1 Can spray paints explode? Spray cans contain gas at a high pressure (between 2 and 8 atm) that helps to get the contents out. These cans are metal containers, so the gas is at a constant volume. If they are placed near a heat source, the gas heats up and its pressure increases (Gay-Lussac’s law). The pressure can be so high that the walls of the can cannot support it and it explodes. If a can of spray paint is thrown into a fire, it can explode! SOLVED PROBLEM 3 When a 500 mL can of spray paint is empty, the gas inside exerts a pressure of 1 atm at room temperature, which is 20 °C. If it is placed near fire, it can reach 800 °C. What pressure will the gas exert at that time? 1. Write down the two states of the gas with their quantities. p1 = 1 atm V1 = 500 mL T1 = 20 °C p2 = ? V2 = 500 mL T2 = 800 ºC 2. Identify the law to apply. For a transformation when V = constant, apply Gay-Lussac’s law. p T p T 1 1 2 2 = 3. M ake p2 the subject. p T p T p T p T p T T p 1 1 2 2 1 2 2 1 2 2 1 1 = → ⋅ = ⋅ → = ⋅ 4. Before substituting the data, write all the amounts of each quantity in the same units. The temperature must be in kelvin: T1 (K) = T1 (°C) + 273 = 20 °C + 273 = 293 K T2 (K) = T2 (°C) + 273 = 800 °C + 273 = 1073 K Apply Gay-Lussac’s law: p T T p 2 2 1 1 = = = ⋅ ⋅ 1073 K 293 K 1 atm 3.7 atm 8 A 700 cm3 rigid container was filled with nitrogen gas. The manometer indicated a pressure of 100 kPa at 25 °C. What temperature will the gas be if the manometer indicates a pressure of 5 atm? 10 The manometer on a 100 L cylinder indicates that the gas inside it exerts a pressure of 1 atm at room temperature (20 °C). What pressure will it exert when its temperature reaches 130 ºC? 9 Pressure cookers cook food faster and with less water. At the high pressure inside, water boils at over 100 °C. Look at the diagram and answer: a) What type of matter is in the space above the fill limit line? What state is it in? b) Why does it have an airtight lid? c) Explain the function of the vent pipe and the safety valve. What could happen if it didn’t have them? d) It is necessary to check that the valves are not blocked, due to the risk of explosion. Use Gay-Lussac’s law to explain why it could explode. A C T I V I T I E S Vent pipe (releases steam when the pressure reaches the limit) Safety valve Airtight lid Fill limit line T R U E OR FALSE ? 15
RkJQdWJsaXNoZXIy