Key Concepts:

A physical change, such as a state readjust or dissolving, does not create a new substance, but a chemical readjust does.In a chemical reaction, the atoms and molecules that connect with each various other are referred to as reactants.In a chemical reaction, the atoms and molecules developed by the reaction are dubbed products. In a chemistry reaction, just the atoms current in the reaction can end up in the products. No brand-new atoms space created, and also no atoms space destroyed.In a chemical reaction, reactants contact each other, bonds in between atoms in the reactants room broken, and atoms rearrange and form new bonds to do the products.

You are watching: When a chemical reaction occurs, what always stays the same between reactants and products?


The teacher will use a small candle fire to demonstrate a chemical reaction between the candle wax and also oxygen in the air. Student will watch a molecular computer animation of the burning of methane and oxygen together a version of a comparable reaction. College student will use atom model cut-outs to version the reaction and also see that all the atom in the reactants show up in the products.


Students will be able to explain that for a chemical reaction to take place, the bonds between atoms in the reactants room broken, the atoms rearrange, and new bonds between the atoms are formed to make the products. College student will also be may be to describe that in a chemistry reaction, no atom are produced or destroyed.


Download the student activity sheet, and also distribute one per student once specified in the activity. The activity sheet will serve as the “Evaluate” component of every 5-E great plan.


Be sure you and the student wear correctly fitting goggles. Be careful when lighting the candle. Be certain that the match and candle are totally extinguished when you space finished v the demonstration.

Materials for the Demonstration

Tea light candle or other tiny stable candle MatchesGlass jar, big enough come be put over the candle

Materials because that Each Student

Atom cut-outs from the task sheetSheet the colored document or construction paperColored pencilsScissorsGlue or tape

Review what happens throughout a physical change and introduce the idea of chemical change.

Tell students the in ahead chapters they have actually studied different facets of physics change. Once atoms and also molecules rate up or slow-moving down, the is a physical change. When they readjust state from fluid to heavy or native gas come liquid, that is a physical change. When a substance is dissolved by water or some various other solvent, a brand-new substance has not really been formed. The ion or molecules deserve to still come earlier together to form the initial substance.

Let students recognize that in this chapter they will discover what happens during a chemical change. In a chemical change, the atoms in the reaction rearrange themselves and bond together in different way to form one or more new commodities with different characteristics than the reactants. When a new substance is formed, the adjust is called a chemistry change.

As a demonstration, irradiate a candle and explain what is happening utilizing the terms reactants, products, and also chemical reaction.

Explain that in most chemical reactions, two or much more substances, called reactants, interact to create different substances dubbed products. Call students that burning a candle is an instance of a chemical reaction.

Materials for the Demonstration

Tea irradiate candle or other tiny stable candle MatchesGlass jar, large enough come be put over the candle


Carefully irradiate a tea irradiate candle or other small candle.Keep the candle burning together you ask students the questions below. You will placed the candle the end in the second part of the demonstration.

Expected results

The wick will record on fire and also the flame will certainly be continual by the chemistry reaction.

The following question is not easy and also students are not intended to understand the answer at this point. However, thinking around a candle burn in terms of a chemistry reaction is a good place come start occurring what it way when substances reaction chemically.

Ask students:

What do you think space the reaction in this chemical reaction? Wax and also oxygen indigenous the air room the reactants.

Students frequently say that the string or wick is burning. It is true the the string of the wick go burn yet it’s the wax ~ above the string and not so much the string itself that burns and also keeps the candle burning. Explain that the molecules that make up the wax incorporate with oxygen native the waiting to do the products carbon dioxide and also water vapor.

Point the end to students the this is just one of the significant characteristics that a chemistry reaction: In a chemistry reaction, atoms in the reactants integrate in new and various ways to type the molecule of the products.

Students might be surprised the water deserve to be created from combustion. Because we usage water come extinguish a fire, it may seem strange that water is actually produced by combustion. You might want to let students understand that when they “burn” food in their bodies, they additionally produce carbon dioxide and also water.

Place a jar end the candle to assist students realize that oxygen is a reactant in the burning of a candle.

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

Ask students to do a prediction:

Will the candle quiet burn if one of the reaction (wax or oxygen) is no longer available? Students may guess the the candle will not burn because both reactants are compelled for the chemistry reaction come continue.


Carefully location a glass jar end the lit candle.


Expected Results

The fire goes out.

Ask students:

Why do you think the flame goes out as soon as we placed a jar over the candle? place a jar over the candle boundaries the lot of oxygen in the air about the candle. Without sufficient oxygen to react through the wax, the chemistry reaction cannot take it place and also the candle can not burn. Once a candle burns because that a while, it eventually gets smaller and smaller. Wherein does the candle wax go? when a candle burns, the candle wax appears to “disappear.” that doesn’t really disappear, though: It reaction chemically, and also the new products enter the air.

Note: part curious students may ask what the fire is made of. This is a great question and also not trivial come answer. The fire is burn 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 move to a greater energy state. Once the electron come back down, energy is exit in the type of light.


Have students do a model to present that in a chemistry reaction the atom of the reaction rearrange to type the products.

Question come Investigate

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

Materials for Each Student

Atom design cut-outs (carbon, oxygen, and also hydrogen)Sheet that colored document or building paperColored pencilsScissorsGlue or tape


Prepare the AtomsColor the carbon atom black, the oxygen atoms red, and also leave the hydrogen atom white. Use scissors to carefully cut out the atoms.Build the Reactants

On a paper of paper, ar the atoms with each other to do the molecule of the reaction on the left next of the chemistry equation for the burning of methane.

Write the chemical formula under every molecule of the reactants. Additionally draw a + sign between the reactants.

After you room sure that students have actually made and written the formula because that the reactant molecules, call students the they will rearrange the atoms in the reactants to kind the products.

Build the ProductsDraw an arrowhead after the 2nd oxygen molecule to show that a chemistry reaction is taking place.Rearrange the atoms in the reactants to make the molecule in the products on the appropriate side that the arrow. Create the chemistry formula under each molecule the the products. Additionally draw a + sign between the products.

Tell students that in a chemical reaction, the atom in the reaction come apart, rearrange, and also make brand-new bonds to form the products.

Represent the chemical EquationHave students usage their remaining atoms to make the reactants again to represent the chemical reaction as a complete chemical equation. Glue or ice the atom to the file to make a an ext permanent chemistry equation of the burning of methane.Extend

Introduce 2 other combustion reactions and also have students inspect to view whether or not they are balanced.

Tell college student that, in enhancement to the wax and methane, some other common hydrocarbons space propane (the fuel in outdoor gas grills), and butane (the fuel in disposable lighters). Have students counting the number of carbon, hydrogen, and also oxygen atoms in the reactants and products of each equation to view if the equation is balanced. They should record the variety of each type of atom in the chart on their activity sheet.

See more: What Is A Valence Electron And Why Is The Valence Shell Important


Lighting an out gas grill—Combustion of propane

C3H8 + 5O2 → 3CO2 + 4H20

Using a disposable lighter—Combustion the butane

2C4H10 + 13O2 → 8CO2 + 10H2O

After students have counted increase each kind of atom, testimonial their answers come make sure they know how to translate subscripts and coefficients.