Calcium carbonate decomposes at high temperatures to give calcium oxide and carb
ID: 942476 • Letter: C
Question
Calcium carbonate decomposes at high temperatures to give calcium oxide and carbon dioxide as shown below. CaCO3(s) CaO(s) + CO2(g) The KP for this reaction is 1.16 at 800°C. A 5.00 L vessel containing 10.0 g of CaCO3(s) was evacuated to remove the air, sealed, and then heated to 800°C. Ignoring the volume occupied by the solid, what will be the overall mass percent of carbon in the solid once equilibrium is reached?
A) 5.36% carbon by mass
B) 5.56% carbon by mass
C) 5.76% carbon by mass
D) 5.96% carbon by mass
E) None of the above
Explanation / Answer
CaCO3(s) ------> CaO(s) + CO2(g)
Kp = PCO2
Molar mass of CaCO3 = 100 g
Thus, moles of CaCO3 present in 10 g of it = mass/molar mass = 10/100 = 0.1
moles of CO2 formed = (P*V)/(R*T) = (1.16*5)/(0.0821*1073) = 0.066
Thus, At eqb., moles of CaCO3 left unreacted = initial moles of CaCO3 - moles of CO2 formed = 0.034
mass of CaCO3 left unreacted = moles*molar mass = 3.4 g
Thus, mass of solid carbon = moles of unreacted CaCO3 *molar mass of C = 0.034*12 = 0.408
moles of CaO formed = moles of CaCO3 reacted = 0.066
mass of CaO formed = moles*molar mass = 0.066*56 = 3.696
% of solid carbon = (0.408/3.4+3.696)*100 = 5.76 %