Chapter 8 Chemical reactions

Chemical Reaction Represents a chemical change Reactants products When a chemical change occurs the products have a different set of properties than the reactants. Follows the Law of the Conservation of Mass

Law of the conservation of mass Matter can not be destroyed or created it can only be rearranged. Mass of the reactants must equal the mass of the products. That is why all chemical reactions must be balanced.

Balancing Equations Preliminaries- if a word problem, identify the reactants and the products of the reaction. Write the equation in chemical reaction form Generally stated as A + B C First do an atom count of the reactants and of the products. Second – adjust coefficients to make the number of atoms for each element equal on both sides.

Example LiAlH 4 + H 2 O LiOH + Al(OH) 3 + H 2 1- Li 1-Al 6 - H 1- O 1 –Li 1- Al 6- H 4- O

Example Al(NO 3 ) 3 + NaOH Al(OH) 3 + NaNO 3

Types of Chemical Equations Single displacement reactions Double displacement reactions Decomposition reactions Synthesis reactions Combustion reactions

Single and double displacement General form of a single displacement reaction Single Displacement A+ BC B + AC (redox reactions) Double displacement AB + CD AD + CB

Decomposition and Synthesis Decomposition reactions general formula AB A + B Synthesis reactions general formula A + B AB

Combustion reactions Will always follow the same pattern- template A + O 2 CO 2 + H 2 O + Energy C 4 H 8 + O 2 CO 2 + H 2 O + Energy C 4 H 8 + 6O 2 4CO 2 +4H 2 O+Energy

Percent Yield Percent yield = actual amount of the product/ the theoretical amount of the product X 100. Until we do stoichiometry,the theoretical amount will be given to you. Once we completed 9.2, you will be able to find out the theoretical amount yourself.

Example The actual amount in a reaction is 39.7 g, the predicted amount was 65.6 grams. What is the percent yield? (39.7g/ 65.6g ) x 100 = 60.5%

More on combustion equations Balance the equations Use the molar heat of combustion to find the amount of heat evolved. Review terms exothermic endothermic

Chemical reaction symbols Solid – cr Gas – g Liquid/ dissolved in water - aq