Physical Changes: Experimental Investigation | 物理变化：实验探究

📚 Physical Changes: Experimental Investigation | 物理变化：实验探究

Physical changes are transformations that alter the form or appearance of a substance but do not change its chemical identity. In experimental physics and chemistry, investigating these changes helps students understand key concepts such as states of matter, energy transfer, and separation techniques. This article explores several classic experiments that demonstrate physical changes, focusing on melting, boiling, dissolving, distillation, and more.

物理变化是改变物质形态或外观但不会改变其化学组成的转化过程。在实验物理和化学中，探究这些变化有助于学生理解物质状态、能量传递和分离技术等关键概念。本文探讨多个展示物理变化的经典实验，重点包括熔化、沸腾、溶解、蒸馏等。

1. What is a Physical Change? | 什么是物理变化？

In a physical change, no new substances are formed. The particles of the substance rearrange or change state, but their chemical composition remains the same. Examples include changes of state (melting, freezing, boiling, condensing, sublimation), dissolution, and physical deformation. These changes are often easily reversible.

在物理变化中，没有新物质生成。物质的粒子重新排列或改变状态，但其化学组成保持不变。例子包括状态变化（熔化、凝固、沸腾、凝结、升华）、溶解和物理形变。这些变化通常很容易逆转。

---

2. Investigating Melting: From Ice to Water | 探究熔化：从冰到水

To investigate melting, place crushed ice in a beaker and insert a thermometer. Gently heat the beaker while stirring continuously. Record the temperature every minute. You will observe that the temperature remains constant at 0 °C while the ice is melting, even though heat is being supplied. This plateau represents the melting point of pure water. The energy absorbed goes into breaking the intermolecular forces rather than raising the temperature.

为探究熔化，将碎冰放入烧杯中并插入温度计。缓慢加热烧杯，同时持续搅拌。每隔一分钟记录温度。你会观察到，尽管在加热，冰熔化时温度稳定在 0 °C。这个平台期代表了纯水的熔点。吸收的能量用于打破分子间作用力，而非升高温度。

---

3. Investigating Boiling: Water to Steam | 探究沸腾：从水到水蒸气

A similar approach is used to study boiling. Heat water in a flask with a thermometer. Record temperature as the water warms and eventually boils. Pure water boils at 100 °C at standard atmospheric pressure. During boiling, the temperature stays constant despite continuous heating. The steam produced is still water vapour, a physical change.

研究沸腾采用类似方法。在烧瓶中加热水并插入温度计。记录水升温并最终沸腾的温度。在标准大气压下纯水在 100 °C 沸腾。沸腾过程中，尽管持续加热，温度保持不变。产生的水蒸气仍是水蒸气，属于物理变化。

---

4. Conservation of Mass in Physical Changes | 物理变化中的质量守恒

When a physical change occurs, mass is conserved. A simple experiment: weigh a sealed container of ice. Allow it to melt completely and weigh again. The mass remains unchanged. This demonstrates that mass is neither created nor destroyed during a physical change. Even if the container is open and water evaporates, the total mass of the system (including water vapour) is conserved if accounted for.

发生物理变化时，质量守恒。一个简单实验：称量一个密封的装有冰的容器。让它完全融化后再称量。质量保持不变。这表明物理变化中质量既不会被创生也不会被消灭。即使容器敞开且水蒸发，考虑水蒸气在内的系统总质量仍守恒。

---

5. Dissolving and Filtering: Separating a Solid from a Liquid | 溶解与过滤：从液体中分离固体

Dissolving salt in water is a physical change; the salt particles are surrounded by water molecules but no new substance forms. To separate sand from a salt-sand mixture: add water to dissolve the salt, then filter. The sand remains on the filter paper (residue), while the salt solution (filtrate) passes through. Filtration works because sand particles are too large to pass through the filter pores.

盐溶于水是物理变化；盐粒子被水分子包围，但没有形成新物质。要从盐沙混合物中分离沙子：加水溶解盐，然后过滤。沙子留在滤纸上（滤渣），而盐溶液（滤液）透过滤纸。过滤有效是因为沙粒太大无法通过滤纸孔隙。

---

6. Evaporation to Recover Solute: Salt from Saltwater | 蒸发回收溶质：从盐水中获得盐

After filtration, the salt can be recovered by evaporation. Pour the filtrate into an evaporating dish and gently heat. The water evaporates, leaving behind solid salt crystals. This shows that dissolved solids can be reclaimed without chemical change. Evaporation is useful when the solid has a high melting point and does not decompose on heating.

过滤后，可通过蒸发回收盐。将滤液倒入蒸发皿中缓慢加热。水蒸发掉，留下固态盐晶体。这表明溶解的固体可被回收而没有发生化学变化。当固体的熔点高且加热不会分解时，蒸发法很实用。

---

7. Simple Distillation: Separating a Liquid from a Solution | 简单蒸馏：从溶液中分离液体

Simple distillation separates a liquid from a solution by boiling and condensing. As the solution is heated, the liquid with the lower boiling point vaporises first. The vapour travels to a condenser where it cools and condenses back into liquid, collected as distillate. For example, distilling saltwater yields pure water. This is a physical separation method.

简单蒸馏通过沸腾和冷凝从溶液中分离液体。加热溶液时，沸点较低的液体首先汽化。蒸气进入冷凝器，冷却后冷凝回液态，收集为馏出液。例如，蒸馏盐水得到纯水。这是一种物理分离方法。

---

8. Separating Immiscible Liquids: Oil and Water | 分离不互溶液体：油和水

Immiscible liquids like oil and water do not mix. They form two layers with the denser liquid at the bottom. A separating funnel can be used to drain off the lower layer, leaving the upper layer. This technique relies on density differences and is purely physical, as no chemical reaction occurs between the liquids.

不互溶液体如油和水不相混。它们形成两层，密度较大的液体在下层。可使用分液漏斗放出下层液体，留下上层液体。该技术利用密度差异，完全是物理过程，因为液体间不发生化学反应。

---

9. Sublimation: Solid to Gas | 升华：固体变气体

Some substances, like iodine or carbon dioxide (dry ice), undergo sublimation—changing directly from solid to gas when heated, bypassing the liquid phase. In an experiment, heating iodine crystals in a beaker produces purple vapour, which can re-deposit as solid on a cold watch glass. This is a physical change because the chemical identity remains I₂ (iodine molecules). Similarly, dry ice changes from solid CO₂ to gaseous CO₂.

一些物质如碘或二氧化碳（干冰）会发生升华——加热时直接从固体变为气体，跳过液态阶段。实验中将碘晶体在烧杯中加热，产生紫色蒸气，可在冷表面皿上重新凝华为固体。这是物理变化，因为化学身份仍为 I₂（碘分子）。类似地，干冰从固态 CO₂ 变为气态 CO₂。

---

10. Compressing Gases: Demonstrating Particle Theory | 压缩气体：证明粒子理论

A plastic syringe filled with air demonstrates the compressibility of gases. Seal the nozzle, push the plunger; the gas volume decreases significantly. This illustrates that gas particles are far apart. When the plunger is released, it returns to its original volume, showing that compression of a gas is a physical change. No new substance is formed; only the space between particles changes.

一个充有空气的塑料注射器可以演示气体的可压缩性。封住喷嘴，推动活塞；气体体积显著减小。这表明气体粒子之间距离很远。当松开活塞，它回到原体积，表明气体压缩是一种物理变化。没有新物质形成，只有粒子间距发生改变。

---

Published by TutorHao | Physics Revision Series | aleveler.com

更多咨询请联系16621398022（同微信）