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.
This is the end of the preview. Sign up
access the rest of the document.
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.