CH 6 notes

# 63 enthalpy h and enthalpy change δh enthalpy is a

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6.3 Enthalpy (H) and Enthalpy change (ΔH) - enthalpy is a state function and is related to q. State functions are independent of any history of the system and depend only on its current state (which is determined by Temperature and Pressure variables). ΔH = Σ (ΔH products ) – (ΔH reactants ) - We will be using this equation at the end of the chapter. skip the section on enthalpy and internal energy (pg 233) 6.5 Thermochemical equations - Here we will be working with chemical equations that contain thermochemical data. 2Na (s) + 2H 2 O (l) 2 NaOH (aq) + H 2 (g) ΔH = -368.6 kJ Manipulating thermochemical equations: 1. When you swtich the reactants and products, the sign of the enthalpy change changes. 2 NaOH (aq) + H 2 (g) 2Na (s) + 2H 2 O (l) ΔH = 368.6 kJ 2. When you divide or multiply the coefficients in a chemical equation by an number, you must do the same to the enthalpy term

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When you divide the above equation by 2…. NaOH (aq) + 1/2H 2 (g) Na (s) + H 2 O (l) ΔH = 184.3 kJ 3. The enthalpy change for a chemical reaction can be used as a conversion factor! Given the combustion of methane, how much heat (energy) is given off when 10.0 grams is combusted? CH 4 (g) + 2O 2 (g) CO 2 (g) + 2H 2 O (l) ΔH = -890.3 kJ NOTE: the enthalpy term is the amount of energy given off when ONE MOLE of methane is combusted...this is the CF we need for the problem.
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• Fall '11
• Coffman

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