Unit 7 - Chemical Reactions

Introduction:

Unit 7 is by far my favorite unit of the year other than the gas law chapter. It focuses on chapter 8, which covers chemical reactions and reaction types, including predicting products and ionic/net ionic equations. Students must master the ability to predict products and determine reactions types as we move forward towards unit 8, which is the hardest chapter of the year.

Student Objectives - Unit 7:

7.1

a. Four observations that suggest a chemical reaction is taking place are the evolution of energy as heat and light, the production of a gas, a change in color and the formation of a precipitate.

b. A balanced chemical equation represents, with symbols and formulas, the identities and relative amounts of reactants and products in a chemical reaction.

7.2

a. Synthesis reactions are represented by the general equation: A + X ----> AX

b. Decomposition reactions are represented by the general equation: AX ----> A + X

c. Single-displacement reactions are represented by the general equation: A + BX ----> AX and

Y + BX ----> BY + X

d. Double displacement reactions are represented by the general equation: AX + BY ----> AY + BX

e. In a combustion reaction, a substance combines with oxygen, releasing energy in the form of heat and light.

7.3

a. Activity series list the elements in order of their chemical reactivity and are useful in predicting whether a chemical reaction will occur.

b. Chemists determine activity series through experiments.

Ohio Department of Education - Chemistry Standards:

In the physical science syllabus, coefficients were introduced to balance simple equations. Other representations including Lewis structures and three-dimensional models also were used and manipulated to demonstrate the conservation of matter in chemical reactions. In this course, more complex reactions will be studied, classified and represented with chemical equations and three dimensional models. Classifying reactions into types can be a helpful organizational tool in recognizing patterns of what may happen when two substances are mixed (see Note). Some general types of chemical reactions are oxidation/reduction, synthesis, decomposition, single replacement, double replacement (including precipitation reactions and some acid-base neutralizations) and combustion reactions. Some reactions can fit into more than one category. For example, a single replacement reaction also can be classified as an oxidation/reduction reaction. Identification of reactions involving oxidation and reduction as well as indicating what substance is being oxidized and what is being reduced are appropriate in this course. However, balancing complex oxidation/reduction reactions will be reserved for more advanced study.

Organic molecules release energy when undergoing combustion reactions and are used to meet the energy needs of society (e.g., oil, gasoline, natural gas) and to provide the energy needs of biological organisms (e.g., cellular respiration). When a reaction between two ionic compounds in aqueous solution results in the formation of a precipitate or molecular compound, the reaction often occurs because the new ionic or covalent bonds are stronger than the original ion-dipole interactions of the ions in solution. Laboratory experiences (3-D or virtual) with different types of chemical reactions must be provided.

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