Others say that the balloon was 23 metres high and 14 metres wide. Calculate the temperature of the air in the balloon (in degrees Celsius) for this situation as well. (Assume the balloon to be spherical, and then elongated by a factor 23/14 in height).

1 answer

To calculate the temperature of the air in the balloon using the given dimensions, we first need to find the volume of the balloon, assuming it is a sphere elongated by a factor of 23/14 in height.

  1. Determine the dimensions:

    • Height (h) = 23 meters
    • Width (diameter) (d) = 14 meters, therefore the radius (r) = d/2 = 14/2 = 7 meters.
  2. Calculate the volume of the balloon: Since the balloon can be approximated to an ellipsoid due to its elongated shape, the volume \( V \) of an ellipsoid is given by the formula:

    \[ V = \frac{4}{3} \pi a b c \]

    where \( a \), \( b \), and \( c \) are the semi-principal axes of the ellipsoid.

    For our case:

    • The height (along the vertical axis) \( c \) is half of 23 meters, which is \( c = \frac{23}{2} = 11.5 \) meters.
    • The same radius applies for the width (along both horizontal axes), so:
      • \( a = b = 7 \) meters.

    Substituting the values into the volume formula: \[ V = \frac{4}{3} \pi (7)(7)(11.5) \]

    Calculate:

    \[ V = \frac{4}{3} \pi (49)(11.5) \approx \frac{4}{3} \pi (563.5) \approx 2362.35 \text{ cubic meters (approximately)} \]

  3. Using the Ideal Gas Law to find temperature: The ideal gas law is given by: \[ PV = nRT \] where \( P \) is the pressure, \( V \) is the volume, \( n \) is the number of moles of gas, \( R \) is the ideal gas constant (approximately \( 8.314 , \text{J/(mol K)} \)), and \( T \) is the temperature in Kelvin.

    To find the temperature \( T \): \[ T = \frac{PV}{nR} \]

    We need the pressure \( P \) and the number of moles \( n \) of air in the balloon. Assuming standard atmospheric pressure \( P \approx 101325 , \text{Pa} \) and that air is approximately \( 1 \text{ mole/L} \approx 0.001 \text{ m}^3 \), we can first approximate the number of moles.

    • The density of air is about \( 1.225 , \text{kg/m}^3\), and the molar mass of air is about \( 28.97 , \text{g/mol} \approx 0.02897 \text{ kg/mol} \).

    Let's find the mass of air: \[ m = \text{density} \times \text{volume} = 1.225 , \text{kg/m}^3 \times 2362.35 , \text{m}^3 \approx 2893.98 , \text{kg} \]

    Now, calculating the number of moles \( n \): \[ n = \frac{m}{\text{molar mass}} = \frac{2893.98 , \text{kg}}{0.02897 , \text{kg/mol}} \approx 99996.67 , \text{moles} \]

  4. Now substitute into the ideal gas law: Given \( P = 101325 , \text{Pa} \), \( V \approx 2362.35 , \text{m}^3 \), and we already calculated \( n \):

    \( R \) is approximately \( 8.314 , \text{J/(mol K)} \) (use proper units),

    \[ T = \frac{PV}{nR} = \frac{101325 \times 2362.35}{99996.67 \times 8.314} \]

    Calculate \( T \): \[ T \approx \frac{239317128.75}{833680.82} \approx 286.56 , \text{K} \]

  5. Convert Kelvin to Celsius: \[ T_{\text{Celsius}} = T_{\text{Kelvin}} - 273.15 \approx 286.56 - 273.15 \approx 13.41 , \text{°C} \]

Thus, the temperature of the air in the balloon is approximately \( 13.41 , \text{°C} \).