Calculate the mass of methane that must be burned to provide enough heat to convert 320.0 g of water at 46.0°C into steam at 122.0°C. (Assume that the H2O produced in the combustion reaction is steam rather than liquid water.)
Water is heated from 46 0C to 1220C
Energy needed to raise the temperature of 320 g water from
460C to 1000C, will be
Q = m*s*t
where Q is heat energy, m is the mass of water, s is the specific
heat (s for waster is 4.2 J/g 0C) and t is the
temperature difference.
=> Q = 320 * 4.2 * (100-46)
=> Q = 72576 J
Energy required to get water to turn to steam = Mass X Specific
latent heat of vaporization of water
= (320)(2260)
= 723200 J
Energy needed to get steam up to 122°C =
Q = m*s*t
= (320)(4.2)(22)
=29568 J
Total heat required = 72576 + 723200 + 29568 = 825344 J
for methane is 890 Kj/mol, Mol. Wt of methane is 16 g/mol
Heat produced per gram of methane = 890 / 16 = 55.625 kJ/g
So, mass of methane required = 825344 J /55.625 kJ/g = 14.84 g
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