Question

Natural gas burns in air to form carbon dioxide and water, releasing heat. CH4(g)+2O2(g)→CO2(g)+2H2O(g) ΔHorxn = -802.3 kJ You may want to reference (Page 269) Section 6.6 while completing this problem.What minimum mass of CH4 is required to heat 85.0 g of water by 23.0 ∘C? (Assume 100% heating efficiency.) (For water,Cs= 4.18 J/g∘C).

Answer 1

CH4(g)+2O2(g)→CO2(g)+2H2O(g) ΔHorxn = -802.3 kJ

m   = 85g

cs = 4.18J/g-⁰C

$\Delta$T   = 23⁰c

q   = mc$\Delta$T

    = 85*4.18*23

    = 8171.9J

     = 8.1719KJ

The combustion energy of CH4 = 802.3Kj/mole

8.1719KJ/802.3Kj/mole = 0.010186 moles of CH4

mass of CH4 = no of moles * gram molar mass

                       = 0.010186*16   = 0.163g of CH4