溶解并非总是放热的

比较不同盐溶解时的温度变化

Thermochemistry Beginner (Middle School) 25 分钟 ~$8.00

目标

比较不同盐（NaOH、CaCl₂、NH₄NO₃、KNO₃）的溶解焓，证明溶解可以是放热或吸热过程。

背景

Students often assume dissolving always releases heat. This experiment tests four salts: NaOH and CaCl₂ dissolve exothermically (temperature rises), while NH₄NO₃ and KNO₃ dissolve endothermically (temperature drops). The results illustrate that lattice energy vs hydration energy determines the sign of ΔH.

安全警告

  • NaOH is extremely corrosive
  • NH₄NO₃ is an oxidizer
  • Wear goggles and gloves

所需PPE

goggles gloves

材料

  • Sodium hydroxide pellets (10 g)
    Exothermic
  • Calcium chloride (10 g)
    Exothermic
  • Ammonium nitrate (10 g)
    Endothermic
  • Potassium nitrate (10 g)
    Endothermic
  • Distilled water (400 mL)

设备

4 polystyrene cups Thermometer Stirring rod Analytical balance

步骤

1

Add 100 mL water to each of four labeled cups. Record the initial temperature of each.

5 分钟
2

Add 10 g NaOH to cup 1. Stir and record the maximum temperature.

3 分钟 Very exothermic — NaOH is corrosive
3

Add 10 g CaCl₂ to cup 2. Stir and record the maximum temperature.

3 分钟
4

Add 10 g NH₄NO₃ to cup 3. Stir and record the minimum temperature.

3 分钟
5

Add 10 g KNO₃ to cup 4. Stir and record the minimum temperature.

3 分钟
6

Create a table ranking the salts from most exothermic to most endothermic.

3 分钟
7

Discuss why some dissolve exothermically and others endothermically (lattice energy vs hydration energy).

5 分钟

预期结果

NaOH: +15-20°C rise. CaCl₂: +10-15°C rise. NH₄NO₃: -15-20°C drop. KNO₃: -5-10°C drop. Clear demonstration that dissolution can be either exothermic or endothermic.

清理

NaOH and CaCl₂ solutions should be neutralized before disposal. All solutions can be poured down the drain after dilution.

详情

类别
Thermochemistry
难度
Beginner (Middle School)
时长
25 分钟
预估费用
$8.00
步骤数
7
材料
5

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Frequently Asked Questions

What is the objective of 溶解并非总是放热的?
比较不同盐（NaOH、CaCl₂、NH₄NO₃、KNO₃）的溶解焓，证明溶解可以是放热或吸热过程。
How difficult is 溶解并非总是放热的?
This experiment is rated as Beginner (Middle School). It takes approximately 25 minutes to complete.
What safety precautions are needed for 溶解并非总是放热的?
Key safety precautions include: NaOH is extremely corrosive; NH₄NO₃ is an oxidizer; Wear goggles and gloves.
What materials are needed for 溶解并非总是放热的?
The main materials required are: Sodium hydroxide pellets, Calcium chloride, Ammonium nitrate, Potassium nitrate, Distilled water.
What results should I expect from 溶解并非总是放热的?
NaOH: +15-20°C rise. CaCl₂: +10-15°C rise. NH₄NO₃: -15-20°C drop. KNO₃: -5-10°C drop. Clear demonstration that dissolution can be either exothermic or endothermic.