Enthalpy (Chemistry)

Question

Consider the reaction: 

2 SO2 (g) + 2 H2O (g) --> 2 H2S (g) + 3 O2 (g)

Calculate the  rxn using the standard enthalpy of formation data provided.

SO2 (g) -296.8 kj/mol

H2O (g) -241.8 kj/mol

H2S (g) -20.17 kj/mol

O2 (g) 0 kj/mol

Answer 1

When given data about the products and reactants, in general, you can use these data to find information about the overall reaction. In the current problem you are asked to find ∆Hº of the reaction given ∆H values for formation of the reactants and products. In this case we use the expression

∑n∆H_products - ∑n∆H_reactants, i.e. sum of enthalpy formation of products - sum enthalpy formation reactants

Sum of products:

(2)(-20.17) + (3)(0) = -40.34 + 0 = -40.34 kJ

Sum of reactants:

(2)(-296.8) + (2)(-241.8) = -593.6 + -483.6 = -1077.2 kJ

sum products - sum reactants = -40.34 kJ - (-1077.2 kJ) = 1037 kJ = ∆Hºrxn