Thermal Energy and Matter: Heat, Temperature, and Specific Heat
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Thermal Energy and Matter
Work and Heat
Heat is the transfer of thermal energy from one object to another because of a temperature difference. Heat flows spontaneously from hot objects to cold objects. Temperature is a measure of how hot or cold an object is compared to a reference point. On the Kelvin scale, absolute zero is defined as a temperature of 0 kelvins. As an object heats up, its particles move faster, on average. The average kinetic energy of the particles increases. One way that heat flows is by the transfer of energy in collisions. On average, high-energy particles lose energy. Low-energy particles gain energy.
Thermal Energy
Thermal energy is the total potential and kinetic energy of all the particles in an object and depends on the mass, temperature, and phase (solid, liquid, or gas) of an object.
Thermal Contraction and Expansion
Thermal expansion is an increase in the volume of a material due to a temperature increase. Thermal expansion occurs when particles of matter move farther apart as temperature increases.
Specific Heat and Temperature Change
Specific heat is the amount of heat needed to raise the temperature of one gram of a material by one degree Celsius. The lower a material’s specific heat, the more its temperature rises when a given amount of energy is absorbed by a given mass.
Example: When a car is heated by the sun, the temperature of the metal door increases more than the temperature of the plastic bumper. The iron in the door has a lower specific heat than the plastic in the bumper.
It takes 4.18 joules of energy to raise the temperature of 1.00 gram of water by 1.00 degree Celsius. How much energy is needed to heat 2.00 grams of water to the same temperature? Which material in the table has the highest specific heat? The lowest?
Material (at 100 kPa) | Specific heat (J/g°c) |
Water | 4.18 |
Plastic (polypropylene) | 1.84-2.09 |
Air | 1.01 |
Iron | 0.449 |
Silver | 0.2335 |
Q= Heat energy (J) M= Mass (g) C= Specific heat (J/g°c) T= Change in temperature (°c) tf-ti
Calorimeter
A calorimeter is an instrument used to measure changes in thermal energy. A calorimeter is used to measure specific heat. A sample is heated and placed in the calorimeter. The temperature change is observed.