What does hess's law say about the total enthalpy change for a reaction

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8.98 dm3 of hydrogen gas is collected at 38.8 °c. find the volume the gas will occupy at -39.9 °c if the pressure remains constant.

Chlorine and water react to form hydrogen chloride and oxygen, like this: 2cl2 (g) + 2h2o (g) → 4hcl (g) + o2 (g) also, a chemist finds that at a certain temperature the equilibrium mixture of chlorine, water, hydrogen chloride, and oxygen has the following composition: compound concentration at equilibrium cl2 0.55m h2o 0.57m hcl 0.53m o2 0.34m calculate the value of the equilibrium constant kc for this reaction. round your answer to 2 significant digits.