Remembering 1 State what happens to the pressure as gas is heated inside a container. The pressure greatly increases as the gas inside the container expands and pushes against the sides of the container. 2 State the temperatures at which water expands and contracts in the way that is opposite to what other substances do. Between 4ºC and 0ºC. 3 State whether liquids expand more or less than solids when heated. Give a reason for your answer. Liquids expand and contract more than solids because their molecules are more loosely bonded. 4 List the following in order from least to greatest expansion when heated: concrete, Pyrex, brass, platinum. Pyrex Platinum Concrete Brass Understanding 5 Describe why particles in a substance take up more space when heated. Because as they heat the vibrate more and loosen the bonds between their molecules which makes them expand. 6 Describe what the particles in a gas are doing to cause pressure. They are vibrating and expanding at a high rate because there are barely any bonds between the molecules. 7 Describe what happens to the movement of the particles in a solid as it is heated. The molecules vibrate a lot and the bonds between the molecules weaken. 8 Explain why it is more important to have a constriction in a clinical thermometer than in a laboratory one. 9 Explain why invar is often used to make accurate technical instruments that are used in hot situations. Because it has minimal expansion. 10 Explain why a clinical thermometer is usually shaken after use. To allow it to return to it’s original state. Applying 11 Identify two uses of expanding liquids. To completely fill a container. For use in thermometers. 12 a. Identify two problems that expanding solids can cause. They can create cracks. In clocks they can make time inaccurate. b. Explain how each problem is overcome. By using solids that expand at the same rate. By using solids that expand minimally or at the same rate or both. 13 Draw a diagram to demonstrate how a bimetallic strip can be used in a light switch that is activated by the heat of your hand. Analysing 14 Use the expansion table on page 51 to assess which solid or solids expand: a. Most when heated Aluminum. b. Least when heated Invar c. The same as steel Concrete d. The same as platinum Glass e. Three times more than wood Glass and Platinum f. Four times more than Pyrex. Iron 15 An old-­‐fashioned incandescent light globe is made of glass with a platinum filament. a. Use the table on page 51 to state the expansion abilities of both glass and platinum Glass expands at a rate of 0.9 mm at 100ºC platinum also expands at a rate of 0.9 mm at 100ºC. b. Describe what you notice about their expansion abilities. They both expand at the same rate. c. Assess why the answer to part b is important. Because if they expanded at different rates the fuses would break. 16 Calculate by how much these materials would expand. N a. A 1 meter steel rod heated so that its temperature rises by 100°C 1.1 mm. b. A 1 meter plank of wood that increases in temperature by 1°C 0.003 mm c. A 2 meter block of concrete heated so that its temperature goes up by 10°C 0.22 mm d. A 50 centimeter iron rod that increases in temperature by 100°C. 0.6 mm 17 Assess which type of bimetallic strip would bend most when heated: one made of iron and brass, or one made of iron and aluminum? One of iron and aluminum. Evaluating 18 Propose a reason why you think mercury or coloured alcohol is used in thermometers instead of coloured water. Because mercury/coloured alcohol expand at a different rate and thermometers have been marked in certain places that will only work with mercury/coloured alcohol. 19 Propose a reason why bridges have small gaps at each end. To allow for the road’s expansion. 20 Some barbecue hotplates make sounds when they are first heated or begin to cool down. Propose what causes these sounds. Perhaps it is the sound of the hotplates expansion.