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Thermochemistry

Thermochemistry. Hess’s Law. Focus of lesson. To understand the principles underpinning Hess’s law To apply the principles to a practical experiment. Hess’s Law. “…. the heat change for a chemical reaction is independent of the pathway”

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Thermochemistry

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  1. Thermochemistry Hess’s Law

  2. Focus of lesson • To understand the principles underpinning Hess’s law • To apply the principles to a practical experiment

  3. Hess’s Law • “….the heat change for a chemical reaction is independent of the pathway” • “Only depends on the initial conditions of the reactants and the final conditions of the products”

  4. Example • Example:If carbon is burned completely to carbon dioxide, the thermochemical equation is: C (s) + O2 (g) → CO2 (g) ∆rH = -393 kJ/mol • If carbon is incompletely burned to carbon monoxide, and then carbon monoxide is reacted with oxygen to form carbon dioxide, the result is the same, but a different path was taken. • C (s) + 0.5 O2 (g) → CO (g) ∆rH = -282 kJ/mol • CO (g) + 0.5 O2 (g) → CO2 (g) ∆rH = -111 kJ/mol • ∆rH1 = ∆rH2 + ∆rH3- 393 = -282 + -111

  5. Today’s experiment

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