Recreational Vehicle (RV) Technician Practice Test

What causes the pressure in a propane container to be near zero?

1. Expansion of the gas

2. Cooling of the propane

3. Leakage of gas

4. Overfilling

The correct answer is: Cooling of the propane

The pressure in a propane container can drop near zero primarily due to the cooling of the propane. When propane transitions from a liquid to a gaseous state, it absorbs heat from its surroundings. If the ambient temperature around the propane container decreases significantly, the propane inside can also cool down. As the propane gas cools, its molecules lose energy and move closer together, which results in a decrease in pressure. This phenomenon is governed by Charles's Law, which states that at a constant volume, the pressure of a gas is directly proportional to its temperature. Therefore, when the temperature drops, the pressure correspondingly decreases. In the case of propane, if the temperature gets low enough, the pressure can approach zero or become extremely low, affecting the ability to use the propane effectively in appliances and systems designed for its operation. Other factors such as gas leakage or overfilling could also influence pressure readings, but they do not typically bring the pressure down to near zero as directly as a significant drop in temperature does.