HEAT and HEAT TRANSFER

1. HEAT and HEAT TRANSFER Investigation One

2. What is Heat? • The term used to describe the total of all the energy within a substance. • Heat is also known as thermal energy. • Includes both potential and kinetic energy • The flow of energy from warmer matter to cooler matter.

3. Matter • 3 states of matter • Solid, Liquid, and Gas • All are composed of molecules • Composed of one or more atoms • Vibrate and move within each state of matter • Molecules have Kinetic Energy because of their movement and Potential Energy because of the stored energy to break and reform bonds

4. Kinetic Energy • Energy is the ability to do work • Kinetic energy • The energy that an object has because of its motion. • The faster an object moves, the more kinetic energy it has.

5. Potential Energy • Potential energy is stored energy or energy that an object has due to its position. • Molecules in matter also experience forces that attract them to each other. • These forces are called bonds. • Because bonds require energy to form and break, molecules also have potential energy.

6. potential energy and kinetic energy relation to heat • Temperature is the measure of the average kinetic energy of molecules. • Increases or decreases in temperature reflect an increase or decrease in the kinetic energy of a solid, liquid or gas. • Higher temperature=more kinetic energy • Lower temperature=less kinetic energy

7. The Law of Conservation of Energy • States that energy can be neither created nor destroyed. • Changes in heat and kinetic energy of the molecules follow the Law of Conservation of Energy. • When substances have different kinetic energies come in contact with each other, kinetic energy is transferred from molecule to molecule.

8. The Law of Conservation of Energy • The direction of transfer is always the same. • Energy is transferred from areas of higher kinetic energy to areas of lower kinetic energy. • Heat is transferred from areas of higher heat to areas of lower heat.

9. Transfer of Thermal Energy • When a liquid is heated, the molecules begin to move faster. • As the kinetic energy of the molecules increases, the molecules not only move faster, but also farther apart from each other and the liquid expands. • Warmer= Expand

10. Transfer of Thermal Energy • When a liquid cools the kinetic energy of the molecules decrease • Molecules move slower with each vibration • There is smaller separation between individual molecules and the liquid contracts • Cool= Contract

11. Thermometer • An instrument that uses a substance that changes when it is heated or cooled. • Mercury • Alcohol • Oil • Uses a numerical scale • Fahrenheit and Celsius • Both use the boiling point and freezing point of water as their reference points

12. Boiling Point • The temperature at which a liquid becomes a gas. • Above boiling point the gaseous form of matter predominates • Below the boiling point the liquid form predominates • 212° F and 100° C boiling points of water

13. Freezing Point • The temperature at which a liquid becomes a solid. At the freezing point there are equivalent amounts of liquid and solid molecules • Above the freezing point the liquid form of the matter predominates • Below the freezing point the solid form of the matter predominates • 32°F and 0° C freezing points of water

14. Relationship between Heat, Kinetic Energy and Temperature • Heat is the transfer of thermal energy which includes both kinetic and potential energy • Temperature is a measure of the average kinetic energy of a substance or in an environment • When heat is transferred from areas of higher to lower heat, kinetic energy is transferred from areas of higher to lower kinetic energy

15. Relationship between Heat, Kinetic Energy and Temperature • The result if an increase in temperature in the area that once had the lower kinetic energy and decrease in temperature in the area that once had the higher kinetic energy • The transfer stops when both areas are equivalent

16. Changes in Matter accompany Changes in Heat • Matter expands when heated and contracts when cooled because of changes in the kinetic energy of molecules. • Changes in heat can also result in changes in the state or phases of matter because of changes in kinetic and potential energy of molecules

17. Heat and Heat Transfer Investigation 2

18. Kinetic Energy • Heat is transferred from areas of higher kinetic energy (higher temperature) to areas of lower kinetic energy (lower temperature). • Increases in the kinetic energy of the liquid molecules in the thermometer caused the liquid to expand and move up the glass column of the thermometer. • Decreases in the kinetic energy of the liquid molecules resulted in the contraction of the liquid and the of liquid moved down the column of the thermometer.

19. Kinetic Energy • In general, molecules within a gas move more quickly than the molecules of a liquid. • Molecules of a liquid move more quickly than the molecules in a solid. • Therefore… • The kinetic energy of the molecules of gas is higher than the kinetic energy of molecules of a liquid. • The kinetic energy of the molecules of a liquid is higher than the kinetic energy of the molecules in a solid.

20. Changes in Phase of Matter • The physical change from one state of matter to another is called a change of state or phase. • Occurs most often between the solid and liquid states, and between the liquid and gas states.

21. Changes of State • The state of a substance depends on the amount of thermal energy it possesses. • The more thermal energy a substance has, the faster its particles move. • Since gas has more thermal energy than a liquid, the particles of a gas move faster than the particles of the same substance in the liquid or solid state.

22. Changes of State • Matter will change from one state to another if thermal energy is absorbed or released. • As thermal energy increases, a substance changes from a solid to a liquid, and then to a gas. • A substance changes from a gas to a liquid and to a solid as thermal energy is removed from it.

23. Changes of State

24. Solid-Liquid Changes of State • Melting: The change of state from a solid to a liquid. • Occurs when a solid absorbs thermal energy. • As the thermal energy of the solid increases, the rigid structure of its particles begins to break down. • The particles become freer to mover around. • The temperature at which solid changes to a liquid is called the melting point.

25. Freezing • The change of state from a liquid to a solid is called freezing. • Freezing occurs when a substance loses thermal energy. • The temperature at which a substance changes from a liquid to a solid is called its freezing point. • For a given substance, the freezing point and the melting point are the same. • The only difference between the two is whether the substance is gaining or releasing thermal energy.

26. Liquid-Gas Change of State • Vaporization: The process by which matter changes from the liquid to the gas state. • During this process, particles in a liquid absorb thermal energy. • This causes the particles to move faster. • Eventually they move fast enough to escape the liquid as gas particles.

27. Evaporation • If vaporization takes place at the surface of a liquid, it called evaporation. • At higher temperatures, vaporization can occur below the surface of a liquid as well. This process is called boiling. • When a liquid boils, gas bubbles formed within the liquid rise to the surface. • The temperature at which a liquid boils is called its boiling point.

28. Condensation • A change from the gas state to the liquid state is called condensation. • You have seen beads of water appear on the outside of a cold drinking glass…why? • Water vapor that is present in the air loses thermal energy when it comes in contact with the cold glass. • When a gas loses a sufficient amount of thermal energy, it will change to a liquid.

29. Thermal Expansion • As the thermal energy of a substance increases, its particles spread out and the substance expands. • This is true even when the substance is not changing state. • The expanding of matter when it is heated is known as thermal expansion. • When a substance is cooled, thermal energy is released. • This means that the motion of the particles slows down and the particles move closer together. • So as a substance is cooled, it contracts or decreases in size.

30. Thermometers • In a common thermometer, a liquid such as mercury or alcohol is sealed within a glass tube. • As the liquid is heated, it expands and climbs up the tube. • As the liquid is cooled, it contracts and flows down the tube.

31. Changes in Thermal Energy Relate to Freezing and Boiling Points of Water • The boiling point of water represents the transfer of enough thermal energy to increase the kinetic energy of molecules and break bonds of molecules so that water changes from liquid to a gas • The freezing point of water represents the transfer of thermal energy such that kinetic energy of molecules and the formation of bonds between molecules results in the change of liquid water to solid ice

32. Adding a solute change the freezing and boiling point of water • Adding a solute to water decreases the freezing and boiling point of water and it increases its boiling point.

33. Heat and Heat Transfer Investigation 3

34. transferring of Heat • There are three ways that heat can move. • Heat is transferred by conduction, convection, and radiation. • The blacksmith who is making the horseshoes experiences all three.

35. Conduction • In the process of conduction, heat is transferred from one particle of matter to another without the movement of matter itself. • Example: A metal spoon in a pot water being heated on an electric stove. • The fast moving particles of the hot electric coil collide with the slow moving particles of the cool pot.

36. Conduction • Heat is transferred, causing the slower particles to move faster. • Then the particles of the pot collide with the particles at one end of the spoon. • As the particles move faster, the metal spoon becomes hotter. • This process of conduction is repeated all along the metal until the entire spoon becomes hot.

37. Convection • If you watch a pot of hot water on the stove, you will see the water moving. • Convection, is the movement that transfers heat with the water. • In convection, heat is transferred by the movement of currents within a fluid (a liquid or gas).

38. Convection • When the water at the bottom of the pot is heated, the particles move faster, and they also move farther apart. • As a result, the heated water becomes less dense. • The heated water rises and the surrounding cooler water flows into its place.

39. Convection Currents • This flow creates a circular motion known as a convection current. • For example, convection currents are used to transfer heated air throughout a building. • As the air near the baseboard heater is heated, it becomes less dense and rises. • When the warm air rises, the surrounding cool air flows into its place.

40. Radiation • Radiation is the transfer of energy by electromagnetic waves. • You can feel radiation from a bonfire or a heat lamp across a distance of several meters.

41. Radiation • There is an important difference between radiation and the processes of conduction and convection. • Radiation does not require matter to transfer thermal energy. • All of the sun’s energy that reaches Earth travels through millions of kilometers of empty space.

42. Heat Moves One Way • If two substances have different temperatures, heat will flow from the warmer object to the colder one. • When heat flows into a substance, the thermal energy of the substance increases. • As the thermal energy increases, its temperature increase. • At the same time, the temperature of the substance giving off heat decreases. • Heat will flow from one substance to another until the two substances have the same temperature.

43. Specific Heat • When an object is heated its temperature rises. • But the temperature does not rise at the same rate for all objects. • The amount of heat required to raise. • The temperature depends on the chemical makeup of the material. • Different materials need more or less heat to change their temperature by the same amount.

44. Specific Heat • Scientists have defined a quantity to measure the relationship between heat and temperature change. • The amount of energy required to raise the temperature of 1 kilogram of a substance by 1 Kelvin is called its specific heat. • The unit of measure for specific heat is joules per kilogram-kelvin. (J/kg·K)

45. Specific Heat of Common Substances

46. Specific Heat • Materials with a high specific heat can absorb a great deal of thermal energy without a great change in temperature. • The energy gained or lost by an object is related to the mass, change in temperature, and specific heat of the material. • You can calculate specific heat changes with the following formula: • Change in energy= Mass x Specific heat x change in temperature

47. How can the ability to absorb heat be measured as a specific physical property of matter • Specific heat capacity is a measure of the amount of heat energy (joules) required to raise the temperature of 1 gram of a substance by 1 degree centigrade. • Different substances require different amounts of energy in order to raise their temp by 1°C