The Mpemba effect: competition and resources


Help discover why warm water freezes quicker than cold water. The Royal Society of Chemistry offered £1000 for the best and most creative explanation of this phenomenon, known as the Mpemba effect. View the winning entry, try the experiment for yourself, or read the original paper.

Type of Activity

working independently



Age Group

Primary to 18 years

The Mpemba effect

The Mpemba effect is the phenomenon where hot water freezes quicker than cold water. The Royal Society of Chemistry offered £1000 to the person or team producing the best and most creative explanation as to why this occurs.

We received 22 000 entries to the competition. These were whittled down to just 11 finalists by the panel of expert judges and the public vote.

The winner of the competition, Nikola Bregovic, research assistant in the field of physical chemistry at the Department of Chemistry, University of Zagreb, Croatia, was announced on the 10th of January 2013.


The Royal Society of Chemistry investigated the Mpemba Effect with Hermes2012. The Avogadro's Lab Experiment is from the January 2012 edition of our student chemistry magazine The Mole.

The original paper - Cool? - is made available with kind permission from IOP Publishing. Article DOI link:

If you teach primary science, click the headings below to find out how to use this resource:

Skill development

Children will develop their working scientifically skills by:

  • Using a range of scientific equipment to take accurate and precise measurements or readings, with repeat readings where appropriate.
  • Drawing conclusions and raising further questions that could be investigated, based on their data and observations.
  • Using appropriate scientific language and ideas to explain, evaluate and communicate their methods and findings.
  • Selecting and planning the most appropriate ways to answer science questions, recognising and controlling variables where necessary, including:
    • Carrying out comparative and fair tests.
  • Recording data and results using scientific diagrams and labels, classification keys, tables, scatter graphs, bar and line graphs.
  • Asking their own questions about scientific phenomena.

Learning outcomes

Children will:

  • Observe that some materials change state when they are heated or cooled, and measure or research the temperature at which this happens in degrees Celsius.

Concepts supported

Children will learn:

  • That materials and substances can change from one state to another, and that these changes are often reversible.
  • That hot water freezes quicker than cold water.

Suggested activity use

This resource could be used with a whole class to carry out the investigation. Children could work in small groups to carry out a simple comparative test on whether hot or cold water freezes first.

This initial experiment may lead to children asking follow-up questions that they would like to investigate, e.g. does water with salt in freeze quicker than water without? Do all hot liquids freeze quicker than cold liquids?

Practical considerations

To carry out this activity, access to a freezer would be required, and if children are working in groups, quite a large amount of freezer space is needed.

Thermometers will need to be provided for children to measure the temperature of their water.

Please take into account health and safety considerations, and act accordingly. Extra care and adult supervision will be required when working with hot water.

Children will need to check the experiment at regular intervals to see which one freezes first.