Answer to Question #141104 in General Chemistry for tanya

Question

Suppose a boil water notice is sent out advising all residents in the area to boil their water before drinking it or using it for cooking. You need to boil 15.0 L
of water using your natural gas (primarily methane) stove. What volume of natural gas is needed to boil the water if only 12.9%
of the heat generated goes towards heating the water. Assume the density of methane is 0.668 g/L
, the density of water is 1.00 g/mL
, and that the water has an initial temperature of 23.4 °C
. Enthalpy of formation values can be found in this table. Assume that gaseous water is formed in the combustion of methane.

Answer 1

Q=mc∆T=15000 x 4.186 x 76.6 = 4 809 714 J.

ΔH_cº_CH4 = (1*ΔH_fº_CO2 + 2*ΔH_fº_H2O) -(1*ΔH_fº_CH4 + 2*ΔH_fº_O2)

                                = (1*-394 kJ/mol + 2*-293 kJ/mol) – (1*-74.5 kJ/mol + 2*0kJ/mol)

                               =-905.5 kJ/mol

4 809 714 J./0.129 x 1000 = 37 284, 6047

37 284,6047/905.5= 41,1757092 moles of CH4.

16 x 41,1757092/0.668 = 986,244531 L.