LO: I understand what is meant by Hess’s law.

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Presentation transcript:

LO: I understand what is meant by Hess’s law.

Hess’s law states that the enthalpy change for a reaction is dependent on the reactants and products and not on the route taken. For example: H1 C + 2H2 CH4 + O2 + O2 + 2O2 H2 H3 H4 CO2 + 2H2O H1 = H2 + xH3 - H4 LO: I understand what is meant by Hess’s law.

Calculations Involving Hess’s Law LO: I know how to calculate enthalpy changes using Hess’s law.

Calculate the enthalpy of formation of Silane (SiH4). + Hf Hc(silicon) = -911 kJmol-1 Hc(silane) = -1517 kJmol-1 Hc(hydrogen) = -286 kJmol-1 Hf Hc(reactants) Hc(products)   -911 + 2x-286) -1517)   34 kJ mol-1  LO: I know how to calculate enthalpy changes using Hess’s law.