Gas laws

Gas Law in Chemistry

1. Md.Jamil Uddin Shihab ID-192800016 Department of EEE EU Gas Laws by

2. The gas is highly compressible and expandable. As the temperature, pressure and other quantities change, the volume of the gas changes drastically. Scientists at different times have come up with a number of formulas to explain these effects and other properties of the gas. These are 1.Boyle's formula 2.Charles's formula 3.Avogadro's formula 4.Gay Lusak's formula

3. Boyle’s Law Pressure is inversely proportional to volume when temperature is held constant. P 1 V 1 = P 2 V 2

4. Effect of change in Pressure on the Volume of a Gas –Boyle’s Law Pressure and volume are inversely related at constant temperature. 𝑃 ∝ P ∝ 1/v P= K/V PV=K P 1 V 1 = k = P 2 V 2 P 1 V 1 = P 2 V 2 Father of Mordern Chemistry Robert Boyle

5. Boyle’s Law: P 1 V 1 = P 2 V 2

6. A Graph of Boyle’s Law

7. Boyle’s Law – Isotherms When P of a gas is plotted against V at different temperature, hyperbola curves are obtained which are called Isotherms. As the temperature increases, the isotherms goes away from both the axis. This is due to increase in volume at higher temperature.

8. Charles’s Law The volume of a gas is directly proportional to temperature, and extrapolates to zero at zero Kelvin. ( P = constant) Temperature MUST be in KELVINS!

9. Charles’ Law: V 1 /T 1 = V 2 /T 2

10. A Graph of Charles’ Law

11. Effect of change in Temperature on the Volume of gas – Charles’s Law At constant Pressure, volume of given mass of a gas increase or decreases by decreases by 1/273 times of its original original volume at 0 o C for every 1 o C rise Jacques-Alexandre Charles ‹#›

12. Derivation of Critical Form of Charles’s Law Suppose the volume of a gas at 0 o C = V o 𝑜 𝑜 Volume at 1 o C = 𝑉 = 𝑉 + 𝑉 1 𝑜 273 𝑜 𝑜 Volume at 2 o C = 𝑉 = 𝑉 + 𝑉 2 𝑜 273 𝑡 Volume at t o C = 𝑉 = 𝑉 + 𝑉 𝑡 𝑜 273 𝑜 𝑉 𝑡 = 𝑉 𝑜 1 + 𝑡 273 𝑉 = 𝑉 𝑡 𝑜 273+𝑡 273 𝑡 + 273 = 𝑇 𝐾𝑒𝑙𝑣𝑖𝑛 𝑇𝑒𝑚𝑝𝑒𝑟𝑎𝑡𝑢𝑟𝑒 𝑉 𝑡 = 𝑉 𝑜 𝑇 𝑡 𝑉 = 𝑉 𝑜 273 273 𝑇 9

13. Charles’s law - Isobar When volume of gas is plotted against temperature at different pressures, a straight line is obtained. Each constant pressure line is called Isobar. ‹#›

14. Absolute Zero ‹#› According to Charles’s law: At constant Pressure, volume of given mass of a gas increase or decreases decreases by 1/273 times of its original volume at 0 o C At exact -273 o C the volume of a given mass of gas reduces to zero.As, -273 o C = 0K The temperature at which the given volume of a gas reduces to Zero is called Absolute Zero i.e. 0K or -273 o C. Actually all the gases liquefy or solidify before they reach -273 o C. This temperature is considered to as the lowest possible temperature.

15. Absolute Zero Graph:

16. Avogadro’s Law At constant temperature and pressure, the volume of a gas is directly related to the number of moles. V ∝ n V=Kn V1/n1=V2/n2 Amedeo Avogadro ‹#›

17. Avogadro’s Law: ‹#› V 1 /n 1 =V 2 /n 2

18. Avogadro’s Law – Molar Volume It has been calculated that if we have 1 dm 3 of H 2 gas, its mass at STP will be 0.09 g ∴ 0.09 g H 2 at STP = 1 dm 3 2.016g of H 2 at STP =1/0.09 x 2.106 = 22.414 dm 3 2.016g of H 2 =1 mol ‹#› Hence 1 mol H 2 at STP will occupy volume 22.414 dm 3 This volume is called Molar volume.

19. Avogadro’s Law Equal volumes of all gases at same temperature and pressure must contains equal number of molecules ‹#›

20. Gay Lussac’s Law The pressure and temperature of a gas are directly related, provided that the volume remains constant. Temperature MUST be in KELVINS!

21. A Graph of Gay-Lussac’s Law

22. Ideal Gases Ideal gases are imaginary gases that perfectly fit all of the assumptions of the kinetic molecular theory. Gases consist of tiny particles that are far apart relative to their size. Collisions between gas particles and between particles and the walls of the container are elastic collisions No kinetic energy is lost in elastic collisions

23. Ideal Gases (continued) Gas particles are in constant, rapid motion. They therefore possess kinetic energy, the energy of motion There are no forces of attraction between gas particles The average kinetic energy of gas particles depends on temperature, not on the identity of the particle.

24. Real Gases Do Not Behave Ideally Real gases DO experience inter-molecular attractions Real gases DO have volume Real gases DO NOT have elastic collisions

25. Deviations from Ideal Behavior Likely to behave nearly ideally Gases at high temperature and low pressure Small non-polar gas molecules Likely not to behave ideally Gases at low temperature and high pressure Large, polar gas molecules

26. The Combined Gas Law The combined gas law expresses the relationship between pressure, volume and temperature of a fixed amount of gas.