Chemical Forums
Chemistry Forums for Students => Undergraduate General Chemistry Forum => Topic started by: Win,odd Dhamnekar on July 03, 2021, 12:42:51 AM
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Standard enthalpy of combustion
(ΔH°c)) is the enthalpy change when 1 mole of a substance burns (combines vigorously with oxygen) under standard state conditions; it is sometimes called “heat of combustion." at 25°C and one ATM pressure. [itex]\Delta H^{\circ}_c[/itex] of Acetylene is -1301.1 kJ mol-1
Although the gas used in an oxyacetylene torch (below Figure) is essentially pure acetylene, the heat produced by combustion of one mole of acetylene in such a torch is likely not equal to the enthalpy of combustion of acetylene mentioned above. Considering the the standard conditions for which above ΔH°c value of acetylene are reported, suggest an explanation.
How to answer this question? What is the answer to this question?
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Well, what is the difference between standard conditions and conditions in a torch flame?
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Air-acetylene produces a flame temperature of around 4000° F (2200° C). This is hot enough to solder aluminum work glass, repair radiators and braze plumbing fixtures. It is not hot enough to weld steel. When acetylene is burned in pure oxygen, the flame temperature may be as high as 5730° F (3166° C).
The oxyacetylene process produces a high temperature flame over 3,000 degrees C, by combustion of pure oxygen and acetylene.