Water vapor emerges (from what it comes out of) and then rises. Water is a liquid, not a gas.

1. The gas rises/ goes up. 2. Water starts to evaporate/ is about to turn into gas.

They’re not wrong, but sound more natural like this : 1. The gas rises [no preposition] 2. The water starts to come out as gas [no article] It could be better to say ‘escape’ for ‘come out’ if you are referring to a valve on a pressure vessel, or even emission from the ground.

However，you should firstly write the second sentence and then write the first sentence, that will be better for the sentences' order.

The second sentence is wrong.｀gas’ means ｀ranqi’.