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14.1 Chemical Reactions

Learn about chemical reactions, including indicators of a chemical change, the law of conservation of mass, and how to balance chemical equations. Understand the reactants and products involved in reactions and discover helpful tips for balancing equations.

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14.1 Chemical Reactions

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  1. 14.1 Chemical Reactions

  2. Chemical Reactions Chemical reaction: the process of breaking chemical bonds and reforming new bonds to make new substances

  3. Evidence of Chemical Change Four indicators of a chemical change: 1. Formation of new gas 2. Formation of new solid 3. Release energy (heat or light) 4. Color change Coke and Chlorine Iodine Clock Reaction Chameleon Reaction

  4. Reactants and Products Reactant: starting substance(s) Product: new substance(s) formed

  5. Reaction Symbols arrow = “to produce” The small symbols in the parentheses (s, l, g, aq) indicate the phase of each substance in the reaction.

  6. Law of Conservation of Mass Law of Conservation of Mass: Mass cannot be created or destroyed, only rearranged.

  7. Law of Conservation of Mass Mass of reactants = mass of products

  8. Example • 5.0 g of magnesium (Mg) burns in 1.0 g of oxygen (O2). How many grams of magnesium oxide (MgO) should be produced? Mg + O2 MgO

  9. Check-In • 10.2 g of Lithium Fluoride (LiF) and an unknown amount of sodium chloride (NaCl) react to form 13.5 g of Lithium chloride (LiCl) and 21.2 g of Sodium fluoride (NaF). How many grams of sodium chloride reacted? LiF + NaCl  LiCl + NaF

  10. A Reminder:Numbers in Chemical Formulas

  11. Balancing Chemical Equations The law of conservation of mass tells us that atoms and molecules must be balanced on both sides of a chemical equation.

  12. Balancing Chemical Equations coefficient subscript • Rules: • Subscripts (small numbers) CANNOT be changed. • Coefficients (big numbers) placed in front of the chemical formula.

  13. Balancing Chemical Equations coefficient subscript Write in pencil So you can Erase!! • Balancing Steps: • Draw a line to separate reactants from products • Make a list! – each element on each side • --Write in the same order • Add coefficients if needed (change your list!)

  14. Balancing Chemical Equations ___Li2S + ___ Cl2 → ___ LiCl + ___S

  15. Balancing Chemical Equations ___Mg + ___ O2 → ___ MgO

  16. Balancing Chemical Equations Example #1 ___Cu2S + ___ O2 → ___ Cu2O + ___ SO2

  17. Balancing Chemical Equations Example #2 ___Al + ___O2 → ___ Al2O3

  18. Balancing Chemical Equations EXIT SLIP ___ CO2 + ___ H2 → ___ CH4 + ___ H2O

  19. Hints for balancing: • Save single elements (Al, Cu, Na) and diatomic molecules (I2, Cl2, O2) for last. C2H4 + O2→ CO2 + H2O

  20. Hints for balancing: • Find Common Multiples KClO3→ KCl + O2

  21. Hints for balancing: • Keep polyatomic ions together H2SO4 + Ca3(PO4)2→ Ca(H2PO4)2 + CaSO4

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