Thermal Energy Conduction Thermal energy is transferred between
Thermal Energy
Conduction • Thermal energy is transferred between objects in three ways. • One type of thermal energy transfer is called conduction. • Heat flow happens between objects in direct contact with each other which have different temperatures. • The result of uninterrupted heat transfer from high-temperature objects to lower-temperature ones is thermal equilibrium, which occurs when the two objects have reached the same temperature.
Conduction • When you touch a container of boiling water, your hand will feel extremely hot. Duh, ya think? • The reason for this is that heat flows from the boiled water to the container, and then from the container to your hand, to approach thermal equilibrium.
Convection • Convection is another type of heat transfer. • It occurs when groups of molecules at different temperatures within a fluid, either gas or liquid, flow between different areas of the fluid. • The mixture of groups of molecules with different temperatures yields convection. • When a person drives their car in the summer without turning on the air conditioner, they may want to open the windows to cool the vehicle’s interior.
Radiation • Another important type of heat transfer is radiation. • Radiation occurs from the random movements of atoms and molecules in substances, which generate electromagnetic waves. • Thermal radiation has the ability to transmit in a vacuum. • This is why solar energy can travel through outer space, which has no air.
Thermal Equilibrium • It is a natural process that thermal energy moves toward thermal equilibrium, indicated when the temperature between two objects becomes the same. • Heat always flows from warmer objects to cooler ones. • For instance, an ice cube in the open air melts into water. • This tells us that it absorbs heat from the surroundings. • The temperature of the ice cube increases, and the temperature of the cube’s surroundings decreases. • Equal temperatures are achieved when this process ends.
Thermal Properties • Different objects have different thermal properties. • Objects that do not easily transfer thermal energy are called insulators. • Wood, for example, is commonly used as an insulator. • Thick paper, which contains wood fibers, can also be applied as an insulator. • Objects that can transfer thermal energy easily are called conductors. • Metals are usually good thermal conductors.
Amount of Heat Absorbed or Released • As heat is added to a substance, the kinetic energy increases. • As kinetic energy increases, motion increases eventually breaking intermolecular attractions causing a state of matter change. • When a substance is going through a phase change, the temperature is held constant. • For instance, the melting point of salt (sodium chloride) is 801°C.
Amount of Heat Absorbed or Released • We can take a piece of solid Na. Cl and heat to reach its melting point. • The temperature will stay the same the entire time as long as there is still solid. • This is because the energy is being used to break the intermolecular attractions instead of raising the temperature. • Once these intermolecular attractions are broken and solid Na. Cl has turned into molten Na. Cl, the temperature can increase again.
Cooling Curves • A cooling curve is similar to a heating curve except the temperature is being lowered versus rising temperature. • During a cooling curve, kinetic energy and particle motion decrease as temperature decreases. • Conversely, this shows a slope when temperature is dropping and a plateau when the substance is in a phase change indicating that the temperature is constant. • The phase changes that these cooling curves display are condensing points and freezing points.
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