chemisty help?

Question

explain why the production of gas does not always mean that a chemical reaction is taking place
i just don't understand it.

and can you explain why this is the answer to this question.
A clear liquid in an open container evaporates. after 3 days a solid is left. the orginal liquid was a ....MIXtURE

so why isn't it a compound?

Answer 1

The production of gas can be the result of evaporation. Think about water evaporating and producing steam (water vapor). Also, some chemicals are "volatile," meaning they evaporate closer to room temperature (meaning they readily produce a gas).

And as an answer to your second question: when something is dissolved into a liquid such as water, it is simply broken down into extremely tiny particles, so it can hardly be detected as a solid. A good example would be salt water. It appears to be a pure liquid, but when the water is evaporated, you are left with the salt, in a solid state.

-It isnt a compound because the water molecules are still water molecules and the salt molecules are still salt molecules, they are just floating around each other. In a compound, two things become chemically bonded, in which case would produce a completely different substance.

Answer 2

well an example you just said, evaporation, evaporation isn't a chemical reaction its a physical reaction, and produces gas.

And if the clear liquid evaporates leaving some other stuff behind it wasn't an element because it wasn't pure, and because it seperated in a physical reaction it wasn't a compound, so the only other classification it could be would be a mixture, two or more substances mixed together, but can be seperated by non-chemical means.

Answer 3

The liquid is a mixture because when the liquid evaporated, there was a solid remaining. Thus there must have been two parts to the liquid.