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Gas Law Notes Chemistry Semester IIPowerPoint Presentation

Gas Law Notes Chemistry Semester II

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Ideal Gas Equation

- The variables of the physical nature of gases:
- n : the number of particles (moles)
- P : pressure
- V : volume
- T : temperature expressed always in K

Ideal Gas Equation

- Charles stated that volume varies directly with temperature
- Boyle stated volume varies inversely with pressure
- So…combining these notions, we can set pressure times volume as equal to a constant times the temperature, where the constant is the same every time it is calculated.
- Mathematically this is shown…

Ideal Gas Law

Boyle’s Law pressure times volume = a constant

Charles’ Law: volume is proportional to temperature

Combining the two yields the ideal gas law

Restated Ideal Gas Law: …

Ideal Gas Law

nRis a constant, n is the moles and R is the universal gas constant

R =8.31 L kPa /mol K

Ideal Gas Law Problem

- What is the volume of a container holding 2.00 moles of a substance at 831.67 kPa and 500K?

Problem Set Up

- P = 831.67 kPa
- V = ?
n = 2.00 moles

T = 500K

R = 8.31 L kPa/moles K

- PV = nRT

Problem cont’d

- 831.67*V = 2.00*8.31*500
- V = 9.99 L

Combined Gas Law

- Lab experiments are rarely at STP, usually mathematical corrections must be made.
- Corrections are made by multiplying of the original volume (V1) by 2 ratios (1 for temp. and the other for pressure)
- The math derivation looks like this:

Combined Gas Law Problems

- A 7.51 m3 volume @ 59.9 kPa and 5 °C should be corrected to STP. What is the new volume?
- P1V1 = P2V2
T1 T2

Set Up

- V1 = 7.51 m3
- P1 = 59.9 kPa
- T1 = 5 °C
- P2 = 101.3 kPa
- T2 = 0 °C
- V2 = ? Find this
- Remember convert T to Kelvin!
- Now solve it!

Solution

- 59.9 * 7.51 = 101.3 * V2
278 273

- 59.9 * 7.51 * 273 = V2
278 * 101.3

- V2 = 4.36 m3

next question…

- Another problem: A helium balloon with volume = 410mL is cooled from 27 °C to -27 °C. P is reduced from 110 kPa to 25 kPa. What is the new V of gas @ the lower temp. and pressure?

Set Up

- V1 = 410 mL
- P1 = 110 kPa
- T1 = 27 °C
- P2 = 25 kPa
- T2 = -27 °C
- V2 = ? Find this

Answer

- V2 = 1479 mL

Guy Lussac’s Law

Guy Lussac’s Law relates pressure and temperature….

To be used when volume and moles

are kept constant

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