How Molecules Are Broken Apart and Put Back Together Again

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Lesson 6.1

What is a Chemical Reaction?

Key Concepts:

• A physical change, such every bit a state change or dissolving, does not create a new substance, merely a chemical alter does.
• In a chemical reaction, the atoms and molecules that interact with each other are called reactants.
• In a chemical reaction, the atoms and molecules produced by the reaction are called products.
• In a chemic reaction, only the atoms present in the reactants can end upward 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 use a small candle flame to demonstrate a chemical reaction between the candle wax and oxygen in the air. Students will see a molecular animation of the combustion of methane and oxygen as a model of a similar reaction. Students will use cantlet model cut-outs to model the reaction and run across that all the atoms in the reactants evidence up in the products.

Objective

Students volition be able to explain that for a chemical reaction to take place, the bonds between atoms in the reactants are broken, the atoms rearrange, and new bonds between the atoms are formed to make the products. Students volition besides exist able to explain that in a chemic reaction, no atoms are created or destroyed.

Evaluation

Download the pupil activity sheet, and distribute one per educatee when specified in the activity. The activity canvass will serve as the "Evaluate" component of each 5-E lesson plan.

Condom

Be certain you and the students vesture properly fitting goggles. Be careful when lighting the candle. Exist sure that the lucifer and candle are completely extinguished when you lot are finished with the demonstration.

Materials for the Demonstration

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

Materials for Each Pupil

• Atom cut-outs from the activity canvas
• Sheet of colored paper or construction paper
• Colored pencils
• Scissors
• Glue or tape

1. Review what happens during a physical alter and introduce the idea of chemical change.

   Tell students that in previous capacity they have studied dissimilar aspects of physical change. When atoms and molecules speed up or deadening down, that is a physical alter. When they change state from liquid to solid or from gas to liquid, that is a physical change. When a substance is dissolved past water or another solvent, a new substance has non really been formed. The ions or molecules can still come back together to grade the original substance.

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

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

   Explicate that in nearly chemic reactions, two or more substances, chosen reactants, interact to create different substances chosen products. Tell students that burning a candle is an example of a chemical reaction.

   Materials for the Demonstration

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

   Procedure

   1. Carefully light a tea light candle or other small candle.
   2. Go along the candle burning every bit you lot ask students the questions beneath. Y'all volition put the candle out in the second part of the demonstration.

   Expected Results

   The wick will grab on fire and the flame volition be sustained by the chemical reaction.

   The following question is not like shooting fish in a barrel and students are not expected to know the answer at this indicate. Even so, thinking most a candle burning in terms of a chemical reaction is a skilful place to first developing what information technology means when substances react chemically.

   Ask students:

   What do you lot think are the reactants in this chemical reaction?

   Wax and oxygen from the air are the reactants.

   Students frequently say that the string or wick is burning. It is truthful that the string of the wick does burn but it'south the wax on the string and not so much the cord itself that burns and keeps the candle burning. Explain that the molecules that make upwardly the wax combine with oxygen from the air to make the products carbon dioxide and water vapor.

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

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

3. Identify a jar over the candle to help students realize that oxygen is a reactant in the burning of a candle.

   Remind students that air is a mixture of gases. Explain that when something burns, information technology reacts with the oxygen in the air.

   Ask students to make a prediction:

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

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

   Procedure

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

      

   Expected Results

   The flame goes out.

   Ask students:

   Why do you recall the flame goes out when we 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: It reacts chemically, and the new products go into the air.

   Note: Some curious students may ask what the flame is made of. This is a great question and not trivial to reply. The flame is called-for wax vapor. The light of the flame is caused by a procedure called chemiluminescence. Energy released in the chemical reaction makes electrons from different molecules move to a college energy country. When the electrons come back down, energy is released in the form of light.

4. Innovate the chemical equation for the combustion of marsh gas and explicate that atoms rearrange to become different molecules.

   Explain to students that wax is fabricated of long molecules called alkane and that paraffin is made upwards of only carbon atoms and hydrogen atoms bonded together. Molecules made of merely carbon and hydrogen are chosen hydrocarbons. Tell students that you will use the simplest hydrocarbon (methane) every bit a model to show how the wax, or any other hydrocarbon, burns.

   Project the epitome Chemical Reaction betwixt Methane and Oxygen.

   Bear witness students that there is methyl hydride and oxygen on the left side of the chemical equation and carbon dioxide and water on the correct side. Explicate 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 water, similar to the chemical reaction between methane and oxygen.

   Explicate to students that the chemical formula for methane is CH₄. This means that methane is made up of ane carbon atom and 4 hydrogen atoms.

   Show students that the other reactant is 2 molecules of oxygen gas. Indicate out that each molecule of oxygen gas is made up of two oxygen atoms bonded together. It tin can be disruptive for students that oxygen the cantlet, and oxygen the molecule, are both called oxygen. Permit students know that when nosotros talk about the oxygen in the air, it is always the molecule of oxygen, which is two oxygen atoms bonded together, or O_two.

   Ask students:

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

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

   Note: Exit this equation projected throughout the activity in the Explore department of this lesson. Students will demand to refer to information technology as they model the chemical reaction.

   Give Each Student an Activity Sail.

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

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

   Question to Investigate

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

   Materials for Each Educatee

   • Cantlet model cut-outs (carbon, oxygen, and hydrogen)
   • Sheet of colored paper or construction paper
   • Colored pencils
   • Pair of scissors
   • Glue or record

   Procedure

   1. Fix the Atoms

      1. Color the carbon atoms black, the oxygen atoms ruby, and leave the hydrogen atoms white.
      2. Utilise scissors to carefully cutting out the atoms.

   2. Build the Reactants

      1. On a sheet of paper, 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 chemical formula under each molecule of the reactants. Also depict a + sign between the reactants.

   After y'all are certain that students accept made and written the formula for the reactant molecules, tell students that they volition rearrange the atoms in the reactants to form the products.

   1. Build the Products

      1. Draw an pointer after the second oxygen molecule to show that a chemical reaction is taking place.
      2. Rearrange the atoms in the reactants to brand the molecules in the products on the right side of the pointer.
      3. Write the chemic formula under each molecule of the products. Also describe a + sign between the products.

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

   1. Represent the Chemic Equation

      1. Have students use their remaining atoms to make the reactants again to correspond the chemical reaction as a complete chemical equation.
      2. Glue or tape the atoms to the paper to brand a more permanent chemical equation of the combustion of marsh gas.

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

   Project the animation Moving Chemic Equation for the Combustion of Methyl hydride.

   Testify students that the atoms in methane and oxygen need to come apart just similar in their models. As well point out that the atoms suit themselves differently and bond once again to course new products. This is also like their model. Be sure that students realize that the atoms in the products just come from the reactants. There are no other atoms available. No new atoms are created and no atoms are destroyed.

   Explicate to students that chemical reactions are more than 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 demand to collide and interact with each other in order for their bonds to break and rearrange. Also, the animation shows all of the atoms in the reactants coming apart and rearranging to form the products. But in many chemical reactions, only some bonds are broken, and groups of atoms stay together as the reactants grade the products.

   Read more about the combustion of methyl hydride in the instructor background department.

   Guide students every bit you 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?

   Show students how to use the large number (coefficient) in front of the molecule and the fiddling 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 certain type of atom are in a molecule. The coefficient tells how many of a particular type of molecule at that place are. So if there is a coefficient in front of the molecule and a subscript later an atom, you lot need 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 2H₂O. The coefficient means that in that location are two molecules of water. The subscript means that each water molecule has two hydrogen atoms. Since each water molecule has 2 hydrogen atoms and there are ii water molecules, at that place must be 4 (2 × two) hydrogen atoms.

   Table 1. 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

   Note: The coefficients actually point the ratios of the numbers of molecules in a chemical reaction. It is not the actual number as in two molecules of oxygen and i molecule of methane since there are usually billions of trillions of molecules reacting. The coefficient shows that there are twice equally many oxygen molecules as methane molecules reacting. It would exist correct to say that in this reaction there are two oxygen molecules for every methane molecule.

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

   Ask students:

   Are atoms created or destroyed in a chemical reaction?

   No.

   How do you lot know?

   There are the same number of each type of atom on both the reactant side and the product side of the chemical equation nosotros explored.

   In a physical modify, similar changing country from a solid to a liquid, the substance itself doesn't really alter. How is a chemical change unlike from a physical modify?

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

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

   Project the image Balanced Equation.

   Explain that the balance shows the mass of methane and oxygen on one 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 cease up in the products and that no new atoms are created and no atoms are destroyed.

8. Introduce two other combustion reactions and accept students bank check to run into whether or non they are balanced.

   Tell students that, in addition to the wax and methane, another common hydrocarbons are propane (the fuel in outdoor gas grills), and butane (the fuel in dispensable lighters). Have students count the number of carbon, hydrogen, and oxygen atoms in the reactants and products of each equation to see if the equation is counterbalanced. They should tape the number of each type of atom in the chart on their activity sail.

   

   Lighting an outdoor gas grill—Combustion of propane

   C₃H_eight + 5O₂ → 3CO_two + 4H_two0

   Using a dispensable lighter—Combustion of butane

   2C₄H_x + 13O_two → 8CO₂ + 10H_twoO

   Later students have counted upward each type of atom, review their answers to make sure they know how to interpret subscripts and coefficients.

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

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