J.R. S. answered 05/25/21
Ph.D. University Professor with 10+ years Tutoring Experience
methane = CH4
oxygen = O2
CH4 + 2O2 ==> CO2 + 2H2O + energy (heat) ... balanced equation
This is an exothermic reaction so heat energy is a product. The 3 moles of methane is meaningless unless we know the ∆H of the reaction. The impact of the gaseous product (CO2) on the environment depends on what you believe carbon dioxide does to the environment. I'll leave it to you to read about that and provide your own answer.