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Heat

Heat. Temperature and Thermal Equilibrium. Defining Temperature. Adding or removing energy usually changes temperature When you touch an object and it feels hot, energy is leaving the object and flowing into you

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Heat

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  1. Heat Temperature and Thermal Equilibrium

  2. Defining Temperature • Adding or removing energy usually changes temperature • When you touch an object and it feels hot, energy is leaving the object and flowing into you • When you touch an object and it feels cold, energy is leaving you and flowing into the object

  3. Defining Temperature • Temperature is proportional to the kinetic energy of the atoms and molecules • The more energy the particles have, the higher the temperature • For monatomic gases (O2, H2, etc), the only energy we’re concerned with is translational kinetic energy • For other substances, the particles could rotate or vibrate, so they also have rotational kinetic energy and vibrational kinetic and potential energies

  4. Defining Temperature • Internal energy - the energies associated with atomic motion • Symbolized by U • Change in internal energy is symbolized by ΔU • For ideal gases, internal energy depends only on temperature • Other factors are involved for other substances

  5. Defining Temperature • Temperature is only meaningful when it is stable • Thermal equilibrium – the state in which two bodies in physical contact with each other have identical temperatures • No net energy exchange • Basis for using a thermometer • Matter expands as temperature increases • Thermal expansion

  6. Defining Temperature • Coefficient of volume expansion – indicator the ability of a substance to change volume as temperature expands • Highest for gases; lowest for solids • Most things contract as they get colder • Water is unique • At temperatures around freezing (4 to 0°C), water expands • Explains why ice floats, and canned beverages explode in the freezer

  7. Measuring Temperature • Thermometers use some property that changes as temperature changes • Mercury and alcohol expand as temperature rises, so their volumes increase • Must be calibrated at a fixed temperature • Usually at thermal equilibrium in a mixture of ice and water (called the ice point, 0°C) and at a mixture of steam and water (called the steam point, 100°C) • Thermometer is then divided into evenly spaced degrees

  8. Measuring Temperature • Fahrenheit – uses freezing temperature of salt water as 0 • Fresh water freezes at 32oF • Water boils at 212oF • Celsius – uses freezing temperature of water as 0 • Water boils at 100oC

  9. Measuring Temperature • Celsius-Fahrenheit Conversion • Fahrenheit temperature = (9/5*Celsius temperature)+32.0 • TF=9/5TC+32.0 • Fahrenheit-Celsius Conversion • Celsius temperature = 5/9(Fahrenheit temperature-32.0) • TC=5/9(TF-32.0)

  10. Measuring Temperature • Kelvin – uses absolute zero • Absolute zero – the temperature at which an object’s energy is minimal • Has never been reached • The lowest recorded temperature is .000001 K • Water freezes at 273.15K • Water boils at 373.15K • Celsius-Kelvin Conversion • Kelvin temperature = Celsius temperature + 273.15 • T=TC+273.15

  11. Measuring Temperature

  12. Measuring Temperature

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