what must occur for a change to be a chemical reaction?

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Lesson six.i

What is a Chemical Reaction?

Fundamental Concepts:

• A physical change, such as a land change or dissolving, does not create a new substance, but a chemical change does.
• In a chemical reaction, the atoms and molecules that interact with each other are chosen reactants.
• In a chemical reaction, the atoms and molecules produced by the reaction are chosen products.
• In a chemical reaction, merely the atoms present in the reactants tin can stop up in the products. No new atoms are created, and no atoms are destroyed.
• In a chemical reaction, reactants contact each other, bonds between atoms in the reactants are broken, and atoms rearrange and form new bonds to make the products.

Summary

The instructor will utilize a small candle flame to demonstrate a chemical reaction between the candle wax and oxygen in the air. Students will run into a molecular blitheness of the combustion of methane and oxygen as a model of a like reaction. Students will use atom model cut-outs to model the reaction and meet that all the atoms in the reactants evidence up in the products.

Objective

Students will be able to explain that for a chemical reaction to take identify, the bonds between atoms in the reactants are broken, the atoms rearrange, and new bonds between the atoms are formed to brand the products. Students will also exist able to explain that in a chemical reaction, no atoms are created or destroyed.

Evaluation

Download the student activeness sheet, and distribute i per student when specified in the activity. The activity sheet will serve as the "Evaluate" component of each five-E lesson plan.

Safety

Be sure you and the students habiliment properly fitting goggles. Exist careful when lighting the candle. Be sure that the match and candle are completely extinguished when you are finished with the demonstration.

Materials for the Demonstration

• Tea lite candle or other pocket-sized stable candle
• Matches
• Glass jar, large enough to be placed over the candle

Materials for Each Student

• Atom cutting-outs from the action sheet
• Canvass of colored paper or structure newspaper
• Colored pencils
• Pair of scissors
• Glue or record

1. Review what happens during a physical modify and introduce the thought of chemical change.

   Tell students that in previous chapters they have studied dissimilar aspects of concrete change. When atoms and molecules speed upwardly or slow down, that is a physical change. When they change land from liquid to solid or from gas to liquid, that is a physical alter. When a substance is dissolved past h2o or some other solvent, a new substance has not actually been formed. The ions or molecules can nevertheless come back together to course the original substance.

   Let students know that in this chapter they volition explore what happens during a chemical change. In a chemic change, the atoms in the reactants rearrange themselves and bond together differently to course ane or more new products with dissimilar characteristics than the reactants. When a new substance is formed, the change is called a chemical alter.

2. As a demonstration, calorie-free a candle and explain what is happening using the terms reactants, products, and chemical reaction.

   Explain that in well-nigh chemic reactions, two or more substances, called reactants, interact to create different substances called products. Tell students that burning a candle is an example of a chemical reaction.

   Materials for the Demonstration

   • Tea low-cal candle or other small stable candle
   • Matches
   • Glass jar, large plenty to exist placed over the candle

   Procedure

   1. Carefully light a tea calorie-free candle or other small candle.
   2. Keep the candle burning as you ask students the questions below. You lot volition put the candle out in the second function of the demonstration.

   Expected Results

   The wick will catch on burn down and the flame volition be sustained past the chemic reaction.

   The following question is not easy and students are non expected to know the answer at this point. However, thinking virtually a candle called-for in terms of a chemical reaction is a good place to start developing what it ways when substances react chemically.

   Enquire students:

   What exercise y'all call back are the reactants in this chemic reaction?

   Wax and oxygen from the air are the reactants.

   Students often say that the string or wick is called-for. Information technology is true that the string of the wick does burn but it's the wax on the string and non so much the cord itself that burns and keeps the candle called-for. Explain that the molecules that make up the wax combine with oxygen from the air to brand the products carbon dioxide and water vapor.

   Point out to students that this is one of the major characteristics of a chemical reaction: In a chemical reaction, atoms in the reactants combine in new and dissimilar ways to course the molecules of the products.

   Students may be surprised that water can exist produced from combustion. Since nosotros use water to extinguish a fire, it may seem strange that water is actually produced by combustion. You may want to let students know that when they "burn" food in their bodies, they also produce carbon dioxide and water.

3. Place a jar over the candle to assistance students realize that oxygen is a reactant in the called-for of a candle.

   Remind students that air is a mixture of gases. Explicate that when something burns, it reacts with the oxygen in the air.

   Ask students to brand a prediction:

   Will the candle however burn if one of the reactants (wax or oxygen) is no longer available?

   Students may estimate that the candle will not burn considering both reactants are required for the chemical reaction to continue.

   Process

   1. Advisedly place a drinking glass jar over the lit candle.

      

   Expected Results

   The flame goes out.

   Ask students:

   Why do you think the flame goes out when nosotros put a jar over the candle?

   Placing a jar over the candle limits the corporeality of oxygen in the air around the candle. Without enough oxygen to react with the wax, the chemic reaction cannot take place and the candle cannot burn.

   When a candle burns for a while, it somewhen gets smaller and smaller. Where does the candle wax go?

   When a candle burns, the candle wax seems to "disappear." It doesn't actually disappear, though: Information technology reacts chemically, and the new products get into the air.

   Note: Some curious students may ask what the flame is made of. This is a great question and non petty to answer. The flame is burning wax vapor. The calorie-free of the flame is acquired by a procedure called chemiluminescence. Energy released in the chemical reaction makes electrons from different molecules move to a higher energy state. When the electrons come back down, energy is released in the form of light.

4. Introduce the chemical equation for the combustion of methane and explain that atoms rearrange to go different molecules.

   Explain to students that wax is fabricated of long molecules called paraffin and that methane series is fabricated up of only carbon atoms and hydrogen atoms bonded together. Molecules made of only carbon and hydrogen are called hydrocarbons. Tell students that you lot will employ the simplest hydrocarbon (methyl hydride) as a model to show how the wax, or any other hydrocarbon, burns.

   Project the image Chemical Reaction between Marsh gas and Oxygen.

   Show students that at that place is methane and oxygen on the left side of the chemical equation and carbon dioxide and h2o on the right side. Explain that the molecules on the left side are the reactants and the ones on the correct side are the products. When the candle was burning, the paraffin reacted with oxygen in the air to produce carbon dioxide and h2o, similar to the chemical reaction between methane and oxygen.

   Explicate to students that the chemic formula for methane is CH₄. This means that methane is made upward of one carbon cantlet and 4 hydrogen atoms.

   Show students that the other reactant is two molecules of oxygen gas. Indicate out that each molecule of oxygen gas is fabricated up of two oxygen atoms bonded together. It tin can be confusing for students that oxygen the atom, and oxygen the molecule, are both chosen oxygen. Let students know that when we talk about the oxygen in the air, it is e'er the molecule of oxygen, which is two oxygen atoms bonded together, or O₂.

   Ask students:

   Where do the atoms come from that brand the carbon dioxide and the water on the right side of the equation?

   The atoms in the products come up from the atoms in the reactants. In a chemical reaction, bonds between atoms in the reactants are broken and the atoms rearrange and class new bonds to make the products.

   Notation: Leave this equation projected throughout the activity in the Explore section of this lesson. Students will need to refer to information technology equally they model the chemical reaction.

   Give Each Student an Activity Sheet.

   Students volition tape their observations and answer questions about the activeness on the activity sheet. The Explicate It with Atoms and Molecules and Take It Further sections of the activity sail will either be completed as a course, in groups, or individually, depending on your instructions. Look at the teacher version of the activeness sheet to notice the questions and answers.

5. Have students brand a model to show that in a chemical reaction the atoms of the reactants rearrange to class the products.

   Question to Investigate

   Where do the atoms in the products of a chemical reaction come from?

   Materials for Each Pupil

   • Atom model cut-outs (carbon, oxygen, and hydrogen)
   • Canvass of colored paper or construction paper
   • Colored pencils
   • Scissors
   • Glue or tape

   Process

   1. Prepare the Atoms

      1. Colour the carbon atoms black, the oxygen atoms red, and leave the hydrogen atoms white.
      2. Use scissors to carefully cut out the atoms.

   2. Build the Reactants

      1. On a sheet of newspaper, place the atoms together to make the molecules of the reactants on the left side of the chemical equation for the combustion of methane.

         
      2. Write the chemic formula under each molecule of the reactants. Too draw a + sign between the reactants.

   After y'all are sure that students take made and written the formula for the reactant molecules, tell students that they will rearrange the atoms in the reactants to grade the products.

   1. Build the Products

      1. Describe an arrow afterward the second oxygen molecule to show that a chemical reaction is taking identify.
      2. Rearrange the atoms in the reactants to brand the molecules in the products on the right side of the pointer.
      3. Write the chemical formula under each molecule of the products. As well draw a + sign between the products.

   Tell students that in a chemical reaction, the atoms in the reactants come up autonomously, rearrange, and make new bonds to course the products.

   1. Represent the Chemical Equation

      1. Have students use their remaining atoms to make the reactants over again to represent the chemical reaction as a complete chemical equation.
      2. Mucilage or tape the atoms to the paper to make a more permanent chemic equation of the combustion of methane.

6. Help students count upwardly the number of atoms on each side of the equation.

   Projection the animation Moving Chemical Equation for the Combustion of Methane.

   Prove students that the atoms in methane and oxygen need to come autonomously just like in their models. Too indicate out that the atoms accommodate themselves differently and bond again to form new products. This is also similar their model. Be certain that students realize that the atoms in the products only come from the reactants. There are no other atoms available. No new atoms are created and no atoms are destroyed.

   Explain to students that chemic reactions are more complicated than the simplified model shown in the animation. The animation shows that bonds between atoms in the reactants are broken, and that atoms rearrange and form new bonds to make the products. In reality, the reactants need to collide and interact with each other in gild for their bonds to break and rearrange. Likewise, the animation shows all of the atoms in the reactants coming apart and rearranging to class the products. Only in many chemic reactions, but some bonds are cleaved, and groups of atoms stay together as the reactants class the products.

   Read more nearly the combustion of methane in the teacher groundwork department.

   Guide students as yous answer the following question together:

   How many carbon, hydrogen, and oxygen atoms are in the reactants compared to the number of carbon, hydrogen, and oxygen atoms in the products?

   Testify students how to use the large number (coefficient) in front of the molecule and the piddling number after an atom of the molecule (subscript) to count the atoms on both sides of the equation. Explain to students that the subscript tells how many of a sure type of atom are in a molecule. The coefficient tells how many of a particular blazon of molecule at that place are. So if in that location is a coefficient in front of the molecule and a subscript after an atom, you demand to multiply the coefficient times the subscript to get the number of atoms.

   For example, in the products of the chemical reaction at that place are 2H_iiO. The coefficient means that there are ii molecules of h2o. The subscript means that each water molecule has ii hydrogen atoms. Since each water molecule has 2 hydrogen atoms and there are two water molecules, in that location must be 4 (2 × 2) hydrogen atoms.

   Tabular array one. Counting atoms on the reactant and product side of the chemical equation for the combustion of methane.

   Atoms	Reactant Side	Production Side
   Carbon
   Hydrogen
   Oxygen

   Annotation: The coefficients actually indicate the ratios of the numbers of molecules in a chemical reaction. It is not the actual number as in 2 molecules of oxygen and one molecule of methyl hydride since at that place are unremarkably billions of trillions of molecules reacting. The coefficient shows that in that location are twice every bit many oxygen molecules equally methane molecules reacting. It would be correct to say that in this reaction at that place are two oxygen molecules for every methane molecule.

7. Explain that mass is conserved in a chemical reaction.

   Ask students:

   Are atoms created or destroyed in a chemical reaction?

   No.

   How do y'all know?

   In that location are the same number of each type of atom on both the reactant side and the production side of the chemic equation we explored.

   In a physical change, like irresolute state from a solid to a liquid, the substance itself doesn't really change. How is a chemical modify different from a physical alter?

   In a chemical change, the molecules in the reactants interact to grade new substances. In a physical change, like a state alter or dissolving, no new substance is formed.

   Explain that another fashion to say that no atoms are created or destroyed in a chemical reaction is to say, "Mass is conserved."

   Projection the paradigm Balanced Equation.

   Explicate that the balance shows the mass of marsh gas and oxygen on ane side exactly equals the mass of carbon dioxide and water on the other. When an equation of a chemical reaction is written, it is "balanced" and shows that the atoms in the reactants terminate up in the products and that no new atoms are created and no atoms are destroyed.

8. Introduce two other combustion reactions and have students check to encounter whether or non they are balanced.

   Tell students that, in addition to the wax and marsh gas, another common hydrocarbons are propane (the fuel in outdoor gas grills), and butane (the fuel in disposable lighters). Take students count the number of carbon, hydrogen, and oxygen atoms in the reactants and products of each equation to see if the equation is balanced. They should record the number of each type of atom in the chart on their action sheet.

   

   Lighting an outdoor gas grill—Combustion of propane

   C₃H₈ + 5O₂ → 3CO₂ + 4H₂0

   Using a disposable lighter—Combustion of butane

   2C₄H₁₀ + 13O₂ → 8CO₂ + 10H₂O

   After students take counted up each type of cantlet, review their answers to make sure they know how to translate subscripts and coefficients.

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Source: https://www.middleschoolchemistry.com/lessonplans/chapter6/lesson1

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