Chapter 12Chapter 12Temperature and Heat

Temperature – Average kinetic energy of molecules.

Heat – Transfer of energy due to temperature difference; flows from hot to cold.

12.1 – Common Temp 12.1 – Common Temp ScalesScales

95 32F CT T 59 ( 32)C FT T

12.2 – The Kelvin Temp 12.2 – The Kelvin Temp ScaleScale 273.15k cT T

12.4 – Linear Thermal 12.4 – Linear Thermal ExpansionExpansionMost materials expand when heated and

contract when cooled.

The change in length (ΔL) depends on…

1. the material (α)

2. the original length (L0)

3. the temperature change (ΔT)

0L L T α = coefficient of linear expansion [1/C°]

Bimetallic Strip – 2 different metals bonded together.

A coiled bimetallic strip can be used in a thermostat

Which material has a higher coefficient of linear expansion?

12.5 – Volume Thermal 12.5 – Volume Thermal ExpansionExpansion

0V V T V0 = original volume [m3]

β = coefficient of volume expansion [1/C°]

Liquids typically expand more than solids; for most solids, β = 3α. TABLE 12.1 (p.351)

ASSIGN:

Ch. 12 #2, 5, 10, 13, 17, 26, 28 p. 375

12.6 – Heat & Internal Energy12.6 – Heat & Internal Energy

Heat (Q) – transfer of energy due to a temperature difference, naturally flows from hot to cold.Heat is measured in Joules

Internal Energy (U) – sum of energy due to molecular motion in a substance.

A substance can’t have heat but can have internal energy.

12.7 – Specific Heat Capacity12.7 – Specific Heat Capacity

Specific Heat Capacity (c) – the heat needed to be supplied or removed to change the temperature of a substance.

Table of values on page 359

Q mc T Heat (J)

mass (kg)

Specific heat (J/(kg∙C°)

Change in temp (°C)

When two objects transfer heat with no heat loss to the surroundings…

lost gainedQ Q

12.7 – Latent Heat12.7 – Latent HeatLatent Heat – the heat that must be supplied or removed to change the phase of a substance.

Lf – latent heat of fusion (solid <-> liquid)

Lv – latent heat of vaporization (liquid <-> gas)

Ls – latent heat of sublimation (solid <-> gas)

Heat (J) mass (kg)

latent heat (J/kg)

Q mL

Table of values on page 364

12.7 – Latent Heat12.7 – Latent Heat

Lf – latent heat of fusion (solid <-> liquid)

= 33.5 x 104 J/kg

= 80 cal/g

Lv – latent heat of vaporization (liquid <-> gas)

= 22.6 x 105 J/kg

= 540 cal/gTable of values on page 364

For water….

12.8 – Equilibrium Between 12.8 – Equilibrium Between PhasesPhasesEquilibrium Vapor Pressure – the pressure of the vapor that coexists in equilibrium with the liquid.

Boiling Point – the temperature where the vapor pressure of the liquid equals the atmospheric pressure.

12.8 – Equilibrium Between 12.8 – Equilibrium Between PhasesPhases

Water boils when its vapor pressure equals the atmospheric pressure.

ASSIGN:

Ch. 12 #41, 44, 45, 51, 52, 62,