Final answer:
Generally, the formation of gaseous compounds involves greater energy changes than the formation of solid compounds. Therefore, producing OsO4 as a gas likely releases more heat than forming it as a solid. Chemical reactions which release or absorb heat are termed exothermic or endothermic, respectively.
Step-by-step explanation:
To determine which reaction produces more heat, we need to consider the thermodynamics of the process. Generally speaking, gases have higher enthalpy than solids; therefore, the second reaction, which produces osmium tetroxide (OsO4) as a gas, would involve greater energy change compared to the first reaction, where osmium tetroxide is produced as a solid.
Chemical reactions that release heat into the surrounding are termed exothermic, while those that absorb heat from the surrounding are called endothermic. For example, the combustion of hydrogen gas to form water (2H2(g) + O2(g) → 2H2O(l) + 135 kcal) is exothermic as it releases heat. On the contrary, the formation of nitrogen monoxide from nitrogen and oxygen (N2(g) + O2(g) + 45 kcal → 2NO(g)) is endothermic as it requires an input of heat.