Teacher"s Overview


In this investigation, students are challenged to make cautious observations about a burning candle to uncover the chemical and physical alters that make it work.

You are watching: Lighting a candle chemical or physical change


Students will certainly desribe their observations around a burn candle to discover the chemical and also physical alters that make it work.


Be sure to wear safety and security goggles when making nearby observations, tie your hair back if you have long hair, and always be conscious of wherein the fire is with respect to your clothing—do not lean over the flame.Burning candle are open up flames that can reason burns. Fluid wax is hot and can reason burns to the skin.

Materials for Each Group

Tea light candleMatchesSmall manufacturer or evaporating food (such together 50 mL or 100 mL)BalanceRuler or meter stickString (for measure circumference)Stopwatch

Time Required

One class period, roughly 45–50 minutes.

Lab Tips

Tea candles can be purchased in large quantities, as can tapered candles from hardware stores. Candles of various colors, sizes, and also shapes can enrich the monitorings made by the class.

We room all acquainted with burn candles, but how much have actually we really viewed while looking in ~ one? In this practice you will be challenged to observe a burning candle through the lens of chemistry. You may be surprised by how much is really happening in what seems prefer a familiar process!

First us will shot to watch details past our usual method of looking in ~ a candle, and also then we will look for proof of the physics or chemistry nature of any kind of changes that space taking place. Take care in recording your observations—try come imagine that you have never watched a burning candle before!

Obtain a tea irradiate candle, matches, and also any measure up equipment obtainable to you. Before lighting the candle, make 3 qualitative observations and three quantitative observations of the candle.Qualitative monitorings describe attributes or characteristics, quantitative monitorings involve quantities, or measurements. You might choose amongst many nature to observe: color, texture, mass, physical dimensions, density, aroma… or any kind of others you have the right to think of. Use as numerous of her physical senses together possible, and be sure to incorporate units for any kind of of your quantitative observations.

Use a complement to closely light the candle.Repeat the procedure of make qualitative and quantitative monitorings of the burning candle, this time making six of each type of observation. (Some of her observations may relate to nature you have currently recorded, that might be an altering now the the candle is burning.) when again usage all your senses to do qualitative observations. Ask yourself what you have the right to measure for the quantitative observations.

For your observations and measurements, think about not just the physics candle, but likewise consider its influence on the wait in the room surrounding it.

Now lay out a thorough drawing of the burning candle, an enlargement the the section about a centimeter native the top of the candle come the topmost tip of the flame:

Label the adhering to regions the the candle in her drawing:

solid waxliquid waxregion that wick there is no flameregion the wick v flameregion the the wick that glows

Now identify as many different facets of the fire itself and also label lock in the drawing. When you have completed recording her observations and drawings, prepare to blow out the candle, and be prepared to make additional observations as you carry out this!Blow the end the candle and also record two qualitative and two quantitative observations of the candle automatically after that is extinguished:

Qualitative observationsQuantitative observations

Interpreting Evidence

part One

Now that we have paid close fist to the nature of a burning candle, we can start to analyze what we’ve watched in terms of phase changes and also chemical reactions.In a phase change (from hard to liquid or from liquid to gas) the corpuscle of a substance (in this case the molecules of wax) will adjust the plan they have actually with every other. Together a heavy they will certainly be closely packed together and also unable to relocate freely. In the fluid they will be able to flow roughly each other but will still be close together, and also as a gas they will fly openly apart however they will still it is in wax molecules and also will have the very same structure they had actually as molecule in the solid and also the fluid phases:


waxes from plants and animals have various structures. Right here is a molecule comparable to wax— a product that is typically a major component that the candle wax.

In the box below, usage small, solitary shapes come represent entire wax molecules, and also sketch their arrangement in the 3 physical phases:


based on your observations of the burn candle, did you discover evidence because that the readjust from the heavy wax phase to the liquid wax phase?


describe this proof as especially as possible.


explain this evidence as especially as possible.

Did you discover evidence because that the change from the fluid wax step to the gaseous wax phase?

A physics candle is written of wax neighboring a wick. Look increase the meaning of the verb “to wick,” and also write that down.Describe the wicking process in the burning candle, and be certain your description consists of the physics state the the wax and the wick.As a candle burns, the wax slowly disappears indigenous sight. Is over there a physical adjust in the wax that would certainly account for this disappearanceIf the wax was simply undergoing physics change, would certainly you expect the candle to produce heat and light as it does once a candle burns?The procedure of burning (as protest to evaporating) is a chemical reaction, a chemistry change. The wax molecules room undergoing a chemical change; they are changing into various molecules through reacting v a substance in the air. What is this problem in the air that a candle requirements to burn?

Interestingly, a candle releases energy through the very same kind of reaction the your body provides to acquire energy. Host your breath for a moment. What is your body craving? This is the very same substance the candle demands to burn in a chemical adjust that we contact combustion.

We deserve to represent the combustion of a candle like this:


complete the complying with sentence that restates this equation:

Two molecules of wax react v ____________ molecules of oxygen to produce__________ molecules of _____________________________ and ___________ molecule of __________________.

We space not mindful of oxygen in the air due to the fact that it is one odorless and also colorless gas, and also at the temperature the a burning candle, both the CO2 and the H2O are additionally gases that are invisible to us. We can see evidence of chemistry change, however, if us restrict the amount of oxygen that is allowed to react with the wax.

If much less oxygen is available, one feasible outcome in the burning of wax is

Relight the candle and lower the bottom of a small beaker or a clear watch glass right into the flame so that the fire touches the surface of the glass. Hold it there because that a minute (where the restricts few of the air flow to the flame) and then remove it.

What do you watch on the bottom of the beaker? What can this substance be and where did the come from?How does this provide evidence the a chemical reaction is acquisition place?Wipe the bottom the the manufacturer clean and also place an ice cream cube inside it. Hold the beaker several centimeters over (not in) the fire and allow the candle come burn. Have the right to you check out a substance developing on the bottom of the beaker? What could this problem be and also where did the come from? could it have actually come indigenous the melting ice cream inside the beaker?Consider the flame itself. Is the fire a substance created by the candle? What monitorings lead you to think that the fire is matter? In what ways does the fire seem choose energy?Is the following statement true or false: “As a candle burns, wax turns right into fire.” If this isn’t specific statement, have the right to you restate it correctly?

Finally, allow us take into consideration the physical phase of the wax as it reacts through the oxygen to produce carbon dioxide and water. Prepare to observe carefully! Blow the end the candle and very quickly bring a complement close to the wick. Shot to notice exactly wherein the lit wood splint is with respect to the wick once the candle reignites.

Do this number of times to watch if you watch something interesting. Note any kind of evidence you have actually observed the helps to determine the physical step of the wax as soon as it reacts through oxygen.

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What phase is the wax in as soon as it mixes through oxygen in the air and undergoes a chemistry change?Based on your observations, in which phase (solid, liquid, or gas) is the wax most likely to undergo a chemical change?Explain why this is the case based upon your sketches of wax in solid, liquid, and gas phases.How might this (your price to inquiry above) describe a sign that claims NO SMOKING near the pumps in ~ a gas station?Look earlier at your diagrams of the candle flame. Can you identify the region where the wick chin is undergoing combustion? where is this region?What is fire? Is it issue or is that energy? describe your answer.In a quick paragraph, summary the transforms that a candle undergoes when it burns. Incorporate the adhering to words into the paragraph in a meaningful way: wax, wick, step change, chemical reaction, vaporize, melt, transforms, solid, liquid, gas, energy, light, and heat.