Calculate the standard enthalpy change of following reaction aligned & CH _ 4( ~g ) +2 O _ 2( ~g ) CO _ 2( ~g ) +2 H ₂ O _ ( ) & If _ f H ^ ( CH ₄ )=-75 ~kJ ~mol ⁻¹ & _ f H ^ ( CO ₂ )=-394 ~kJ ~mol ⁻¹ & _ f H ^ ( H ₂ O )=-286 ~kJ ~mol ⁻¹ aligned

Step-by-step solution

The standard enthalpy change for the reaction CH₄(g) + 2O₂(g) CO₂(g) + 2H₂O(l) is determined using the relation H^ _ r = n H^ _ f ( products ) - m H^ _ f ( reactants ) , where H^ _ f values are given as -75~ kJ~mol⁻¹ for CH₄ , -394~ kJ~mol⁻¹ for CO₂ , -286~ kJ~mol⁻¹ for H₂O , and 0~ kJ~mol⁻¹ for elemental oxygen. The sum for products is 1 (-394) + 2 (-286) = -966~ kJ , and for reactants is 1 (-75) + 2 0 = -75~ kJ . H^ _ r = -966 - (-75) = -891~ kJ . The correct choice is A .