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Chemical Reactions

Chemical Reactions. The story. Meet 2H 2 O. Hi there. So is this. This is H 2 O. They weren’t always so happy. Chemical Equations & Reactions. Hmph. You’re out of control. Bbbllgghh!!. Meet O 2. You need me. I’m important. Meet H 2. He’s light. He’s fast. He’s crazy!.

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Chemical Reactions

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  1. Chemical Reactions The story

  2. Meet 2H2O Hi there. So is this. This is H2O.

  3. They weren’t always so happy.

  4. Chemical Equations & Reactions

  5. Hmph. You’re out of control Bbbllgghh!!

  6. Meet O2 You need me. I’m important.

  7. Meet H2 He’s light. He’s fast. He’s crazy! B-b-b-b-b

  8. One day… Hey! Quit it!

  9. One day…

  10. Chemical Reactions Bonds are broken and new bonds are formed. Bonds in H2 & O2 break.

  11. Chemical Reactions Bonds are broken and new bonds are formed. WHAM! WHAM! WHAM! WHAM! New bonds form.

  12. Chemical Reactions New substances are formed. Water is formed 2 gases react

  13. Parts of a Reaction Reactants: The chemicals you have before the reaction That’d be us. Tbtbbhth! Tbtbbhth! H2 H2 O2

  14. Parts of a Reaction Products: The substances created in the reaction H2O H2O

  15. Parts of a Reaction Chemical Equation Reactants Products 2H2 + O2 2H2O

  16. Chemical Reactions During chemical reactions atoms are not created or destroyed. They’re just rearranged. 2 oxygen atoms 4 hydrogen atoms 2 oxygen atoms 4 hydrogen atoms

  17. How can you tell if a chemical reaction has happened? Let me give you some hints.

  18. Is it a chemical reaction? If a gas is produced it might be a chemical reaction. Look for the bubbles!

  19. Is it a chemical reaction? If it changes color it might be a chemical reaction. Like iron rusting!

  20. Is it a chemical reaction? If it gets hotter it might be a chemical reaction.

  21. Is it a chemical reaction? Formation of a solid (precipitate) Observations: “Cloudy” “Foggy” Solid at bottom

  22. Is it a chemical reaction? Or…if it gets colder it might be a chemical reaction.

  23. Exothermic Reactions Exothermic reactions release energy. These reactions feel hot.

  24. Endothermic Reactions Endothermic reactions absorb energy. These reactions feel cold.

  25. Describing a Chemical Reaction Indications of a Chemical Reaction • Evolution of heat, light, and/or sound • Production of a gas • Formation of a precipitate • Color change

  26. Chemical Equations Shows the formulas of the reactants and products in a chemical reaction CH4 + O2 CO2 + H2O Reactants Products

  27. Word Equations Uses the names of the reactants and products. CH4 + O2 CO2 + H2O methane + oxygen carbon dioxide + water Methane reacts with oxygen to produce carbon dioxide and water

  28. Symbols Used in Chemical Equations Yields or produces – separates products & reactants Used to indicate a reversible reaction A reactant or product in the solid state or precipitate A reactant or product in the liquid state A reactant or product in the gaseous state A reactant or product in an aqueous solution (dissolved in water) (s) (l) (g) (aq)

  29. Additional Symbols Used in Chemical Equations Formation of a gas (product only) Formation of a solid/precipitate (product only) Temperature at which reaction is carried out Reactants are heated Use of a catalyst to speed up reaction Important information is usually written above arrow i.e. pressure or other reaction conditions 15 oC D MnO2 2 atm

  30. Balancing Equations

  31. 4 Al(s) + 3 O2(g) 2 Al2O3(s) Chemical Equations product reactants Depict the kind of reactants and products and their relative amounts in a reaction. Numbers in the front: stoichiometric coefficients.

  32. 4 Al(s) + 3 O2(g) 2 Al2O3(s) Chemical Equations 4 g Al + 3 g O2 yield 2 g Al2O3 This equation means: 4 Al atoms + 3 O2 molecules yield 2 molecules of Al2O3 or 4 Al moles + 3 O2moles yield 2 moles of Al2O3 2 mol Al2O3@102g/mol 4 mol Al@27g/mol 3 mol O2@32g/mol 108 g + 96 g = 204 g

  33. Chemical Equations Atoms present at the beginning (reactants) and at the end (products) do not change THEREFORE, Amount of matter does not change. The Law of Conservation of Matter

  34. Chemical Equations Because of the conservation of matter, An equation must be balanced. → must have the same NUMBER of atoms of EACH kind on both sides.

  35. CH4 + 2 O2 CO2 + 2 H2O Reactants Products 1 C atom 1 C atom 4 H atoms 4 H atoms 4 O atoms 4 O atoms

  36. Cl H H H Cl Cl Cl H reactants products reactants products H H Cl Cl Unbalanced and Balanced Equations H Cl Cl Cl H H H2 + Cl2 2 HCl (balanced) (unbalanced) H2 + Cl2 HCl 2 1 2 2 1 2 2 2

  37. Image Sources Water Molecule http://commons.wikimedia.org/wiki/File:Water-3D-vdW.png Oxygen and Hydrogen Molecules http://en.wikipedia.org/wiki/File:Nitrogen-3D-vdW.png POW! http://www.scribbleonwalls.com/images/products/comc_05.jpg Shiny Can http://www.flickr.com/photos/99347433@N00/315475438/ Rusty Can http://www.flickr.com/photos/25149679@N00/466492041/ Burning Match http://www.flickr.com/photos/8070463@N03/3069201840/ Icicles http://www.flickr.com/photos/14316700@N08/3075538662/ Bonfire http://www.flickr.com/photos/dominicspics/1902322480/ Icy branches http://www.flickr.com/photos/laszlo-photo/426155665/

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