Question

Why are fossil fuels bad?

Answer 1

Consider hydrocarbon combustion. It turns biomass (i.e. fixed carbon) into gaseous `CO_2`.

Explanation:

The world's hydrocarbon reserves were laid down by forests in past eras. Of course, now we use these hydrocarbons as an energy source to drive our motors.

I will use combustion of hexanes as an example:

`C_6H_14(g) + (13/2)O_2(g) rarr 6CO_2(g) + 7H_2O(l)`

As a triatomic molecule, carbon dioxide is very efficient at storing energy (much more so than diatomic dioxygen and dinitrogen. Why? Because the linear triatom has more degrees of freedom). Our industrial society is busy replacing fixed hydrocarbon reserves with gaseous `CO_2`. Increased concentrations of carbon dioxide in the atmosphere results in greater heat capture, and net warming of the planet since pre-industrial times.

Of course there are many other nuances and factors to consider (and no doubt you will hear some).