Oxidation. Heat of combustion

Combustion to carbon dioxide and water is characteristic of organic compounds under special conditions it is used to determine their content of carbon and hydrogen (Sec. 2.26). 

Combustion of methane is the principal reaction taking place during the 

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FLUORETHYLENE (75-02-5) Flammable gas. Able to polymerize unless inhibited (0.2% terpenes are recommended). Violent reaction with oxidizers. Heat of combustion forms toxic hydrogen fluoride gas. May accumulate static electrical charges, and may cause ignition of its vapors. 

Explosives and propellants are mixtures of fuel and oxidizer. The intensity of combustion is determined by the heat of combustion per pound of material, the material s density, the gas volume generated per volume of material, and the rate of deflagration or detonation. The latter, the most important variable, is determined by the speed at which fuel and oxidizer molecules combine. 

The standard heat of combustion (ziH") of a chemical substance (usually an organic compound) is the same as the standard heat of reaction for complete oxidation of 1 mole of the substance in pure oxygen to yield COj(g) and HjO(f) as products. A reference state of 25°C and 1 atm is assumed in quoting standard heats of combustion in cal/g-mole. The value of AH" is always negative because combustion is an exothermic reaction. Note that the standard heats of combustion for carbon and hydrogen are the same as the heats of formation for CO,(g) and HjO(f), respectively. 

Heat of combustion is the heat liberated or absorbed when one gram mole of the substance is completely oxidized to liquid water and CO2 gas at one atmosphere and 20°C or 25°C. (Cj-C hydrocarbons and cyclohexane at 25°C, others at 20°C). The gross heating value in Btu/ft could be calculated as follows ... 

Suppose we are interested in the heat of combustion of nitric oxide, NO ... 

Heal content, 110. 116 change (luring a reaction, 110 of a substance, 109 Heat of combustion of diamond, 122 graphite, 122 hydrazine, 47 hydrogen, 40 methane, 123 Heat of formation, 113 Heat of reaction, 135 between elements, table, 112 oxidation of HC1, 160 oxidation of sulfur dioxide, 161 predicting, 112 Heat of reaction to form ammonia, 112 Br atoms, 290 carbon dioxide, 112 carbon monoxide, 112 Cl atoms, 290 CO + Hi, 110 ethane, 112 F atoms, 290 H atoms, 274 hydrogen chloride, 160 hydrogen iodide, 112 iron(Ill) oxide, 162 Li atoms, 290 Li + Br, 290 Li + F, 290 Na + Cl, 290 NHs products, 114 Na atoms, 290 NO, 112 NOj, 112... 

Favre and Silbermann (1852) measured the heat of combustion of carbon in nitrous oxide, and found ... 

Fuel cells are electrochemical devices transforming the heat of combustion of a fuel (hydrogen, natural gas, methanol, ethanol, hydrocarbons, etc.) directly into electricity. The fuel is electrochemically oxidized at the anode, whereas the oxidant (oxygen from the air) is reduced at the cathode. This process does not follow Carnot s theorem, so that higher energy efficiencies are expected up to 40-50% in electrical energy and 80-85% in total energy (heat production in addition to electricity). 

Gorbunov, V. V. et al., Combustion, Expls, Shockwaves, 1986, 22, 726 Not merely cupric oxide, but the fluoride, chloride and sulfide all form mixtures with heats of combustion above 2 kJ/g. The equivalent lead compounds are less active. 

Heat of combustion the enthalpy change for the complete oxidation of a compound => for a hydrocarbon means converting it to C02 and water. 

The flow rate of CO is multiplied by the heat of combustion of CO (11.7 MJ/m3 of CO at 20°C) to obtain the heat release rate from CO if CO burns to C02. This heat release rate plus heat release rate from the wall is the potential heat release rate if CO is further oxidized to C02. 

Values of yields for various fuels are listed in Table 2.3. We see that even burning a pure gaseous fuel as butane in air, the combustion is not complete with some carbon monoxide, soot and other hydrocarbons found in the products of combustion. Due to the incompleteness of combustion the actual heat of combustion (42.6 kJ/g) is less than the ideal value (45.4 kJ/g) for complete combustion to carbon dioxide and water. Note that although the heats of combustion can range from about 10 to 50 kJ/g, the values expressed in terms of oxygen consumed in the reaction (Aho2) are fairly constant at 13.0 0.3 kJ/g O2. For charring materials such as wood, the difference between the actual and ideal heats of combustion are due to distinctions in the combustion of the volatiles and subsequent oxidation of the char, as well as due to incomplete combustion. For example,... 

The flaming results extend to = 4 in Figures 2.3 and 2.4, at which point gas phase combustion appears to cease. However, combustion must continue since the heat of combustion remains nonzero. This is due to oxidation of the remaining solid fuel. If we consider wood, it would be the oxidation of the surface char composed primarily of carbon. From Example 2.3, we obtain the heat of combustion for carbon (going to CO2) as 32.8 kJ/g carbon. From Figure 2.4, we see a significant production of carbon monoxide at < > 4, and therefore it is understandable that Figure 2.3 yields a lower... 

The heat of combustion of a fuel is defined as the amount of heat released when unit quantity is oxidized completely to yield stable products. 

The feed stream containing H2S is incinerated with air to oxidize all sulfur compounds to SO2. The heat of combustion is partially recovered by raiding medium-pressure steam (400-600 psig) in a waste heat boiler. The gas is washed and demisted, then dried with concentrated H2S0i. The gas is then compressed, preheated, and enters a fixed-bed catalytic reactor. In the reactor SO2 is converted to S0a ... 

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