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Chemical vs. Physical Changes

Chemical vs. Physical Changes. Physical Change No new compounds are formed Ex. Cutting, ripping, dissolving, phase changes…. Chemical vs. Physical Changes. Chemical Change Bonds are broken and the atoms in compounds are rearranged New Compounds are created

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Chemical vs. Physical Changes

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  1. Chemical vs. Physical Changes • Physical Change • No new compounds are formed • Ex. Cutting, ripping, dissolving, phase changes…

  2. Chemical vs. Physical Changes • Chemical Change • Bonds are broken and the atoms in compounds are rearranged • New Compounds are created • Are the result of chemical reactions

  3. Chemical Reactions • Evidence • Bubbling, Cloudy solution, Temperature Change, Color Change, Smoke, Light, Heat • Reactants: what you start with • Products: what you end with

  4. Can be written as a sentence or an equation: Methane reacts with oxygen to form carbon dioxide and water. or CH4 + O2 CO2 + H2O (REACTANTS)  (PRODUCTS)

  5. Law of Conservation of Mass • During a chemical reaction, atoms CANNOT be created nor destroyed, only rearranged! • In other words, the number of atoms of each element in the reactants must equal the number of atoms in the products. • CHEMICAL EQUATIONS MUST BE BALANCED!!!

  6. How to Balance Equations • Count the number of atoms on each side of the reaction. • Put a coefficient in front of one molecule that has too few atoms of an element. • Count the number of atoms again. • If all are equal—YOU ARE DONE! If not—REPEAT steps 2-3 until they are!

  7. Reactants: C – 1 H – 4 O – 2 NOT BALANCED!!!!!!! Products: C – 1 H – 2 O – 2 + 1 = 3 CH4 + O2 CO2 + H2OCount the number of atoms:

  8. Reactants: C – 1 H – 4 O – 2 * 2 = 4 BALANCED!!!!!!!!!! Products: C – 1 H – 2 * 2 = 4 O – 2 + 2 = 4 CH4 + 2O2 CO2 + 2H2OPut in coefficients:

  9. Types of Reactions • Addition/Synthesis: two or more elements combine to form a new compound A + B  AB Shortcut – only one product

  10. Types of Reactions • Decomposition: one compound breaks apart to form two or more products AB  A + B Shortcut – only one reactant

  11. Types of Reactions • Single-Replacement (Displacement): an element replaces another element in a compound A +BX  AX + B Shortcut - one element & one compound on both sides

  12. Types of Reactions • Double-Replacement (Displacement): two elements in different compounds switch places AX + BY  BX + AY Shortcut - Two compounds with elements switching places in each

  13. Combustion: a compound containing carbon and hydrogen combines with oxygen to form carbon dioxide and water • AB + O2 CO2 + H2O By Bailey Harp

  14. Types of Reactions • Combustion: a compound containing carbon and hydrogen combines with oxygen to form carbon dioxide and water AB + O2 CO2 + H2O

  15. Types of Reactions • Exothermic: reactions that give energy off to their surroundings. • See a flame or feel heat (hand warmers, MREs) • Endothermic: reactions that absorb energy from their surroundings. • Feel cold (instant ice packs)

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