1. Given that the standard enthalpy of formation of atomic hydrogen, H(g), is -2

Question

1. Given that the standard enthalpy of formation of atomic hydrogen, H(g), is -219.0 kJ/mol, find the standard reaction enthalpy for the reaction H2(g) -> 2H(g)

2. Sulfur has two solid forms - a (or rhombic) and b (or monoclinic). The standard enthalpies of combustion, in which the product is SO2, are -296.53 kJ/mol for S(s,a) and -296.86 kJ/mol for S(s,b) a 298 K. Find the standard reaction enthalpy for the process S(s,a) -> S(s,b) at 298 K.

3.The enthalpy of vaporization of water at 373 K and 1 bar is 40.7 kJ/mol and the molar heat capacities are 75.3 J/(mol K) for liquid and 33.6 J/(mol K) for gaseous water. Find the enthalpy of vaporization of water at 273 K and 1 bar. Express result in kJ/mol and type in value only.

Explanation / Answer

1)standard reaction enthalpy for the reaction H2(g) -> 2H(g)=2*-219.0=-438.0kJ/mol

2)standard reaction enthalpy for the process S(s,a) -> S(s,b) at 298 K=-296.53 kJ/mol+-296.86 kJ/mol=0.33kJ/mol

3)enthalpy of vaporization of water at 273 K=enthalpy of vaporization of water at 373 K-Cp(373-273)=40.7kJ/mol-0.0753*100kJ/mol=33.17kJ/mol

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