Pressure & Behavior of Gases Chapter 3.3 and 3.4 Notes

Pressure The amount of force exerted on a given area of surface Pressure=Force/Area; P=F/A SI unit for pressure is the pascal (Pa); SI unit for force is the newton (N) 1 Pa=1 N/m 2 *pressure in a fluid exerts pressure evenly in all directions Example: blood pressure is even throughout your body

Buoyant Force The upward force of a liquid; keeps matter afloat if you push a rubber duck to the bottom of the bathtub, it pops back up to the surface when you release it Pressure increases with depth—at greater depths, the forces pushing up on an object are greater than the forces pushing down

Archimedes’ principle Archimedes’ principle: used to find the buoyant force by water displacement Water displacement = weight of the object If Archimedes was in a bathtub, the water would overflow; the amount of water that overflows should be equal to the weight of the person in the bathtub

Pascal’s Principle A change in pressure at any point in an enclosed fluid will be transmitted equally to all parts of the fluid Pressure In = Pressure Out P 1 = P 2 P 1 = initial action (pumping a car jack) P 2 = reaction or final action (the car goes up) If the pressure in a container is increased at one point, the pressure increases at all points by the same amount.

Properties of Gases 1. Gases expand to fill their containers 2. Gases spread out easily and are miscible 3. Gases have low densities and are compressible 4. Gases are mostly empty space

Gas Laws Predict how gases behave in specific situations Boyle’s Law Gay-Lussac’s Law Charles’s Law

Boyle’s Law When volume of a gas increases, pressure increases When volume of a gas decreases, pressure decreases Temperature is constant for Boyle’s law to apply P 1 V 1 =P 2 V 2 Initial pressure x initial volume = final pressure x final volume

Gay-Lussac’s Law Relates pressure and temperature Pressure of a gas increases as temperature increases Pressure of a gas decreases as temperature decreases Volume stays constant

Charles’s Law Relates volume and temperature Volume of a gas increases as temperature increases Volume of a gas decreases as temperature decreases Pressure stays constant