The Gas Laws

Intro to the Gas Laws! Take notes!

• http://www.youtube.com/watch?v=a8EFY2kfC Z4

How could the Ghostbusters stop Stay Puft Marshmellow man??

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Boyle’s Law

As external pressure on a gas increases, • • Temperature must remain

________________

Eg. If the pressure is decreased by half, the volume doubles.

Any relation you think???

What does Boyle’s Law mean?

Suppose you have a cylinder with a piston in the top so you can change the

__________

. The cylinder has a gauge to measure

_______

, is contained so the

___________

of gas is constant, and can be maintained at a constant

____________________

A decrease in volume will result in increased pressure.

Hard to picture? Let’s fix that!

What does Boyle’s Law mean?

• http://www.grc.nasa.gov/WWW/K 12/airplane/aboyle.html

Application of Boyle’s Law

• • • Boyle’s Law can be used to predict the interaction of pressure and volume.

If you know the initial pressure and volume, and have a target value for one of those variables, you can predict what the other will be for the same amount of gas under constant temperature.

Let’s try it!

Application of Boyle’s Law

If you know three of the four, you can calculate the fourth.

Application of Boyle’s Law

Solving for V 2 , the final volume equals 2 liters.

So, to increase the pressure of 4 liters of gas from 1 KPa to 2 KPa, the volume must be reduced to 2 liters.

Sample Problem

• A sample of helium gas is collected at room temperature in a 4.50L balloon at standard atmospheric pressure. The balloon is then submerged in a tub of water, also at room temperature, such that the external pressure is increased to 110.2kPa. What would the final volume of the balloon become?

Boyle’s Law: Summary

Gases and Temperature Changes

• • • • http://www.youtube.com/watch?v=77Ej_Ayug xk Gases expand at the same ratio For each degree rise in temperature, gases will expand by 1/273 of their initial volume.

So, if a gas at 0 degrees Celsius was heated to 273 DC, it’s volume would double.

The Kelvin Scale and Absolute Zero

Charles’ Law

• • This law is named for Jacques Charles, who studied the relationship

______________________

around the turn of the 19 th century.

He determined that for:

What does Charles’ Law mean?

Suppose you have that same cylinder with a piston in the top allowing

_______

to change, and a heating/cooling element allowing for changing

_________________________

The force on the piston head is constant to maintain

___________

, and the cylinder is contained so the

__________

of gas is constant.

.

Hard to picture? Let’s fix it (again)!

Charles’ Law at Work…

As the temperature increases, the volume increases. Conversely, when the temperature decreases, volume decreases.

Application of Charles’ Law

• • • Charles’ Law can be used to predict the interaction of temperature and volume.

If you know the initial temperature and volume, and have a target value for one of those variables, you can predict what the other will be for the same amount of gas under constant pressure.

Let’s try it!

Application of Charles’ Law

V 1 = initial volume T 1 = initial temperature V 2 = final volume T 2 = final temperature If you know three of the four, you can calculate the fourth.

Application of Charles’ Law

V 1 T 1 V 2 = 2.5 liters = 250 K = 4.5 liters

V 1 / T 1 = V 2 / T 2

T 2 = ?

Solving for T of 200 K.

2, the final temperature equals 450 K.

So, increasing the volume of a gas at constant pressure from 2.5 to 4.5 liters results in a temperature increase

Sample Question

• • Using a glass syringe, a scientist draws exactly 25.5cm

3 of dry oxygen at 20 DC from a metal cylinder. She needs to heat the oxygen for an experiment, so she places the syringe in an oven at 65 DC and leaves it 30 minutes. Assuming at AP remains the same, what volume will the oxygen occupy?

*remember you need to use

KELVINS

Charles’ Law: Summary

• • • Volume / Temperature = Constant V 1 / T 1 = V 2 / T 2 With constant pressure and amount of gas, you can use these relationships to predict changes in temperature and volume.

Gay – Lussac’s Law

• • • The pressure of a fixed amount of gas, at a constant volume, is directly proportional to it’s Kelvin temperature.

So, P1/T1 = P2/T2 Similar to Charles Law

Sample Problem

• A cylinder of chlorine gas is stored in a concrete-lined room for safety. The cylinder is designed to withstand 50atm of pressure. The pressure gauge reads 35 atm at 23.2DC. An accidental fire in the room next door causes the temperature in the storage room to rise to 87.5DC. What will the pressure gauge read at this temperature?

Let’s Put it all Together!

• • • • • First, STP: standard temperature and pressure

101.3Kpa and 0DC

We live at SATP: standard ambient temperature and pressure.

25DC and 100kPa

What would happen if we combined the formulas of Boyle, Charles and Gay-Lussac?

The Combined Gas Law!

Sample Problem

• Sandra is having a birthday party on a mild winter’s day. The weather changes and higher pressure (103.0kPa) cold front (-25DC) rushes into town. The original air pressure was -2DC and the pressure was 100.8kPa. What will happen to the volume of the 4.2L balloons that were tied to the front of the house?

Sample Problem

• • An automated instrument has been developed to help drug-research chemists determine the amount of nitrogen in a compound. Any compound containing C, N, and H is reacted with copper (II) oxide to produce CO 2 , H 2 0 and N 2 gases. These gases are collected separately and analyzed. In an analysis of 39.8mg caffeine using this instrument, 10.1mL of N 2 gas is produced at 23DC and 746torr. What must the new temperature of N increased to 780torr?

2 be, in DC, if the volume is increased to 12.0mL and the pressure