Lesson 4 COMBINED GAS LAW The combined gas

Lesson 4 COMBINED GAS LAW

The combined gas law is not a new law but a combination of Boyle's and Charles' laws, hence the name the combined gas law.

In short, this combined gas law is used when it is difficult to keep either the temperature or pressure constant. (do not copy) In many experiments with gases, keeping either the pressure or temperature constant is not even attempted.

Boyle’s Law T and n are controlled variables Charles’s Law p and n are controlled variables Pressure temperature law v and n are controlled variables

If these formulas are combined, we find that the product of the pressure and volume of a gas sample is proportional to its absolute temperature in Kelvin; k is a constant and so the formula can also be written

Example 1 Helium in a 100 m. L container at a pressure of 66. 6 k. Pa is transferred to a container with a volume of 250 m. L. What is the new pressure if no change in temperature occurs? G V 1 = 100 m. L P 1 = 66. 6 k. Pa V 2 = 250 m. L S R P 2 = ? P A P 1 V 1 = P 2 V 2 = 26. 6 k. Pa Therefore the pressure in the 250 m. L container is 26. 6 k. Pa.

What if the temperature changes from 15° C to 20 °C ? G V 1 = 100 m. L P 1 = 66. 6 k. Pa T 1 = 20 °C = V 2 = 250 m. L T 2 = 15° R A P 2 = ? S 293. 15 K = 26. 2 k. Pa C = 288. 15 P Therefore the pressure in the 250 m. L container at 15° C is 26. 2 k. Pa.

Example 2 A gas has a volume of 225 m. L at 75 o. C and 175 k. Pa. What will be its volume at a temperature of 20 o. C and a pressure of 1. 0 X 105 k. Pa? G V 1 = 225 m. L P 1 = 175 k. Pa S T 1 = 75° C = 348. 15 = 0. 332 m. L T 2 = 20 °C = 293. 15 K P 2 =1. 0 x 105 k. Pa R A V 2 = ? P Therefore the new volume is 0. 332 m. L.

Questions Page 438 # 26 -34