How would $\ce{H2SO4}$ react to heat? I assume that it would form toxic sulfur (di/tri)oxide, but I can't find any information on this.
I'm concerned about fire hazards specifically, so assume very intense heating and very low concentration.
2 Answers
$\begingroup$
$\endgroup$
2
Sulfuric acid, $\ce{H2SO4}$, having an enthalpy of formation of $-814\ \mathrm{kJ/mol}$, is quite stable and won't decompose easily.
The decomposition of $\ce{H2SO4}$ to $\ce{H2O}$ and $\ce{SO3}$ is predominant between $400$ and $700\ \mathrm K$. The formation of a small amount of gaseous sulfuric acid can be observed. Above $673\ \mathrm K$, the equilibrium constant of the reaction R1 becomes higher than 1 and increases rapidly.
$$\ce{H2SO4 <=> H2O + SO3}\tag{R1}$$
The second process is the reduction of sulfur trioxide to $\ce{SO2}$. This endothermic reaction needs a high temperature to take place, the equilibrium constant of the reaction R2 being higher than 1 above $1050\ \mathrm K$.
$$\ce{SO3 <=> SO2 + \dfrac12O2}\tag{R2}$$
So, you only have to worry when the temperature reaches $400\ \mathrm K$, or $127\ \mathrm{^\circ C}$ (false precision).
-
1$\begingroup$ @YdobEmos Usually available sulfuric acid is dissolved in water (except sulfuric acid in which case there is little water), so the temperature would be limited by the water. $\endgroup$– DHMOOct 11, 2016 at 14:41
-
3$\begingroup$ In aqueous solution, you also have to worry about the water boiling and spitting acid at you. A speck of hot sulphuric acid on a mucus membrane is not a pleasant experience. $\endgroup$ Oct 11, 2016 at 17:36
$\begingroup$
$\endgroup$
0
First, you don't need to worry about fire: sulphuric acid is non-flammable.
Around $1000$ kelvin, this reaction would occur:
$$\ce{2H2SO4 <=> 2SO2 + 2H2O + O2}$$
This is industrially used for the production of hydrogen gas, and the total reaction cycle is called the sulphur-iodine cycle.