Paraffin Wax - an Exothermic Reaction: Caution

Parafinn wax demonstration

"What are we doing to help kids achieve?"

I met some amazing teachers at Chem Ed 2019. Two of these teachers are Yvonne Clifford and Sharon Geyer who ran a workshop about chemical demonstrations. One in particular caught my attention. The demonstration was an exothermic process with paraffin wax. Here is the demonstration.

The teacher takes a few grams of paraffin wax and places it in a small test tube. The demonstrator then carefully heats it until it melts and then gets the wax to a rigorous boil. The demonstrator turns off the flame and then sticks the test tube of boiling wax in a bath of ice water behind a safety shield. A big ball of fire shoots from the test tube.

Here is what I think is happening. The process of a phase change from a solid to liquid to gas is endothermic. It takes the heat from the burner to make this happen. The reverse process is exothermic. When the wax goes from a gas to a liquid to a solid energy is released. This energy, ideally, goes from the system of the wax into the ice water. Or, at least some of it does. There is a free side to the paraffin, the top side of the open test tube. In theory, energy can also exit this side as well. If it does, and it does, the heat could ignite any paraffin that happens to still be a vapor. Since this happens quickly, there is still enough vapor above the free surface. Essentially, the vapor ignites causing a flame. It is surprising in that people generally do not expect a flame to shoot out of a test tube when it is placed in ice water.  

 

Video 1: Parafinn wax demo on Chad Husting's ChemCast Science Videos YouTube Channel (accessed 8/f8/2019

This is important for a couple of reasons. First, if you ever plan on doing this as a demonstration with or without students, you must be extremely careful. You must practice this first and complete a risk assessment. Always wear goggles and use a safety shield. If any of this makes you nervous, do not do it. Also, I have known several teachers who have used paraffin with students in the past to have them do experiments with melting points and or phase change. It is simple, inexpensive and the stuff of candles. What could go wrong? Well, the vapor is also extremely flammable as you have now seen in the video. So....please...be carefull with parafinn. It does not always behave the way you think it will.

Collection: 

Safety

General Safety

For Laboratory Work: Please refer to the ACS .  

For Demonstrations: Please refer to the ACS Division of Chemical Education .

Other Safety resources

: Recognize hazards; Assess the risks of hazards; Minimize the risks of hazards; Prepare for emergencies

 

Safety: Video Demonstration

Demonstration videos presented here are not meant as tools to teach chemical demonstration techniques. They are meant as a tool for classroom use. The demonstrations may present safety hazards or show phenomena that are difficult for an entire class to observe in a live demonstration.

Those performing the demonstrations shown in this video have been trained and adhere to best safety practices.

Anyone thinking about performing a chemistry demonstration should first read and then adhere to the  These guidelines are also available at ChemEd X.

NGSS

Students who demonstrate understanding can use a model to describe how variations in the flow of energy into and out of Earth’s systems result in changes in climate.

More information about all DCI for HS-ESS2 can be found  and further resources at .

Summary:

Students who demonstrate understanding can use a model to describe how variations in the flow of energy into and out of Earth’s systems result in changes in climate.

Assessment Boundary:

Assessment of the results of changes in climate is limited to changes in surface temperatures, precipitation patterns, glacial ice volumes, sea levels, and biosphere distribution.

Clarification:

Examples of the causes of climate change differ by timescale, over 1-10 years: large volcanic eruption, ocean circulation; 10-100s of years: changes in human activity, ocean circulation, solar output; 10-100s of thousands of years: changes to Earth's orbit and the orientation of its axis; and 10-100s of millions of years: long-term changes in atmospheric composition.