IB Chemistry Topic 1: Stoichiometric Relationships | IB化学主题1：化学计量关系

📚 IB Chemistry Topic 1: Stoichiometric Relationships | IB化学主题1：化学计量关系

Stoichiometry is the quantitative study of reactants and products in chemical reactions. It connects the particulate nature of matter, the mole concept, and measurable quantities such as mass, volume, and concentration. Mastery of this topic is essential for all later IB Chemistry topics, as it underpins calculations in energetics, kinetics, equilibrium, acids and bases, and organic chemistry.

化学计量学是研究化学反应中反应物和产物的定量关系的学科。它把物质的微粒性质、摩尔概念以及质量、体积、浓度等可测量联系起来。掌握本主题对后续所有IB化学内容都至关重要，因为它是能量学、动力学、平衡、酸碱和有机化学计算的基础。

1. The Particulate Nature of Matter | 物质的微粒性质

All matter is composed of tiny particles—atoms, molecules, or ions—in constant motion. In a solid, particles are closely packed in a regular arrangement and vibrate in fixed positions; in a liquid, particles are still close but can slide past one another; in a gas, particles are far apart and move rapidly in random directions. Changes of state are physical changes because no new substance is formed; the particles themselves are unchanged, only their arrangement, spacing, and freedom of movement alter.

所有物质都由微小的粒子——原子、分子或离子——组成，它们处于不断运动中。固体中粒子紧密排列成规则结构，只能在固定位置振动；液体中粒子仍然靠近但可以相互滑动；气体中粒子相距很远，快速且无规则地运动。状态变化是物理变化，因为没有生成新物质；粒子本身没有改变，只是排列方式、间距和运动自由度发生了变化。

The kinetic molecular theory states that temperature is a measure of the average kinetic energy of particles. Heating increases particle kinetic energy, which explains expansion, melting, boiling, and diffusion. Chemical change, by contrast, involves the rearrangement of atoms to form new substances; bonds are broken and new bonds are formed, so the identity of the substance changes.

分子动理论指出，温度是粒子平均动能的量度。加热会增加粒子的动能，这可以解释膨胀、熔化、沸腾和扩散。与此不同，化学变化涉及原子的重新排列，生成新物质；旧的化学键断裂、新的化学键形成，因此物质的种类发生了改变。

2. Elements, Compounds and Mixtures | 元素、化合物与混合物

An element is a pure substance containing only one type of atom and cannot be broken down into simpler substances by chemical means. A compound is a pure substance containing two or more elements chemically combined in fixed proportions. A mixture contains two or more substances physically combined, with variable composition; its components can be separated by physical methods.

元素是只含一种原子的纯净物质，不能通过化学方法分解成更简单的物质。化合物是两种或多种元素以固定比例化学结合形成的纯净物质。混合物是两种或多种物质物理混合而成，组成比例可变；其组分可用物理方法分离。

For example, oxygen gas O₂ is an element; water H₂O is a compound; air is a mixture of nitrogen, oxygen, argon, and other gases. Homogeneous mixtures have uniform composition, such as solutions, while heterogeneous mixtures have visibly different parts.

例如，氧气 O₂ 是单质；水 H₂O 是化合物；空气是氮气、氧气、氩气和其他气体的混合物。均相混合物具有均匀的组成，如溶液；非均相混合物则具有肉眼可见的不同部分。

3. Chemical Equations and Balancing | 化学方程式与配平

A balanced chemical equation shows the chemical formulas of reactants and products and their relative numbers. It must obey the law of conservation of mass: atoms are neither created nor destroyed, so the number of each type of atom must be equal on both sides. State symbols (s), (l), (g), and (aq) show solid, liquid, gas, and aqueous solution.

配平的化学方程式表示反应物和产物的化学式及其相对数量。它必须遵守质量守恒定律：原子既不会被创造也不会被消灭，因此每种原子的数目在两边必须相等。状态符号 (s)、(l)、(g) 和 (aq) 分别表示固态、液态、气态和水溶液。

For the combustion of hydrogen, balancing gives two molecules of hydrogen reacting with one molecule of oxygen to produce two molecules of water. Coefficients refer to moles when the equation is interpreted quantitatively.

对于氢气的燃烧，配平后得到两个氢分子与一个氧分子反应生成两个水分子。当从定量角度解释方程式时，系数代表摩尔数。

2H₂(g) + O₂(g) → 2H₂O(l)

Balancing by inspection is usually sufficient at IB level: first balance elements that appear in the fewest formulas, leave hydrogen and oxygen until last, and check that all coefficients are in the lowest whole-number ratio.

在IB阶段，通常用观察法配平即可：先配平出现次数最少的元素，把氢和氧留到最后处理，并检查所有系数是否处于最简整数比。

4. The Mole Concept and Avogadro’s Constant | 摩尔概念与阿伏伽德罗常数

The mole (mol) is the SI unit for amount of substance. One mole contains exactly 6.02 × 10²³ elementary entities, which may be atoms, molecules, ions, electrons, or formula units. This number is

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