When a vehicle is parked in the sunlight on a hot summer day, the temperature inside can approach 55 deg C. one company has patented a non-CFC propelled aerosol that can be sprayed inside a vehicle to reduce the temperature to 25 deg C within seconds. the spray contains a mixture of 2 liquids, 10% ethanol and 90% water by mass.
1) Use thermochemical equations and the corresponding enthalpy changes to explain how the spray works (note-this is not a chemical reaction).
2)1g of the aerosol is sprayed into a hot vehicle. how much heat can be absorbed due to vaporization of the aerosol?
Note: (delta)H-vaporization of water is 44.0kJ/mol and (delta)H-vaporization of ethanol is 38.56 kJ/mol
Any amount of help would be very much appreciated.
1) To explain how the spray works, we need to consider the process of vaporization. Vaporization is the phase transition from a liquid to a gas and requires energy input, typically in the form of heat.
In this case, the spray contains a mixture of 10% ethanol and 90% water by mass. When the spray is released inside the hot vehicle, the heat from the surroundings is transferred to the aerosol particles. The ethanol and water in the aerosol absorb this heat and undergo vaporization.
The enthalpy change (ΔH) for vaporization of water is given as 44.0 kJ/mol, while the enthalpy change for vaporization of ethanol is 38.56 kJ/mol. The enthalpy change represents the heat absorbed or released during the phase transition.
When the ethanol and water evaporate, they absorb heat from the surrounding environment, thus cooling it down. This is because the heat energy is used to break the intermolecular bonds and overcome the attractive forces between the liquid particles. As a result, the temperature inside the vehicle decreases rapidly, reaching 25°C within seconds.
It's important to note that while the spray does not involve a chemical reaction, the heat required for the vaporization process is still obtained from the surroundings, resulting in a cooling effect.
2) Now, let's calculate the amount of heat that can be absorbed due to the vaporization of 1g of the aerosol.
First, we need to determine the amount of ethanol (in grams) and water (in grams) present in the aerosol.
Ethanol:
10% of 1g = 0.1g
Water:
90% of 1g = 0.9g
Next, we need to convert the mass of ethanol and water to moles using their molar masses.
Molar mass of ethanol (C2H5OH) = 46.07 g/mol
Molar mass of water (H2O) = 18.02 g/mol
Ethanol moles:
0.1g / 46.07 g/mol = 0.00217 mol
Water moles:
0.9g / 18.02 g/mol = 0.04994 mol
Now, we can calculate the total heat absorbed due to vaporization:
Heat absorbed = (moles of ethanol × ΔHvap of ethanol) + (moles of water × ΔHvap of water)
Heat absorbed = (0.00217 mol × 38.56 kJ/mol) + (0.04994 mol × 44.0 kJ/mol)
Heat absorbed ≈ 0.0837 kJ + 2.1976 kJ
Heat absorbed ≈ 2.2813 kJ
Therefore, approximately 2.2813 kJ of heat can be absorbed due to the vaporization of 1g of the aerosol.