Calorimetry

Heat transfer, specific heat, and enthalpy changes

Calorimetry measures heat changes during chemical or physical processes. In a coffee-cup calorimeter (constant pressure), the heat released or absorbed by a reaction is captured by the surrounding solution. Using q = mcΔT, where c for dilute aqueous solutions ≈ 4.184 J/(g·°C), we calculate q_solution. By conservation of energy, q_rxn = -q_solution. The molar enthalpy ΔH_rxn = q_rxn/n (per mole of limiting reagent). For mixing two solutions at different temperatures (no reaction), the final temperature is the weighted average: T_f = (m₁c₁T₁ + m₂c₂T₂)/(m₁c₁ + m₂c₂). Hess's Law states that ΔH for an overall reaction equals the sum of ΔH values for individual steps, regardless of the path taken.