Question

1) A hot air balloon consists of a very large bag filled with heated air at 120.0 °C produced from a propane burner. It has a basket hanging under it in which several people can ride. The average hot air balloon has a volume of 2.80 × 103 m3 when fully inflated.
a) Determine the work (in kJ) needed to inflate the balloon under an external air pressure of 1.00 atm.

b) The specific heat of the air found in the balloon has a value of 0.9313 J g-1 °C-1. The hot air which contains some carbon dioxide and water vapour, products of the propane combustion, has an average molar mass of 32.0 g mol-1 at a pressure of 1.00 atm. If the initial temperature of the air was 25.0 °C, how much heat (in kJ) is required to warm the air up to 120.0 °C? (Assume ideal gas conditions)

c) The amount of energy released by the combustion of one mole of propane gas, C3H8(g), is 1995 kJ. What is the minimum mass (in kg) of propane needed to inflate the balloon with hot air to a temperature of 120.0 °C?
The answers are:
a) -2.84 x 10^5 kj
b) 2.46 x 10^5 kj heat is required or 3.23 x 10^5 heat is required (depending on temp used was 298.15K )
c) 11.7 kj or 13.4 kj depending on mass.

I don't understand how to get these answers, can you please explain!

Answer 1

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