📚 IB Physics: Utilization and Impacts of Fossil Fuels | IB物理：化石燃料的利用与影响
Fossil fuels — coal, oil and natural gas — are the most widely used energy sources in the modern world. In IB Physics, they are studied in the context of energy production, efficiency and environmental consequences. This article explores how fossil fuels are utilized and analyses their physical and environmental impacts.
化石燃料——煤、石油和天然气——是现代世界使用最广泛的能源。在IB物理中，我们从能量生产、效率和环境后果的背景下研究它们。本文探讨化石燃料如何被利用，并分析其物理和环境的影响。
1. Definition and Types of Fossil Fuels | 化石燃料的定义与种类
Fossil fuels are hydrocarbons formed from the remains of ancient organisms under high pressure and temperature over millions of years. They are classified into three main types: coal, oil and natural gas. Coal exists as a solid, oil as a liquid, and natural gas as a gas, each with varying carbon and hydrogen content.
化石燃料是古代生物遗骸在高温高压下经过数百万年形成的碳氢化合物。它们分为三大类：煤、石油和天然气。煤是固态，石油是液态，天然气是气态，它们的碳氢含量各不相同。
The simplest fossil fuel is natural gas, mainly methane (CH₄). Oil is a mixture of hydrocarbons, while coal has a higher carbon ratio and often contains sulfur and mineral impurities. In physics, we focus on their energy content and the way chemical bonds store energy.
最简单的化石燃料是天然气，主要成分是甲烷（CH₄）。石油是碳氢化合物的混合物，而煤的碳比例更高，常含有硫和矿物质杂质。在物理学中，我们关注它们的能量含量以及化学键储存能量的方式。
2. Chemical Energy and Combustion | 化学能与燃烧
During combustion, hydrocarbon molecules react with oxygen to produce carbon dioxide and water, releasing chemical energy in the form of heat. For example, the complete combustion of methane is given by:
在燃烧过程中，碳氢化合物分子与氧气反应生成二氧化碳和水，以热的形式释放化学能。例如，甲烷完全燃烧的方程式为：
CH₄ + 2O₂ → CO₂ + 2H₂O + heat
The energy is released when the products have lower bond enthalpy than the reactants. Bond breaking absorbs energy while bond formation releases energy; the net difference is the exothermic heat of reaction. This thermal energy can then be used to produce steam or mechanical work.
当生成物的键焓低于反应物时，能量被释放。断键吸收能量，而成键释放能量；净差值就是放热反应热。这些热能随后可用于产生蒸汽或机械功。
3. Calorific Value and Energy Density | 热值与能量密度
The calorific value, or heating value, is the quantity of heat released when a unit mass of fuel is completely burned. It is measured in joules per kilogram (J kg⁻¹) or MJ kg⁻¹. Energy density may also be expressed per unit volume, for example MJ m⁻³.
热值是单位质量的燃料完全燃烧所释放的热量。单位是焦耳每千克（J kg⁻¹）或兆焦每千克（MJ kg⁻¹）。能量密度也可表示为单位体积的能量，例如 MJ m⁻³。
q = Q / m
Typical values for coal are around 15–35 MJ kg⁻¹, for oil about 42–45 MJ kg⁻¹, and for natural gas about 50 MJ kg⁻¹. Higher energy density means more useful energy can be stored in a smaller mass, which is crucial for transport applications.
典型热值：煤约为15–35 MJ kg⁻¹，石油约为42–45 MJ kg⁻¹，天然气约为50 MJ kg⁻¹。更高的能量密度意味着可以用更小的质量储存更多有用能量，这对交通运输应用至关重要。
| Fuel | State | Calorific value / MJ kg⁻¹ | Main uses |
|---|---|---|---|
| Coal | Solid | 15–35 | Electricity generation |
| Oil | Liquid | 42–45 | Transport, heating |
| Natural gas | Gas | ~50 | Heating, power generation |
4. Fossil Fuel Power Stations | 化石燃料发电站
In a thermal power station, the chemical energy of fuel is converted to heat, then to kinetic energy of steam, then to mechanical energy of a turbine, and finally to electrical energy by a generator. This is an energy transformation chain: chemical → thermal → kinetic → mechanical → electrical.
在火力发电站，燃料的化学能先转化为热能，再转化为蒸汽的动能，进而转化为涡轮机的机械能，最后通过发电机转化为电能。这是一个能量转换链：化学能 → 热能 → 动能 → 机械能 → 电能。
Each step involves losses. Modern fossil fuel plants have an overall efficiency of about 30–45%. Combined-cycle gas turbines can reach up to 60%. The wasted energy is mostly transferred to the surroundings as low-grade heat through cooling towers or exhaust gases.
每一步都存在损耗。现代化石燃料电厂的整体效率约为30–45%。联合循环燃气轮机可达到60%。损耗的能量大部分通过冷却塔或废气以低品位热能的形式传递到环境中。
5. Efficiency and Energy Losses | 效率与能量损失
Efficiency is defined as the ratio of useful output energy to total input energy. For a power station, useful output is electrical energy, while input is the chemical energy stored in the fuel.
效率定义为有用输出能量与总输入能量之比。对发电站而言，有用输出是电能，而输入是燃料中储存的化学能。
η = (Eout / Ein) × 100%
Losses occur in various stages: incomplete combustion, heat lost in flue gases, friction in turbines, and electrical resistance in generators. High-entropy waste heat inevitably reduces the maximum possible efficiency, as described by the second law of thermodynamics.
损失发生在多个阶段：不完全燃烧、烟气余热损失、涡轮机摩擦以及发电机中的电阻损耗。正如热力学第二定律所描述，高熵废热不可避免地降低了可能的最大效率。
6. Heat Engines and the Carnot Limit | 热机与卡诺极限
A fossil fuel power plant operates as a heat engine that takes energy from a hot reservoir (the boiler) and exhausts some to a cold reservoir (the environment). The Carnot efficiency sets the maximum theoretical efficiency:
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