📚 Energy and Changes of State | 能量与物态变化
Energy is central to changes of state. When a substance melts, boils, condenses or freezes, its particles gain or lose energy. This energy does not always make the substance hotter; during a change of state, energy can be used to rearrange particles instead. Understanding these energy transfers helps explain everyday processes such as ice melting, water boiling, and steam condensing.
能量是物态变化的核心。当物质熔化、沸腾、冷凝或凝固时，其粒子会获得或失去能量。这些能量并不总是使物质温度升高；在物态变化过程中，能量可能用于重新排列粒子。理解这些能量转移有助于解释冰融化、水沸腾和水蒸气冷凝等日常现象。
1. States of Matter and Particle Model | 物质三态与粒子模型
Matter usually exists in three states: solid, liquid and gas. In a solid, particles are closely packed in a regular pattern and vibrate in fixed positions. In a liquid, particles are still close together but can slide past one another. In a gas, particles are far apart and move rapidly in all directions.
物质通常以三种状态存在：固态、液态和气态。在固态中，粒子紧密排列成规则结构，并在固定位置振动。在液态中，粒子仍然靠近，但可以相互滑动。在气态中，粒子相距很远，并向各个方向快速运动。
The particle model explains why solids keep their shape, liquids flow and take the shape of a container, and gases spread out to fill any space. Changes of state happen when particle arrangement and movement change, not when the particles themselves change into different substances.
粒子模型解释了为什么固体保持形状、液体会流动并呈容器形状、气体会扩散并充满任何空间。物态变化发生时，改变的是粒子的排列和运动方式，而不是粒子本身变成不同的物质。
2. Temperature, Heat and Internal Energy | 温度、热量与内能
Temperature measures the average kinetic energy of particles in a substance. Heat is energy transferred from a hotter object to a colder one because of a temperature difference. Internal energy is the total kinetic energy and potential energy stored in all the particles of a substance.
温度衡量物质中粒子的平均动能。热量是由于温度差而从较热物体传递到较冷物体的能量。内能是储存在物质所有粒子中的总动能和势能。
When a substance is heated, its internal energy increases. This can raise the temperature or cause a change of state. The same heat input can have different effects depending on whether a change of state is occurring: during a state change, the temperature does not rise even though internal energy continues to increase.
当物质受热时，其内能增加。这可能导致温度升高或发生物态变化。相同的热量输入可能产生不同效果，取决于是否正在发生物态变化：在物态变化期间，即使内能继续增加，温度也不会上升。
3. Energy and Particle Movement | 能量与粒子运动
Adding energy to a solid makes its particles vibrate faster. If enough energy is added, the particles overcome some of the attractive forces holding them in place, and the solid melts. Removing energy makes particles move more slowly and come closer together, often causing a gas to condense or a liquid to freeze.
向固体添加能量会使粒子振动更快。如果能量足够，粒子会克服部分把它们固定在原位的吸引力，固体就会熔化。移除能量会使粒子运动变慢并彼此靠近，通常会导致气体冷凝或液体凝固。
The strength of forces between particles determines melting and boiling points. Substances with strong forces between particles need more energy to change state than substances with weaker forces. This is why metals, which have strong metallic bonds, melt at much higher temperatures than ice.
粒子之间作用力的强弱决定了熔点和沸点。粒子间作用力强的物质比作用力弱的物质需要更多能量才能发生物态变化。这就是为什么具有强金属键的金属比冰的熔化温度高得多。
4. Melting: Solid to Liquid | 熔化：从固态到液态
Melting is the change from solid to liquid. At the melting point, particles gain enough energy to break out of their fixed positions but still remain close together. The temperature stays constant during melting even though heat is still being supplied, because the added energy is used to overcome attractive forces rather than to speed up particles.
熔化是从固态变为液态的过程。在熔点，粒子获得足够能量脱离固定位置，但仍然彼此靠近。在熔化过程中，即使持续供热，温度也保持不变，因为所加能量用于克服吸引力，而不是使粒子加速。
For pure water, melting occurs at 0 °C. The energy supplied during melting is used to weaken the bonds between particles, not to increase their kinetic energy, so the thermometer reading does not rise until all the solid has melted. This is why a mixture of ice and water stays at 0 °C until all the ice has disappeared.
纯水在0 °C时熔化。熔化过程中输入的能量用于减弱粒子间的键，而不是增加其动能，因此直到所有固体熔化完毕，温度计读数才会上升。这就是为什么冰水混合物会保持在0 °C，直到所有冰都消失。
5. Freezing: Liquid to Solid | 凝固：从液态到固态
Freezing is the reverse of melting. When a liquid is cooled, particles lose kinetic energy and move more slowly. At the freezing point, particles arrange into a regular solid pattern, releasing energy to the surroundings as bonds form between them.
凝固是熔化的逆过程。当液体冷却时，粒子失去动能，运动变慢。在凝固点，粒子排列成规则的固体结构，并在彼此形成键的同时向周围环境释放能量。
Freezing of pure water occurs at 0 °C, the same temperature as melting. The temperature remains steady while the liquid turns into solid because energy is being removed as particles form bonds. This released energy can warm the surroundings slightly, which is why frost can protect some plants from extreme cold.
纯水在0 °C凝固，与熔点相同。液体转变为固体时温度保持稳定，因为粒子形成键的同时能量被移走。这些释放的能量可以稍微温暖周围环境，这就是为什么霜冻有时能保护一些植物免受极寒。
6. Boiling: Liquid to Gas | 沸腾：从液态到气态
Boiling is the change from liquid to gas throughout the whole liquid at a specific temperature called the boiling point. Bubbles of gas form inside the liquid and rise to the surface. For water, this happens at 100 °C at standard atmospheric pressure.
沸腾是在特定温度（沸点）下，整个液体内部由液态转变为气态的过程。液体内部形成气泡并上升到表面。在标准大气压下，水在100 °C时沸腾。
During boiling, the temperature does not increase even though heat is continuously supplied. The added energy is used to separate particles completely, allowing them to escape as gas. This requires much more energy than melting because gas particles must move far apart and overcome almost all attractive forces.
沸腾过程中，即使持续供热，温度也不会升高。所加能量用于使粒子完全分离，让它们以气体形式逸出。这比熔化需要更多能量，因为气体粒子必须移动得很远，并克服几乎所有吸引力。
7. Condensing: Gas to Liquid | 冷凝：从气态到液态
Condensing is the change from gas to liquid. When a gas is cooled, particles lose kinetic energy and come closer together. At the condensation point, particles form weak bonds and become a liquid, releasing energy to the surroundings.
冷凝是从气态变为液态的过程。当气体冷却时，粒子失去动能并彼此靠近。在冷凝点，粒子形成较弱键并变为液体，同时向周围环境释放能量。
Condensation occurs at the same temperature as boiling for a pure substance. You can see condensation on a cold window or on the outside of a cold glass because water vapour in the air loses energy when it touches the cold surface. The released energy slightly warms the surface.
纯物质的冷凝温度与沸点相同。你可以在冷窗户或冷玻璃杯外壁看到冷凝现象，因为空气中的水蒸气接触到冷表面时会失去能量。释放的能量会稍微使表面变暖。
8. Evaporation and Boiling Compared | 蒸发与沸腾的对比
Evaporation is different from boiling. It happens only at the surface of a liquid and can take place at any temperature below the boiling point. Particles near the surface with enough kinetic energy escape into the air, even if the bulk of the liquid is not hot enough to boil.
蒸发不同于沸腾。蒸发只发生在液体表面，并且可以在低于沸点的任何温度下进行。表面附近具有足够动能的粒子会逸入空气中，即使液体整体温度尚未达到沸腾所需的程度。
Evaporation causes cooling because the fastest particles leave, lowering the average kinetic energy of the remaining liquid. This is why sweating cools the skin. Boiling, by contrast, needs heat from an external source and occurs throughout the liquid at a specific temperature.
蒸发会导致冷却，因为运动最快的粒子离开，降低了剩余液体的平均动能。这就是出汗使皮肤凉爽的原因。相比之下，沸腾需要外部热源，并且在特定温度下发生在整个液体内部。
9. Sublimation and Deposition | 升华与凝华
Some substances can change directly from solid to gas without becoming liquid. This is called sublimation. Solid carbon dioxide, known as dry ice, sublimes at room temperature, turning into carbon dioxide gas without leaving a liquid puddle.
某些物质可以直接从固态变为气态而不经过液态，这称为升华。固态二氧化碳，即干冰，在室温下升华，变为二氧化碳气体，不会留下液体水坑。
Deposition is the reverse: a gas turns directly into a solid. This occurs when water vapour in the air forms frost on a very cold surface. Sublimation absorbs energy from the surroundings, while deposition releases energy to the surroundings.
凝华是相反的过程：气体直接变为固体。当空气中的水蒸气在非常冷的表面上形成霜时，就会发生凝华。升华从周围环境吸收能量，而凝华向周围环境释放能量。
10. Heating and Cooling Curves | 加热与冷却曲线
A heating curve shows how temperature changes as a substance is heated at a steady rate. The graph rises, then flattens during melting, rises again, flattens during boiling, and then rises if heating continues. The flat sections show changes of state where energy is absorbed but temperature does not change.
加热曲线显示物质在匀速受热时温度如何变化。曲线上升，在熔化期间变平坦，再次上升，在沸腾期间变平坦，如果继续加热则再次上升。平坦段表示物态变化，此时能量被吸收，但温度不变。
A cooling curve has flat sections too, where freezing and condensing release energy but temperature stays constant. These plateaus are at the same temperatures as the melting point and boiling point for a pure substance, showing that changes of state are reversible.
冷却曲线也有平坦段，在凝固和冷凝时释放能量但温度保持恒定。对于纯物质，这些平台与熔点和沸点处于相同温度，表明物态变化是可逆的。
11. Latent Heat and Energy Changes | 潜热与能量变化
Latent heat is the energy absorbed or released during a change of state without a change in temperature. Latent heat of fusion is involved in melting and freezing; latent heat of vaporisation is involved in boiling and condensing. The word latent means hidden, because the energy does not show up as a temperature change.
潜热是物态变化过程中吸收或释放的能量，且温度不发生变化。熔化潜热与熔化和凝固有关；汽化潜热与沸腾和冷凝有关。潜热一词中的潜字表示隐藏，因为这种能量不会表现为温度变化。
Vaporisation requires much more latent heat than fusion because gas particles are extremely spread out and almost free from one another. This is why a boiling kettle needs a large amount of energy to turn all the water into steam, even though the temperature stays at 100 °C.
汽化所需的潜热远大于熔化，因为气体粒子极度分散，彼此几乎不受束缚。这就是为什么烧水壶需要大量能量才能把所有水变成蒸汽，即使温度始终保持在100 °C。
12. Conservation of Energy in Changes of State | 物态变化中的能量守恒
Energy is always conserved during changes of state. When a substance melts or boils, it absorbs energy from its surroundings. When it condenses or freezes, it releases exactly the same amount of energy back to the surroundings, as long as no energy is lost in other ways.
物态变化中能量始终守恒。物质熔化或沸腾时，会从周围环境吸收能量。当它冷凝或凝固时，只要没有能量以其他方式损失，就会向周围环境释放完全相同的能量。
This reversible energy transfer is why steam burns can be severe: when steam condenses on skin, it releases a large amount of latent heat. Understanding energy conservation helps us predict how much heating or cooling is needed in real processes, from refrigeration to weather formation.
这种可逆的能量传递解释了为什么蒸汽烫伤会很严重：当蒸汽在皮肤上冷凝时，会释放大量潜热。理解能量守恒有助于我们预测实际过程中需要多少加热或冷却，从制冷到天气形成都是如此。
Published by TutorHao | Chemistry Revision Series | aleveler.com
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