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) The spray works based on the principle of evaporation. When the aerosol is sprayed inside the hot vehicle, the mixture of ethanol and water undergoes evaporation. Evaporation is a phase change process where a liquid turns into a gas by overcoming intermolecular forces.
To understand why the temperature decreases during evaporation, we need to consider the concept of enthalpy (ΔH). Enthalpy is the heat content of a system, and during evaporation, energy is required to break the intermolecular forces and convert the liquid into a gas. This energy is absorbed from the surrounding environment, resulting in a decrease in temperature.
The enthalpy change during the phase change process of vaporization can be calculated using the equation ΔH = n × ΔHvap, where ΔHvap is the enthalpy of vaporization and n is the number of moles of the substance undergoing vaporization.
In the spray, the main components are water and ethanol. Each component will contribute to the overall enthalpy change.
2) To calculate the heat absorbed due to the vaporization of the aerosol, we need to determine the number of moles of water and ethanol in 1g of the aerosol.
First, we need to convert the mass of water and ethanol to moles using their molar masses. The molar mass of water (H2O) is approximately 18.015 g/mol, and the molar mass of ethanol (C2H5OH) is approximately 46.07 g/mol.
For the water component:
1g of aerosol contains 90% water, so the mass of water is 0.9g.
The number of moles of water (nwater) can be calculated as:
nwater = mass of water / molar mass of water
For the ethanol component:
1g of aerosol contains 10% ethanol, so the mass of ethanol is 0.1g.
The number of moles of ethanol (nethanol) can be calculated as:
nethanol = mass of ethanol / molar mass of ethanol
Once we have the values for nwater and nethanol, we can calculate the total enthalpy change (ΔH) for the vaporization of the aerosol using the equation:
ΔH = (nwater × ΔHvap water) + (nethanol × ΔHvap ethanol)
Substituting the given values of ΔHvap water (44.0 kJ/mol) and ΔHvap ethanol (38.56 kJ/mol), along with the calculated values of nwater and nethanol, we can find the total heat absorbed due to vaporization.
By calculating this, we can determine how much heat is absorbed from the hot vehicle, resulting in a decrease in temperature.