1. Unit I: CHEMICAL REACTIONS I.4 Introduction to Chemical Equations

2. Chemical Change One or more new substances are formed in a chemical reaction New substances formed by a chemical reaction or chemical change have properties different from those of the starting materials

3. Chemical Reactions In chemical reactions  The starting materials are called reactants  The resulting materials are called products

4. Signs --- that a chemical change has occurred Bubbles of gas appear Precipitate forms  Formation of solids in liquids Change in colour  Clear  cloudy New smells Reactant used up Difficult to reverse Smoke Energy (heat, light, sound) A change in volume A change in conductivity A change in melting or boiling point

5. Chemical Change

6. Chemical Reaction Equations equation Is an equation that shows the chemicals used up and produced during a chemical reaction REACTANTS  PRODUCTS

7. Chemical Word Equation Uses words to describe the REACTANTS and PRODUCTS Eg. Sodium and chlorine react to form sodium chloride

8. Coefficients the numbers in front of symbols  Refer to the numbers of molecules of each species involved in reaction

9. Unit I: CHEMICAL REACTIONS I.4 The Conservation Laws

10. System Part of the universe being studied in a particular location

11. Closed System CLOSED A CLOSED system nothing can enter or leave the system It exchanges energy (heat and work) but not matter with the environment.

12. Closed System

13. Open System Open System Open System  Things can enter and leave the system  It exchanges energy (heat and work) and matter with the environment.

14. Open System

16. The Four Laws of Conservation 1. Law of Conservation of Mass The total mass in a closed system does not change during a chemical reaction

17. The Four Laws of Conservation 2. Law of Conservation of Atoms Total number and type of atoms in a closed system does not change during a chemical reaction Mg Mg Mg Mg Na Whoa! Where did you come from!

18. The Four Laws of Conservation 3. Law of Conservation of Electrical Charge  The total electrical charge in a closed system does not change during a chemical reaction

21. The Four Laws of Conservation 4. Law of Conservation of Energy  The total energy in a closed system does not change during a chemical reaction Relative types of energy may change but the total amount of energy remains the same

22. The Four Laws of Conservation

24. Hebden Do Exercises 1 and 2 on page 106 and 3 to 5 on page 107