We can use hess's law to calculate enthalpy changes that cannot be measured. one such reaction is the conversion of methane to ethylene: 2ch4(g)⟶c2h4(g) 2h2(g) part a calculate the δh∘ for this reaction using the following thermochemical data: ch4(g) 2o2(g)⟶co2(g) 2h2o(l) δh∘

Asubstance is held in an open container. its particles move past one another at random speeds but do not leave the container. heat is removed from the system, and the particles slow down. when enough heat is removed, the particles no longer have enough speed to overcome the weak attractive forces between them. when this happens, the substance enters its solid state. the process described above is known as .