2. Gas laws. The Boyle-Mariotte law In the 17th centur y, Robert Boyle in England and Edme Mariotte in France studied the variations in the pressure of a gas when the volume of the container changed and the temperature remained constant. We can perform similar experiments, applying the scientific method . Experiment ⇒ Use a thermostatic bath and set the temperature to TA. • Move the piston to set the volume to V1. • On the manometer, read the value of the pressure, p1. • Write down the values of V1 and p1 in a row in a table. • Repeat until there are several rows of data. ⇒ Change the temperature of the thermostatic bath to TB. • Repeat the steps to obtain another series of data. TA p1 TA p2 1 Data collection 15 12 9 6 3 15 30 p (atm) V (L) 0 0 TA < TB A Experiment A (constant TA) Experiment B (constant TB) V (L) p (atm) V (L) p (atm) 30 0.5 30 1 15 1.0 15 2 10 1.5 10 3 7.5 2.0 7.5 4 6.0 2.5 6.0 5 5.0 3.0 5.0 6 3.0 5.0 3.0 10 2 Table Graph dependent variable dependent variable independent variable independent variable Data analysis ⇒ The greater the volume, the lower the pressure, and vice versa. ⇒ In each row, the product of p × V remains constant. Its value depends on the temperature. ⇒ The pressure-volume graph is a hyperbola. ⇒ The curvature of the hyperbola depends on the temperature. 3 Conclusion ⇒ Pressure and volume are inversely proportional quantities. 4 4 Why does a plastic bottle get crushed during a plane landing? p × V = constant p1 × V1 = p2 × V2 The Boyle-Mariotte law When a gas experiences transformations at a constant temperature, the product of the pressure it exerts and the volume it occupies remains constant. CHALLENGE V1 V2 B 12
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