镁的燃烧热

用赫斯定律和氧化镁测定ΔH

Thermochemistry Advanced (University) 50 分钟 ~$12.00

目标

由于直接测量不可行，用赫斯定律间接测定镁的燃烧焓。

背景

The combustion of Mg in O₂ is too vigorous for direct calorimetry. Instead, we measure: (1) Mg + HCl → MgCl₂ + H₂, and (2) MgO + HCl → MgCl₂ + H₂O. Combined with the known ΔH for H₂ + 0.5O₂ → H₂O, Hess's law gives ΔH(combustion) of Mg.

安全警告

  • HCl is corrosive
  • Mg + HCl produces flammable H₂ gas
  • Do not perform near open flames
  • Wear goggles and gloves

所需PPE

goggles gloves lab_coat

材料

  • Magnesium ribbon (0.5 g)
  • Magnesium oxide (MgO) (1 g)
  • Hydrochloric acid (HCl) (200 mL)
    1M

设备

Polystyrene cup calorimeter Thermometer Analytical balance Graduated cylinder Lid

步骤

1

Reaction 1: Add 50 mL 1M HCl to the calorimeter. Record temperature. Add 0.25 g Mg ribbon. Record max temperature.

8 分钟 H₂ produced — no flames
2

Calculate ΔH1 for Mg + 2HCl → MgCl₂ + H₂.

5 分钟
3

Clean the calorimeter. Reaction 2: Add 50 mL 1M HCl. Record temperature. Add 0.5 g MgO. Record max temperature.

8 分钟
4

Calculate ΔH2 for MgO + 2HCl → MgCl₂ + H₂O.

5 分钟
5

Use Hess's law: ΔH(combustion) = ΔH1 - ΔH2 + ΔH(H₂ combustion). ΔH(H₂ + 0.5O₂ → H₂O) = -285.8 kJ/mol.

5 分钟
6

Compare calculated ΔH with accepted value (-601.6 kJ/mol).

5 分钟

预期结果

ΔH1 ≈ -462 kJ/mol, ΔH2 ≈ -146 kJ/mol. ΔH(comb) = -462 - (-146) + (-286) = -602 kJ/mol, close to the accepted -601.6 kJ/mol.

清理

Neutralize HCl waste. Dispose of MgCl₂ solution down the drain. Rinse calorimeter.

详情

类别
Thermochemistry
难度
Advanced (University)
时长
50 分钟
预估费用
$12.00
步骤数
6
材料
3

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Frequently Asked Questions

What is the objective of 镁的燃烧热?
由于直接测量不可行，用赫斯定律间接测定镁的燃烧焓。
How difficult is 镁的燃烧热?
This experiment is rated as Advanced (University). It takes approximately 50 minutes to complete.
What safety precautions are needed for 镁的燃烧热?
Key safety precautions include: HCl is corrosive; Mg + HCl produces flammable H₂ gas; Do not perform near open flames.
What materials are needed for 镁的燃烧热?
The main materials required are: Magnesium ribbon, Magnesium oxide (MgO), Hydrochloric acid (HCl).
What results should I expect from 镁的燃烧热?
ΔH1 ≈ -462 kJ/mol, ΔH2 ≈ -146 kJ/mol. ΔH(comb) = -462 - (-146) + (-286) = -602 kJ/mol, close to the accepted -601.6 kJ/mol.