Temperature Change - Types and Meanings

Temperature Change - Types and Meanings 1. a) Describe two things that humans do to warm up. Humans wear coats to keep warm. They also build fires to warm up. (b) Describe two things that animals other than humans do to warm up. Some animals such as lizards sit out in the sun on rocks to warm up. Other animals, like many birds, migrate to warmer areas in order to stay warm. 2. Briefly summarize the particle theory in your own words. The particle theory says that all matter is made of particles that are moving around. Particles have spaces between them and are attracted to each other. Particles move faster as they absorb more energy. 3. Complete the following table. 1. Table 1 Descriptions of Three States of Matter Solid Liquid Gas Volume constant fairly constant changing Shape definite takes shape of container takes shape of container Type of particle motion vibrating vibrate, rotate, move past each other vibrate, rotate, move past each other Spaces between particles small large small, but greater than in a solid 4. Use the particle theory to explain why gases expand more than liquids or solids when they are heated. Gas particles move so fast, bonds cannot form easily between individual particles. Fast-moving particles move greater distances, so when gases are heated their particles move even faster and the gas expands. 5. Write a definition of “heat,” using your own words. Heat is the transfer of thermal energy from a warmer object to a cooler object. 6. From what you have seen or read, list two examples each of: (a) thermal expansion in solids The metal in a bridge expands in the heat. So does the wood in a desk drawer. (b) thermal expansion in liquids Mercury in a thermometer expands when the temperature increases. As Earth’s temperature increases, the oceans expand. (c) thermal expansion in gases Overinflated car tires can burst when they expand. A balloon expands when the gas inside is heated. 7. (a) List five situations where heat plays a role in your daily life (for example, cooking an egg). I light a fire to cook food when camping. I wear heavy clothing to keep warm in the winter. I wear light clothing to keep from overheating in the summer. I heat solder to join metal in shop class. I blow on hot liquids to keep from burning myself while drinking. (b) Give three examples of state changes that you see happening in your daily life. Snow melting is an example of a change of state. So is steam forming when you take a shower. Ice cubes freezing are also an example of a change of state. 8. Solids expand slightly when heated. For this reason, bridges and railway tracks are built with expansion joints. Use the particle theory to explain what might happen on a hot day if expansion joints were not used. On a hot day, the extra thermal energy causes the particles in a solid to vibrate more quickly and expand. If there were no expansion joints then the heat would cause the swelling bridge to buckle and possibly break. 9. You are boiling vegetables on the stove and notice the lid of the pot moving up and down. Use the particle theory to explain what is happening. The heat from the stove causes water particles in the pot to absorb energy and turn into water vapour, or gas. As the gas gets hotter it expands and pushes the lid up, letting some of the water vapour escape. 10. (a) Many containers that hold food are made of glass sealed with a metal lid. These lids can be difficult to remove. Holding the lid of the jar under hot water for a short time makes the lid easier to remove. Explain why this works. When a metal lid is heated by the hot water, it expands faster than the glass jar. Even a slight expansion can loosen the lid’s grip on the jar. (b) An auto mechanic is having difficulty loosening the nut on a bolt using only a wrench and a pair of pliers. How can the mechanic use the ideas in this chapter to solve this problem? The mechanic should heat the nut. Just like the lid on a jar, the nut will expand enough to loosen its grip on the bolt, making it easier to remove with a wrench and pliers. 11. (a) Some people hang wet clothing out to dry on warm, sunny days. Why does wet clothing dry in this weather? Wet clothing dries because the water molecules in the clothing absorb the Sun’s energy. Eventually those water molecules absorb enough energy to heat up and evaporate as a gas. (b) Some people hang wet clothing out to dry even on freezing cold days. Will wet clothes dry in this weather? Yes, eventually the clothes will dry, although it could take a long time. As long as it is sunny, the water molecules will absorb the Sun’s energy and eventually turn from liquid to gas. (c) What would happen to juicy vegetables left on a plate in a freezer for a long time? How can this be prevented? Juicy vegetables will eventually become dried out because the water in them will be drawn to the surface and form ice crystals. The ice crystals will get bigger as water particles from inside the freezer attach themselves to the vegetables. The best way to prevent this is to put the vegetables in a plastic bag, which blocks the ice crystals from the surrounding air.