Gas laws: Boyle's, Charles's, and Avogadro's Laws - SS1 Chemistry Lesson Note

Gas laws are a set of fundamental principles in the field of physics and chemistry that describe the behaviour of gases under different conditions. These laws, including Boyle's law, Charles's law, and Avogadro's law, provide insights into the relationships between pressure, volume, temperature, and the amount of gas. We will delve into the intricacies of these gas laws, their equations, and their practical applications:

 

Boyle's Law:

Boyle's law, formulated by Robert Boyle in the 17th century, states that the pressure of a fixed amount of gas is inversely proportional to its volume, at constant temperature. Mathematically, Boyle's law can be expressed as:

 

   P1V1 = P2V2

 

where P1 and V1 are the initial pressure and volume, respectively, and P2 and V2 are the final pressure and volume, respectively.

 

This law implies that when the volume of a gas decreases, the pressure increases, and vice versa, as long as the temperature remains constant. Boyle's law is essential in understanding the behaviour of gases in various applications, such as in scuba diving, where changes in pressure affect the volume of gases in diving cylinders.

 

Charles's Law:

Charles's law, formulated by Jacques Charles in the late 18th century, states that the volume of a fixed amount of gas is directly proportional to its absolute temperature, at constant pressure. Mathematically, Charles's law can be expressed as:

                                                V1 / T1 = V2 / T2

 

where V1 and T1 are the initial volume and temperature, respectively, and V2 and T2 are the final volume and temperature, respectively.

 

According to Charles's law, as the temperature of a gas increases, its volume also increases, provided that the pressure remains constant. This law is particularly significant in applications such as hot air balloons, where temperature changes affect the volume of the gas inside the balloon.

 

Avogadro's Law:

Avogadro's law, formulated by Amedeo Avogadro in the early 19th century, states that equal volumes of gases, at the same temperature and pressure, contain an equal number of particles (atoms, molecules, or ions). Avogadro's law is based on the concept that gases occupy the same amount of space when compared on an equal basis. Mathematically, Avogadro's law can be expressed as:

 

                                                V1 / n1 = V2 / n2

 

where V1 and n1 are the initial volume and number of particles, respectively, and V2 and n2 are the final volume and number of particles, respectively.

 

Avogadro's law has significant implications for understanding the relationship between the volume and amount of gas. It helps determine the molar volume of gases and is crucial in the development of the concept of the mole and the calculation of stoichiometry in chemical reactions.

 

Combined Gas Law:

The combined gas law combines Boyle's law, Charles's law, and Avogadro's law into a single equation that relates the initial and final conditions of a gas sample. The combined gas law is expressed as:

 

                                    (P1V1) / (T1n1) = (P2V2) / (T2n2)

 

where P1, V1, T1, and n1 represent the initial pressure, volume, temperature, and number of particles, respectively, and P2, V2, T2, and n2 represent the final pressure, volume, temperature, and number of particles, respectively.

 

The combined gas law allows for the calculation of the final state of a gas sample when changes occur in its pressure, volume, temperature, or amount, as long as other variables are kept constant.

 

Ideal Gas Law:

The ideal gas law combines the concepts of Boyle's law, Charles's law, and Avogadro's law with the addition of the ideal gas constant (R) to describe the behaviour of ideal gases. The ideal gas law is expressed as:

   PV = nRT

where P is the pressure, V is the volume, n is the number of moles, R is the ideal gas constant, and T is the temperature (in Kelvin).

 

The ideal gas law allows for the calculation of any of the four variables (pressure, volume, number of moles, or temperature) when the other three are known. It serves as a fundamental equation in understanding the behaviour of gases and is widely used in various fields, including chemistry, physics, and engineering.

 

Gas laws, including Boyle's law, Charles's law, Avogadro's law, the combined gas law, and the ideal gas law, provide a framework for understanding the relationships between pressure, volume, temperature, and the amount of gas. These laws have significant applications in various scientific and practical contexts, from scuba diving to hot air balloons, and they form the basis for understanding the behaviour of gases in diverse fields of study.