Question

What mass of natural gas CH4 must you burn to emit 270 kJ of heat?

Answer 1

Equation representing the combustion of CH CH4(g) 202(8)CO2(8) + 2H2O(g) kJ = | (1 mol) -393.5 + 2 mol)1-24 1.8 mol mol kJ (1 mol) -74.31 (2 mol) mol - - 802.3 kJ According to the equation, 802.3 kJ of heat is transferred when 1 mole of CH, is burned. Molar mass of CH4 - 16.04 g/mol Mass of CH, burned 16.04 g CH4 = 270 ķ.x 802.3 5.40 g CH4 Therefore, amount of CH4 burned to emit 270 kJ ofheat is 5.40 g.

Answer 2

The combustion of methane gas is represented by
CH₄ (g) + 2 O₂ (g) ------> CO₂ (g) + 2 H₂O (g)

The calculation for the heat of combustion for methane is then:

heat of combustion = [heat of formation of CO₂ (g) + 2 x heat of formation of H₂O (g)] - [heat of formation of CH₄ (g) + 2 x heat of formation of O₂ (g)]
   = [ -393.5 kJ + 2x(-241.8 kJ)] - [-74.8 kJ + 2x(0 kJ)]
   = - 802.3 kJ

So, the heat of combustion is - 802.3 kJ per mole of methane.

Using stoichiometric relations, we can now solve for the amount of CH₄ needed to produce 270 kJ heat. (The value is -270 kJ because heat was RELEASED.)

-270 kJ x = 5.40 g CH₄

Answer 3

CH4 + 2O2 -----> CO2 + 2H2O 1 mol CH4 emits 802.3 kJ 270 kJ x (1 mol / 802.3 kJ) = 0.336 mol CH4 0.336 mol CH4 x (16.0 g / 1 mol) = 5.376 g CH4