Question

Difficulty: MediumGas Laws and the Ideal Gas Equation

A high-altitude weather research probe contains 0.030 m30.030\text{ m}^3 of helium gas at a pressure of 1.00×105 Pa1.00 \times 10^5\text{ Pa} and a temperature of 27C27^\circ\text{C} at ground level. During ascent, the gas expands to a volume of 0.050 m30.050\text{ m}^3 while its temperature rises to 127C127^\circ\text{C}. Assuming the helium behaves as an ideal gas, what is the new pressure of the gas in the probe?

  1. A
    4.50×104 Pa4.50 \times 10^4\text{ Pa}
  2. 8.00×104 Pa8.00 \times 10^4\text{ Pa}Answer
  3. C
    2.22×105 Pa2.22 \times 10^5\text{ Pa}
  4. D
    2.82×105 Pa2.82 \times 10^5\text{ Pa}

Answer

The new pressure of the helium gas is 8.00×104 Pa8.00 \times 10^4\text{ Pa}.
Converting temperatures to absolute scale gives T1=300 KT_1 = 300\text{ K} and T2=400 KT_2 = 400\text{ K}. Rearranging the combined gas equation P1V1T1=P2V2T2\frac{P_1 V_1}{T_1} = \frac{P_2 V_2}{T_2} for final pressure P2P_2 yields P2=1.00×105×0.0300.050×400300=8.00×104 PaP_2 = 1.00 \times 10^5 \times \frac{0.030}{0.050} \times \frac{400}{300} = 8.00 \times 10^4\text{ Pa}.

Step-by-Step Solution

1
Convert temperatures from Celsius to Kelvin
T1=27+273=300 KT_1 = 27 + 273 = 300\text{ K} and T2=127+273=400 KT_2 = 127 + 273 = 400\text{ K}
Gas laws require absolute temperature in Kelvin to maintain proportional thermodynamic relationships.
2
Apply the combined gas law formula
P1V1T1=P2V2T2    P2=P1×V1V2×T2T1\frac{P_1 V_1}{T_1} = \frac{P_2 V_2}{T_2} \implies P_2 = P_1 \times \frac{V_1}{V_2} \times \frac{T_2}{T_1}
Mass of the gas is constant while pressure, volume, and temperature all change simultaneously.
3
Substitute given values and calculate final pressure
P2=1.00×105×0.0300.050×400300=8.00×104 PaP_2 = 1.00 \times 10^5 \times \frac{0.030}{0.050} \times \frac{400}{300} = 8.00 \times 10^4\text{ Pa}
Multiplying initial pressure by the volume contraction ratio (0.600.60) and temperature expansion ratio (1.3331.333) gives the new pressure.

Key Concept

Combined Gas Law
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