1. Chemical Reactions

2. Chemical Equation Describes what you had before and then after the change Reactants: substances that undergo change Products: new substances formed Reactants Products

3. Chemical Equation Chemical equation: representation of a chemical reaction in which the reactants and products are expressed as formulas Examples: C + O 2 CO 2

4. Conservation of Mass Antoine Lavoisier 1743-1794 ◦ Law of conservation of mass: mass is neither created nor destroyed in a chemical reaction Mass of the products is always equal to the mass of the reactants

5. Balancing Equations H 2 + O 2 H 2 O NOT BALANCED! Number of atoms on the reactant side MUST equal the number of atoms on the product side!!!

6. Balancing Equations H 2 + O 2 H 2 O Use Coefficients to balance equations 2H 2 + O 2 2H 2 O

7. Example Cu + O 2 CuO Balanced or unbalanced???

8. Examples Na + Cl 2 NaCl H 2 + Cl 2 HCl AgNO 3 + Cu Cu(NO 3 ) 2 + Ag BaS + PtF 2 BaF 2 + PtS

9. Types of Reactions

10. Classifying reactions Reactions are often classified by the type of reactant or the number of reactants and products General types include: ◦ Synthesis reaction ◦ Decomposition reaction ◦ Single-replacement ◦ Double-replacement ◦ Combustion

11. Synthesis Two or more substances react to form a single substance A + B AB Example: 2Cu + O 2 2CuO

12. Decomposition Compound breaks down into two or more simpler substances AB A + B Example: CaCO 3 CaO + CO 2

13. Single Replacement One element takes the place of another element in a compound A + BC B + AC Example: Cu + 2AgNO 3 2Ag + Cu(NO 3 ) 2

14. Double Replacement Two different compounds exchange positive ions and form two new compounds AB + CD AD + CB Example: CaCO 3 + 2HCl CaCl 2 + H 2 CO 3

15. Combustion Substance reacts rapidly with oxygen, often producing heat and light

16. Breaking and Forming Bonds Breaking bonds: ◦ Requires energy  Example: Propane grills have a starter that produces a spark Forming bonds: ◦ Releases energy  Example: heat and light are given off by a propane grill

17. Exothermic Reaction Chemical reaction that releases energy to its surroundings

18. Endothermic Reaction Chemical reaction that absorbs energy from its surroundings

19. Exothermic vs Endothermic Exo: ◦ Reactants have more energy than products  AB+ CD+ 450 J AD + CB Endo: ◦ Products have more energy than reactants  AB + CD AD + CB + 450 J

20. Reaction Rates

21. Reactions over time Any change that happens over a period of time can be expressed as a rate Reaction rate: rate at which reactants change into products over time ◦ Tell us how fast a reaction is going  How fast reactants are being consumed  How fast the products are being formed  How fast energy is being absorbed or released

22. Factors Affecting Reaction Rates Reaction rate depends on how often particles collide ◦ More frequent = increase reaction rate ◦ Less frequent = decrease reaction rate Temperature Surface area Concentration Stirring Catalysts

23. Temperature Increase in temperature = increase in reaction rate Decrease in temperature = decrease in reaction rate

24. Surface Area An increase in surface area increases the exposure of reactants to one another An increase in surface area = increase in reaction rate

26. Stirring Stirring causes collisions to occur more rapidly Stirring = increase in reaction rate

27. Concentration Concentration = number of particles in a given volume Greater the concentration = increase in reaction rate

28. Catalysts Catalyst: substance that affects the reaction rate without being used up in the reaction ◦ Used to speed up reactions or used to enable a reaction at a lower temperature ◦ Written over the arrow because it is not used up 2SO 2 + O 2 2SO 3 V2O3V2O3

29. Catalysts In order for a reaction to occur, particles must collide with enough energy to break the bond ◦ Catalyst lowers this energy barrier ◦ Provides a surface area for reacting particles to come together