📚 Using Particle Theory to Explain Dissolving | 用粒子理论解释溶解
When sugar disappears into a cup of tea, it has not vanished. The sugar particles have separated and spread evenly between the water particles. Particle theory helps us explain this everyday process at the microscopic level.
当糖在一杯茶中消失时，它并没有真的消失。糖粒子已经分离并均匀分散在水粒子之间。粒子理论帮助我们在微观层面解释这个日常过程。
1. Particle theory basics | 粒子理论基础
All substances are made of tiny particles that are too small to see. In solids, particles are closely packed in a regular arrangement and vibrate in fixed positions. In liquids, particles are still close together but can slide past one another. In gases, particles are far apart and move quickly in all directions.
所有物质都由微小粒子组成，这些粒子小到肉眼无法看见。固体中粒子紧密排列且规则，只在固定位置振动。液体中粒子仍然彼此靠近，但可以相互滑动。气体中粒子相距很远，并快速向各个方向运动。
The spaces between particles are important for dissolving. When a solid dissolves, its particles must be able to fit into the spaces between liquid particles.
粒子之间的空隙对溶解很重要。当固体溶解时，其粒子必须能够进入液体粒子之间的空隙。
2. What is dissolving? | 什么是溶解？
Dissolving is the process in which a solid, liquid or gas mixes completely with a liquid to form a clear mixture. The substance that dissolves is called the solute, and the liquid it dissolves in is called the solvent. The resulting mixture is called a solution.
溶解是固体、液体或气体与液体完全混合形成透明混合物的过程。被溶解的物质称为溶质，溶质溶解其中的液体称为溶剂。形成的混合物称为溶液。
A key observation is that a solution is usually transparent, meaning light passes through it. However, transparency does not mean the solute has disappeared; its particles are simply too small to scatter light in the same way as larger grains.
一个关键观察是溶液通常是透明的，即光可以穿过。然而透明并不意味着溶质消失了；只是其粒子太小，不能像较大颗粒那样散射光。
3. Solute, solvent and solution | 溶质、溶剂与溶液
In salt water, salt is the solute and water is the solvent. In a fizzy drink, carbon dioxide gas is the solute and water is the main solvent. The solvent is usually the substance present in the larger amount.
在盐水中，盐是溶质，水是溶剂。在汽水中，二氧化碳气体是溶质，水是主要溶剂。溶剂通常是数量较多的物质。
Different solutes dissolve in different solvents. For example, nail varnish dissolves in propanone but not in water. Particle theory helps explain why: the forces between solute and solvent particles must be similar in strength for mixing to happen easily.
不同溶质溶解于不同溶剂。例如，指甲油溶解于丙酮而不溶于水。粒子理论可以帮助解释原因：溶质和溶剂粒子之间的作用力必须相似，混合才容易发生。
4. How particles mix | 粒子如何混合
When a soluble solid is added to water, the water particles collide with the solid surface. These collisions knock solute particles away from the surface one by one. The solute particles then move into the spaces between water particles.
当可溶性固体加入水中时，水粒子与固体表面碰撞。这些碰撞将溶质粒子一个接一个地从表面撞离。溶质粒子随后进入水粒子之间的空隙。
At the particle level, the solute particles become surrounded by solvent particles. This is why the solid seems to disappear: the individual particles are now separated and spread throughout the liquid.
在粒子层面，溶质粒子被溶剂粒子包围。这就是固体看似消失的原因：单个粒子已经分离并分散在整个液体中。
5. Spreading out: diffusion | 扩散：粒子分散
Once a solute has dissolved, its particles do not stay in one place. They move randomly and spread from an area of higher concentration to an area of lower concentration. This spreading process is called diffusion.
一旦溶质溶解，其粒子不会停留一处。它们随机运动，从浓度较高的区域向浓度较低的区域扩散。这个扩散过程称为扩散。
Diffusion is faster in liquids than in solids because liquid particles can move around. It is faster still in gases because gas particles move more quickly and have larger spaces between them.
液体中的扩散比固体中快，因为液体粒子可以移动。气体中扩散更快，因为气体粒子运动更快，粒子之间的空隙更大。
Even without stirring, a sugar solution will eventually become evenly mixed because of diffusion. Stirring simply speeds this up.
即使不搅拌，糖溶液最终也会因扩散而混合均匀。搅拌只是加快了这个过程。
6. Why stirring speeds dissolving | 为什么搅拌加快溶解
Stirring moves fresh solvent particles into contact with the solute surface. It also carries dissolved solute particles away from the surface, preventing a concentrated layer from building up.
搅拌使新的溶剂粒子与溶质表面接触。它还将已溶解的溶质粒子从表面带走，防止形成高浓度层。
Without stirring, solute particles near the surface slow down further dissolving because the local solution becomes more crowded. Stirring removes this crowded layer and allows more collisions between solvent and undissolved solute.
不搅拌时，表面附近的溶质粒子会减慢进一步溶解，因为局部溶液变得更拥挤。搅拌移除了这层拥挤区域，使溶剂与未溶解溶质之间发生更多碰撞。
7. Why temperature speeds dissolving | 为什么温度升高加快溶解
Heating a solvent gives its particles more kinetic energy. The solvent particles move faster and collide with the solute surface more often and with greater force.
加热溶剂使其粒子获得更多动能。溶剂粒子运动更快，与溶质表面碰撞更频繁、更有力。
This means solute particles are knocked off the surface more quickly. It also helps the solute particles spread faster through the solvent because diffusion is faster at higher temperatures.
这意味着溶质粒子更快地从表面被撞离。这也有助于溶质粒子在溶剂中更快分散，因为温度越高扩散越快。
However, heating does not always increase the amount of solute that can dissolve. For some solutes, solubility increases with temperature, but for gases, solubility usually decreases as temperature rises.
然而，加热并不总能增加可溶解的溶质数量。对某些溶质，溶解度随温度升高而增大；但对气体，溶解度通常随温度升高而减小。
8. Smaller pieces dissolve faster | 更小的颗粒溶解更快
A sugar cube dissolves more slowly than the same mass of granulated sugar. Powdered sugar dissolves even faster. Particle theory explains this by surface area.
一块方糖比相同质量的砂糖溶解得慢。糖粉溶解得更快。粒子理论用表面积来解释这一点。
Smaller pieces expose more solute surface to the solvent. More surface area means more solvent particles can collide with solute particles at the same time, so dissolving happens more quickly.
更小的颗粒使更多溶质表面暴露在溶剂中。更大的表面积意味着同一时间有更多溶剂粒子能与溶质粒子碰撞，因此溶解更快。
The total mass of solute stays the same. We have only changed the size of the pieces, not the amount of substance.
溶质的总质量保持不变。我们只改变了颗粒的大小，没有改变物质的量。
9. Saturated solutions | 饱和溶液
If you keep adding solute to a solvent, eventually no more solute will dissolve. Undissolved solute collects at the bottom. At this point, the solution is saturated.
如果你不断向溶剂中加入溶质，最终不会再有溶质溶解。未溶解的溶质聚集在底部。此时溶液达到饱和。
In a saturated solution, particles are still moving. Dissolved solute particles leave the solution and rejoin the solid at the same rate as solid particles dissolve. This is a dynamic balance, not a stopped process.
在饱和溶液中，粒子仍在运动。溶解的溶质粒子从溶液中析出回到固体的速率，与固体粒子溶解的速率相同。这是一种动态平衡，而不是停止的过程。
The maximum mass of solute that can dissolve in 100 g of water at a given temperature is called solubility. Solubility values are different for different substances.
在给定温度下，最多能溶解在100克水中的溶质质量称为溶解度。不同物质的溶解度数值不同。
10. Dissolving is a physical change | 溶解是物理变化
Dissolving is usually a physical change, not a chemical reaction. The solute and solvent do not form new substances. Salt dissolved in water is still salt, and water is still water.
溶解通常是物理变化，不是化学反应。溶质和溶剂没有形成新物质。溶解在水中的盐仍然是盐，水仍然是水。
We can recover the solute by evaporating the solvent. For example, heating salt water drives off the water as vapour, leaving solid salt behind. This is evidence that the salt particles were only mixed with water particles, not chemically changed.
我们可以通过蒸发溶剂回收溶质。例如，加热盐水使水以蒸汽形式逸出，留下固体盐。这证明盐粒子只是与水粒子混合，并没有发生化学变化。
Some dissolving processes also release or absorb heat, but this does not mean a new substance is made. The energy change comes from particles forming new attractions between solute and solvent.
有些溶解过程也会放热或吸热，但这并不意味着生成了新物质。能量变化来自溶质与溶剂粒子之间形成新的吸引作用。
11. Dissolving vs melting | 溶解与熔化对比
Dissolving and melting are often confused. Melting is a change of state from solid to liquid caused by heating a pure substance. Dissolving involves a solute mixing with a solvent and does not require the solute to melt first.
溶解和熔化经常被混淆。熔化是纯物质受热由固态变为液态的物态变化。溶解涉及溶质与溶剂混合，并不要求溶质先熔化。
A solid dissolves in water even when the temperature is far below its melting point. For example, salt dissolves in cold water but salt does not melt until about 801 °C.
固体在远低于其熔点的温度下也能溶于水。例如，盐在冷水中可以溶解，但盐要到约801 °C才熔化。
In melting, only one substance is present and its particles gain enough energy to break free from fixed positions. In dissolving, at least two substances are present and solvent particles help separate solute particles.
熔化时只有一种物质，其粒子获得足够能量从固定位置挣脱。溶解时至少有两种物质，溶剂粒子帮助分离溶质粒子。
12. Investigating dissolving | 溶解实验探究
A simple investigation can test how temperature affects dissolving. Add the same mass of sugar to equal volumes of cold and warm water, stir each for the same number of turns, and time how long it takes for the sugar to disappear.
一个简单的实验可以测试温度如何影响溶解。将相同质量的糖加入等体积的冷水和温水中，各搅拌相同次数，记录糖消失所需的时间。
Controlled variables include the mass of sugar, the volume of water, the stirring speed and the shape of the container. The independent variable is the water temperature. The dependent variable is the dissolving time.
控制变量包括糖的质量、水的体积、搅拌速度和容器形状。自变量是水的温度。因变量是溶解时间。
A fair test ensures that any difference in dissolving time is caused by temperature alone. Repeating the experiment and calculating a mean improves reliability.
公平测试确保溶解时间的任何差异仅由温度引起。重复实验并计算平均值可提高可靠性。
Particle theory then helps us interpret the results: warmer water particles move faster, collide more energetically and spread the solute faster.
然后粒子理论帮助我们解释结果：温水粒子运动更快，碰撞更有力，并更快地分散溶质。
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