الغازات - الطاقة الكيميائية .. الفيزياء

Gases - Chemical Energy .. Physics

Gas

Matter exists in three different states: solid, liquid and gas.

Gasses are characterized by the fact that their atoms or molecules move randomly and at a tremendous numerical speed and that collisions between them are frequent due to their abundance. A gas confined in a container is characterized by its pressure, which results from the collisions of its molecules with the walls of the container itself.

It is known that the number of collisions of gas molecules with the walls of the container in which it is located increases as its volume decreases, and thus the value of its pressure increases. The equation that links the volume of a gas H and its pressure D is known as Boyle's Law and is as follows: D = Th / H where Th represents a fixed quantity.

It is worth noting that the temperature of a gas is a measure of the average kinetic energy of its molecules. The speed of the molecules increases as their temperature increases, and the result is that the pressure increases if the volume remains constant; or that the volume increases if the pressure remains constant. Charles's law states that a one-degree Celsius (°C) increase in temperature of any gas will increase its volume by 1/273 of the volume it occupies at zero degrees Celsius.

We conclude from this that the volume of a gas theoretically disappears if its temperature drops to -273, i.e. to absolute zero.

It is known that reaching this temperature is difficult in practice. However, the colors show that using a thermometer that starts at absolute zero is very important in many fields. The temperature on this scale is called Kelvin, or absolute temperature, or thermodynamic temperature.

(Boyle's law links the pressure and volume of a gas at a constant temperature)

Boyle's and Charles's laws can be combined into one law called the ideal gas, and it is expressed by the equation P × H = R × D, which is applied to a unit of gas quantity and in which the absolute temperature is represented by the letter D and the gas constant by the letter R. Natural gases deviate slightly from this equation, especially if their pressure value increases as a result of the weakness of the attractive forces between their molecules that are very close to each other.

Regardless of the composition of the gas, quantities of it with equal volume, pressure and temperature contain an equal number of molecules (Avogadro's hypothesis) of about 2.7 × 1910 molecules/cm3, and the number of collisions that occur for each of them is 5 × 910 collisions per second.

The volume of the gas is proportional to its temperature if its pressure is constant (Charles' law), and its pressure is proportional to its temperature if its volume is constant.