Thermal Expansion and Specific Heat

Document Sample
Thermal Expansion and Specific Heat Powered By Docstoc
					Thermal Expansion and
    Specific Heat
     16-1 Continued
      Thermal Contraction and
            Expansion
• Thermal expansion
  – An increase in the volume of a material due to
    temperature increase

  – Particles move farther apart as temperature
    increases
• Example
  – Glass thermometer
          Heat Transfer
• Specific Heat (c)          Specific Heat Values
  – amount of energy               (J/(kg·K))
    required to raise the   Water             4184
    temp. of 1 kg of        Alcohol           2450
    material by 1 degree    Aluminum           920
    Kelvin                  Carbon (graphite) 710
  – units: J/(kg·K)         Sand               664
    or J/(g·°C)             Iron               450
                            Copper             380
                            Silver             235
         Specific heat cont.
• The lower a material’s specific heat, the
  more it’s temperature rises when a given
  amount of energy is absorbed by a given
  mass
            Heat Transfer

• Calorimeter
  – device used to
    measure
    changes in
    thermal energy

  – in an insulated
    system,           Coffee cup Calorimeter


        heat gained = heat lost
            Heat Transfer
                             Specific Heat Values
• Which sample will take          (J/(kg·K))
  longer to heat to        Water              4184
  100°C?                   Alcohol            2450
                           Aluminum            920
                           Carbon (graphite) 710
                           Sand                664
                           Iron                450
  50 g Al     50 g Cu      Copper              380
                           Silver              235

  • Al - It has a higher specific heat.
  • Al will also take longer to cool down.
        Heat Transfer


       Q = m ×c × ΔT
Q:    heat (J)
m:    mass (kg)
ΔT:   change in temperature (K or °C)
C:    specific heat (J/kg·K or J/g.oC)

                 – Q = heat loss
ΔT = Tf - Ti     + Q = heat gain
                  Heat Transfer
   • A 32-g silver spoon cools from 60°C to 20°C.
     How much heat is lost by the spoon?

GIVEN:             WORK:
m = 32 g           Q = m·C· ΔT
Ti = 60°C          ΔT = 20°C - 60°C = – 40°C
Tf = 20°C
Q=?                Q = (32g) (.235J/g·°C) (– 40°C)
C = .235 J/g·°C    Q = -300.8 J
                  Heat Transfer
   • How much heat is required to warm 230 g of
     water from 12°C to 90°C?

GIVEN:            WORK:
m = 230 g         Q = m·C· ΔT
Ti = 12°C         m = 230 g
Tf = 90°C         ΔT = 90°C - 12°C = 78°C
Q=?               Q = (230 g)(4.184 J/g·oC) (78 C)
                                              o



C= 4.184 J/g·oC   Q = 75,061 J
 • A piece of iron at a temperature of 145°C
   cools off to 45°C. If the iron has a mass of
   10g and a specific heat of 0.449 J/g·oC,
   how much heat is given up?
GIVEN:            WORK:
m = 10 g          Q = m·ΔT·C
Ti = 145°C        m = 10 g
Tf = 45°C         ΔT = 45°C - 145°C = -100°C
Q=?               Q = (10 g)(-100oC)(.449 J/g·oC)
C= .449 J/g·oC    Q = - 449 J