ヘスの法則の検証

三つの反応を用いてエンタルピーが状態関数であることを確認する

Thermochemistry Advanced (University) 60 分 ~$15.00

目的

三つの関連する反応のエンタルピー変化を測定し、ΔH1+ΔH2=ΔH3を示すことでヘスの法則を検証する。

背景

Hess's law states that the total enthalpy change for a reaction is independent of the pathway. This is verified by measuring: (1) NaOH(s) → NaOH(aq), (2) NaOH(aq) + HCl(aq) → NaCl(aq), and (3) NaOH(s) + HCl(aq) → NaCl(aq). The sum ΔH1 + ΔH2 should equal ΔH3.

安全上の警告

  • NaOH pellets are extremely corrosive and generate heat when dissolved
  • HCl is corrosive
  • Wear goggles and gloves throughout

必要なPPE

goggles gloves lab_coat

材料

  • Sodium hydroxide pellets (8 g)
    Anhydrous
  • Hydrochloric acid (HCl) (150 mL)
    1M
  • Sodium hydroxide solution (50 mL)
    1M
  • Distilled water (200 mL)

器具

Polystyrene cup calorimeter (2 cups nested) Thermometer Analytical balance Graduated cylinder Stopwatch Lid with hole

手順

1

Reaction 1: Add 50 mL distilled water to the calorimeter. Record temperature. Add 2 g NaOH pellets. Stir and record max temperature.

8 分 Exothermic — NaOH dissolving
2

Calculate ΔH1 for dissolution. Repeat for accuracy.

5 分
3

Reaction 2: Add 50 mL 1M HCl to the calorimeter. Record temperature. Add 50 mL 1M NaOH. Record max temperature.

8 分
4

Calculate ΔH2 for neutralization.

5 分
5

Reaction 3: Add 50 mL 1M HCl to the calorimeter. Record temperature. Add 2 g NaOH pellets directly. Record max temperature.

8 分 Very exothermic
6

Calculate ΔH3 for combined dissolution + neutralization.

5 分
7

Compare ΔH1 + ΔH2 with ΔH3. They should be approximately equal, verifying Hess's law.

8 分

予想される結果

ΔH1 (dissolution) ≈ -44 kJ/mol, ΔH2 (neutralization) ≈ -57 kJ/mol, ΔH3 (combined) ≈ -101 kJ/mol. ΔH1 + ΔH2 should equal ΔH3 within experimental error (±10%).

後片付け

Neutralize all solutions before disposal. Rinse calorimeter cups. Dry and store equipment.

詳細

カテゴリ
Thermochemistry
難易度
Advanced (University)
所要時間
60 分
推定費用
$15.00
ステップ数
7
材料
4

その他の実験

コーヒーカップ熱量測定 40 min コールドパックの化学 20 min マグネシウムの燃焼熱 50 min 吸熱反応のデモンストレーション 20 min 氷の融解エンタルピー 25 min 溶解は常に発熱ではない 25 min 爆弾熱量測定シミュレーション 45 min 酢酸ナトリウムの発熱結晶化 30 min 金属の比熱容量 40 min

Frequently Asked Questions

What is the objective of ヘスの法則の検証?
三つの関連する反応のエンタルピー変化を測定し、ΔH1+ΔH2=ΔH3を示すことでヘスの法則を検証する。
How difficult is ヘスの法則の検証?
This experiment is rated as Advanced (University). It takes approximately 60 minutes to complete.
What safety precautions are needed for ヘスの法則の検証?
Key safety precautions include: NaOH pellets are extremely corrosive and generate heat when dissolved; HCl is corrosive; Wear goggles and gloves throughout.
What materials are needed for ヘスの法則の検証?
The main materials required are: Sodium hydroxide pellets, Hydrochloric acid (HCl), Sodium hydroxide solution, Distilled water.
What results should I expect from ヘスの法則の検証?
ΔH1 (dissolution) ≈ -44 kJ/mol, ΔH2 (neutralization) ≈ -57 kJ/mol, ΔH3 (combined) ≈ -101 kJ/mol. ΔH1 + ΔH2 should equal ΔH3 within experimental error (±10%).