{[ promptMessage ]}

Bookmark it

{[ promptMessage ]}

KThur18

# KThur18 - Thermodynamics Cascade du Sallanches 1 Standard...

This preview shows pages 1–11. Sign up to view the full content.

This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document
2 Standard Enthalpies and Stoichiometry The enthalpy changes associated with a reaction make use of a quantity called the extent of a reaction . The extent of a reaction is given the symbol ξ (Greek lower case xi). Consider the following reaction aA + bB cC + dD
3 Stoichiometry The reaction is sometimes written: v 1 A 1 + v 2 A 2 v 3 A 3 + v 3 A 3 The letters v are called the stoichiometric coefficients. These terms are negative for reactants and positive for products. The importance of the extent is that ξ is the same for all the reactants and the products. The extent is calculated from: i i i v n n 0 - = ξ

This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document
4 Example 2A + B 3C + 2D When the reaction is carried out, 1 mole of A and three moles of B are reacted. At the end of the reaction there will be 1.5 moles of C and 1 mole of D and there will be 2.5 moles of B left over.
5 Extent 5 . 0 2 1 0 = - - = A ξ If we specify the enthalpy of a reaction then the stoichiometry of the reaction must also be specified. 5 . 0 3 0 5 . 1 = - = C ξ 5 . 0 1 3 5 . 2 = - - = B ξ 5 . 0 2 0 1 = - = D ξ At the end of the reaction there will be 1.5 moles of C and 1 mole of D and there will be 2.5 moles of B left over.

This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document
6 Standard States Enthalpy is a state function. The changes that occur are dependent on the states of the reactants and products. Therefore H values are quoted for a precise set of conditions, that is the standard state of a substance at a specified temperature in its pure form at 1 bar. (1 bar is 10 5 Pascals). Enthalpy under these conditions is given the symbol H o
7 Measuring Enthalpies The heat supplied to a system at constant pressure is equal to the increase in enthalpy. The classic method to measure heat change in a chemical process is calorimetry. One of the most common reactions to study by this method is oxidation (combustion) and this is done using a bomb calorimeter. P q H =

This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document
8 Bomb Calorimeter http://www.colby.edu/chemistry/PChem/lab/EnthalpyofFormation.pdf
9 Bomb Calorimeter

This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document
10 Experiment The calorimeter is calibrated by measuring the rise in temperature caused by the complete oxidation of a sample of known heat of combustion. A common standard is benzoic acid (-3227 kJ mol -1 ).
This is the end of the preview. Sign up to access the rest of the document.

{[ snackBarMessage ]}

### Page1 / 26

KThur18 - Thermodynamics Cascade du Sallanches 1 Standard...

This preview shows document pages 1 - 11. Sign up to view the full document.

View Full Document
Ask a homework question - tutors are online