Hess's Law

A chemical reaction usually doesn’t happen in one step, but through a series of steps. To determine the overall energy or heat involved we use Hess’s Law

Hess's Law

To determine the overall energy or heat of a reaction look to isolate each compound given within that chemical reaction. 

Problem: Calculate the ?Hrxn for CO(g) + NO (g) -----> CO2 (g) + N2 (g) ?H = ? Given the following set of reactions: CO2 (g) -----> CO (g) + O2 (g) ?H1 = 283.0 kJ N2 (g) + O2 (g) ----> 2 NO (g) ?H2 = 180.6 kJ

5m

Problem: Calculate the ?Hrxn for ClF (g) + F2 (g) -----> ClF3 (g) ?Hrxn = ? Given the following reactions: Cl2O (g) + F2O -----> 2 ClF (g) + O2 (g) ?Hrxn = - 167.4 kJ 4 ClF3 (g) + 4 O2 (g) -----> 2 Cl2O (g) + 6 F2O (g) ?Hrxn = 682.8 kJ 2 F2 (g) + O2 (g) -----> 2 F2O (g) ?Hrxn = -181.7 kJ

6m