1. Chemical Reactions and Equations CHEMISTRY PART 3

2. Chemical Reaction  What is a chemical reaction?  A chemical reaction : is a process in which one set of substances called reactants is converted to a new set of substances called products.  reactants  products

3. Some physical evidence to look for that shows a reaction has occurred:  a color change  formation of a solid (precipitate) within a clear solution  evidence of a gas  evolution or absorption of heat How do we know a chemical reaction has occurred ?

4. Chemical Formula Substitute chemical formulas for names, to obtain the following expression. nitrogenreact oxygento nitrogen monoxide with gasform dioxide gas NO + O 2  NO 2

5. (c) McGraw Hill Ryerson 2007 When a chemical reaction occurs, new compounds are created, BUT… –No new matter is created or destroyed rearrangedchange partners –No new matter is created or destroyed; atoms are just rearranged as the atoms change partners to form new compounds. 3 –If there are 3 atoms of oxygen in the reactants, there MUST be 3 atoms of oxygen in the products. –Number of each atom in reactants = number of each atom in products. The law of conservation of mass: –Mass of reactants = mass of products If you could collect and measure all of the exhaust from this car, you would find that mass of reactants (gas + O 2 ) = mass of products (exhaust).

6. Types of Reactions Synthesis reaction:A + B  AB Decomposition reactions: AB  A + B Single -Displacement reactions: AB + C  AC + B Double-Displacement reactions: AB + CD  AD + CB

7. Balancing Equations (Stoichiometry)

8. balanced chemical equation coefficientsA balanced chemical equation shows all atoms and the coefficients tells us how many molecules (and atoms) there are. ensures number of each atom same on both sides –Balancing ensures that the number of each atom is the same on both sides of the reaction arrow. 42 4K + O 2  2K 2 O K K K K K K K K K K K K K K K K OO O O

9. (c) McGraw Hill Ryerson 2007 count atoms to balanceUsing the law of conservation of mass, we can count atoms to balance the number of atoms in chemical equations. –Word equation: methane + oxygen  water + carbon dioxide –Skeleton equation:CH 4 + O 2  H 2 O + CO 2 To balance the compounds, take note of how many atoms of each element occur on each side of the reaction arrow. See Page 207

10. Video over how to balance equations  http://www.schooltube.com/video/7f9c94c1a297431d9dfd/Balanci ng%20Chemical%20Equations%20(Stoichiometry)%20-%20Lesson http://www.schooltube.com/video/7f9c94c1a297431d9dfd/Balanci ng%20Chemical%20Equations%20(Stoichiometry)%20-%20Lesson

11. Endothermic Reaction VS Exothermic reaction

12. Energy Diagrams pg 637