Temperature Section 9.1

Determining an object’s temperature with precision requires a standard definition of temperature and a procedure for making measurements that establish how “hot” or “cold” objects are.

Four different temperature scales Fahrenheit- water freezes at 32° F and boils at 212° F. Celsius – water freezes at 0° C and boils at 100° C. Kelvin – this scale begins at absolute zero and each Kelvin is the same as 1° C. Rankine – this scale begins at absolute zero and each Rankine is the same as 1° F.

The change in temperature of a substance can only be achieved by adding or removing energy.

Temperature is proportional to the kinetic energy of atoms and molecules.

The energies associated with atomic motion are referred to as internal energy, which is proportional to the substance’s temperature(assuming no phase change)

For an ideal gas, the internal energy depends only on the temperature of the gas. For nonideal gases, as well as for liquids and solids, other properties contribute to the internal energy.

The symbol U stands for internal energy, and ΔU stands for a change in internal energy.

internal energy  the energy of a substance due to both the random motions of its particles and to the potential energy that results from the distances and alignments between the particles

Temperature is meaningful only when it is stable.

thermal equilibrium the state in which two bodies in physical contact with each other have identical temperatures

As a thermometer comes into thermal equilibrium with an object, the object’s temperature changes slightly. In most cases the object is so massive compared with the thermometer that the object’s temperature change is insignificant.

Matter expands as its temperature increases.

Increasing the temperature of a gas at constant pressure causes the volume of the gas to increase. This increase occurs not only for gases, but also for liquids and solids. In general, if the temperature of a substance increases, so does its volume. This phenomenon is known as thermal expansion.

If two cups of hot chocolate, one at 50°C and the other at 60°C, are poured together in a large container, will the final temperature of the double batch be less than 50°C? between 50°C and 60°C? greater than 60°C?

A cup of hot tea is poured from a teapot, and a swimming pool is filled with cold water. Which one has a higher total internal energy? Which has a higher average kinetic energy?

Different substances undergo different amounts of expansion for a given temperature change. The thermal expansion characteristics of a material are indicated by a quantity called the coefficient of volume expansion. Gases have the largest values for this coefficient. Liquids have much smaller values.

In general, the volume of a liquid tends to decrease with decreasing temperature. However, the volume of water increases with decreasing temperature in the range between 0°C and 4°C. Also, as the water freezes, it forms a crystal that has more empty space between the molecules than does liquid water. This explains why ice floats in liquid water. It also explains why a pond freezes from the top down instead of from the bottom up. If this did not happen, fish would likely not survive in freezing temperatures.

Solids typically have the smallest coefficient of volume expansion values. For this reason, liquids in solid containers expand more than the container. This property allows some liquids to be used to measure changes in temperature.

Calibrating thermometers requires fixed temperatures.

Temperature units depend on the scale used.

Temperature values in the Celsius and Fahrenheit scales can have positive, negative, or zero values.

But because the kinetic energy of the atoms in a substance must be positive, the absolute temperature that is proportional to that energy should be positive also.

Because the kinetic energy of the atoms in a substance must be positive, the absolute temperature that is proportional to that energy should be positive also. This temperature is designated in the Kelvin scale as 0.00 K, where K is the symbol for the temperature unit called the kelvin. Temperatures in this scale are indicated by the symbol T.

A temperature difference of one degree is the same on the Celsius and Kelvin scales. The two scales differ only in the choice of zero point

The Rankine scale is the absolute temperature scale that corresponds with the Fahrenheit scale.

What are the equivalent Celsius and Kelvin temperatures of 50.0°F?