States of Matter
IGCSE Chemistry Topic 1 13:32 English narration · English + 中文 subtitles burned in
Chapters
Transcript
Sit in a room while someone makes coffee next door.
坐在房间里，隔壁有人在煮咖啡。
Soon you can smell it, even from across the room.
很快你就能闻到——即使隔着整个房间。
How?
为什么？
Everything around you is made of tiny particles, far too small to see.
你周围的一切都由微小的粒子组成，小到看不见。
And those particles are always moving.
而这些粒子一直在运动。
The coffee smell reaches you because its particles drift and spread through the air.
咖啡的气味能到达你，是因为它的粒子在空气中飘散开来。
That one simple idea — moving particles — explains solids, liquids and gases, and everything that happens to them.
运动的粒子这一个简单的想法， 就能解释固体、液体和气体，以及它们发生的一切。
Welcome to states of matter.
欢迎来到物质的状态。
We will meet the particle model, watch matter change state, and see why gases spread.
我们将认识粒子模型，观察物质如何改变状态， 并了解气体为什么会扩散。
Let's begin.
让我们开始吧。
Everything around you is made of tiny particles.
你周围的一切都由微小的粒子组成。
Those particles can be atoms, or molecules, or ions — different kinds of building blocks, but all of them count as particles.
这些粒子可以是原子、分子或离子—— 不同种类的积木，但都算粒子。
The kinetic particle theory says these particles are always moving.
粒子动理论说，这些粒子一直在运动。
How close they are, how they are arranged, and how they move decides whether matter is a solid, a liquid, or a gas.
它们靠得多近、如何排列、如何运动，决定了物质是固体、液体还是气体。
Learn that picture well: almost every explanation in this topic starts from it.
把这幅图记牢：本专题几乎每一个解释都从它开始。
All matter comes in three states: solid, liquid and gas.
所有物质都有三种状态：固体、液体和气体。
The difference is how the particles are arranged, and how they move.
区别在于粒子如何排列、如何运动。
In a solid, the particles are packed close in a regular pattern, and only vibrate in place.
在固体中，粒子紧密排列成规则的图案，只在原位振动。
In a liquid, they are still close, but they can slide past each other.
在液体中，它们仍然靠得很近， 但能彼此滑过。
In a gas, they are far apart and move quickly, in every direction.
在气体中，它们相距很远，向各个方向快速运动。
Look again at the three columns.
再看这三列。
Kinetic particle theory compares separation, arrangement, and motion.
粒子动理论比较间距、排列和运动。
In a solid, particles are touching and very close, in a regular pattern, and they only vibrate about fixed positions.
在固体中，粒子彼此接触、非常靠近， 呈规则图案，只在固定位置附近振动。
In a liquid, particles are still close together, but the arrangement is random — no fixed pattern — and they move and slide past each other.
在液体中，粒子仍然靠得很近，但排列是随机的—— 没有固定图案——它们移动并彼此滑过。
In a gas, particles are far apart, the arrangement is random, and they move quickly in all directions.
在气体中，粒子相距很远，排列随机， 向各个方向快速运动。
Packed and regular; close and random; far apart and free.
紧密而规则；靠近而随机；远离而自由。
That is the picture you must be able to draw.
这就是你必须能画出来的图。
Strong forces of attraction hold the particles together.
强大的引力把粒子束缚在一起。
In a solid the forces are strong enough to hold every particle in place, so a solid keeps its shape.
在固体中，这些力强到足以把每个粒子固定在原位， 所以固体保持形状。
In a liquid the forces are weaker, so particles can move around each other while staying close.
在液体中，力较弱，粒子可以彼此移动，同时保持靠近。
In a gas the particles move so fast that the forces hardly act at all, so the gas spreads out to fill any space.
在气体中，粒子运动太快，力几乎不起作用，所以气体扩散开来填满任何空间。
When you explain melting or boiling later, you are really talking about particles gaining enough energy to overcome these forces.
稍后解释熔化或沸腾时，你其实是在说粒子获得了足够的能量来克服这些力。
You can tell the three states apart without a microscope.
不用显微镜，你也能区分这三种状态。
A solid has a fixed shape and a fixed volume, and you cannot squeeze it smaller.
固体有固定的形状和固定的体积， 而且你无法把它挤得更小。
A liquid keeps its volume, but takes the shape of its container, and it flows.
液体保持自己的体积，但会呈现容器的形状，并且会流动。
A gas has no fixed shape and no fixed volume; it flows, spreads out to fill any container, and it is easy to compress.
气体没有固定的形状，也没有固定的体积；它会流动、扩散开来填满任何容器， 而且容易被压缩。
Solids and liquids are dense; a gas is not, because its particles are so spread out.
固体和液体密度大；气体密度小，因为它的粒子相距太远。
Sum it up in a table.
用表格总结一下。
Shape: fixed for a solid; takes the container for a liquid; fills the whole container for a gas.
形状：固体固定；液体随容器；气体充满整个容器。
Volume: fixed for solid and liquid; fills the container for a gas.
体积：固体和液体固定；气体充满容器。
Can it be compressed?
能否被压缩？
Solid: no.
固体不能。
Liquid: almost none.
液体几乎不能。
Gas: yes, easily.
气体可以，而且很容易。
Does it flow?
会不会流动？
Solid: no.
固体不会。
Liquid and gas: yes.
液体和气体会。
Density means how much mass is packed into a given volume — high for solids and liquids, low for gases.
密度是指一定体积里装了多少质量——固体和液体高，气体低。
Link each row back to the particle picture: fixed shape needs strong forces and fixed positions; easy compression needs empty space between particles.
把每一行都连回粒子图：固定形状需要强力和固定位置； 容易压缩需要粒子之间有空隙。
When you heat or cool a substance, it can change from one state to another.
加热或冷却一种物质时，它可以从一种状态变成另一种。
Ice cubes in a warm glass are a solid becoming a liquid — a change of state you can watch.
温水杯里的冰块就是固体变成液体——一种你能亲眼看到的状态变化。
You must know the name of every change, and which way heat is moving: heating drives solid toward liquid toward gas; cooling reverses each step.
你必须知道每一种变化的名称，以及热量朝哪个方向走： 加热推动固体变成液体再变成气体；冷却则使每一步反过来。
Heat or cool a substance, and it can change state.
加热或冷却一种物质，它就能改变状态。
Each change has a name.
每种变化都有名字。
Heating a solid melts it into a liquid; cooling a liquid freezes it back.
加热固体，它熔化成液体； 冷却液体，它又凝固回去。
A liquid becomes a gas in two ways: boiling, all through the liquid at the boiling point, and evaporating, only at the surface and at any temperature.
液体变成气体有两种方式：沸腾，发生在整个液体中、在沸点时； 蒸发，只发生在表面、在任何温度下。
Cooling a gas condenses it back to a liquid.
冷却气体，它又凝结回液体。
And a few substances go straight from solid to gas, skipping the liquid — that change is called sublimation.
还有少数物质会直接从固体变成气体，跳过液体——这种变化叫做升华。
A pure solid melts at one fixed temperature, the melting point.
纯固体在一个固定温度熔化，这个温度叫熔点。
A pure liquid boils at one fixed temperature, the boiling point.
纯液体在一个固定温度沸腾， 这个温度叫沸点。
Remember the reverse too: the same substance freezes at its melting point and condenses at its boiling point.
也要记住反向过程：同一种物质在它的熔点凝固， 在它的沸点凝结。
Impure samples often melt or boil over a range of temperatures — exam questions use that to test purity.
不纯的样品往往在一段温度范围内熔化或沸腾—— 考题常用这一点来检验纯度。
Put the names on a cycle.
把这些名称放进一个循环。
Heating: solid to liquid is melting; liquid to gas is boiling — or evaporation if only the surface is changing below the boiling point.
加热：固体到液体是熔化；液体到气体是沸腾—— 如果只在表面、且低于沸点，则是蒸发。
Cooling: gas to liquid is condensation; liquid to solid is freezing.
冷却：气体到液体是凝结； 液体到固体是凝固。
Solid straight to gas is sublimation.
固体直接到气体是升华。
Keep the arrows straight in your head: heat one way, cool the other.
在头脑中把箭头理直： 加热一个方向，冷却另一个方向。
Evaporation and boiling both give a gas, but they are not the same process.
蒸发和沸腾都产生气体，但它们不是同一种过程。
Here is sublimation in real life.
这就是现实中的升华。
This purple gas is iodine.
这种紫色气体是碘。
The dark solid at the bottom was warmed gently, and instead of melting, it turned straight into a gas.
底部深色的固体被轻轻加热， 它没有熔化，而是直接变成了气体。
Higher up, where it is cooler, the gas turns back into a solid.
在上方较凉的地方，气体又变回固体。
No liquid ever appears.
整个过程中从未出现液体。
Each change of state is really a change in the energy of the particles.
每一种状态变化，其实都是粒子能量的变化。
Heat a solid, and the particles gain energy and vibrate faster.
加热固体，粒子获得能量、振动加快。
At the melting point they have enough energy to break away from their fixed places and slide around — the solid melts.
在熔点时，它们有足够的能量离开固定位置并四处滑动——固体熔化了。
Heat a liquid, and the particles move faster still.
加热液体，粒子运动得更快。
At the boiling point they have enough energy to fully escape the forces of attraction and become a gas.
在沸点时，它们有足够的能量完全摆脱引力而变成气体。
Cooling does the opposite: the particles lose energy, move more slowly, and the forces of attraction pull them back together.
冷却则相反：粒子失去能量、运动变慢，引力又把它们拉回到一起。
During a change of state the energy goes into breaking the forces of attraction, not into making the particles move faster.
在状态变化期间，能量用于破坏引力，而不是让粒子运动得更快。
That is why the temperature stays the same while a substance is melting or boiling.
这就是为什么物质在熔化或沸腾时温度保持不变。
The heat is still going in — you can feel the flame — but it is spent on loosening the bonds between particles.
热量仍在进入——你能感觉到火焰—— 但能量花在了松开粒子之间的束缚上。
Only when every particle has made the change does extra energy speed them up again, and the temperature rises.
只有当每个粒子都完成变化之后， 多余的能量才会再次让它们加速，温度才上升。
Now heat a solid steadily, and record its temperature.
现在稳定地加热一块固体，并记录它的温度。
At first the temperature climbs.
一开始温度上升。
But when it starts to melt, the line goes flat — the temperature stops rising, even though heat is still going in.
但当它开始熔化时，曲线变平——温度停止上升，尽管热量还在不断进入。
The same thing happens again at the boiling point.
在沸点处又会发生同样的事。
During these flat parts, the energy is not making the particles faster. It is breaking the forces that hold them together.
在这些平坦的部分，能量不是让粒子变快， 而是在破坏把它们束缚在一起的力。
Only when the change is finished does the temperature climb once more.
只有当变化完成后，温度才会再次上升。
A cooling curve is the reverse of a heating curve: temperature against time as the substance cools.
冷却曲线是加热曲线的反向：物质冷却时温度随时间的变化。
It has a flat part at the boiling point, where the gas condenses to liquid, and a flat part at the melting point, where the liquid freezes to solid.
它在沸点处有一段平坦部分，气体在此凝结成液体；在熔点处也有一段平坦部分， 液体在此凝固成固体。
As the particles slow down, thermal energy is released to the surroundings.
当粒子变慢时，热能释放到周围环境中。
That released energy is why condensation and freezing can warm the air or the container around them.
正是这些释放的能量，使凝结和凝固能温暖周围的空气或容器。
A gas pushes on the walls of its container.
气体推挤容器的壁。
That push, spread over the area of the wall, is the pressure of the gas.
这个推力分摊在壁的面积上，就是气体的压强。
Pressure comes from the gas particles hitting the walls.
压强来自气体粒子撞击器壁。
Hit harder, or hit more often, and the pressure rises.
撞得更猛，或撞得更勤，压强就升高。
Every gas explanation below uses this idea: nothing about particles getting bigger — only how they move and how often they collide.
下面每一个关于气体的解释都用到这个想法：与粒子变大无关—— 只与它们如何运动、以及碰撞有多频繁有关。
If you heat a fixed mass of gas while keeping the pressure the same, its volume increases.
如果加热固定质量的气体，同时保持压强不变，它的体积会增大。
Using the particle theory: heating gives the particles more kinetic energy, so they move faster.
用粒子理论：加热给粒子更多动能，所以它们运动得更快。
They hit the walls harder and more often.
它们撞击器壁更猛、更勤。
To keep the pressure the same, the gas must take up more space, so the volume gets bigger.
为了保持压强不变，气体必须占据更大的空间，所以体积变大。
Faster particles need more room if the wall push is not allowed to rise.
如果不允许壁上的推力升高，更快的粒子就需要更多的空间。
If instead the volume is fixed — a sealed, rigid container — heating the gas makes the pressure rise.
如果体积是固定的——密封的刚性容器——加热气体会使压强升高。
The particles cannot spread out, so their harder, more frequent collisions with the walls simply push harder on the same area.
粒子无法散开，所以它们对器壁更猛、更勤的碰撞，只是在相同面积上推得更用力。
Same mass, same box, higher temperature: higher pressure.
相同质量、相同盒子、更高温度：更高压强。
Exam answers must say "hit the walls harder and more often," not "the particles expand."
考试答案必须说 「撞击器壁更猛、更勤」，而不是「粒子膨胀了」。
Gases respond to heat, and to pressure.
气体对热和压力都有反应。
Heat a gas, and its particles move faster and push out harder — so at the same pressure, the gas takes up more space. Its volume grows.
加热气体，它的粒子运动更快、推得更用力—— 所以在相同的压力下，气体占据更大的空间，体积变大。
Now squeeze a gas into a smaller space.
现在把气体压进更小的空间。
The particles hit the walls more often, so the pressure rises.
粒子撞击器壁的次数更多，所以压强升高。
Push harder, and the volume shrinks.
压得越用力，体积就越小。
Remember: the particles themselves do not change size — only how fast they move, and how often they hit.
记住：粒子本身不改变大小——改变的只是它们运动的快慢，以及撞击的频率。
If you increase the pressure on a fixed mass of gas while keeping the temperature the same, its volume decreases.
如果增大固定质量气体上的压强，同时保持温度不变，它的体积会减小。
Squeezing the gas into a smaller space packs the particles closer, so they hit the walls more often — and that more frequent hitting is what a higher pressure means.
把气体压进更小的空间，粒子靠得更近，所以撞击器壁更勤—— 而更频繁的撞击正是更高压强的含义。
Temperature fixed means average particle speed stays roughly the same; only the collision rate with the walls goes up as the box shrinks.
温度固定意味着粒子的平均速率大致不变； 只有与器壁的碰撞频率随着盒子变小而升高。
This spreading of particles has a name: diffusion.
粒子的这种散开有一个名字：扩散。
Particles move randomly, in every direction.
粒子向各个方向随机运动。
When they are crowded in one place, that random movement carries them, bit by bit, into the empty space — from where they are concentrated, to where they are not.
当它们在某处很拥挤时，这种随机运动会把它们一点一点带到空的地方—— 从浓的地方，到稀的地方。
That is how the coffee smell reached you.
咖啡的气味就是这样到达你的。
Diffusion happens in gases and in liquids, but never in solids, because solid particles cannot move around.
扩散发生在气体和液体中，但从不发生在固体中，因为固体粒子无法四处移动。
Diffusion is the spreading of particles from a region where they are crowded to a region where they are spread out — that is, from high concentration to low concentration.
扩散是粒子从拥挤的区域散开到稀疏的区域——也就是从高浓度到低浓度。
It happens because particles are always moving in random directions.
它发生是因为粒子一直在向随机方向运动。
Over time they fill the space evenly.
随着时间推移，它们均匀填满空间。
That is why you can smell food from across a room: smell particles move and mix with the air until they reach your nose.
这就是为什么你能隔着房间闻到食物：气味粒子运动并与空气混合，直到到达你的鼻子。
No fan is required — random motion alone is enough.
不需要风扇——仅靠无规则运动就足够了。
Do lighter particles diffuse faster?
更轻的粒子扩散得更快吗？
Yes.
是的。
Here is a famous experiment.
这是一个著名的实验。
Cotton soaked in ammonia sits at one end of a long tube; cotton soaked in hydrogen chloride sits at the other.
浸过氨水的棉花放在长管的一端； 浸过氯化氢的棉花放在另一端。
Both gases diffuse along the tube and meet, making a white ring.
两种气体沿管子扩散并相遇，形成一个白色的环。
But look where the ring forms — not in the middle.
但看看环在哪里形成——不在中间。
Ammonia is the lighter gas, so its particles move faster and travel further.
氨是较轻的气体，所以它的粒子运动更快、走得更远。
The two gases meet nearer the hydrogen chloride end.
两种气体在靠近氯化氢的那一端相遇。
Lighter always means faster.
更轻总是意味着更快。
Lighter gas particles move faster than heavier ones at the same temperature.
在相同温度下，较轻的气体粒子比质量较大的运动得更快。
So a gas with a smaller relative molecular mass — a smaller mass for each molecule — has a faster rate of diffusion.
所以相对分子质量较小的气体——每个分子质量更小——扩散速率更快。
In the tube experiment, ammonia has relative molecular mass seventeen, and hydrogen chloride has about thirty-six point five.
在试管实验中，氨的相对分子质量是十七，氯化氢大约是三十六点五。
Ammonia is lighter, so it diffuses faster and travels further.
氨更轻，所以扩散更快、走得更远。
The white ring of ammonium chloride forms nearer the hydrogen chloride end.
氯化铵的白环形成在靠近氯化氢的一端。
The reaction is ammonia plus hydrogen chloride making ammonium chloride.
反应是氨加上氯化氢生成氯化铵。
Worked example.
例题。
Bromine, relative molecular mass one hundred and sixty, and ammonia, relative molecular mass seventeen, are released at the same moment from opposite ends of a long tube.
溴的相对分子质量是一百六十，氨是十七，它们在同一时刻从长管两端放出。
Which travels further before they meet?
在相遇之前，哪一个走得更远？
Compare the relative molecular masses.
比较相对分子质量。
Ammonia's is far smaller, so its molecules move faster at the same temperature and it diffuses more quickly.
氨的小得多，所以在相同温度下 分子运动更快，扩散也更快。
Ammonia therefore travels the greater distance, and the two gases meet nearer the bromine end.
因此氨走过的距离更大，两种气体在靠近溴的一端相遇。
The rule is always "lighter means faster" — argue from relative molecular mass, never from how big the formula looks on paper.
规则永远是「更轻意味着更快」——要从相对分子质量论证， 绝不要看化学式在纸上写起来有多大。
Three marks to lock in.
锁住三个分。
First: during melting and boiling, the temperature stays constant, because the energy breaks the forces between particles instead of speeding them up.
第一：在熔化和沸腾时，温度保持不变，因为能量在破坏粒子间的力， 而不是让它们加速。
Second: evaporation happens only at the surface, at any temperature; boiling happens all through the liquid, at one fixed temperature.
第二：蒸发只发生在表面，在任何温度下都能发生； 沸腾发生在整个液体中，在一个固定的温度下。
Third: in diffusion, the lighter gas — the one with the smaller relative molecular mass — moves faster, so the ammonia ring forms nearer the hydrogen chloride end.
第三：在扩散中，较轻的气体—— 相对分子质量较小的那个——运动更快，所以氨形成的环靠近氯化氢的那一端。
Master these three, and this topic is yours.
掌握这三点，这个专题就是你的了。