Chapter 16 Section 3 Behavior of Gases

Pressure The kinetic theory states that gas particles are constantly moving and colliding with anything in their path. These collisions of these particles in the air result in atmospheric pressure.

Pressure – is the amount of force exerted per unit of area, or (P = F/A) (pressure = force/area). It is measured in units called Pascal (Pa), the SI unit for pressure.

Gases are confined within their containers. A bicycle tire will remain inflated because of the collisions the air particles have with the walls of their container. This collection of forces, caused by the collisions of the particles, pushes the walls of the container outward.

The greater collisions within the tire, the stronger (inflated) it will feel.

As you leave the Earth, the pressure of the Earth begins to decrease as you get closer to space. The amount of force that is exerted on your body from the atmosphere is 101,300 Newtons on every square meter, or the weight of a large truck.

The closer you get to outer space, the pressure decreases The closer you get to outer space, the pressure decreases. All balloons that float towards outer space pop. Why?

Boyle’s Law If you have a container, a balloon, and you squash it, what will happen to the pressure? Of course it will increase until the balloon pops because of the increased pressure! What if we put that in science terms:

science terms If you lower the volume (that means make it smaller) or (the space of the container) then the pressure will increase. What if we did the opposite? What happens to all those helium balloons that you send up into the atmosphere? As you ascend (move higher into) the atmosphere, the pressure decreases causing the balloon’s volume (space inside) to swell.

What if we did the opposite What if we did the opposite? What happens to all those helium balloons that you send up into the atmosphere? As you ascend (move higher into) the atmosphere, the pressure decreases causing the balloon’s volume (space inside) to swell.

Science Terms Science Terms: As you decrease the pressure, then the volume will increase. Examples: Weather Balloons They are designed to travel To extreme heights into the Atmosphere. They can swell 30 to 200 times their size.

Formula Boyle’s Law P1 V1 = P2 V2

Problem A balloon has a volume of 10.0L at a pressure of 101 kPa. What will the new volume be when the pressure drops to 43 kPa? Write down your units or what you have!!!!!

Question? Why do the words “keep away from heat” appear on pressurized spray canisters? IT Will EXPLODE!!!

Charles Law You know that gases expand when they are heated. Because particles in the hot air are farther apart than particles in the cool air, the hot air is less dense than the cool air. This difference in density allows the hot air balloon to rise.

Science Terms The volume of a gas will increase with increasing temperature, as long as pressure does not change. Same as the opposite: the volume of a gas shrinks with decreasing temperature. Here is a balloon that was placed in liquid nitrogen.

Example Hot air balloons: Because the gas particles move faster, they begin to strike the walls of their container more often and with more force. The walls have room to expand so instead of increased pressure, the volume increases. What would happen to a balloon that you put over boiling water? No, it would not pop, it would expand due to the heated steam that is hitting the balloon.

Formula Charles Law V1 / T1 = V2 / T2 Notice that the SI Units. What does “T” stand for? No, it is not time. Remember, time is measured in seconds or “s”.

Problem What would the resulting volume of a 2.0-L balloon at 25.0°C that was placed in a container of ice water at 3.0°C? Hint: What must you do with the temperature? Convert it to Kelvin!! To find Kelvin you add °C + 273.