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