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Unformatted text preview: property. The magnitude of H is dependent upon the amounts of reactants consumed. Doubling the reactants, doubles the amount of enthalpy. 2. Reversing a chemical reaction results in the same magnitude of enthalpy but of the opposite sign . For example, splitting two moles of water to produce 2 moles of H 2 and 1 mole of O 2 gas requires the input of +483.6 kJ of energy. 3. The enthalpy change for a reaction depends upon the state of the reactants and products. The states (i.e . g, l, s or aq ) must be specified. CH 4 (g) + 2O 2 (g) -> CO 2 (g) + 2H 2 O(g) H = -802 kJ Given the above thermochemical equation for the combustion of methane, how much heat energy is released when 4.5 grams of methane is burned (in a constant pressure system)? The negative sign (exothermic) indicates that 225.5 kJ of energy are given off by the system into the surroundings....
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