Properties of Gases: 18 MCQs with answers

It has neither a fixed shape nor a fixed volume.

A gas has neither a fixed shape nor a fixed volume because its particles are far apart and move freely, spreading out to fill any container.

Collisions of gas particles with the walls

Pressure is the total force per unit area from countless gas particles colliding with the container walls.

Gas particles have large empty space between them.

The large interparticle space in gases allows particles to be pushed closer together under pressure, making gases highly compressible.

The average kinetic energy of the particles

Temperature measures the average kinetic energy of gas particles — the hotter the gas, the faster the particles move.

Boyle's Law

Boyle's Law states that at constant temperature, the pressure of a fixed amount of gas is inversely proportional to its volume.

$PV = nRT$

The ideal gas law is $PV = nRT$, relating pressure, volume, number of moles, the gas constant, and absolute temperature.

True

The ideal gas law $PV = nRT$ relates pressure, volume, temperature, and number of moles of a gas.

The pressure increases and volume stays constant.

In a rigid container the volume is fixed. Heating makes particles move faster and hit the walls harder and more often, so pressure increases (Gay-Lussac's Law).

Pressure increases because volume decreases.

Boyle's Law states that at constant temperature, pressure is inversely proportional to volume. Reducing volume increases pressure.

It increases because absolute temperature increases.

Charles's Law states that at constant pressure, volume is directly proportional to absolute temperature. Warming the gas increases its volume.

Because gas particles diffuse due to random motion.

Diffusion is the spontaneous mixing of gas particles due to their random motion, allowing the perfume to spread quickly through the room.

Helium is less dense than air.

Helium is less dense than air, so the buoyant force from the displaced air is greater than the balloon's weight, making it float.

Gas density is much lower than that of solids and liquids.

Because gas particles are spread far apart, gases have much lower density than solids and liquids. For example, air is about $1.2\ \text{kg/m}^3$ while water is $1000\ \text{kg/m}^3$.

High pressure and low temperature

At high pressure and low temperature, gas particles are close together and attractive forces become significant, causing deviation from ideal behaviour.

It becomes four times the original.

Using the combined gas law $\frac{P_1 V_1}{T_1} = \frac{P_2 V_2}{T_2}$: if $T_2 = 2T_1$ and $V_2 = V_1/2$, then $P_2 = P_1 \cdot \frac{T_2}{T_1} \cdot \frac{V_1}{V_2} = P_1 \cdot 2 \cdot 2 = 4P_1$.

Because the container is rigid, so volume is fixed and pressure increases instead.

In a rigid container, volume cannot change. Adding more gas increases the number of particles hitting the walls, so pressure increases instead.

4 atm

Using Gay-Lussac's Law, which states that pressure is directly proportional to temperature at constant volume, we can set up the ratio: \( \frac{P_1}{T_1} = \frac{P_2}{T_2} \). Plugging in the values: \( \frac{2 \text{ atm}}{300 ext{ K}} = \frac{P_2}{600 ext{ K}} \). Solving for \( P_2 \) gives \( P_2 = 4 \text{ atm}…

2 atm

According to Boyle's Law, \( P_1 V_1 = P_2 V_2 \). Given \( P_1 = 1 \text{ atm} \), \( V_1 = 10 \text{ L} \), and \( V_2 = 5 \text{ L} \), we can rearrange to find \( P_2 \): \( P_2 = \frac{P_1 V_1}{V_2} = \frac{1 \text{ atm} \times 10 \text{ L}}{5 \text{ L}} = 2 \text{ atm} \).