The relationship between pressure and temperature of a gas is given by Gay-Lussac's pressure-temperature law. This law says that the pressure (P) of a solid mass of gas held in a constant volume is directly proportional to its Kelvin temperature (T). Therefore, when the pressure of a particular system increases, the temperature of that system also increases and vice versa. Gas laws describe the behavior of gases with regard to pressure, volume, temperature and quantity. Gases are one of those states of aggregation that are either very strongly compressed or expanded to fill a large space.

### Key areas covered

**1. What is pressure** *- definition, pressure of a gas* **2. What is temperature** *- definition, measurement* **3. What is the relationship between pressure and temperature** *- Gay-Lussac's law*

*Key Terms: Gas, Gay-Lussac Law, Kelvin, Pressure, Temperature*

## What is pressure

Pressure is a continuous physical force exerted on an object by something in contact with it. It is calculated as the force per unit area. Looking at a closed gas chamber surrounded by a vacuum, the pressure that the gas exerts on the walls of the chamber depends on three factors. They are the amount of gas in the chamber, the volume of the chamber and the temperature of the gas. If the other parameters are constant, the pressure in the chamber is directly proportional to the amount of gas in the chamber; it is inversely proportional to the volume of the chamber; it is directly proportional to the temperature of the gas in the chamber. The pressure is defined in *Figure 1* *.*

Atmospheric pressure is created by the weight of the air above us. At sea level it is 10 ^{5} Pa.

## What is temperature

The temperature is the degree of warmth that is present in a substance or object. It represents the internal energy contained in a particular system. The temperature can be measured with a thermometer that is calibrated in various units of measurement. The Celsius scale is the most widely used scale for measuring temperature, which is given in ° C. The temperature unit according to the International System of Units (SI) is Kelvin (K). A thermometer is shown in *Figure 2.*

At the coldest theoretical temperature, which corresponds to absolute zero, the thermal movement of the particles in a matter is minimal. The absolute zero point is 0 K and is -273.14 ° C.

## What is the relationship between pressure and temperature?

The relationship between pressure and temperature is described in relation to gases. Gay-Lussac's law is the gas law, which describes the pressure-temperature relationship. It says that at a constant volume, the pressure of a certain amount of a certain gas is directly proportional to its Kelvin temperature. It can be written as:

- P ∝ T, or
- P / T = k where k is a constant or
- P
_{1}/ T_{1}= P_{2}/ T_{2}

When the temperature of a particular system is increased, the molecules in the gas move faster and put more pressure on the wall of the gas container. This increases the pressure on the system. When the temperature of the system is decreased, the pressure will decrease. Therefore, if the volume is constant, the pressure of a certain gas is directly proportional to the temperature.

### diploma

The pressure of a certain amount of gas is directly proportional to the temperature at a certain volume. As the temperature of a system rises, so does the pressure, and vice versa. The relationship between pressure and temperature of a gas is given by Gay-Lussac's law.

##### Reference:

1. "9.2 Relating pressure, volume, quantity and temperature: The ideal gas law." *Chemistry* , available here .

##### Image courtesy:

1. “Pressure range” by Klaus-Dieter Keller - Own work (CC BY-SA 3.0) via Commons Wikimedia 2. “1134182” (CC0) via Pixabay