Chapter 6
6
Chemical Reactions
Study Goals
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Classify a change in matter as a chemical change or a physical change.
Show that a balanced equation has an equal number of atoms of each element on the reactant side
and the product side.
Write a balanced equation for a chemical reaction when given the formulas of the reactants and
products.
Classify an equation as a combination, decomposition, replacement and/or combustion reaction.
Describe the features of an oxidation-reduction reaction.
Describe the factors that affect the rate of a reaction.
Use the concept of reversible reactions to explain chemical equilibrium.
Chapter Outline
6.1 Chemical Changes
Explore Your World: Evidence of a Chemical Change
6.2 Chemical Equations
6.3 Balancing a Chemical Equation
6.4 Types of Reactions
Health Note: Smog and Health Concerns
6.5 Oxidation-Reduction Reactions
Explore Your World: Oxidation of Fruits and Vegetables
6.6 Energy in Chemical Reactions
Health Note: Hot Packs and Cold Packs
Explore Your World: Hotter or Colder?
Explore Your World: How Fast Can it Go?
6.7 Rate of Reaction
6.8 Chemical Equilibrium
Explore Your World: Modeling an Equilibrium System
Health Note: Oxygen, Hemoglobin, and Carbon Monoxide Poisoning
Health Note: Homeostasis: Regulation of Body Temperature
Chapter Summary and Demonstrations
1.
Chemical Reactions and Equations
Examples of physical and chemical changes introduce the idea of chemical reaction. The process of
writing and balancing a chemical equation is carefully explained with several sample problems. In
the final sections of the chapter, mole relationships and mole conversion factors in an equation are
written from the equation coefficients and used to calculate the grams or moles of a reactant or
product in a reaction.
Demonstration: I use examples of an everyday process to introduce the idea of writing an equation.
A cooking example: 2 slices of bread + 3 slices turkey + 1 slice tomato + 2 lettuce leaves = 1
turkey-tomato-lettuce sandwich. Any recipe could be used. A sport example: 1 can tennis balls + 2
tennis racquets + 1 net + 2 players = 1 tennis game.
Chemical Reactions
2.
Energy in Chemical Reactions
The heat of reaction is described as the energy difference between reactants and products. In
exothermic reactions, heat is released; in endothermic, heat is absorbed. The rate of reaction is the
speed at which products form and can be increase by adding more reactant, raising the temperature,
or adding a catalyst.
Demonstration: Obtain some hot packs and/or cold packs at a pharmacy. Have students read the
labels to determine contents. Then have them hit the packs to break the vials. Describe the results.
Which solution reaction was exothermic? Which reaction was endothermic? In which pack was the
energy of the reactant higher than the product?
Laboratory Suggestions
Lab 10 Chemical Reactions and Equations
Students carry out a variety of chemical reactions that demonstrate the combustion of magnesium,
the reactions of zinc and CuSO4 (aq), metals and acid, and double replacement reactions. Students
describe the physical properties of the reactants and the products to show evidence of reaction. A
balanced equation is written for each reaction and the type of reaction is determined.
A. Magnesium and Oxygen
B. Zinc and Copper (II) Sulfate
C. Metals and HCl
D. Reactions of Ionic Compounds
E. Sodium Carbonate and HCl
Laboratory Skills to Demonstrate
Proper handling of reagent bottles and water disposal
Labeling test tubes and organizing beakers
Balancing a chemical equation.
Identifying the type of reaction
Lab 11 Reaction Rates and Equilibrium
In an exothermic reaction, heat is released causing the temperature of the surroundings to increase.
An endothermic reaction absorbs heat, which causes a drop in the temperature of the surroundings.
The rate or speed at which a reaction occurs depends on the amounts of the reactants, the
temperature, and the presence of a catalyst. When a reaction begins, reactants are converted to
products. As the reaction proceeds, products react to form reactants. Increasing reactants shifts a
reversible reaction to products; an increase in products shifts the equilibrium to reactants.
A. Exothermic and Endothermic Reactions
B. Rates of Reactions
C. Reversible Reactions
D. Iron (III)-thiocyanate equilibrium
Laboratory Skills to Demonstrate
Describe how to write heat as a reactant or product in an equation.
Review the factors that affect the rate of a reaction.
Review the effects of temperature, reactants and products on a reversible reaction.
Relate the change in appearance of a reactant or product to a shift in equilibrium.