Chapter 16 Section 3

Pressure What did we learn about gas particles from the kinetic theory? –They are constantly moving and colliding with anything in their path –The collisions result in pressure –Pressure is the amount of force per unit of area

Pressure Gases are often confined within a container Ex: –Balloon –Bicycle tire

Pressure Why does the balloon and bicycle tire remain inflated? –Due to the collisions of the air particles with the walls of the container –The collection of forces pushes the walls outward –The more air that is pumped in the more collisions that occur and the more the container expands.

Pressure What about a bicycle tire? Can that continue to expand? –Since the tire can’t expand much the pressure increases inside the tire

Pressure Pascal (Pa) –The unit we use to measure pressure –SI unit –Pressure = Force / Area –At sea level atmospheric pressure is kPa (kilopascals) This means at the Earth’s surface the atmosphere exerts 101,300 N on every square meter

Boyle’s Law What happens to gas pressure if we decrease the size of the container? –The particles are now squeezed into a smaller space –Now they hit the wall of the container more often –The pressure increases!

Boyle’s Law What happens if we increase the size of the container? –The particles have more space –They hit the walls less often –The gas pressure decreases!

Boyle’s Law Boyle’s Law: –If you decrease the volume of a container of gas and hold the temperature constant the pressure will increase. –An increase in the volume of a container can cause the pressure to drop if the temperature remains constant.

Boyle’s Law Figure 21 –As a balloon rises the pressure drops and the volume of the balloon increases As the pressure decreases the volume increases As the pressure is increased the volume will decrease

Boyle’s Law in Action Pressure x Volume = a constant –If the temperature is held constant –As the pressure and volume change indirectly the constant remains the same –P 1 V 1 = P 2 V 2

Boyle’s Law in Action Using the equation P 1 V 1 = P 2 V 2 –We know that the initial pressure and volume is equal to the final pressure and volume –Volume-Pressure Equation

Pressure-Temperature Relationship What happens if you heat an enclosed gas? –The particles will strike the wall more often –Because the canister is a solid the volume cannot increase –If the pressure is greater than the canister can hold it will explode –At a constant volume an increase in temperature results in an increase in pressure

Charles’s Law What did we learn about the thermal expansion of gas particles from section one? –The particles in the hot air balloon are further apart then particles in cool air –The hot air is less dense than the cool air and the balloon rises

Charles’s Law Charles’s Law: –Volume of a gas increases with increasing temperature as long as pressure does not change –Volume of a gas decreases with decreasing temperature as long as the pressure does not change

Charles’s Law As the gas is heated the particles move faster and further apart They strike the walls of the container more often and with more force In a balloon the walls have room to expand so instead of the pressure increasing the volume increases

Using Charles’s Law Formula for Charles’s Law: –V 1 / T 1 = V 2 / T 2 –Temperature is in Kelvin –The pressure must be held constant –Example problem: 2.0 L balloon at 25.0 degrees C is placed in a container of ice water at 3 degrees C