Chemical Reactions Chapter Six As chemical reactions occur

Chemical Reactions Chapter Six

As chemical reactions occur, substances are changed into new substances.

Indicators of chemical reactions include: Changes in temperature Formation of a gas Formation of a precipitate Changes in color Release of light Electricity changes Sounds

In chemical reactions, reactants are changed into products.

2 H 2 + O 2 → 2 H 2 O

As a chemical reaction happens, energy is involved. Energy is required to break chemical bonds. Energy is released as bonds form. The sum of these two actions determines if the reaction will cause the environment to heat up or get colder.

An exothermic reaction gives off heat.

An endothermic reaction absorbs heat.

Reaction Types • • • Synthesis Decomposition Single displacement Double displacement Combustion

In a synthesis reaction, elements or small molecules join together to make larger compounds. Na + Cl 2 → 2 Na. Cl Your polymerization reactions (slime) were synthesis reactions also.

In decomposition reactions, larger molecules come apart to form elements and smaller molecules. The electrolysis of water is a good example. 2 H 2 O → 2 H 2 + O 2

Single displacement reactions usually involve an active metal that replaces a less active metal in a compound. Fe + Cu. Cl 2 → Fe. Cl 2 + Cu

Double displacement reactions occur between two salt solutions that rearrange to form a colored precipitate. Ag. NO 3 + Na. Cl → Ag. Cl + Na. NO 3

Combustion reactions occur when hydrocarbons react with oxygen to give carbon dioxide and water. C 3 H 8 + 5 O 2 → 3 CO 2 + 4 H 2 O

Reaction rate can change. It can be controlled by changing the: • • • Temperature of the reactents Surface area of the reactents Concentration of the reactents Changing the pressure of gases Reacting smaller molecules Using catalysts (enzymes)

Some reactions are reversable.