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Gas Laws

Gas Laws. Boyle’s Law. Demo. Bell Jar and Marshmallow. The marshmallow is getting bigger (expanding – volume increases). Why?. How do volume and pressure relate to each other?. Shaving Cream Demo. What is boyle’s law?.

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Gas Laws

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  1. Gas Laws

  2. Boyle’s Law

  3. Demo Bell Jar and Marshmallow • The marshmallow is getting bigger (expanding – volume increases). Why? • How do volume and pressure relate to each other?

  4. Shaving Cream Demo

  5. What is boyle’s law? • The volume of a given amount of gas varies inversely with its pressure if the temperature remains constant • Inverse Relationship – as pressure increases, the volume decrease by the same factor • Example: If pressure doubles, the volume decreases by ½ • Example: If the pressure decreases by a factor of 4, the volume will _____________. Quadruple

  6. Boyle’s Law Formula: P1V1 = P2V2 • Remember, if pressure increases from P1 to P2, then volume must _________ from V1 to V2. • So, if pressure decreases from P1 to P2, then volume must _________ from V1 to V2. Decrease Increase

  7. Boyle’s law graph

  8. Boyle’s Law Example • A sample of helium gas in a balloon is compressed from 4.0L to 2.5L, at a constant temperature. If the pressure of the balloon started at 210kPa, what will the final pressure (P2) be?

  9. Boyle’s law example answer • Formula: P1V1 = P2V2 • What do we know? • P1 = 210 kPa • V1 = 4.0 L • P2 = ______ • V2 = 2.5 L • (210kPa)(4.0L) = (P2)(2.5L) • P2 = 336 kPa

  10. Charles’ Law

  11. Demo Erlenmeyer Flask and a balloon Why does the balloon expand? How do temperature and volume relate to each other?

  12. What is Charles’ Law? • The volume of a given mass of gas is directly proportional to its Kelvintemperature when held at constant temperature • Direct Relationship – as temperature increases, the volume increases by the same factor

  13. Charles’ law graph

  14. Charles’ law Formula: V1= V2 T1 T2 • Remember, if pressure increases from P1 to P2, then volume must _________ from V1 to V2. • So, if pressure decreases from P1 to P2, then volume must _________ from V1 to V2. Increase Decrease

  15. Charles’ Law Example • A gas sample at 40.0oC occupies a volume of 2.32L. If the temperature is raised to 75.0oC, what will its volume be? (always assume the 3rd variable is constant if it is not mentioned) (K = oC + 273) What is absolute zero? Why do we use Kelvin instead of Celsius degrees when working with gases?

  16. Temperature must be in Kelvin! K = oC + 273

  17. Charles’ Law Example Answer Formula: V1= V2 T1T2 • What do we know? • We must convert from degrees Celsius to Kelvin • (K = oC + 273) • T1 = 40.0o C + 273 = 313 K • T1 = 75.0o C + 273 = 348 K • V1= 2.32 L • T1 = 40.0o C • V2 = ______ • T2 = 75.0o C 2.32 L = V2 313 K 348 K V2 = 2.58 L

  18. Gay-Lussac’s Law

  19. Demo Egg in a bottle

  20. What is Gay-Lussac’s law • The pressure of a given mass of gas varies directly with the Kelvintemperature when the volume remains constant. • Direct Relationship – as temperature increases, the volume increases by the same factor

  21. Gay-Lussac’s Law Formula: P1= P2 T1 T2 • Remember, if pressure increases from P1 to P2, then temperature must _________ from T1to T2. • So, if pressure decreases from P1 to P2, then temperature must _________ from T1to T2. Increase Decrease

  22. Gay-lussac’s law graph

  23. Gay-lussac’s law Real World Example Pressure cooker is sealed so that the volume is constant. Pressure increases in the cooker as temperature increases

  24. Gay-lussac’slaw Example The pressure of a gas tank is 3.20atm at 22oC. If the temperature raises to 60oC, what will be the pressure in the gas tank?

  25. Temperature must be in Kelvin! K = oC + 273

  26. Gay-lussac’s law Example answer Formula: P1= P2 T1T2 • What do we know? • We must convert from degrees Celsius to Kelvin • (K = oC + 273) • T1 = 22.0o C + 273 = 295 K • T1 = 60.0o C + 273 = 333 K • P1= 3.20 atm • T1 = 22.0o C • P2 = ______ • T2 = 60.0o C 3.20 atm = P2 295 K 333 K P2 = 3.61 atm

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