Ready, Set, Reaction!


Match Game!



30 minutes or longer
Chemistry, Engineering

In PDQ 2 you recorded data as your candle burned. Now you are challenged to demonstrate your mastery over CO2 by carefully controlling it in a closed environment.


After studying chemical reactions and understanding the behavior of CO2 gas generated in the candle experiment, you are now challenged to go further!   You will now add additional candles to your closed chamber experiment and come to a deeper understanding of the relationship between the exothermic reaction in the candles and the production of CO2 gas.  Get ready for the ultimate challenge as you demonstrate your understanding of this reaction and use it to control exactly when your candles will extinguish.


By completing this experiment and conducting the scientific observations associated with it you will master the following knowledge! Good luck science explorer!

  • Different types of substances can “react” with one another to create a chemical change in the substances.
  • Chemical Reaction:
    • When two substances react with one another to create a new, different substance.
    • Causes a change in the composition of a substance.
    • Can cause physical and chemical changes in substances – even creating gas where there was none before.
    • Can require energy (endothermic) to take place or produce energy (exothermic).
  • CO2:
    • An invisible and odorless gas.
    • Exhaled by human beings.
    • Can be generated through a chemical reaction of baking soda and vinegar.
  • The pH scale tells us if a substance is a base or an acid.   
  • Vinegar (acetic acid) is an acid and baking soda (sodium bicarbonate) is a base
  • Scientific sensors allow us to measure the scientific world around us with better precision and accuracy.
  • Fire is both a chemical and physical reaction.

What You'll Need

These are the same materials used PDQ 2 with the addition of extra candles and blocks to place the candles at different heights.

  • IOS or Android smart device with Bluetooth Low Energy (BLE) to connect to databot™
  • databot™ + Phyphox App installed on your smart device.
  • Container with an airtight lid.
    In the activity demonstrations, we are using an OXO brand, 4.2 liters,
    the storage container that has a push-button airlock feature. container that has a push button airlock feature.  
  • Tea candles – 3
  • Blocks to elevate the candles (LEGO type blocks work well).
  • Lighter (Long-Handled) 


  • Conduct PDQ 2 of this module successfully.
  • Use a lab notebook to carefully write down your findings as you conduct this experiment – you will see a chart format below.  This challenge will take several attempts to master and the better your note-taking, the faster you will conquer it!

Challenge (25 mins)

As a team or individually experiment with the timing of when your candle(s) extinguish inside your test chamber.  There are several variables associated with this challenge:

  • The number of candles in the chamber.  More candles burning means more chemical reaction and  more CO2 production.
  • The height of the candles makes a difference in how quickly or slowly they go out.  Test this by doing two candles at different heights.  Try it with three.  Time the amount of time required with each configuration and which candles go out first and at which heights

Use the following table  to record your findings and take careful notes.  Look for patterns!

Question: Why do candles at different heights go out at different times?

After experimenting with the different configurations, you are ready for the big challenge!  Using all your scientific knowledge, now place the number of candles required at the correct heights to carefully control the CO2 production and put out the candles at precisely 95 seconds. 

Please note that you may need to adjust your timing challenge based on the “chamber” size you are using.  The experiments conducted in this module were all done in a 4 liter container.  If  you have a smaller or larger container you may need to adjust.

Go Further

Extend your mastery by trying some modifications!

  • Monitor the relative humidity level (RH) in the chamber and the temperature.  Challenge yourself to engineer a candle configuration that will produce a specific humidity level in the chamber. 
  • Challenge yourself to produce a specific temperature level. 
  • Can you control more than of  your output variables – CO2, temperature, or humidity –  at a time by simply adjusting the candles?

Deep Thoughts to Ponder

If you conducted the Cave of Dogs activity, you observed the behavior of candles when in the presence of CO2.  Does your experiment here match the behavior you saw in the Cave of Dogs?  Why or why not?  

Cool bananas – you are now a chemical engineer demonstrating mastery of your environment!

It’s now time for some community and group hugs. Next and final stop – a collaboration activity. Enjoy!

Next Step, Collaboration!

Educator Info

Challenges like this truly encourage critical thinking and mastery by the students.  By carefully gathering data and creating a final working solution students will better understand some of the variables going on inside the test chamber.  By learning to control the output they are demonstrating a certain level of mastery. 

Time permitting, the modifications suggested will provide further reinforcement of the overall module learning objectives.

One of the interesting things in this experiment is that the candles will go out from the highest to lowest.  As the candles generate heat as well as CO2, the hot layer of air traps the CO2 above the candles, but as CO2 accumulates its density and increasing abundance push down from the top, extinguishing the candles one by one. In the Cave of Dogs experiment, we have an open container releasing the heat of the candles and feed the CO2 in from an alternate source.  Consequently, its higher density causes the CO2 to settle lower in the chamber and build up, putting the candles out from the bottom up.   For students who have done both activities, this is a great challenge for them to explain why this happening.  Why do they go out bottom up in one experiment and top down in another?  Science!

Educator Info

Ready, Set, Reaction! by Robert O. Grover & Team databot is licensed under a Creative Commons Attribution 4.0 International License. Permissions beyond the scope of this license may be available at