What causes gas pressure in a closed container?

1. When you inhale, the volume of your chest cavity increases, and air moves into your lungs. When you exhale, the volume of your chest cavity decreases, and air is pushed out of your lungs. Changes in the volume, the temperature, the pressure, and the number of particles have predictable effects on the behavior of a gas.

2. Pressure What causes gas pressure in a closed container? Pressure is the result of a force distributed over an area. Collisions between particles of a gas and the walls of the container cause the pressure in a closed container of gas.

3. Pressure A moving hockey puck exerts pressure on any object it hits. A layer of shatterproof glass protects spectators. • The faster the puck is traveling, the greater the force of the puck on the glass. A greater force means more pressure. • The smaller the area of impact is, the greater the pressure. If the edge of the puck hits the glass, it exerts more pressure than if the face of the puck hits the glass.

4. Pressure The SI unit of pressure is derived from SI units for force and area. • Force is measured in newtons (N). • Area is measured in square meters (m2). • The SI unit for pressure, the pascal (Pa), is shorthand for newtons per square meter. • Scientists often express larger amounts of pressure in kilopascals. One kilopascal (kPa) is equal to 1000 pascals.

5. Pressure The helium atoms in a balloon are constantly moving. There are more than 1022 helium atoms in a small balloon. • When many particles collide with the walls of a container at the same time, they produce a measurable pressure. • The more frequent the collisions, the greater the pressure is. • The speed of the particles and their mass also affect the pressure.

6. Factors That Affect Gas Pressure What factors affect gas pressure? Factors that affect the pressure of an enclosed gas are its temperature, its volume, and the number of its particles.

7. Factors That Affect Gas Pressure Temperature Raising the temperature of a gas will increase its pressure if the volume of the gas and the number of particles are constant.

8. Factors That Affect Gas Pressure The firefighter is using a pressure gauge to check the air pressure in a tire on a firetruck. If he checks the tire pressure again after a long drive on a highway, he will find that the pressure has increased.

9. Factors That Affect Gas Pressure The motion of tires on the highway heats the tires and increases tire pressure. • As the temperature rises, the average kinetic energy of the particles in the air increases. • With increased kinetic energy, the particles move faster and collide more often with the inner walls of the tires. • Faster-moving particles hit the walls with greater force. • More collisions and increased force cause the pressure of the air in the tires to rise.

10. Factors That Affect Gas Pressure Volume Reducing the volume of a gas increases its pressure if the temperature of the gas and the number of particles are constant.

11. Factors That Affect Gas Pressure Twist the cap onto a plastic bottle and then squeeze it. What happens? • The volume of the plastic bottle begins to decrease. • As the volume decreases, the particles of trapped air collide more often with the walls of the bottle. • The pressure in the bottle increases.

12. Factors That Affect Gas Pressure Movement of a muscle called the diaphragm changes the volume of your chest cavity. • The volume increases when you inhale. The pressure decreases and air flows to your lungs. • The volume decreases when you exhale. The pressure increases and air flows from your lungs. Inhaling Exhaling Diaphragm contracts. Rib cage is lifted up and out. Diaphragm relaxes. Rib cage moves down and in. Lungs Rib Cage Diaphragm

13. Factors That Affect Gas Pressure Number of Particles Increasing the number of particles will increase the pressure of a gas if the temperature and the volume are constant. The more particles there are in the same volume, the greater the number of collisions and the greater the pressure.

14. Assessment Questions • What causes the pressure to increase if more gas particles are added to a closed container? • an increase in the number of collisions between the gas and the container walls • a decrease in the volume of the container • a decrease in the size of each particle as the number of particles increases • an increase in the number of collisions between air particles and the outside of the container

15. Assessment Questions • What causes the pressure to increase if more gas particles are added to a closed container? • an increase in the number of collisions between the gas and the container walls • a decrease in the volume of the container • a decrease in the size of each particle as the number of particles increases • an increase in the number of collisions between air particles and the outside of the containerANS: A

16. Assessment Questions • When first blown up, a balloon is firm because of the air pressure inside it. However, after time, the balloon becomes soft as the air pressure inside drops. What could have caused the air pressure to decrease? • increase in air temperature • decrease in the balloon's volume • decrease in the number of air particles as they leaked out of the balloon • a chemical reaction between the air particles and the balloon

17. Assessment Questions • When first blown up, a balloon is firm because of the air pressure inside it. However, after time, the balloon becomes soft as the air pressure inside drops. What could have caused the air pressure to decrease? • increase in air temperature • decrease in the balloon's volume • decrease in the number of air particles as they leaked out of the balloon • a chemical reaction between the air particles and the balloon ANS: C

18. Assessment Questions • When the temperature of the gas in closed container is increased, the pressure increases.TrueFalse

19. Assessment Questions • When the temperature of the gas in closed container is increased, the pressure increases.TrueFalse ANS: T