# Charles's law explained

### Charles's Law:

Charles's law, sometimes referred to as the law of volumes, show the effects of absolute temperature on the volume of a gas at constant pressure. This absolute temperature must be measured with the kelvin scale, and not the celcius scale. This is so because the zero value on the kelvin scale corresponds to a complete stoppage of molecular motion; that is, the ideal gas particles becomes fixed in a position, just like solid particles.

Please read more on the state of matter and characteristics of solids here.

The details of Charles's law emphasizes on the expansion of a gas when its temperature is increased at a constant pressure, and its subsequent contraction when the temperature is reduced. In this regard, when a gas becomes heated, its volume increases, and when cooled, the volume decreases proportionately. This is shown below: From the above image, we can see that the gas occupied a lesser volume (V1) at a lower temperature (T1).

At a higher temperature (T2), the volume occupied by the gas (V2) increases proportionately. We can therefore infer that temperature and volume are directly proportional in the sense that when one (temperature) increases, the other (volume) increases accordingly, and vice versa.

You can read on the concept of heat and temperature here.

Absolute temperature refers to the temperature of an object or a substance on the kelvin scale where zero is taken as absolute zero. This zero point implies that the particles (or molecules) making up the substance exhibit their minimum motion. In short, a substance becomes solid at this temperature and can no longer become colder.

• The absolute temperature may also be referred to as thermodynamic temperature.

The absolute zero temperature on the celcius scale is -273.15oC. However, calculations involving Charles's law must be solved using the kelvin temperature. In order to convert celsius to kelvin temperature, the value '273.15' should be added to the celcius temperature. For example, if we were to convert 100oC to kelvin temperature, it becomes '100 + 273.15' = 373.15K.

Please see worked examples on Charles law here.

The graph below shows Charles's law through the celsius scale. At the absolute zero temperature; that is, zero kelvin or -273.15oC, notice that the volume occupied by the gas is zero (when traced to the right, as shown in the above graph). As the temperature increases, the volume also increases. This is further explained through the kelvin scale (graph) below: From the above graph, notice that the temperature is measured in kelvin. At absolute zero temperature (zero kelvin or 0K), the volume occupied by the gas equals zero. As the temperature increases, the volume also increases proportionately. Therefore, Charles's law uses a straight line graph running through 0 kelvin or -273.15oC to represent the relationship between the volume and temperature of a gas (at constant pressure).

You can read on the physical properties of matter here.

Charles's law states that the volume of a given mass of gas is directly proportional to the absolute temperature of the gas, provided the pressure remains constant.

The French physicist, Jacques Charles (1746-1823) formulated this law in 1780.

Charles's law may also be restated that the kelvin temperature and volume will always be in direct proportion if the pressure exerted on a dry gaseous sample remain constant.

With reference to Charles's law, the following equations are derived:

• V = T

• V/T = k (constant )..... Equation 1

• V = Volume, T = Temperature and k = Constant

• The value of k is dependent on the pressure of gas, amount of the gas and the unit of gas measurement.

• Increase in Volume = Increase in Temperature

• Increase in V1 = Increase in T1

• Increase in V2 = Increase in T2

• V1 = Initial Volume

• T1 = Initial Temperature

• V2 = Final Volume

• T2 = Final Temperature

• Substituting into Equation 1

• V1/T1 = V2/T2..... Equation 2

• Cross multiply

• V1 T2 = V2 T1..... Equation 3

Please see worked examples on Boyles law here.

Various instances of Charles's law have been observed on substances, objects or processes at different temperatures. Examples are:

• Deodorant sprays, insecticides and perfumes

• Dented table tennis ball

• Turkey timer

• Hot air balloon

• Car tyres

• Helium balloons

• Pool floats

• Aerosols

• Human lungs 