energy and Reactions • Energy is needed to break chemical bonds to start a chemical reaction. example- a match is needed to light gasoline on fire (but once it’s lit, WATCH OUT!)

  7. II. Energy and Reactions B. Energy is released when bonds form • Energy is released as heat, light, sound, or electricity. C. chemical energy- energy stored in atoms & molecules. 1. Chemical energy can be released in a reaction

  8. II. Energy and Reactions D. Exothermic Reaction • Releases energy (gets hotter) • Exothermic reactions release more energy than they absorb.

  9. II. Energy and Reactions E. Endothermic Reaction • Absorbs energy (gets colder) • Endothermic reactions absorb more energy than they release.

  10. III. Five Types of Chemical Rx • Synthesis Reaction- two substances combine to form a more complex compound. a) A + B  AB b) 2 Na + Cl2  2 NaCl

  11. III. Five Types of Chemical Rx 2. Decomposition Reaction- a compound is broken down into at least two products. a. AB  A + B b. 2H2O  2H2 + O2

  12. III. Five Types of Chemical Rx 3. Combustion Reaction- a compound burns in oxygen gas (O2). a. O2 will always be a reactant in a combustion reaction. b. Anytime there is a flame, it is a combustion reaction. c. 2 Mg + O2 2 MgO

  13. III. Five Types of Chemical Rx 4. Single Displacement Reaction- one element knocks another element out of a compound • AX + B  AB + X • CaCl2 + 2Na  2NaCl + Ca

  14. III. Five Types of Chemical Rx 5. Double Displacement Reaction- two compounds switch ions with each other. • AX + BY  AY + BX • Pb(NO3)2 + K2(CrO4)  Pb(CrO4) + 2K(NO3)

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