REPRESENTING ENTHALPY CHANGES. 1. ΔH Notation 2. Thermochemical Equation 3. Potential Energy Diagram.

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Presentation transcript:

REPRESENTING ENTHALPY CHANGES

1. ΔH Notation 2. Thermochemical Equation 3. Potential Energy Diagram

 the ΔH is written outside the balanced chemical equation RECALL: + ΔH means ENDOTHERMIC - ΔH means EXOTHERMIC

2 SO 2 + O 2  2SO 3 ΔH = kJ “When 2 moles of SO 2 react with 1 mole of O 2, 2 moles of SO 3 are produced and kJ of energy are released.” 1)What is the molar enthalpy of formation for SO 3 ? 2)What will the ΔH be if 4 moles of SO 2 react with excess O 2 ?

 a balanced chemical equation which includes the ΔH for the rxn as either a reactant (LEFT side) or product (RIGHT side) exothermic - ΔH energy quantity as a PRODUCT endothermic +ΔH energy quantity as a REACTANT

1) Write a thermochemical equation for the following: N 2 + 3H 2  2 NH 3 ΔH = kJ (i.e., ΔH notation)

2) Write the thermochemical equation using ΔH notation: CO kJ  C + O 2 (i.e., thermochemical equation)

 all stoichiometric ratios apply to the energy component 2 Fe + 3 CO kJ  Fe 2 O CO “When 2 mol of Fe react with 3 mol of CO 2, 6.39 kJ of energy are consumed. 1 mol of Fe 2 O 3 and 3 mol of CO are produced”.

1) Rewrite the thermochemical equation so that the coefficient in front of the Fe is a 1 2) How many kJ are required to completely react 8.00 g of Fe?

Exothermic Energy Rxn Coordinate

Exothermic Energy Rxn Coordinate

Exothermic Energy Rxn Coordinate Energy of the Reactants Energy of the products -ΔH energy released

Endothermic Energy Rxn Coordinate

Endothermic Energy Rxn Coordinate Energy of the Reactants Energy of the products +ΔH energy absorbed

Construct a PE diagram for the reaction: N 2 + O kJ  2NO

Endothermic Energy Rxn Coordinate N 2 + O 2 2NO ΔH = kJ