A diver checks a compressed-air cylinder before a training session. Fig. 1 shows the cylinder fitted with a pressure gauge and valve. The cylinder volume is...
Question 1 Report
A diver checks a compressed-air cylinder before a training session. Fig. 1 shows the cylinder fitted with a pressure gauge and valve. The cylinder volume is 12.0 litres and the gauge reads 200 bar at 20 degrees C. During a hot journey, the cylinder is left in sunlight. The diver does not open the valve, so the mass and volume of gas remain constant.
(a) State what happens to the gas pressure if the cylinder becomes hotter. [1]
(b) Explain this change using the particle model of a gas. [3]
(c) Calculate the temperature in kelvin when the temperature is 20 degrees C. [1]
(d) Calculate the pressure at 50 degrees C, assuming pressure is proportional to absolute temperature. [4]
(e) Describe why the gauge is checked before the diver enters water. [2]
(f) State one reason why the cylinder is made from thick metal rather than thin plastic. [1]
Answer Details
(a) The gas pressure increases if the cylinder becomes hotter. [1]
(b) Gas molecules gain kinetic energy and move faster. They collide with the cylinder walls more frequently and each collision has a greater force. The greater force per unit area means greater pressure. [3]
(c)
\[20\degree\text{C}+273=293\text{ K}\]
Temperature = \(293\text{ K}\). [1]
(d) Temperature must be in kelvin:
\[50\degree\text{C}+273=323\text{ K}\]
At constant volume, \(p\) is proportional to \(T\):
\[p_2=200\times\frac{323}{293}=220.5\ldots\text{ bar}\]
Pressure \(\approx220\text{ bar}\). [4]
(e) Checking the gauge confirms that there is sufficient gas for the dive and can identify unsafe low pressure or a leak. It helps the diver plan the dive safely. [2]
(f) Thick metal is used to withstand the very large internal pressure and prevent rupture. [1]
Download The App On Google Playstore
Everything you need to excel in your exams
