Calculating the Pressure Inside a Can of Hair Spray Using Freon-12

The Role of Freon-12 in Spray Cans

Prior to the discovery that freon-12 (CF₂Cl₂) was harmful to the Earth’s ozone layer, it was frequently used as the dispersing agent in spray cans for products like hair spray. Its enthalpy of vaporization at its normal boiling point of -29.2°C is 20.25 kJ mol^-1.

Estimating the Pressure Inside the Can

To estimate the pressure inside a can of hair spray using freon-12 at 40°C, the temperature of a can that has been standing in sunlight, we can use the Clausius-Clapeyron equation. Since the enthalpy of vaporization doesn't change with temperature, we can calculate the pressure based on the given data.

Calculations and Answer

At the normal boiling point, the vapor pressure of freon-12 is equal to atmospheric pressure, which is 1 atm. By using the Clausius-Clapeyron equation:

ln(p₂/1) = (ΔH_vap/R) * (1/T₁ - 1/T₂)

Substituting the values:

ln(p₂/1) = (20250/8.3145) * (1/243.8 - 1/313)

ln(p₂/1) = 2435.50424 * 9.068x10^-4

ln(p₂) = 2.2086

p₂ = e^2.2086

p₂ ≈ 9.10 atm

Is it important to consider the environmental impact of substances like freon-12 when used in consumer products?

Yes, it is crucial to consider the environmental impact of substances like freon-12 as they can have harmful effects on the Earth's ozone layer, contributing to issues such as ozone depletion and climate change.