Ch. 8 Chemical Equations and Reactions 8.1 Describing Chemical Reactions

Hints of Chemical Reaction heat or light heat or light gas bubbles gas bubbles precipitate precipitate color change color change

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

Word Equations uses names instead of formulas uses names instead of formulas Can act as bridge between word problem and actual chemical equation Can act as bridge between word problem and actual chemical equation Example Example Solid sodium oxide is added to water at room temperature and forms sodium hydroxide. Solid sodium oxide is added to water at room temperature and forms sodium hydroxide.

Chemical Reactions chemical equation chemical equation represents identities and relative amounts of reactants and products in the chemical reaction represents identities and relative amounts of reactants and products in the chemical reaction uses symbols and formulas to represent chemicals uses symbols and formulas to represent chemicals Uses coefficients to balance amounts Uses coefficients to balance amounts

Symbols Used in Equations yieldsreversible above arrow: or heat heated MnO 2 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

Subscripts Subscripts-found after the element, tells how many of the element. Ex: CO 2 There is one C and two O Ex:Al 3 (SO 4 ) 2 There are three Al, two S and eight O

Coefficients- BIG number found in front of molecules We’ll call all bonded atoms molecules for the purpose of simplicity Tells the number of molecules which in turn tells the number of atoms ex: 2MgO there are 2 Mg and 2 O

How to write elements... most pure elements are written as elemental symbol most pure elements are written as elemental symbol diatomic molecules diatomic molecules molecule containing only 2 atoms molecule containing only 2 atoms some elements normally exist this way (BrINClHOF twins) some elements normally exist this way (BrINClHOF twins) H 2, O 2, N 2, F 2, Cl 2, Br 2, I 2, At 2 H 2, O 2, N 2, F 2, Cl 2, Br 2, I 2, At 2 other exceptions other exceptions sulfur: S 8 sulfur: S 8 phosphorus: P 4 phosphorus: P 4