Sulfuric acid (H2SO4), the most widely produced chemical in the world, is amde yb a two-step oxidaiton of sulfur to sulfur trioxide, SO3, followed by reaciton with water. Calculate ΔH°f for SO3 in kJ/mol, given the following data: S(s) + O2(g) → SO2(g) ΔH° = -296.8 kJ SO2(g) + 1/2 O2(g) → SO3(g) ΔH° = -98.9 kJ

Verified step by step guidance

1. Identify the overall reaction for the formation of SO3 from its elements in their standard states. The overall reaction is: S(s) + 3/2 O2(g) → SO3(g).
2. Break down the overall reaction into the given steps and write down the enthalpy changes for each step. Step 1: S(s) + O2(g) → SO2(g), ΔH° = -296.8 kJ. Step 2: SO2(g) + 1/2 O2(g) → SO3(g), ΔH° = -98.9 kJ.
3. Add the enthalpy changes from the two steps to find the overall enthalpy change for the formation of SO3. Use the equation: ΔH°(overall) = ΔH°(step 1) + ΔH°(step 2).
4. Substitute the given values into the equation from step 3 to calculate the overall ΔH° for the formation of SO3.
5. The calculated ΔH° for the formation of SO3 from sulfur and oxygen is the ΔH°f (standard enthalpy of formation) of SO3.

Key Concepts

Hess's Law

Hess's Law states that the total enthalpy change for a chemical reaction is the sum of the enthalpy changes for the individual steps of the reaction, regardless of the pathway taken. This principle allows us to calculate the enthalpy change for a reaction by using known enthalpy changes of related reactions, making it essential for determining ΔH°f values.

Standard Enthalpy of Formation (ΔH°f)

The standard enthalpy of formation (ΔH°f) is defined as the change in enthalpy when one mole of a compound is formed from its elements in their standard states. It is a crucial concept in thermodynamics, as it provides a reference point for calculating the enthalpy changes of various reactions, including the formation of sulfur trioxide (SO3) in this case.

Enthalpy Change (ΔH)

Enthalpy change (ΔH) refers to the heat content change of a system at constant pressure during a chemical reaction. It can be either exothermic (releasing heat, ΔH < 0) or endothermic (absorbing heat, ΔH > 0). Understanding how to manipulate ΔH values from given reactions is essential for calculating the enthalpy of formation for compounds like SO3.