Question

When you one mole of coal is burnt with one mole of oxygen , it makes one mole of carbon dioxide. So burning 12 gm of coal in a minute (60s) would release how much heat?

Answer 1

Burning of coal is written as-

C + O2 -------------> CO2

i.e one mole of coal is burnt with one mole of oxygen , it makes one mole of carbon dioxide.

Now mass of Coal taken = 12g

Again coal = carbon = has an atomic mass or molecular mass = 12g per mole i.e molar mass of Coal = 12g/mole

Thus moles of Coal present in 12 g = mass/ molar mass

= 12g/ 12g/mole

= 1 mole

Thus burning 12 g of coal = 1 mole of coal can be written as-

C + O2 -------------> CO2

Here the heat released = enthalpy of reaction = ∆Hrxn = ∆H^o_fproduct - ∆Hreactant

   = ∆H^o_f(CO2) - ∆H^o_f(C) - ∆H^o_f(O2)

Putting the ∆H^o_f values from a reference table-

∆Hrxn = ∆H^o_f(CO2) - ∆H^o_f(C) - ∆H^o_f(O2)

= ∆H^o_f(-393.509) - ∆H^o_f(0) - ∆H^o_f(0) heat of formation for pure elements is Zero

= -393.509 kJ/mole

Thus burning 12 gm of coal in a minute (60s) would release 393.509 kJ heat