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Chemical Reactions

Explore the world of chemical reactions with examples, equations, and tips for balancing reactions. Learn the difference between physical and chemical changes, and master the art of balancing equations with this comprehensive guide.

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Chemical Reactions

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  1. Chemical Reactions

  2. Chemical Reactions: • Chemical Changes involve a re-arrangement of atoms producing new substances with new properties. • A chemical change cannot easily be reversed.

  3. A physical change does not produce a new substance and can be easily reversed • Examples of physical changes include boiling, melting, freezing, dissolving….

  4. The Equation: Original Substances → New Substances (Reactants) (Products) A(s) + B(l) → C(g) + D(aq) Where: + Reads “plus” or “and” or “reacted with” → Reads “yields” or “produces” • Solid • Liquid • Gas (aq) aqueous (dissolved in water)

  5. Word Equation: Carbon Dioxide Water Baking Soda Vinegar Salt

  6. Skeleton Equation: CO2 H2O NaHCO3 CH3COOH NaC2H3O2

  7. Balanced Equation: CO2 H2O NaHCO3 CH3COOH Balance this equation for bonus marks NaC2H3O2

  8. Balancing equations: • The number of atoms in the reactants and number of the atoms in products must balance. • Place the correct coefficients in front of each formula (you do not need to write 1’s) to balance the reactants and products ___K + ___O2→ ___K2O K= K= O= O=

  9. Balancing equations • You can also balance from left to right • Remember you cannot change the subscripts in the formulas of the compounds. ___Fe2O3→ ___Fe + ___O2

  10. Other hints: • Save balancing the hydrogen and oxygen until the end for very large equations ___Al(OH)3 + ___H2CO3→ ___Al2(CO3)3 + ___H2O

  11. Other hints: • You can reduce coefficients, but it is an all or nothing process! __Mg(OH)2 + __ HCl → __ MgCl2 + __ H20

  12. Assignment: • Workbook: • Read p 74-76 • Questions P77 Q1-20, p78 Q1-12 • Be careful of diatomic molecules (H2, O2…) • Use Pencil…or things will get messy!

  13. Classifying chemical reactions: Intro: Compound: when two or more different elements are combined ex: H2O, CaCO3, Al2(SO4)3 Free element: when an element is not combined with another (Al, Fe, Zn) • Sometimes a free element can be combined with itself • Cl2, O2, H2 (diatomic molecules) • even P4 and S8

  14. 1) Synthesis: • When free elements combine into a compound Free + Free → Compound A + B → AB 2Al + 3Cl2 → 2AlCl3 4K + O2 → 2K2O

  15. 2) Decomposition: • The opposite of synthesis • When a compound breaks up into free elements. Compound → Free + Free + … AB → A + B 2NaCl → 2 Na + Cl2 8CaSO4 → 8Ca + S8 + 16O2

  16. 3) Single Replacement: • When a free element and a compound react. A + BC → Free + Compound → Na + MgCl2 → CaI2 + O2 →

  17. 4) Double Replacement • When two compounds react AB + XY → BaBr2 + K2O → Na2CO3 + MgCl2 → Compound + Compound → 2 new compounds

  18. 5) Neutralization: • A special double replacement reaction between an ACID and a BASE Acid andBase→Salt and Water HCl +NaOH→NaCl + H2O

  19. Assignment: • p 123 quick check • P 131 Q# 1-3

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