Chemical Reactions and Evidence

2. Chemical Reactions and Evidence Physical Science

3. A) Chemical Reactions • Chemical Reaction- the process that turns one set of chemical substances into another one set • Chemical reactions are studied by specialized scientist called chemist-they study all things atomic • Antoine-Laurent de Lavoisier is considered to be the father of modern chemistry, thanks to his intensive study of reactions during the mid 1700’s • Was the first to publish the law of conservation of mass • The total mass of things that go into a reaction(products) equals the total mass of all things that are produced during the reaction(products) • Mass is neither created or destroyed in a RXN, it only changes forms

5. How do we know when a chemical reaction has taken place? Absorb or Release of Heat -gets hot or gets cold or releases light ? Production of a Gas -can you smell it, like something rotting? -do you see bubbles in the liquid? Formation of a solid, called a precipitate -it “rains” or precipitates out of the solution -it is usually a different color?

6. Chemical Vs. Physical Change • Physical changes are only concerned with changes in energy or states of matter ( S,L,G) • Starting and ending material are the same thing, thought they may look different • EX- Ice melting, Water evaporating

7. B) Writing Chemical Reactions When a clear aqueous solution of potassium iodide is mixed with a clear aqueous solution of lead nitrate it produces(yields ) a clear solution of potassium nitrate and a yellow solid precipitate called lead(II) iodide Pb(NO3)2(aq) + KI(aq)  PbI2(s) + KNO3(aq) Reactants Products

8. Symbols Used in an Equation • (g) means gaseous phase • (l) means liquid phase • (s) means solid phase • (aq) means dissolved in water • means yield (produces)

9. Writing Word Equations • Aqueous silver nitrate reacts with solid copper metal to form solid silver and copper (II) nitrate.

10. Types of Chemical Reactions • Synthesis or Combination • Two or more substances chemically combine to become one substance • Pattern A + B AB + • Mg + Cl2 MgCl2 _

11. Types of Rxns. Cont… • Decomposition • One substance breaks down into two or more substances. • Pattern • AB A + B + MgCl2 Mg + Cl2

12. Types of Rxns. Cont. • Single Replacement • When a single element switches placement with the anion or cation of another compound • Pattern • AB + C AC + B • + + • NaCl + K Na + KCl

13. Types of Rxns. Cont. • Double Replacement • When the cations and anions of two different compounds switch places • Pattern • AB + CD AD + CB • + + • KCl + MgOH KOH + MgCl2

14. Pb(NO3)2(aq) + KI(aq)  PbI2(s) + KNO3(Aq) Reactants Pb- N- O- K- I- Products Pb- N- O- K- I- 1 2 6 1 1 1 1 3 1 2

15. C) Balancing Chemical Equations The conservation of mass says that you must equal amounts of reactants and products You can never change the chemical formulas in the equation *DO NOT CHANGE THE CHEMICAL FORMULAS* You can only alter the equation to balance it by adding coefficients, big numbers in from of a chemical formula to make everything equal ___Pb(NO3)2(aq) + ___KI(aq)  ___PbI2(s) + ____KNO3(Aq)

16. ___Pb(NO3)2(aq) + ___KI(aq)  ___PbI2(s) +____KNO3(Aq) Reactants Pb- N- O- K- I- Products Pb- N- O- K- I- 1 2 6 1 1 1 1 3 1 2

17. 2 ___Pb(NO3)2(aq) + ___KI(aq)  ___PbI2(s) +____KNO3(Aq) Reactants Pb- N- O- K- I- Products Pb- N- O- K- I- 1 2 6 2 2 1 1 3 1 2

18. 2 2 ___Pb(NO3)2(aq) + ___KI(aq)  ___PbI2(s) +____KNO3(Aq) Reactants Pb- N- O- K- I- Products Pb- N- O- K- I- 1 2 6 2 2 1 2 6 2 2

19. Pb(NO3)2(aq) + 2KI(aq)  PbI2(s) + 2KNO3(Aq) YAY!!! We Have a Balanced Equation

20. Practice Equations SnO2 + H2 → Sn + H2O N2 + H2 → NH3 C3H8(g) + O2(g)  CO2(g)+ H2O(g) Na(s) + HCl(aq) → NaCl(aq) + H2(g)

21. B4H10(g) + O2(g) -- B2O3(g) + H2O(g) Na3PO4 + Fe2O3 -- Na2O + FePO4 NaCl(aq) + AgNO3(aq) → NaNO3(aq) + AgCl(s)