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JAMB Physics 2019 Paper

Question : 71

Total: 100

^3

. Calculate the volume

Solution:

Concept:

Use the combined gas law since the amount of helium remains constant while pressure and temperature change.

Explanation:

Convert initial temperature to kelvin:

T_1 = 273^\circ\text{C} + 273 = 546\text{ K}

At STP,

T_2 = 273\text{ K}

and

P_2 = 76\text{ cmHg}

Given:

P_1 = 114\text{ cmHg}

V_1 = 2667\text{ cm}^3

Using

\dfrac{P_1V_1}{T_1} = \dfrac{P_2V_2}{T_2}

V_2 = V_1 \times \dfrac{P_1}{P_2} \times \dfrac{T_2}{T_1}

V_2 = 2667 \times \dfrac{114}{76} \times \dfrac{273}{546}

V_2 = 2667 \times 1.5 \times 0.5

V_2 = 2667 \times 0.75 = 2000.25\text{ cm}^3

The mass of helium is extra information and is not needed here.

Answer:

2000.25\text{ cm}^3

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