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.

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

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

Table 1.7 Specific Heat of Common Substances

Substance Specific Heat

(cal/ g·oC)Substance Specific Heat

(cal/ g·oC)

Water 1.00 Stone (avg.) 0.19

Ice 0.49 Iron 0.16

Wood (avg.) 0.42 Copper 0.093

Air 0.24 Brass 0.091

Aluminum 0.22 Tin 0.055

Glass 0.21 Lead 0.031

change heat mass object an to

etemperatur specific sobject' dtransferre Heat

TCmQ

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?

Sample Problem

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

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

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

Example for Water

Ice

Water

Ice and

water

Water and

Steam

Steam

Melting point/freezing point

Boiling point

• 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.

m

QH f

m

QHv

Table 1.8 Heat of Fusion (Hf) and Vaporization (Hv) of Selected Substances

Substance Hf (cal/g) Hv (cal/g)

Water 79.8 540

Iron, Fe 63.7 1503

Copper, Cu 49.0 1212

Silver, Ag 25.0 564

Gold, Au 15.3 392

Lead, Pb 5.9 207

Back to Problem

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.

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)?

Links

• Virtual experiment: Heating Curves– http://www.harcourtschool.com/activity/hotplate/index.

html

• Heating Curve Tutorial– http://www.kentchemistry.com/links/Matter/HeatingCu

rve.htm

• Heat Problems– http://dbhs.wvusd.k12.ca.us/webdocs/Thermochem/The

rmochem-WS1.html