Temperature Scales

Temperature Scales

The Temperature of a substance is a measurement of the average kinetic energy of the particles. The particles of all substances as the same temperature have the same average kinetic energy. When two bodies of different temperatures collide, the temperature difference between them indicates the direction of heat flow. The heat will flow from the higher temperature to the lower temperature until both have the same temperature.

So what's Heat then? Heat is the measure of the amount of energy transferred from one substance to another. Heat is measured is units of calories or joules.

The average kinetic energy depends only on the temperature of the substance, not on the nature or amount of material. Thus, 10 g of water at 50 degrees celsius has a greater average kinetic energy than 500 g of solid Iron at 20 degrees celsius.

Temerpature is measured by thermometers. You will learn how to measure temperature and make conversions between Celsius and Kelvin Temperatures.

Temperature Conversions

Kelvin Scale

The Kelvin scale is the only scale that has an absolute zero.

Celsius Scale

The Celsius scale is what we commonly use in the science classroom.

Comparisons

Boiling point = 100 C and 373 K

Freezing point = 0 C and 273 K

Notice that they are seperated by 100

Absolute Zero = -273 K and 0 K

You must know this formula..but don't worry, it's on you Reference tables!

K = °C + 273

Practice Problem

What kelvin temperature is equivalent to 35 degrees Celsius?

K = °C + 273

K = 35 + 273 = 308

Measurement of Heat Energy

The amount of heat given off or absorbed in a reaction can be calculated using the following equation:

q = mCDT

q = eat (in joules)

m = mass of the substance

C = Specific Heat Capacity of Substance

DT = (initial Temp - Final Temp)

So What's Specific Heat Capacity?

Specific Heat Capacity is the amount of heat required (in joules) to raise 1 gram of the substance 1 degree celsius.

Listed below is a table of Specific Heat Capacities for some substances. Notice that water has a very high value...ever wonder why your pool takes so long to heat up???

Example Problem

How many joules are absorbed when 50.0 g of water are heated from 30.0 Celsius to 58.6 Celsius?

q = mCDT = (50.0g) (4.18 J/gC) (28.4 C)

q = 5936 J

Heat of Fusion

The amount of heat needed to convert a unit mass of a substance from solid to liquid at its melting point is called the Heat of Fusion. The heat absorbed by the substance during the melting process increases the potential energy of the substance without increasing the kinetic energy..

What's that mean? The temperature does NOT increase during this phase change.

Heat of Vaporization

During the boiling process, a substance in the liquid phase is converted to the gaseous (vapor) phase. The temperature remains constant because the heat energy increases the potential energy without increasing the average kinetic energy. What does this mean..? The potential energy is being used to convert the substance from a liquid to a vapor.As heat is added, the particles absorb sufficient energy to overcome the attractive forces holding them in the liquid phase...the temperature then increases in the vapor phase.