Lesson PLan Chemical Reactions

Lesson Plan

Chemical Reactions

Context

A chemical reaction involves the breaking and reforming of chemical bonds to create new substances. Every reaction involves energy and must express the conservation of mass. Chemical reactions are important in everyday life. Understanding the energy and equilibrium of reactions is important in industry.

Essential Questions

What is a chemical reaction? How can the conservation of mass during a reaction be demonstrated? What are the different types of reactions and how can their products be predicted? How does the periodic table help predict the reactivity of elements? How is energy involved in a chemical reaction? What is chemical equilibrium? How is equilibrium impacted by temperature and concentration of reactants and products?

Enduring Understandings

A chemical reaction is the breaking and forming of chemical bonds to produce new substances. Chemical reactions can be expressed as equations. These demonstrate the law of conservation of mass by showing

an equal number of atoms of each element in the reactants and products. Chemical reactions can be classified by type, which helps to predict products. They can also be classified by energy

loss or gain. The ordering of the elements on the periodic table reflects trends in reactivity. Chemical equilibrium is reached when the rate of a forward reaction equals the rate of a reverse reaction. The equilibrium of a chemical reaction can be manipulated to maximize the amount of products made.

Time

Three to four 50-minute class periods

Grade Level

Grades 9?12

Differentiation

Activities can be completed as one class group or can be assigned to individuals, small groups, or pairs according to ability and skill levels.

Materials

Rosen Digital's Core Concepts: Chemistry database Water Ammonium chloride Steel wool Vinegar Beakers Styrofoam coffee cups Thermometers

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Chemical Reactions

Scales Graduated cylinders Calculators

Student Learning Objectives

Students will be able to balance chemical reactions and calculate simple mole conversions to demonstrate the conservation of mass.

Students will be able to identify different types of chemical reactions. Students will use the type of reaction and the periodic table to predict the products of reactions. Students will describe the energy associated with a reaction and whether it is absorbed or released. Students will define chemical equilibrium. Students will predict the effect of temperature and concentration changes on chemical reactions.

Next Generation Science Standards Addressed

HS-PS1-2.

Construct and revise an explanation for the outcome of a simple chemical reaction based on the outermost electron states of atoms, trends in the periodic table, and knowledge of the patterns of chemical properties. [Clarification Statement: Examples of chemical reactions could include the reaction of sodium and chlorine, of carbon and oxygen, or of carbon and hydrogen.] [Assessment Boundary: Assessment is limited to chemical reactions involving main group elements and combustion reactions.]

HS-PS1-4. HS-PS1-5.

Develop a model to illustrate that the release or absorption of energy from a chemical reaction system depends upon the changes in total bond energy. [Clarification Statement: Emphasis is on the idea that a chemical reaction is a system that affects the energy change. Examples of models could include molecular-level drawings and diagrams of reactions, graphs showing the relative energies of reactants and products, and representations showing energy is conserved.] [Assessment Boundary: Assessment does not include calculating the total bond energy changes during a chemical reaction from the bond energies of reactants and products.]

Apply scientific principles and evidence to provide an explanation about the effects of changing the temperature or concentration of the reacting particles on the rate at which a reaction occurs. [Clarification Statement: Emphasis is on student reasoning that focuses on the number and energy of collisions between molecules.] [Assessment Boundary: Assessment is limited to simple reactions in which there are only two reactants; evidence from temperature, concentration, and rate data; and qualitative relationships between rate and temperature.]

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HS-PS1-6. HS-PS1-7.

Refine the design of a chemical system by specifying a change in conditions that would produce increased amounts of products at equilibrium.* [Clarification Statement: Emphasis is on the application of Le Chatelier's Principle and on refining designs of chemical reaction systems, including descriptions of the connection between changes made at the macroscopic level and what happens at the molecular level. Examples of designs could include different ways to increase product formation including adding reactants or removing products.] [Assessment Boundary: Assessment is limited to specifying the change in only one variable at a time. Assessment does not include calculating equilibrium constants and concentrations.]

Use mathematical representations to support the claim that atoms, and therefore mass, are conserved during a chemical reaction. [Clarification Statement: Emphasis is on using mathematical ideas to communicate the proportional relationships between masses of atoms in the reactants and the products, and the translation of these relationships to the macroscopic scale using the mole as the conversion from the atomic to the macroscopic scale. Emphasis is on assessing students' use of mathematical thinking and not on memorization and rote application of problem-solving techniques.] [Assessment Boundary: Assessment does not include complex chemical reactions.]

NGSS Science and Engineering Practices Addressed

Developing and Using Models Using Mathematics and Computational Thinking Constructing Explanations and Designing Solutions

NGSS Crosscutting Concepts Addressed

Patterns: Different patterns may be observed at each of the scales at which a system is studied and can provide evidence for causality in explanations of phenomena. (HS-PS1-2), (HS-PS1-5)

Energy and Matter: The total amount of energy and matter in closed systems is conserved. (HS-PS1-7) Changes of energy and matter in a system can be described in terms of energy and matter flows into, out of, and within that system. (HS-PS1-4)

Stability and Change: Much of science deals with constructing explanations of how things change and how they remain stable. (HS-PS1-6)

Scientific Knowledge Assumes an Order and Consistency in Natural Systems: Science assumes the universe is a vast single system in which basic laws are consistent. (HS-PS1-7)

Common Core ELA Standards Addressed

WHST.9-12.7

Conduct short as well as more sustained research projects to answer a question (including a self-generated question) or solve a problem; narrow or broaden the inquiry when appropriate; synthesize multiple sources on the subject, demonstrating understanding of the subject under investigation. (HS-PS1-6)

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Common Core Mathematics Standards Addressed

MP.2 Reason abstractly and quantitatively. (HS-PS1-5), (HS-PS1-7) MP.4 Model with mathematics. (HS-PS1-4)

Introduction

1. Ask students to read the Core Concepts: Chemistry article Chemical Reaction Basics.

2. Discuss the reading with guiding questions.

a. What is a chemical reaction? b. What is the difference between a reactant and a product? c. How is energy involved in a chemical reaction? d. What are some forms of energy? e. How is the periodic table important to describing chemical reactions?

The Periodic Table and Reactivity

1. Begin the discussion of the reactivity of elements with the noble gases. Direct students to use the Core Concepts: Chemistry database to explore the noble gases independently or in pairs. Ask students to find out everything they can about these elements and to record their findings.

2. Once students have completed their research, ask what they found. Create a list of properties together.

3. Guide the discussion toward the number of valence electrons in the noble gases and why this makes them unreactive.

a. Having eight valence electrons is a stable configuration. b. All other elements react in such a way as to gain eight valence electrons to achieve this stability. c. Point out the exceptions, such as hydrogen or helium, which only need two valence electrons to be stable. d. Using the Periodic Table Reference Guide, show students how to determine the number of valence electrons the

elements in groups 1, 2, and 13 through 18 have. 4. Use examples to illustrate how elements react with each other to create compounds that give them stable electron

configurations. Demonstrate for the students, using these element combinations, how to draw Lewis dot diagrams. Show that each bond includes two shared electrons for a covalent bond. For ionic bonds, show that electrons are transferred and charges formed on the atoms to create ions. Include dot diagrams of one or two noble gases to demonstrate that these atoms are already stable and will not react.

a. Sodium and chlorine b. Magnesium and oxygen c. Hydrogen and nitrogen 5. Ask students to create three of their own element combinations and dot diagrams.

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Balancing Reactions

1. Guide students through one round of the Chemical Reactions: Moving Molecules activity.

a. Select hydrogen first b. Add chlorine c. Add magnesium d. Add nitrogen e. Balance the final equations together as a class and explain how this demonstrates the conservation of mass. 2. Ask the students to start the activity over and make their own choices to explore the possible reactions. Each student should complete two full sets of four balanced equations. Students can print, email, or save their activity results as a PDF.

Types of Reactions

1. Introduce the types of chemical reactions including combination, decomposition, single replacement, double replacement, and combustion. Write out balanced equations to show examples of each type. Examples could include:

a. Combination ? hydrogen gas and oxygen gas to produce water b. Decomposition ? mercury (II) oxide to produce liquid mercury and oxygen gas c. Single replacement ? magnesium and silver nitrate to produce silver and magnesium nitrate d. Double replacement ? barium chloride and potassium carbonate to produce solid barium carbonate and potassium

chloride e. Combustion ? methane gas and oxygen gas to produce carbon dioxide gas and water vapor 2. Ask the students to go through their completed Chemical Reactions: Moving Molecules results to identify the different types of reactions they created and balanced.

Energy of Reactions

1. Begin the discussion of energy by defining endothermic and exothermic.

a. endothermic ? the reaction takes in energy; the surroundings become cooler b. exothermic ? the reaction gives off energy; the surroundings become warmer 2. Demonstrate an example of each type of reaction and allow students to observe the temperature change.

a. Demonstrate an endothermic reaction by dissolving ammonium chloride in water. The container should become cooler. b. Demonstrate an exothermic reaction by soaking steel wool in vinegar to start the rusting process. The container should

become warmer. c. Use a thermometer in each demonstration to show students that heat is absorbed or released.

Chemical Equilibrium

1. Ask students to read the Core Concepts: Chemistry section Understanding Equilibrium. Define equilibrium as a point a reaction reaches when the rate of the forward reaction equals the rate of the reverse reaction. Address a common misconception: Equilibrium does not mean that the amounts of reactants and products are equal to each other. It means that the amounts remain constant.

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