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Chemical Reactions 1 or more substances changed into a new substance or substances

Chemical Reactions 1 or more substances changed into a new substance or substances. YIELD. Reactants: substances about to react Products: new substances produced Reactants Products. Law of Conservation of Mass.

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Chemical Reactions 1 or more substances changed into a new substance or substances

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  1. Chemical Reactions1 or more substances changed into a new substance or substances

  2. YIELD Reactants: substances about to react Products: new substances produced Reactants Products

  3. Law of Conservation of Mass mass can neither be created nor destroyed in a chemical reaction

  4. Indicators of State • (s) or (cr): solid • (l): liquid • (aq): aqueous dissolved in water • (g): gas

  5. All Chemical Equations MUST BE BALANCEDNEVER change subscripts…Only change coefficients!

  6. Writing Balanced Chemical Equations • Describe the reaction in words • Rewrite using formulas and symbols • (Check for diatomic elements!) • 3. Check equation for atom balance • 4. Choose coefficients that balance the equation

  7. Types of Chemical Reactions

  8. Synthesis: 2 or more substances combine to form another more complex substance A+B  AB Decomposition: 1 substance breaks down into 2 or more simpler substances AB  A+B

  9. Single Displacement: 1 element replaces another in a compound A + BC  AC + B Cu + Ag(NO3)  Cu(NO3) + Ag

  10. Double Displacement: 2 ionic compounds in solution • Precipitate • Water • Gas AB + CD  AD + CB AgNO3(aq) + NaCl (aq)  AgCl (s) + NaNO3 (aq)

  11. Bond Energy • The amount of energy required to put a bond together is equal to the amount it takes to pull them apart. • Bonding to hydrogen atoms together absorbs 436 kj of energy. • When two hydrogen atoms are split how much energy is released? • 436 kj

  12. Endothermic Reaction: net absorption of energy • More energy is required to break bonds than to form new ones • Bonds formed have greater potential energy than bonds that were broken • Ex. Ice packs Exothermic Reaction: net release of energy • Less energy is required to break old bonds than to form new ones • Bonds formed have less potential energy than the bonds that were broken • Ex. Hand warmers

  13. Bond Energy and Conservation of Energy • Energy released in an exothermic reaction is NOT CREATED BY THE REACTION! • It was stored as potential energy in the bonds of the reactants • In an endothermic reaction the products store energy as potential energy rather than releasing it as heat.

  14. Activation Energy • Energy that may be needed to start a reation • Used to break the bonds in the reactants

  15. Catalyst: • A catalyst can increase the rate of a chemical reaction • Decreases the activation energy • Decreases costs making rxn more economical • The human body uses enzymes to catalyze reactions

  16. Exploring ad Catalyst: Lab In A Nutshell • The reaction did not take place until the heated copper was added • The copper was not consumed by the reaction • Regains original color • 2Cu + O2  2CUO • CuO + C2H5OH  C2H4O + H2O + Cu

  17. Read Catalysts for Food Production p. 319- 321

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