Chimie des Poches de Froid

Étude de la dissolution endothermique du nitrate d'ammonium

Thermochemistry Beginner (Middle School) 20 min ~$6,00

Objectif

Mesurer la variation de température lors de la dissolution du nitrate d'ammonium dans l'eau, démontrant un processus de dissolution endothermique utilisé dans les poches de froid instantanées.

Contexte

Ammonium nitrate dissolves endothermically in water, absorbing heat from the surroundings and causing a significant temperature drop. This principle is used in commercial instant cold packs for first aid. The dissolution has ΔH = +25.7 kJ/mol.

Avertissements de sécurité

  • Ammonium nitrate is an oxidizer — keep away from organic materials and heat
  • Do not mix with anything other than water for this experiment
  • Wear goggles

EPI requis

goggles

Matériaux

  • Ammonium nitrate (NH₄NO₃) (30 g)
    Or from a commercial cold pack
  • Distilled water (100 mL)
    Room temperature

Équipement

Polystyrene cup calorimeter Thermometer Stirring rod Analytical balance

Procédure

1

Add 100 mL of distilled water to the polystyrene cup calorimeter. Record the initial temperature.

3 min
2

Weigh 30 g of ammonium nitrate.

2 min Ammonium nitrate is an oxidizer
3

Add the ammonium nitrate to the water. Stir gently to dissolve.

3 min
4

Record the temperature every 30 seconds as it drops. Note the minimum temperature.

5 min
5

Feel the outside of the cup — it should feel cold.

1 min
6

Calculate ΔH of dissolution per mole: q = mcΔT, n = mass/M(NH₄NO₃), ΔH = q/n.

5 min

Résultats attendus

Temperature should drop 15-20°C. 30 g NH₄NO₃ = 0.375 mol. q = 100 × 4.18 × ΔT. Calculated ΔH should be approximately +25 kJ/mol (±15%).

Nettoyage

The ammonium nitrate solution is safe to dispose down the drain (dilute). Rinse the calorimeter.

Détails

Catégorie
Thermochemistry
Difficulté
Beginner (Middle School)
Durée
20 min
Coût estimé
$6,00
Étapes
6
Matériaux
2

Plus d'expériences

Calorimétrie en Gobelet de Café 40 min Capacité Calorifique Spécifique des Métaux 40 min Chaleur de Combustion du Magnésium 50 min Cristallisation Exothermique de l'Acétate de Sodium 30 min Démonstration de Réaction Endothermique 20 min Enthalpie de Fusion de la Glace 25 min La Dissolution n'Est Pas Toujours Exothermique 25 min Simulation de Calorimétrie en Bombe 45 min Vérification de la Loi de Hess 60 min

Frequently Asked Questions

What is the objective of Chimie des Poches de Froid?
Mesurer la variation de température lors de la dissolution du nitrate d'ammonium dans l'eau, démontrant un processus de dissolution endothermique utilisé dans les poches de froid instantanées.
How difficult is Chimie des Poches de Froid?
This experiment is rated as Beginner (Middle School). It takes approximately 20 minutes to complete.
What safety precautions are needed for Chimie des Poches de Froid?
Key safety precautions include: Ammonium nitrate is an oxidizer — keep away from organic materials and heat; Do not mix with anything other than water for this experiment; Wear goggles.
What materials are needed for Chimie des Poches de Froid?
The main materials required are: Ammonium nitrate (NH₄NO₃), Distilled water.
What results should I expect from Chimie des Poches de Froid?
Temperature should drop 15-20°C. 30 g NH₄NO₃ = 0.375 mol. q = 100 × 4.18 × ΔT. Calculated ΔH should be approximately +25 kJ/mol (±15%).