KEY2CHEM

Properties of Gases

The gas phase is defined by having particles that are far apart and in constant random motion. The gas particles collide with one another by elastic collisions; as such, the kinetic energy of a gas sample is constant at a given temperature. As such, generally particles have limited interparticle attraction to one another and are considered to have a negligible volume relative to the volume of the container. At low temperatures or high pressures, however, the particle volume and interparticle forces become significant; correction factors must be employed to better model this behavior.

Example 1.

The _______ of a gas is due to the collisions of gas particles with the walls of the container, causing a force distributed over the area of the container walls.

A. temperature

B. pressure

C. velocity

Solution

B. pressure

$$\text{pressure} = \frac{\text{force}}{\text{area}}$$ The collisions of gas particles with container walls produces a force distributed over the area of the container walls.

Example 2.

At the same temperature, all gases have the same ______________.

A. average kinetic energy

B. speed

C. mass

Solution

A. average kinetic energy

Temperature is proportional to average kinetic energy. At a given temperature, all gases (regardless of identity) will have the same average kinetic energy. Based on identity, gases will have different speeds.

Example 3.

Which gas is least likely to behave as an ideal gas at $$25^\circ\text{C}$$?

A. $$\require{mhchem}\ce{Cl2}$$

B. $$\require{mhchem}\ce{CO2}$$

C. $$\require{mhchem}\ce{H2O}$$

Solution

C. $$\require{mhchem}\ce{H2O}$$

Based on the strong hydrogen bonding intermolecular forces in water, the interparticle forces cannot be considered negligible, and its behavior deviates from ideal behavior.