Lesson 2:
Matter and Energy
Temperature
Introduction
In many of the experiments performed in a treatment plant it is required that we measure the actual temperature of a liquid. On some occasions it is the temperature change which accompanies a reaction that is required. The accuracy and precision of the thermometer are probably the main factors which affect such measurement, but good technique is also important to ensure that the true temperature is measured. On this page we will discuss temperature and how to measure it properly. Then, on the following pages, we will consider how diffusion and the three states of matter are related to temperature.
Temperature Defined
Temperature is a measurement of heat energy. And, as you may remember from the last lesson, heat is a form of kinetic energy, meaning that there must be some movement involved. So what sort of motion does temperature measure?
Random movement of atoms.
Although it may sound counterintuitive, all molecules and atoms are constantly in motion. In solids, the molecules and atoms are merely bouncing back and forth while staying in the same arrangement. But in liquids and gases, the molecules and atoms are moving randomly, constantly changing their orientation. In both cases, the random movement of the atoms and molecules in the substance is a form of kinetic energy.
It is this random kinetic energy of molecules and atoms which is known as heat. Temperature is a measurement of the average kinetic energy of the atoms or molecules in the substance being measured. The atoms of a substance which has a high energy tend to move around a lot, so the substance will have a high temperature. In contrast, a low temperature means that the atoms move around very little.
Measuring Temperature
We measure temperature using various types of thermometers. Your are probably most familiar with the bulb type of thermometer shown below.
A bulb thermometer is a very simple instrument made up of a thin tube connected to a bulb containing some sort of liquid (often alcohol or mercury). To measure the temperature of a substance, the bulb of the thermometer is placed in the substance. If the substance is warmer than the bulb, then heat energy is transferred from the substance to the bulb. The liquid in the bulb expands when heated, so some liquid is forced up into the tube above the bulb. We read the temperature based on how high the liquid rises in the tube.
The heat transfer involved in measuring temperature takes time, so all temperature measurements require a certain amount of delay. Some types of thermometers have been developed to minimize the time delay. For example, electrical thermometers detect temperature using thermistors, which change their electrical resistance in response to temperature. Electrical thermometers, as well as infrared thermometers, tend to have a shorter time delay during temperature measurement than simple bulb thermometers do.
Another factor to consider when measuring temperature is accuracy. The accuracy of any temperature reading depends on the transfer of energy between the object being measured and the thermometer as well as on the thermometer's ability to measure the energy. In water and wastewater treatment, the Environmental Protection Agency recommends that temperature be read and recorded at +0.1° C.
Units
There are three units for measuring temperature which you may come in contact with. You are probably most familiar with Fahrenheit (F) and Celsius (C). In addition, you may remember that we mentioned the unit Kelvin (K) in the last lesson. The table below lists some important temperatures on each scale.
oF Water Boils 212 100 373 Room Temperature 72 23 296 Water Freezes 32 0 273 Absolute Zero -460 -273 0 0°K is the temperature at which substances have no heat energy. This means that atoms and molecules are absolutely still and do not move. As mentioned in the last lesson, it is impossible to reach a temperature of absolute zero.
There may be times you will need to convert from one scale to another, such as from Celsius to Fahrenheit or vice versa. Below are the conversion formulae to use:
Here are some examples in how to use the conversions:
Convert 35°C to degrees Fahrenheit.
Convert 68°F to degrees centigrade.
