Heating and Cooling Concepts

A spark from a firework does not contain much heat energy even though it may be very hot. A cup of tea, even though it may not be very hot, can still burn your tongue because it contains a lot of heat energy.

Heat is the transfer of energy from a higher temperature object to a lower temperature object. Units of heat energy are called joules (J) or kilojoules (kJ).

Temperature is a measure of how hot or cold something is, measured in degrees Celsius (°C) with a thermometer.

<p>As temperature increases, the particles inside a substance gain more energy, causing them to move faster and more vigorously.</p> Signup and view all the answers

<p>Absolute zero is the temperature at which the particles of a substance stop moving, which is -273°C or 0 Kelvin.</p> Signup and view all the answers

<p>The Kelvin scale is a temperature scale starting at absolute zero (-273°C) and uses the same degree size as the Celsius scale.</p> Signup and view all the answers

<p>As a liquid is heated, its particles gain energy and move faster, allowing them to roll over each other more easily.</p> Signup and view all the answers

<p>a liquid to a gas = Evaporation a solid to a liquid = Melting a gas to a liquid = Condensation a liquid to a solid = Freezing</p> Signup and view all the answers

<p>The heat energy comes from the surroundings, including the air, the work surface, and any other objects in contact with the ice cube.</p> Signup and view all the answers

<p>Metals are the best conductors of heat because they allow heat to travel through them easily.</p> Signup and view all the answers

<p>An insulator is a material that is a poor conductor of heat. Examples of insulators include glass, plastics, and wood.</p> Signup and view all the answers

<p>When one end of a metal bar is heated, the heated particles gain thermal energy and vibrate faster. This vibration is transferred to neighboring particles, causing them to vibrate faster as well. This process continues along the bar, effectively conducting heat energy from the heated end to the other end.</p> Signup and view all the answers

<p>The base of a saucepan is made of metal because it is a good conductor of heat, enabling efficient transfer of heat from the cooker to the food inside the saucepan.</p> Signup and view all the answers

<p>The handle of a saucepan is made of plastic because it is a good insulator, preventing the handle from getting too hot and making it safe to hold.</p> Signup and view all the answers

<p>Polar bears have a thick coat of fur because fur is a good insulator, trapping a layer of warm air close to the skin and preventing heat loss from the bear's body.</p> Signup and view all the answers

<p>Birds fluff out their feathers in winter to trap more air within their feathers, creating a thicker insulating layer that prevents heat loss from their body.</p> Signup and view all the answers

<p>Liquids and gases can carry heat because their particles are free to move around, allowing for the transfer of heat energy through convection currents.</p> Signup and view all the answers

<p>A heater warms the air in a room by convection. The heater warms the air directly around it, making the air less dense. This warm air rises, and the cooler, denser air from elsewhere in the room replaces it, creating a continuous cycle of warm air rising and cool air replacing it. This process distributes heat throughout the entire room.</p> Signup and view all the answers

<p>A room with a high ceiling takes longer to heat because the warm air rises, and the volume of air to be heated is greater. This means that the convection current needs to travel a longer distance to distribute the heat throughout the room.</p> Signup and view all the answers

<p>Convection cannot happen in solids because the particles in a solid are fixed in a framework, preventing them from moving freely and creating convection currents.</p> Signup and view all the answers

<p>This heat travels as tiny electromagnetic waves called infrared waves. The hotter an object is, the more infrared radiation it emits. No particles are involved, unlike in the processes of conduction and convection, so radiation can even work through the vacuum of space. This is why we can still feel the heat of the Sun, although it is 150 million km away from the Earth.</p> Signup and view all the answers

<p>Some surfaces are better at emitting (giving off) thermal radiation than others. Good emitters of radiation are also good absorbers. White or silvery surfaces are poor absorbers because they reflect most of the radiation. That is why in hot, sunny countries houses are often painted white to keep them cool inside.</p> Signup and view all the answers

<p>A dark surface absorbs and emits more thermal radiation than a shiny surface.</p> Signup and view all the answers

<p>White or silvery surfaces are poor absorbers of thermal radiation, meaning they reflect most of the heat, preventing the house from absorbing too much thermal energy and keeping it cooler.</p> Signup and view all the answers

<p>Black surfaces absorb more heat than white surfaces. Therefore, the interior of a black car will heat up more quickly than a white car because it absorbs more of the Sun's thermal radiation.</p> Signup and view all the answers

<p>Aluminum foil is a good insulator, preventing heat loss from the food by reducing thermal radiation.</p> Signup and view all the answers

<p>Black surfaces are better absorbers of thermal radiation, allowing them to absorb more heat from the central heating system and release it more efficiently into the room.</p> Signup and view all the answers

<p>The vacuum flask was designed and invented by Scottish scientist Sir James Dewar in 1892, and the Thermos company was the first to mass-produce them for everyday use.</p> Signup and view all the answers

<p>A vacuum flask is designed to minimize heat transfer between the inside and outside of the flask. The vacuum between the walls prevents heat transfer by conduction and convection, while the reflective lining reduces heat transfer by radiation.</p> Signup and view all the answers

<p>The silver lining in a vacuum flask is a reflective surface that reduces heat transfer by radiation.</p> Signup and view all the answers

<p>The diagram shows the process of evaporation. Heat energy is being added to the liquid, causing the particles to gain kinetic energy and move faster. Some of the particles at the surface gain enough energy to break free from the liquid and become gas particles.</p> Signup and view all the answers

<p>Heat energy is needed to make evaporation happen.</p> Signup and view all the answers

<p>The energy for evaporation can come from various sources, such as a stove burner, sunlight, or even just the surrounding air.</p> Signup and view all the answers

<p>One example of evaporation in the home is when water boils in a kettle, where heat energy from the stove burner causes the water to evaporate into steam.</p> Signup and view all the answers

<p>The spark has little heat energy.</p> Signup and view all the answers

<p>joules</p> Signup and view all the answers

<p>heat coming from the Sun</p> Signup and view all the answers

<p>Molecules at the heated end move faster than at the other end.</p> Signup and view all the answers

<p>convection current</p> Signup and view all the answers

<p>True</p> Signup and view all the answers

<p>False</p> Signup and view all the answers

<p>True</p> Signup and view all the answers

<p>False</p> Signup and view all the answers

<p>When a solid melts, its particles gain enough energy to break free from their rigid framework and start moving more freely, allowing them to roll over each other.</p> Signup and view all the answers

<p>When a liquid evaporates, particles at the surface gain enough energy to break free from the liquid and become gas particles.</p> Signup and view all the answers

<p>At 0°C, ice melts and changes state from a solid to a liquid.</p> Signup and view all the answers

<p>At 100°C, water boils and changes state from a liquid to a gas, forming steam.</p> Signup and view all the answers

<p>The temperature of boiling water remains constant because all the added heat energy is being used to change the state of the water from liquid to gas, not to increase the temperature of the water itself.</p> Signup and view all the answers

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<p>a) The base of a saucepan is made of metal because metal is a good conductor of heat, allowing heat to transfer quickly from the stove to the food. b) The handle of a saucepan is made of plastic because plastic is a good insulator and will not get as hot as metal when the saucepan is placed on the stove. c) Polar bears have a thick coat of fur because fur traps air, which is a good insulator. This helps to keep the polar bear warm in cold climates. d) Birds fluff up their feathers in winter because the air trapped between the feathers acts as a good insulator, helping to keep the bird warm.</p> Signup and view all the answers

<p>Houses in hot countries are often painted white because white surfaces are poor absorbers of thermal radiation. This helps to keep the inside of the house cooler by reflecting much of the Sun's heat energy away.</p> Signup and view all the answers

<p>Black surfaces are better absorbers of heat than white surfaces. This means that a black car absorbs more heat from the Sun, causing the interior to warm up more quickly than a white car.</p> Signup and view all the answers

<p>Aluminium foil helps keep food warm because it is a good reflector of thermal radiation. It reflects heat back towards the food instead of allowing it to escape.</p> Signup and view all the answers

<p>Central heating radiators work better if they are painted black because black surfaces are better absorbers of heat than lighter surfaces. This means that a black radiator will absorb more heat from the hot water inside and transfer it more efficiently to the surrounding air.</p> Signup and view all the answers

<p>In the kinetic theory model of an evaporating liquid, the particles gain kinetic energy, allowing some of them to break free from the surface of the liquid and enter the gaseous state. The faster-moving particles at the surface have enough energy to overcome the attractive forces holding them in the liquid state.</p> Signup and view all the answers

<p>When a solid melts, the particles gain enough kinetic energy to break free from their fixed positions in the solid structure and begin to move more freely. They transition from a rigid, ordered arrangement to a more fluid, disordered arrangement.</p> Signup and view all the answers

<p>When a liquid evaporates, the particles gain even more kinetic energy than during melting. This allows them to break free from the surface of the liquid and become gas particles, moving freely and independently.</p> Signup and view all the answers