3-3: The Behavior of Gases. 8 th Grade Physical Sciences

Transcription

1 8 th Grade Physical Sciences

2 How Gas Behaves To understand how a gas behaves, we must first remind ourselves about volume, temperature, and pressure Volume How much space it takes up m 3 - meters cubed Temperature You know, thermal energy K - degrees kelvin (starts at zero) Pressure The force exerted by the gas on the matter around it Pa Pascals (force divided by the area)

3 How Gas Behaves At 20 C, the temperature in this room, gas molecules are going about twice as fast as a jet plane 1000 mph.

4 How Gas Behaves This exerts a force on the balloon s inside walls keeping it stretched out.

5 How Gas Behaves What do you think will happen to the balloon if I slow down the gas particles? (fill in answer here) How can I slow the particles down? (fill in answer here)

6 Charles s Law A French scientist, Jacques Charles, noticed how temperature and volume were related. Charles s Law states that as T increases, so does V as long as the pressure stays constant.

7 Charles s Law This can be graphed to show a straight line, which goes through zero called a directly proportional relationship.

8 Charles s Law

9 Boyle s Law In the 1600 s, a scientist named Robert Boyle noticed a relationship between P and V.

10 Boyle s Law Boyle s Law states if a gas V increases, its P decreases and viceversa, as long as the temperature remains constant.

11 Boyle s Law The product of P and V is a constant this relationship is called inversely proportional.

12 Boyle s Law Try multiplying pairs of points and see if they are the same.

13 More Conclusions Pressure Cooker We can also make another conclusion. Pressure of a gas inside a fixed container (constant volume) will increase if its temperature is increased and viceversa.

14 More Conclusions The faster particles will exert a stronger force on the walls of the container. Pressure Cooker

15 More Conclusions: Not needed for test Here is the long and the short of it all The IDEAL GAS LAW PV=nRT n = # of gas particles in moles R = Universal gas constant = J/mol K 1 mole = Avogadro s Number = 6.022x10 23 molecules You will learn about this in Chemistry and Physics» Avogadro s number is the number of carbon atoms in 12 grams of carbon.

16 Real World Examples Truck tires on a hot day Constant V Increased T What happens to P? (Fill in answer here)

17 Real World Examples

18 Real World Examples Bike pump Constant T Decreased V when you push down. What happens to P? (Fill in answer here)

19 Real World Examples Can of pressurized air Decreased P in can as air is let out Constant V size of can doesn t change. What happens to T? (hint P1/T1=P2/T2) (Fill in answer here)

20 Real World Examples Let s say: T1=294 deg K (70 deg F) P1=18,000 kpa If I empty half the can, what will the can s temperature be? Use approximate rule P1/T1 = P2/T2

21 Real World Examples 18,000 / 294 = 9000 / T2 T2 = 294 * 9000/18,000 T2 = 147 K or -195 F It won t be quite that cold but it will be very cold!!! Careful!!!

22 Real World Examples Air Conditioners

23 Summary Charles s Law states that as T increases, so does V, and vice-versa - (constant P) - directly proportional Boyle s Law states that as V decreases, P increases and vice-versa (constant T) inversely proportional If T increases, then P will increase and viceversa (constant V).