5.23 Gas Pressure | 5.23 气体压强

📚 5.23 Gas Pressure | 5.23 气体压强

Gas pressure is one of the key topics in the Edexcel IGCSE Science (Physics) syllabus, usually numbered 5.23 in the ‘Solids, liquids and gases’ section. This article explains the particle model, the cause of gas pressure, the factors that influence it, and the calculations you may need to perform in exams.

气体压强是 Edexcel IGCSE 科学（物理）考纲中「固体、液体和气体」部分的重点内容，通常对应编号 5.23。本文将讲解分子动理论、气体压强的产生原因、影响气体压强的因素，以及考试中可能涉及的计算题。

1. What Is Gas Pressure? | 什么是气体压强？

Gas pressure is the force exerted by a gas on the walls of its container per unit area. In a sealed container, billions of gas particles constantly move in random directions. When they collide with the walls, each collision exerts a tiny force. The total force per unit area on the inner surface is the pressure we measure.

气体压强是气体对其容器壁单位面积所施加的力。在密闭容器中，无数气体粒子沿随机方向不断运动。当它们与器壁碰撞时，每一次碰撞都会产生微小的力。这些力在单位总面积上的总和就是我们所测到的压强。

2. The Kinetic Particle Model | 分子动理论

The kinetic particle model states that all matter is made of tiny particles that are in constant motion. In a gas, the particles are far apart, move rapidly and freely, and have weak forces between them. Because their kinetic energy is high, they travel in straight lines until they collide with something.

分子动理论认为，所有物质都由不断运动的微小粒子构成。气体中粒子间距很大，运动快速而自由，粒子间作用力很弱。由于动能较高，它们沿直线运动，直到与物体碰撞。

Gas particles are much further apart than solid or liquid particles.

气体粒子之间的距离比固体或液体粒子大得多。
They move at hundreds of metres per second at room temperature.

室温下它们以每秒数百米的速度运动。
Collisions with the container wall are perfectly elastic overall.

总体上，与器壁的碰撞是完全弹性的。

3. How Do Gases Exert Pressure on Surfaces? | 气体如何对表面产生压强？

Every time a gas particle hits a wall, it changes direction and momentum. According to Newton’s second law, a change in momentum requires a force. The wall pushes on the particle, and the particle pushes back on the wall. Billions of these microscopic collisions per second add up to a macroscopic pressure.

每当气体粒子撞击器壁时，它的运动方向和动量都会发生改变。根据牛顿第二定律，动量变化需要力的作用。器壁推粒子，粒子同时也会反推器壁。每秒亿万次这样的微观碰撞叠加起来，就形成了宏观上的压强。

4. Measuring Gas Pressure | 气体压强的测量

Gas pressure is measured in pascals (Pa). 1 Pa equals 1 newton per square metre (1 N/m²). For larger pressures, kilopascals (kPa) or atmospheres (atm) are often used: 1 atm ≈ 101 kPa.

气体压强的单位是帕斯卡（Pa）。1 帕斯卡等于 1 牛顿每平方米（1 N/m²）。较大压强常使用千帕（kPa）或标准大气压（atm）：1 atm ≈ 101 kPa。

Common instruments include the bourdon gauge and a simple manometer. In exams, you may also read pressure values from a digital sensor linked to a data logger.

常见测量工具有布尔登压强计和简易气压计（U 形管）。考试中有时也会要求你读取连接数据记录器的数字传感器所显示的压强值。

5. Factors That Affect Gas Pressure | 影响气体压强的因素

For a fixed mass of gas, two factors mainly affect pressure:

对于一定质量的气体，主要有两个因素影响压强：

Temperature – increasing temperature raises the average kinetic energy of the particles.

温度 – 温度升高会增大粒子的平均动能。
Volume – decreasing volume forces particles to hit the walls more often.

体积 – 体积减小使粒子更频繁地撞击器壁。

If both temperature and volume change together, the effect on pressure depends on the combination. The gas equation pV/T = constant summarises this relationship for an ideal gas.

如果温度和体积同时改变，压强的变化取决于两者的组合方式。理想气体的状态方程 pV/T = 常数总结了这一关系。

6. Temperature and Pressure at Constant Volume | 恒定体积下温度与压强的关系

When a gas is heated in a fixed sealed container, the volume cannot change. The hotter particles move faster and hit the walls with greater force and more frequently. This increases the pressure.

当气体在密闭的固定容器中被加热时，体积无法改变。温度更高的粒子运动更快，撞击器壁的力度更大、频率也更高，因此压强增大。

The pressure is directly proportional to the temperature measured in kelvin (K): p₁/T₁ = p₂/T₂.

在开尔文温标下，压强与温度成正比：p₁/T₁ = p₂/T₂。

p₁/T₁ = p₂/T₂ (at constant volume)

p₁/T₁ = p₂/T₂ （体积不变时）

7. Volume and Pressure at Constant Temperature (Boyle’s Law) | 恒定温度下体积与压强的关系（玻意耳定律）

At a constant temperature, the pressure of a fixed mass of gas is inversely proportional to its volume. Squeezing a gas into a smaller volume increases the number of collisions per second with the walls, so pressure rises.

在温度不变时，一定质量气体的压强与体积成反比。将气体压缩到更小的体积，每秒与器壁的碰撞次数增加，因此压强上升。

p ∝ 1/V or pV = constant

p ∝ 1/V 或 pV = 常数

For two states of the same gas:

对同一气体的两个状态：

p₁V₁ = p₂V₂

8. Using Boyle’s Law in Calculations | 玻意耳定律的计算应用

Boyle’s law is a favourite exam topic. You are often given two sets of pressure and volume values and asked to find an unknown.

玻意耳定律是考试常见考点。题目通常会给出两组压强和体积数据，要求求出未知量。

Example: A gas occupies 120 cm³ at a pressure of 100 kPa. What volume would it occupy at 150 kPa, assuming constant temperature?

示例： 某气体在压强为 100 kPa 时体积为 120 cm³。若温度不变，在 150 kPa 下体积变为多少？

Using p₁V₁ = p₂V₂:

根据 p₁V₁ = p₂V₂：

100 × 120 = 150 × V₂

V₂ = 12000 ÷ 150 = 80 cm³

Always check that pressure and volume units are consistent. Convert units if necessary.

请务必检查压强和体积单位是否一致，必要时进行单位换算。

9. Applications of Gas Pressure in Everyday Life | 气体压强在日常生活中的应用

Gas pressure examples appear all around us. In a syringe, pulling the piston back expands the gas and reduces its pressure, so liquid can be drawn in. In aerosols, the gas inside remains at high pressure; when the valve opens, the gas expands and pushes the product out.

气体压强在我们身边随处可见。注射器中，向后拉动活塞会让气体体积增加、压强降低，从而将液体吸入。喷雾罐内气体保持高压；当阀门打开时，气体膨胀并把内容物推出。

Other applications include:

其他应用包括：

Car tyres – tyre pressure affects road safety and fuel efficiency.

汽车轮胎 – 胎压影响行车安全和燃油效率。
Hot air balloons – heating the air inside makes it less dense, creating lift.

热气球 – 加热内部空气使其密度降低，从而产生升力。
Scuba diving – water pressure increases with depth, affecting the volume of air in a diver’s lungs.

潜水 – 水压随深度增大，会影响潜水员肺部空气的体积。

For each of these, the kinetic model of matter helps explain the observed behaviour.

对于这些例子，分子动理论都能帮助解释我们观察到的现象。

10. Common Misconceptions and Exam Tips | 常见误区与考试要点

Many students confuse pressure with force. Pressure is force per unit area, so a small force on a tiny area can still create a large pressure. Another common mistake is ignoring the Kelvin unit when using the temperature–pressure relationship. Always convert Celsius to kelvin (K = °C + 273) in gas calculations.

很多同学会把压强和力混淆。压强是单位面积上的力，因此很小的力作用在很小的面积上也能产生很大的压强。另一个常见错误是在温度–压强关系式中忽略了开尔文单位。在气体计算中，请务必将摄氏度转换为开尔文（K = °C + 273）。

In exams, remember to:

考试中请记住：

Read the question carefully to see whether temperature is constant.

仔细读题，确认温度是否保持不变。
Use the correct formula: p₁/T₁ = p₂/T₂ for constant volume, p₁V₁ = p₂V₂ for constant temperature.

使用正确公式：体积不变时用 p₁/T₁ = p₂/T₂，温度不变时用 p₁V₁ = p₂V₂。
State the relationship between pressure and volume as ‘inversely proportional’, not ‘proportional’.

描述压强与体积的关系时要说「成反比」，而不是「成正比」。
Show your working and give units in your final answer.

写出计算过程并在最终答案中给出单位。

Understanding the particle model will help you answer both calculation and explanation questions with confidence.

理解分子动理论能帮助你自信地回答计算题和解释题。

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5.23 Gas Pressure | 5.23 气体压强