Unit 8: Chemical Reactions

Changes of Matter Physical Changes:  do not change the composition of a substance. melting, vaporizing, dissolving, size, etc. Chemical Changes:  result in new substances. burning, rusting, decomposition, etc. ABBA Demo

1)gas production 2)color change 3)energy transfer (temp change, light) 4)precipitate formation 4 Clues of Chemical Change (solid forms from solution) Chemical Change: new & different substances formed.

Chemical Reaction Chemical Equation: A+B AB REACTANTS PRODUCTS present at the start of the rxn produced in the rxn at the end yields

Law of Conservation of Mass In a chemical reaction, matter is neither created nor destroyed. Atoms are rearranged. 4H 2O 4H 2O

mass of reactants = mass of products ? Law of Conservation of Mass

N 2 H 4 + O 2  N H 2 O Chemical Equations N 2 H 4 + O 2  N 2 + H 2 O Coefficient - # of units of each substance Balancing Equations mass is conserved (same before & after) WHY?

1. Count atoms on each side. 2. Add Coefficients to make # of atoms equal. coefficient  subscript = # atoms How many N’s in:2 Fe(NO 3 ) 2 3. Check atom balance!!! 3 Balancing Steps Chemical Equations H 2 + O 2  H 2 O

2 3 2  2 3  6     3  Al + CuCl 2  Cu + AlCl 3 Al Cu Cl Aluminum and copper(II) chloride form copper and aluminum chloride. Chemical Equations

1.Which of the following is a chemical reaction? A.melting of lead B.dissolving sugar in water C.rusting of iron D.crushing of stone (new substance) Quick Quiz!

2.Which of the following is NOT a possible clue that a chemical change is taking place? A.a change of state B.a change in color C.production of a gas D.formation of a precipitate Quick Quiz.

3.Why do we have to balance equations? A.it’s so much fun! B.it’s the law of the west C.it’s the law of consternation of moose D.it’s the law of conservation of mass Quick Quiz.

4.During any chemical change, the mass of the final products is… A.always equal to the mass of the starting reactants. B.always greater than the mass of the starting reactants. C.always less than the mass of the starting reactants. D.sometimes different than the mass of the starting reactants. Quick Quiz.

5.What is the coefficient of HCl when the following reaction is balanced? __Al + __HCl → __AlCl 3 + __H 2 ___Al___ ___H___ ___Cl___ A. 1B. 2C. 3D Al + 6 HCl → 2 AlCl H 2 Quick Quiz.