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Acetylene (systematic name: ethyne) is the chemical compound with the formula C 2 H 2 and structure H−C≡C−H.It is a hydrocarbon and the simplest alkyne. [8] This colorless gas is widely used as a fuel and a chemical building block.
For many substances, the formation reaction may be considered as the sum of a number of simpler reactions, either real or fictitious. The enthalpy of reaction can then be analyzed by applying Hess' law, which states that the sum of the enthalpy changes for a number of individual reaction steps equals the enthalpy change of the overall reaction.
The standard Gibbs free energy of formation (G f °) of a compound is the change of Gibbs free energy that accompanies the formation of 1 mole of a substance in its standard state from its constituent elements in their standard states (the most stable form of the element at 1 bar of pressure and the specified temperature, usually 298.15 K or 25 °C).
For example, acetylene has a heat of formation of +227.4 kJ/mol (+54.2 kcal/mol), indicating a much higher energy content compared to its constituent elements. The highly exothermic combustion of acetylene is exploited industrially in oxyacetylene torches used in welding.
The enthalpy of formation of one mole of ethane gas refers to the reaction 2 C (graphite) + 3 H 2 (g) → C 2 H 6 (g). Standard enthalpy of hydrogenation is defined as the enthalpy change observed when one mole of an unsaturated compound reacts with an excess of hydrogen to become fully saturated.
J.A. Dean (ed), Lange's Handbook of Chemistry (15th Edition), McGraw-Hill, 1999; Section 6, Thermodynamic Properties; Table 6.4, Heats of Fusion, Vaporization, and Sublimation and Specific Heat at Various Temperatures of the Elements and Inorganic Compounds
Low heat values are calculated from high heat value test data. They may also be calculated as the difference between the heat of formation ΔH ⦵ f of the products and reactants (though this approach is somewhat artificial since most heats of formation are typically calculated from measured heats of combustion).. [1]
The contribution of the muscle to the specific heat of the body is approximately 47%, and the contribution of the fat and skin is approximately 24%. The specific heat of tissues range from ~0.7 kJ · kg−1 · °C−1 for tooth (enamel) to 4.2 kJ · kg−1 · °C−1 for eye (sclera).