When a vehicle is parked in the sunlight on a hot summer day, the temperature in

Question

When a vehicle is parked in the sunlight on a hot summer day, the temperature inside can approach 55 degree C. One company has patented a non-CFC propelled aerosol that can be sprayed insight a vehicle to reduce the temperature to 25 degree C within seconds. The spray contains a mixture of two liquids: 10% ethanol C_2H_5OH, and 90% water by mass. (a) Use thermochemical equations, and the corresponding enthalpy changes, to explain how the spray works. (b) 1.0 g of the aerosol is sprayed into a hot vehicle. How much heat (in kJ) can be absorbed due to vaporization of the aerosol? (c) Do you think there are any risks associated with using a spray like the one described above? Explain your answer.

Explanation / Answer

a) An aerosol is a mass of small droplets (mixture of water + ethanol) which will vaporize very quickly and in this process it absorbs heat from the atmosphere in the car hence cooling it.

Heat absorbed by the aerosol is = Mass of Ethanol x Hvap +Mass of water x Hvap.

This heat is provided by the air in the car = Mass x T x specific heat of air

Equation: C2H5OH + H2O = 2CO2 + 6H2

b)

In 1.0 g of the aerosol-

Mass of ethanol = 1.0 g x 10/100 = 0.1g

Mass of water = 1.0 g x 90/100 = 0.9g

Heat absorbed by the aerosol is = heat absorbed by ethanol + heat absorbed by water

Heat absorbed by ethanol –

C2H5OH + H2O = 2CO2 + 6H2

Moles ethanol = mass/molar mass = 0.1 g/44g/mol = 0.00227mol

So heat absorbed = moles of Ethanol x Hvap

    = 0.00227mol x 38.56kJ/mol = 0.0876KJ

Heat absorbed by water-

Moles water = mass/molar mass = 0.9/18 = 0.05 moles

So heat absorbed = moles of water x Hvap

    = 0.05 moles x 44 kJ/mol = 2.2 KJ

Heat absorbed by the aerosol = Heat absorbed by ethanol + Heat absorbed by water-

                                                     = 0.088 KJ + 2.2KJ =2.288KJ

c) There are many risks associated with using a spray like aerosol

i)Irritation of airways, coughing, and difficulty in breathing

ii) Inhaled ethanol vapor might affect your driving and cause you to fail a breathalyzer test.

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