Enthalpy Change, ∆_rH of a Reaction - Reaction Enthalpy - Thermochemical Equations

On the basis of thermochemical equations (a), (b) and (c), find out which of the algebric relationships given in options (i) to (iv) is correct.

(a) \[\ce{C (graphite) + O2 (g) -> CO2 (g) ; ∆_rH = xkJ mol^{-1}}\]

(b) \[\ce{C (graphite) + 1/2 O2 (g) -> CO (g) ; ∆_rH = ykJ mol^{-1}}\]

(c) \[\ce{CO (g) + 1/2 O2 (g) -> CO2 (g) ; ∆_r H = zkJ mol^{-1}}\]

During complete combustion of one mole of butane, 2658 kJ of heat is released. The thermochemical reaction for above change is ______.

\[\ce{∆_f U^Θ}\] of formation of \[\ce{CH4 (g)}\] at certain temperature is – 393 kJ mol^–1. The value of \[\ce{∆_f H^Θ}\] is ______.

The standard molar entropy of \[\ce{H2O (l)}\] is 70 JK^–1 mol^–1. Will the standard molar entropy of \[\ce{H2O (s)}\] be more, or less than 70 JK^–1 mol^–1?

The molar enthalpy of vapourisation of acetone is less than that of water. Why?

If the combustion of 1g of graphite produces 20.7 kJ of heat, what will be molar enthalpy change? Give the significance of sign also.

Derive the relationship between ∆H and ∆U for an ideal gas. Explain each term involved in the equation.