A medium size apartment house is equipped with a heating furnace (boiler) for generating hot water d — Physical Chemistry — Thermodynamics Chemistry Question
Boiler
A medium size apartment house is equipped with a heating furnace (boiler) for generating hot water during the cold months. The nominal heating power of the furnace is 116 kW. The building has an oil tank with a storage capacity of 4 m 3 of heating oil. The enthalpy of combustion of the oil, which consists mostly of heavy liquid saturated hydrocarbons, is 43 000 kJ kg –1 and its density is about 0.73 g cm –3.
Indicate how long the heater can operate continuously before it becomes necessary to refill the tank.
A) 5 h B) 2.2 days C) 12 days D) 3.3 weeks E) 2.1 months
Model Answer
Tank capacity: m = V ρ = 4 m 3 × 0.73 g cm –3 = 2920 kg
Heating power P = 116 kW
Consumption rate = 116 kJ s –1 / 4.3 × 10 7 J kg –1 = 2.70 × 10 –3 kg s –1 = 9.73 kg h –1
Operation duration t = m / consumption rate = 2920 kg / (2.70 × 10 –3 kg s –1) = 1.08 × 10 6 s = 300 h = 12.5 days
The answer C) is correct.
What is the approximate mass of CO2 generated and released into the atmosphere per hour when the furnace is operating?
A) 300 g B) 1 kg C) 5 kg D) 10 kg E) 30 kg
Model Answer
CnH2n+2 + ½ (3n+1) O2 n CO2 + (n+1) H2O
m(CO2) / m(CnH2n+2) = 44n / (14n + 2) = 22 / (7 + 1/n)
This ratio does not depend heavily on n; for a representative value of n = 10 the ratio takes the value of 3.1.
Since consumption rate is 9.73 kg h –1,
m(CO2) = 9.73 kg h –1 × 3.1 = 30.2 kg h –1
The answer E) is correct.