Writing Balanced Equations for Combustion Reactions Write the balanced equation for the reaction that occurs when methanol, CH3OH(/), is burned in air. Write the balanced equation for the reaction that occurs when ethanol, C2H50H (/), burns in air.
Solution 2PE Step 1 Combustion reactions are rapid reactions that produce a flame. Most of the combustion reactions we observe involve O from air as a2eactant.illustrate a general class of reactions involving the burning or combustion of hydrocarbon compounds (compounds that contain only carbon and hydrogen, such as CH and C H ). 4 2 6 When hydrocarbons are combusted, they react with O to form CO and H O. (Whe2there is an 2 2 insufficient quantity of O present, 2rbon monoxide, CO, will be produced. Even more severe restriction of O will2ause the production of fine particles of carbon that we call soot. Complete combustion produces CO . Unless spec2ically stated to the contrary, we will take combustion to mean complete combustion.) The number of molecules of O required in the reaction a2 the number of molecules of CO and H O form2 depend o2the composition of the hydrocarbon. For example, the combustion of propane, C H , a gas used for cooking and home heating, is 3 8 described by the following equation: C3H8(g)+5O2(g)3CO2(g)+4H2O(l). Step 2 We first recall that when any compound containing C, H, and O is combusted, it reacts with the O (g) in air to produce CO (g) and H O(l). Thus, the unbalanced equation is 2 2 2 CH3OH(l)+O2(g)CO2(g)+H2O(l) Because CH OH 3s only one C atom, we can start balancing the equation using the coefficient 1 for CO . Because CH OH has four H atoms, we place a coefficient 2 in front of H O to balance 2 3 2 the H atoms: CH3OH(l)+O2(g)CO2(g)+2H2O(l) This gives four O atoms among the products and three among the reactants (one in CH OH and 3 two in O 2 We can use the fractional coefficient 3/2in front of O to provi2 four O atoms among the reactants (there are 3/2x 2 = 3 O atoms in3/2O ): 2 CH3OH(l)+3/2O2(g)CO2(g)+2H2O(l)