Chemical

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. Writing Chemical Equations • 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

4. Writing Chemical Equations • 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)

5. Word Equations • 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. Vinegar Baking Soda

6. Chemical Equations • 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.

7. Chemical Equations • 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.

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) + O2 (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. Balancing Chemical Equations • 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

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

13. Examples • Write the balanced chemical equation for the reaction between hydrogen and chlorine to give hydrochloric acid • H2 + Cl2 HCl H – 2 H - 1 Cl – 2 Cl – 1 • H2 + Cl2 2HCl H – 2 H - 2 Cl – 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 + CaBr2 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(NO3)2 2 KNO3 + PbI2

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 Cl2  2 FeCl3 • 2 Na + Cl2  2NaCl • CaO + H2O  Ca(OH)2 • Mg + O2  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 Na3N  2 Na + 3 N2 • NH4NO3  N2O + 2H2O • 2H2O  H2 + O2

19. Combustion • Combustion – when O2 combines with a hydrocarbon to form CO2 and H2O • Of the form: hydrocarbon + O2 CO2 + H2O • For example: • 2CH4 + O2  CO2 + 2H2O • 2CH3OH + 3O2  2CO2 + 4H2O

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 + H2 • Cu + 2AgNO3  2 Ag + Cu(NO3)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(NO3)2 • Ag + Cu(NO3)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 + AlCl3 • 3Mg + 2AlCl33MgCl2 + 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. • Br2 + MgCl2 • Br2 + MgCl2 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(NO3)2 + 2KI  PbI2 + 2KNO3 • Na2CO3 + 2AgNO3 2NaNO3 + Ag2CO3

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) • NaCO3 • Soluble • PbSO4 • Insoluble (precipitate) • Co(OH)2 • Insoluble (precipitate) • Ba(NO3)2 • Soluble • (NH4)3PO4 • soluble

32. Reactions with a gas • Carbonates, bicarbonates, and sulfides react with acids to form a gas • For example: • HCl + Na2S  • 2HCl + Na2S H2S (g) + 2NaCl • The sulfide or carbonate formed will result in the gas

33. Reactions with a gas • HCl + NaHCO3  • HCl + NaHCO3  H2CO3 (g) + NaCl • HCl + NaHCO3  H2O + CO2 (g) + NaCl

34. Will these reactions occur? • Will the following reaction occur? If so, complete and balance the reaction. • Na2CO3 + AgNO3 • Na2CO3 + AgNO3Ag2CO3 + NaNO3 • Na2CO3 + AgNO3Ag2CO3 (s) + NaNO3 • Na2CO3 + 2AgNO3Ag2CO3 (s) + 2NaNO3

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 + H2O

36. Will these reactions occur? • Will the following reaction occur? If so, complete and balance the reaction. • NaOH + K2SO4  • NaOH + K2SO4  Na2SO4 + KOH • NaOH + K2SO4  Na2SO4 (aq) + KOH (aq) • NaOH + K2SO4 NR