Hot and Cold

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In this activity, learners explore temperature changes from chemical reactions by mixing urea with water in one flask and mixing calcium chloride with water in another flask. They observe that the urea flask gets cold and the calcium chloride flask gets hot. The main idea is that some chemical processes release heat energy and are exothermic, while some chemical processes absorb heat energy and are endothermic. This activity is currently used in the Nature of Matter Unit in OMSI's Chemistry Lab. Cost estimates are per 100 learners.

Quick Guide

Preparation Time:
5 to 10 minutes

Learning Time:
Under 5 minutes

Estimated Materials Cost:
$1 - $5 per group of students

Age Range:
Ages 4 - adult

Resource Types:
Activity, Experiment/Lab Activity


Materials List (per group of students)

  • (2) 250-mL erlenmeyer flasks
  • (2) 1-tsp measuring spoons
  • (2) small plastic funnels
  • 25-mL graduated cylinder
  • 1kg calcium chloride pellets (CaCl2-anhydrous)
  • 1kg urea (NH2CONH2)
  • 250-mL squeeze bottle
  • (2) small jars with lids


  • Physical Sciences
    • Heat and Thermodynamics
      • Heat and Temperature
      • Heat Transfer
    • Chemistry
      • Solutions


To use this activity, learners need to:

  • see
  • read
  • touch

Learning styles supported:

  • Involves hands-on or lab activities


This resource is part of:

Access Rights:

  • Free access



Funding Source:

  • National Science Foundation, 9355628