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- - 47. Consider the combustion of propane: C,Hg(s) + 502(8) → 3C02(g) + 4H20(1) AH = -2221 kJ Assume that all the heat in Example 6.3 comes from the com- bustion of propune. What mass of propane must be burned to furnish this amount of energy assuming the heat transfer pro- cess is 60.% efficient?
OW Interactive Example 6.3 Internal Energy, Heat, and Work A balloon is being inflated to its full extent by heating the air inside it. In the final stages of this process, the volume of the balloon changes from 4.00 x 10L to 4.50 X 10L by the addition of 1.3 X 10% of energy as heat. Assuming that the nodallart on Iis page is O Cengage learning 2014
proce Chapter 6 Thermochemistry balloon expands against a constant pressure of 1.0 arm, calculate AE for the (To convert between Latin and J, use I L • atm = 101.31.) Solution Where are we going? To calculate AE Whar do we know? > V, = 4.00 x 10L > a = +1.3 X 10%) > P = 1.0 atm > IL atm = 101.3 J > V, = 4.50 X 10L What do we need? ► AE = q +w How do we get there? What is the work done on the gas? w = -PAV What is AV? Carlos Cano Shutterstock.com burner is used to heat the air balloon. AV = V, - v. = 4.50 X 10^L – 4.00 x 10ʻL = 5.0 x 105L What is the work? w = -PAV = -1.0 atm x 5.0 x 10ʻL = -5.0 x 10ʻL• atm The negative sign makes sense because the gas is expanding and doing work on the units of J and w is given in units of L - atm, we must change the work to units of joules: surroundings. To calculate AE, we must sum q and w. However, since q is given in w = -5.0 X 10 Leatmx = -5.1 X 10') 101.3J atm Then AE = + w = (+1.3 X 10) + (-5.1 x 10']) = 8 X 10') Reality Check | Since more energy is added through heating than the gas expends do- ing work, there is a net increase in the internal energy of the gas in the balloon. Hence AE is positive.