Both 汽(qì) and气(qì) share a phonetic similarity and related conceptual basis.
Differences
汽(qì):
汽 specifically refers to “steam” or “vapor”, which is most commonly used in contexts related to steam or steam-powered machinery. It is often seen in compound words that pertain to steam or vapor.
e.g.
我喜欢喝汽水。(Wǒ xǐhuān hē qìshuǐ.) I like to drink soda.
汽车是最常见的交通工具。(Qìchē shì zuì chángjiàn de jiāotōng gōngjù.) Cars are the most common form of transportation.
桑拿房里的蒸汽很大。(Sāngná fáng lǐ de zhēngqì hěn dà.) The steam in the sauna is very strong.
电动车不需要汽油。(Diàndòngchē bù xūyào qìyóu.) Electric cars do not need gasoline.
气(qì):
气 primarily refers to “air” or “gas” and is used in a variety of contexts related to air, gas, weather, breath, or even emotions. It can also imply the concept of “energy” or “aura” in certain contexts, especially within traditional Chinese medicine and martial arts.
e.g.
最近的空气质量不太好。(Zuìjìn de kōngqì zhìliàng bù tài hǎo.) The air quality is not very good lately.
今天天气不错。(Jīntiān tiānqì bùcuò.) The weather is nice today.
她又生气了。(Tā yòu shēngqìle.) She was angry again.
这个演唱会气氛太好了。(Zhège yǎnchàng huì qìfēn tài hǎole.) The atmosphere of this concert was so good.
这个人气焰嚣张，因为他是大老板的儿子。(Zhège rén qìyàn xiāozhāng, yīnwèi tā shì dà lǎobǎn de érzi.) This person is arrogant and overbearing because he is the son of a big boss.
她气喘吁吁是因为刚跑了3000米。(Tā qì chuǎn xū xū shì yīnwèi gāng pǎo le sān qiān mǐ.) She is gasping for breath because she just ran 3000 meters.
孩子在学校被同学打了，家长气势汹汹地来学校了。(Háizi zài xuéxiào bèi tóngxué dǎ le, jiāzhǎng qìshì xiōngxiōng de lái xuéxiào le.) The child was hit by a classmate at school, and the parent came to the school furiously.
Summary
While both characters relate to concepts of air or gas, 气(qì) has a broader range of meanings, including air, gas, and metaphorical uses like mood or energy, whereas 汽(qì) is more specifically related to steam or vapor.
Exercise
