122-10 - Standard Enthalpies of Formation The standard...

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

View Full Document Right Arrow Icon
Standard Enthalpies of Formation The standard enthalpy of formation of a substance, denoted H f o , is the enthalpy change for the formation of one mole of a substance in its standard state from its component elements in their standard state. Note that the standard enthalpy of formation for a pure element in its standard state is zero.
Background image of page 1

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

View Full DocumentRight Arrow Icon
Background image of page 2
Standard Enthalpies of Formation The l aw of summation of heats of formation states that the enthalpy of a reaction is equal to the total formation energy of the products minus that of the reactants. Σ is the mathematical symbol meaning “the sum of”, and m and n are the coefficients of the substances in the chemical equation . . ) reactants ( H m ) products ( H n H o f o f o - =
Background image of page 3

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

View Full DocumentRight Arrow Icon
A Problem to Consider • You record the values of H f o under the formulas in the equation, multiplying them by the coefficients in the equation. - You can calculate H o by subtracting the values for the reactants from the values for the products. ) 9 . 45 ( 4 - ) 0 ( 5 ) 3 . 90 ( 4 ) 8 . 241 ( 6 - ) g ( O H 6 ) g ( NO 4 ) g ( O 5 ) g ( NH 4 2 2 3 + +
Background image of page 4
How is the heat of sublimation, H sub , the enthalpy change for the reaction: H 2 O (s) H 2 O (g) related to H fis and H vap ?
Background image of page 5

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

View Full DocumentRight Arrow Icon
Fuels Food fills three needs of the body: - It supplies substances for the growth and repair of tissue. - It supplies substances for the synthesis of compounds used in the regulation of body processes. - It supplies energy. About 80% of the energy we need is for heat. The rest is used for muscular action and other body processes
Background image of page 6
Fuels • A typical carbohydrate food, glucose (C 6 H 12 O 6 ) undergoes combustion according to the following equation. + ) g ( O 6 ) s ( O H C 2 6 12 6 kJ -2803 H ); l ( O H 6 ) g ( CO 6 o 2 2 = + One gram of glucose yields 15.6 kJ (3.73 kcal) when burned.
Background image of page 7

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

View Full DocumentRight Arrow Icon
Fuels A representative fat is glyceryl trimyristate, C 45 H 86 O 6 . The equation for its combustion is: + ) g ( O ) s ( O H C 2 2 127 6 86 45 kJ -27,820 H ); l ( O H 43 ) g ( CO 45 o 2 2 = + One gram of fat yields 38.5 kJ (9.20 kcal) when burned. Note that fat contains more than twice the fuel per gram than carbohydrates contain.
Background image of page 8
Figure 6.15: Sources of energy consumed in the United States (1996).
Background image of page 9

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

View Full DocumentRight Arrow Icon
Fuels Fossil fuels account for nearly 90% of the energy usage in the United States. Anthracite, or hard coal, the oldest variety of coal, contains about 80% carbon. Bituminous coal, a younger variety of coal,
Background image of page 10
Image of page 11
This is the end of the preview. Sign up to access the rest of the document.

This document was uploaded on 12/14/2010.

Page1 / 55

122-10 - Standard Enthalpies of Formation The standard...

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

View Full Document Right Arrow Icon
Ask a homework question - tutors are online