gas pressure 同air pressure

1.
任何 gas（氣體）碰撞到 the surface of solid/liquid materials，都會導致 pressure。由 gas 所導致的 pressure 稱為 gas pressure（氣壓）。

換句話說，任何 gas 都會導致 gas pressure。例如一瓶 carbon dioxide gas 之中，carbon dioxide 會導致 gas pressure。而一瓶 nitrogen gas 和 oxygen gas 的mixture 中，nitrogen gas 和 oxygen gas 亦會導致 gas pressure。

air（空氣）是人最常接觸到的 gas，由 air 所導致的 gas pressure，就稱為 air pressure。簡單來說，air pressure 是 gas pressure 的一種。


2.
問題應是：can you help him to label the substance with different state of matter at room temperature? 因為state of matter 受 temperature 影響，所以這裡應是指 at room temperature，通常設定為 25oC。

任何一個 substance, 在 m.p. (melting point) 以下的 temperatures 是 solid（固體），在 m.p. 與 b.p. (boiling point) 之間的 temperatures 是 liquid（液體），在 b.p. 以上是 gaseous（氣體）。

A 的 m.p. 是 -30oC，而 b.p. 是 100oC。即 -30oC 以下是 solid，-30oC 至 100oC 是 liquid，而 100oC 以上是 gaseous。由於 room temperature 介乎 -30oC 與 100oC 之間，所以 A 是 liquid。

B 的 m.p. 是 300oC，而 b.p. 是 600oC。即 300oC 以下是 solid，300oC 至 600oC 是 liquid，而 600oC 以上是 gaseous。由於 room temperature 在 300oC 以下，所以 B 是 solid。

C 的 m.p. 是 -150oC，而 b.p. 是 -50oC。即 -150oC 以下是 solid，-150oC 至 -50oC 是 liquid，而 -50oC 以上是 gaseous。由於 room temperature 在 -50oC 以上，所以 C 是 gaseous。
=

Gas pressure:
In a mixture of ideal gases, each gas has a partial pressure which is the pressure which the gas would have if it alone occupied the volume The total pressure of a gas mixture is the sum of the partial pressures of each individual gas in the mixture.

Air pressure(atomspheric pressure):
Atmospheric pressure is sometimes defined as the force per unit area exerted against a surface by the weight of air above that surface at any given point in the Earth's atmosphere. In most circumstances atmospheric pressure is closely approximated by the hydrostatic pressure caused by the weight of air above the measurement point. Low pressure areas have less atmospheric mass above their location, whereas high pressure areas have more atmospheric mass above their location. Similarly, as elevation increases there is less overlying atmospheric mass, so that pressure decreases with increasing elevation. A column of air one square inch in cross-section, measured from sea level to the top of the atmosphere, would weigh approximately 65.5 newtons (14.7 lbf). The weight of a 1 m2 (11 sq ft) column of air would be about 101 kN (10.3 tf).


Liquid's boiling point is 100'C
Solid is more diffcult to boil,so the boiling point should higher than
Liquid and Gas.
Gas is more easy to boiling, so gas's boiling point is the smaller.

gas係某種氣體，而air係包含多種氣體。
a嘅boiling point係100度，水滾係100度，所以係液體。
b嘅melting point係300度，鉛或錫係300多度，所以係固體。
c嘅boiling point係-50度，可能係固體二氧化碳，算係氣體啩。