1. 1 What is a physical change? In a physical change, identity and composition substance do not change. state can change or material can be torn into smaller pieces.

2. 2 What is a chemical change? In a chemical change, reacting substances form new substances with different compositions and properties. chemical reaction takes place.

3. 3 What is a chemical reaction? In a chemical reaction chemical change produces one or more new substances change in composition of one or more substances old bonds are broken and new bonds are formed atoms in reactants are rearranged to form one or more different substances. Fe and O 2 form rust (Fe 2 O 3 ).

4. 4 Law of Conservation of Mass Indicates chemical reaction matter cannot be created nor destroyed. no change in total mass occurs in a reaction. mass of products is equal to mass of reactants.

5. 5 What are chemical equations? chemical equation chemical formulas of reactants on left of arrow and products on right. atoms are not gained or lost ReactantsProduct C(s) O 2 (g) CO 2 (g) Symbols states of reactants. states of products. reaction conditions number of reactant atoms is equal to the number of product atoms

6. 6 Let’s look at a balanced chemical equation! In a balanced chemical equation, same number of each type of atom on reactant side and on product side of a balanced equation. numbers called coefficients used in front of one or more formulas. Al + S  Al 2 S 3 Not Balanced 2Al + 3S  Al 2 S 3 Balanced 2 Al = 2 Al 3 S = 3 S

7. 7 balance following equation, Fe 3 O 4 (s) + H 2 (g)  Fe(s) + H 2 O(l) work on one element at a time. use only coefficients in front of formulas. do not change any subscripts. Fe:Fe 3 O 4 (s) + H 2 (g)  3Fe(s) + H 2 O(l) O:Fe 3 O 4 (s) + H 2 (g)  3Fe(s) + 4H 2 O(l) H: Fe 3 O 4 (s) + 4H 2 (g)  3Fe(s) + 4H 2 O(l) Steps in Balancing an Equation

8. 8 1. Need equation with correct formulas. NH 3 (g) + O 2 (g)  NO(g) + H 2 O(g) 2. Determine if equation is balanced. above, not all atoms are balanced. 3. Balance using coefficients in front of formulas. 4NH 3 (g) + 5O 2 (g)  4NO(g) + 6H 2 O(g) 4. Check atoms (elements) equal both sides. 4 N (4 x 1 N) = 4 N (4 x 1 N) 12 H (4 x 3 H) = 12 H (6 x 2 H) 10 O (5 x 2 O)= 10 O(4 O + 6 O) Balancing Chemical Equations

9. 9 Balancing with polyatomic ions MgCl 2 (aq) + Na 3 PO 4 (aq)  NaCl(aq) + Mg 3 (PO 4 ) 2 (s) Balance PO 4 3- as a unit MgCl 2 (aq) + 2Na 3 PO 4 (aq)  NaCl(aq) + Mg 3 (PO 4 ) 2 (s) 2 PO 4 3- = 2 PO 4 3- Balance Mg and Cl 3MgCl 2 (aq) + 2Na 3 PO 4 (aq)  6NaCl(aq) + Mg 3 (PO 4 ) 2 (s) 3 Mg 2+ = 3 Mg 2+ 6 Na + = 6 Na + 6 Cl - = 6 Cl -

10. 10 What is a mole? A collection term states a specific number of items. 1 dozen donuts = 12 donuts 1 ream of paper = 500 sheets 1 case = 24 cans

11. 11 A mole: collection that contains same number of particles as there are carbon atoms in 12.0 g of carbon. 6.02 x 10 23 atoms of an element (Avogadro’s number) 1 mole element Number of Atoms 1 mole C = 6.02 x 10 23 C atoms 1 mole Na = 6.02 x 10 23 Na atoms 1 mole Au= 6.02 x 10 23 Au atoms A mole of covalent compound has Avogadro’s number of molecules. 1 mole CO 2 = 6.02 x 10 23 CO 2 molecules 1 mole H 2 O = 6.02 x 10 23 H 2 O molecules of ionic compound contains Avogadro’s number of formula units. 1 mole NaCl = 6.02 x 10 23 NaCl formula units 1 mole K 2 SO 4 = 6.02 x 10 23 K 2 SO 4 formula units A mole can be expressed as:

12. 12 Using Avogadro’s number Avogadro’s number is used to convert moles of a substance to particles 1 mole = 6.02 x 10 23 particles Conversion Factors: 6.02 x 10 23 particles and 1 mole 1 mole6.02 x 10 23 particles How many Cu atoms are in 0.50 mole Cu? 0.50 mole Cu x 6.02 x 10 23 Cu atoms 1 mole Cu = 3.0 x 10 23 Cu atoms

13. 13 Using Avogadro’s number Avogadro’s number is used to convert particles of a substance to moles Conversion Factors: 6.02 x 10 23 particles and 1 mole 1 mole6.02 x 10 23 particles How many moles of CO 2 are in 2.50 x 10 24 molecules CO 2 ? 2.50 x 10 24 molecules CO 2 x 1 mole CO 2 6.02 x 10 23 molecules CO 2 = 4.15 mole CO 2

14. 14 What is molar mass? molar mass mass of one mole of an element or compound. atomic mass expressed in grams.

15. 15 Molar mass of a compound molar mass of a compound is sum of molar masses of elements in formula. Example: Calculate molar mass of CaCl 2. ElementNumber of Moles Atomic MassTotal Mass Ca140.1 g/mole 40.1 g Cl235.5 g/mole 71.0 g CaCl 2 111.1 g

16. 16 Molar Mass of K 3 PO 4 Calculate molar mass of K 3 PO 4. Elemen t Number of Moles Atomic Mass Total Mass in K 3 PO 4 K339.1 g/mole 117.3 g P131.0 g/mole 31.0 g O416.0 g/mole 64.0 g K 3 PO 4 212.3 g Let’s calculate molar mass of : S, NaCl, Fe,

17. 17 Collision theory of reactions chemical reaction occurs when collisions between molecules have sufficient energy to break bonds in the reactants. bonds between atoms of the reactants (N 2 and O 2 ) are broken and new bonds (NO) can form.

18. 18 What is activation energy? minimum energy needed for a reaction to take place collision provides energy equal to or greater than activation energy, product can form

19. 19 C + 2 H 2 CH 4 + 18 kcal In an exothermic reaction, heat is released. energy of products is less than energy of reactants. heat is a product. There are exothermic reactions

20. There are endothermic reactions In an endothermic reaction Heat is absorbed. The energy of the products is greater than the energy of the reactants. Heat is a reactant (added). N 2 + O 2 + 43.3 kcal 2NO

21. 21 Reaction Rate and Catalysts Reaction rate: speed reactant is used up speed at which product forms Catalyst increases rate of a reaction. lowers energy of activation. is not used up during reaction increases when temperature rises because reacting molecules move faster providing more colliding molecules with energy of activation