At 25 °C and 1 atm pressure

CHEMISTRY · Multi-part · CBSE · Chemistry · The Amazing World of Solutes, Solvents, and Solutions · The Amazing World of Solutes, Solvents, and Solutions

Problem

At 25 °C and 1 atm pressure, the following approximate densities are reported in data handbooks: • helium gas: 0.18 kg m−30.18\,\text{kg}\,\text{m}^{-3} • water vapour (steam): 0.60 kg m−30.60\,\text{kg}\,\text{m}^{-3} • air: 1.2 kg m−31.2\,\text{kg}\,\text{m}^{-3} • carbon dioxide: 1.8 kg m−31.8\,\text{kg}\,\text{m}^{-3} Read the data carefully and answer the questions that follow. (i) List the four gases in the descending order of their densities. (ii) A hot-air balloon rises in the atmosphere after the air inside it is heated. Using the idea of density, give a qualitative explanation of this observation without employing any equations. (iii) Describe how the density of a fixed mass of an ideal gas changes when the temperature is increased at constant pressure. Justify your answer by referring to the microscopic picture of gas molecules.

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