Compilation
Heat: a form of energy
Heat
In physics and chemistry, heat is energy transferred from one body to another by thermal interactions.[1][2] The transfer of energy can occur in a variety of ways, among them conduction,[3] radiation,[4] and convection. Heat is not a property of a system or body, but instead is always associated with a process of some kind, and is synonymous with heat flow and heat transfer.
Heat flow from hotter to colder systems occurs spontaneously, and is always accompanied by an increase in entropy. In a heat engine, internal energyof bodies is harnessed to provide useful work. The second law of thermodynamics prohibits heat flow directly from cold to hot systems, but with the aid of a heat pump external work can be used to transport internal energy indirectly from a cold to a hot body.
Transfers of energy as heat are macroscopic processes. The origin and properties of heat can be understood through the statistical mechanics of microscopic constituents such as molecules and photons. For instance, heat flow can occur when the rapidly vibrating molecules in a high temperature body transfer some of their energy (by direct contact, radiation exchange, or other mechanisms) to the more slowly vibrating molecules in a lower temperature body.
Example:
1:It takes 487.5 J to heat 25 grams of copper from 25 °C to 75 °C. What is the specific heat in Joules/g·°C?
2: What is the heat in Joules required to melt 25 grams of ice? What is the heat in calories?
Useful information: heat of fusion of water = 334 J/g = 80 cal/g
Solution:
1: Use the formula
q = mcΔT
where q = heat energy m = mass c = specific heat
ΔT = change in temperature
487.5 J = (25 g)c(75 °C - 25 °C)
487.5 J = (25 g)c(50 °C)
Solve for c:
c = 487.5 J/(25g)(50 °C) c = 0.39 J/g·°C
Answer:
The specific heat of copper is 0.39 J/g·°C.
2: Use the formula
q = m·ΔHf
where q = heat energy m = mass
ΔHf = heat of fusion
q = (25 g)x(334 J/g) q = 8350 J
Heat
In physics and chemistry, heat is energy transferred from one body to another by thermal interactions.[1][2] The transfer of energy can occur in a variety of ways, among them conduction,[3] radiation,[4] and convection. Heat is not a property of a system or body, but instead is always associated with a process of some kind, and is synonymous with heat flow and heat transfer.
Heat flow from hotter to colder systems occurs spontaneously, and is always accompanied by an increase in entropy. In a heat engine, internal energyof bodies is harnessed to provide useful work. The second law of thermodynamics prohibits heat flow directly from cold to hot systems, but with the aid of a heat pump external work can be used to transport internal energy indirectly from a cold to a hot body.
Transfers of energy as heat are macroscopic processes. The origin and properties of heat can be understood through the statistical mechanics of microscopic constituents such as molecules and photons. For instance, heat flow can occur when the rapidly vibrating molecules in a high temperature body transfer some of their energy (by direct contact, radiation exchange, or other mechanisms) to the more slowly vibrating molecules in a lower temperature body.
Example:
1:It takes 487.5 J to heat 25 grams of copper from 25 °C to 75 °C. What is the specific heat in Joules/g·°C?
2: What is the heat in Joules required to melt 25 grams of ice? What is the heat in calories?
Useful information: heat of fusion of water = 334 J/g = 80 cal/g
Solution:
1: Use the formula
q = mcΔT
where q = heat energy m = mass c = specific heat
ΔT = change in temperature
487.5 J = (25 g)c(75 °C - 25 °C)
487.5 J = (25 g)c(50 °C)
Solve for c:
c = 487.5 J/(25g)(50 °C) c = 0.39 J/g·°C
Answer:
The specific heat of copper is 0.39 J/g·°C.
2: Use the formula
q = m·ΔHf
where q = heat energy m = mass
ΔHf = heat of fusion
q = (25 g)x(334 J/g) q = 8350 J