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Dive into the intricacies of heat, temperature, and thermal equilibrium. Learn about defining temperature, measuring it accurately with various scales, and exploring the concept of thermal expansion.
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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 • When you touch an object and it feels cold, energy is leaving you and flowing into the object
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
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
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
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
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
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
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)
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
