2. Chemical equation: A set of symbols and chemical formula is representing the reactants and products molecules in the chemical reaction and the conditions of the reaction.

3. Chemical reaction: Breaking the bonds in reactants molecule and forming new bonds in the product.

4. Activity: Burning magnesium ribbon in air:

5. Observation: magnesium burns with a glowing light and change to white powder. Conclusion: magnesium reacts with oxygen (reactants) to form a new substance which is magnesium oxide (product).

6. The equation:

7. Law of constant ratios: The compound is formed due to the combination of elements at constant mass ratio. *The total amount of reactants masses is equal to the total amount of products masses. *N.B: chemical equation should be balanced *(Number of atoms in reactants = Number of atoms in the products)

8. Example:

9. Types of chemical reaction:

10. A. Combination of an element with another element:

11. B. Combination of an element with a compound:

12. C. Combination of a compound with a compound:

13. Chemical reaction in our life: A-useful applications of chemical reactions: Such as: medicines, fertilizers, fuel, plastics and others.

14. B-Negative effects of chemical reactions on human and environment: 1-Fuel burning: Carbon dioxide (CO 2 ): a greenhouse gas as it permits the penetration of thermal rays from the sun to Earth and never let them return back. Carbon monoxide (CO): dangerous gas as it causes (headache, fainting, stomach ache and death)

15. 2-Sulpher oxides: SO2 (sulpher dioxide) and SO3 (sulpher trioxide) cause: acidic rain – respiratory system malfunction – building corrosion. 3-Nitrogen oxides: Such as: Nitric oxide (NO) - Nitrogen dioxide (NO2) -they are acidic gases produced at the time of lightening. -They are poisonous and affect the nervous system and eye of man. 4-Burning of coal and cellulose fibers: Such as burning paper and cigarettes cause air pollution and lung cancer.