Chapter 1.4.2: Temperature in Thermal Systems

1. Chapter 1.4.2: Temperature in Thermal Systems • Objectives: • Define specific heat, heat of fusion, and heat of vaporization • Use specific heat, heat of fusion, and heat of vaporization to solve problems involving heat transfer.

2. Specific Heat • Units for Thermal Energy and Heat • Joule (J) • calorie (cal) • British thermal unit (Btu) • Specific heat, C – amount of energy required to raise the temperature of a unit mass of a substance one temperature unit. • Possible units? • J/g·oC cal/g·oC kJ/kg·oC

3. C is an intrinsic physical property, like  does not depend on amount but only on the substance itself.

4. Table 1.7 Specific Heat of Common Substances

6. Sample Problem • How much energy must be absorbed by 20.0 g of water to increase its temperature from 83.0 °C to 94.0 °C?

7. Sample Problem • The specific heat of iron is 0.16 cal/g·oC. Convert this value to specific heat in J/g·oC.

8. Example 1.15, p. 72 • A teakettle hold 0.5 liters of water. How much heat is needed to increase the temperature from 20oC to 100oC. Hints: water = 1.00 g/ml; and 0.5L = 500 mL

9. Change of State • Linear relationship between heat transfer and temperature does NOT hold during a change of state • Temperature stays constant during the phase change, i.e. T = 0 during the phase change

10. Boiling point Melting point/freezing point Example for Water Steam Water and Steam Water Ice and water Ice

11. Melting point (m.p.) – temperature at which a substance melts (or freezes if losing energy). • Boiling point (b.p.) – temperature at which a substance turns to gas (or condenses if losing energy). • Heat of fusion, Hf – amount of energy required to melt one gram of solid. • Heat of vaporization, Hv – amount of energy required to vaporize one gram of a liquid.

12. Table 1.8 Heat of Fusion (Hf) and Vaporization (Hv) of Selected Substances Back to Problem

13. Sample Problems • Convert the heat of fusion of iron to heat of fusion in kJ/kg. • How much heat is required to vaporize 0.5 kg of gold.

14. Example 1.17 Melting Ice and Warming Water • A 10.0 g ice cube has a temperature of -5.0 oC. How much heat is needed to melt the ice cube and warm the resulting water to room temperature (20 oC)?

15. Links • Virtual experiment: Heating Curves • http://www.harcourtschool.com/activity/hotplate/index.html • Heating Curve Tutorial • http://www.kentchemistry.com/links/Matter/HeatingCurve.htm • Heat Problems • http://dbhs.wvusd.k12.ca.us/webdocs/Thermochem/Thermochem-WS1.html