Problem.
During the chemical reaction
2 mol of oxygen
O₂
interacting with
4 mol of hydrogen
H₂ produces
4 mol of water
H₂O
2H₂ + O₂ → 2H₂O
Heat released during the process is equal to
9.7×10⁵ J.
What fraction of mass is transformed into heat during reaction?
Solution.
Mass and energy are related by the equation
E = mc²
and thus energy released during chemical reaction is
δE = δmc²
where
δm is change in the mass of interacting particles.
So
δm = = = 1.08×10⁻¹¹ kg
Molar mass of hydrogen
H₂ is equal to
2 g,
while molar mass of oxygen is
32 g so original mass of reactants is
m = 7.2×10⁻² kg
and fraction of mass transformed into heat during reaction is
= = 1.5×10⁻¹⁰ kg