Physical Science PDF

are some that change directly from solid state to gaseous state and vice versa without changing into the liquid state. Activity _____________ 1.13 enclosed in a cylinder? Will the particles come closer? Do you think that increasing or decreasing the pressure can change the state of matter? Take some...

are some that change directly from solid state to gaseous state and vice versa without changing into the liquid state. Activity _____________ 1.13 enclosed in a cylinder? Will the particles come closer? Do you think that increasing or decreasing the pressure can change the state of matter? Take some camphor. Crush it and put it in a china dish. Put an inverted funnel over the china dish. Put a cotton plug on the stem of the funnel, as shown in Fig. 1.7. Fig. 1.8: By applying pressure, particles of matter can be brought close together Fig. 1.7: Sublimation of camphor Now, heat slowly and observe. What do you infer from the above activity? A change of state directly from solid to gas without changing into liquid state is called sublimation and the direct change of gas to solid without changing into liquid is called deposition. Applying pressure and reducing temperature can liquefy gases. Have you heard of solid carbon dioxide (CO2)? It is stored under high pressure. Solid CO2 gets converted directly into gaseous state on decrease of pressure to 1 atmosphere* without coming into liquid state. This is the reason that solid carbon dioxide is also known as dry ice. Thus, we can say that pressure and temperature deter mine the state of a substance, whether it will be solid, liquid or gas. 1.4.2 EFFECT OF CHANGE OF PRESSURE We have already learnt that the difference in various states of matter is due to the difference in the distances between the constituent particles. What will happen when we start putting pressure and compress a gas Deposition Fig. 1.9: Interconversion of the three states of matter * atmosphere (atm) is a unit of measuring pressure exerted by a gas. The unit of pressure is Pascal (Pa): 1 atmosphere = 1.01 × 105 Pa. The pressure of air in atmosphere is called atmospheric pressure. The atmospheric pressure at sea level is 1 atmosphere, and is taken as the normal atmospheric pressure. 8 SCIENCE Rationalised 2023-24