Chemical Reactions Mr. Halfen Oct. 2013

Physical Changes Chemical substances do not change. Physical changes are reversible. Characteristic properties can be the keys to designing techniques to separate mixtures or to reverse physical changes. Examples (2):

Chemical Changes Chemical changes (aka chemical reactions) change old substances into different ones. These are difficult to reverse. All chemical reactions involve a change in energy.

Energy Change Endothermic - net energy change is the addition of energy Exothermic - net energy change is the loss of energy The energy change is often in the form of heat energy.

Types of Reactions - 1 (copy diagram from p. 111) Synthesis - 2 or more substances combine to form one substance Example: Decomposition - one substance reacts to form 2 or more products

Types of Reactions - 2 Combustion - the reaction of a substance with oxygen and the release of energy (exothermic) If a flame is produced, combustion is called burning. Example:

Types of Reactions - 3 Displacement - when a more reactive element replaces a less reactive element in a compound Single Displacement – one element is exchanged between the reactants Double Displacement – elements are exchanged between the reactants Example:

Ionic Precipitation The production of an insoluble solid from the reaction of two or more compounds. Example:

Acid-Base Neutralization In general, the reaction of an acid & a base to produce a salt and water. Example:

Redox Reactions Oxidation-reduction reactions always occur in pairs. In these reactions, one element loses electrons and another gains electrons. Example: (insert redox table)

Electrolysis A reaction in which ions move towards electrodes due to an electrical current. Example:

Definitions electrolyte - cathode - anode - cation - anion – catalyst –

Signs of a Chemical Reaction Bubbling/effervescence/production of a gas Formation of a precipitate/solid Change in temperature Change in color Light given off

Problems 4.1 p. 107 #1 4.2 What law does a balanced chemical equation represent? 4.2 p. 110 #1 4.3 p. 116 #2 4.4 p. 119 #1 & #2 4.5 p. 128 #1 & #2 Exam pp. 133 - 135 #2, #3, & #5