Publication No. 13011
Many reactions produce heat, in fact when people think of chemical reactions, heat production is often expected. However, endothermic reactions, reactions which consume heat, can be just as exciting. One of the most striking examples of this is when the solids barium hydroxide and ammonium thiocyanate are mixed together in a beaker.
Ammonium thiocyanate, NH4SCN, 10 g*
Barium hydroxide octahydrate, Ba(OH)2•8H2O, 20 g*
Erlenmeyer flask, small, with stopper, or a 50-mL beaker
Thermometer graduated to at least –30 ºC
*Materials included in kit.
Barium salts are toxic by ingestion. Ammonium thiocyanate is also toxic by ingestion. Use caution when handling the beaker or flask. Use tongs if available. The temperatures involved are cold enough to freeze skin. Ammonia vapor is very irritating to eyes and the respiratory tract. Do not allow students to inhale this gas. Review the Safety Data Sheets before beginning this activity. Wear chemical splash goggles, chemical-resistant gloves and a chemical-resistant apron. Please review current Safety Data Sheets for additional safety, handling and disposal information.
Please consult your current Flinn Scientific Catalog/Reference Manual for general guidelines and specific procedures, and review all federal, state and local regulations that may apply, before proceeding. Use Flinn Suggested Disposal Method #27h for the products of this reaction.
Student Worksheet PDF
Correlation to Next Generation Science Standards (NGSS)†
Science & Engineering PracticesDeveloping and using models
Analyzing and interpreting data
Engaging in argument from evidence
Disciplinary Core IdeasMS-PS1.B: Chemical Reactions
MS-PS3.B: Conservation of Energy and Energy Transfer
MS-PS3.D: Energy in Chemical Processes and Everyday Life
HS-PS1.B: Chemical Reactions
HS-PS3.B: Conservation of Energy and Energy Transfer
HS-PS3.D: Energy in Chemical Processes
Crosscutting ConceptsCause and effect
Systems and system models
Energy and matter
MS-PS1-2. Analyze and interpret data on the properties of substances before and after the substances interact to determine if a chemical reaction has occurred.
Answers to Questions
This demonstration would be a great way to introduce the concept of heat as a reactant or product. In this reaction, heat is a reactant. It is absorbed from the surroundings as the reaction proceeds. The surroundings lose so much heat that water freezes!
Ba(OH)2∙8H2O(s) + 2NH4SCN(s) + heat → Ba(SCN)2(aq) + 2NH3(aq) + 10H2O(l)This demonstration can be expanded into a lab on thermodynamics by using other ammonium salts. These include ammonium chloride (7 g) and ammonium nitrate (10 g). Have your energetic students (no pun intended) write the equations for these reactions. Thermodynamic data is available for the reaction between barium hydroxide and ammonium chloride or ammonium nitrate. These data can then be tested using calorimetry.
Atkins, P. W. General Chemistry; W. H. Freeman: New York, 1989; p 188.