Is it possible that CO2 changes into CH4 - and under what conditions is this possible?

Answer 1

No. CO2 contains the elements carbon and oxygen, whereas CH4 contains carbon and hydrogen, and elements are immutible unless they are radioactive and undergo radioactive decay. If you are thinking of something like a chemical reaction in which CO2 is a reactant and CH4 is a product, that might be possible. But if that is the case, the atoms of the reactants are rearranged to form the products, but one element would not actually change into another element. For example, in the following chemical reaction, CO2 reacts with H2O to form the products CH4 and O2. Note that the total number of atoms of each element is the same on each side of the equation, which means that the atoms of each element were rearranged, but the elements did not change identity.

CO2 + 2H2O --> CH4 + 2O2

Answer 2

Yes, it is possible for CO2 to change into CH4 through a process called methanation. This typically occurs under high temperatures (around 300-400°C) and with the presence of a catalyst, such as nickel, which can facilitate the conversion of CO2 and H2 into CH4. Methanation is often used in industrial processes to produce synthetic natural gas or renewable methane.