Gas Laws. Book page Syllabus /09/2016

Transcription

1 Gas Laws Book page Syllabus /09/2016

2 What do all these have in common?

3 Can you explain: How To Get A Egg Into A Bottle Rally Robin

4 1. Students number off. 2. Teachers asks a question and gives think time. (30 seconds) 3. Students privately write own answers [solo time]. (30 seconds) 4. Students stand up, put heads together [huddle up], show answers, discuss, and coach if necessary. 5. Students sit down when everyone knows the answer or has something they can share. 6. Teacher calls a number; that numbered student from each group stands and simultaneously answers the teacher s question. 7. Teammates praise [CELEBRATE] students who responded.

5 What do you think? Is there a lowest temperature that you can reach? If there is, why? What is temperature? What does it describe? How can you convert between Kelvin and Celsius End End

6 Aim Understand how temperature, pressure and volume are related Key words Boyle s Law Charles Law Temperature Law Combined Gas Laws

7 Have you ever wondered? If you pump up a tyre or ball, what happens to the amount of space the air takes up?

8 Keep volume constant

9 Temperature Law Temperature (K) Pressure (torr) k (torr/k) , P T P T k

10 How does temperature affect pressure? The higher the temperature of a gas, the greater the kinetic energy of the particles. They move faster and collide with the walls of the container more frequently and with greater force. This increases the pressure of the gas when volume is constant. higher temperature higher pressure Pressure and temperature are directly proportional. pressure (Pa) temperature (K) = constant P 1 T 1 = P 2 T 2

11 The Pressure-Temperature Law A gas has a pressure of 1000 Pa at a temperature of 295 K. What is the pressure when it is heated to 395 K? P 1 T 1 = P 2 T 2 P 2 = P 1 T 1 T 2 P 2 = P 2 = 1339 Pa

12 Keep temperature constant

13 Boyle s Law Volume (ml) Pressure (torr) k (ml torr) x x x x 10 3 P V PV = k

14 How does volume affect pressure? When the temperature of a gas is kept constant, a change in volume causes a change in pressure. Particles collide more frequently with the container wall when the volume is smaller. This increases the pressure. larger volume Pressure and volume are inversely proportional. lower pressure pressure (Pa) volume (m 3 ) = constant P 1 V 1 = P 2 V 2

15 Students take turns writing on own paper then pass it on to teammates: 1. Teacher announces topic / gives think time. 2. Each teammate writes his/her short answer to the topic on own paper then passes the paper on to the next teammate. 3. Writing continues until the teacher says stop.

16 Boyle s Law Can you explain why? Balloon in the vacuum pump.mp4

17 Boyle s Law Example: A gas syringe contains m 3 of CO 2 at a pressure of 100 kpa. If the volume is reduced to m 3, what is the new pressure? P 2 = P 1 V 1 = P 2 V 2 P 1 V 1 V 2 P 2 = 100, P 2 = 143 kpa

18 Keep Pressure constant

19 Charles s Law Volume (ml) Temperature (K) k (ml/k) V T V T k

20 Charles s Law Charles' Law Can you explain what happened? Simultaneous Round table

21 How does temperature affect volume? If a gas is in a container that does not have a fixed volume, then it will expand as it is heated. The pressure on the walls of the container will cause it to expand, so pressure stays constant. higher temperature larger volume Temperature and volume are directly proportional. volume (m 3 ) temperature (K) V 1 T 1 = constant = V 2 T 2

22 Charles Law Example: A gas has an initial temperature of 300 K and initial volume of 0.2 m 3. What is the volume when it is heated to 330 K? V 1 T 1 V 2 = = V 2 = V 2 T 2 T 2 V 1 T V 2 = 0.22 m 3

23 The Combined Gas Law The Combined Gas Law brings together the Pressure- Temperature Law, Boyle s Law and Charles Law. It describes the relationship between volume, pressure and temperature, whether or not any variable is kept fixed. It is generally written as: pressure volume temperature = constant To compare the behaviour of a gas in different conditions, the following form of the equation is used: P 1 V 1 T 1 = P 2 V 2 T 2

24 Gas Law Problems A gas has an initial temperature of 3 o C and occupies an initial volume of 100 ml at 150kPa. Find its new volume when its pressure changes to 200 kpa and the temperature is changed to 8 o C. Solution P 1 = 150kPa and P 2 = 200 kpa T 1 = 3 o C and T 2 = 8 o C V 1 = 100 ml and V 2 =? P 1 xv 1 = P 2x V 2 solve for V T 1 T 2 2 V 2 = P 1xV 1 T 1 x T 2 P 2 Convert 0 C to Kelvin: T 1 = = 276K T 2 = = 281K Plug in numbers: V 2 = 150x100x281 = ml 276x200

25 Gas Law Problems A gas pressure is 765 torr at 296 K. At what temperature will the pressure be 560 torr if the volume is held constant? Solution P 1 T 1 = P 2 T 2 Given: P 1 = 765 torr P 2 = 560 torr T 1 = 296 K T 2 =? T 2 = 560x = K T 2 = P 2xT 1 P 1

26 Using the Combined Gas Law

27 Plenary - Gas laws summary

28 Key words Boyle s Law - For a fixed amount of an ideal gas kept at a fixed temperature, pressure and volume are inversely proportional. Charles Law "For a fixed mass of gas, at a constant pressure, the volume is directly proportional to the absolute temperature." Pressure - temperature Law It states that, for a given mass and constant volume of an ideal gas, the pressure exerted on the sides of its container is directly to its absolute temperature. Combined Gas Laws - Pressure is inversely proportional to volume, or higher volume equals lower pressure. Pressure is directly proportional to temperature, or higher temperature equals higher pressure.