Teacher"s Overview


In this examination, students are challenged to make mindful monitorings about a burning candle to find the chemical and physical changes that make it job-related.

You are watching: Why is burning a candle a chemical change


Students will certainly desribe their observations about a burning candle to discover the chemical and also physical changes that make it work.


Be certain to wear safety goggles while making cshed monitorings, tie your hair back if you have lengthy hair, and always be mindful of where the flame is via respect to your clothing—carry out not lean over the flame.Burning candles are open up flames that have the right to reason burns. Liquid wax is warm and can reason 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 have the right to be purchased in large amounts, as have the right to tapered candles from hardware stores. Candles of various colors, sizes, and forms can enwell-off the observations made by the class.

We are all acquainted through burning candles, yet how much have we really watched while looking at one? In this exercise you will be tested to observe a burning candle via the lens of chemistry. You may be surprised by exactly how a lot is really happening in what appears favor a acquainted process!

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

Obtain a tea light candle, matches, and also any type of measuring equipment accessible to you. Before lighting the candle, make 3 qualitative monitorings and also 3 quantitative monitorings of the candle.Qualitative monitorings explain features or features, quantitative observations involve amounts, or dimensions. You might pick among many kind of properties to observe: color, texture, mass, physical dimensions, thickness, aroma… or any others you can think of. Use as many of your physical senses as possible, and also be certain to include devices for any of your quantitative observations.

Use a enhance to very closely light the candle.Repeat the procedure of making qualitative and quantitative observations of the burning candle, this time making 6 of each type of observation. (Some of your observations might relate to properties you have currently tape-recorded, that might be changing currently that the candle is burning.) Once aobtain use all your senses to make qualitative observations. Ask yourself what you can measure for the quantitative observations.

For your monitorings and dimensions, take into consideration not only the physical candle, yet likewise think about its influence on the air in the space neighboring it.

Now sketch a detailed illustration of the burning candle, an enlargement of the percent about a centimeter from the optimal of the candle to the topthe majority of pointer of the flame:

Label the complying with regions of the candle in your drawing:

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

Now differentiate as many various elements of the flame itself and also label them in the drawing. When you have actually completed recording your observations and drawings, prepare to blow out the candle, and be ready to make even more monitorings as you carry out this!Blow out the candle and document two qualitative and also 2 quantitative observations of the candle automatically after it is extinguished:

Qualitative observationsQuantitative observations

Interpreting Evidence

Part One

Now that we have actually paid cshed attention to the properties of a burning candle, we can start to translate what we’ve checked out in terms of phase transforms and chemical reactions.In a phase adjust (from solid to liquid or from liquid to gas) the pshort articles of a substance (in this case the molecules of wax) will readjust the setup they have actually via each various other. As a solid they will certainly be closely packed together and also unable to move openly. In the liquid they will have the ability to flow about each various other however will certainly still be close together, and as a gas they will fly easily apart yet they will still be wax molecules and will certainly have the same structure they had as molecules in the solid and the liquid phases:


Waxes from plants and pets have actually various frameworks. Here is a molecule similar to wax— a product that is typically a major component of the candle wax.

In the boxes listed below, use little, single forms to reexisting whole wax molecules, and sketch their arrangement in the three physical phases:


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


Describe this evidence as particularly as possible.


Describe this evidence as especially as possible.

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

A physical candle is created of wax surrounding a wick. Look up the interpretation of the verb “to wick,” and also create it dvery own.Describe the wicking procedure in the burning candle, and also be sure your description has the physical state of the wax and the wick.As a candle burns, the wax slowly disappears from sight. Is tbelow a physical readjust in the wax that would account for this disappearanceIf the wax was simply undergoing physical adjust, would certainly you expect the candle to produce heat and also light as it does as soon as a candle burns?The process of burning (as opposed to evaporating) is a chemical reactivity, a chemical adjust. The wax molecules are undergoing a chemical change; they are transforming into various molecules by reacting through a substance in the air. What is this substance in the air that a candle demands to burn?

Interestingly, a candle releases energy through the exact same type of reaction that your body provides to attain power. Hold your breath for a moment. 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 deserve to reexisting the burning of a candle favor this:


Complete the complying with sentence that rmansions this equation:

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

We are not aware of oxygen in the air bereason it is an odorless 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 deserve to watch evidence of chemical readjust, but, if we restrict the amount of oxygen that is enabled to react via the wax.

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

Relight the candle and also reduced the bottom of a tiny 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 moment (where it restricts some of the air flow to the flame) and then rerelocate it.

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

Finally, let us consider the physical phase of the wax as it reacts through the oxygen to create carbon dioxide and water. Prepare to observe carefully! Blow out the candle and also extremely quickly bring a complement cshed to the wick. Try to alert precisely wbelow the lit wooden splint is through respect to the wick once the candle reignites.

Do this a number of times to watch if you observe something amazing. Note any evidence you have observed that helps to identify the physical phase of the wax as soon as it reacts with oxygen.

See more: How Do You Determine The Number Of Electrons That Go Into The Lewis Structure Of A Molecule?

What phase is the wax in when it mixes with oxygen in the air and also undergoes a chemical change?Based on your monitorings, in which phase (solid, liquid, or gas) is the wax a lot of likely to undergo a chemical change?Exsimple why this is the instance based on your sketches of wax in solid, liquid, and gas phases.How can this (your answer to question above) explain a authorize that states NO SMOKING close to the pumps at a gas station?Look ago at your diagrams of the candle flame. Can you recognize the region where the wick itself is undergoing combustion? Wright here is this region?What is fire? Is it matter or is it energy? Explain your answer.In a brief paragraph, summarize the changes that a candle undergoes as soon as it burns. Incorporate the complying with words into the paragraph in a systematic way: wax, wick, phase change, chemical reactivity, vaporize, melt, transdevelops, solid, liquid, gas, energy, light, and also warmth.