Gas Laws

Section 3.2

Gas and Pressure

• Pressure—result of force distributed over an area

Gas and Pressure

• The wider the arrow, the greater the force. Which has the greatest pressure? The least pressure?

What causes pressure?

• In a gas, it’s all about collisions– Atoms in a gas are constantly moving

• Collisions push against container and create pressure

What affects pressure?

1) Temperature of gas2) Volume of gas3) Number of particles in gas

http://intro.chem.okstate.edu/1314F00/Laboratory/GLP.htm

Temperature and Pressure

Overall, increasing the temperature increases the pressure

Higher temperature increases particle speed energy collisions pressure

http://intro.chem.okstate.edu/1314F00/Laboratory/GLP.htm

Volume and Pressure

Overall, decreasing the volume increases the pressure

Less space means more collisions collisions pressure

http://intro.chem.okstate.edu/1314F00/Laboratory/GLP.htm

Number of Particles and Pressure

Overall, increasing the number of particles increases the pressure

More particles means more collisions collisions pressure

http://intro.chem.okstate.edu/1314F00/Laboratory/GLP.htm

The Gas Laws

Charles’s Law Boyle’s Law

Charles’s Law

Jacques Charles Collected data on temperature

and volume

Charles’s Law

Extended line to hit x-axis

                                                                                                                                                                                                  

Charles’s Law

Temperature at which the volume is 0L is –273.15 C, or 0K.

Absolute zero Volume of gas is directly

proportional to the temperature (in Kelvin) if pressure and particle number are same

                                                                                                                                                                                                  

Charles’s Law

V1 = V2

T1 T2

V1 = Initial volume T1= Initial temperature (K)

V2 = Final volume T2= Final temperature (K)

Sample Problems

1. Steps: Identify any knowns as either V1, T1, V2, or T2

2. Make sure that all temperature values are in Kelvin

3. Plug knowns in equation4. Double-check that answer and

units make sense

http://www.chem.uiuc.edu/webFunChem/charleslaw/CLsample.htm

A sample of gas at 101.3kPa had a volume of 1.2L at 100oC. What would its volume be at 0oC at the same pressure?

Vf = 0.88L

A balloon had a volume of 75L at 25oC. To what does the temperature need to raised in order for the balloon to have a volume of 100L at the same pressure?

Tf = 124oC

Boyle’s Law

Robert Boyle Collected data on pressure and

volume

Boyle’s Law

Boyle’s Law

Volume of gas is inversely proportional to the pressure if the volume and particle number are same

Boyle’s Law

P1V1 = P2V2

V1 = Initial volume P1= Initial pressure

V2 = Final volume R2= Final pressure

Sample Problems

1. Steps: Identify any knowns as either V1, P1, V2, or P2

2. Plug knowns in equation3. Double-check that answer and

units make sense

http://www.chem.uiuc.edu/webFunChem/BoylesLaw/SampleProb6.htm

The volume of the lungs is measured by the volume of air inhaled or exhaled.  If the volume of the lungs is 2.400 L during exhalation and the pressure is 101.70 KPa, and the pressure during inhalation is 100.01 KPa, what is the volume of the lungs during inhalation?

2.441 L

It is hard to begin inflating a balloon.  A pressure of 800.0 Kpa is required to initially inflate the balloon 225.0 mL.  What is the final pressure when the balloon has reached it's capacity of 1.2 L?

150 Kpa

Combined Gas Law

Describes the relationship between the temperature, volume, and pressure of a gas when the number of particles is constant

Combined Gas Law

P1V1 = P2V2

T1 T2

V1 = Initial volume V2 = Final volume

T1 = Initial temperature (K) T2 = Final temperature (K)

P1 = Initial Pressure P2 = Final Pressure

A gas takes up a volume of 17 liters, has a pressure of 2.3 atm, and a temperature of 299 K. If I raise the temperature to 350 K and lower the pressure to 1.5 atm, what is the new volume of the gas?

If I have 2.9 L of gas at a pressure of 5 atm and a temperature of 50

0C, what will be the temperature of the gas if I decrease the volume of the gas to 2.4 L and decrease the pressure to 3 atm?

If I have 17 liters of gas at a temperature of 67 0C and a pressure of 88.89 atm, what will be the pressure of the gas if I raise the temperature to 94 0C and decrease the volume to 12 liters? 136 atm

160 K

30.6 L

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practice problems