Chemistry · THERMODYNAMICS

According to Hess's Law of Constant Heat Summation, if an overall chemical reaction \( \text{A} \rightarrow \text{B} \) proceeds directly along one path with enthalpy change \( \Delta_r H \), and along an indirect path \( \text{A} \rightarrow \text{C} \rightarrow \text{D} \rightarrow \text{B} \) with intermediate enthalpy changes \( \Delta_r H_1, \Delta_r H_2, \Delta_r H_3 \), which relation is fundamentally obeyed due to enthalpy being a state function?

1. \( \Delta_r H = \Delta_r H_1 - \Delta_r H_2 + \Delta_r H_3 \)
2. \( \Delta_r H = \frac{\Delta_r H_1 + \Delta_r H_2 + \Delta_r H_3}{3} \)
3. \( \Delta_r H = \Delta_r H_1 \times \Delta_r H_2 \times \Delta_r H_3 \)
4. \( \Delta_r H = \Delta_r H_1 + \Delta_r H_2 + \Delta_r H_3 \)