Question

Calculate the mass of methane that must be burned to provide enough heat to convert 347.0 g of water at 18.0°C into steam at 110.0°C.

(Assume that the H₂O produced in the combustion reaction is steam rather than liquid water.)

Answer 1

1)

mass of water = 347 g

to warm water at 36.0C to 100C = m x Cp water x (100 - 18)

                                                    = 347 x 4.18 x 82

                                                    = 118937 J

to turn water at 100 to steam at 100C = 347 x 10^-3 x heat of vaporisation

                                                              = 0.347 x 2264 kJ

                                                              = 785608 J

to warm steam at 100 to 110 C = 347 x Cp steam x (110 - 100) J

                                                  = 347 x 1.996 x 10

                                                  = 6926 J

total heat = 118937 + 785608 + 6926

                = 911.5 kJ

1 mol of methane can give 810 kJ/mol of heat

?? mol --------------          911.5 kJ heat

moles of methane = 1.125 moles

mass = moles x molar mass

          = 1.125 x 16

          = 18 g

mass of methane = 18 g