study-note-4-42 - H is the enthalpy change for a reaction....

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5.5 How is Δ H different from Δ H ° ? Δ H is the enthalpy change for a reaction. Δ H ° is the enthalpy change for a reaction occurring at 25 ° C and 1 atm. What is another name for Δ H ° ? Standard heat of reaction (25 ° C and 1 atm are standard conditions). Why is it useful to express Δ H ° values instead of Δ H values? The Δ H for a reaction changes for different conditions of temperature and pressure. Δ H ° allows for the comparison of different chemical reactions (and are used later in Hess’s law calculations). What is a thermochemical equation? A chemical equation written with its value of Δ H ° . For example: N 2 (g) + 3H 2 (g) 2NH 3 (g) Δ H ° = -92.38 kJ How many moles of product are formed in a thermochemical equation? Any number of moles can be formed, though the value of Δ H ° will vary depending on this number. In what three ways can a thermochemical equation be manipulated? They can be reversed, multiplied by some factor, or added together.
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This note was uploaded on 04/12/2011 for the course CHEM 1010 taught by Professor Marshall during the Spring '11 term at North Texas.

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