Question

(a) How does the average kinetic energy of molecules compare with the average energy of attraction between molecules in solids, liquids, and gases? (b) Why does increasing the temperature cause a solid substance to change in succession from a solid to a liquid to a gas? (c) What happens to a gas if you put it under extremely high pressure?

Short answer

(a) In solids, the kinetic energy of molecules is relatively low, and the intermolecular attraction energy is high. In liquids, the kinetic energy is higher than in solids, and the intermolecular attraction energy is less than in solids but still significant. In gases, the kinetic energy is the highest, and the intermolecular attraction energy is the weakest or almost negligible. (b) When the temperature of a solid substance is increased, the average kinetic energy of particles increases, causing the substance to change from solid to liquid at the melting point and liquid to gas at the boiling point. (c) When a gas is subjected to extremely high pressure, the particles are forced closer together, and the volume decreases, causing the gas to transform into a liquid or a solid through compression.

Step-by-step solution

(a) Comparing kinetic energy and intermolecular attraction energy in solids, liquids, and gases

In solids, the atoms or molecules are closely packed together and have a definite shape and volume. The kinetic energy of molecules in solids is relatively low, while the intermolecular attraction energy is high. In liquids, atoms or molecules are loosely packed and have no definite shape, but they have a definite volume. In this case, the average kinetic energy is higher than in solids, and the intermolecular attraction energy is less than in solids but still significant enough to keep the particles together. In gases, atoms or molecules are far apart, with no definite shape and volume. The average kinetic energy in gases is the highest among all three states of matter, while the intermolecular attraction energy is the weakest or almost negligible.

(b) Effects of increasing temperature on a solid substance

When the temperature of a solid substance is increased, the average kinetic energy of the particles also increases. 1. Solid to Liquid - When the energy added is sufficient to overcome the intermolecular attraction, the solid substance starts to melt, changing into a liquid state. The melting point is the temperature at which the solid turns into a liquid. 2. Liquid to Gas - As the temperature continues to increase and the kinetic energy of the particles becomes greater, the intermolecular attraction further weakens. Once the energy is enough to completely overcome the intermolecular attraction between the particles, the substance starts to boil and transform from a liquid to a gaseous state. The boiling point is the temperature at which the liquid turns into a gas.

(c) Effects of high pressure on a gas

When a gas is subjected to extremely high pressure, the particles are forced closer together, and the volume decreases. Due to the increased proximity of particles, the intermolecular attraction forces start playing a more significant role. As a result, the gas may combine to form a liquid or even a solid, depending on the nature of the substance and the applied pressure. This process of transforming a gas into a liquid or a solid due to high pressure is known as compression.