Which of the following statements is incorrect concerning the thermochemical equation below?
2SO3(g) 2SO2(g) + O2(g); H° = 198 kJ
a. The enthalpy of the reactants exceeds that of the products.
b. The reaction is endothermic.
c. For the reaction 2SO2(g) + O2(g) 2SO3(g), H° = –198 kJ.
d. The external pressure is 1 atm.
e. For every mole of SO3(g) consumed, 99 kJ of heat at constant pressure is consumed as well.
The correct statement concerning the thermochemical equation is:
c. For the reaction 2SO2(g) + O2(g) 2SO3(g), H° = –198 kJ.
This statement is incorrect because the correct statement regarding the reaction is ΔH° = 198 kJ, not -198 kJ.
To determine which statement is incorrect concerning the thermochemical equation, let's analyze each option:
a. The enthalpy of the reactants exceeds that of the products.
This statement is correct. In the given equation, 2 moles of SO3(g) decompose to form 2 moles of SO2(g) and 1 mole of O2(g). Since the reactants have a higher number of moles than the products, the enthalpy of the reactants exceeds that of the products.
b. The reaction is endothermic.
This statement is correct. The given equation shows the production of products from reactants and therefore represents an endothermic reaction. The positive value of delta H (198 kJ) indicates that heat is absorbed during the reaction.
c. For the reaction 2SO2(g) + O2(g) 2SO3(g), H° = –198 kJ.
This statement is incorrect. The given equation represents the reverse reaction of the original equation. In the reverse reaction, the sign of delta H is opposite. Therefore, for the reaction 2SO2(g) + O2(g) → 2SO3(g), ΔH° is +198 kJ.
d. The external pressure is 1 atm.
The statement does not provide enough information to determine its correctness. The external pressure is not indicated in the given equation.
e. For every mole of SO3(g) consumed, 99 kJ of heat at constant pressure is consumed as well.
This statement is incorrect. The heat released or absorbed during a reaction is given by the value of delta H, not by the stoichiometric coefficients. The given equation states that the delta H value is 198 kJ, not 99 kJ.
Therefore, the incorrect statement is c. For the reaction 2SO2(g) + O2(g) → 2SO3(g), ΔH° = –198 kJ.