Practical Investigation 2 Boyles Law 1.1 Aim: To investigate the - PowerPoint PPT Presentation

Practical Investigation 2 Boyle’s Law

1.1 Aim: To investigate the relationship between pressure and the volume of an enclosed gas at a constant temperature

1.2 Hypothesis: The greater the pressure of gas, the smaller (less) the volume of the gas.

2.3.1 What is the independent variable? Pressure

2.3.2 What is the dependent variable? Volume

3.1 Use the table to record the results. Also indicate the correct SI unit in each column. Pressure of Volume of pV �𝟒 gas (kPa) gas (cm 3 ) 80 43 0,023 3 440 90 37 0,027 3 330 100 33 0,030 3 300 110 30 0,033 3 300 120 27 0,037 3 240 130 24 0,042 3 120 140 22 0,045 3 080

3.2.1 Pressure versus volume Graph of pressure versus volume 250 Pressure (kPa) 200 150 100 50 10 20 30 40 50 0 Volume (cm 3 )

3.3 Now draw a graph of Pressure vs 1/Volume. Graph of pressure versus 1 / volume 250 Pressure (kPa) 200 150 100 50 0,01 0,02 0,03 0,04 0,05 0 1/volume (cm -3 )

4. Conclusion A graph of p versus V produces a hyperbolic curve, characterised by an inverse proportionality. Therefore, p is possibly inversely proportional to V. This is confirmed by drawing a graph of p versus 1 / . It produces a straight line through the origin, so p α 1 / , provided T is constant; so p = / , provided T is constant; so pV = k.

4. Conclusion The values in the table (column 4) also confirm that this product (pV) is a constant. The gradient of the straight line is given by: p ÷ 1 / = pV = k ≡ Pa × = N / × = N.m = J The product pV is therefore an indication of the internal energy of the gas particles. The temperature remained constant throughout, so the temperature was related to the internal kinetic energy, which also remained constant. The constant, k, is dependent on temperature.

At very high pressures, where the volume of the gas particles themselves have to be taken into account, i.e. if the gas in the apparatus is not completely dry, so that the water vapour liquefies, or if the gas in the apparatus itself liquefies, the graph will show the following deviation: Graph of pressure versus 1 / V 250 Pressure (kPa) 200 150 100 50 0,01 0,02 0,03 0,04 0,05 0 1/volume (cm -3 )

If the experiment is carried out at a higher temperature, the gradient of the graph will also be larger since the internal kinetic energy of the molecules are now also higher and the gradient, or k, related to the energy will also be larger.

5.1 The shape of graph 1 of pressure versus volume is a hyperbolic curve and thus the pressure is possibly inversely proportional to volume.

5.2 The shape of graph 2 of pressure versus the reciprocal of volume is a straight line through the origin. The pressure is thus inversely proportional to the volume of an enclosed gas.

5.3 Define Boyle's law… 5.3.1 in words The volume of an enclosed gas is inversely proportional to the pressure of the gas provided the temperature of the gas is constant.

5.3 Define Boyle's law… 5.3.2 in symbols p

5.4.1 Is the gradient of the graph p versus 1 / V constant? Yes

5.4.2 What quantity was kept constant during this experiment? Temperature

5.4.3 Determine by cancellation of units what the dimension (unit) of the gradient is. pV = k thus m 3 = N/m 2 m 3 = N.m = J. Pa

5.4.4 What does the gradient of graph 2 represent? Energy (Temperature)

5.5 Briefly explain what is meant by an “ideal gas”. 5.5.1 Particles are identical 5.5.2 Particles have no volume 5.5.3 Gas has a volume only due to motion of the particles 5.5.4 No attractive or repulsive forces between particles 5.5.5 Collisions are completely elastic

5.6 The product pV (remains constant / increases / decreases) when investigating the relationship between pressure and volume of an ideal gas.

5.7 Identify TWO causes of possible deviations from the ideal gas state that occur with non-ideal gases under high pressure and / or low temperature. At high pressure an actual gas will liquefy. At low temperatures, an actual gas will condense (liquefy).

5.8.2 Which of the gases N 2 , CO 2 , H 2 and He should show the most ideal behaviour? He – small atom and weak forces between atoms H 2 – small volume and weak intermolecular forces

5.10 Is the gas closest to ideal at high or low temperatures? High temperature

5.11 Why is it necessary to allow at least 3 minutes between readings? So that the temperature of the enclosed gas can return to room temperature each time.

5.16 Why should the temperature be measured in Kelvin ? The pressure of a gas is not zero at zero o C, but theoretically at 0 K.

5.17 What is meant by STP? (273 K) 0 o C and 101,3 kPa