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  • So you just strained a muscle and the inflammation is unbearable.

    一旦你拉傷肌肉,受傷發炎痛苦不堪,

  • You wish you had something ice-cold to dull the pain,

    你會想用冰敷減緩疼痛,

  • but to use an ice pack, you would have had to put it in the freezer hours ago.

    但使用冰袋,你得在數小時前 把它放入冰箱裡才行。

  • Fortunately, there's another option.

    還好,我們還有其他的選擇,

  • A cold pack can be left at room temperature until the moment you need it,

    冰敷袋可以在室溫下保存, 直到你需要它的那一刻,

  • then just snap it as instructed and within seconds you'll feel the chill.

    使用幾秒鐘後就會讓你覺得冰涼,

  • But how can something go from room temperature to near freezing

    但是,如何在這麼短的時間內

  • in such a short time?

    由室溫降到接近冰點呢?

  • The answer lies in chemistry.

    答案在化學裡。

  • Your cold pack contains water and a solid compound,

    你的冰敷袋中裝有水和固體化合物,

  • usually ammonium nitrate, in different compartments separated by a barrier.

    通常是硝酸銨,袋中物質由屏障分隔。

  • When the barrier is broken, the solid dissolves

    當屏障被打破,固體遇水溶解,

  • causing what's known as an endothermic reaction,

    就會發生吸熱反應,

  • one that absorbs heat from its surroundings.

    反應時由周遭環境中吸收熱量,

  • To understand how this works,

    要了解其工作原理,

  • we need to look at the two driving forces behind chemical processes:

    我們需要看一下化學反應 背後的兩種驅動力:

  • energetics and entropy.

    熱力學和熵,

  • These determine whether a change occurs in a system and how energy flows if it does.

    這些決定反應發生與否及能量流動情形。

  • In chemistry, energetics deals with the attractive and repulsive forces

    在化學中,熱力學處理粒子與分子層次中

  • between particles at the molecular level.

    吸引力和排斥力問題。

  • This scale is so small that there are more water molecules in a single glass

    在這個尺度下,一杯水所含的分子數目

  • than there are known stars in the universe.

    比已知的宇宙星星還多。

  • And all of these trillions of molecules are

    這些萬億個分子

  • constantly moving, vibrating and rotating at different rates.

    以不同的速率不斷移動、振動和旋轉。

  • We can think of temperature as a measurement of the average motion,

    我們可將溫度視為這些 運動平均的度量結果。

  • or kinetic energy, of all these particles,

    或者也可代表粒子的平均動能。

  • with an increase in movement meaning an increase in temperature,

    粒子運動愈激烈、溫度就越高。

  • and vice versa.

    反之亦然。

  • The flow of heat in any chemical transformation

    熱在任何化學變化中的轉換,

  • depends on the relative strength of particle interactions

    取決於在每一種物質在特定化學狀態時,

  • in each of a substance's chemical states.

    粒子相互作用的相對強度。

  • When particles have a strong mutual attractive force,

    當粒子具有很強的吸引力時,

  • they move rapidly towards one another, until they get so close,

    它們彼此快速靠近到很近的距離,

  • that repulsive forces push them away.

    造成排斥力作用,推開彼此。

  • If the initial attraction was strong enough,

    如果最初的吸引力夠強大,

  • the particles will keep vibrating back and forth in this way.

    粒子將以此方式來回震盪。

  • The stronger the attraction, the faster their movement,

    吸引力越強大、運動越快,

  • and since heat is essentially motion,

    因為熱的本質就是運動,

  • when a substance changes to a state in which these interactions are stronger,

    當物質狀態改變時,交互作用變得更強,

  • the system heats up.

    系統即增溫。

  • But our cold packs do the opposite,

    但冰敷袋的情形恰巧相反,

  • which means that when the solid dissolves in the water,

    當固體溶解在水中時,

  • the new interactions of solid particles and water molecules with each other

    固體粒子與水分子的交互作用

  • are weaker than the separate interactions that existed before.

    比之前個別單獨存在時弱,

  • This makes both types of particles slow down on average,

    所以平均來看,兩種粒子都變慢了,

  • cooling the whole solution.

    所以溶液整體是變冷的。

  • But why would a substance change to a state where the interactions were weaker?

    但為何物質狀態改變時, 交互作用會變弱?

  • Wouldn't the stronger preexisting interactions keep the solid from dissolving?

    先前存在較強的交互作用力, 是否會使固體無法溶解呢?

  • This is where entropy comes in.

    這就要用熵來解釋了。

  • Entropy basically describes how objects and energy

    熵基本上是描述物體與能量

  • are distributed based on random motion.

    隨機動態分布的程度。

  • If you think of the air in a room, there are many different possible arrangements

    如果你考慮房間裡的空氣,

  • for the trillions of particles that compose it.

    億萬個分子會有許多 可能的相異位置分布情形,

  • Some of these will have all the oxygen molecules in one area,

    其中可能一個區域中都是氧分子,

  • and all the nitrogen molecules in another.

    另一個區域中都是氮分子,

  • But far more will have them mixed together,

    但更可能是兩者混在一起,

  • which is why air is always found in this state.

    這就是為什麼找到的空氣總是這種狀態。

  • Now, if there are strong attractive forces between particles,

    現在,如果兩種氣體分子間 有很強的吸引力,

  • the probability of some configurations can change

    氣體分子分布的情形就會改變了,

  • even to the point where the odds don't favor certain substances mixing.

    甚至有某物不喜歡 與他種物質相混合的地步。

  • Oil and water not mixing is an example.

    油和水不相互混合就是一個例子。

  • But in the case of the ammonium nitrate, or other substance in your cold pack,

    但硝酸銨或者冰敷袋內容物的情形,

  • the attractive forces are not strong enough to change the odds,

    吸引力未強大到不溶於水,

  • and random motion makes the particles composing the solid separate

    再者,隨機運動使得顆粒組成的固體

  • by dissolving into the water and never returning to their solid state.

    因溶解到水中而分離, 且再也無法回復到固體的狀態。

  • To put it simply, your cold pack gets cold because random motion

    簡單來說,你的冰敷袋會變冷,

  • creates more configurations where the solid and water mix together

    源自於固體和水混合時, 隨機運動使粒子分布情形變得雜亂,

  • and all of these have even weaker particle interaction,

    這些都讓粒子交互作用變得更弱,

  • less overall particle movement,

    整體粒子的運動更少了,

  • and less heat than there was inside the unused pack.

    具有比未混和前較少的熱能。

  • So while the disorder that can result from entropy

    因此來自熵的混亂,

  • may have caused your injury in the first place,

    也許先前造成你的傷害,

  • its also responsible for that comforting cold that soothes your pain.

    但也很盡責的藉低溫減緩你的疼痛。

So you just strained a muscle and the inflammation is unbearable.

一旦你拉傷肌肉,受傷發炎痛苦不堪,

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B2 中高級 中文 TED-Ed 粒子 固體 分子 吸引力 運動

【TED-Ed】冰敷袋如何快速降溫 (The chemistry of cold packs - John Pollard)

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    稲葉白兎 發佈於 2015 年 07 月 09 日
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