Given: C graphite + O 2 g → CO 2 g ; Δ r H o = − 393 .5 kJ mol − 1 H 2 g + 1 2 O 2 g → H 2 O l ; Δ r H o = - 285 .8 kJ mol - 1 CO 2 g + 2 H 2 O l → CH 4 g + 2 O 2 g ; Δ r H o = + 890 .3 kJ mol - 1 Based on the above thermochemical equations, the value of Δ r H o at 298 K for the reaction C graphite + 2 H 2 g → CH 4 g will be:

Step-by-step solution

The standard enthalpy of formation is defined as the change in enthalpy when one mole of a substance in the standard state (1 atm of pressure and 298.15 K) is formed from its pure elements under the same conditions. The enthalpy of combustion of a substance is defined as the heat energy given out when one mole of a substance burns completely in oxygen. The formation reaction of methane is C graphite + 2 H 2 g → CH 4 g The heat of combustion data for C ( graphite ) , H 2 g and CH 4 g ∆ H f o = ∑ ∆ H Combustion react