1 1. Gases 1.1. The states of matter Review the states of matter and their characteristics. 1.2. The study of gases The volume of a gas depends on temperature and pressure. The scientific method can be used to find the relationship between these quantities. We cannot use a single experiment to measure the relationship between the three variables. We have to design experiments in which one of them remains constant ( for example, temperature), we vary the second variable ( for example, volume) and measure its ef fect on the third (pressure). The independent variable is the quantity we var y. The dependent variable is the quantity in which we measure the ef fect. In addition , we have to use a device that allows us to read the value of the three quantities and var y the independent variable in each case. In all the experiments we must measure these quantities: volume (V ), pressure (p) and temperature (T ). During the 17th centur y, several scientists carried out experiments in England and France. They were able to establish the gas laws. 3 Make three drawings that explain the characteristics of matter in each of the states. Draw little balls to represent the particles that form matter as in the image. Solids They have a fixed shape and volume. They cannot expand or be compressed . Liquids They have a variable shape, but a fixed volume. They do not expand , and can be compressed a little. Gases They have a variable shape and volume. They can expand and be compressed . Device used to study gases. 30 L 20 L 10 L 0 L Thermometer Movable piston (it goes up or down to change the volume) Manometer Temperature must always be expressed in K (SI unit). If it is measured in °C, we must convert the unit: T (K) = T (°C) + 273 Volume and pressure can be expressed in any unit. We must use the same unit throughout the experiment. CHALLENGE Liquid Liquid 11
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