Reaction enthalpy of an endothermic reaction - Introduction to entropy with Cobra SMARTsense

Principle

In this experiment, the endothermic reaction of barium hydroxide with ammonium thiocyanate is investigated. The system absorbs heat from the surroundings, leading to a significant temperature decrease. Using a calorimeter, the temperature change is measured, and from this, the molar reaction enthalpy is calculated. Afterwards, the determined values can be compared with literature values, and possible causes for deviations can be discussed. Furthermore, the role of entropy as the driving force for the spontaneous reaction becomes clear.

The experiment can be carried out with the supplied stirring rod or alternatively with a magnetic stirrer (see recommended accessories).

Tasks

1. The students set up a simple student calorimeter.
2. They measure the temperature change after adding ammonium thiocyanate to a barium hydroxide solution.
3. They calculate the molar reaction enthalpy and compare the determined value with the literature value, discussing possible causes for deviations.

Learning objectives

The students deepen their knowledge of endothermic processes and learn to relate chemical processes to reaction enthalpy. They set up a simple calorimeter and analyze the endothermic reaction of barium hydroxide with ammonium thiocyanate by measuring the temperature. Furthermore, the importance of entropy for the spontaneity of chemical reactions becomes understandable. Students also learn to recognize how experimental results can deviate from literature values and what causes these deviations may have.

Benefits

• Easy execution and promotion of technical understanding with a self-assembled calorimeter made of standard laboratory equipment.
• Clearly illustrates the role of entropy as the driving force of chemical reactions.
• Strong everyday relevance (e.g., explanation of how cold packs work).
• Experiment relevant for final exams in thermodynamics (enthalpy and entropy).
• Quantitative analysis using digital sensors (Cobra SMARTsense).
• Combination of classical school experiment and modern data acquisition.
• Opportunity to discuss measurement deviations compared to literature values.
• Fast and easy experiment preparation (experiment instructions and risk assessment available).