Doña Barbara

Section 1:
Matter can be described in terms of two kinds of properties- physical properties and chemical properties. Changes in matter can be described in terms of physical changes and chemicalchanges.

-physical property: is a characteristic of a substance that can be observed without changing the substance into another substance.
-chemical property: is a characteristic of a substance thatdescribes its ability to change into other substances.

Chemical reactions involve two main kinds of changes that you can observe –formation of new substances and changes in energy.

-changes inproperties: a solid may appear when two solutions are mixed. A solid that forms from solution during a chemical reaction is called a precipitate.

-changes in energy:
*endothermic reaction: is areaction in which energy is absorbed.
*exothermic reaction: a reaction that releases energy in the form of heat.

Section 2:
Chemical equations use chemical formulas and other symbols instead ofwords to summarize a reaction. Structure:
*reactants: the substances you have at the beginning.
*products: when the reaction is complete, you have new substances.

The principle of conservation ofmass states that, in a chemical reaction, the total mass of the reactants must equal the total mass of the products. To describe a reaction accurately, a chemical equation must show the same number ofeach type of atom on both sides of the equation.

Many chemical reactions can be classified in one of the three categories:
*Synthesis: when two or more elements or compounds combine to make a morecomplex substance.
*Decomposition: breaks down compounds into simpler products.
*Replacement: when one element replaces another in a compound, or when two elements in different compounds tradeplaces.

Section 3:
All chemical reactions need a certain amount of activation energy to get started.
Chemist can control rates of reactions by changing factors such as surface area, temperature, and...