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 ethylene glycol, C2H4(OH)2, burns in air.
Solution1PE Step 1 Combustion reactions are rapid reactions that produce a flame. Most of the combustion reactions we observe involve O from air as a r2ctant.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. (When t2re is an 2 2 insufficient quantity of O present, carbon monoxide, CO, will be produced. Even more severe 2 restriction of O will cause the production of fine particles of carbon that we call soot. Complete 2 combustion produces CO . Unless speci2cally stated to the contrary, we w ill take c ombustion to mean c omplete combustion.) The number of molecules of O required in the reaction and 2e number of molecules of CO and H O formed2epend on 2e composition of the hydrocarbon. For example, the combustion of propane, C H , a gas used for co3in8and home heating, is 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 2g) in air to produce CO (g) and 2 O(l). Thus,2he unbalanced equation is 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 2Because CH OH h3 four H atoms, we place a coefficient 2 in front of H O to balance 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 )2We can use the fractional coefficient 3/2in front of O to provid2four 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) Step 3 Although the equation is now balanced, it is not in its most conventional form because it contains a fractional coefficient. If we multiply each side of the equation by 2, we will remove the fraction and achieve the following balanced equation: 2CH3OH(l)+3O2(g)2CO2(g)+4H2O(l).