In: Chemistry
Think of a BBQ in which you use charcoal to cook your food. You may start with 10 pounds of charcoal. After you finish cooking the food, you may only have a small amount of ash left in the grill. What happened to the charcoal? Does the Law of Conservation of Mass apply to the burning of the charcoal? Clearly explain your position. Hint: Consider that the type of reaction between charcoal and oxygen in air and the identity of products formed.
Charcoal contains mainly Carbon and some ash. Ash does not undergo combustion reaction. Combustion is nothing but the reaction between Carbon present in coal and oxygen present in air. Air contains 21% O2 and 79% N2. N2 does not participate in the combustion reaction which is represented as
C(s)+ O2(g) ---------->CO2(g)
assuming coal contains only carbon and ash
charcoal given = 10 lb, let x= amount of carbon , 10-x= amount of ash
moles of Carbon in coal = mass/atomic weight= x/12,
moles of Oxygen required= x/12 ( 1 mole of Carbon requires 1 mole of Oxygen to react and produce 1 mole of CO2)=0.08x
Air required= 0.08x/0.21 =0.4x, N2 present in supplied air = 0.4x*0.79= 0.32x, moles of O2= 0.08x
mass of O2 supplied =moles* molar mass = 0.08*32x= 2.56x) lbs. mass of N2= 0.32x*28 =8.96xlbs
moles of CO2 formed = 0.08x, Mass of CO2 formed =0.08x*44 = 3.56x lbs
so C( x lb)+ O2(2.56x) + 0.32x(N2) +ash (10-x)---> 3.56x (CO2)+ 0.32x (N2)+ash (10-x)
law of conservation is obeyed.