What happens to chemical bonds during a chemical reaction?

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Lesson 6.ane

What is a Chemical Reaction?

Fundamental Concepts:

• A concrete modify, such equally a land change or dissolving, does not create a new substance, merely a chemical alter does.
• In a chemic 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 chosen products.
• In a chemical reaction, simply the atoms nowadays in the reactants tin terminate upwards in the products. No new atoms are created, and no atoms are destroyed.
• In a chemic reaction, reactants contact each other, bonds betwixt atoms in the reactants are broken, and atoms rearrange and form new bonds to make the products.

Summary

The teacher will employ a small-scale candle flame to demonstrate a chemical reaction between the candle wax and oxygen in the air. Students will meet a molecular blitheness of the combustion of methane and oxygen every bit a model of a similar reaction. Students volition employ cantlet model cut-outs to model the reaction and see that all the atoms in the reactants testify upwards in the products.

Objective

Students will be able to explain that for a chemical reaction to have place, the bonds between atoms in the reactants are cleaved, the atoms rearrange, and new bonds between the atoms are formed to make the products. Students volition also be able to explain that in a chemical reaction, no atoms are created or destroyed.

Evaluation

Download the student activity sheet, and distribute 1 per student when specified in the activity. The action sail will serve as the "Evaluate" component of each 5-East lesson program.

Safety

Be certain you and the students wear properly fitting goggles. Exist careful when lighting the candle. Exist sure that the match and candle are completely extinguished when y'all are finished with the demonstration.

Materials for the Demonstration

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

Materials for Each Educatee

• Atom cut-outs from the action sheet
• Sheet of colored paper or construction paper
• Colored pencils
• Scissors
• Mucilage or tape

1. Review what happens during a concrete change and introduce the idea of chemic modify.

   Tell students that in previous capacity they have studied unlike aspects of physical alter. When atoms and molecules speed up or slow down, that is a physical modify. When they change state from liquid to solid or from gas to liquid, that is a physical change. When a substance is dissolved by water or some other solvent, a new substance has non really been formed. The ions or molecules tin can still come back together to form the original substance.

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

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

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

   Materials for the Demonstration

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

   Procedure

   1. Carefully light a tea light candle or other small candle.
   2. Keep the candle called-for as you ask students the questions below. You lot will put the candle out in the 2nd office of the sit-in.

   Expected Results

   The wick volition catch on fire and the flame will exist sustained past the chemical reaction.

   The following question is not easy and students are non expected to know the answer at this point. However, thinking about a candle burning in terms of a chemical reaction is a practiced place to start developing what it means when substances react chemically.

   Ask students:

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

   Wax and oxygen from the air are the reactants.

   Students ofttimes say that the string or wick is burning. It is true that the cord of the wick does burn but it's the wax on the string and not so much the string itself that burns and keeps the candle burning. Explain that the molecules that make upward the wax combine with oxygen from the air to brand the products carbon dioxide and h2o vapor.

   Indicate 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 different ways to form the molecules of the products.

   Students may be surprised that water tin can be produced from combustion. Since we apply water to extinguish a fire, it may seem strange that h2o is actually produced by combustion. You may want to let students know that when they "burn down" food in their bodies, they also produce carbon dioxide and h2o.

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. Explicate that when something burns, it reacts with the oxygen in the air.

   Ask students to brand a prediction:

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

   Students may estimate that the candle volition not burn down because both reactants are required for the chemic reaction to continue.

   Procedure

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

      

   Expected Results

   The flame goes out.

   Enquire students:

   Why exercise y'all retrieve the flame goes out when we put a jar over the candle?

   Placing a jar over the candle limits the amount of oxygen in the air effectually the candle. Without enough oxygen to react with the wax, the chemic reaction cannot accept identify and the candle cannot burn.

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

   When a candle burns, the candle wax seems to "disappear." Information technology doesn't really 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 answer. The flame is called-for wax vapor. The light of the flame is caused by a process called chemiluminescence. Energy released in the chemical reaction makes electrons from different molecules movement to a college energy land. When the electrons come up back downwards, free energy is released in the form of light.

4. Introduce the chemical equation for the combustion of methyl hydride and explain that atoms rearrange to go dissimilar molecules.

   Explain to students that wax is fabricated of long molecules called alkane series and that paraffin is made upwardly of only carbon atoms and hydrogen atoms bonded together. Molecules made of only carbon and hydrogen are chosen hydrocarbons. Tell students that y'all will use the simplest hydrocarbon (methane) as a model to bear witness how the wax, or any other hydrocarbon, burns.

   Project the image Chemic Reaction between Methane and Oxygen.

   Show students that at that place is marsh gas and oxygen on the left side of the chemic equation and carbon dioxide and water on the right side. Explain that the molecules on the left side are the reactants and the ones on the right 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.

   Explain to students that the chemical formula for methane is CH_iv. This means that methane is made up of one carbon atom and 4 hydrogen atoms.

   Show students that the other reactant is ii molecules of oxygen gas. Betoken out that each molecule of oxygen gas is made upwards of two oxygen atoms bonded together. It can be disruptive for students that oxygen the atom, and oxygen the molecule, are both chosen oxygen. Permit students know that when we talk well-nigh 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 make 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 form new bonds to brand the products.

   Note: Leave this equation projected throughout the action in the Explore section of this lesson. Students will need to refer to it as they model the chemical reaction.

   Give Each Pupil an Action Canvas.

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

5. Accept students make a model to bear witness 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 chemical reaction come from?

   Materials for Each Student

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

   Process

   1. Prepare the Atoms

      1. Color the carbon atoms blackness, the oxygen atoms red, and leave the hydrogen atoms white.
      2. Use pair of scissors to carefully cut out the atoms.

   2. Build the Reactants

      1. On a sail 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 nether each molecule of the reactants. Also draw a + sign between the reactants.

   Afterwards you are certain that students have made and written the formula for the reactant molecules, tell students that they will rearrange the atoms in the reactants to course the products.

   1. Build the Products

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

   Tell students that in a chemic reaction, the atoms in the reactants come apart, rearrange, and brand new bonds to grade the products.

   1. Represent the Chemical Equation

      1. Have students use their remaining atoms to brand the reactants again to represent the chemical reaction every bit a consummate chemical equation.
      2. Mucilage or tape the atoms to the newspaper to make a more permanent chemic equation of the combustion of methane.

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

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

   Show students that the atoms in marsh gas and oxygen need to come apart just like in their models. Too point out that the atoms arrange themselves differently and bond again to class new products. This is also like their model. Be sure that students realize that the atoms in the products only come up from the reactants. There are no other atoms available. No new atoms are created and no atoms are destroyed.

   Explain to students that chemical reactions are more complicated than the simplified model shown in the animation. The animation shows that bonds between atoms in the reactants are cleaved, 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 guild for their bonds to break and rearrange. Also, the animation shows all of the atoms in the reactants coming autonomously and rearranging to form the products. But in many chemical reactions, but some bonds are broken, and groups of atoms stay together as the reactants course the products.

   Read more nearly the combustion of methyl hydride in the teacher background section.

   Guide students equally you respond 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 big number (coefficient) in forepart of the molecule and the little 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 there are. Then if at that place is a coefficient in front of the molecule and a subscript after an atom, y'all demand to multiply the coefficient times the subscript to get the number of atoms.

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

   Tabular array one. Counting atoms on the reactant and production side of the chemical equation for the combustion of methyl hydride.

   Atoms	Reactant Side	Production Side
   Carbon
   Hydrogen
   Oxygen

   Annotation: The coefficients actually point the ratios of the numbers of molecules in a chemical reaction. Information technology is non the bodily number equally in two molecules of oxygen and ane molecule of methyl hydride since there are usually billions of trillions of molecules reacting. The coefficient shows that there are twice as many oxygen molecules every bit methane molecules reacting. It would exist correct to say that in this reaction there are two oxygen molecules for every methane molecule.

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

   Ask students:

   Are atoms created or destroyed in a chemic reaction?

   No.

   How do you know?

   At that place are the same number of each type of atom on both the reactant side and the product side of the chemical equation we explored.

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

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

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

   Project the image Balanced Equation.

   Explain that the balance shows the mass of methane and oxygen on 1 side exactly equals the mass of carbon dioxide and water on the other. When an equation of a chemical reaction is written, information technology is "balanced" and shows that the atoms in the reactants end up in the products and that no new atoms are created and no atoms are destroyed.

8. Innovate 2 other combustion reactions and have students check to see whether or non they are balanced.

   Tell students that, in addition to the wax and methane, some other mutual hydrocarbons are propane (the fuel in outdoor gas grills), and butane (the fuel in disposable lighters). Have students count the number of carbon, hydrogen, and oxygen atoms in the reactants and products of each equation to meet if the equation is counterbalanced. They should record the number of each type of cantlet in the nautical chart on their action canvas.

   

   Lighting an outdoor gas grill—Combustion of propane

   C₃H_viii + 5O₂ → 3CO₂ + 4H₂0

   Using a dispensable lighter—Combustion of butane

   2C₄H_x + 13O₂ → 8CO₂ + 10H₂O

   Afterward students accept counted up each blazon 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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