Chemical Formulas and Equations

Changes in Matter Matter can undergo 2 types of changes… 1.Physical Change (only affects physical properties; ex: size, shape, solid, liquid, gas) 2.Chemical Change (produces new substances that have different properties than original substances) Chemical Reaction- A process that produces a chemical change.

Chemical Equations Reactants- Substances that react Products- Substances that form Chemical Equation- Tells chemists the reactants, products and proportions of each substance present. (some tell physical state of each substance)

Describe a Chemical Reaction 1.Use Words Reactants are listed on left side of the arrow, separated from each other by a plus (+) sign Products are placed on right side of arrow, also separated by a plus (+) sign The (Arrow) → = produces Use chemical names instead of common names in equations

Conservation of Mass Law of Conservation of Mass- The mass of the products must be the same as the mass of the reactants in the chemical reaction. –Atoms are never lost or created in a chemical reaction; they just change partners

Balancing Chemical Equations Same # of atoms on left side of → need to be on right side as well.

Energy (Exothermic) Energy Released (bonds break in reactants and new bonds are formed in the product) –Products are more stable and bonds have less energy than those of the reactants –Extra energy is released (light, sound, and thermal energy)

Energy (Endothermic) Energy Absorbed (reactants are more stable and bonds have less energy than the products)

Reactions Endothermic Reactions- Absorb thermal energy. Exothermic Reactions- Release thermal energy. –Burning is exothermic energy Energy can be released rapidly (charcoal) or slowly (rust) –“Energy” can be included in the equation, but not necessary

Classifying Chemical Reactions Synthesis- Puts things together for products Decomposition- Breaks down compounds Replacement- Elements of compounds are rearanged