Chemical Equations and Reactions

1. Chemical Equations and Reactions 8.1 Describing Chemical Reactions

2. Chemical Reactions • Chemical Reaction – the process by which one or more __________ are changed into one or more _________ substances • Follows the law of ________ of mass • Chemical equation – represents, with _______ and formulas, the __________ and relative molar amounts of the _________ and products in a ________ reaction

3. Indication of Chemical Rxn • Evolution of ______ as heat or light • Production of a ___ • Formation of ___________ • _____ change

4. Characteristics of Chemical Equations • The equation must represent _____ facts • The equation must contain correct ________ for the _________ and the _________ • The law of conservation of ____ must be satisfied

5. Definitions • Coefficient – a small ______ number that appears in _____ of a formula in a chemical ________ • Placed in front to _______ an equation • Word Equation – an equation in which the _________ and products in a ________ reaction are represented by _____

6. Word Equations • Does not give _______ • Methane plus oxygen yields carbon dioxide plus water. • Remember ________ molecules. • CH4 + O2 CO2 + H2O • Formula equation – __________ reactants & products of a chem rxn by their _______ & ________

7. Completing the reaction • Use _______ to indicate ______. • CH4(g) + O2(g) CO2(g) + H2O(g) • Other symbols on page ___ of book • Also _____ to follow the ___ of ____________ of mass • Add ___________ to _______ eqn.

8. Equations 800 K C2H6 (g) C2H4 (g) + H2 (g) Physical Catalyst State Products Reactants Cr2O3

9. Definitions • Reversible reaction – a chemical ________ in which the products __-_____ the original reactants. • Catalyst – ______ up a reaction _______ being used up ______ the reaction.

10. Significance of a Chemical Rxn • The coefficients indicate ________ not ________ amts. • The relative ______ can be determined by the rxn’s ___________. • The _______ rxn has the same relative _______ of substances as the _______ rxn.

11. Balancing Chemical Reactions • Write the unbalanced formula eqn. • Count the # of each element • Insert coefficients for atoms • Check to make sure both sides are the same.

12. Balancing Chemical Reactions • Delay balancing elements (like H and O) that occur in several reactants or products. • If the same polyatomic ions appear on both sides of the equation, treat them as single units, like monatomic ions.

13. Balancing Chemical Reactions 3. After considering 1&2, balance elements left to right. 4. Remember, balancing 1 element may unbalance others. 5. For ionic equations, be sure charges are balanced.

14. Balancing Chemical Reactions • Ammonia plus oxygen yields nitrogen monoxide plus water plus heat. • _____ equations • Need to make sure ionic _______ are balanced • HCl + H2O  Cl- + H3O+

15. Practice • Write the ____ and _______ equations for the chemical reaction that occurs when _____ sodium oxide is _____ to water at room temp and _____ sodium hydroxide (dissolved in the water). Include _______ for physical states & _______ the eqn

16. Practice • Try balancing the following equations… • __Li + __AlCl3  __LiCl + __Al • __C + __SO2  __CS2 + __CO • __C3H8 + __O2  __CO2 + __H2O • __Al(OH)3 + __HBr  __AlBr3 + __H2O

17. More Practice • __Rb + __S8 __Rb2S • __NH3 + __O2  __N2 + __H2O • __C6H12O6+ __O2  __CO2 + __H2O • __C3H8O + __O2  __CO2 + __H2O