Ch. 8 Chemical Equations and Reactions 8.1 Describing Chemical Reactions

Chemical Reactions when a substance changes identity reactants- original products- resulting law of conservation of mass total mass of reactants = total mass of products

Chemical Reactions chemical equation represents identities and relative amounts of reactants and products in the chemical reaction uses symbols and formulas

Hints of Chemical Rxn heat or light gas bubbles precipitate can also happen with physical changes gas bubbles means a gas is being created as product precipitate solid is being created color change

Writing Chemical Equations most pure elements written as elemental symbol diatomic molecules molecule containing only 2 atoms some elements normally exist this way H2, O2, N2, F2, Cl2, Br2, I2 other exceptions sulfur: S8 phosphorus: P4

Word Equations uses names instead of formulas helps you to write formula equation

Example Description: Solid sodium oxide is added to water at room temperature and forms sodium hydroxide. Word Equation: sodium oxide + water  sodium hydroxide Formula Equation: Na2O + H2O  NaOH Na2O + H2O  2NaOH

Symbols Used in Equations yields reversible above arrow: or heat heated MnO2 or Pt catalyst 25°C specific T requirement 2 atm specific P requirement after a formula: (s) solid (l) liquid (aq) aqueous: dissolved in water (g) gas

Coefficients whole numbers in front of formula distributes to numbers of atoms in formula specifies the relative number of moles and molecules involved in the reaction used to balance the equation

Equations cannot tell us: if the reaction will actually occur depends on many factors affecting energy the speed of the reaction depends on chemical kinetics can be very slow, almost unnoticeably how the bonding actually changes formula may not clearly show bonding