📚 Stoichiometric Relationships | 化学计量关系
Stoichiometry is the branch of chemistry that deals with the quantitative relationships between the amounts of reactants and products in a chemical reaction. It uses the mole concept, balanced equations, and molar relationships to predict how much of each substance is consumed or produced. Mastering stoichiometric calculations is essential for laboratory work, industrial processes, and IB Chemistry examinations.
化学计量学是化学的一个分支，研究化学反应中反应物与产物之间的数量关系。它利用摩尔概念、配平方程式和摩尔关系来预测每种物质消耗或产生的量。掌握化学计量计算对于实验工作、工业过程以及IB化学考试至关重要。
1. The Mole and Avogadro's Number | 摩尔与阿伏伽德罗常数
es, which can be atoms, molecules, ions, or formula units. This number is known as Avogadro's constant (Nₐ or L).
摩尔（符号：mol）是物质的量的SI单位。1摩尔恰好含有6.02 × 10²³个基本微粒，可以是原子、分子、离子或化学式单元。这个数称为阿伏伽德罗常数（Nₐ或L）。
Using the mole, chemists can convert between the number of particles and measurable mass, linking the microscopic world to macroscopic quantities.
利用摩尔，化学家可以在粒子数目和可测量质量之间进行转换，从而将微观世界与宏观量联系起来。
ₐ, where n is the amount in mol, N is the number of particles, and Nₐ = 6.02 × 10²³ mol⁻¹.
关系式为：n = N / Nₐ，其中n是物质的量（mol），N是粒子数，Nₐ = 6.02 × 10²³ mol⁻¹。
2. Molar Mass and Relative Mass | 摩尔质量与相对质量
Molar mass (M) is the mass of one mole of a substance, expressed in g mol⁻¹. Numerically, it is equal to the relative atomic mass (Aᵣ) or relative formula mass (Mᵣ).
摩尔质量（M）是1摩尔物质的质量，以g mol⁻¹为单位。其数值等于相对原子质量（Aᵣ）或相对式量（Mᵣ）。
| Element / Compound | Relative mass | Molar mass (g mol⁻¹) |
|---|---|---|
| C | Aᵣ = 12.01 | 12.01 |
| O₂ | Mᵣ = 32.00 | 32.00 |
| H₂O | Mᵣ = 18.02 | 18.02 |
The mass (m), amount (n), and molar mass (M) are connected by:
质量（m）、物质的量（n）和摩尔质量（M）之间的关系为：
n = m ÷ M
example, to find the amount in 24.02 g of carbon: n = 24.02 g ÷ 12.01 g mol⁻¹ = 2.00 mol.
例如，计算24.02 g碳的物质的量：n = 24.02 g ÷ 12.01 g mol⁻¹ = 2.00 mol。
3. Empirical and Molecular Formulae | 实验式与分子式
The empirical formula is the simplest whole-number ratio of atoms of each element in a compound. The molecular formula shows the actual number of atoms of each element in a molecule.
实验式是化合物中各元素原子的最简整数比。分子式表示一个分子中各元素原子的实际数目。
To determine empirical formula from mass data: convert mass (or percentage) to moles, divide by the smallest number of moles, and obtain whole-number ratios.
从质量数据确定实验式的步骤：将质量（或百分比）转换为摩尔数，除以最小摩尔数，得到整数比。
Molecular formula = n × empirical formula, where n = Mᵣ(molecular) ÷ Mᵣ(empirical).
分子式 = n × 实验式，其中 n = 分子Mᵣ ÷ 实验式Mᵣ。
Example: A compound contains 40.0% C, 6.7% H, and 53.3% If its molar mass is 180 g mol⁻¹, then n = 180 ÷ 30 = 6, so molecular formula is C₆H₁₂O₆.
示例：某化合物含40.0% C、6.7% H和53.3% O（质量分数），实验式为CH₂O。若其摩尔质量为180 g mol⁻¹，则n = 180 ÷ 30 = 6，分子式为C₆H₁₂O₆。
4. Balancing Chemical Equations | 配平化学方程式
A balanced chemical equation
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