What I just released is a gas called methane. but lets ask a real question. Look at this bath bomb. Now I'll shake it in the water. See that? Pressure and fizz builds up and we see a gas. However, is this gas a new substance or was it there?
The gas is a new substance because a chemical reaction created a chemical change and a new product was formed. This is similar to vinegar and baking soda. We know this because the ingriedients in the bath bomb are the normal substances and only substances from the bath bomb, apart from contamination, we only know its solid form for now, When combined with water, the chemical change forces gas bubbles to form. The gases in the bubbles are in gas form and they are different from the substances we started with. The difference from a physical change which would be if the gas was already there and a chemical change which would be the new matter that it created also contributed to my theory because a physical change is when matter changes from but not chemical identity. Questions or concerns?