2 What are combustion reactions? A combustion reaction occurs when a compound that contains carbon and hydrogen is burned in Oxygen gas (O2). It always produces carbon dioxide and water vapor.Example:CH4 + 2 O2 CO H2OMany times the compound also contains oxygen2C3H4O3 + 5 O2 6 CO H2ONotice the products remain the same.
3 Using a combustion reaction to find empirical formula. Vitamin C is a compound made up of carbon, hydrogen and oxygen atoms. When we combust 1.00g of vitamin C we produce 1.50g of carbon dioxide and 0.408g of water vapor. Find the empirical formula of vitamin C.#1 We know that it is a combustion reaction so:CxHyOz + O2 CO2 + H2O#2 We notice that all the carbon atoms from vitamin C became part of carbon dioxide so;1.50g CO2 x 1 mole CO2 / 44 g = moles of CO2Since there is only 1 atom of carbon in CO2 we have moles of C
4 #3 We have 0.408 g of H2O so all the hydrogen atoms from vitamin C became part of the water vapor. 0.408 g H2O x 1 mole H2O / 18 grams = moles of H2ONotice thee are TWO atoms of hydrogen in H2O so;We have 2x = moles of Hydrogen#4 We now go back to Vitamin C, CxHyOzWe know we have:moles of C x 12g/1 mole of C= .409g of Cmoles of H x 1g / 1mole of H = .0454g of HOxygen = ( )= .546 g of O
5 #5 We now know the grams of each of the elements that make up vitamin C C = .409g x 1mole C/ 12g = molesH = g x 1mole H/ 1g = molesO = g x 1mole O/ 16 g = molesDivide all moles by smallest answerC= .0341/.0341 =1H= .0454/.0341 = 1.33O = .0341/ .0341= 1Multiply all answers by 3 and we getC3 H4 O3
6 Homework 1.Balance the following reactions A) CaO + HNO3 Ca(NO3)2 + H2OB) NH3 + H2SO4 (NH4)2SO42.Given the following reaction, find the grams of H2O are produced2C6H O2 12 CO H2OYou start with 125 grams of C6H6 and 875 g of O23. Find the empirical formula of a compound that is made up of C,H and O. When you combust 2.00g of the compound in excess oxygen gas you produced 3.83g of CO2 and 2.35g of H2O