Thermochemistry – classify the heat change for CS2 formation For the reaction C(s) + 2 S(s) → CS2(l) with a heat change of 104.2 kJ, identify the correct thermochemical term represented by this value.

Introduction / Context:
Thermochemical data classify heats according to the process: formation, combustion, fusion, solution, etc. Correctly naming a heat effect requires checking both the reactants and the product states relative to their standard reference forms.

Given Data / Assumptions:

• Reaction: C(s) + 2 S(s) → CS2(l).
• Magnitude of heat change: 104.2 kJ (sign convention omitted in the prompt; classification is requested).
• Elements in their standard states form one mole of a compound.

Concept / Approach:
The standard heat of formation is defined as the enthalpy change when one mole of a compound is formed from its constituent elements in their standard states at a specified temperature and pressure. Here, solid carbon and solid sulfur are elemental standard forms, and the product is liquid carbon disulfide. Hence the given heat corresponds to the heat (enthalpy) of formation of CS2(l). It is not combustion (which would involve oxygen), fusion (solid ↔ liquid of the same substance), or solution (dissolving a solute into a solvent).

Step-by-Step Solution:

Verification / Alternative check:
Thermochemical tables list ΔH_f for CS2(l) derived from exactly such a reaction basis (with appropriate sign).

Why Other Options Are Wrong:

• Solution: Would need a solvent and solute.
• Combustion: Would consume oxygen to form fully oxidized products.
• Fusion: Phase change of the same substance, not chemical reaction.

Common Pitfalls:
Misreading the absence of oxygen; assuming any exo/endothermic value implies combustion. Always check whether the process forms the compound from its elements.

Final Answer:
formation