1. Chemical Reactions Pg. 63

2. Evidence of chemical reactions When atoms rearrange to form different substances, a chemical reaction takes place Also called a chemical change Temperature change, energy in the form of heat or light, a color change, odor, gas bubbles, appearance of a solid

3. Representing chemical reactions • Use equations to represent chemical reactions • Starts with reactants and produces products • Shows the direction in which a chemical reaction will proceed • Use an arrow to show direction (its like an equal sign) • More than one reactant/product  separate with + • Reactants  Products yields

4. Symbols After each reactant or product, the state of matter is listed in parentheses If the product or reactant is dissolved in water, we say it is aqueous (s) (l) (g) (aq)

5. Word and skeleton equations • Word equations are written out versions of a chemical equation: • Skeleton equations are written from word equations • You have to keep in mind the state of the element • Have to remember diatomic elements • MUST know how ionic compounds are put together

6. Practice problems Hydrogen (g) + bromine (g)  hydrogen bromide (g) Carbon monoxide (g) + oxygen (g)  carbon dioxide (g)

7. Balancing chemical equations Must account for conservation of mass Each side must have the same number of each element Chemical equationsare statements that use chemical formulas to show the identities and relative amounts of the substances involved in the reaction Use the guess and check method Add coefficients so that the numbers will match on each side

8. Examples • CH4 + O2 CO2 + H2O • Li + H2O  LiOH + H2 • Na(NO3) Na(NO2)+ O2