Teacher"s Overview


In this examination, students are tested to make mindful observations around a burning candle to uncover the chemical and also physical alters that make it work-related.

You are watching: What chemical change occurs when a wax candle burns?


Students will certainly desribe their observations about a burning candle to uncover the chemical and also physical transforms that make it occupational.


Be sure to wear safety goggles while making close observations, tie your hair earlier if you have long hair, and also constantly be aware of wright here the flame is via respect to your clothing—do not lean over the flame.Burning candles are open flames that have the right to cause burns. Liquid wax is warm and also deserve to cause burns to the skin.

Materials for Each Group

Tea light candleMatchesSmall beaker or evaporating dish (such as 50 mL or 100 mL)BalanceRuler or meter stickString (for measuring circumference)Stopwatch

Time Required

One course period, approximately 45–50 minutes.

Lab Tips

Tea candles deserve to be purchased in large amounts, as deserve to tapered candles from hardware stores. Candles of different colors, sizes, and also forms can enaffluent the monitorings made by the class.

We are all acquainted with burning candles, but just how a lot have actually we really viewed while looking at one? In this exercise you will be tested to observe a burning candle with the lens of chemistry. You may be surprised by just how much is really happening in what appears choose a acquainted process!

First we will attempt to observe details beyond our usual means of looking at a candle, and also then we will certainly look for proof of the physical or chemical nature of any type of changes that are occurring. Take care in recording your observations—try to imagine that you have never watched a burning candle before!

Obtain a tea light candle, matches, and any type of measuring equipment obtainable to you. Before lighting the candle, make 3 qualitative monitorings and 3 quantitative observations of the candle.Qualitative monitorings explain features or characteristics, quantitative monitorings involve quantities, or measurements. You may choose among many kind of properties to observe: color, texture, mass, physical dimensions, density, aroma… or any others you deserve to think of. Use as many kind of of your physical senses as feasible, and also be sure to include units for any type of of your quantitative monitorings.

Use a match to closely light the candle.Repeat the process of making qualitative and also quantitative monitorings of the burning candle, this time making 6 of each sort of monitoring. (Some of your observations might relate to properties you have already taped, that may be changing now that the candle is burning.) Once aacquire usage all your senses to make qualitative monitorings. Ask yourself what you have the right to meacertain for the quantitative monitorings.

For your monitorings and measurements, take into consideration not only the physical candle, however also take into consideration its influence on the air in the area neighboring it.

Now sketch a thorough illustration of the burning candle, an enlargement of the percent about a centimeter from the peak of the candle to the topa lot of guideline of the flame:

Label the following regions of the candle in your drawing:

solid waxliquid waxregion of wick without flameregion of wick via flameregion of the wick that glows

Now identify as many kind of different facets of the flame itself and label them in the illustration. When you have actually completed recording your observations and illustrations, prepare to blow out the candle, and also be ready to make further observations as you carry out this!Blow out the candle and also record 2 qualitative and two quantitative observations of the candle instantly after it is extinguished:

Qualitative observationsQuantitative observations

Interpreting Evidence

Part One

Now that we have actually phelp close attention to the properties of a burning candle, we have the right to begin to interpret what we’ve checked out in regards to phase transforms and chemical reactions.In a phase adjust (from solid to liquid or from liquid to gas) the particles of a substance (in this case the molecules of wax) will certainly readjust the setup they have with each various other. As a solid they will certainly be closely packed together and unable to relocate easily. In the liquid they will certainly be able to circulation about each various other yet will still be cshed together, and as a gas they will fly freely acomponent but they will certainly still be wax molecules and will certainly have actually the same structure they had as molecules in the solid and also the liquid phases:


Waxes from plants and animals have different structures. Here is a molecule comparable to wax— a material that is usually a major component of the candle wax.

In the boxes below, use small, single forms to reexisting entire wax molecules, and also sketch their arrangement in the 3 physical phases:


Based on your observations of the burning candle, did you find proof for the change from the solid wax phase to the liquid wax phase?


Describe this proof as particularly as feasible.


Describe this evidence as especially as feasible.

Did you discover evidence for the adjust from the liquid wax phase to the gaseous wax phase?

A physical candle is created of wax neighboring a wick. Look up the meaning of the verb “to wick,” and also compose it dvery own.Describe the wicking process in the burning candle, and be sure your summary contains the physical state of the wax and also the wick.As a candle burns, the wax slowly disshows up from sight. Is tright here a physical change in the wax that would account for this disappearanceIf the wax was ssuggest undergoing physical change, would you intend the candle to develop heat and also light as it does once a candle burns?The procedure of burning (as opposed to evaporating) is a chemical reactivity, a chemical readjust. The wax molecules are undergoing a chemical change; they are changing into various molecules by reacting via a substance in the air. What is this substance in the air that a candle needs to burn?

Interestingly, a candle releases power with the exact same type of reactivity that your body provides to attain energy. Hold your breath for a minute. What is your body craving? This is the exact same substance the candle demands to burn in a chemical adjust that we call combustion.

We can reexisting the combustion of a candle choose this:


Complete the adhering to sentence that restates this equation:

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

We are not conscious of oxygen in the air bereason it is an odormuch less and also colormuch less gas, and also at the temperature of a burning candle, both the CO2 and the H2O are also gases that are invisible to us. We can see proof of chemical change, but, if we restrict the amount of oxygen that is allowed to react through the wax.

If less oxygen is easily accessible, one feasible outcome in the burning of wax is

Relight the candle and also lower the bottom of a small beaker or a clear watch glass into the flame so that the flame touches the surchallenge of the glass. Hold it tright here for a minute (wright here it restricts some of the air circulation to the flame) and also then rerelocate it.

What do you observe on the bottom of the beaker? What could this substance be and wbelow did it come from?How does this provide evidence that a chemical reaction is taking place?Wipe the bottom of the beaker clean and area an ice cube inside it. Hold the beaker numerous centimeters over (not in) the flame and also enable the candle to burn. Can you view a substance developing on the bottom of the beaker? What might this substance be and where did it come from? Could it have come from the melting ice inside the beaker?Consider the flame itself. Is the flame a substance produced by the candle? What monitorings lead you to think that the flame is matter? In what methods does the flame seem prefer energy?Is the adhering to statement true or false: “As a candle burns, wax turns right into fire.” If this isn’t an accurate statement, deserve to you restate it correctly?

Finally, let us consider the physical phase of the wax as it reacts via the oxygen to develop carbon dioxide and water. Prepare to observe carefully! Blow out the candle and incredibly quickly lug a match cshed to the wick. Try to notification specifically where the lit wooden splint is via respect to the wick as soon as the candle reignites.

Do this a number of times to watch if you observe something interesting. Note any kind of proof you have actually observed that helps to identify the physical phase of the wax as soon as it reacts through oxygen.

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What phase is the wax in once it mixes via oxygen in the air and also undergoes a chemical change?Based on your observations, in which phase (solid, liquid, or gas) is the wax a lot of most likely to undergo a chemical change?Explain why this is the situation based on your sketches of wax in solid, liquid, and gas phases.How can this (your answer to question above) describe a sign that says NO SMOKING near the pumps at a gas station?Look back at your diagrams of the candle flame. Can you recognize the area wright here the wick itself is undergoing combustion? Wright here is this region?What is fire? Is it matter or is it energy? Exsimple your answer.In a short paragraph, summarize the changes that a candle undergoes when it burns. Incorporate the complying with words into the paragraph in a meaningful way: wax, wick, phase readjust, chemical reaction, vaporize, melt, transforms, solid, liquid, gas, power, light, and also warmth.