Teacher\"s Overview


In this investigation, student are tested to make careful observations around a burn candle to find the chemical and also physical alters that make it work.

You are watching: A burning candle is undergoing a physical change


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


Be certain to wear safety and security goggles while making nearby observations, tie your hair ago if you have long hair, and constantly be conscious of whereby the fire is with respect to your clothing—do no lean over the flame.Burning candle are open up flames the can reason burns. Fluid wax is hot and can reason burns to the skin.

Materials for Each Group

Tea light candleMatchesSmall maker or evaporating dish (such together 50 mL or 100 mL)BalanceRuler or meter stickString (for measure up circumference)Stopwatch

Time Required

One course period, approximately 45–50 minutes.

Lab Tips

Tea candles deserve to be to buy in huge quantities, as deserve to tapered candle from hardware stores. Candle of various colors, sizes, and also shapes deserve to enrich the observations made through the class.

We are all familiar with burn candles, but how much have actually we really seen while looking in ~ one? In this exercise you will certainly be tested to watch a burning candle through the lens the chemistry. You may be surprised by just how much is yes, really happening in what seems like a acquainted process!

First we will try to watch details past our usual means of looking at a candle, and then we will look for evidence of the physics or chemical nature of any kind of changes that are taking place. Take treatment in recording your observations—try to imagine the you have actually never checked out a burn candle before!

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

Use a match to very closely light the candle.Repeat the process of make qualitative and also quantitative observations of the burn candle, this time making six of each sort of observation. (Some of your observations may relate to nature you have currently recorded, that may be transforming now that the candle is burning.) as soon as again use all her senses to make qualitative observations. Ask yourself what you deserve to measure because that the quantitative observations.

For her observations and measurements, consider not just the physical candle, but likewise consider its influence on the wait in the room surrounding it.

Now map out a detailed drawing that the burn candle, one enlargement that the section about a centimeter native the optimal of the candle to the topmost reminder of the flame:

Label the following regions of the candle in your drawing:

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

Now identify as numerous different elements of the flame itself and also label them in the drawing. When you have actually completed recording your observations and also drawings, prepare come blow the end the candle, and also be all set to make more observations together you carry out this!Blow out the candle and record two qualitative and two quantitative monitorings of the candle instantly after it is extinguished:

Qualitative observationsQuantitative observations

Interpreting Evidence

component One

Now the we have actually paid close fist to the properties of a burn candle, us can start to analyze what we’ve seen in regards to phase changes and chemical reactions.In a phase change (from solid to liquid or from fluid to gas) the corpuscle of a substance (in this case the molecules of wax) will readjust the plan they have with each other. As a heavy they will be very closely packed together and unable to move freely. In the fluid they will have the ability to flow about each other yet will still be close together, and also as a gas they will certainly fly easily apart however they will certainly still be wax molecules and also will have the very same structure they had as molecules in the solid and the fluid phases:


waxes from plants and also animals have various structures. Right here is a molecule similar to wax— a material that is generally a significant component that the candle wax.

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


based on your monitorings of the burning candle, walk you uncover evidence for the change from the solid wax step to the fluid wax phase?


explain this evidence as specifically as possible.


define this proof as particularly as possible.

Did you find evidence because that the change from the liquid wax step to the gas wax phase?

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

Interestingly, a candle releases energy through the exact same kind of reaction that your body uses to achieve energy. Host your breath because that a moment. What is your body craving? This is the exact same substance the candle needs to burn in a chemical adjust that we speak to combustion.

We can represent the combustion of a candle prefer this:


complete the complying with sentence the restates this equation:

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

We room not conscious of oxygen in the air since it is one odorless and also colorless gas, and also at the temperature the a burning candle, both the CO2 and also the H2O are additionally gases that space invisible to us. We deserve to see evidence of chemistry change, however, if us restrict the lot of oxygen that is enabled to react v the wax.

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

Relight the candle and also lower the bottom that a small beaker or a clear watch glass right into the flame so that the flame touches the surface ar of the glass. Organize it there for a moment (where the restricts few of the air circulation to the flame) and also then eliminate it.

What execute you observe on the bottom the the beaker? What can this substance be and also where did that come from?How does this carry out evidence that a chemistry reaction is acquisition place?Wipe the bottom the the maker clean and also place an ice cube within it. Host the beaker numerous centimeters over (not in) the flame and permit the candle to burn. Deserve to you check out a substance developing on the bottom that the beaker? What can this substance be and where did that come from? might it have actually come native the melting ice inside the beaker?Consider the fire itself. Is the fire a substance created by the candle? What observations lead you to think the the flame is matter? In what ways does the flame seem choose energy?Is the complying with statement true or false: “As a candle burns, wax turns right into fire.” If this isn’t an accurate statement, have the right to you restate the correctly?

Finally, permit us consider the physical phase of the wax as it reacts v the oxygen to create carbon dioxide and water. Prepare to observe carefully! Blow the end the candle and very quickly carry a enhance close to the wick. Try to notice exactly whereby the lit wooden splint is with respect come the wick when the candle reignites.

Do this numerous times to view if you watch something interesting. Note any evidence you have actually observed the helps to identify the physical phase of the wax when it reacts with oxygen.

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What phase is the wax in as soon as it mixes through oxygen in the air and undergoes a chemical change?Based on her observations, in which step (solid, liquid, or gas) is the wax most likely to experience a chemical change?Explain why this is the case based on your sketches of wax in solid, liquid, and gas phases.How can this (your prize to concern above) define a authorize that claims NO SMOKING near the pumps in ~ a gas station?Look back at her diagrams of the candle flame. Have the right to you recognize the an ar where the wick chin is experience combustion? wherein is this region?What is fire? Is it issue or is that energy? define your answer.In a short paragraph, summary the transforms that a candle undergoes as soon as it burns. Combine the following words right into the paragraph in a meaningful way: wax, wick, step change, chemical reaction, vaporize, melt, transforms, solid, liquid, gas, energy, light, and also heat.