Class 11th science chemistry(Some Basic Concepts Of Chemistry)

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Chemistry is referred to as Central Science as it interconnects geology, biology, environmental science, and physics to each other. Chemistry is a discipline where people of ancient India had the knowledge of scientific phenomenon before the emergence of modern science. Any substance on earth contains matter. A substance that occupies physical space and has inertia is called matter. There are three states of matter viz solid, gas, liquid. Matter can also be
classified into compounds, mixtures or elements.

Laws Of Chemical Combination

  • Law of Conservation of Mass – It states that during a chemical reaction, the mass of the products and reactants will always be equal.
  • Law of Definite Proportions – It states that every chemical compound will contain a fixed and constant proportion by mass, of its constituent elements. Joseph Proust proposed this law.
  • Law of Multiple Proportions – It is a rule of stoichiometry formulated by John Dalton.
  • Gay Lussac’s Law of Gaseous Volumes – Gay Lussac gave this law in the year 1808. This law was properly explained by Avogadro.
  • Avogadro Law – It states that when the temperature and pressure conditions are same, gases of equal volumes contain the same number of molecules.
The above-described laws led to Dalton’s atomic theory.

Gay Lussac’s law

This law shows the relationship between the temperature and pressure of a gas. According to Gay-Lussac’s law, the pressure of an ideal gas is directly proportional to its temperature. This law states that at constant volume of a close container, we may conclude that if the pressure inside container increases, the temperature inside the container also increases.
Formula: This law can be expressed in the equation as follows:
P1T1 = P2T2
where,
P1 = Initial Pressure (atm)
P2 = Final Pressure (atm)
T1 = Initial Temperature (Kelvin)
T2 = Final Temperature (Kelvin)
Gay Lussac’s law of combining gas volumes:
Key points regarding Gay Lussac’s law:
  • Volume should be constant
  • Pressure vs Temperature graph is linear for ideal gasses.
Gay Lussac's Law
  • Temperature and pressure are directly proportional to each other
Avogadro’s law statement – Under constant temperature and pressure, the relationship between the volume of gas and the number of moles is direct. This law is also known as Avogadro’s Principle or Avogadro’s hypothesis. This hypothesis was first published by Amadeo Avogadro in the year 1811.

For a specific mass of an ideal gas, the volume and number of moles of the gas are directly proportional, at constant pressure and temperature.



According to Gay Lussac’s theory, at constant volume, the pressure of a fixed amount of a gas varies directly with the temperature. Avogadro used the conclusions of Gay Lussac’s theory and dalton's atomic theory to derive a relationship between volume and the amount of gas. According to Avogadro’s law, equal volumes of all gases under the same conditions of temperature and pressure contain an equal number of molecules.
Mathematically it can be stated as,
V ∝ n
Where,
V= volume of gas
n = number of moles
V= k n
Where k is the constant of proportionality.
The number of molecules in one mole is given by Avogadro’s constant, also known as Avogadro’s number
NA  = 6.023 × 1023.
Volume of one mole of gas can be calculated at STP (standard temperature and pressure) with the help of ideal gas equation.
Pressure at STP= 1025 Pa
Temperature at STP = 273.15K
V=R(nt/T)
⇒V=8.314*273.15*10-5
⇒V=22.710981 L
Hence, according to Avogadro’s law, one mol of all gases at STP(standard temperature and pressure) will contain 22.710981 L of gas. Number of moles can be given in terms of molar mass as,
n=m/M
Where m = mass of gas under investigation
M = molar mass
By Avogadro’s law,
n = km/M
m = m/v = d
Where d is the density of the gas.
Form the above equation we can also deduce that the density of a gas is directly proportioned to the molar mass of the gas. The above equation is useful in the identification of a gas from the calculation of its molar mass. This law is useful while comparing the same substance under two different conditions. For example: at constant temperature and pressure, if the volume and number of moles of gas changes from V1 to V2 and N1 to N2respectively. This can be expressed as,
V1/n1=V2/n2
Generally, only ideal gases are found to follow Avogadro’s law. However, real gases follow this law when forces of interaction between the gaseous molecules are practically negligible. This generally happens at very high temperature and low pressure.

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