1. Chemical Reactions

2. Did a Chemical Reaction Take Place? There are several ways to tell if a chemical reaction has occurred… –Temperature change –Color change –Odor –Precipitate is formed (solid) –Gas is formed

3. A substance that undergoes a reaction is called a reactant. –Reactants are written on the left of the arrow When reactants undergo a chemical change, each new substance formed is called a product. –Products are written on the right of the arrow Reactants  Products Writing Chemical Equations

4. Reactants – starting chemical Products – substances that are formed + separates substances (usually read as “and”)  separates reactants from products (usually read as gives, produces, or yields) Writing Chemical Equations

5. The simplest way to represent a reaction is by using words to describe all the reactants and products, with an arrow placed between them to represent change. Reactants are placed to the left of the arrow, and products are placed to the right. Plus signs are used to separate reactants and also to separate products. Word Equations VinegarBaking Soda

6. Word equations describe reactants and products, but they are long and awkward and do not adequately identify the substances involved. Word equations can be converted into chemical equations by substituting chemical formulas for the names of compounds and elements. Chemical Equations

7. The equation for the reaction of vinegar and baking soda can be written using the chemical formulas of the reactants and products. By examining a chemical equation, you can determine exactly what elements make up the substances that react and form. Chemical Equations

8. Chemical Reactions It may also be important to know the physical state of each reactant and product. Symbols in the parentheses are put after formulas to indicate the state of the substance. Solids, liquids, gases, and in water (aqueous) solutions are indicated by the symbols (s), (l), (g), and (aq).

9. Try this example… Write the skeleton equation for solid magnesium reacting with oxygen gas to give solid magnesium Mg (s) + O 2 (g)  MgO You can see that you have to remember how to write formulas and what elements are diatomic in order to write equations!

10. The mass of the products is always the same as the mass of the reactants that react to form them. The law of conservation of mass summarizes these findings. Matter is neither created nor destroyed during a chemical reaction. What you start with has to equal what you end with Balancing Chemical Equations

11. For a chemical equation to accurately represent a reaction, the same number of each kind of atom must be on the left side of the arrow as are on the right side.

12. 1.Write the skeleton equation for the reaction 2.Count the number of atoms of each element of the reactants 3.Count the number of atoms of each element of the reactants 4.Add / Change the coefficients to make the numbers of each element equal 5.YOU CAN NEVER CHANGE A SUBSCRIPT! 6.Write the coefficients in the lowest possible ratio 7.Check your work Steps for Balancing Chemical Equations

13. Examples Write the balanced chemical equation for the reaction between hydrogen and chlorine to give hydrochloric acid H 2 + Cl 2  HCl H – 2 H - 1 Cl – 2 Cl – 1 H 2 + Cl 2  2HCl H – 2 H - 2 Cl – 2

14. More examples Write and balance the reaction between sodium hydroxide and calcium bromide to give calcium hydroxide and sodium bromide 2 NaOH + CaBr 2  Ca(OH) 2 + 2NaBr

15. More examples Write and balance the reaction for potassium iodide reacting with lead (II) nitrate to form potassium nitrate and lead (II) iodide 2 KI + Pb(NO 3 ) 2  2 KNO 3 + PbI 2

16. Classification of Reactions There are 5 major classifications of reactions: –Synthesis (Combination) –Decomposition –Combustion –Single Replacement –Double Replacement (Metathesis)

17. Synthesis (Combination) Synthesis – when 2 or more substances react to produce 1 product Of the form: A + B  AB Examples: –2 Fe + 3 Cl 2  2 FeCl 3 –2 Na + Cl 2  2NaCl –CaO + H 2 O  Ca(OH) 2 –Mg + O 2  MgO

18. Decomposition Decomposition – when a single compound breaks down into 2 or more compounds Of the form: AB  A + B Note that this is the exact opposite of synthesis Examples: –2 Na 3 N  2 Na + 3 N 2 –NH 4 NO 3  N 2 O + 2H 2 O –2H 2 O  H 2 + O 2

19. Combustion Combustion – when O 2 combines with a hydrocarbon to form CO 2 and H 2 O Of the form: hydrocarbon + O 2  CO 2 + H 2 O For example: –2CH 4 + O 2  CO 2 + 2H 2 O –2CH 3 OH + 3O 2  2CO 2 + 4H 2 O

20. When Balancing Combustion Reactions Put a two in front of the hydrocarbon to start. Balance them in the order C, H, O Make sure your answer is in the lowest whole number ratio

21. Single Replacement Single Replacement – when the atoms of one element replace the atoms of another element in a compound Of the form : A + BX  B + AX For example: –2 Li + 2HOH  2 LiOH + H 2 –Cu + 2AgNO 3  2 Ag + Cu(NO 3 ) 2

22. Activity Series

23. Single Replacement Reactions In order for a single replacement reaction to occur, the element that is by itself must be strong enough to push the other element out of the way. The activity series show you the relative pushing power of the elements. In order for the reaction to occur, the lone element must be above the element in the compound Otherwise…NO REACTION  NR

24. Single Replacement Reactions You need to know which chart you are to look at…metals or halogens. A metal can replace another metal A halogen can replace another halogen

25. Will these reactions occur? Will the following reaction occur? If so, complete and balance the reaction. Ag + Cu(NO 3 ) 2  Ag + Cu(NO 3 ) 2  NR No reaction because Ag is below Cu in the Activity series of metals

26. Will these reactions occur? Will the following reaction occur? If so, complete and balance the reaction. Mg + AlCl 3  3Mg + 2AlCl 3  3MgCl 2 + 2 Al The reaction WILL occur because Mg is above Al in the activity series

27. Will these reactions occur? Will the following reaction occur? If so, complete and balance the reaction. Br 2 + MgCl 2  Br 2 + MgCl 2  NR This reaction will NOT occur because Br is not above Cl in the activity series of halogens

28. Double Replacement (Metathesis) Double Replacement – a reaction involving the exchange of ions between 2 compounds Of the form: AX + BY  BX + AY Examples: –Pb(NO 3 ) 2 + 2KI  PbI 2 + 2KNO 3 –Na 2 CO 3 + 2AgNO 3  2NaNO 3 + Ag 2 CO 3

29. Double Replacement (Metathesis) In order for a double replacement reaction to take place, one of 3 things must be formed: Precipitate (solid) Gas Weak electrolyte – usually water

30. Solubility Rules

31. Soluble or Insoluble? Classify the following as soluble or insoluble? (Hint: insoluble means precipitate) NaCO 3 Soluble PbSO 4 Insoluble (precipitate) Co(OH) 2 Insoluble (precipitate) Ba(NO 3 ) 2 Soluble (NH 4 ) 3 PO 4 soluble

32. Reactions with a gas Carbonates, bicarbonates, and sulfides react with acids to form a gas For example: HCl + Na 2 S  2HCl + Na 2 S  H 2 S (g) + 2NaCl The sulfide or carbonate formed will result in the gas

33. Reactions with a gas HCl + NaHCO3  HCl + NaHCO 3  H 2 CO 3 (g) + NaCl HCl + NaHCO 3  H 2 O + CO 2 (g) + NaCl

34. Will these reactions occur? Will the following reaction occur? If so, complete and balance the reaction. Na 2 CO 3 + AgNO 3  Na 2 CO 3 + AgNO 3  Ag 2 CO 3 + NaNO 3 Na 2 CO 3 + AgNO 3  Ag 2 CO 3 (s) + NaNO 3 Na 2 CO 3 + 2AgNO 3  Ag 2 CO 3 (s) + 2NaNO 3

35. Will these reactions occur? Will the following reaction occur? If so, complete and balance the reaction. HCl + NaOH  HCl + NaOH  NaCl + HOH HCl + NaOH  NaCl + H 2 O

36. Will these reactions occur? Will the following reaction occur? If so, complete and balance the reaction. NaOH + K 2 SO 4  NaOH + K 2 SO 4  Na 2 SO 4 + KOH NaOH + K 2 SO 4  Na 2 SO 4 (aq) + KOH (aq) NaOH + K 2 SO 4  NR