📚 Uses of Ammonia and Ammonium Compounds | 氨与铵化合物的用途
Ammonia, NH₃, is one of the most important industrial chemicals in the world. Over 150 million tonnes are produced annually, mainly by the Haber process from nitrogen and hydrogen. Its largest single use is in fertiliser production, but ammonia and ammonium salts also feed into the manufacture of nitric acid, explosives, synthetic fibres, cleaning products and refrigeration systems. Understanding these uses links core A-level topics such as equilibria, acid-base behaviour, nitrogen chemistry and industrial processes.
氨（NH₃）是世界上最重要的工业化学品之一，年产量超过 1.5 亿吨，主要通过哈伯法由氮气和氢气合成。氨最大的用途是生产肥料，但氨和铵盐还用于制造硝酸、炸药、合成纤维、清洁产品以及制冷系统。理解这些用途可以将 A-level 中平衡、酸碱行为、氮化学和工业过程等核心主题联系起来。
This article works through the chemistry behind each major use, section by section, so that you can move confidently between the structural chemistry of the ammonia molecule and the industrial, environmental and examination consequences of it.
本文将逐节梳理每一项主要用途背后的化学原理，帮助你在氨分子的结构化学与其工业、环境及考试后果之间自如切换。
1. Ammonia as a Key Industrial Chemical | 氨——重要的工业化学品
Ammonia is a colourless, pungent gas with the formula NH₃. It boils at about −33 °C at 1 atm, which means it can be liquefied by moderate compression alone - an enormous practical advantage for storage, pipeline transport and refrigeration. It is also exceptionally soluble in water: roughly 700 volumes of ammonia gas dissolve in 1 volume of water at 20 °C, giving a concentrated solution of about 13–14 mol dm⁻³ sold as 'ammonia solution' or 'ammonia water'.
氨是一种无色、有刺激性气味的气体，化学式为 NH₃。它在常压下的沸点约为 −33 °C，这意味着只需中等程度的加压即可液化——这对储存、管道运输和制冷来说是巨大的实用优势。氨还极易溶于水：20 °C 时约 700 体积的氨气可溶于 1 体积的水，得到浓度约 13–14 mol dm⁻³ 的浓溶液，市售称为"氨水"。
Because ammonia is a weak Brønsted–Lowry base, it reacts with acids to form ammonium salts, in which the ammonium ion is NH₄⁺. In water the following equilibrium is set up, and it is this equilibrium that makes ammonia solution alkaline and gives it its cleaning and buffer applications.
由于氨是一种弱的 Brønsted–Lowry 碱，它能与酸反应生成铵盐，其中的铵离子为 NH₄⁺。在水中建立如下平衡，正是这一平衡使氨水呈碱性，并赋予它清洁与缓冲的应用。
NH₃(aq) + H₂O(l) ⇌ NH₄⁺(aq) + OH⁻(aq)
The nitrogen atom in ammonia has a lone pair, so ammonia can act as a ligand and as a nucleophile. This lone pair is central to many of its uses, from forming ammonium salts to making organic nitrogen compounds.
氨中的氮原子带有一对孤电子对，因此氨可以作为配体和亲核试剂。这对孤电子对是氨许多用途的核心，从形成铵盐到制造有机含氮化合物都离不开它。
As a ligand, ammonia donates its lone pair to a transition metal ion, for example in the deep blue tetraamminecopper(II) ion formed when excess ammonia is added to copper(II) solution, or in hexaamminecobalt(III) chloride. As a nucleophile, it attacks electron-deficient carbon atoms, for example in the reaction with a bromoalkane to give a primary amine. Industrially, ammonia is made by the Haber process, an exothermic reversible reaction that is a classic Le Chatelier case study.
作为配体，氨把孤电子对给予过渡金属离子，例如向铜(II)溶液中加入过量氨水时生成的深蓝色四氨合铜(II)离子，以及六氨合钴(III)氯化物。作为亲核试剂，它进攻缺电子的碳原子，例如与溴代烷反应生成伯胺。在工业上，氨由哈伯法合成，这是一个放热的可逆反应，是勒夏特列原理的经典案例。
N₂(g) + 3H₂(g) ⇌ 2NH₃(g) ΔH = −92 kJ mol⁻¹
Typical conditions are 400–450 °C, 200 atm and an iron catalyst with potassium and aluminium oxide promoters. The moderately high temperature is a compromise between rate and equilibrium yield, and the high pressure favours the side with fewer gas moles - a point examiners return to again and again.
典型条件为 400–450 °C、200 atm，并使用加有钾、氧化铝助催化剂的铁催化剂。中等偏高的温度是速率与平衡产率之间的折中，而高压有利于气体摩尔数较少的一侧——这是考官反复考查的要点。
2. Fertilisers and the Nitrogen Cycle | 肥料与氮循环
The largest use of ammonia is in the manufacture of nitrogen-containing fertilisers. Plants need nitrogen to synthesise proteins and nucleic acids, but most cannot use atmospheric N₂ directly. Ammonia provides 'fixed' nitrogen that can be converted to ammonium or nitrate ions in the soil.
氨最大的用途是制造含氮肥料。植物需要氮来合成蛋白质和核酸，但大多数植物不能直接利用大气中的 N₂。氨提供了"固定"氮，可在土壤中转化为铵根离子或硝酸根离子。
Atmospheric nitrogen is unreactive because of the very strong N≡N triple bond, with a bond enthalpy of about 994 kJ mol⁻¹. Breaking it requires either the high energy of a lightning strike, the nitrogenase enzyme of nitrogen-fixing bacteria such as Rhizobium in root nodules, or the industrial conditions of the Haber process. Ammonia produced industrially is therefore the entry point for most of the nitrogen in the world's food supply.
大气中的氮气由于极强的 N≡N 三键（键焓约 994 kJ mol⁻¹）而十分惰性。要打断它，需要闪电的高能量、根瘤中根瘤菌等固氮细菌的固氮酶，或哈伯法的工业条件。因此，工业生产的氨是全球粮食供应中大部分氮元素的起点。
In the soil, ammonium ions are oxidised by nitrifying bacteria in a two-stage process called nitrification, producing nitrite and then nitrate, which is the form most readily absorbed by roots.
在土壤中，铵根离子被硝化细菌经两阶段氧化过程（称为硝化作用）转化为亚硝酸根，进而转化为硝酸根，后者是最容易被根系吸收的形式。
2NH₄⁺ + 3O₂ → 2NO₂⁻ + 4H⁺ + 2H₂O then 2NO₂⁻ + O₂ → 2NO₃⁻
Nitrate ions are very soluble and are not held by soil particles, so they leach readily into groundwater and rivers. The consequences are eutrophication - algal blooms, oxygen depletion and fish kills - and, in drinking water, nitrate levels above about 50 mg dm⁻³ are linked to methaemoglobinaemia in infants.
硝酸根离子极易溶解且不被土壤颗粒吸附，因此很容易淋溶进入地下水和河流。其后果是富营养化——藻类暴发、溶氧耗尽和鱼类死亡；而在饮用水中，硝酸盐含量超过约 50 mg dm⁻³ 与婴儿高铁血红蛋白血症有关。
A further loss route is denitrification, in which anaerobic bacteria reduce nitrate back to N₂ and N₂O. The N₂O released is a potent greenhouse gas with a global warming potential roughly 270 times that of CO₂, so over-application of fertiliser has a climate cost as well as an economic one.
另一条损失途径是反硝化作用，厌氧细菌把硝酸根还原回 N₂ 和 N₂O。释放的 N₂O 是一种强效温室气体，其全球变暖潜能约为 CO₂ 的 270 倍，因此过量施肥不仅浪费成本，还带来气候代价。
3. Ammonium Nitrate and Other Ammonium Fertilisers | 硝酸铵与其他铵态肥料
Ammonium nitrate is made by neutralising ammonia solution with nitric acid. The reaction is strongly exothermic, and the concentrated melt is sprayed into a prilling tower to give solid prills or granules coated to reduce moisture uptake.
硝酸铵由氨水与硝酸中和制得。该反应强烈放热，浓缩熔融液被喷入造粒塔，制成固体颗粒，并加包膜以减少吸湿。
NH₃(aq) + HNO₃(aq) → NH₄NO₃(aq) ΔH negative
Ammonium nitrate is popular because it supplies nitrogen in two forms: the ammonium ion, which is retained by the negatively charged soil, and the nitrate ion, which is immediately available to plants. Its nitrogen content is also high, which keeps transport costs down.
硝酸铵之所以受欢迎，是因为它同时提供两种形态的氮：被带负电的土壤吸附固定的铵根离子，以及可被植物立即吸收的硝酸根离子。它的含氮量也很高，从而降低了运输成本。
Other ammonium salts are made in similar acid-base reactions. Ammonium sulfate is a by-product of nylon manufacture and of flue-gas desulfurisation; urea is made from ammonia and carbon dioxide under pressure; ammonium phosphates supply both nitrogen and phosphorus.
其他铵盐也通过类似的酸碱反应制得。硫酸铵是尼龙生产和烟气脱硫的副产物；尿素由氨与二氧化碳在加压条件下制得；磷酸铵则同时提供氮和磷。
| Fertiliser | 肥料 | Formula | 化学式 | % N by mass | 含氮质量分数 | Note | 备注 |
| Ammonium nitrate | NH₄NO₃ | 35.0 | Both NH₄⁺ and NO₃⁻; oxidising |
| Urea | CO(NH₂)₂ | 46.7 | Highest N content; slow release |
| Ammonium sulfate | (NH₄)₂SO₄ | 21.2 | Also supplies sulfur; acidic |
| Diammonium phosphate | (NH₄)₂HPO₄ | 21.2 | N plus P; NPK 18-46-0 |
Because ammonium ions are acidic in solution, continued use of ammonium fertilisers tends to acidify soil, and farmers must add lime (calcium carbonate or calcium oxide) periodically to maintain pH.
由于铵根离子在溶液中呈酸性，长期使用铵态肥料会使土壤酸化，农民必须定期施用石灰（碳酸钙或氧化钙）以维持 pH。
4. Nitric Acid and the Ostwald Process | 硝酸与奥斯特瓦尔德法
The second largest use of ammonia is as the raw material for nitric acid, made by the Ostwald process. Ammonia is first oxidised over a platinum-rhodium gauze catalyst at about 850–900 °C; the reaction is strongly exothermic and, once started, the plant runs without external heating.
氨的第二大用途是作为硝酸的原料，即通过奥斯特瓦尔德法制硝酸。氨首先在约 850–900 °C 下于铂-铑网催化剂上被氧化；该反应强烈放热，一旦启动，装置无需外部供热即可运行。
Step 1: 4NH₃(g) + 5O₂(g) → 4NO(g) + 6H₂O(g) ΔH = −905 kJ mol⁻¹
Step 2: 2NO(g) + O₂(g) → 2NO₂(g)
Step 3: 3NO₂(g) + H₂O(l) → 2HNO₃(aq) + NO(g)
The NO produced in step 3 is recycled back into step 2, so the overall equation is effectively the addition of ammonia and oxygen to give nitric acid and water.
第 3 步生成的 NO 会循环回到第 2 步，因此总反应式实际上就是氨与氧气生成硝酸和水。
NH₃ + 2O₂ → HNO₃ + H₂O
Nitric acid is a strong acid and a powerful oxidising agent. Most of it goes straight back into ammonium nitrate manufacture, closing the nitrogen loop between the Haber and Ostwald processes. The remainder is used in explosives, in the nitration of aromatic compounds for dyes and pharmaceuticals, and in the production of nylon.
硝酸是强酸，也是强氧化剂。其中大部分直接回流用于生产硝酸铵，从而把哈伯法与奥斯特瓦尔德法之间的氮循环闭合起来。其余部分用于炸药、为染料与药物进行的芳烃硝化反应，以及尼龙的生产。
The Ostwald process is a favourite exam context because it combines catalyst chemistry, oxidation states, enthalpy of reaction and atom economy in a single flow diagram.
奥斯特瓦尔德法之所以是考试的热门情境，是因为它在一张流程图中同时结合了催化剂化学、氧化态、反应焓和原子经济性。
5. Explosives and Propellants | 炸药与推进剂
Ammonium nitrate is not only a fertiliser; it is also the basis of many industrial explosives. When mixed with a fuel oil it becomes ANFO, a cheap and relatively safe blasting agent used in quarrying and mining. Its power comes from the fact that the solid contains both the oxidising nitrate groups and, in the ammonium ion, reducing hydrogen.
硝酸铵不仅是肥料，也是许多工业炸药的基础。与燃料油混合后即成 ANFO，一种廉价且相对安全的爆破剂，用于采石和采矿。它的威力来自固体中同时含有氧化性的硝酸根和铵根中可被氧化的氢。
2NH₄NO₃(s) → 2N₂(g) + O₂(g) + 4H₂O(g) ΔH large and negative
The key point is that the products are all gases: three moles of gas per two moles of solid, released with a very large negative enthalpy change, produce a sudden pressure wave. At lower temperatures a different decomposition gives nitrous oxide, which is why ammonium nitrate must be stored cool and away from fuels and sources of ignition.
关键在于产物全是气体：每 2 mol 固体生成 3 mol 气体，伴随很大的负焓变，从而产生突然的压力波。在较低温度下，分解方式不同，会生成一氧化二氮，这正是硝酸铵必须低温储存、远离燃料和火源的原因。
Nitric acid also provides the nitro groups in high explosives such as TNT (trinitrotoluene, made by nitrating toluene) and glyceryl trinitrate (nitroglycerine, made by esterifying glycerol), and in ammonium perchlorate, NH₄ClO₄, used as the oxidiser in solid rocket boosters. Historical disasters such as Texas City in 1947 and Beirut in 2020 illustrate why ammonium nitrate storage is now heavily regulated.
硝酸还为 TNT（三硝基甲苯，由甲苯硝化制得）、硝酸甘油（由甘油酯化制得）以及用作固体火箭助推器氧化剂的高氯酸铵 NH₄ClO₄ 提供硝基。1947 年得克萨斯城和 2020 年贝鲁特等历史灾难，说明了为何如今硝酸铵的储存受到严格监管。
From an A-level perspective, the value of these examples is that they show oxidation and reduction happening within a single compound, and they connect the nitrogen chemistry of the syllabus to real safety and legislation contexts.
从 A-level 的角度看，这些例子的价值在于展示了同一化合物内部发生的氧化还原反应，并把课程中的氮化学与真实的安全与法规情境联系起来。
6. Synthetic Fibres, Polymers and Plastics | 合成纤维、聚合物与塑料
Ammonia and its derivatives are essential to the polymer industry because many polymers contain nitrogen in amide linkages. Nylon-6,6, the classic condensation polymer, is formed from hexanedioic acid and hex
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