Temperature is a measure of the average kinetic energy of the particles in a substance. It is the kinetic energy of a typical particle.

When two substances are the same temperature they are said to be in thermal equilibrium.

Thermal expansion is the enlarging of a material when its temperature is raised.

The coefficient of linear expansion tells how much an object will gain in length, and the coefficient of volume expansion gives the gain in volume.

The fact that matter gains volume and length when heated is the principle of operation of many thermometers.

TF = 9/5 TC + 32

TC = 5/9 (TF - 32)

TK = TC + 273

0° C is 32° F, the freezing point of water.

100° C is 212° F, the boiling point of water.

These two points in the Kelvin scale are 273 and 373.

0 in the Kelvin scale is the lowest possible temperature, absolute zero, -273° C, -460° F.

When two things in contact have different temperatures, energy will move from the warmer object to the cooler one.

This energy that is transferred is called heat. Heat is only defined when it is being transferred.

When two objects are the same temperature, heat energy is still being transferred between the two objects.

But each of the objects gains and loses the same amount so the net energy transfer is zero.

When a nail is hammered into a piece of wood, the movement of the nail is kinetic energy. This energy cannot just disappear, it is absorbed as internal energy of the wood and the nail.

If we consider these changes in internal energy, ∆U, the total energy is a conserved property.

∆PE + ∆KE + ∆U = 0

∆PE + ∆KE + ∆U = 0

This is another statement of the law of conservation of energy.

Some materials change temperature rapidly when heat energy is added, others don’t change much at all.

This is measured in terms of specific heat capacity.

Q = cp m ∆T

Q = cp m ∆T• Q is the heat added in joules

• m is the mass in kg

• ∆T is temperature change in C°

• cp is the heat capacity in J/kg•C°

The specific heat capacity is different for different substances.

Water is 4186 J/kg•C°.

A 0.050 kg metal bolt is dropped into a beaker of 0.15 kg of water at 21.0°C. The bolt and water reach an equilibrium temp of 25.0° C. If the metal has a cp of 899 J/kg•C°, find the initial temp of the bolt.

This determination of specific heat capacity is called calorimetry and is a common physics activity.

If heat is added to ice at a temperature below the freezing point of water, the ice will increase in temp until it reaches 0°C. It will remain at 0°C until all the ice is melted even though energy is still being added.

The energy is breaking the associations that are holding the water in a solid phase. The same thing happens at 100°C when the water boils.

Suppose you are cooking spaghetti for dinner, and the instructions say to boil the noodles in water for ten minutes. To cook spaghetti in an open pot with the least amount of energy, should you turn up the burner to its fullest so the water vigorously boils, or should you turn down the burner so the water barely boils?

Each particular substance requires a definite amount of heat energy to accomplish these phase changes.

The latent heat is the heat per kilogram that must be added or removed when a substance changes from one phase to another at a constant temperature. The unit is the J/kg.

The latent heat of fusion Lf refers to a solid to liquid change. The latent heat of vaporization Lv refers to a liquid to gas change.

Q = mL

How much energy is removed when 10.0 g of water is cooled from steam at 133.0°C to liquid at 53.0°C?

Heat TransferConvection is the transfer of heat by the bulk movement of a fluid. Convection can be natural or forced.

Conduction is the transfer of heat through a material, any bulk motion of the material playing no role in the transfer. The free electrons in a metal allow heat energy to be transferred very easily.

Materials that conduct heat well are thermal conductors. Those that conduct heat poorly are thermal insulators.

Air, like most gases, has a low thermal conductivity and is a good insulator when convection is kept at a minimum.

Radiation is the transfer of heat by electromagnetic waves. All objects radiate energy in the form of electromagnetic waves, but the temperature must be over 1000 K for the light to be visible.