Unit 6 – Lesson 1 Chemical Reactions

A chemical reaction is when the bonds between atoms of a substance are broken and the atoms rearrange and form new bonds to make substances.

How do you know when a chemical reaction occurs? What is your evidence? Temperature change Light Color Change

Appearance of a solid (precipitate) Gas formation Formation of

Reactant(s)  Product(s)  What is used in a reaction What is produced/made during a reaction

calcium + oxygen  calcium oxide Uses symbols and formulas to show what happens in a chemical reaction Chemical equation  Symbol Purpose + Separates more than one reactant or product  Separates reactants from products. Indicates direction of reaction (s) solid (aq) dissolved in water (l) liquid (g) gas Word equation - calcium + oxygen  calcium oxide reactants product Formula (skeleton) equation - Ca + O2  CaO reactants product

Law of Conservation of Mass In a chemical reaction, matter is not created or destroyed This means that you have to have the same number of each type of atom on each side of the chemical equation. After you write a chemical equation you have to balance it to make sure that the same number of atoms of each element are on each side.

SO3 = 1 sulfur & 3 oxygen 3SO3 = 3 sulfur & 9 oxygen Balancing Equations TIPS A coefficient is the number placed in FRONT of an element or compound. Coefficients are used to balance the number of atoms on each side. 2H2O - coefficient is 2 When counting atoms you multiply the compound by the coefficient. SO3 = 1 sulfur & 3 oxygen 3SO3 = 3 sulfur & 9 oxygen

NEVER change subscripts for a compound or polyatomic ion Make sure all formulas are written correctly before attempting to balance Balance oxygen LAST

Steps 1. Write the skeleton/formula equation. Make sure all the formulas are written correctly! CH4 + O2  CO2 + H2O 2. Complete an atom inventory CH4 + O2  CO2 + H2O 1 1 C H O 4 2 2 3

___CH4 + ___O2  ___CO2 + ___H2O 3. Add coefficients to make the atoms balance ___CH4 + ___O2  ___CO2 + ___H2O C H O 1 1 4 2 2 3 2 2 4 4 4

Practice Write a balanced chemical equation for the reaction in which aluminum reacts with oxygen to produce aluminum oxide. ____Al 4 + ___O2 3  ___Al2O3 2 4 1 2 Al O 4 6 2 3 6

Write a balanced chemical equation for the reaction in which hydrochloric acid reacts with calcium carbonate to produce calcium chloride, water, and carbon dioxide. __HCl 2 + __CaCO3  __CaCl2 + __H2O + __CO2 1 2 H Cl Ca C O 1 2 1 1 1 1 3 3

__BeF2 + __ Al2O3  __ BeO+ __ AlF3 1 1 Be F Al O 2 3 2 1 3 1 __BeF2 + __ Al2O3  __ BeO+ __ AlF3 3 3 2

__PbO + __HCl  __H2O + __PbCl2 1 1 Pb O H Cl 1 1 1 2 1 2 __PbO + 2HCl  __H2O + __PbCl2