Unit 5: Chemical Reactions Section 1: Describing Reactions Chemical Reaction Law of Conservation of Mass Chemical Equations and Balancing

A. Physical and Chemical Changes During a physical change, some properties of a material change, but the composition of the material does not change. Examples of physical changes: Grinding Cutting Folding Cracking Filing Bending Phase changes (melting, boiling, condensing, etc)

A. Physical and Chemical changes A change that involves one or more substances turning into new substances is called a chemical change. Examples of chemical changes: decomposing rusting exploding burning oxidizing tarnishing fermenting

PA. Physical and Chemical Changesand Chemical Changes A magnet separates iron from sulfur. This is an example of a physical change. A mixture of iron filings and sulfur can be changed. a) A magnet separates the iron from the sulfur. b) Heat combines iron and sulfur in a compound. Classifying Which change is a chemical change? Explain.

PhA. Physical and Chemical Changesand al and Chemical Changes A mixture of iron and sulfur is heated. The iron and sulfur react and form iron sulfide. This is an example of a chemical change. A mixture of iron filings and sulfur can be changed. a) A magnet separates the iron from the sulfur. b) Heat combines iron and sulfur in a compound. Classifying Which change is a chemical change? Explain.

B. Chemical Reaction Chemical Change: new & different substances formed. 4 Evidences of Chemical Reaction: energy transfer (hot or cool) color change gas formed precipitate formed (solid)

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

C. Law of Conservation of Mass In a chemical reaction, matter is neither created nor destroyed. Atoms can only rearrange. 4H 2O 4H 2O

D. Chemical Equations N2H4 + O2  N2 + H2O N2H4 + O2  N2 + 2 H2O Balancing Equations N2H4 + O2  N2 + H2O N2H4 + O2  N2 + 2 H2O Coefficient - # of units of each substance

coefficient  subscript = # atoms D. Chemical Equations 3 Balancing Steps 1. Count atoms on each side. 2. Use coefficients to make atoms equal. coefficient  subscript = # atoms How many N’s in: 2 Fe(NO3)2 3. Double check atom balance!!!

D. Chemical Equations 3 2 Al + CuCl2  Cu + AlCl3 Al Cu Cl 2 3 3 2 Aluminum and copper(II) chloride form copper and aluminum chloride. 3 2 Al + CuCl2  Cu + AlCl3 Al Cu Cl 2 3 3 2 2 3 2 2   2 3  6   6 1 1 2 3  3

Quick Quiz! Which of the following is a chemical reaction? melting of lead dissolving sugar in water rusting of iron crushing of stone

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

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

__Al + __HCl → __AlCl3 + __H2 Quick Quiz. What is the coefficient of HCl when the following reaction is balanced? __Al + __HCl → __AlCl3 + __H2 ___Al___ ___H___ ___Cl___ A. 1 B. 2 C. 3 D. 6 2 Al + 6 HCl → 2 AlCl3 + 3 H2 1 1 1 2 1 3