Question

What is the reaction corresponding to the standard enthalpy of formation of K2SO3(s)?

Answer 1

Answer:

• 2K(s) + (1/8) S₈ (s) + (3/2) O₂(g)  →  K₂SO₃ (s)

Explanation:

The standard enthalpy of formation of a substance is the change in enthalpy that happens when one mole of the substance is formed from the elements in their standard states.

Thus, to calculate the standard state of formation of a compound you must:

• 1. Identify the elements that form the compound
• 2. Identify the standard form of each element
• 3. Set the equation to form one mole of the compound, which may require to use fractional coefficients for some of the elements.

Applying that to our compound K₂SO₃

1. Elements:

• potassium, K;
• sulfur, S; and
• oxygen, O.

2. Standard forms of the elements:

• potassium: solid, K(s)
• sulfur: solid, octatomic molecules, S₈ (s)
• oxygen: diatomic gas, O₂(g)

3. Reaction:

• K(s) + S₈ (s) + O₂(g)  →  K₂SO₃ (s)

Balance, keeping one mole of  K₂SO₃. You will need to use fractional coefficients for some elements:

• 2K(s) + (1/8) S₈ (s) + (3/2) O₂(g)  →  K₂SO₃ (s) ← answer