2. 1 Chemical Equations and Reactions What are they?

3. 2 chemical reaction- one or more substances are changed into new substances. Reactant – substances that react Product – new substances produced reactants products 2Na + Cl 2 2NaCl

4. 3 Evidence of Reactions Bubbling (gives off a gas) Precipitate-solid that falls out of solution Temperature change Color change

5. 4 Chemical Equation Expression that describes a chemical reaction using chemical formulas and other symbols SymbolMeaning (cr)Crystalline solid (l)(l) Liquid (g)Gas (aq)Aqueous-solid dissolved in water

6. 5 Symbol for Chemical Equations “Pb(NO 3 ) 4 ” is a formula.  Means produces (or yields) + Means added together Subscripts - Number of a particular atom in a molecule Coefficients – Number of molecules Pb(NO 3 ) 4 + 4KI  PbI 4 + 4KNO 3

7. 6 First Described the “Law of Conservation of Mass” Father of Modern Chemistry 1743 - 1794

8. 7 Conservation of Mass Antoine Lavoisier found that the mass of the reactants and the products are equal, even when the states of matter change. Matter is neither created nor destroyed. Hg + O 2 HgO He started with: 10g of Mercury Oxide (HgO) He ended up with: and 9.3g Mercury… 0.7g Oxygen became a gas 10 g. = 0.7 + 9.3 g....But what happened to the O 2 ?

9. 8 Conservation of atoms-the number of each type of atom on the reactants side of the chemical equation MUST be equal to the number of each type of atom on the products side of the equation. Coefficient-represent the number of units of each substance taking part in the reaction Balanced chemical equation-the same number of atoms of each element on both sides of the equation

10. 9 Lavoisier’s Chemical Equation: Hg (mercury) can exist by itself... but, oxygen will need to bond with another oxygen to make O 2 (diatomic) HgO  Hg +O2O2 2 2 To balance the atoms we need to: This balances the equation! Put the coefficient of 2 in front the product Hg. Put the coefficient of 2 in front of reactant HgO.

11. Is this balanced? N N N N H H H H N N H H H H H H Why or Why Not? Let’s Count the Atoms: There are 2 nitrogen atoms There are 2 hydrogen atoms 1 nitrogen and 3 hydrogen… N2N2 NH 3 H2H2 10

12. 11 Atoms can only bond in certain ways… remember the criss-cross method. subscripts. That’s why we can’t change the subscripts. H H H H N N N N N N N N N N N N N N N N H H H H H H H H H H H H H H H H N N N N N N N N H H H H H2H2 N2N2 N2N2 N2N2 N2N2 N2N2 H2H2 H2H2 H2H2 H2H2

13. 12 Here is what it means... Subscripts - Small #’s below an element. Coefficients - Large #’s in front of the formulas. 2H22H2 H2H2 When balancing equations, we can only change the coefficients! H H H H H H H H H H H H I can’t live without you!

14. Now, back to the balancing... N N N N H H H H N N H H H H H H N2N2 NH 3 We can only change coefficients before the symbols. 1 molecule of nitrogen 1 molecule of hydrogen 1 molecule of ammonia H2H2 11 1 13

15. 14 Do both sides have the same amount of atoms? N 2 + H 2 NH 3 NHNH 2 1 2 3

16. 15 N 2 + 3 H 2 2NH 3 Then it is a balanced equation. Do both sides have the same amount of atoms? N 2 + H 2 NH 3 NHNH 2 1 2 3 2 3 (2) (6)

17. 16 Four Steps to Balance Equations: 1. List the metals, nonmetals, oxygen, and hydrogen below arrow. 2. Count the number of atoms you have on both sides. 3. Balance by changing the coefficients and recounting. 4. Start the process again if it still does not balance.

18. 17 1. Set up your equation. H 2 + O 2  H 2 O List the elements in this order below the equation: Metals, Nonmetals, Oxygen, and Hydrogen O H Metals Nonmetals Oxygen Hydrogen

19. 18 2. Count the number of atoms you have of each on both sides. H 2 + O 2  H 2 O O H 2 1 2 2

20. 19 H 2 + O 2  H 2 O O H 2 1 2 2 (2) 2 (4) 2 (4) 3. Balance by changing the coefficients and recounting. Need to have at least 2 “O” But it changes the number of “H” How are you going to make “H” add up to 4? Is this balanced? Yes!

21. 20 Mg + HCl  H 2 + MgCl 2 Mg Cl 1 1 2 1 (2) 2 (2) Let’s try another: Need to have at least 2 “Cl” Changing the Cl changes the “H”? Is this balanced? Yes! H 2 1

22. 21 Na + HCl  NaCl + H 2 Na Cl H 1 1 1 2 1 1 (2) 2 In this case, we will start with hydrogen since it is the only one unbalanced. Let’s try another:

23. 22 Na + HCl  NaCl + H 2 Na Cl H 1 1 1 2 1 1 (2) 2 (2) (2) 2 But, changing the hydrogen in HCl affects the number of chlorine atoms.

24. 23 Changing the chlorine on the product side affects the sodium (Na) on the reactants side. So we must now change sodium as well. Na + 2HCl  NaCl + H 2 Na Cl H 1 1 1 2 1 1 (2) (2) (2) 2 2 (2) (2)

25. 24 Independent Practice

26. 25 5 Types of Chemical Reactions Synthesis Decomposition Single Displacement Double Displacement Combustion

27. 26 Synthesis A + B  AB 2H 2 + O 2  2H 2 O Two or more substances combine to form a new one.

28. 27 Decomposition AB  A + B 2MgO  2Mg + O 2 One substance breaks down or decomposes into 2 or more simpler substances. Most reactions require heat, light or electricity.

29. 28 Single Displacement A + BC  AC + B Zn + Cu(NO 3 ) 2  Zn(NO 3 ) 2 + Cu One element replaces another in a compound

30. 29 Double Displacement AB + CD  AD + CB HCl + NaOH  HOH + NaCl (H 2 O) The negative ion of one compound replaces the negative ion of the other compound to form 2 new compounds. Usually forms a precipitate, water or a gas.

31. 30 Combustion Takes place when both CO 2 and H 2 O are the ONLY products CH 4 + 2O 2 CO 2 + 2H 2 O + energy

32. 31 Independent Practice

33. 32 Energy in Reactions In a chemical reaction energy is either released or absorbed. –The energy can be Heat Light Sound Electricity

34. 33 Energy in Reactions Exothermic reactions –Some form of energy is given off by the reaction Heat given off causes reaction mixture to feel hot Examples-burning wood, dynamite explosion Endothermic reactions –Energy must be provided for the reaction to take place Absorbs so much heat that the container feels cold Example-frequently used to obtain a metal from its ore, using an electric current, chemical cold packs