Does a chemical reaction have to give off a gas?

Answer 1

No, not necessarily. An explosion might be be a sign of a chemical reaction (or a mechanical reaction, for that matter), since it's really just an enormous release of energy all at once.

Chemical reactions usually do exhibit some sort of observable change, though. For example, there may be a release or absorption of heat (in exothermic and endothermic reactions, respectively), a change in state of matter (solid, liquid, gas), or a change in color.

Answer 2

An explosion may be the result of a chemical reaction. Such is the case if we set off a stick of TNT. But it may be nuclear, as in the case of a nuclear weapon, or may be mechanical, as in the case of the blast created when a compressed gas cylinder with a failing weld is filled and blows up. There can be several causes for an explosion.

Answer 3

not always but frequently there is. some chemicals when you mix them together are harmless but some can cause dangerous side affects. most of the time there will be some chemical reaction or change of colour when you mix chemicals. :)

Answer 4

No, they may merely result in an increase in temperature. As an example acetic acid in vinegar reacts with magnesium hydroxide in milk of magnesia. The reaction does release energy, which can be noted as the temperature of the solution increases noticeably, but the only visible change is that the solution turns from white to clear.

Answer 5

Yes, chemical reactions always involve chemical changes. The definition of a chemical reaction is a chemical change that takes place when combining two or more chemical substances. Of course, not every substance present for a reaction will necessarily undergo a chemical change: some may exit the reaction as the same material, even if their presence serves to catalyze the reaction.

Answer 6

No, the vast majority do not.

Answer 7

Yes.