1. Chapter 14- Gas Laws

2. Variables that describe a gas
Pressure (P)- atm, kPa, mmHg, torr
Volume (V)- mL, L
Temperature (T)- Kelvin*****
K=⁰C + 273
Amount (n)- moles
Remember: STP is-
0 ⁰C or 273 K
1 atm = kPa = 760 mmHg or torr

3. Boyle’s Law
Pressure varies inversely with constant temperature
As pressure increases, volume decreases
P1 x V1 = P2 x V2
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4. Example problem
When 1.2 L of a gas at 0.65 atm is subjected to a pressure of 0.98 atm at constant temperature, what will the volume be?

5. Charles’ Law
Temperature varies directly with constant pressure
Temperature MUST be in
Kelvin (K= C + 273)
As temperature increases, volume increases 
V1 = V2
T T2
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6. Example problem
A sample of gas has its temperature increased from 30⁰C to 50 ⁰C. The new volume is 375 mL. What was the original volume assuming pressure remained constant? (Must turn to K)

7. Gay-Lussac’s Law
Pressure varies directly with constant volume.
Temperature MUST be in Kelvin
 As pressure increases, temperature increases.
P1 = P2
T T2

8. Example problem
A gas at kPa has a temperature of 15⁰C. When the pressure is increased to 900 mmHg at constant volume, what does the temperature become?

9. Combined Gas Law Only need to remember this one to get the other 3
Amount of gas does not vary but pressure, temperature and volume do
P1 xV1 = P2 x V2
T T2

10. Example Problem
A gas has a pressure of 95.6 kPa, volume of 3.6 L and a temperature of 20⁰C. What is the volume at STP?

11. Ideal gas law What is an ideal gas?
A gas which has no intermolecular forces and the volume of the particles is zero.
Real gases act most like ideal gases at high temperatures and low pressures.
P x V = n x R x T
Pressure must be in atm or kPa
Volume must be in L
n is moles
R is the gas constant ( atm*L/mol*K or
8.31 kPa*L/mol*K)
Temperature must be in Kelvin

12. Example problems
What is the volume of 1.5 mol of gas that has a pressure of kPa and a temperature of 30⁰C?
How many grams of oxygen gas are there in a sample with a pressure of 0.75 atm, volume of 250 mL and a temperature of 15⁰C?

13. Dalton’s law of partial pressures
At constant volume and temperature, the total pressure of a sample of gases is equal to the sum of the partial pressures of the component gases.
Ptotal = P1 + P2 + P3 + …

14. Example PRoblem
The atmosphere is made up of many gases (N2, O2, CO2 and other gases). If the partial pressure of N2 is kPa, O2 is kPa, CO2 is 0.04 kPa and the other gases is 0.95 kPa, what is the total pressure?